* GB785693 (A)

Description: GB785693 (A) ? 1957-11-06

Improvements in or relating to process and apparatus for chemical nickelplating

Description of GB785693 (A)

-m ^ X A-Wbe, 1 R id Ail A ', PATENT SPECIFICATION Date of Application and filing Complete Specification:July 9, 1953. No 19063/53. Application made in United States of America on July 19, 1952. Complete Specification Published: Nov 6, 1957. Index at acceptance:-Class 82 ( 2), F(IB 1 B: 2 U), F 4 (A: E: F: G: J: K: W: X), F 5. International Classification:-C 23 c. COM 1 IPLETE SPECIFICATION Improvements in or relating to process and apparatus for Chemical Nickel Plating ERRATA SPECIFICATION No 785,693 Page 2,line 82, after " in" insert ' said bath in. Page 7, line 29, after "composition" insert noted was periodically regenerated by : dditions" Page 7, line 50, for " basic " read " basis Page 9, line 34, for " merical" read " mercial" Page 10, line 59, after " valve " insert " 104 " Page 11, line 95, after " necessary " insert "," Page 14, line 86, for " carbonyl " read " carboxyl " Page 15, line 45, for " chamber " read " condenser " Page 15, line 53, after " first " insert " flash" THE PATENT OFFICE, 16th December, 1957. conditions. In our copending application Serial No. 17206/53 (Serial No 761,062) there is disclosed a third batch process of chemically plating a catalytic material, such as steel, with nickel, by contacting the material with a bath containing nickel ions and hypophosphite ions and an exaltant in the form of a simple short chain saturated aliphatic dicarboxylic acid and/or a soluble salt

thereof That process is also carried on under certain optimum conditions. In the second and third batch processes mentioned above, the plating reaction involved, represented, for instance, by the equation: cat. ( 1) 2 Na(H PO) + CH 20 + Ni Cl > surf. 2 T 2 Na H(HPOQ) + Ni' + 2 HCI HI 1 lPrice 3 s 6 d l 1 in a period of two hours The regeneration of the plating bath is unsatisfactory because it has been found that regeneration of a batch bath produces a laminar structure in the coating. Thus it is of great practical value to be able to deposit any desired thickness of nickel, while the concentrations of the reagents are kept within the optimum ranges mentioned in order to achieve the best quality of plating and the highest plating rate Insofar as the maintenance of a substantially constant p H is concerned, periodic or continuous addition of a soluble alkali hydroxide or a soluble alkaline salt provides a means of achieving this objective; and, also, this result may be attained by the addition of a buffer salt or a combination of buffers, i e, compounds comprising the anion of a weakly dissociated acid and a cation able to form a strong base. 78593 785,693 ij PATENT SPECIFICATION Date of Application and filing Complete Specification:July 9, 1953. No 19063/53. Application made in United States of America on July 19, 1952. Complete Specification Published: Nov 6, 1957. Index at acceptance:-Class 82 ( 2), F( 1 B 1 B: 2 U), F 4 (A: E: F: G: J: K: W: X), F 5. International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to process and apparatus for Chemical Nickel Plating We, GENERAL AMERICAN TRANSPORTATION CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 135 South La Salle Street, Chicago 90, Illinois,, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to chemical nickel plating and more particularly to an improved process of an apparatus for chemical nickel plating utilizing the bath solutions of prior nickel plating processes. A batch process for chemically plating with nickel by the use of a plating bath including nickel ions and hypophosphite ions has previously been proposed in which the concentration of the bath is

maintained at a predetermined value by the addition of the reagents of the bath at regular intervals. In a second prior batch process of chemically plating a catalytic material, such as steel, with nickel, the material is contacted with an acid bath containing nickel ions and hypophosphite ions and a buffer, and that process is carried on under certain optimum conditions. In our copending application Serial No. 17206/53 (Serial No 761,062) there is disclosed a third batch process of chemically plating a catalytic material, such as steel, with nickel, by contacting the material with a bath containing nickel ions and hypophosphite ions and an exaltant in the form of a simple short chain saturated aliphatic dicarboxylic acid and/or a soluble salt thereof That process is also carried on under certain optimum conditions. In the second and third batch processes mentioned above, the plating reaction involved, represented, for instance, by the equation: cat. ( 1) 2 Na(I 1,PO) + CHO + Ni Cl, -> surf. 2 Na H(HPO,) + Ni W + 2 HCI H, lPrice 3 s 6 d l ?, results in a rapid increase of the hydrogen ion concentration in the bath and may be measured by the corresponding decrease in the p H of the bath, which in turn will considerably slow down the rate of nickel plating and eventually stop the reaction altogether. Moreover, in order to obtain high nickel plating rates, these processes must be carried out within the optimum p H ranges of the specific baths, and in order to retard or prevent the formation of black precipitate in the baths, the ratio between the volume of the bath, expressed in cm', and the surface area of the catalytic material that is to be plated, expressed in cm 2, V/A, should be kept below 10. On the other hand, in any batch or static system without regeneration, there is a limit to the thickness of the nickel coat which may be plated, while maintaining a high quality thereof Further, the rate of plating decreases as the bath is exhausted, with the consequence that a mucfh longer time is required to obtain an equal increment of thickness near the end of the process than in the beginning Practically speaking, the ultimate thickness obtainable in a batch or static process is in the range of 0 0005 inches to 0 0010 inches in a period of two hours The regeneration of the plating bath is unsatisfactory because it has been found that regeneration of a batch bath produces a laminar structure in the coating. Thus it is of great practical value to be able to deposit any desired thickness of nickel, while the concentrations of the reagents are kept within the optimum ranges mentioned in order to achieve the best

quality of plating and the highest plating rate Insofar as the maintenance of a substantially constant p H is concerned, periodic or continuous addition of a soluble alkali hydroxide or a soluble alkaline salt provides a means of achieving this objective; and, also, this result may be attained by the addition of a buffer salt or a combination of buffers, i e, compounds comprising the anion of a weakly dissociated acid and a cation able to form a strong base. 785,693 2 785,693 The present invention involves improved process steps for maintaining substantially constant the relative and optimum concentrations and proportions of the reagents in the bath, as well as the holding of the p H of the bath within any desired narrow optimum limits, while permitting the plating of any desired thickness of a continuous and homogeneous coating of nickel on the surface area of a catalytic material in a simple and efficient manner In carrying out the process of the present invention, it may be observed that if the volume of the bath were infinite, while the surface area of the catalytic material to be plated was small, the p H value of the bath would not change, provided sufficient agitation is supplied to avoid any local variation In other words, if a small object to be plated is placed im a relatively large volume of well agitated bath, the drop in p H due to the plating reaction is so minute as to be practically without effect On the other hand, it has been found that in a static (as opposed to a dynamic) system, excessive agitation of the bath decreases both the plating rate and the quality of the plating, and that a large ratio of the bath volume to the catalytic surface area (V/A), tends to favor the formation of black precipitate Further, and of great importance, a relatively high temperature of the bath tends to favor the formation of black precipitate even in the absence of a catalyst, by spontaneous thermal decomposition In order to obtain, in addition to other things, the advantage of a large volume of available bath without encountering the disadvantage of a V/A ratio outside of the optimum range, the plating operation proper, according to the present invention, is carried out in a relatively small insulated and heated plating chamber, through which the bath, first preheated to the proper temperature, flows at a relatively low rate, a much larger proportion of the bath being stored in a relatively large reservoir at a substantially lower temperature at which the rate of thermal decomposition is low, for example, substantially at room temperature or even higher The overflow from the plating chamber is returned directly to the reservoir for re-use; and when the solution in the reservoir is partly exhausted, it may be regenerated by the periodic or continuous addition of the contained reagents. The present invention provides a continuous process of chemically plating with nickel a solid body of catalytic material, which

comprises providing an aqueous solution of a nickel salt and a hpyophosphite, wherein the ratio between the nickel ions and the hypophosphite ions in said solution is within a first predetermined range and the absolute concentration of the hypophosphite ions in said solution is within a second predetermined range and the p H of said solution is within a third predetermined range, storing a first portion of said solution at a relatively low temperature well below the boiling point thereof in a reservoir, holding a second portion of said solution as a bath at a relatively high temperature slightly below the boiling 70 point thereof in a plating chamber, circulating said solution from said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal 75 thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber and before 80 return thereof to said reservoir, immersing said body ia said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon 85 that is desired, and adding during said time interval soluble reagents to said solution in said reservoir to maintain in said bath in said plating chamber during said time interval said ratio and said absolute concentration and 90 said p H respectively in said first and said second and said third predetermined ranges, The present invention also provides a process of chemically plating with nickel a solid body of catalytic material employing an 95 aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type having substantially predetermined concentration characterized by stability and a low plating rate at a temperature within a first 100 given range disposed well below the boiling point thereof and by instability and a high plating rate at a temperature within a second given range disposed near the boiling point thereof; said process comprising providing a 105 solution as specified, storing said solution in a reservoir at a temperature within said first range and at said predetermined concentration, withdrawing said solution from said reservoir and heating it to a temperature 110 within said second range and diluting it some. what below said predetermined concentration and introducing it into a plating chamber, withdrawing said solution from said plating chamber and cooling it to a temperature with 115 in said first range and concentrating it substantially back to said predetermined concentration and returning it to said reservoir, and immersing said body in said solution in said plating chamber 120 The present invention further provides chemical nickel plating apparatus

comprising a reservoir for storing a first portion of an aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type at 125 a relatively low temperature, a plating chamber for holding a second portion of said solution as a bath at a relatively high temperature, a condenser, means for conducting said solution from said reservoir into said 130 785,693 785,693 3 condenser, means for injecting live steam into said solution in said condenser in order to heat said solution therein substantially to said relatively high temperature, means for coixducting said solution from said condenser into said plating chamber, a flash tank, means for conducting said solution from said plating chamber into said flash tank, means for main. taining a subatmospheric pressure in said flash 0 tank by withdrawing and discharging to the exterior water vapor from said solution therein in order to cool said solution therein substantially to said relatively low temperature, and means for conducting said solution from said flash tank back into said reservoir. The advantages of the present invention will be understood from the foregoing and following description taken with the accompanying drawing, in which Figure 1 is a schematic diagram of an arrangement of apparatus for carrying out the process of one embodiment of the present invention. Figure 2 is a diagrammatic illustration of a system and apparatus for chemical nickel plating the interiors of containers or tanks, embodying the present invention, and in which the method of the present invention may be carried out. Referring now to Fig 1, the dynamic system there illustrated comprises a reservoir containing a large volume of the solution 11 and a plating chamber 12 containing a small volume of the bath 13, the lower portion of the reservoir 10 being connected to the lower portion of the plating chamber 12 by a conduit 14 A valve 16 is arranged in the conduit 14 so as to allow regulation of the rate of flow of the solution 11 from the reservoir 10 into the bath 13 in the plating chamber 12 The upper portion of the solution 11 in the reservoir 10 is disposed at a suitable elevation above the upper portion of the bath 13 in the plating chamber 12, whereby the flow of the solution 11 through the conduit 14 takes place by the action of gravity, the bath 13 in the plating chamber 12 being overflowed from the upper portion thereof into a surrounding launder 17 that communicates via a conduit 18 with a variable speed liquid pump 19 The pump 19 normally returns the overflowed bath 13 via a conduit 20 to the upper portion of the solution 11 in the reservoir 10; and the conduit 20 is also connected via a normally closed valve 21 to a draw-off conduit 22 The intermediate portion of the conduit 14 is provided with a serpentine

section 14 a that is enclosed by a jacket 23; and the wall of the plating chamber 12 is provided with a surrounding jacket 24. The jackets 23 and 24 are arranged in communicating relation; steam is supplied via a pipe 25 into the heating chambers defined by the jackets 23 and 24; and condensate is removed from these heating chambers via a pipe 26 Thus the solution 11 in the serpentine section 15 of the conduit 14 is preheated to the temperature required by any particular plating bath prior to the introduction thereof into the plating chamber 12; and the bath 13 contained in the plating chamber 12 is heated 70 to maintain the temperature noted. A heat exchanging device is shown at 29 which is utilized to reduce the temperature of the bath before it is reintroduced into the storage chamber 11 In small systems this 75 cooling device may be eliminated as the natural cooling effect of the parts 10, 16, 17 and 18 may suffice. The catalytic material that is to be plated with the nickel is immersed in the bath in the 80 plating chamber 12, and is withdrawn therefrom after a time interval corresponding to the thickness or weight of the nickel coating or plating thereon that is desired Finally, the reservoir 10 is provided with a drain pipe 27 85 that is normally closed by an associated valve 28; and of course the component elements of the apparatus or system are formed of noncatalytic materials such as glass, quartz and synthetic resins, to prevent the plating of nickel 90 thereon Thus the major differences between the solution 11 in the reservoir and the bath 13 in the plating chamber are temperature, the presence of a catalytic material, volume and chemical composition The average 95 chemical composition of the bath 13 and the solution 11 are different to the extent that nickel has been removed and hypophosphite oxidized to the products of its reaction These differences in composition, however, are by no 100 means as marked as the difference in a batch plating bath between the initiation and conclusion of the plating cycle The resultant advantages have heretofore been described. In carrying out any of these processes, the 105 materials that may be coated or plated with nickel include for example such common materials as iron, cobalt, nickel and palladium. Some materials, not catalytic by themselves, can be plated by the use of iron as an initia 110 tor For instance, copper can be used as a basis material, by contacting it with an iron wire to initiate the plating reaction, after which the wire is removed It should, therefore, be understood that whenever we refer to a cata 115 lytic material, we mean thereby a basis material that is catalytic by itself or one that is made catalytic by association with another material The following elements are examples of noncatalytic materials which

ordinarily 120 may not be nickel plated; bismuth, cadmium, tin and lead Prior to immersing a specimen of catalytic or other basis material to be nickel plated in the bath contained in the plating chamber, the specimen should be first 125 mechanically cleaned to remove any oxide and mill scale; also, the specimen should be degreased and then lightly pickled in a suitable acid, such as HCI. In carrying out the process of the present 130 785,693 invention, employing the appartus illustrated, and to demonstrate that under these conditions no buffer is needed to produce a good nickel plating, the following tests were performed; baths of the character used in the above second mentioned prior process were employed that contained only nickel ions, hypophosphite ions and sodium ions, nickel hydroxide being dissolved in hypophosphorous acid to produce nickel hypophosphite, and sodium hypophosphite being added to obtain the proper concentrations The p H of the baths were about 3 0 as prepared, and were then adjusted with sodium hydroxide to the optimum values of 4 5 to 4 6 The plating rates (R) determined from these plating tests are reported as R x 10 ' where R is expressed in gms/cmi/min These baths thus prepared and having the specific compositions noted were employed in the plating of steel samples with the following resultsTABLE I Tests Bath composition by analysis Ni ++ mole/liter (HPO 2) mole/liter p H adjusted to Test conditions Total volume of bath, liters Volume of plating chamber, cm 3 Area of steel sample, cm 2 V/A Average rate of flow, cm 3/min. Duration of test, time Temperature, 'C. Results Weight of plating, gms. Rate of plating, (Rx IO) Final p H Appearance No 1 0.0853 0.261 4.61 300 5.88 9 hrs. 97-99 2.0281 0.74 3.61 Bright No 2 0.0860 0.2462 4.61 300 5.88 2 hrs 54 mins. 0.730 0.82 4.18 Bright and smooth No 3 0.0862 0.259 5.51 300 5.8 C 114 2 hrs 42 mins. 0.593 0.72 4.06 Bright smooth From Table I, it may be seen that the rate of nickel plating expressed in gm/cm 2/min. is low, but fairly constant, regardless of the rate of flow of the bath and regardless of the length of time of the plating operation. Much higher rates of nickel plating can be achieved in accordance with the process of the present invention by using a buffer as 30 indicated in the above second mentioned prior process or by employing a bath of the character of that disclosed in our above copending Application For example, using the 785,693 -4 reduced or of the hypophosphite which does the reducing, thereby eliminating any slowing down of the reaction Thus the over-all rate of plating is higher Actually, we have

found the rate increase to be even more substantial than could be expected to result from the constancy of the plating solution It is believed that the laminar flow which helps to remove the hydrogen bubbles has a decided effect in speeding up the rate. The following tests were carried out in accordance with the process of the present invention employing baths of the character set forth in our above copending Application wherein the solution in the reservoir was periodically regenerated by the addition of small amounts of Ni Cl 2 and Na(HPO). These baths thus prepared and having the specific compositions noted were employed in the plating of steel samples with the following results: latter type bath a rate of nickel deposition of 4.75 x 10-' gms/cm'/niin was achieved. A very important advantage of the dynamic system of the present process over the batch techniques of the prior processes mentioned above resides in the circumstance that the chemical composition of the actual plating bath changes very slowly This results in ( 1) a very homogeneous composition of the coating which effects a better control of the physical and chemical properties thereof, and ( 2) a substantially faster plating. This first result flows from the fact that if any additions are needed to make up for exhaustion of certain reagents, such additions are made in the reservoir thus insuring the constancy of the bath in the plating chamber as will be shown below The second advantage follows from the first Because of the constancy of the plating bath in the plating chamber, there is no dilution to any appreciable extent of the amount of nickel to be 785,693 785,693 TABLE II Tests Bath composition by analysis Ni ++ mole/liter (H 2 PO 2) mole/liter (C 4 H 404) (succinate ion) mole/liter p H adjusted to Test Conditions Total volume of bath, liters Volume of plating chamber, cm 3 Area of steel sample, ci 2 V/A Average rate of flow, cm 3/min. Duration of test, mins. Temp, O C. Cycle No 1 0.09 0.225 0.06 4.48 1.7 Cycle No 3 0.09 0.225 0.06 4.61 1.7 Results Weight of plating, gm. Rate of plating (Rx 10) Final p H Appearance 0.7499 4.69 4.22 Bright and smooth 0.6760 0 8405 0 5350 5.41 4.36 Ditto 5.8 4.73 4.35 Ditto Ditto Analysis of plating % Ni 95.9 7.4 From Table II it will be observed that the specific composition of the nickel-phosphorus coatings through cycle 7 varies only slightly. (Due to the small quantity of coated material relative to basis material, this type of analysis is subject to some variation The ranges and values given are considered within the analytical error)

Further it is specifically 94.1 6.97 92.3 7.64 94.3 8.9 pointed out that this continuous and homogeneous plating produced by the dynamic system of the present invention is entirely different in character from a composite plating that is sequentially built up employing a plurality of batch plating operations of the general character of the above second mentioned prior process and disclosed in our Cycle No 5 0.09 0.225 0.06 4.50 1.7 Cycle No 7 0.09 0.225 0.06 4.50 1.7 is different laminar structure than when employing the method of the present invention. Moreover, it is noted that the dynamic system of the present invention allows the continuous plating of large weights or thick coatings of nickel as compared with the prior batch plating operations This circumstance is aptly demonstrated by the following test in which there was employed a bath of the general character of that set forth in our above copending Application This bath thus prepared and having the specific compositions of Ni Cl 2 and Na(HP 02) to the reservoir and was employed in the plating of a steel sample with the following results: above copending Application It is postulated that this difference resides in the circumstance that when a series of batch plating operations are employed to obtain a relatively thick composite coating, a series of layers of coating are readily obtained In any case, the layers of coating exhibit a stratified characteristic, whereby the coating is not homogeneous and uniform throughout either with respect to specific chemical composition in regard to nickel and phosphorous or with respect to hardness and other physical properties When the article to be plated remains in the bath but periodic additions are made to the plating bath as in the first prior batch process mentioned above, there is an entirely TABLE III Bath composition by analysis Ni ++ mole/liter (H P 02) mole/liter (C 4 H 404) mole/liter p H adjusted to 0.09 0.225 0.06 4.58 Results Weight of plating, gins. Plating thickness, mils. Plating rate (R X 104) 12.1578 3.44 Appearance Bright and smooth Test Conditions Total, volume of bath, liters Volume of plating chamber, cm 3 Area of steel sample, cm 2 V/A Average rate of flow, cm 3/min. Duration of test, time Temp, 'C. 300 103 2.9 hrs 15 mins. In conjunction with Table III, it will be specifically observed that over 12 grams of nickel were deposited in this test to form a coating on the steel sample having a thickness of 5 mils Moreover, there is no critical limitation to the ultimate thickness of the nickel coating that may be deposited, since the solution in the reservoir may be readily periodically or continuously regenerated in.

the manner previously explained to preserve both the concentrations and proportions of the reagents thereof and also to hold the desired p H thereof, whereby the efficiency of the bath in the plating chamber is constant. In order to demonstrate that equivalent results may be readily obtained employing samples formed of basic materials other than steel, a test was conducted employing a bath of general character of that set forth in our above copending Application, wherein the bath was employed in the plating of copper tubing, with the following results. 785,693 785,693 TABLE IV Base Material Activation (Catalyst) Copper Tubing Iron Bath composition by analysis Ni ++ mole/liter as Ni C 12 (H 2 PO) mole/liter as Na(H 2 P 202) (CH 04) mole/liter as Na 2 (C 4 H 1404) p H adjusted to 0.067 0.225 0.06 4.45 Test Conditions Total vol of bath, liters Vol of plating chamber, cm 3 Area of sample 21 cm 2 V/A 3 1 Average rate of flow, cm 3/min 40 Duration of 2 hrs. test time 15 mins. Temp, -C 98 Results Weight of plating, gm. Rate of plating (R x 104) 0.9962 3.8 Appearance Bright and smooth The dynamic system of the present invention has also been tested with the use of a bath suggested for the prior batch process Nickel Sulphate (Ni SO, 7 H 20) Sodium Hypophosphite (Nail. Sodium Acetate (Na CH,023. Water (H 20) Total The following results were obtained: TABLE V. Approximate time Volume of solution in reservoir Volume of plating bath Area of steel plated Average flow per minute Temperature Initial p H Final p H Weight gain Rate (R x 104) Appearance minutes 780 c c. c c. em 2 6 c c /min. 970 C. 5.05 4.3 7483 gins. 3.4 Slightly rough Turning now to Fig 2 of the drawings the chemical nickel plating process and apparatus is illustrated in conjunction with the production of the interior lining for the body hla of first mentioned above and having the following composition: 3.5 parts by weight P 02 H 20 1 part by weight 1120) 1 5 parts by weight 94 parts by weight parts by weight the tank 10 a, of the composition previously described, but it will be understood that suchprocess and apparatus may be used to plate other articles The apparatus of Fig 2 essentially comprises a reservoir 35, including a storage compartment 36 and a communicating regeneration compartment 37 The bottom wall of the storage compartment 36 is provided with a drain conduit 38 arranged adjacent to the lowermost portion thereof that is

controlled by a manually operable valve 39; and, likewise, the bottom wall of the compartment 37 is provided with a drain conduit 40 arranged adjacent to the lowermost portion thereof that is controlled by a manually operable valve 41 The communication between the compartments 36 and 37 is preferably somewhat above the respective bottom walls thereof, as indicated at 42; a series of diffusion baffles 43 are arranged in the storage 785,693 compartment 36; and a series of mixers or agitators 44 are arranged in the regeneration compartment 37 and carried by a drive shaft that is operated by a suitable electric motor 46 The reservoir 35 as a whole, is adapted to store the bulk of a quantity of aqueous chemical nickel plating solutions of the nickel cation-hypophosphite anion type; while the tank i O a is adapted to hold, as a bath, a relatively small portion of the solution mentioned; whereby the volume of the reservoir 35 may be approximately 15,000 gallons, and the volume of the tank i O a may be approximately 10,000 gallons In the reservoir 35, the bulk of the solution is stored at a relatively low temperature well below the boiling point thereof, at about 1500 F and at a relatively high concentration with respect to the water content thereof; whereas in the tank l Oa, the small portion of the solution is held at a relatively high temperature slightly below the boiling point thereof, at about 210 F., and at a relatively low concentration with respect to the water content thereof. The chemical nickel plating solution that is employed may be any suitable nickel cationhypophosphite-anion type, such, for example, as those described above. In the production of the chemical nickel plating baths mentioned above the nickel cations may be suitably derived from come mercial nickel chloride, and the hypophosphite anions may be suitably derived from, commerical sodium hypophosphite. Further, the system comprises two motor driven pumps 47 and 48, a filter 49, two condensers 50 and 51, two flash tanks 52 and 53, two steam jet vacuum pumps 54 and 55, and a plating tank 56, as well as various commnuncating conduit structures and auxiliaries, described more fully hereinafter A "flash tank " is a chamber in which a subatmospheric pressure is maintained with the result that when the solution is introduced therein, there is a very rapid evaporation or " flash " which occurs due to the lower pressure conditions. The lower portion of the storage compartment 36 is connected to a conduit 57 that includes a manually operable valve 58; and O the upper portion of the storage compartment 36 is connected to a conduit 59 that includes a manually operable valve 60; and the conduits 57 and 59 are interconnected by a bypass conduit 61 that includes a manually operable valve 62 The conduits 61 and 57 are connected by a conduit

63, including a manually operable) valve 64 and a check valve 65, to the inlet of the pump 47; and, likewise, the conduits 59 and 61 are commonly connected by a conduit 66, including a manually operable valve 67 and a check valve 68, to the inlet of the filter 49 The outlet of the pump 47 is connected by a conduit 69, including a manually operable valve 70, to the inlet of the filter 49; and the outlet of the filter 49 is connected by a conduit 71, including a manually operable valve 72, to the upper portion of the condenser 50 Also, a liquid flow measuring device 73, preferably a " Rotameter," is operatively connected to the conduit 71 by 70 an, arrangement, including two manually operable valves 74 and 75, and two check valves 76 and 77, so that the flow of the solution through the conduit 71 into the condenser 50 may be appropriately metered 75 In view of the foregoing, it will be understood that by appropriate manipulation of the valves 58, 60, 62 and 64, the solution may be drawn into the inlet of the pump 47 either from the lower portion of the storage com 80 partment 36 or from the upper portion thereof Also, by appropriate manipulation of the valve 70, the rate of flow of the solution from the outlet of the pump 47 may be governed. Further, by appropriate manipulation of the 85 valve 67 some of the solution from the outlet of the pump 47 may be by-passed around the filter 49 back into the inlet of the pump 47; whereby the pump 47 may be controlled to pump the solution at its full capacity, while 90 permitting a variable amount of the solution to pass through the filter 49 In any case, the solution is withdrawn from the storage compartment 36 by the pump 47 and discharged into the upper portion of the condenser 50; 95 and from the lower portion of the condenser 50, the solution is conducted via a conduit 78, including a check valve 79, into either or both the tank la and the plating tank 56. More particularly, the conduit 78 is connected 100 to the inlet of the plating tank 56 via a manually operable valve 80 and a check valve 81, and is connected to the tank i O a by a manually operable valve 82 and a check valve 83 Also the solution in the conduit 78 105 may be conducted back into the regeneration compartment 37 via a conduit 84, including a manually operable valve 85 and a check valve 86; which arrangement is utilized for a purpose more fully explained hereinafter 110 Live steam at a pressure of about 125 pounds per square inch gauge in a steam supply conduit 87 is conducted via a manually operable valve 88 into the jet mechanism of the steam jet vacuum pump 54; water vapor is drawn 115 from the upper portion of the flash tank 53 via a conduit 89 into the jet mechanism of the steam jet vacuum pump 54; and the steam and the water vapor from the steam jet vacuum pump 54 are injected via a conduit 90 into the 120 upper portion of the condenser 50 In the operation of the steam jet vacuum pump 54, approximately

1500 pounds of steam per hour is conducted through the conduit 87, and approximately 1500 pounds of water 125 vapor per hour is conducted through the conduit 89, whereby the 3000 pounds of steam and water vapor are injected via the conduit 90 into the condenser 50 effecting both heating and dilution of the solution 130 conducted through the conduit 71 into the upper portion of the condenser 50 Specifically, the solution conducted via the conduit 71 into the upper portion of the condenser 50 has a temperature of about 1500 F, and is heated to a temperature of about 2100 F, and conducted into the conduit 78, and thence either into the plating tank 56 or into the tank l Oa or into both of the two-last-mentioned containers Also the rate of flow of the solution in the conduit 71 is about 94 gallons per minute, and the rate of flow of the solution in the conduit 78 is about 100 gallons per minute; whereby it is apparent that the solution from the storage compartment 36 is appropriately diluted in the condenser 50 before it is conducted into the plating tank 36 or into the tank 10 a. Also an auxiliary live steam injector 91 is arranged in the lower portion of the condenser 50 and is connected by a by-pass conduit 92 to the steam supply conduit 87, the conduit 92, including a manually operable valve 93 and a check valve 94 Thus, it will be understood that the valve 93 may be suitably manipulated in order to permit a predetermined by-pass of steam from the steam supply conduit 87 directly via the auxiliary injector 91 into the condenser 50. Furthermore, a conduit 95 is arranged in bypassing relation with respect to the conduit 92 between the steam supply conduit 87 and the auxiliary steam injector 91, which conduit 95 includes two check valves 96 and 97 and a temperature control valve 98 The temperature control valve 98 is connected by a capillary tube 99 to a temperature control bulb 100 arranged in a casing 101 disposed in the conduit 78; whereby the temperature of the solution in the conduit 78 governs, through the bulb 100 and the capillary tube 99, the position of the temperature control valve 78 so as to govern the amount of steam that passes through the temperature control valve 98 and consequently through the bypass conduit 95 from the steam supply conduit 87 into the auxiliary steam injector 91. The arrangement above described, including the temperature control valve 98 allows automatic adjustment of the temperature of the solution in the conduit 78 by governing the total amount of live steam that is injected thereinto by the auxiliary steam injector 91 in the condenser 50. The solution from the outlet of the plating tank 56 is conducted via a check valve 102 into a conduit 103; and, likewise, the solution from the tank l Oa is conducted via a check valve into the conduit 103; and the conduit 103 communicates with the upper portion of the flash tank

53 The lower portion of the flash tank 53 is connected to the upper portion of the flash tank 52 by a conduit 105, including a check valve 106; and the lower portion of the flash tank 52 communicates via a check valve 107 with a conduit 108 that includes a manually operable valve 109 that is connected to a conduit 110, including a check valve 111, extending to the inlet of the pump 48 The outlet of the pump 48 is 70 connected to a conduit 112 that includes a manually operable valve 113; and the conduits 108 and 112 are inter-connected by a by-pass conduit 114 that includes a manually operable valve 115 Finally, the conduit 112 includes 75 a manually operable valve 116 and two check valves 117 and 118 and communicates with the upper portion of the regeneration compartment 37 Also connected to the conduit 112 is a liquid flow measuring device 119, 80 preferably a "Rotameter," by an arrangement, including two manuallv operable valves and 121 and two check valves 122 and 123, so that the flow of the solution through the conduit 112 back to the regeneration corm 85 partment 37 may be metered. The upper portion of the flash tank 52 is connected to the lower portion of the condenser 51 by a conduit 124, including a manually operable valve 125; the upper por 90 tion of the condenser 51 is connected to a cool water supply conduit 126, containing cool water at about 90 ' F, and including a manually operable valve 127 and a check valve 128; the lower portion of the condenser 51 is con 95 nected to a drain conduit 129; and the upper portion of the condenser 51 is connected via a conduit 130 to the jet mechanism of the steam jet vacuum pump 55 Also, the jet mechanism of the steam jet vacuum pump 55 100 is connected via a manually operable valve 131 to the steam supply conduit 87; and the outlet of the steam jet vacuum pump 55 is discharged through a conduit 132 and a vent fixture 133 to the atmosphere 105 The solution conducted from the conduit 78 into the plating tank 56 and into the tank l Oa may have a temperature of about 210 ' F.; and the solution conducted from the plating tank 56 and the tank car l Oa into the 110 conduit 103 and thence into the upper portion of the flash tank 53 may have a temperature of approximately 210 ' F Now the operation of the steam jet vacuum pump 54 draws a partial vacuum in the flash tank 53 via the 115 conduit 89 that may correspond to about 12 inches to 14 inches of Hg, whereby the subatmospheric pressure in the flash tank 53 effects evaporation of water vapor from the solution in the flash tank 53 so that it is 120 cooled therein Consequently, the solution conducted from the flash tank 53 may have a temperature of about 180 ' F, and is, of course, accordingly more concentrated than the solution conducted thereinto, as a conse 125 quence of the evaporation of the water vapor therefrom The solution conducted from the lower portion of the flash tank 53

into the conduit 105 and thence into the upper portion of the flash tank 52 may have a tempera 130 It O 785,693 785,693 if ture of approximately 1800 F, as previously noted Now the operation of the steam jet vacuum pump 55 and the condenser 51 draw a partial vacuum in the flash tank 52 via the conduit 124 that may correspond to about 22 inches of Hg, whereby the subatmospheric pressure in the flash tank 52 effects evaporation of water vapor from the solution in the flash tank 52 so that it is cooled therein Consequently, the solution conducted from the flash tank 52 may have a temperature of about F, and is, of course, accordingly more concentrated than the solution conducted thereinto, as a consequence of the evaporation of the water vapor therefrom. The withdrawal of water vapor from the flash tank 53 and the subsequent injection of this water vapor by the steam jet vacuum pump 54 into the condenser 50 brings about a conversion of heat in the system and effects a corresponding concentration of the solution in the flash tank 53, whereas the withdrawal of water vapor from the flash tank 52 and the subsequent discharge thereof from the condenser 51 to the exterior prevents an overall dilution of the solution in the system and effects a corresponding concentration of the solution in the flash tank 52 In the operation of the system, the total amount of steam that is injected into the condenser 50 from the steam supply conduit 87 per unit time is substantially equal to the total amount of water vapor withdrawn from the flash tank 52 and discharged by the condenser 51 to the exterior per unit time, so that during continuous operation of the system, there is no overall and undesired substantial dilution of the solution or substantial expansion of the total volume thereof, provided the exterior heat losses are compensated for or kept to a minimum in accordance with the foregoing method. In the operation of the system, the plating tank 56 may be employed for the purpose of nickel plating the fittings and other accessories of the tank 10 a, whereas the portion of the solution held in the tank i O a brings about the plating upon the interior surface thereof as the tank l Oa is rotated about its longitudinal axis by suitable motor and roller mechanism which need not be described in detail. The tank l Oa holds a pool of the solution as a bath having the volume of about 5,000 ' gallons, since the tank car l Oa is retained only about half full of the solution as it is rotated. As the nickel plating reaction proceeds, the solution in the tank car l Oa is decomposed bringing about the production of hydrogen gas therein that accumulates in the upper portion thereof In order to prevent a gas lock in the tank i O a there is provided substantially U-shaped conduits 134 and 135 respectively communicating between the interior of the tank car l Oa adjacent to the associated ends thereof

and the atmosphere. The conduits 134 and 135 are provided with check valves 136 and 137, respectively, in order to prevent the entry of air into the tank car 10 a. As the tank car 10 a is continuously rotated the pool of' solution remains in the lower por 70 tion thereof, and the upper portion of the. tank car 10 a disposed above the level of the solution therein, indicated by the broken line a, is wet by a film of the solution so that the nickel plating reaction proceeds upon 75 both the upper and lower portions of the interior surface thereof Accordingly, the tank car 10 a must be rotated at a suitable speed in order to prevent undue depletion of the film of solution carried by the upper por 80 tion of the interior surface thereof; and it has beenfound that by rotating the tank car 10 a at a speed of about 15 r p m (revolutions per minute) the film of solution carried by the upper portion of the interior surface thereof 85 is not depleted by an amount greater than %, with respect to the normal consistency of the solution contained in the lower portion of the tank 10 a. Of course, as the plating operation proceeds 90 there is a tendency for the total quantity of solution contained in the system to be depleted somewhat with respect to the normal or standard composition thereof, whereby it is necessary in order to prevent this tendency, 95 periodically to regenerate the plating solution in the system by the addition of appropriate reagents in the regeneration compartment 37. More particularly, the reagents are added in the regeneration compartment 37 during 100 operation of the motor 46 so that the mixers 44 quickly place the reagents into solution; and the addition of the reagents is sufficiently frequent so that the composition of the solution does not materially depart from the 105 normal or standard composition previously noted More specifically, the nickel cations and the hypophosphite anions tare depleted during the plating operation, whereby appropriate amounts of commercial nickel chloride and 110 sodium hypophosphite are added periodicall in the regeneration compartment 37 Also as the plating operation proceeds, the acidity of the solution is increased; and in order to prevent the undesirable reduction in the 115 p H thereof, an appropriate weak alkali, such for example, as commercial sodium bicarbonate is added in the regeneration compartment 37 The arrangement whereby the reagents mentioned are added in the regeneration con 1 120 partment 37 is very advantageous in view of the fact that the bulk of the plating solution is retained in the communicating regeneration compartment 37 and storage compartment 36, whereby the consist 125 ency of the plating solution that is circulated from the storage compartment 36 into the plating

tank 56 and into the tank car a does not depart appreciably from the normal or standard consistency thereof, This 130it' 785,693 785,693 arrangement is very advantageous in view of the circumstance that the retention of the plating solution in the plating tank 56 and in the tank l Oa substantially at the normal or standard consistency thereof prevent stratification of the layer of nickel that is deposited upon the article placed in the plating tank 56 and of the liner that is produced upon the interior surface of the tank 10 a Specifically, the liner is smooth, continuous and substantially homogeneous and totally devoid of stratification or lamination by virtue of the carrying out of the plating operation employing the plating solution in such a manner that the consistency thereof does not depart materially from the normal or standard consistency initially established in the storage compartment 36. After the tank car 10 a has been provided 2 Q with the desired lining the plating solution is removed therefrom by rotating the tank car l Oa so that the throat 18 a is arranged at the bottom and a suitable connection is made via a fitting, not shown, carried by the cover 19 a, to an associated conduit 138, including a manually operable valve 139 At this time, the pump 48 may be operated, with the valve 139 in its open position and the valve 109 in its closed position in order to withdraw the plating solution from the tank l Oa and to discharge it via the conduit 112 and thence into the regeneration compartment 37 for storage therein and in the storage compartment 36 Thereafter the connection between the fixture, not shown, carried by the cover 19 a and the conduit 138 is disconnected, and the tank car l Oa may be removed by an overhead crane, not shown, from the supportroller mechanism. When the operation of the plating system is first initiated the bulk of the plating solution stored in the storage compartment 36 and in the regeneration compartment 37 may be substantially below the normal operating temperature of about 150 F, whereby it is thus necessary to bring about an initial warmup of the plating solution before circulation thereof through the plating tank 56 and the tank car loa This may be readily accomplished by closing the valves 80 and 82 in in order to cut off thie circulation of the plating solution through the plating tank 56 and through the tank car 10 a and by opening the valve 85 in order to accommodate local circulation of the plating solution from the conduit 78 through the conduit 84 back into the regeneration compartment -37 During this warm-up period, the plating solution is circulated by the pump 47 through the storage compartment 36, the filter 49 and the condenser 50 and thus into the conduit 79 and back via the conduit 84 into the regeneration compartment 37 In this local circulation of the plating solution, live steam is injected thereinto

in the condenser 50 This local circulation is continued until the bulk of the solution is appropriately preheated to the temperature of about 150 F in the storage compartment 36 Thereafter the valve 85 may be closed and the valves 80 and 82 may be 70 opened in order to bring about the circulation of the plating solution through the plating tank 56 and the tank car 1 Oa, in the manner previously explained. In the foregoing description of the mode 75 of operation of the plating system in carrying out this embodiment of the present invention, the tank car 10 a has been described as being formed of steel, which, of course, is the normal case, but it is noted that the tank 80 car 1 Oa may be formed of any suitable catalytic material Likewise, the articles or fixtures that are plated in the plating tank 56 may be formned of steel or any other suitable catalytic material N this connection, it is 85 noted that the following elements are catalytic and may be readily nickel plated: copper, silver, gold beryllium, boron, germanium, aluminium, thallium, silicon, carbon, vanadium molybdenum, tungsten, chromium, 90 selenium, tellurium, titanium, iron, cobalt, nickel, palladium and platinum; whereas the following elements are noncatalytic and may not ordinarily be nickel plated: bismuth, cadmium, tin, lead and manganese Of the 95 catalytic elements noted, the following are particularly good catalysts in the chemical nickel plating baths mentioned: aluminium, carbon, chromium, cobalt, iron, nickel and palladium Of course, it will be understood 100 that various and sundry alloys of the catalytic elements mentioned may be readily plated, and that the chemical nickel plating reaction is autocatalytic so that once it is initiated it proceeds automatically Also such non 105 conductors as vitreous, ceramic and plastic materials are noncatalytic and may not ordinarily be nickel plated employing the present method. Finally, in the system the interior surfaces 110 of the various tanks 35, 50, etc, the various conduits 71, 78, etc, and the various elements 73, 119, etc must be appropriately lined with glass porcelain, plastic material or other nonconductive and noncatalytic substance in 115 order to prevent chemical plating of nickel thereupon in an undesirable manner. In our application No 32470/55 (Serial No 785,697) there is described and claimed a process of chemically plating with nickel 120 the interior of a hollow container formed of a catalytic material which comprises providing an aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type having a predetermined composition and 125 characterized by a high plating rate at a temperature within a given range disposed near the boiling point thereof, rotating said container throughout a given time interval about a substantially horizontal axis, main 130 2 A process according

to claim 1, wherein 65 the first portion comprises the bulk of said solution and the second portion forms only a small portion of said solution. 3 A process according to claim 1 or 2, wherein said solution is introduced into the 70 lower portion of said plating chamber and continuously withdrawn from the upper portion thereof. 4 A process according to claim 1 or 2, and wherein the volumetric rate of circulation of 75 said solution in cubic feet per minute does not exceed the volume of said bath in cubic feet in said plating chamber. A process according to claim 1, wherein said first portion of said solution is at a rela 80 tively high concentration, and the second portion of said solution is at a relatively low concentration, the first portion of the solution withdrawn from said reservoir being diluted substantially to said relatively low concentra 85 tion before being introduced into said plating chamber, and the solution withdrawn from said plating chamber being concentrated substantially to said relatively high concentration before being returned to said reservoir 90 6 A process according to claim 1 or 5, wherein said solution is passed through a condenser between the reservoir and the plating chamber then through a flash tank between the plating chamber and the reservoir, said 95 solution being simultaneously heated substantially to said relatively high temperature and being diluted substantially to said relatively low concentration by injecting a controlled amount of live steam thereinto in said con 100 denser, and said solution being simultaneously cooled substantially to said relatively low temperature and being concentrated substantially to said relatively high concentration by maintaining a subatmospheric pressure in said 105 flash tank by withdrawing and discharging to the exterior water vapour from said solution in said flash tank. 7 A process according to claim 6, wherein the amount by weight of said live steam intro 110 duced into said solution in said condenser and the amount by weight of said water vapour withdrawn from said solution in said flash tank are substantially equal. 8 A process according to claim 6 or 7, 115 wherein the rate of live steam introduction into said solution in said condenser is about 3 % of the rate of circulation of said solution through said plating chamber. 9 A process according to claim 1, 5, 6, 7 120 or 8, wherein said relatively low temperature of said solution in said reservoir is about 1500 F and said relatively high temperature of said solution in said plating chamber is about 2100 F 125 A process according to claim 1 or 5, wherein the solution withdrawn from said plating chamber is introduced into a first flash tankj a subatmospheric pressure is maintained taining during said rotation and throughout said time

interval said container at least partially filled with said solution, and circulating during said rotation and throughout said time interval said solution from the exterior into said container and therethrough and back to the exterior, wherein said solution when introduced into said container has a temperature within said given range, and wherein the rate of circulation of said solution through said container is sufficiently high to maintain the temperature of said fill within said given range and to prevent substantial departure of the composition of said fill from said predetermined composition. In our application No 32471/55 (Serial No. 785,698) there is described and claimed a container formed of a catalytic material and provided with a smooth, continuous and substantially homogeneous lining intimately bonded to the interior surface thereof and comprising an alloy of nickel and phosphorus, said alloy containing 3 to 11 % phosphorus by weight.

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* GB785694 (A)

Description: GB785694 (A) ? 1957-11-06

Improvements in or relating to process and bath for the chemical plating ofa catalytic material with nickel

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PATENT SPECIFICATION Date of Application and filing Complete Specification: Nov 12, No 31365153. Application made in United States of America on June 3, 1953. z, /' Complete Specification Published: Nov6, 1957. 785,694 1953. Index at acceptance: -Class 82 ( 2), F( 1 BIB: 2 U), F 4 (A: E: F: 'G: J: K: W: X). International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to Process and Bath for the Chemical Plating of a Catalytic Material with Nickel We, GENERAL AMERICAN TRANSPORTATION CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 135, South La Salle Street, Chicago, Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to improved processes of chemical nickel plating of catalytic materials employing baths of the nickel cationhypophosphite anion type containing stabilizing agents. The chemical nickel plating of a catalytic material employing an aqueous bath of the nickel cation-hypophosphite anion type is based upon the catalytic reduction of nickel cations to metallic nickel and the corresponding oxidation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface The reactions take place when the body of catalytic material is immersed in the plating bath, and the exterior surface of the body of catalytic material is coated with nickel. The following elements -are catalytic for the oxidation of hypophosphite and thus may be directly nickel-plated: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum The following elements are examples of materials which may be nickelplated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, silver, gold, beryllium, germanium, aluminium, carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium and uranium The following elements are examples of non-catalytic materials which ordinarily may not be nickelplated: bismuth, cadmium, tin, lead and zinc. The activity of the catalytic materials varies considerably; and the following elements are particularly good catalysts in the chemical

lPtice 3 s 6 d l nickel plating bath: iron, cobalt, nickel and palladium The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are both catalytic; and the reduction of the nickel cations to metallic nickel in the plating bath proceeds until all of the nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to phosphite anions, in the presence of an excess of nickel cations Actually the reactions are slowed-down rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations to form an acid, which, in turn, lowers the p H of the bath, and the reducing power of the hypophosphite anions is decreased as the p H value of the bath decreases Moreover, there is a tendency for the early formation in the plating bath of a " black precipitate " that comprises a random chemical reduction of the nickel cations Of course, this formation of the black precipitate comprises a decomposition of the plating bath; and is particularly objectionable in that it causes the nickel deposit to be coarse, rough and frequently porous. For the dual purposes of increasing the stability of the plating bath (preventing the formation of the black precipitate mentioned), and of increasing the normal plating rate of the bath, various baths of the present type have been suggested employing different additives or agents that serve either as buffers or as exaltants, such as a buffer in the form of a soluble salt of an organic acid, and specifically sodium acetate; and in our copending application No 17206/53 (Specification Serial No. 761,062), there is disclosed a chemical nickel plating bath of the nickel cation-hypophosphite anion type that contains as an additive an exaltant in the form of a soluble salt of a idkice2-,1 rob le l -2 C% (i,, K, -z i,-c simple short-chain saturated aliphatic dicarboxylic acid, such as sodium succinate. In carrying out the chemical nickel plating process, particularly in a continuous system such as disclosed in Application No 19063/53 (Serial No 785,693), it has been discovered that an initially stable plating bath becomes unstable after some use, and notwithstanding the content of the buffer, or the exaltant, or both It is believed that the formation of the black precipitate starts at the surfaces of suspensoids (solid particles of dust, microcrystalline precipitate of ferric hypophosphite, nickel phosphite), present in the plating bath; and the presence of these suspensoids in the plating bath is evidenced by the observation of Tyndall beams when a shaft of light is passed through the clear filtered plating bath, even when freshly prepared.

The present invention is predicated upon the discovery that plating baths of the nickel cation-hypophosphite anion types mentioned may be stabilized to a high degree, without material depression of the plating rates thereof, by the further addition thereto of a trace amount of a thio compound stabilizing additive as defined hereinafter. The present invention provides a nickel plating bath which comprises an aqueous solution containing nickel ions, hypophosphite ions and an amount of a thio compound stabilizing additive as defined hereinafter so as not substantially to reduce the plating rate of the bath and so as to inhibit random decomposition of the bath. The present invention further provides the process of chemically plating a catalytic material with nickel which comprises contacting said material with a bath as defined above. It has been discovered that plating baths of the character mentioned are stabilized by the presence therein of extremely small amounts of sulphide ions (S" 1), which hydrolyze, in the presence of water, to sulphydric ions (SHI) In larger quantities sulphide ions added to the plating bath, for example as HS, are a catalytic poison, and will considerably reduce the plating rate, or stop plating altogether However, at the proper level, sulphide ions prevent random decomposition of the plating bath and the formation of the black precipitate mentioned; the minimum quantity of sulphide ions in the plating bath to achieve stability being approximately 10 parts per 1,000,000,000 parts of the plating bath by weight. It is believed that the sulphide ions selectively attach themselves to the suspensoids in the plating bath thereby preventing the suspensoids from serving as nuclei for the random decomposition of the plating bath and the formation of the objectionable black precipitate. Sulphur (as such, or as inorganic or possibly organic sulphides) is generally present in very small amounts (of the order of 10 parts per 1,000,000,000 parts) in water and in the chemicals ordinarily used to prepare the plating bath Elemental sulphur (particularly in a reducing medium) hydrolyzes to hydrogen 70 sulphide; and any other soluble sulphide present in the acid plating bath will also bring about the formation of hydrogen sulphide which is volatile at elevated temperatures and thus escapes from the plating bath As a result 75 of this loss of sulphide ions, by boiling off of the hydrogen sulphide, the plating bath becomes unstable after a short time interval, as previously noted Wherever sulphide ions are not fortuitously present in the plating bath in 80 at least the above concentration, they should be added, preferably as lead sulphide. It is thought that the addition of traces of a thio compound that continuously releases sulphide ions in controlled amounts in the 85 quantities previously mentioned achieves the stabilization of the

plating bath; and it is believed that this is the mechanism of the stabilization Of course, the cations of the stabilizing additive must not comprise catalytic 90 poisons in the particular range where they are being used for stabilization; nor should they be themselves catalysts for the oxidation of hypophosphite to phosphite For practical purposes the S " ion (possibly Sill ion) can be 95 controlled continuously by the following two broad classes of thio compound comprising the stabilizing additives of this invention. 1) Heavy metal and other inorganic sulphides that are stable and practically insoluble in the 100 plating bath under plating conditions; i e in an aqueous acid solution having a p H above 2 5 and particularly in the range from 3 0 to 5 5, and at temperatures above 90 C, provided the cation bound to the sulphur is not a catalyst 105 for the oxidation of hypophosphite; in other words, that it does not belong to Group VIII of the Periodic System. 2) Other organic and inorganic thiocompounds that are water-soluble and soluble 110 under plating conditions in the plating bath, and which hydrolyze with respect to their sulphur at a rate such that a concentration of at least 10 ppb (parts per billion) of liberated S" is continuously maintained in the aqueous 115 plating bath. Insofar as the first class is concerned, it is not necessary to supply the metallic sulphides as such, as there appears to be usually enough sulphur or sulphide ions present in the bath as 120 impurities It is sufficient, therefore, merely to add traces of element whose cations form sulphides that are stable and practically insoluble under plating conditions in the aqueous acid plating bath; and an excess of these 125 cations should be avoided as most of them are catalytic poisons The elements that form such stabilizing additives are: lead, copper, bismuth, tin, selenium, tellurium, tungsten, thorium, titanium, zinc, manganese and rhenium Pre 130 785,694 use; or the bath may be continuously regenerated, the steel object being removed after the desired thickness of nickel has been deposited thereon. With respect to the composition of the 70 bath, it comprises an aqueous solution containing nickel cations, hypophosphite anions, a buffer or exaltant, and a thio compound For example, the nickel cations may be derived from nickel chloride; and the hypophosphite 75 anions may be derived from sodium, potassium, lithium, calcium, magnesium, strontium, barium, hypophosphites, or various combinations thereof Specifically, a suitable bath may be formed in an exceedingly simple manner by 80 dissolving in a hydrochloric acid-water solution nickel chloride and sodium hypophosphite; and then the buffer or exaltant and the stabilizing agent are added thereto, as explained more fully hereinafter The desired p H of the bath 85 is established by the eventual introduction thereinto of additional hydrochloric acid

and is appropriately adjusted by the addition thereto of a weak alkali, preferably sodium bicarbonate 90 The terms " cation," " anion," and "ion" as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present in the plating bath; i e, both undissociated and dissociated 95 material In other words, 100 % dissociation is assumed when the terms noted are used in connection with molar ratios and concentrations in the plating bath. The stabilizing effects of the various corm 100 pounds of the first class were determined from a series of plating tests that were made employing a " standard " test plating bath of the general character of that disclosed in our previously-mentioned application, No 17206/53 105 (Serial No 761,062), except that the chemical ingredients were highly purified; this standard test plating bath had a volume of 50 cc and a temperature between 98 C and 100 C; and therein low carbon steel samples were plated 110 that had a surface area of 20 cm 2 and that had been vapor-degreased, electro-cleaned, and pickled in a 10 % HQI solution The standard test plating bath was produced from a solution containing nickel as nickel hypophosphite ( 0 09 115 mpl), sodium hypophosphite ( 0 045 mpl), sodium succinate ( 0 06 mpl), sodium chloride ( 0.18 mpl), and enough water to make one liter, the p H having been adjusted to a value of 4.6 with pure HGI, whereby the nickel cation/ 120 hypophosphite anion ratio was 0 4 The stabilizing agents were then added to the standard test plating bath by measuring the proper volume from stock solutions containing 1,000 ppm thereof; and the plating rates (R) 125 were measured in gms /cm'/min, but for convenience the specific values in the results of the plating tests set forth hereinafter are expressed as R x 104 In these tests stability is indicated by the time in minutes 130 ferred elements are lead, tellurium and tin, and suitable concentration of these elements in nickel plating baths according to the present invention are respectively 0 1 to 10 parts Pb cations per 1,000,000 parts of the bath by weight (preferably between 1 and-5 parts by weight of Pb S per 1,000,000 parts by weight of said bath are used); up to 200 parts by weight of tellurium per 1,000,000 parts by weight of the bath; and up to 125 parts by weight of tin per 1,000,000 parts by weight of the bath. Insofar as the second class is concerned, the organic and inorganic thio-compounds are active to achieve stabilization; typical examples are soluble inorganic thio-sulphates, thiocyanates, xanthates, " Aerolloats," thio-acids, thioamines (such as thiocarbanilide or thiourea), organic sulphides, which organic chemicals have a very low dissociation constant (K) relative to their sulphur atoms. Also in connection with the first class, it is noted that certain of

the stabilizing agents increase the normal plating rate of the plating bath in addition to achieving stability; i e lead, tin and manganese; while other of these stabilizing agents improve the appearance of the plated article with reference to brightness in addition to achieving stability; i e selenium and tellurium. In accordance with the nickel plating process of the present invention, the article to be nickel-plated and normally formed of a catalytic material, is properly prepared by mechanically cleaning, degreasing and light pickling, substantially in accordance with standard practices in electroplating processes. For example, in the nickel plating of a steel object, it is customary mechanically to clean the rust and mill scale from the object, to degrease the object, and then lightly to pickle the object in a suitable acid, such as hydrochloric acid The article is then immersed in a suitable volume of the bath containing the proper proportions of nickel cations, hypophosphite anions, buffer or exaltant, and stabilizing agent, the p H of the bath having been, if necessary, adjusted to an optimum value by the addition of an appropriate acid or base, and the bath having been heated to a temperature just below its boiling point, such as 990 C, at atmospheric pressure Almost immediately hydrogen bubbles are formed on the catalytic surface of the steel object and escape in a steady stream from the bath, while the surface of the steel object is slowly coated with metallic nickel (containing some phosphorus) The reaction is continued until the color of the bath (green at the start) shows the absence of nickel, or until the evolution of hydrogen stops, or until it is determined that the required thickness of the nickel coating has been deposited on the steel object Of course, the steel object is then removed from the bath and rinsed off with water, and is then ready for 785,694 that elapsed before 'black precipitate" was formed; and the appearance of the nickel deposited upon the samples were noted In describing the appearance of a test sample, the following symbols are employed: B= Semi-bright (satin); BB=Bright; VB=Very bright; S = Smooth; SR= Slightly rough; R = Rough; D = Dull; Sp = Spotted. Two "blank" plating tests were first run employing only the test samples in the standard test plating bath (without the addition of any stabilizing agent), with the following results: Duration of Test Weight gain, gins. Plating rate R x 104 Sample appearance Time to black ppt. min 60 min. 0.0948 4.74 B-S None B-SR mins. From the two above blank plating tests, it is apparent that the standard test plating bath is unstable since noticeable decomposition thereof takes place within 20 minutes; and hereafter a plating bath is

considered "unstable" in the event it decomposes within a time interval of 60 minutes. Three stability tests were then run employing the standard test plating bath (without the test samples) at a plating temperature for the purpose of demonstrating the stabilizing effect of lead sulphide Specifically in the three stability tests lead sulphide in the respective amounts of 52 ppb, 43 ppb and zero ppb were added to the standard test plating bath, thereby establishing the respective levels of S ions therein of 8 ppb, 7 ppb and zero ppb; whereby the respective times at which black precipitate formation was observed were: 120 minutes, 16 minutes and 13 minutes Accordingly, the three stability tests clearly demonstrate that the level at which the S" ion is effective as a stabilizer in the presence of lead is well-defined, the lower threshold of effectiveness being at about 8 ppb and definitely in the range 10 to 100 ppb, as will appear more fully hereinafter. In a series of these plating tests employing the standard test plating bath containing lead as the stabilizing agent, derived from PBCI 1, the following results were obtained: a) Rate Tests 10 minutes ppm of Pb"0 0 01 0 04 0 07 0 10 0 20 Wt gain Plating Rate Rx 104 Sample appear. 0.0919 0 0987 4.59 4 94 0.0985 0 1037 4.93 5 18 B-S BB-S BB-S BB-S 0.0907 0 0994 4.54 4 97 BB-S BB-S Time to black ppt. ppm of Pb 0.40 0 50 1 0 10 0 50 0 Wt gain Plating rate Rx 104 Sample appear. 0.0986 0 0899 0 0938 4.93 4 49 BB-S BB-S 0.0554 0 0001 4.69 2 77 BB-S BB-S Time to black ppt. D 785,694 none 785,694 b) Stability tests 60 minutes ppm of Pb Wt gain 0 O 01 0 04 0 07 0 10 0 20 0.1892 0 2110 0 2092 0 2122 0 1896 0 1902 Sample appear. BB-S BB-S BB-S BB-S BB-S BB-S Time to black ppt 16 ppm of Pb O d Wt gain 37 35 43 stable 4 1 0 10 0 0.1948 0 1907 50.0 0.1763 0 0001 Sample Appear. Time to black ppt. BB-S BB-S BB-S Some of these plating tests employing the standard test plating bath containing lead as the stabilizing agent, derived from Pb(NO,)2, were repeated; and the following results were obtained: ppm of Pb"Duration of Test mins. 1.0 2.0 1.0 2.0 10 60 60 0.0927 0 0771 0.1719 0 1596 4.68 3 85 Sample Appearance BB-S BB-S Time to black ppt none none In view of the foregoing plating tests employing in the standard test plating bath lead as the stabilizing agent, it will be observed that about 0 1 ppm of PB" is required in order to obtain a stable bath; and at about 10 ppm of Pb, the plating rate starts to decline Finally, the peculiar phenomenon is exhibited that the trace of lead between 0 01 and 1 0

ppm BB-S BB-S stable actually enhances or exalts the plating rate, a maximum exaltation appearing between 0 01 and 0 07 ppm. In a series of these plating tests employing the standard test plating bath containing tin 20 as the stabilizing agent, the following results were obtained: D Wt gain Plating rate Rx 104 785,694 a) Rate tests ppm of Sn" Wt gain Plating rate Rx 104 Sample appear. Time to black ppt. minutes 0.1 0.1064 5.32 0.5 0.1072 5.36 0.0880 4.40 0.1135 5.68 B-S B-S B-S B-S none 0.0998 4.99 0.0910 4.56 0.0847 4.26 B-S B-S B-S b) Stability tests 60 minutes ppm of Sn" 0 1 O 5 Wt gain 0 2189 0 2204 Sample appear B-S B-S Time to black ppt 40 40 0.1865 B-S 0.2220 B-S 0.1905 B-S 0.1872 B-S 0.1776 B-S stable In view of the foregoing plating test employ In a series of these plating tests employing ing in the standard test plating bath tin as the the standard test plating bath containing stabilizing agent, the stabilizing range is about manganese as the stabilizing agent the follow 10 2.0 to 50 0 ppm, the plating rate being in ing results were obtained: creased at 2 0 ppm. a) Rate tests 10 minutes ppm of Mn 0 1 Wt gain 0 0948 0 9068 Plating rate 4 74 4 84 Rx IO 4 Sample appear. Time to black ppt. 0.1046 5.23 3.3 5 0.1050 0 0792 5.25 3 96 0.0812 4.06 0.0987 4.94 B-S B-S BB-S BB-S BB-S BB-S B-R b) Stability tests 60 minutes ppm of Mn 0 1 2 Wt gain 0 1903 0 1933 0 1952 Sample appear B-SR B-SR BB-S Time to-black ppt 20 30 stable In view of the foregoing plating tests employing in the standard test plating bath manganese as the stabilizing agent, it will be observed that stabilization is obtained at concentrations between 1 0 and 4 0 ppm and that 0.0969 4.84 B-R 3.3 5 10 0.1943 0 1864 0 1921 BB-S B-SR B-SR stable 40 40 the plating rate is somewhat enhanced. In a series of these plating tests employing the standard test plating bath containing 20 selenium as the stabilizing agent, the following results were obtained: 785,694 a) Rate tests 10 minutes ppm of Se O" 1 Wt gain 0 0750 Plating rate Rx 104 3 75 Sample appearance BB-S Time to black ppt. b) Stability tests 60 mi ppm of Se O Wt gain Sample appearance Time to black ppt. inutes 0.1969 BB-S In view of the foregoing plating tests employing in the standard test plating bath selenium as the stabilizing agent, it will be observed that at about 5 0 ppm of selenium the bath is stabilized; and in passing, it is noted that identical results were obtained with a) Rate tests 10 minutes ppm of Te O 1 Wt gain Plating

Rate R x 104 Sample appearance Time to black ppt. ppm of Te O 31 ' Wt gain Plating rate Rx 104 Sample appearance Time to black ppt. 0.0666 3.33 B-S 0.0570 2.85 BB-S 2 5 0.0778 0 0034 3.65 0 17 BB-S BB-S 0.1526 BB-S 0.1391 BB-S stable the selenite and selenate anions with brightening of the nickel deposit. In a series of these plating tests employing 10 the standard test plating bath containing tellurium as the stabilizing agent the following results were obtained: 0.0468 2.34 BB-S 0.0594 2.97 VB-S 0.0468 2.34 BB-S 0.0431 2.15 BB-S 0.0564 2.82 VB-S 785,694 b) Stability tests 60 minutes ppm of Te Wt gain Sample appearance Time to black ppt. ppm of Te OQ 11 Wt gain Sample appearance Time to black ppt. 0.1 0.1495 0 1285 0 1218 0 1128 B-S BB-S B-S B-S stable 1 5 10 160 0.1324 0 1341 0 1388 0 1900 BB-S VB-S VB-S BB-S stable In view of the foregoing plating tests employing in the standard test plating bath tellurium as the stabilizing agent, it will be observed that stabilization is obtained at about 0.1 ppm and that very bright relatively soft nickel deposits are obtained In passing, it is noted that the tellurate anion gives results identical to those obtained with the tellurite anion, as probably the Te O," anion is reduced to the Te O,1 " anion by the hypophosphite. In a series of these plating tests employing the standard test plating bath containing bismuth as the stabilizing agent, the following results were obtained: a) Rate tests 10 minutes ppm of Bi Wt gain Plating rate Rx 104 Sample appearance 0.5 0.0654 0 0832 0 0610 0 0708 3.27 4 16 BB-S 3.05 BB-S BB-S 3.54 BB-S Time to black ppt. b) Stability tests 60 minutes ppm of BiWt gain Sample appearance 0.5 0.1491 0.1524 0 1514 0 1442 BB-S BB-S BB-S BB-S stable In view of the foregoing plating tests employing in the standard test plating bath bismuth as the stabilizing agent, it will be observed that stabilization occurs at concentrations between 1 0 and 5 0 ppm, the maxistable mum rate being at about 1 0 ppm. In a series of these plating tests employing the standard test plating bath containing 25 copper as the stabilizing agent, the following results were obtained: Time to black ppt. 785,694 a) Rate tests 10 minutes ppm of Cu' Wt gain Plating rate Rx 104 Sample appearance Time to black ppt. b) Stability tests 60 minutes ppm of Cu" Wt gain 10 22 1 50 100 221 500 0.1222 0 1271 0 1264 0 1310 1388 0 1509 0 1850 Sample appear B-SR BB-S BB-S B-S B-S DR Time to black ppt. DR 29 42 stable

Some of these plating tests employing the cation (Cu) were repeated; and the following 5 standard test plating bath containing cuprous results were obtained: ppm of Cu' Wt gain Sample appearance Time to black ppt. 10 20 50 0.1282 0 1216 0 1123 0 0862 B-S In view of the foregoing plating tests employing in the standard test plating bath copper as the stabilizing agent, it will be observed that the cupric cation (Cu) is stabilizing within the range 20 to 50 ppm; while the cuprous cation (Cu) is stabilizing a) Rate tests 10 minutes B-S B-S BB-S stable above 10 ppm. In a series of these plating tests employing I 5 the standard test plating bath containing rhenium as the stabilizing agent, the following results were obtained: ppm of Re O O Wt gain Plating rate Rx 10 Sample appearance 0.0860 0 0907 0 0848 0 0726 4.30 4 54 B-S B-S 4.24 3.63 B-SR B-SR Time to black ppt. b) Stability tests 60 minutes ppm of Re O 41 Wt gain Sample appearance Time to black ppt. 0.1528 0 1526 0 1556 0 1527 B-S B-S B-SR B-SR 20 40 0.0700 22.1 3.53 0.1059 none 5.29 B-S none Some of these plating tests employing the cation were repeated, and the following results standard test plating bath containing Re were obtained: ppm of Re 1 5 10 Wt gain Sample appearance Time to black ppt. In view of the foregoing plating tests employing in the standard test plating bath rhenium as the stabilizing agent, it will be observed that -the perrhenate anion Rel O,' is not stabilizing, whereas the Re cation is stabilizing at a concentration of about 5 ppm. In a series of these plating tests employing the standard test plating bath containing thorium as the stabilizing agent, the following results were obtained: Stability tests 60 minutes ppm of Th Wt gain Sample appearance Time to black ppt. 1 5 10 0.1301 B-S stable In view of the foregoing plating tests employing in the standard test bath thorium as the stabilizing agent, it will be observed that the peculiar condition is encountered that stabilization is obtained in the range 1 to 5 ppm, but not at higher concentrations at about 0.1213 B-S stable 0.1233 B-S 10.0 ppm, the plating rate being somewhat reduced. In a series of these plating tests employing 25 the standard test plating bath containing titanium as the stabilizing agent, the following results were obtained; Stability tests 60 minutes ppm of TiWt gain Sample appearance Time to black ppt. ppm of Ti Wt gain Sample appearance Time to black ppt.

In view of the foregoing plating tests employing in the standard test plating bath titanium as the stabilizing agent, it will be observed that the Ti- cation produces stabilization at about 1 0 ppm with dull plating and considerable reduction in the plating rate; but that the Ti cation is stabilizing at about 5 0 ppm with a low plating rate. In a series of these plating tests employing the standard test plating bath containing tungsten as the stabilizing agent, the following 40 results were obtained: 0.1173 B-S 0.0996 B-S stable 0.0502B-S stable 0.1033 D 0.0048 D no plating D stable 0.1309 BB-S 0.1060 B-S stable 0.0803 B-S stable 785,694 785,694 Stability tests 60 minutes ppm of W 03-' Wt gain Sample appearance Time to black ppt. In view of the foregoing plating tests employing in the standard test plating bath tungsten as the stabilizing agent, it will be observed that stabilization is obtained at a concentration rather sharply defined at 5 0 ppm, the plating rate being somewhat reduced. In a series of these plating tests employing the standard test plating bath containing zinc as the stabilizing agent, the following results 10 were obtained: Stability tests 60 minutes ppm Zn" Wt gain 10 20 30 50 0.1303 0 1321 0 1318 0 1259 O 1100 0 1093Sample appear. Time to black ppt. B-S B-S B-S B-S D-S D-S 27 56 41 stable stable stable In view of the foregoing plating tests employing in the standard test bath zinc as the stabilizing agent, it will be observed that stabilization is obtained at about 20 0 ppm and above, the plating rate being somewhat depressed. It is noted that the above-mentioned metallic cations all form sulphides that are both substantially insoluble in the plating bath at a p H above 2 5 and stable at the plating temperature ( 90 C and above) These elements all belong to the recognized qualitative analytical groups I and II, and specifically to subgroups Ia, Ib, M Ib and I Ic As a matter of fact, if both the metals that are catalysts for the oxidation of hypophosphite to phosphite and that form unstable sulphides in boiling water or at p H values above 2 5 are excluded, it can be stated that the inorganic stabilizing elements are those of groups I, M Ib and Ilc. In a series of these plating tests employing the standard test plating bath using a sulphurcontaining molecule (inorganic thio-compounds) as the stabilizing agent, the following results were obtained: a) Rate tests 10 minutes ppm of 5203 Wt gain Plating rate Rx 104 0.5 1

5 10 0.0906 4.53 Sample appearance D-S Time to black ppt. ppm of CNS' O 5 Wt gain 0 1145 Plating rate Rx 104 5 73 Sample appearance B-S none none 0.1286 B-S 0.1350 BB-S stable 0.1336 B-S -0.0912 4.56 B-S 0.0049 0.02 D-R 0.0926 4.63 D-S 0.1077 5.39 None 0.0 B-S Time to black ppt. 785,694 b) Stability tests 60 minutes ppm of 520 o 11 Wt gain Sample appearance Time to black ppt. ppm of CNS Wt gain Sample appearance Time to black ppt. 0.5 1 5 10 0 1450 D-S 0.1458 D-S 0.1490 B-S 0.1240 D-R stable 0.5 0 1742 B-S stable In view of the foregoing plating tests employing in the standard test bath sulphur (inorganic thio-compounds) as the stabilizing agent, it will be observed that the thiosulphate anion stabilizes at concentrations of about 1 0 to 5 0 ppm while the thiocyanate anion stabilizes at concentrations between 0 5 and 1 0 ppm. When the nickel cation concentration in the plating bath is increased, the amount of stabilizing agent that must be added thereto must be disproportionately increased as indicated by the plating test explained below In carrying out these tests, a special " test plating bath was produced from a solution containing nickel as nickel hypophosphite ( 0 18 0.1685 B-S stable mpl), sodium hypophosphite ( 0 09 mpl), sodium succinate ( 0 12 mpl), sodium chloride ( 0.36 mpl), and enough water to make one liter, the p H having been adjusted to a value of 4 63 with pure H 1, whereby the nickel cation/hypophosphite anion ratio was 0 4 This special plating bath had a volume of 50 cc. and a temperature of between 980 C and 1000 C; and therein low carbon steel samples were plated that had a surface area of cm 2 that had been vapor-degreased, electrocleaned and pickled in a T 10 % HC 1 solution. Four "blank" plating tests were first run employing only the test samples in the special test plating bath (without the addition of any stabilizing agent), with the following results: Duration of test (minutes) Wt gain, gms. Plating rate R x 10 W Sample appearance Time to black ppt. 0.0797 3.99 B-R min. 0.0625 0.1376 0.2041 3.13 B-S none B-S min. min. The inconsistencies in these plating tests In a series of these plating tests employing 40 with regard to the weight gains are due to the the special test plating bath containing lead formation of black precipitate in the plating as the stabilizing agent, the following results baths and the trapping thereof in the nickel were obtained: deposits upon the samples. a) Rate Tests 10 minutes ppm of Pb Wt gain Plating rate Rx 104 1 5 10

15 20 0.1111 0 0559 0 0577 0 0544 0 0541 5.56 Sample appearance B-R Time to black ppt 5 min. 2.80 B-S 2.89 B-S 2.72 B-S 2.71 B-S none none none none 785,694 b) Stability tests 60 minutes ppm of Pb" Wt gain Sample appearance B-R 1 5 10 15 20 0.1956 0 1924 0 1965 0 2096 0 2043 BB-S Time to black ppt 5 min 30 min By comparison of the plating tests respectively involving the standard test plating bath and the special test plating bath, it will be observed that as little as 0 1 ppm of Pb" cation is effective to produce stabilization in the standard test plating bath, whereas 15 0 ppm PB cation is required to effect stabilization in the special test plating bath In other a) Rate tests 10 minutes ppm of CN 51 Wt gain Plating rate R x 104 Sample appearance Time to black ppt. b) Stability tests 60 minutes ppm of CN 51 Wt gain Sample appearance Time to black ppt. BB-S BB-S BB-S min stable stable words, in order to obtain stabilization in the special test plating bath containing a 2-fold increase of nickel cation, it is necessary to provide a 150-fold increase of Pb" cation. A few of these plating tests employing the special test plating bath containing sulphur (inorganic thio-compound) as the stabilizing agent were repeated with the following results: 0.1364 6.82 BB-S 0.0025 0.13 B-S 0.0013 0.07 B-S 0.2385 B-S min. Again it will be observed that while stabilization takes place with 0 5 ppm of CN 51 anion in the standard test plating bath more than 1 0 ppm (and less than 5 0 ppm) of CNS' anion is required in the special test plating bath. The effective minimum amounts of the different ones of these stabilizing agents to achieve stabilization are not only a function of nickel cation concentration in the plating baths, as previously explained, but they also depend upon the particular compositions of the plating baths with reference to other constituents To illustrate this phenomena three baths A," c B" and "o C" were prepared having the particular composition with respect to other ingredients as follows: 0.0046 D-S stable 0.0038 D-S stable Bath compositions: (for 1 liter aqueous solution) A Nickel as Nickel hypophosphite 0 09 mpl Sodium hypophosphite 0 045 mpl Sodium chloride 0 18 mpl Sodium succinate 0 06 mpl p H adjusted to 4 60 with pure HCI B Nickel as Nickel hypophosphite 0 09 mpl Sodium hypophosphite 0 045 mpl Sodium chloride 0 18 mpl Amino-acetic acid 0 18 mpl p H adjusted to 4 60 with pure Na OH and HF Cl C Nickel as Nickel hypophosphite 0 09 mpl Sodium hypophosphite 0 045 mpl Sodium chloride 0 18 mpl Malic acid 0 18 mpl Sodium succinate 0 06 mpl p H adjusted to 4 60 with pure Na OH and Fl I Plating tests were conducted for 60 minutes at about

990 C on pickled and degreased samples of the character previously mentioned each having a surface area of 20 cm 2 and the following weight gain figures (gm) were 5 obtained employing no stabilizing agent and the respective stabilizing agents tellurium, lead, and thiocyanate as indicated below: No stabilizing Time to black Bath Initial p H agent added: ppt in min. A B B B C C 4.6 4.5 6.5 8.5 4.50 5.50 0.1892 0.1077 0.2176 0.1597 0.2110 0.2126 29 22 4 32 Initial Bath p H Time to black ppt min. Tellurium ppm. 1 5 10 0.1285 0 1218 0 1128 0.1900 0.1018 0 1037 0 1023 0.2614 0 2592 0 2571 0.2270 0 2570 0 2755 0.1954 0 1828 0 1748 0.2296 0 2324 0 2276 0 1824 Time to black ppt min. Lead ppm. 0.07 1 0.2122 0 1907 0 1763 0 1111 0 0930 0 0739 0 2558 0 2301 0 1864 no effect up to 50 ppm 0 2151 0 2116 0 1986 0 2443 0 2380 0 2320 Initial Bath p H Time to black ppt min. Thiocyanate ppm 1 5 0.1685 no plating 0.1552 0 0016 0 0008 0.2666 0.2908 no plating no plating 0.2131 0 0014 0 0010 0.2284 0 0028 0 0006 4.6 None 4.5 6.5 A B B B C C 8.5 4.50 5.50 20-30 None Bath Initial p H 10 A B B B C C 4.6 4.5 6.5 8.5 4.5 None 20-30 None 5.50 None A B B B C 4.6 4.5 6.5 8.5 4.5 20-30 None 785,694 C 5.50 o addition thereof to the plating bath along with the other regenerating ingredients as noted above. Turning now to the stabilizing agents of the second class or organic -thio-compound type, the sulphhydric flotation collectors have been found to be particularly effective Specifically the xanthates, of the general formula: RO-C-SH (or M) S From the above table, it will be observed that in bath "B," at p H 8 5, while Te cation actually increases the plating rate, Pb cation is of no effect in the range set forth However in other tests (not reported in detail at this point) it has been demonstrated that Pb" cation is effective at 75 ppm (decreased plating rate: 0 1467 gins gained) and at 100 ppm increased plating rate: 0 1852 gms gained. In passing, it is noted that the stabilizing agents can be introduced into the plating bath by other means than by adding a solution of a soluble salt; i e, the plating can be performed in the plating bath in the presence of a strip of metallic lead, providing there are enough S ions in the bath as previously explained. In the foregoing plating tests, steel samples were used for studying the actions of the stabilizing agents, but the same stabilizing effects have been found to hold true in the plating of other materials such as brass, copper, aluminium or manganese. As previously pointed out, initially stable plating baths of the

character disclosed in our application No 17206/53 (Serial No. 761,062), are sometimes fortuitously obtained by the production of these baths from commercial grades of chemical ingredients by virtue of a content of extraneous sulphur and heavy metals cations (lead, copper, manganese or titanium) as impurities; however, this result is not obtained when these baths are formed of sufficiently pure chemical ingredients Moreover the baths even though initially stable due to the fortuitous circumstance mentioned become unstable in use, in continuous plating systems, and particularly in the system disclosed in our application No 19063/53 (Serial No 7815,693) This rendering unstable of the initially stable plating baths after use is brought about fundamentally by the loss therefrom, by boiling off, of hydrogen sulphide. Thus in order both to obtain initial stability and to insure continued stability of the plating bath in use, the inclusion therein of the stabilizing elements as previously described is highly desirable. Specifically in carrying out the present method, particularly when a continuous plating operation of the character of that disclosed in our above mentioned application is employed, it is recommended that the selected stabilizing agent be fed periodically or continuously into the plating bath along with the other regenerating chemicals (particularly the nickel cation and the hypophosphite anion) so as to keep the level thereof substantially constant and at that required, as previously explained; for example, the simplest and safest procedure is to select a stabilizing agent that is known to be active, and unobjectionable with respect to decreasing the plating rate, over a relatively wide range of concentration, such for instance as lead or tin, and to keep the level of concentration thereof within the effective range by the required Where R is an alkyl group, or a hydroaromatic or an aryl group linked through aliphatic substituents, and M an alkali metal (Na or K), are excellent "sulphide controllers " The most common commercial xanthates (and commercial names) that have been found effective are: Potassium ethyl xanthate (Z-3) Sodium ethyl xanthate (Z-4) Sodium isopropyl xanthate,(Z-9) Potassium n-butyl xanthate (Z-7) Potassium sec-butyl xanthate (Z -8) Potassium amyl xanthate (Z-5) Pentasol xanthate (Z 6) Potassium hexyl xanthate (Z 10) The thiophosphates also belong to the sulphhydric class and are well-known as flotation collectors; they comprise reaction products of phosphorus pentasulphide with various organic compounds such as phenols, alcohols, mercaptans (or thioalcohols), amines and nitriles; the products with phenols and alcohols are in common use, known as "Aerofloats" and have the general structural formula: RO S >Pec RO SLH (or M) wherein R is an alkyl or aryl radical and M

100 an alkali metal or ammonium ion. Other useful members of the sulphhydric class are mercaptans (or thioalcohols); thiocarbanilide (diphenyl thiourea); diphenyl thiocarbazide; mercaptobenzothiazole; dithio 105 carbamates and trithiocarbamates Also the oxidation products of the above compound (organic sulphides) are effective. The stabilizing effect of 'the various compounds of the second class were determined 110 from a series of plating tests that were made employing the standard test plating bath and plating conditions previously described; and plating rates (R) were again measured in gms/cm 2/min In these plating tests the 115 stabilizing agents were added to the standard test plating baths from stock solutions containing 1,000 ppm of the organic molecule. In a series of these plating tests employing the standard test plating bath containing 120 potassium ethyl xanthate as the stabilizing agent, the following results were obtained; 785,694 is 785,694 a) Rate tests 10 minutes ppm of xanthate Wt gain, gms. Plating rate R X 101 Sample appearance Time to black ppt. 0.0953 4.76 B-S b) Stability tests 60 minutes ppm of xanthate 1 Wt gain gms 0 1492 0 11 Sample appearance B-S BTime to black ppt 45 In view of the foregoing plating tests employing in the standard test plating bath potassium ethyl xanthate as the stabilizing agent, it will be observed that stabilization is achieved at 5 0 ppm with a slight increase in the plating rate up to about 10 0 ppm and a) Rate tests 10 minutes ppm of xanthate 0 Wt gain, gms 0 0566 Plating rate Rx 10 2 83 p H begin 4 58 p H end 4 09 Sample appearance B-S Time to black ppt none b) Stability tests 60 ppm of xanthate Wt gain, gms. p H begin p H end Sample app. Time to black ppt. minutes 0.1407 4.58 2.72 R 0.1448 4.58 2.63 B 0.1489 B-R 480 -S 0.1533 D-S 250 0.0031 D-R perhaps to 50 0 ppm. In a series of these plating tests employing 10 the standard test plating bath containing potassium methyl xanthate as the stabilizing agent, the following results were obtained: 10 25 0.0850 4.25 4.58 3.81 B-S none 0.1477 4.58 2.66 B 0.0750 3.75 4.58 3.89 B-S none 0.1517 4.58 2.64 B 0.0690 3.45 4.58 3.95 B-S none 0.1522 4.58 2.65 B 0.1540 4.58 2.70 B stable 0.0980 4.90 B-S 0.0985 4.92 B-S 0.0910 4.55 D-S 250 0.0031 0.01 D-R as potassium ethyl xanthate is required to achieve the same degree of stabilization in the standard test plating bath, thereby indicating that the longer carboxylic chain is clearly functional in the formation of a hydrophobic aliphatic chain product upon the suspensoids. In a series of these plating tests employing a standard test plating

bath containing sodium "Aerofloat" as the stabilizing agent, the following results were obtained: In view of the foregoing plating tests employing in the standard test plating bath potassium methyl xanthate as the stabilizing agent, it will be observed that stabilization is achieved at 50 0 ' ppm and above. Comparing the two foregoing groups of plating tests respectively employing in the standard test plating bath potassium ethyl xanthate and potassium methyl xanthate as stabilizing agents, it will be observed that about ten times as much potassium methyl xanthate Stability tests 60 minutes ppm sodium "Aerofloat" Wt gain, gms. 0 1 5 10 20 30 50 300 0.1353 0 1384 0 1415 0 1415 0 1523 0 0060 0 0018 Sample appearance B-R B-S B-S B-S B-S D -no plating Time to black ppt 16 In view of the foregoing plating tests employing in the standard test plating bath sodium "Aeroflcuat" as the stabilizing agent, it wil L be observed that stabilization is obtained from 5-20 ppm with an increased plating Stability tests 60 minutes ppm Sodium "Aerofloat B" 1 Wt gain gms 0 1: rate at the latter concentration. In a series of these plating tests employing the standard test plating bath containing sodium " Aerofloat B " as the stabilizing agent, the following results were obtained: 10 20 30 50 300 386 0 1459 0 1454 0 1502 0 0020 0 0016 Sample appearance Time to black ppt. B-S BB-S BB-S BB-S D In view of the foregoing plating tests employing in the standard test plating bath sodium "Aerofloat B" as the stabilizing agent, it will be observed that stabilization is obtained from 5 0 to 20 0 ppm, with a somewhat increased plating rate in the latter concentration. In a series of these plating tests employing the standard test plating bath containing thiomalic acid as the stabilizing agent, the following results were obtained: (a) Rate tests 10 minutes ppm thiomalic acid 0.5 Wt gain, gms. Plating rate Rx 10 Sample appearance 0.0768 0 0900 0 0903 0 0928 0 0040 3.84 D-S 4.50 B-S 4.51 B-S 4.60 B-S 0.02 D-R none stable no plating 785,694 1 L 7 Time to black ppt. 785,694 b) Stability tests 60 minutes ppm thiomalic acid 0.5 Wt gain, gms. Sample appearance Time to black ppt. 0.1335 0 1415 0 1480 0 1446 0 0040 D-SR B-S B-S B-S D-R stable In view of the foregoing plating tests employing in the standard test plating bath thiomalic acid as the stabilizing agent, it will be observed that stabilization is obtained between 1 0 and 10 0 ppm. In a series of these plating tests employing the standard test plating

bath containing thiocarbanilide as the stabilizing agent the folloving results were obtained: Stability tests 60 minutes ppm thiocarbanilide Wt gains, gms. Sample appearance Time to black ppt. 0.1436 B-S 10 50 0.1456 BB-S stable 0.1313 BB-S no plating stable - In these plating tests since thiocarbanilide is not water-soluble, it was first dissolved in ethylene glycol and then introduced into the standard test plating baths, whereby it was observed that thiocarbanilide stabilizes at 5 O ppm and above, plating being inhibited at 50.0 ppm. In a series of these plating tests employing a standard test plating bath containing thiourea 20 as a stabilizing agent, the following results were obtained: Stability tests 60 minutes ppm thiourea Wt gain, gms. Sample appear. Time to black ppt. 1 5 10 0.1402 BB-S In view of the foregoing plating test employing in the standard test plating bath thiourea as the stabilizing agent, it will be observed that stabilization is achieved within the range from about 1 0 to 10 0 ppm. Again it is pointed out that when the nickel cation concentration in the plating bath is increased, the amount of stabilizing agent that must be added thereto must be dispropor0.1402 BB-S 0.1340 BB-S no plating tionately increased as indicated by the plating tests appearing below utilizing the special test plating bath and plating procedure previously described. In a series of these plating tests employing the special test plating bath containing sodium " Aerofloat " as the stabilizing agent, the following results were obtained: 785; 694 a) Rate tests 10 minutes ppm sodium "Aerofloat" 1 Wt gain, gis. Plating rate Rx 10 Sample appearance Time to black ppt. 0.1309 0 1360 0 1361 0 1311 6.55 BB-R 6.80 6.81 6.56 BB-S BB-S BB-S 0.1212 6.06 BB-S b) Stability tests 60 minutes ppm Sodium "Aerofloat" 1 5 10 15 20 Wt gain, gins 0 2020 0 2429 0 2511 0 2313 0 2302 Sample appearance Time to black ppt. BB-R BB-R BB-S BB-S BB-S 58 stable By comparison of the plating tests respectively involving the standard test plating bath and the special test plating bath, it will be observed that as little as 5 0 ppm of sodium "Aerofloat" is effective to produce stabilization in the standard test plating bath, whereas 20.0 ppm of sodium "Aerofloat" is required to effect stabilization in the special test plating bath However, in the plating tests employing

the special test plating bath, the plating rate is substantially increased and the sample appearance is brighter. While the effective minimum amounts of the different ones of these organic stabilizing agents to achieve stabilization are a function of nickel cation concentration in the plating baths, as explained above, they are otherwise independent of the particular compositions of the plating baths with reference to other constituents This is probably due to the fact that they do not form complexes with such constituents as malic acid, lactic acid and aminoacetic acid Thus the stabilizing agents of the organic type possess this advantage with respect to the stabilizing agents of the inorganic type, previously described Moreover, when the stabilizing agents of the organic type are used in proper amounts, they do not decrease the plating rate over wide rangesand they tend to increase substantially sample brightness; and moreover, they do not appear to have any, adverse action on the adhesion of the nickel plating upon the base metal. Furthermore, due to the exceedingly small amount of sulphide ion controller required in a plating bath, it is immaterial from an economic standpoint which one among those described above is selected and in what quantity it is used within the individual operating range thereof, providing decreased. that the plating rate is not It will be understood that the stabilizing agents described are particularly well-suited for use in continuous nickel plating processes involving regeneration of the ingredients of the character disclosed in our application No. 19063/53 (Serial No 785,693). It should be noted that analytic methods for the " exact " determination of trace quantities of ingredients of the order of magnitude herein employed (for example, sulphide ion controller in parts per 1,000,000,000 parts of the plating bath) are not now available in the art; however, these trace quantities as set forth were determined by carefully eliminating all possible sources of sulphide and other trace ions from the plating bath, and then by adding known quantities thereof to the bath Accordingly, it will be appreciated that the trace quantities given are approximate, but are readily understandable by those skilled in the art, as levels above the maximum obtainable purity of ingredients employed in the formation of the plating bath. In view of the foregoing, it is apparent that there has been provided an improved process of chemical nickel plating of materials employing baths of the nickel cation-hypophosphite anion type containing stabilizing agents, as well as improved baths therefor Further, it will be understood that great advantages are obtained by the utilization of the present process, particularly in continuous nickel

plating operations, since such processes frequently involve exceedingly large volumes of the nickel plating bath that must be stabilized. In the appended claims the term " catalytic material " means any material which can be nickel-plated in an aqueous bath of the nickel cation-hypophosphite anion type with the evolution of hydrogen gas at the catalytic surface, and includes a material comprising an element which is catalytic for the oxidation of hypophosphite anions as previously set forth herein, and materials comprising an element which may be nickel-plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect, as previously set forth herein.

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* GB785695 (A)

Description: GB785695 (A) ? 1957-11-06

Improvements in or relating to processes and baths for chemical plating withnickel

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PATENT SPECIFICATION

Date of Application and filing Complete Specification: Nov 30, 1953. No 33169153. g / 21 Application made in United States of America on Aug 27, 1953. Complete Specification Published: Nov 6, 1957. Index at acceptance:-Class 82 ( 2), F( 1 81 B: 2 U), F 4 (A: E: F: G: J: K: N: W: X). International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to Procesises' and Baths for Chemical Plating with Nickel We, GENERAL AMERICAN TRANSPORTATION CORPORATION, a corporation organised under the laws of the State of New York, United States' of America, of 135, South La Salle Street, City of Chicago, State of Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may he granted to us, and the method by which it is to' be performed, to be particularly described in and by the following statement:- The present invention relates to improved processes of chemical nickel plating of catalytic miaterials employing baths of the nickel cationhypiophosphite anion type and to improved baths therefor. The chemical nickel plating of a catalytic material employing an aqueous bath of the nickel cationhy Vpophbosphite anion type is based upon the catalytic reduction of nickel cation's to mletallic nickel and the corresponding oxidation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface The reactions take place when the body of catalytic material is immersed in the plating bath, and the exterior surface of the body of catalytic material is coated with nickel The following clemnents are catalytic for the oxidation of hypophosphite anions and thus may be directly' nickel plated; iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium iridium and platinum The following elements are examples of materials which may bee nickel plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, silver, gold, beryllium, germanium, aluminiunm, carbon, vanadium molybdenum, tungsten, chromiumi, selenium, titanium and uranium. The following elements; are examples of non. catalytic materials which ordinarily may not be nickel plated: bismuth, cadmium, tin, lead and zinc The activity of the catalytic materials; varies considerably; and the following elements; are particularly good catalysts in' the chemical nickel plating bath: iron, lPrice 3 s 6 d l cobalt, nickel and palladium The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is depiosited on the surface thereof are catalytic; and the reduction of

the nickel cations to metallic nickel in' the plating bath proceeds until all of the nickel cations, have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hyplophosphite anions, have been oxidized to phosphite anions, in the presence of an excess of nickel cations Actually the reactions are slowed-down rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations to form an acid, which, in turn, lowers the p H of the bath, and the reducing power of the hypopholsphite anions is, decreased as the p HM value of the bath decreases Moreover, there is a tendency for the early formiation in the plating bath of a "black precipitate" that comprises a random chemical reduction of the nickel cations Of course, this, formation of the black precipitate comprises a decomposition of the plating bath, and is particularly o'bjecuionable in that it causes, the nickel deposit to' be coarse, rough and frequently porous. For the dual purposes Of retarding the formation of the black precipitate mentioned and of increasing the normal plating rate of the bath, various baths of the present type have been suggested employing different additives A chemical nickel plating bath of ths type, previously suggested, contains, as an, additive, a buffer in the form of a soluble salt of an organic acid, and specifically sodium acetate A typical chemical nickel plating bath of this character is described in cop ending application No 30144/53 (Serial No. 761,567). In carrying out the chemical nickel plating process on a commercial scale employing a p'latin bath of the type mentioned, them ),695 -, cg, 1 1 1 3 may be utilized a continuous system of the character of that disclosed in our copending application Serial No 19,063, filed July 9, 1953 (Serial No 785,693). In carrying out the chemical nickel plating process, particularly in a continuous system of the character described, it has been discovered that after some use, and notwithstanding the presence of a buffer, the bath decomposes with the formation of the previously-mentioned black precipitate Moreover, it has been found that the plating rate of a bath of the character described is not as high as is desirable and that the utilization of a plating bath having an optimum p H as low as that mentioned is not always desirable. The present invention is predicated upon the discovery that in plating baths of the nickel cation-hypophosphite anion type mentioned, the formation of black precipitate may be retarded and the plating rates thereof may be substantially increased by the addition thereto of an aliphatic aminocarboxylic acid and/or a salt thereof; which compounds function to produce an "exaltation" phencmenon Moreover, in the bath

these compounds are amphoteric, producing "zwitterions", and thereby forming stable, watersoluble chelate complexes with nickel so that the useful p H range of the bath can be substantially extended to embrace the neutral and rear alkaline regions, without resulting in precipitation of insoluble basic nickel salts. Further, these compounds are stable at elevated temperatures, i e near the boiling point of the plating bath, so that no reagent loss occurs in the neutral and alkaline zones where purer deposits are obtained Finally, sthese compounds, by forming stable, water-soluble chelate complexes with the nickel ions, retard precipitation of nickel phosphite, which is the normal by-product of the chemical nickel plating process resulting from the oxidation of the hypophosphite anions The last-mentioned feature is particularly important in the above mentioned continuous nickel plating operation, in view of the fact that in such a continuous system the phosphite anion concentration soon builds-up, after a number of cycles, to a point where the solubility of nickel phosphite is exceeded, with the resultant formation of nickel phosphite as a precipitate, and the consequent rough nickel plating. In order to be of utility for the present purpose, the compounds mentioned must, of course, be water-soluble; and moreover, for the purpose of chelate formation with the nickel ions the amino' group should be either in the alpha or beta position with relation to the carboxyl group, so that either five or sixmembered rings will result. Specifically, the zwitterions of the general fornula R COONH,3 + should have the specific structures: R 2 RL CO o NH 3 or F 2 Rt-COONH 3 so that the resulting nickel chelates have the specific structures: to O O R-c-O O-C-R I I H 12 N NI NH 2 or 0 0 2 2 H 2 N Ni NH 2 The hydrogen atoms of the amino group can, of course, be -substituted, as the nitrogen atom alone is necessary for ring closure. Water-soluble salts of amino' acids, alpha or beta-polyamina acids, monoaminopolycarb 80 oxylic acids and polyaminopolycarboxylic acids are suitable for the purpose. It is noted that the chelate complexes (also called "inner cormplexes") are particularly stable since all primary valencies as well as 85 the secondary valencies of the bound metal atom are satisfied While, in an ordinary inorganic cation complex, the coordinated molecules form a first zone around the central cation, which then becomes a new complex 90 ion, this is not the case in chelates; rather in chelates the whole structure represents a new, very slightly dissociated, neutral molecule. In view of the foregoing, it is the primary object of the present invention to provide an 95 improved nickel plating process of the

character described in which the reactions involved are carried out more efficiently and under more stable conditions than heretofore, thereby rendering the process more desirable 100 from a commercial standpoint. The present invention provides a nickel plating bath comprising an aqueous solution of nickel ions and hypophosphite ions and an aliphatic alpha or beta-amrinocarboxylic acid 105 and/or a salt thereof. The present invention also provides a process for chemically plating a catalytic material with nickel which comprises contacting the catalytic material with a bath of the type 110 described above. 785,695 lution with reference to a given hypophosphite solution resulting from the addition thereto of the exaltation agent. Turning now more particularly to' the introduction of the zwitterions into the bath, the following aliphatic amino-acids have been found to be particularly suitable: Aminoacetic acid (Glycine) Alpha-aminopropionic acid (Alpha-Alanine) Beta-aminopropiionic acid (Beta-Alanme) Alpha-amiinobutric acid Aminosuccinic acid' (Aspartic acid) Iminediacetic acid Iminotriacetic acid Ethylenevdiaminotetraacetic acid As a matter of convenience, the zwitterions may be introduced into the plating bath by dissolving therein, the salts, particularly thei alkali salts, of the aliphatic aminocarboxylic acids mentioned This is particularly convenient, 'since the ailkali salts of these aminocarboxylic acids are usually more readily obainabile upon the market. I For the purpuse of studying the increase of thie hydrogen gas evolution due to exaltation with the use of different additives including those involved in, the discovery of the present invention, i e aliphatic amino carboxylic acids, and other additives which have been used or suggested for chemical nickel plating baths, tests were made with test solutions of 50 cc and containing sodium hypophosphite at a concentration of 0 225 mole/ liter (to' which a trace of a nickel salt, i e 0 024 mole/liter was added to' initiate the reaction at a vigorous rate). Pickled pieces of mild steel, 20 em' in area, were introduced for periods of 30 minutes each The different test solutions respectively contained no additive, and additives in the form of salts of the following acids: acetic, citric, lactic, succindc, aminoacetic and aspartic Specifically, the additives, when used, were employed as the sodium salts of the corresponding acids in a concentration of 0.125 mole/lier of the anion, and the hydrogen gas evolved was collected and its volume measured by usual methods The results of these exaltation tests were: In accordance with the process of the present invention, the article

to be nickel plated and normally having a catalytic surface is properly prepared by mechanically cleaning, degreasing and light pickling, substan. tially in accordance with standard practices in electroplating processes, such as described in our copending application No 31365/53 (Serial No 785,694). Instead of using a batch plating process, as described in our above copending application, the steel object may be plated in the plating chamber of the continuous systemn previously mentioned, by the immersion thereof in the plating chamber for an appropriate time interval Thereafter, the steel object is removed from the plating chamber, and is rinsed off with water and is then ready for use. With respect to the composition of the bath, it essentially comprises anl aqueous, solution containing nickel cations, hypophosphite andons and zwitterions For example, the nickel cations may be derived from nickel chloride; the hypophosphite anions may be derived from sodium, potassium etc, hypophosphites or various combinations thereof; and the zwitterions may be derived from an aliphatic aminocarboxylic acid and/or a salt thereof Specifically, a suitable bath may be formed in an exceedingly simple manner by dissolving in water, nickel chloride, sodium hypophosphite and sodium aminoacetate The desired p H of the bath is established by the eventual introduction thereinto of hydrochloric acid or by the addition thereto of a weak alkali, preferably sodium bicarbonate. The termis "cation", "anion" and ion", as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present in the plating bath, i e both undissociated and dissociated material In other words, 100 % dissociation is assumned when the terms noted are used in connection with moilar ratios and concentrations in the plating bath Also hereinafter the expression "per cent exaltation" is employed with the arbitrary definition as the percent increase in the rate of hydrogen evo785,695 785,695 H 2 evolved in 30 min. from 50 cc solution at 0.225 m/I sodium hypophosphite % Exaltation None 80 0 Acetic 155 94 Citric 130 63 Lactic 145 81 Succinic 220 175 Aminoacetic 180 125 dl-Aspartic 250 213 By comparison of the unsubstituted, and the amino-substituted carboxylic acids, it will be observed that a remarkable increase in percentage ex al-tation is produced by the substitution in the organic radical of one amino groups for cnt hydrogen atom In conjunction with these tests, it is noted that exaltateen is independent ef bufferirg efficiency and of the capability of 'the organic compound to csmul-ei the nickel ions with the formation of chelates In other words, the aminocarboxylic acids, and the salts thereof, have the three unrelated properties of

exalting, bufferinga and chelating; all of whicn ale highly advantageous in the nickel platinm process. In the use of amirnocarboxylic acids for clhemrical nickel plating exaltation, it is believel that this plhenomenon results from the formation of a heterorpoly-acid between the organic additive and the hypophosphite anions, which competes with inner-complex (chelate) formation between the nick-l ions and the amrilno-acid radical If the nickel amino-acid chelate is too stable, insufficient nickel cations are available for deposition, and the plating rate becomes low despite the exalting effert produced by the organic additive. In actual plating tests employing plating baths containing aminocarboxylic acids and watwr-soluble salts thereof, it has been found that the p H variations have less influence on plating rates, in the optimum nickel and hypophosphite ion concentration ranges, than is the case with other organic additives This is unquestionably due to the amphoteric character of the zwitterions For example, with aminoacctic ions (Glycine) there are three optimum, although not particularly marked, p H regions,, i e at about 5 5, 6 5 and 85; and in any case, the useful p H range of the plating bath is clearly extended with reference to the previously suggested plating baths buffered with salts of simple, unsubstituted carboxylic acids. On the other hand, in the case of aminoacid salts (as opposed to ordinary buffers) added to theh plating bath, best plating results are obtained when the ratio between the aminro group and the nickel ion is above 1 5; in, ether words, when the amount of amino acid ions is sufficient to complex most or substantig Lly all of the nickel ions contained in the plating bath In this connection, it is pointed cut that substantial exaltation is achieved in the plating bath when the amount of amino radical is above about G 5 and that substantially all of the nickel ions are complexed to form chelates when the amount of amino radical is 2 or above. Again referring to the composition of the aqueous plating bath, thc following concentrations of inri-edients have been found to, be optimum: the absolute hypophosphite ion conrc-ntraticn should be in the range O 15 to 1.20 mole/liter; the nickel ion/hypophosphite anion ratio should be in the range 0 25 to 1.60; the ratio between the aimino group and the nickel ions should be in the range 0 5 to 6.0; and the p H shculd be in, the approximate range 4 5 to 9 0. The exalting and other characteristics of the various aliphatic aminocarboxylic acids in the plating baths were established by a series of plating tests that were made employing a series of test plating baths of the general character of that previously described and having the compositions shown in Table 1 for each of the eight -series of tests This table also indicates the bath temperature and

the time each of the steel samples employed were plated In each series of tests, except Series No 2, properly cleaned steel samples of 20 cm 2 area were employed In Series No 2, cleaned steel samples of 5 cm 2 area ( 16 gauge) were used The volume of the bath was 50 cc in each test. In Series Nos 3 to 7, the sodium aminoacetate content only of the baths was varied Additive (Anion) 0.125 m/I 785,695 in the various, groups of tests, the amounts of hbypophosphite and nickel chloride being maintained constant for each scriesi Lilewise, the nickel chloride content only of the baths in Series, No 8 was, varied in each group of tests The p 1 H of the plating baths was adjusted with sodium, bicarbonate in Series Nos. 1 and 2 with acetic acid and/or caustic soda in Series Nos 3, 4 and 6; with Na OH and Hl in Series No 5; and with ammoniumn hydroxide in Series No S. Iu, the results of the various series of plating tests appearing hereinafter weights of nickel plating deposited are reported in gms, and the plating rates (R) are usually reported as R x 104 where R is expressed in gm/cmn'/nin, although cecasionally plating rates are reported in mils/hour (i e, O 001 "/hour). RESULTS OF PLATING TESTS SERIES NOS 1 TO 8 Series No 1 Initial p H Weight Deposited ( 10 min (gm) Rate (mils/hour) 6.5 (as prepared) 0 0996 1 3 8.5 (as adjusted) 0 1030 1 4 TABLE 1 Bath Composition Sodium Nickel Ratio: Sodium Ratio: Bath Plating Series No Hypophosphite Chloride Nit+/hypo Aminoacetate Amino,/Ni++ Temperature Time (moles/liter) (moles/liter) (moles/liter) OC (Minutes) 1 0 225 0 075 0 33 0 125 1 67 96-98 10 2 0 225 0 09 0 40 0 120 1 32 97-98 60 3 0 225 0 1125 0 50 Variable Variable 97-98 10 (a) 0 06 (a) 0 53 (b) 0 12 (b) 1 067 (c) 0 18 (c) 1 60 4 0 225 00675 1 0 Variable Variable 96 10 (a) 0 0675 (a) 1 O (b) 0 1013 (b) 1 5 (c) 0 135 (c) 2 O 0 22 5 0 0675 0 3 Variable-See Variable-See 97 ( 1 'C) 10 Tabulation of Tabulation of _Results Results 6 0 225 0 0675 0 3 Variable Variable 96 60 (a) 0 0675 (a) 1 0 (b) 0 0113 (b) 1 5 (c) 0 135 (c) 2 O 7 0 225 0 1125 0 5 Variable-See Tabulation of 98 60 Results 8 0 225 Variable-See Tabulation 0 12 98 (a) 10 of Results (b) 60 7 785,695 Series No 2 Initial p H Weight Deposited ( 60 min) Black Precipitate Sample Appearance 5.75 (as Medium bright, prepared) 0 1198 0 1229 None smooth 8.00 (as adjusted) 0 1282 0 1273 None Dull These first and second series of plating tests clearly demonstrate that the present plating baths are satisfactory in the near neutral and basic regions of the p H range. SERIES No 3 The plating was bright and smooth in each of the following groups of tests in which the averages of duplicate tests are set forth:

Group (a) Test: Initial p H Plating rate Rx 104 Test: 6.01 6 49 6 70 2.70 Initial p H Plating rate R x 104 2.91 2.98 6.00 6 78 7 02 3.66 3.36 3.42 Group (c) Test: 1 Initial p H 5 98 Plating rate R x 101 4 44 The above plating tests illustrate that best plating rates are obtained when the ratio of the amino-nickel ions is above about 1 50. The plating rate employing the bath for this series having the composition shown in Table 1, without the addition of sodium Group (a) Test: Initial p H Plating rate R 1 x 104 Group (b) Test: 6.20 6.39 6.62 4.99 4 31 4 89 aminoacetate, at p H 6 4, was only 0 84 x 10 gm/cm'/min. SERIES NO 4 The plating was bright and smooth in each 20 of the following group of tests: 5.92 6.35 6.65 6.90 2.22 2 225 2 18 2 535 Initial p H Plating rate R x 104 Test: Initial p H 6.0 6 29 6 60 6 94 3.22-5 3 98 6.0 6.22 4.03 4 22 6.58 6.95 Plating rate Rx 104 4 30 4 465 4 92 4 73 Group (b) Group (c) In both the third and fourth series of plating tests, it will be obs Irved that v-when the Ni + + /hyophcsphit ion ratio is eithar 0.5 or 0 3, increased plating rates are obtained with increased ratios of amnina/Ni++. Ratio: Anuino/Ni+ 2.0 SERIES NO 5 The plating wloas bright and smoth iii each of the follo-ing tests, in vwich the averages of triplicate tasts are set fori: 3.0 4.0 Initial p H 6 64 6 70 6 68 Final p H 5 58 5 82 5 88 Wt gain 0 0907 0 0984 0 1030 Plating Rate (RX 104) 4 54 4 65 5 15 From the fifth series of plating tests, it will tni observed that the greatest weight gains were achieved with this plating bath when the amnin G/Ni++ ratio was 4 0. Group (a) Test: Initial p H Final p H Weight gain SERIES NO 6 The plating was bright and srooth in each of the following groups of tests in which the averages of duplicate tests are set forth: 5.92 6 35 6 65 6 90 2.90 2 88 2 73 2 81 0.1015 0 1090 0 1110 0 1186 6.0 6 29 3.25 3 49 0.1698 0 1728 6.0 6 22 6 58 6 95 3.37 3 57 4 12 0.1871 0 1956 0 2114 SERIES NO 7 The plating was bright and smooth in each of these plating tests: Aminoacetate ion mole/it. 0 0 06 0 12 0 18 0 24 0 30 Amina/Nit+ 0 53 1 067 1 60 2 135 2 67 Initial p H 6 38 6 42 6 39 6 38 6 43 6 41 Final p H 5 10 2 92 3 15 3 35 4 55 4 92 Wt gain 0 0434 0 1460 0 2282 0 2532 0 2562 0 2593 From the sixth and seventh series of plating tests, it will be observed

that over the time interval of 60 minutes, the weight gains of plating increase with increasing p H and with increasing aminoacetate concentrations. From thie seventh series of plating tests, it will be observed that the weight gains in plating increase rapidly up to an aminloacetate concentration of 0 18 mole/liter, and from thereon, at a much slower rate Moreover, it Group (b) Group (c) Test: Initial p H Final p H Weight gain Test: Initial p H Final p H Weight gain 4.72 0.2141 I' 785,695 SERIES NO 8 The plating was bright and smooth in each of the following groups of tests; will be observed that the differences between the initial and final p H values become smaller as the aminoacetate concentration is increased due to bufering action in the bath. Group (a) Ni 7 +/hypoNi C 12 m/l minute tests 0.128 0 26 0 36 0 512 0 575 0.0288 0 0585 0 0810 0 1152 0 1293 Final p H 5 35 5 42 4 94 5 00 4 88 Plating Rate(Rxl O 4) 3 61 4 54 5 10 5 23 5 63 Ni++/hypo 0 705 0 769 1 026 1 282 1 538 Ni Cl 2 m/1 O 1586 O 1730 0 2308 0 2884 0 3460 Final p H 4 80 4 72 4 32 4 27 4 28 Plating Rate (Rxl O 4) 5 42 4 80 4 29 3 99 4 08 Group (b) Ni++/hypoFinal p H Wt gain Ni++/hypoFinal p H Wt gain 0.647 0.1456 4.86 5.59 minute tests 0.128 0 26 0 36 0 512 0 575 0 657 5.04 3 37 3 18 3 17 3 17 2 90 0.0914 0 1702 0 1896 0 2282 0.2317 0 2300 0.705 0 769 0 1026 0 1282 0 1538 3.08 3 12 2 95 2 80 2 88 0.2234 0 1912 0 2066 0 2031 0.2113 This eighth series of plating tests shows that there is a definite optimum ratio of Ni++/hypophosphite ions in plating baths due to the inclusio in the commercial reagents employed in the production of the plating. bath of stabilizng impurities (particularly lead) with the consequent inclusion in the bath of a trace of amount of sulfide ion controller asi disclosed in our above copending application Serial No 31365/53 (Serial No. 785,694) Specifically, the optimum, ratio of Ni++/hypophosphi"e ions in plating baths containing, amino-acidsi is between 0 575 and 0.650, due to the circumstance noted. In the foregoing series of plating tests, a batch plating process was involved; however, baths of the present type are even more advantageous when employed in the continuous plating system mentioned above Specifically, these baths have a fast plating rate and are stable permitting regeneration of the plating solution in the reservoir in excess of 24 cycles (as contrasted with a few cycles of regeneration employing previously suggested baths of the character mentioned above) before there is an intolerable build-up in the plating bath of the by-product phosphite As a matter of interest, the plating rate of the plating bath in the subsequent cycles of the continuous plating system is increased over the initial cycles

thereof; which phenomenon is not exactly understood. In a ninth series of plating tests, using the continuous plating systems plating baths were employed having the following composition: 785,695 785,695 Test No 1 Sodium hypophosphite Nickel chloride Nickel sulphate Sodium aminoacetate Ratio: Nit+/hypoRatio: Amino/Ni++ Trace ion stabilizer Pb++ Te 7 + Initial p H adjusted with 0.18 m/I Na OH O 225 m/I O 1125 m/l O 225 m/I 0 5 2 20 0.225 m/I 0.1125 m/I 0.225 m/i 0.5 2.0 1 ppm 1 ppm None 1 ppm 6 5 In these plating baths, the nickel ion may be supplied by nickel salts other than the chloride, such, for instance, as the sulphate, which was used in the bath in Tesn No 2. The trace of Pb++ and/or Te+ was added to the plating baths to increase the stability thereof. In, the continuous plating system, 6 liters. of the plating bath were used, -the plating solution being flowed by gravity through a heating coil and then through the plating 6.5 chamber having a capacity of about 30 so that the temperature of the plating bath in the plating chamber was maintained at 99 C (_ 1 C) The plating solution, was regenerated in the reservoir exteriorly of the plating chamber after each cycle by adding thereto the necessary re-agents, and four steel samples of 20 cm' area each ( 80 cm total area) were plated in the plating chamber with the following results: Test No 1: 1 2 6.62 6 62 6 60 6 22 6 19 3 4 5 6 7 8 6.48 6 57 6.29 6 15 6.56 6 51 6 50 6.16 6 29 6 28 Duration (min) Soln Flow Rate cc/min. Wt gain (gms) Plating rate Rx 110 100 89 98 264 101 106 49 63 57 64 58 22 56 54 3.80 2 51 3 34 2 81 3 06 3 57 7 66 4 16 4.13 3 49 4 17 3.95 3 90 4 52 4 91 4 80 9.0 6 0 7 9 6 7 7 7 18 0 8 7 9 9 37.3 55 3 64 O 73 9 Test No 2 Cycle No. Initial p H Final p H Depletion % Cumulative Deplet % 9.0 15 O 22 9 29 6 785,695 Test No 1-cont. Cycle No. Initial p H Final p H Duration (min) 9 10 11 12 13 14 15 16 6.46 6 45 6 49 6 51 6.01 6 19 6.49 6 48 6 48 6 47 6.31 6 31 6 35 6 32 6 30 6 14 126 114 116 110 103 106 147 So In Flow Rate cc/min. 50 49 52 57 55 54 39 Wt gain (gnis) Plating Rate Rx 104 Depletion % Cumulative Deplet % 4.83 4 52 4 69 4 52 4.80 4 96 5 05 5 14 11.5 10 7 11 7 10 7 85.4 96 1 107 2 117 9 4.22 4 56 4 87 6 75 5.21 10.1 5.54 5 75 5 74 10.7 11 6 16.0 128 0 138 7 150 3 166 3 Cycle No 17 18 19 20 21 22 23 24 Initial p H 6 49 6 50 6 48 6 45 6 52 6 46 6 52 6 52 Final p H 6 23 6 25 6 32 6 33 6 32 6 35 6 39 6 42 Duration (min) 136 141 162 136 119 145 136 128 Soln Flow Rate cc/min 42 40 35 42 48 39 42 44 Wt gain (gins) 6 24 6 58 7 14 7 41 5 87 7 50 6 65 6 55 Plating Rate Rx 104 5 73 5 83 5 70 6 81 6 17 6 45 6 22 6 40 Depletion % 14 8 15 6 16 9 17 6 13 9 17 7 15 8 16 5 Cumulative Deplet % 181 1 196 7 213 6 231 2 245 1

262 8 278 6 295 1 This test was stopped after 24 cycles without reaching the point where nickel phosphite precipitated in the plating solution, whereby a total weight of 123 81 gms of nickel was plated from the 6 liters of plating solution without phosphite removal, the volume of the plating solution being kept constant by adding some water as the rate of evaporation was greater than the volume of reagent solution added for regeneration The per cent of depletion is an arbitrary indication of the amount of nickel taken out, as a deposit, from the original solution. is 785,695 Test No 2: Cycle No. Initial p H Final p H Duration (min) Sohn Flow Rate cc/min. Wt Gain Plating Rate Rx 101 Depletion % Cumulative Den I 0/Cycle No 6 7 8 9 10 Initial p H 6 49 6 52 6 52 6 47 6 50 Final p H 6 18 6 29 6 19 6 19 6 32 Duration (min) 101 134 133 127 111 Soln Flow Rate cc/min 56 42 43 45 51 Wt Gain 3 76 4 91 5 03 4 94 4 44 Plating Rate Rx 104 465 4 58 4 71 4 87 5 00 Depletion % 8 9 11 7 12 1 11 7 10 5Cumulative Depl % 60 5 72 2 84 3 96 0 106 5 In all of the foregoing plating tests, steel was used as the plating -base material; however, it should be understood that other materials, such as aluminiuni brass, bronze, plastic (Bakelite-registered Trade Mark), etc, may be plated with very good results using these plating baths In a tenth series of plating tests, plating baths having the composition shown in Table 2 were used to plate the base material indicated Tests Nos 1 to 4 were batch operations in which 50 cc of Test No. Base Material Initial p H plating bath was used, and Test No 5 employed the previously mentioned continuous plating system with a bath volume of 4 5 liters. In each, test, the initial p H of the bath was adjusted to about 6 50 with Na OH and the temperature of the bath was maintained at about 98 C in Tests Nos 1 to 3. In Tests Nos 1 and 2 of this series, the steel and aluminium samples were each; of cm P area and were plated separately with the following results: Weight Gain Plating Rate Rx 104 1 Steel 6 41 0 092 4 26 2 S aluminium 6 41 0 128 5 82 2 Steel 0 0969 4 85 2 S aluminium 0 0984 5 29 6.38 5.96 117 4.66 4.98 11.1 11.1 6.49 6.19 3.51 4.53 8.3 19.4 6.54 6.20 4.05 4.40 9.6 29.0 6.48 6.07 5.39 4.34 12.8 41.8 6.50 6.27 114 4.14 4.53 9.8 51.6 12785,695 In Test No 1 the plating on the 25 aluminium sample showed excellent adhesion; and these results were verified in ai comanion minute test Test No 2 showed good adhesion of a bright, smooth plating on the steel sample, while on the 2 S aluminium sample the plating was very bright and smooth and the adhesion was excellent. In Test No 3, the brass faucets, were plated to 0 4 mil thickness at a

plating rate of 1 mil per 50 minutes and the appearance of the faucets after the plating was unusually good. In Test No 4, the sample of "Bakelite"registered Trade Mark-was prepared as follows The outer layer of skin of the "Bakelite" -registered Trade Mark-sample was removed mechanically with finet emery cloth; and then it was soaked in an aqueous solution. containing 35 ppmi of palladium chloride for 72 hours The sample wasi then thoroughly rinsed in warm water, dried, and the palladium chloride was reduced to metallic palladiumi in a hot aqueous solution of sodium hypophosphite ( 0 335 m/l) until bubbling subsided The plating was initiated instantaneously upon immersion of the prepared "Bakelite"-registered Trade Mark-sample into, the plating bath at a temperature of 92 C The plating appearance was excellent and Cycle No. the adhesion thereof was good In the plating test the bath remained stable and, very clear. In passing, it is noted that further plating testsi showed that a soaking for 3 hours in the aqueous, palladium chloride solution is optimumi for coating adhesion although a soaking time as short as 5 minutes is adequate to obtain initiation of the nickel plating. In succeeding plating tests, the same technique was applied in the preparation of other plastic materials including fiberglass reinforced polyester plastic, neoprene and phenolic plastic (Hycar-regisstered Trade Mark) These plating tests were also highly successful in that the plating appearance was excellent and the adhesion was good. In Test No 5, the "Bakelite" sample was pretreated substantially as in Test No 4, but was soaked for only 15 minutes in palladium chloride solution at a temperature of from 600 to 800 C Thereafter the "Bakelite" sample was rinsed in hot water, and then immersed in a hot aqueous solution of sodium hypophosphite ( 0 225 m/l) until bubbling subsided Thereafter the "Bakelite" sample was rinsed in hot water and transferred to the plating chamber in the continuous plating system; whereby it was plated therein with the following results: Initial p H 6 44 6 51 6 50 6 47 6 45 6 48 6 47 Final p H 5 91 6 15 6 35 6 26 6 17 6 19 6 20 Soln Flow rate cc/min 38 40 38 37 43 40 43 Wt gain gms 3 7475 3 4591 3 2524 4 1670 3 0849 3 9216 4 7550 Cumulative Depletion, % 12 6 24 2 35 2 49 2 63 0 76 4 91 6 SO TABLE 2 Sodium Source Ratio: | Sodium Ratio: | Stabilizing Base Plating Hypophosphite of Ni++ Ni++/hypo Aminoacetate Amjinco/Ni++ Ion Material Time Test No (moles/liter) (moles/liter) (moles/liter) Plated (Minutes) 1 0 225 Nickel 0 5 0 18 1 6 None steel and 11 nitrate 25 ( 0.1125) aluminium 2 0 225 Nickel 0 5 0 18 1 6 None steel and 10 chloride 25 ( 0.1125) aluminium 3 0 225 Nickel 0 4 O 18 2 0 1/2 inch 20 chloride ( 1 ppm) brass ( 0.9) Tet+ faucets ( 1 ppm) 4 0 225 Nickel 0 18 Pb++Bakelite 90 chloride ( 5 ppm) ( 0.1125) 0 225 Nickel 0 5 0

225 2 0 11 b++ Bakelite Continuous sulfate ( 4 ppm) plating ( 0.1125) system -This bath also contained 0 01 m/l of sodium fluoride and 0 20 m/l of sodium nitrate. 00 1 > Ch \ O N W 85,693 In the foregoing ten series of plating tests, the aliphatic aminocarboxylic acid additive in the plating bath consisted of amiinoacetie acid (glycine) or the alkali salt thereof, fundamentally due to the practical circumstance that these compounds are both cheap and readily available in large quantities in the commercial market Moreover, it has been verified that the other aliphatic aminocarboxylic acids do not have any particular advantage over glycine and they are considerably more expensive and only available in small quantities in the market Accordingly, from a practical standpoint, it is recommended that the saturated aliphatic arninocarboxylic acid additive in the plating bath take the form of glycin or sodium aminoacetate However, the other aliphatic aminocarboxylic acids and their salts are entirely satisfactory as additives in the plating bath as indicated by the results of the various series of plating tests reported in Table 3. In Series Nos 11 to 15, properly cleaned steel samples of 20 cm 2 area were plated batchwisei in 50 cc of plating bath maintained at a temperature of about 970 C ( 1 C). In Series Nos 17 and 18, the steel samples were 5 cm 2 area, and in Series No 16, the conditions were substantially the same as previously described with reference to the prior 30 plating tests involving the continuous plating system, except that only 4 liters of the bath were employed and the total area of tlhe steel samples was 60 cm', the temperature of the bath being about 99 C, and the p H of the 35 bath was adjusted with Na HCO, In the other series of tests, the p H was adjusted with Na OH or acetic acid. SERIES NO 11 In these plating tests, the plating was bright and smooth and the specific results were as follows: Duration of Test Initial p H Final p H Wt gain Plating Rate (R x 104) (a) (b) Minutes 60 Minutes 6.10 5.10 0.1050 5.25 6.10 3.10 0.2231 SERIES NO 12 In these plating tests, the plating was bright and smooth in the acid baths, semibright in the substantially neutral baths, and dull in the alkaline baths, and the specific results were as follows: (a) Rate Tests 10 minutes 5.54 6 01 6.52 7 01 7 53 7 99 8 53 9.00 0.0696 0 0923 0 0862 0 0789 0 0847 0 0802 0 0839 0 0831 Plating Rate (R X 104) 3 48 4 62 4.31 3 94 4 424 4 01 4.40 4 16 (b) Plating Tests 60 minutes 5.54 6 01 6.52 7 01 7 53 7 99 8 53 9 00 0.2045 0 2373 0 2544 0 2558 0 2595 0 2325 0 2252 0 2044 Initial p H Wt gain Initial p H Wt gain TABLE 3 Bath Composition p H of Plating Series Sodium Nickel Ratio: Exaltant Ratio: plating Time No Hypophosphite Chloride Ni++/hypo (moles/liter)

Amino/Ni++ Bath (Minutes) (moles/liter) (moles/liter) 11 0 225 0 09 0 4 Alpha-Alanine 2 0 6 1 (a) 10 ( 0,18) (b) 60 12 0 225 0 1125 0 5 Alpha-Alanine 2 0 Variable (a) 10 ( 0.225) (b) 60 13 0 225 0 1125 0 5 Beta-Alanine 2 0 Variable (a) 10 ( 0,225) (b) 60 14 0 225 0 09 0 4 Alpha 2 0 6 5 (a) 10 aminobutyric (b) 60 acid ( 0 18) 0 225 0 1125 0 5 Alpha 2 0 Variable (a) 10 aminobutyric (b) 60 acid ( 0 225) 16 0 225 O 09 0 4 Aspartic acid 2 0 Variable Continuous ( 0.18) system 17 0 225 0 09 0 4 Versene 0 9 Variable 10 ( 0.04) 18 0 225 0 09 Versene Variable Fe-Sp ( 0 04) -4 ppm of Pb++ was added to bath as stabilizer Tetrasodium salt of ethylenediaminoetraacetic acid -An acid sodium salt of ethylenediaminotetraacetic acid N -' 0 _h SERIES NO 13 bright and smooth, and the specific results In these plating tests, the plating was were as follows: Duration of Test (a) minutes (b) minutes Initial p H 6 05 7 58 8 61 6 05 7 58 8 61 Wt gain 0 0523 0 0727 0 0820 0 1294 0 1378 0 1539 Plating Rate (Rx 104) 2 61 3 64 4 10 From a comparison of Series Nos 12 and 13, it will be observed that the plating rates of the bi ta-aminocarboxylic acid plating baths are slower than the alpha-amiinocarboxylic acid plating baths; which is, of course, expected as the complex formation is more difficult due to the steric factor Furthermore, it will be observed that the optimumi plating rates occur in the alkaline range of the plating baths. SERIES NO 14 In these plating tests, the plating was bright and smooth and the specific results were as follows: Duration of Tests Initial p H Final p H Wt gain Plating Rate (R x 101) (a) (b) Minutes 60 Minutes 6.50 5.80 0.0740 3.70 6.50 3.60 0.2401 SERIES NO 15 In these plating tests, the plating was bright and smooth in the acid baths, dull in the substantially neutral baths, and sebright in the alkaline baths, and the specific results were as follows: (a) Rate Tests 10 minutes 5.52 6 05 6 53 7 00 7 56 8 62 9 10 0.0733 0 0684 0 0533 0 0480 0 0464 0 0608 0 0576 Plating Rate (R x 104) 3.66 3 42 2 66 2 40 2 32 3 04 2 88 (b) Plating Tests 60 minutes Initial p H Wt gain 5.53 6 05 6 53 7 00 7 56 8 08 8 62 9 10 0.1902 0 2356 0 2468 0 2465 0 2321 0 2310 0 224 0 2000 In connection with the alpha-aminobutyric acid baths, it is pointed out that while the 10 minutes rates are loew, the 60 minute rates compare very well with those obtained in the ammoacetic acid bath; which circumstance indicates a long initiation period, possibly due to the fact that a longer time is needed for reaching a complexation equilibrium. Cycle No'. SERIE' Initial p H Final p Hi Wt gain (gmna) Plating Rate R x 10;) Duration of cycle (min) Sobn Flow Rate cc/Min. In this Aspartic acid bath, the plating was bright and smooth.

SERIES NO 17 In these plating tests, the plating was bright and smooth and the specific results were as follows: Initial p H 6 0 7 0 8 0 S NO 16 Final p H 3 5 35 4 9 1 2 3 Wt gain(gins) 0 0345 0 0367 0 0679 In passing, it is noted that Versene-regis7.00 6 70 6 60 tered Trade Mark-is chemically identical to 6.40 6 20 6 30 Nullapon registered Trade Mark and 1.4009 1 1415 1 5655 Sequiestrene-registered Trade Mark-that 3.31 3 73 3 89 have also been employed with identical results In these tests, the weight gains, should 72 51 67 be multiplied by four for comparison purposes with the other plating tests (because the area 51.4 78 4 59 6 of the steel sample was 5 cm,' instead of 20 Initial p H Wt gain 785,695 emu as previously); end it will be observed that this additive (ethylenediaminotetraacetic acid) produces optimum results in the alkaline range where this complexing agent is most effective. SERIES NO 18 In these plating tests, the plating was bright and smooth and the specific results were as follows: Initial p H Final p H Wt gain (gms) 5.0 4.3 0.0458 6.0 4.1 0.0530 Again it is noted that in these plating tests the weight gains should be multiplied by four for comparison purposes with the other plating tests. As previously noted, the utilization of an aliphatic aminocarboxylic acid additive in a plating bath of the character previously suggested and described hereinabove, is advan. tageous and a plating bath of this character of the following composition was used in plating tests of Series No 19: Magnesium hypophosphite Nickel acetate Versene( 38 % soin) Initial p H adjusted with acetic acid 0.156 m/l 0.086, Variable ( 0 2 %o and 1 %' corresponding to about 0.0027 and 0 0135 mn/l) 5.69 In 50 cc of this plating bath, properly cleaned steel samarples of 20 cm 2 area were plated for 60 minutes, the temperature of the bath being about 970 C and the following results were obtained: Versene Duration of test-min. Wt gain Stability (min) None 0 2 % 1 0 % 0.1106 stable 0.1168 stable 0.1246 stable None 1 % 29 0.2296 0.2426 stable It is noted that this bath is an acetate buffered bath and that the Versene additive results in increased plating rate and has a stabilizing action at a concentration of 1 % ( 0 0135 m/l). In passing, it is noted that in similar tests "Bakrelite" samples, prepared in the manner previously explained, were plated, and it was found that the initiation period was shortened from about 9 minutes to about 3 minutes, again indicating the advantage of utilizing the aliphatic aminocarboxylic acid additive in an acetate buffered bath of

the character previously mentioned. In a further series of plating tests, several aliphatic aminfccarboxylic acid additives were employed in each bath, and it was discovered that their actions were accumulative and good results were cbtained In these tests, plating baths having the compositicns shown in Table 4 were used In 50 cc of these plating baths, properly clearned stewl samples of 5 cm 2 area were plated for 60 minutes, the temperature-of the-baths bein-g 98 C _(±1 C), with the results showp in, Table 4. 785,695 is TABLE 4 Composition of Bath Sodium Nickel Exaltant Weight Bath Hypophosphite Chloride (moles/liter) Initial Final Gain No (moles/liter) (moles/liter) p H p H (grams) Sodium I O O 225 0 09 aminoacetate 5 74 5 0 0 1214 ( 0.120) Sodium aminoacetate II 0 225 0 09 ( 0 120) 6 0 4 3 0 1563 and Versene ( 0.04) Sodium aminoacetate III 0 225 0 09 ( 0 120) 6 0 4 4 0 1506 and Versene Fe-Sp ( 0.04) Sodium aspartate IV 0 225 0 09 ( 1 120) 6 0 3 8 0 1584 and Versene ( 0.04) In view of the foregoing, it is apparent that there has been provided an improved process of chemical nickel plating, as well as improved plating baths therefor, wherein the baths are of the nickel cation-hypophosphite anion type containing as an additive a compound selected from tbhe group consisting of aliphatic aminocarboxylic acids and salts, thereof The additives, mentioned are very advantageous in the plating bath in that they function both as exaltants and as to the plating rate and as retarders as to the formation of black precipitate Moreover, in, the arrangement, the nickel plating may take place within a wide p H range (from about 4 5 to about 9 0), being most useful around n-eu trality, where the base metal is at least attacked by the plating bath and where plating equipment corrosion is minimized Furthermore, when these additives are used in the optimum proportion (amino/Nit+ about 2 0) they keep the nickel phosphite from precipitating after many cycles in the continuous plating system, rendering it possible to' reach a phosphite concentration of about 1 molar (instead of the usual 0 07 m/l) before precipitation starts in the plating bath. In the appended claims the term "catalytic material" means any material which can be nickel-plated in an aqueous bath of the nickel cation -hypoplhosphite anion type with the evolution of hydrogen gas at the catalytic surface, and includes a material essentially comprising an element which is catalytic for the oxidation of hypophosphite anions as previously set forth herein, and materials essentially comprising an element which may be nickel-plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect, as previously set forth herein. In our Specification No 761,556 there is disclosed a process of

Producing an intimately bonded layer of nickel upon the surface of a solid nonmetallic body, which comprises exposing a fresh roughened surface of said body having secured thereto dispersed growth nuclei consisting of minute particles comprising a catalytic material, and immersing said body in a bath comprising an aqueous solution of a nickel salt and a hypophosphite in order to cause initial nickel plating upon said growth nuclei and subsequent growth, of the nickel plating into a continuous nickel layer upon the fresh roughened surface of said body. 785,695

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* GB785696 (A)

Description: GB785696 (A) ? 1957-11-06

Improvements in or relating to processes and baths for chemical plating withnickel

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The EPO does not accept any responsibility for the accuracy of data and information originating from other authorities than the EPO; in particular, the EPO does not guarantee that they are complete, up-to-date or fit for specific purposes.

^ b W _h es %t A - Il 'z % k 4 ' J PATENT SPECIFICATION

785,696 Date of Application and filing Complete Specification: Dec 31, 1953. No 36334/53. Application made in United States of America on Aug 27, 1953. Complete Specification Published: Nov 6, 1957. Index at acceptance:-Class 82 ( 2), F( 1 A: 1 81 B: 2 U), F 4 (A: E; F: G: J: K: N; W: X). International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to processes and Baths for Chemical Plating with Nickel We, CO Rp W the l Stat Str ERRATA SPECIFICATION No 785,696 Page 2, line 84, after "substantially " insert " completely" Page 2, line 122, for " 1 0/liter " read " 1 0 mole/liter " Page 12, in the Table, for " ( 0 123) " read " ( 0 135) " Page 14, line 18, for " 542 " read " 42 " Page 16, line 26, for " 5 75 " read " 4 75 " Page 18, line 3, for " 6 28 " read " 6 27 " Page 18, at the end of Table, after " 2 0 " insert " ppm " Page 26, line 33, for " range " read " rate" Page 27, line 78, after "C thereof," insert " an aliphatic aminocarboxylic acid and/or a salt thereof," THE PATENT OFFICE, 16th December, 1957. (Serial No 785,695) discloses a process of chemically plating with nickel, a catalytic material, by contacting said material with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and an aliphatic alpha-or-beta-aminocarboxylic acid and/or a salt thereof. In our Specification No 761,556 there is disclosed a process of producing an intimately bonded layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh roughened surface of said body having secured thereto dispersed growth nuclei consisting of minute particles comprising a catalytic material, and immersing said body in a bath comprising an aqueous solution of a nickel salt and a hypophosphite in order to (Price 3 s 6 d l I, _ ' 7 be nickel plated: bismuth, cadmium, tin, lead and zinc The activity of the catalytic materials varies considerably and the following elements are particularly good catalysts in the chemical nickel plating bath: iron, cobalt, nickel and palladium The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are catalytic; and the reduction of the nickel cations to metallic nickel in the plating bath proceeds until all of the nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to phosphite ions, in the presence of an excess of

nickel cations, Price 7/v; if A.-e A 'i 53 PATENT SPECIFICATION ____ Date of Application and filing Complete Specification: Dec31,11 No 36334/53. Application made in United States of America on Aug 27, 1953. ______ Complete Specification Published: Nov6, 1957. 785,696 P 53. Index at acceptance:-Class 82 ( 2), F( 1 A: IBIB; 2 U), F 4 (A; E; F; G; J; K: N; W; X). International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to processes and Baths for Chemical Plating with Nickel We, GENERAL AMERICAN TRANSPORTATION CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 135 South La Salle Street, City of Chicago, State of Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to improved processes of chemical nickel plating employing baths of the nickel cation-hypophosphite anion type and to improved baths therefor, and more particularly to such processes and baths involving a continuous system of the character of that disclosed in our copending application No. 19063/53 (Serial No 785,693). In our Specification No 761,062 there is disclosed a process of chemically plating with nickel under certain optimum conditions, metals and other catalytic materials, by contacting the materials with a bath which comprises an aqueous solution of nickel ions and hypophosphite ions and an unsubstituted, saturated aliphatic dicarboxylic acid having from 3 to 6 carbon atoms in the aliphatic chain and/or a salt thereof. Our copending application No 33169/53 (Serial No 785,695) discloses a process of chemically -plating with nickel, a catalytic material, by contacting said material with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and an aliphatic alpha-or-beta-aminocarboxylic acid and/or a salt thereof. In our Specification No 761,556 there is disclosed a process of producing an intimately bonded layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh roughened surface of said body having secured thereto dispersed growth nuclei consisting of minute particles comprising a catalytic material, and immersing said body in a bath comprising an aqueous solution of a nickel salt and a hypophosphite in order to lPrice 3 s 6 d l cause initial nickel plating upon said growth nuclei and subsequent growth

of the nickel plating into a continuous nickel layer upon the fresh roughened surface of said body 50 The chemical nickel plating of a catalytic material employing an aqueous bath of the nickel cation-hypophosphite anion type is based upon the catalytic reduction of nickel cations to metallic nickel and the corresponding oxi 55 dation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface The reactions take place when the body of catalytic material is immersed in the plating bath, and the exterior surface of the 60 body of catalytic material is coated with nickel. The following elements are catalytic for the oxidation of hypophosphite anions and thus may be directly nickel plated: iron, cobalt, nickel, ruthenium, rhodium, palladium, 65 osmium, iridium and platinum The following elements are examples of materials which may be nickel plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, 70 silver, gold, beryllium, germanium, aluminium, carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium and uranium. The following elements are examples of noncatalytic materials which ordinarily may not 75 be nickel plated: bismuth, cadmium, tin, lead and zinc The activity of the catalytic materials varies considerably and the following elements are particularly good catalysts in the chemical nickel plating bath: iron, cobalt, nickel and 80 palladium The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are catalytic; and the reduction of the nickel cations 85 to metallic nickel in the plating bath proceeds until all of the nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to 90 phosphite ions, in the presence of an excess of nickel cations. In a batch plating process, the reactions are slowed-down rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations to form an acid, which, in turn, lowers the p H of the bath, and the reducing power of the hypophosphite anions is decreased as the p H value of the bath decreases Moreover, there is a tendency for the early formation in the plating bath of a " black precipitate " that comprises a random chemical reduction of the nickel cations Of course, this formation of the black precipitate comprises a decomposition of the plating bath, and is particularly objectionable in that it causes the nickel deposit to be coarse, rough and frequently porous Any fine solid particles suspended in the plating bath, or adhering to the walls of the plating

vessel, at the plating temperature, initiate the formation of the black precipitate by acting as nuclei. In a continuous plating process the reactions are maintained substantially at their initial rates by the regeneration of the plating bath, i e, by the adding thereto of soluble nickel-containing and hypophosphite-containing reagents, as well as an alkali for p H control; however, the problem of preventing the formation of black precipitate in the plating bath and the consequent decomposition thereof is the same as that previously mentioned Moreover, another practical difficulty is encountered in the continuous plating process that is not encountered in the batch plating process in that there is a considerable build-up of the by-product phosphite therein as time proceeds and as a consequence of the cycling of the bath More particularly, while nickel hypophosphite is readily soluble in an aqueous solution, nickel phosphite is much less soluble in an aqueous solution, whereby there is a tendency, as the phosphite concentration of the plating bath builds up, for nickel phosphite to be precipitated therein, and thereby provide the solid particles that serve as nuclei for the formation of the black precipitate therein, previously mentioned In passing it is noted that the initiation of the precipitation of nickel phosphite in the plating bath is indicated by turbidity thereof. In carrying out the chemical nickel plating process on a commercial scale, the continuous system disclosed in our above mentioned copending application may be employed. A typical chemical nickel plating bath that may be employed in the continuous plating process essentially comprises an aqueous acid solution of a nickel salt and a hypophosphite and a buffer in the form of an alkaline acetate; the p H of the bath being within the approximate range 4 5 to 5 6, the absolute concentration of hypophosphite ions in the bath being in the range 0 15 to 0 35 mole/liter, the ratio between nickel ions and hypophosphite ions in the bath being in the range 0 25 to 0 60, and the absolute concentration of acetate ions in the bath being approximately 0 120 mole/liter. In the carrying out of the chemical nickel plating process on a commercial scale employing the continuous system it has been discovered that the above described chemical 70 nickel plating bath is not altogether satisfactory in that the bath does not have as fast a plating rate as is desirable; and moreover, the activity of the bath is within a relatively narrow p H range Furthermore, nickel phosphite begins 75 to precipitate at a phosphite ion concentration of about 0 07 mole/liter so that the stability of the bath is not that desired, and the useful life thereof is entirely too short.

The present invention provides a nickel plat 80 ing bath comprising an aqueous solution of nickel ions and hypophosphite ions and a complexing agent and a separate and different exalting additive, said agent substantially complexing all of the nickel ions in said bath, said 85 additive substantially exalting the plating rate of said bath and comprising ( 1) a simple short chain saturated aliphatic dicarboxylic acid including from 3 to 6 carbon atoms and/or a salt thereof and/or ( 2) an aliphatic aminocar 90 boxylic acid and/or a salt thereof when the complexing agent is other than an aliphatic aminocarboxylic acid and/or a salt thereof. The present invention further provides a process for plating a catalytic material with nickel 95 which comprises contacting the catalytic material with the nickel plating bath described above. The present invention is predicated upon the discovery that plating baths of the nickel 100 cation-hypophosphite anion type mentioned may have their stable life increased, the plating rates thereof may be substantially increased, the useful life thereof may be greatly extended, and the activity thereof with regard to the 105 usable p H range may be greatly broadened by the addition thereto of both a nickel complexing agent and an exalting additive More particularly, the plating baths of the present invention have an increased stable life in that 110 the ability thereof to hold nickel phosphite in solution at high phosphite concentrations is enhanced as evidenced by the clarity of the bath (the lack of turbidity thereof) Also, these plating baths have a nickel plating rate of at 115 least 1 mil/hour ( 0 001 "/hour) or expressed in c.g s units, of at least 3 5 x 10-l gms/cm 2/min. Moreover, these plating baths have an activity within a broad p H range ( 4 5 to 11 0); and no precipitation of nickel phosphite takes place 120 therein even at a phosphite ion concentration in some cases as high as 1 0/liter Further, the plating appearance on both metals and nonmetals is excellent (bright, smooth and nonporous); and the adhesion of the nickel plating 125 on both metallic and non-metallic bodies is excellent (no flaking of the nickel coating in bending, abrading and shock tests). Specifically, the plating baths of the present invention consist essentially of an aqueous solu 130 785,696 785,696 tion of a nickel salt and a hypophosphite and a nickel complexing agent and a separate and different exalting additive The nickel complexing agent is selected from the group consisting of ammonia, amines, acid amines, aminocarbonyls, amine-oxides and polyalcohols, as well as saturated heterocyclic dicarboxylic acids, saturated aliphatic hydroxycarboxylic acids, aliphatic aminocarboxylic acids and aliphatic keto acids, and the salts of these compounds.

The exalting additive is selected from the group consisting of simple short chain saturated aliphatic dicarboxylic acids and aliphatic aminocarboxylic acids, and the salts of these compounds In passing, it is noted that certain of the complexing agents (ammonia and amines) form molecular complexes with the nickel cations, while the remainder of the complexing agents (hydroxycarboxylic acids, aminocarboxylic acids, etc) form inner complexes or chelates with the nickel cations. Further, it is pointed out that the aliphatic aminocarboxylic acids and salts thereof are named both as complexing agents and as exalting additives since these compounds possess these two unrelated characteristics as explained more fully hereinafter. In accordance with the process of the present invention, the complexing agent, if added in sufficient quantity, substantially completely complexes all of the nickel ions in the plating bath, whereby it " ties-up " the nickel cations almost completely releasing only a small fraction thereof depending on the complex stability constant (dissociation constant); whereas the exalting additive increases the plating rate of the plating bath Thus it will be understood that the plating bath, except for the exalting additive, would have an exceedingly low plating rate due to the tyingup of the nickel cations therein However, this tying-up of the nickel cations in the plating bath is the fundamental factor contributing to the clarity of the solution, preventing the formation of precipitated phosphites therein, and giving the bath an exceedingly long life in spite of the build-up of phosphite ions therein to a concentration even in excess of one molar. Of course, the complex nickel in the plating bath must be water-soluble and of medium stability resulting in a bond strong enough to prevent the nickel ions from forming insoluble nickel compounds, such as the phosphite, the succinate or the malonate, and mixed basic salts thereof, as explained more fully hereinafter, but having a stability constant low enough to release the nickel cations required for the nickel plating operation permitting the exalting additive to bring about a plating rate of the bath of at least 3 5 x 10 gms/cm' min, as previously explained. The preferred absolute concentration of hypophosphite anions in the bath is in the range O 15 to 1 20 mole/liter, and the preferred ratio between nickel cations and hypophosphite anions in the bath is in the range 0.25 to 1 60 The absolute concentration of the complexing agent in the bath is preferably sufficient to complex at least 100 % of the nickel cations therein, and the preferred 70 absolute concentration of the exalting additive in the bath is at least 0 04 mole/liter In the plating bath, two separate additives for these two separate functions are employed The p H of the bath is preferably in the general range 75

4.5 to 11 0, depending upon the particular ingredients of the bath, as explained more fully hereinafter; and the bath may be utilized in the plating chamber of the continuous plating system at a temperature slightly below the 80 boiling point thereof and above 900 C, ordinarily at about 97-99 C The widening of the p H range is particularly desirable because adhesion of the plating to the base metal is improved at a low p H 85 In view of the foregoing, it is the primary object of the present invention to provide an improved nickel plating process of the character described, in which the reactions involved are carried out more efficiently and 90 under more stable conditions (clarity of solution) than heretofore, thereby rendering the process more desirable from a commercial standpoint. In accordance with the process of the 95 present invention, the article to be nickel plated and normally having a catalytic surface is properly prepared by mechanical cleaning, degreasing and light pickling substantially in accordance with standard 100 practices in electroplating processes, and as described in our copending Application No. 31365/53 (Serial No 785,694). With respect to the composition of the bath, the nickel cations may be derived from 105 nickel chloride or nickel sulphate, and the hypophosphite anions may be derived from sodium or potassium, hypophosphites or various 'combinations thereof The complexing agent and the exalting additive are introduced 110 into the bath normally as the acids or as the soluble salts thereof; and the desired p H of the bath is established by the eventual introduction thereinto of hydrochloric acid or a weak alkali,:such as sodium bicarbonate 115 The terms " cation," " anion " and " ion " as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present in the plating bath, i e, both undissociated and 120 dissociated material In other words 100 % dissociation is assumed when the terms noted are used in connection with molar ratios and concentrations in the plating bath Also hereinafter the expression " per cent exaltation " is 125 -employed with the arbitrary definition as the per cent increase in the rate of hydrogen evolution with reference to a given hypophosphite solution resulting from the addition thereto of the exalting additive, 130 785,696 Turning now more particularly to the introduction of the nickel complexing agent into the bath, the following examples of saturated aliphatic hydroxycarboxylic acids have been found to be particularly suitable: Rydroxyacetic acid (glycollic acid) Monohydroxysuccinic acid (malic acid) Dihydroxysuccinic acid (tartaric acid) Gluconic acid Citric acid Hydroxymalonic acid Trihydroxyglutaric acid Alpha-hydroxypropionic

acid (lactic acid) Beta-hydroxypropionic acid i 5 1-Beta-hydroxybutyric acid. As a matter of convenience, the salts of the saturated aliphatic hydroxycarboxylic acids mentioned, particularly the alkali salts thereof, may be employed in the preparation of the plating bath, since the alkali salts of these acids are usually more readily obtainable upon the market. An aminoalcohol which has been found to be particularly suitable is 2-aminoethanol. The polyalcohols which have been found to be particularly suitable are trihydroxyalcohol (glycerol) and hexahydroxyalcohol (mannitol). The aliphatic keto-acids which have been found to be particularly suitable are pyruvic acid and levulinic acid. Ammonia may be most conveniently introduced into the bath as ammonium hydroxide; and aliphatic amines which have been found to be suitable are trimethylamine and propylenediamine. Semi-carbazide and diethylene-imide oxide (morpholine) are examples of an aminocarbonyl and an amine-oxide, respectively, which have been found to be suitable. Diglycollic acid is an example of a saturated heteroaliphatic dicarboxylic acid which has been found to be particularly suitable. The following aliphatic amino-acids have been found to be particularly suitable: aminoacetic acid (glycine), alpha-aminopropionic acid (alpha-alanine), beta-aminopropionic acid (beta alanine), alpha aminobutyric acid, aminosuccinic acid (aspartic acid), iminodiacetic acid, iminotriacetic acid and ethylenediaminotetraacetic acid. Of course, the salts of the aliphatic ketoacids, ammonia, the amines, the aminocarbonyl, the amine-oxide, the saturated heteroaliphatic dicarboxylic acids and the aliphatic amino-acids, particularly the alkali salts thereof, may be employed as the complexing agent Turning now more particularly to the introduction of the exalting additive into the bath, the previously mentioned aliphatic aminocarboxylic acids and salts thereof are also particularly suitable as exalting additives, and malonic acid, succinic acid, glutaric acid and adipic acid are examples of simple short chain saturated aliphatic dicarboxylic acids which have been found to be particularly useful as exalting additives. Of course, the salts of the simple short chain saturated aliphatic dicarboxylic acids, particularly the alkali salts thereof, may be employed. As previously noted, both the hydroxycarboxylic acids and the aminocarboxylic acids form water-soluble chelates with the nickel ions in the plating bath that may be either alpha or beta position respectively forming five-membered or six-membered chelate rings.

As previously noted, the stability of the water-soluble nickel chelates formed in the bath by the chelating additives are variable and the order of stability of some of the nickel chelates produced by some of the hydroxy-acids is approximately as follows (from the more stable to the less stable): tartaric acid, malic acid, gluconic acid, citric acid, glycollic acid. An important factor that enters into nickel chelate formation by hydroxy-acids is the p H of the solution; for instance, the following p H values represent the range in which the chelate of nickel with three hydroxy-acids is stable (i e, where no nickel phosphite or basic salts are precipitated in the presence of 0 30 mole/liter of nickel phosphite over a range from room temperature to 1000 C): a S Citric acid -p H 4 6 to 4 8 and 6 5 to 11 0 Malic acid -p H 4 5 to 5 7 Tartaric acid -p H 4 5 to 5 0 For the purpose of studying the increase of the hydrogen gas evolution due to exaltation 100 with the use of different additives including those involved in the discovery of the present invention, i e, simple short chain saturated aliphatic dicarboxylic acids and aliphatic aminocarboxylic additives, and other additives 105 which have been used or suggested for chemical nickel plating baths, tests were made with test solutions of 50 cc and containing sodium hypophosphite at a concentration of 0.225 mole/liter (to which a trace of nickel 110 salt, i e, 0 0024 mole/liter, was added to initiate the reaction at vigorous rate) Pickled pieces of mild steel, 20 cm 2 area, were introduced for periods of 30 minutes each The different test solutions respectively contain no 115 additive, and additives in the form of salts of the following acids: formic, acetic, malonic, succinic, glutaric, tartaric, citric, hydroxypropionic, aminoacetic and aspartic. Specifically the additives, when used, were 120 employed as the sodium salts of the corresponding acids at a concentration of 0 125 mole/liter of the anion; and the hydrogen gas evolved was collected and its volume measured by the usual methods 125 From these exaltation tests, it was observed that the following anions give exaltation values over 100 %' (which appears to be the 783,696 lower limit of practical efficiency): aminoacetic 125 %, glutaric 163 %, succinic 175 %, malonic 213 %, and aspartic 2131 % As a practical matter, it has been discovered that the soluble succinates and aminoacetates are the most suitable, as they are cheap, readily obtainable upon the market in commercial quantities, and produce the desired exaltation to a satisfactory degree. In the formulation of plating baths in accordance with the present invention, at least % of the nickel cations should be complexed so that the ratio of the hydroxy-acid/ Ni++ is at least two for monobasic and dibasic hydroxy-acids, and at least one for tribasic

hydroxy-acids. In the use of aliphatic aminocarboxylic acids and simple short chain saturated aliphatic dicarboxylic acids in the exaltation of nickel plating baths, it is believed that this phenomenon results from the formation of heteropoly-acids between the organic additive and the hypophosphite anions which compete with the nickel complex formation Thus if the nickel complex is too stable, insufficient nickel cations are available for deposition and the plating rate becomes low despite the exalting effect produced by the organic additive The composite complexing effect and exalting effect of the various complexing agents and exalting additives in the plating baths were established by a series of plating tests that were made employing a series of test-plating baths of the general character of those previously described and as set forth more particularly in Table 1 In these plating tests, properly cleaned steel samples of 20 cm 2 area were plated for 10 minutes, the volume of the plating bath being 50 cc and the temperature thereof being about 98 -99 C. In the various plating tests appearing in Table 1 weights of nickel plating deposited are reported in gms; and the plating rates (R) are usually reported as R x 10:1 where R is expressed in gm/cm 2/min, although occasionally plating rates are reported in mils/ hour (i e O 001 "/hour) in some of the other plating tests to be described hereinafter. In a plating bath of the character noted, substantially complete complexing of the nickel ions maintains a clear plating solution but results in a low and impractical plating rate; whereas the addition of an exaltant to the complexed bath will raise the plating rate thereof to a practical value. TABLE 1 Bath Composition Bath Sodium Nickel Complexing Exaltant Initial Final Plating No Hypophosphite Chloride Agent (moles/liter) p H p H Rate (moles/liter) (moles/liter) (moles/liter) (R x 104) 1 0 225 0 0675 Malic acid 4 50 4 16 2 85 ( 0.0675) 5 02 4 35 3 53 2 do do do Sodium 4 50 4 00 3 51 succinate 5 10 4 48 4 28 ( 0.06) 3 do do 2-aminoethanol 4 50 2 54 0 50 ( 0.135) 4 do do do Sodium 4 45 4 08 3 80 succinate ( 0 09) 0 094 0 126 Hydroxyacetic 4 6 4 6 1 84 (glycollic) acid ( O 092) 6 do do do Sodium do do 3 43 succinate ( 0.06) 7 do do Hydroxyacetic do do 1 80 (glycollic) acid ( 0.152) -1 ppm of Pb++ was added as a stabilizing ion 785,696 From a comparison of the plating tests using Baths 1 and 2, it will be observed that the plating rates are substantially exalted by the addition of the small amount of sodium succinate mentioned, the plating rate of Bath 2 at the higher p H being very satisfactory. From a comparison of the plating tests using the Baths 3 and 4, it

will be observed that the plating rate is roughly 7 times higher after the addition of the exaltant In passing, it is noted that the p H values given in these tests are not optimum but were chosen only for comparison purposes. From a comparison of the plating tests using the Baths 5 and 6, it will be observed that the plating rate is substantially exalted by the addition of the small amount of sodium succinate mentioned. From a comparison of the plating tests using the Baths 6 and 7, it will be observed that the higher plating rate of the Bath 6 is due to the exalting additive and not to the total concentration of organic ion present. A series of plating tests were then conducteddemonstrating that the various complexing agents, properly selected as to the obtained stability coefficient, in amounts sufficient to give substantially complete complexation, and used with the addition of an exalting additive, result in chemical plating baths having high rates of deposition. Table 2 sets forth the results and the particular compositions of the aqueous baths employed in a series of these plating tests in which the volume and temperature of the bath, and the samples plated, were the same as for the tests conducted in Baths 1 to 7 set forth in Table 1. zo TABLE 2 Bath Composition Bath Sodium Nickel Complexing Exaltant Initial Final Plating No Hypophosphite Salt Agent (moles/liter) p H p H Rate (moles/liter) (moles/liter) (moles/liter) (R X 104) 8 0 225 Nickel sulphate Malic acid Sodium 5 10 4 60 ( 0.09) ( 0 16) succinate 4 75 4 23 3 09 ( 0.06) 9 do Nickel sulphate Sodium do 4 50 2 65 ( 0.0675) citrate 5 00 3 50 ( 0.05) 5 50 3 56 6.90 4 68 7.65 4 71 7.95 4 50 do Nickel chloride Sodium citrate Sodium 7 50 5 41 ( 0.09) ( 0045) and aminoacetate Diglycollic ( 0 09) acid ( 0 06) 11 do Nickel sulphate Sodium citrate Sodium 7 00 3 91 ( 0.09) ( 0 045) and succinate 7 50 5 41 Sodium ( 0 06) 8 00 5 55 aminoacetate 8 50 5 73 ( 0.09) 9 00 5 95 12 do do Glycollic acid do 4 65 4 05 4 55 ( 0.18) 13 do do Lactic Acid do 4 75 4 05 5 30 ( 0.18) 14 do do Tartaric acid do 4 75 4 23 3 09 ( 0.16) do do Sodium citrate do 6 90 4 90 4 68 ( 0.05) I I l 00 0.0 G\ phosphite takes place in the Bath 13 (lactic acid-succinate), whereby the Baths 8, 12 and are preferred in the continuous plating system, while the bath 13 may be used advantageously for batch plating. In additional plating tests the sodium succinate content of Bath 9 as set forth in Table 2, was modified to 0 02 moles per liter to form Bath 16 and to 0 04 moles per liter to form Bath 17 Otherwise, the composition of Baths 16 and 17 was identical to Bath 9. The plating tests carried out in connection with Bath 9 were repeated with Baths 16 and 17 and the results of duplicate tests were as

follows: Bath No 17 The plating tests conducted with Baths 9 and 11 show the effect of p H variations and it is apparent that these baths are most effective in the alkaline range With certain basic metals, such as aluminium, a high p H? is desirable. It may also be observed from Table 2 that the Bath 13 (lactic acid-succinate) produces the highest plating rate, while the Bath 14 (tartaric acid-succinate) produces the lowest plating rate This is due to the fact that the lactic acid nickel complex is least stable, while the tartaric acid nickel complex is-most stable. When 0 3 moles per liter of phosphite ion is added to these baths precipitation of nickel Bath No. Bath No 16 Test 1 Test 2 Test 1 Test 2 Initial p H 7 30 7 30 7 30 7 30 Final p H 6 60 6 60 6 40 6 40 Wt Gain 0 0772 0 0756 0 0913 0 0906 Rate Rx 104 3 86 3 78 4 57 4 53 In comparing the foregoing results with Table 2, it will be observed that Bath 9 yields the highest plating rate employing 0 06 moles per liter of sodium succinate. In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed: BATH COMPOSITION: No 18: Malic acid -0 135 moles perliter Sodium succinate -0 06 moles per liter Nickel chloride -0 0675 moles per liter Sodium hypophosphite-0 225 moles per liter Ratios: Ni++/hypo 0 33 Hydroxy-acid/Ni++ -2 00 Initial p H adjusted with caustic soda and hydrochloric acid. Utilizing this plating bath properly cleaned steel samples of 20 cm 2 area were plated for minutes and 60 minutes at a variable p H, the volume of the bath being 50 cc and the temperature thereof being 990 C, with the following results: Initial p H Plating rate Rx 104 ( 10 min test) Wt gain in ( 60 min) 4.5 3.51 5.0 4.27 0.1851 0 1866 The optimum p H for Bath 18 is around neutrality and in the alkaline range this plating bath has a tendency to jell It should also be noted that at about p H 7 0 the plating rate is almost 5 0 x 10-1 gms/cm 2/min, i e over 1 4 mils/hour. In passing, it is noted that optimum p 11, which is around 4 6 for a succinate bath (without malic' acid) shifts toward the neutral point in a bath containing all the nickel cations in the form of a complex As will be seen hereinafter the contrary is true when an amino-acid is used as the complexing agent in conjunction with succinate as the exalting additive. In order to determine the effect of increased 5.1 5 5 6.0 7.1 4.28 4 72 4 80 4 91 0.1866 0 1880 0 1885 0 1896 succinate concentrations two additional substantially identical plating tests were run at p H 5 5, one with Bath 18 and another with a Bath 19, having a composition identical to Bath 18 except that the sodium succinate concentration

was adjusted to 0 12 moles per liter In a 10-minute plating test in which the initial p H of each of Baths 18 and 19 was 5.5, Bath 18 resulted in a plating rate of 4.73 x 101 gms/cm 2/min, and Bath 19, in a plating rate of 5 12 x 101 gms/cm'/min. A continuous plating test was conducted utilizing the Bath 19 containing sodium succinate at a concentration of 0 12 mpl, as previously noted; and a plating rate of SO 785,696 g 5.09 x 10-a gms/cm: In another series aqueous bath having tion indicated below BAT Hn O No 20 Malic acid Sodium succinate Nickel chloride Sodium hypopho Ratios: Ni++/hypoHydroxy-acid/l Utilizing this plati L steel samples of 20 e minutes and 60 m bath being 50 cc and being about 990 ( results: Initial p H Plating rate R x 104 ( 10 min test) Wt gain in min. Comparing the Ba it will be observed tl minute nickel deposit the Bath No 20 utili of O 4 rather than t Baths 18 and 19. In another series i Baths 21 to 33 havin E in Table 3, were emp: of the sample treated also indicated in Tat 785,696 /min was achieved In these plating tests, a continuous plating of these plating tests, an system was used, having a plating chamber the particular composi volume of 300 cc The volume of Baths 21 was employed: and 22 was 2 liters, the volume of Baths 24, and 27 to 29 was 4 liters, the volume of OMPOSITION: Bath 26 was 6 liters, the volume of Baths 30, 32 and 33 was 1 liter and the volume of Bath -0.18 mpl 31 was 9 liters The temperature of the baths -0.06 mpl was about 99 C except as to Baths 30 to 33 -0.09 mpl where the temperature was about 100 C. sphite -0 225 mpl In the tests employing Baths 24 to 33, the Bath was regenerated after each cycle by the -0.40 addition of nickel chloride, sodium hypoNi++ -2 0 phosphite and sodium bicarbonate in the reservoir, in the manner disclosed in our above ng bath, properly cleaned mentioned copending application. _m 2 area were plated for In the first test employing Bath 23, the Inutes, the volume of the steel sample was plated for 60 minutes in 100 1 the temperature thereof cc of the bath containing 1 ppm of Pb++ at 1, with the following 990 C; then the bath was regenerated with nickel sulphate and sodium bicarbonate and a new steel sample was plated for 60 minutes in 4.50 5 00 5 50 the regenerated bath In the second test with Bath 23, the " Bakelite " (registered Trade 3.82 4 58 4 47 Mark) samples were plated in the continuous system in which the bath (containing 3 ppm 0.2130 0 2210 0 2227 of Pb++) was regenerated after cycle as described above in connection with Baths 24 ths Nos 18, 19 and 20, to 33 Prior to plating, the outer layer of hat plating rates and 60 skins of the "Bakelite" samples were rets are greater employing moved mechanically with fine emery cloth; zing a Ni+/hypo ratio and then they were soaked in an aqueous he ratio 0 33 as in the

solution containing 35 ppm of palladium chloride for 72 hours; the samples were then f plating tests, aqueous thoroughly rinsed in water, dried, and the g the compositions shown palladium chloride was reduced to metallic loyed The kind and area palladium in a hot aqueous solution of sodium in each of these baths is hypophosphite ( 0 335 mpl) until bubbling ile 3 subsided. TABLE 3 Ratio Bath Sodium Nickel Ratio Complexing Exaltant Stabilizing Tribasic Material No Hypophosphite Salt Ni++ Agent (moles/liter) Ions Hydroxy-acid Plated (moles/liter) (moles/liter) /hypo (moles/liter) to Ni 21 0 225 Nickel Chloride 0 4 Sodium Citrate Aminoacetic Pb++ 1 ppm 0 5 Steel ( 0.09) ( 0 045) acid ( 0 18) Tet+ 1 ppm 60 cm 2 22 do do do Sodium Citrate Sodium Suc Te++ 1 ppm do do ( 0.045) and cinate ( 0 06) Malic acid ( 0.09) 23 do Nickel Sulphate do Malic Acid do Pb++ 1-3 ppm 2 0 Steel ( 0.09) ( 0 18) 20 cm 2 and Bakelite cm 2 24 do do 0 33 Sodium Citrate do Pb++ 5 ppm 0 74 do ( 0.0675) ( 0 05) Zn++ 1 ppm do Nickel Sulphate 0 4 do do Pb++ 5 ppm 0 89 Steel ( 0.09) ( 0 08) 80 cm 2 26 do Nickel Chloride do do do Pb++ 4 ppm 0 8 do ( 0.09) ( 0 725) 27 do do do do Sodium Amino 0 5 Steel ( 0.045) Acetate 60 cm 2 28 do do do do and di do Pb++ 2 5 ppm do do glycollic acid ( 0.06) 29 do do do Malic Acid Aminoacetic Pb++ 1 ppm 1 0 do ( 0.09) acid ( 0 09) Te++ 1 ppm C 7 ' f-4 TALE 3 -continued. Ratio Bath Sodium Nickel Ratio Complexing Exaltant Stabilizing Tribasic Material No Hypophosphite Salt Ni++ Agent (moles/liter) Ions Hydroxy-acid Plated (moles/liter) (moles/liter) /hypo (moles/liter) to Ni do do _ do Sodium Suc Pb++ 2 ppm _ do ( 0.0675) ( 0 123) cinate ( 0 06) 80 cm 2 31 do do do do do ( 0.06) and ( 0 12) Lactic Acid ( 0.2025) 32 do do _ Malic Acid Aminoacetic Pb++ 2 ppm _ do ( 0.09) ( 0 09) acid ( 0 09) 33 do Nickel Chloride do do Pb++ 2 ppm _ do ( 0.0675) ( 0 135) ( 0 0675) Te++ 1 ppm No lead added for stabilization, because lactic acid (and commercial Ni C 12) contain sufficient lead as impurity ( 0 7 ppm in bath), but initially 0.4 moles/liter ofphosphite ions were introduced into the bath for the purpose of examining the ability of the bath to hold phosphite at a reasonably high phosphite ion concentration. a-. 00 1 cl C' 785,696 ii In these plating tests, the initial p H of the plating baths was adjusted with Ha and/or Na OH. RESULTS OF PLATING TESTS EMPLOYING PLATING BATHS 21 TO 33 Baths 21, 22 and 23 (Test 1): Initial p H Final p H Weight gain Rate R x 104 Duration of test, mir Bath 21 6 60 6 35 1 1245 21 L 36 Bath 22 6.80 6.20 1.8397 4.90 Bath 23 (Test 1) Original Regenerated Bath Bath 5.50 5 60 4.50 4 30 0.3215 0 3464 Flow rate solution cc/min.

Bath 23 (Test 2) Cycle No. Initial p H Final p H Wt Gain Rate Rx 104 Duration cycle (min) Flow rate soln. cc/min. Cumul Depl. 5.50 5.01 4.0370 5.52 5.15 3.5900 240 5.52 5.14 3.0650 3.86 5.48 5.12 3.5880 4.14 240 5.55 5.06 4.3099 4.07 5.53 5.28 5.6230 4.6 5.44 5.00 4.2290 4.16 27 22 27 22 27 27 29 19.0 36 0 50 5 67 5 87 9 106 5 135 2 The nickel coatings on the "Bakelite " both thermal shock from -40 ' C to 100 C, samples were of excellent quality, bright and as well as mechanical shock. smooth, and adhesion was excellent, resisting 5 60.6 785,696 Bath 24 Cycle No. Initial p H Final p H Wt gain Rate R x 101 Duration of cycle (min) Flow rate soln. cc/min. 7.20 6.20 1.5672 4.70 71.4 Bath 25 Cycle No. Initial p H Final p H Wt Gain Rate Rx 104 Duration of cycle (nin) Flow rate soln. cc/min. Cumulative Depletion Bath 26 (Results of Cycle No. Initial p H Final p H Wt Gain Rate Rx 10 Duration of Cycle (min) Flow Rate Soln. cc/min. Cumul. Depl % 6.49 6.28 5.29 5.60 7.20 6.00 1.9073 4.74 7.30 6.30 2.3271 5.40 7.20 6.30 2.6916 5.10 S 6.75 6.40 1.9498 5.00 6.50 6.25 2.1617 4.14 6.50 6.30 2.6493 4.33 102 55 5 45 5 60 6 46 40 6.50 5.20 2.84 4.32 12.7 Duplicate Tests) 6.49 6 55 6 6.32 5 65 5 4.96 4 13 3 5.25 4 45 4 6.54 5.82 3.92 5.56 542 30.1 6.52 6.10 4.64 6.17 50.7 6.60 5.68 3.98 5.08 6.58 6.24 3.86 5.80 67.9 6.50 5.80 4.89 5.60 6.50 5.79 5.88 5.35 6.52 5.85 4.89 5.55 6.50 5.98 5.70 5.51 6.56 6.02 4.49 5.45 118 118 116 105 98 109 138 110 129 103 49 49 49 54 58 52 41 52 44 55 16.7 14 7 28 7 26 6 41 3 42 0 58 7 565 75 6 69 9 Bath 27 Cycle No 1 2 Initial p H 700 6 80 Final p H 6 30 640 Wt Gain 12182 15638 Rate Rxl O 4 391 362 Duration of cycle (min) 52 85 Flow rate soln. cc/min 77 47 1 Bath 28: Cycle No 1 2 3 4 Initial p H 680 720 718 720 Final p H 610 650 650 650 Wt Gain 1 9725 1 6111 1 9738 2 558 Rate Rxl O 4 433 490 514 539 Dur of cycle 76 55 64 79 (mm) Flow rate soln 52 7 72 77 62 5 50 6 cc/min. Cycle No 5 6 7 8 9 Initial p H 7 15 7 50 7 15 7 40 7 50 Final p H 6 50 7 10 6 40 6 70 6 80 Wt Gain 2 0079 2 8350 2 9681 2 6999 2 3011 Rate Rx 110 5 58 5 76 6 11 6 34 6 39 Dur of cycle 60 82 81 71 60 (min) Flow rate soln 666 488 494 56-3 666 cc/min.

Hardness tests were performed upon these samples plated with Bath No 28 with results between 600 and 680 Vickers units. 785,696 is 785,606 Bath 29: Cycle No. Initial p H Final p H Wt Gain Rate Rx I 04 Duration of cycle (min) Flow rate soln. cc/min. I 5.40 5.00 4.69 116 Bath 30: Cycle No. Initial p H Final p H Wt Gain (gms) Time, min. Sobn flow rate cc/min. Plating rate Rx 104 Turnover of Ni 0 0125 mpi Bath 31: Cycle No. Ihitial p H Final p H Wt gain gms. Time, min. Soln Flow rate cc/min. Plating rate Rxl O 4 Addition of Pb+ 4.74 4.59 4.67 4.85 5.38 5.08 4.11 5.39 4.91 3.62 100 54 57 5.37 5.07 4.82 126 5.33 4.99 3.56 5.37 5.11 4.03 94 103 61 55 5.04 4 90 4 53 4 77 4 18 4 90 0.0235 0 0332 4.75 4.69 3.68 101 4.72 4.62 4.00 4.55 5 08 5.38 5.07 5.00 126 5.44 5.28 4.96 121 4.96 5 13 0.0461 0 0556 0 0663 0 0796 0 0929 4.75 4.61 3.80 5.75 4.60 3.75 4.73 4.66 4.07 123 4.77 4.68 4.20 127 5.40 4 45 4 14 4 14 None None None 1 pprm None None None 6.50 6.15 0.6837 4.54 6.50 6.12 0.8221 4.42 7.00 6.25 1.1499 4.91 51.3 6.90 6.15 2.6252 4.66 42.6 6.80 6.15 2.6594 4.81 43.7 58.1 plating rate from about 5 0 to 4 5 in Bath No. 31 On the other hand, the Bath No 31 does not respond disadvantageously, as to plating rate, to the addition of other stabilizing ions and molecules (Te++ etc, sulphydric compounds, etc). In passing, it is noted that the plating rate which was up to 4 5 x 10 gms/cm'/min in cycle No 4 dropped to 4 14 x 10 Pl g Ms/cm 2/ min in cycle No 5, after the feeding into the bath of only 1 ppm of Pb++ Even as little as 0.25 ppm of Pbl+ may result in a drop of the Bath 32: Cycle No. Initial p H Final p H Wt gain, gms. 6.80 6.08 3.81 6.80 5.98 4.65 6.78 6.26 3.68 6.80 6.21 3.80 Time, min. Soln flow rate, cc/min. Plating rate Rx 104 Cycle No. Initial p H Final p H Wt gain, gms. Time, min. Soln flow rate, cc/min. Plating rate Rx 104 Cycle No. Initial p H Final p H Wt gain, gms. Time, min.

Soln flow rate cc/min. Plating rate Rx 104 5.06 S 6.81 6.31 3.94 102 4.83 114 5.10 6.50 6.20 1.95 61.5 5.00 11 6.55 6.17 2.59 51.3 6.55 6.30 2.86 5.00 6.50 6.20 2.38 5.42 6.30 6.00 3.61 5.53 6 19 6 09 4.75 6.50 6.20 2.37 5.32 6.50 6.20 2.31 5.28 6.50 6.30 3.03 6.23 785,696 785,696 Cycle No. Initial p H Final p H Wt gain, gms. Time, min. Soln flow rate cc/min. Plating rate Rx I 04 6.70 6.50 1.20 2.45 6.50 5.80 2.71 4.75 6.51 6.28 3.09 5.43 6.49 6.11 3.39 5.72 6.28 6.07 4.18 5.93 Cycle No 19 20 21 22 23 Initial p H 6 27 5 99 6 00 648 6 50 Final p H 6 01 5 80 5 80 6 20 6 18 Wt gain, gms 4 04 4 86 4 49 6 01 5 31 Time, min 77 88 75 90 85 Soln flow rate 48 42 49 49 44 cc/min. Plating rate 6 55 6 93 7 35 8 33 7 83 Rx 104 Excess of stabilizing ions ( 10 0 ppm). After the sixth and twelfth cycles 0 009 mpl of aminoacetic acid were added ( 10 %). Also it is noted that the plating rate of the Bath No 32 is dependent upon the phosphite concentration, whereby the plating rate actually improves as the continuous operation proceeds without resulting in nickel phosphite precipitation. Bath 33: Cycle No. Initial p H Final p H Wt gain, gms. Time, min. Soln flow rate, cc/min. Plating rate Rx 104 Turnover, mpl I 6.50 5.60 4.76 4.97 6.45 5.80 5.36 6.68 5.99 5.41 6.70 7 02 6.51 5.99 6.28 7.84 6.45 5.69 7.64 123 7.75 6.22 5.90 6.14 5.98 5.82 4.50 6.96 5 63 0.0127 0 0270 0 0414 0 0590 0 0808 0 0972 Addition of 2 0 Pb++ and 1 0 ppm Tet+. plating are deposited in one hour at p H 4 5 and 5 0. It should also be noted from Table 4, that in the plating tests employing Bath 43, that the plating rate at a p H of 5 0 is very high. It will also be observed from Table 4 that the complexing of the nickel ions in Baths 44 to 47 gives exceedingly low plating rates, which are boosted by the addition of the proper amount of the exaltant at the proper p H. Table 4 further indicates that in the plating tests employing Bath 54, the p H appears to be rather critical in that the plating rates of 2.81 and 5 34 correspond to the p H values of 4.52 and 4 95. It may also be noted from Table 4 that in the plating tests employing Bath 59, at a p H of 5 5, the 10 minute rate is substantially equal to that obtained at a p H of 5 0, but that in the 60 minute plating tests the weight gain of the plating is substantially higher at the higher p

H. A further plating test employing Bath 50, as set forth in Table 4, was carried out, wherein properly cleaned steel samples of 80 cm' area were plated in a continuous plating system having a plating chamber volume of 300 cc, the volume of the bath being 4 liters and the temperature thereof being 980 C 990 C The p H of the bath was 5 0 and the test was conducted for 120 minutes; the weight gain was 3 9941 gms; and the plating was smooth and bright with good adhesion In this plating test, the calculated plating rate was 4 16 x 10-4 gms/cm'/min. A further series of plating tests were carried out to show the effect of sodium succinate as the exaltant, with various complexing agents. The composition of the plating baths and the results of these further plating tests, are set forth in Table 4. In all of these tests, properly cleaned steel samples having a total area of 20 cm' were plated in 50 cc of the plating bath which was maintained at a temperature of about 990 C. Each of plating Baths 34 to 62 contained 0.0675 moles per liter of nickel chloride and 0.225 moles per litre of sodium hypophosphite. With reference to Bath 34, it is noted that two molecules of glycerol can complex three molecules of nickel; whereby the polyalcohol in the Bath 34 is in excess. From the results of the plating tests with Baths 34 and 36, as shown in Table 4, it will be understood that the bath containing glycerol or mannitol alone, in amounts sufficient to complex completely the nickel ions, gives 10 minute plating rates below 1 0 x 10 ' gms/ cm 2/min. From Table 4, in the plating tests employing Bath 38, it will be observed that the 10 minute rates are relatively low; however, the weight of plating deposited in one hour is quite high This indicated a long initiation period for the plating reaction. Table 4 also indicates in connection with the plating tests employing Bath 39, that the amount of levulinic acid is more than that needed to complex all of the nickel ions in the plating bath (about 50 % excess), and in passing, it is noted that very high weights of 785,696 TABLE 4 Bath Complexing Stabilizing Sodium Plating Initial Weight Plating No Agent Ion Succinate Time p H Gain Rate (moles/liter) (moles/liter) (Minutes) (Grams) R x 104 34 Glycerol Pb+±1 ppm None 10 4 50 0 0095 0 48 ( 0.135) 10 5 0 0 01 0 50 5 50 0 016 0 80 4 50 0 0274 5 0 0 0345 _ 5 50 0 0434 do do 0 06 10 4 50 0 0673 3 36 5 0 0 0995 4 98 4 50 0 1216 5 O 0 1580 36 Mannitol None 10 4 50 0 0088 0 44 ( 0.135) 10 5 0 0 0088 0 44 5 50 0 015 0 75 4 50 0 0304 _ 5 0 0 0350 5 50 0 0441 37 do Pb+±1 ppm 0 06 10 4 5 0 0716 3 58 5 0 0 0890 4 45 4 5 0 1215 _ 5 0 0 1598 38 Pyruvic Acid do 0 06 10 4 48 0 0702 3 47 ( 0.135) 10 4 97 0 0694 3 51 4 48 0 1572 4 97 0 1686 39 Levulinic Acid do 0 06 10 4 0 0 0667 3 34 (

0.2025) 10 4 52 0 0968 4 84 5 02 0 0872 4 36 4 0 0 1422 _ 4 52 0 1870 5 02 0 2065 _ t O 00 0 \ O ' TABLE 4 -continued. Bath Complexing Stabilizing Sodium Plating Initial Weight Plating No Agent Ion Succinate Time p H Gain Rate (moles/liter) (moles/liter) (Minutes) (Gramns) R x 104 Ammonium do None 10 5 03 0 0012 0 06 Hydroxide 60 5 03 0 0032 ( 0.135) 41 do do 0 03 10 5 01 0 0506 2 53 5 01 0 1 42 do do 0 06 10 5 0 0 0804 4 02 5 51 0 0971 4 86 5 0 0 1566 5 51 0 1788 43 do do 0 09 10 5 03 0 1033 5 16 5 03 0 2010 7 44 Trimethylamine do None 10 4 66 0 0044 0 22 ( 0.135) 60 4 60 0 0344 do do 0 03 10 4 52 0 0588 2 94 4 52 0 1052 46 do do 0 06 10 3 93 0 0610 3 05 4 5 0 0841 4 20 5 04 0 0926 4 63 3 93 0 1104 4 5 0 1514 5 04 0 1934 47 do do 0 09 10 4 55 0 0988 4 94 4 55 0 2102 48 Propylene do None 10 5 03 0 0185 0 92 diamine 60 5 03 0 0472 ( 0 0675) 1 do do 0.03 5.03 5.03 0.0694 0.1242 3.47 I N 00 U 1 \.0 (A i 1, 1 TABLE 4 -continued. Bath Complexing Stabilizing Sodium Plating Initial Weight Plating No Agent Ion Succinate Time p H Gain Rate (moles/liter) (moles/liter) (Minutes) (Grams) R x 10 Q do do 0 06 10 4 52 0 0654 3 51 5 0 0 0948 4 74 5 53 0 0908 4 54 6 0 0 0715 3 57 4 52 0 1267 5 0 0 1683 5 33 0 1996 51 do do 0 09 10 5 03 0 0952 4 76 5 03 0 2028 52 1-2 Amino do None 10 3 5 0 0078 0 39 ethanol 10 40 0 0108 0 54 ( 0.135) 10 4 5 0 01 0 50 53 do do 0 03 10 3 52 0 0140 0 70 4 05 0 0326 1 63 4 46 0 0435 2 18 54 do do 0 06 10 3 48 0 0128 0 64 4 05 0 0408 2 04 4 52 0 0562 2 81 4 95 0 1067 5 34 4 95 0 2024 do do 0 09 10 3 53 0 0247 1 24 4 03 0 0523 2 62 4 45 0 0760 3 80 5 02 0 0881 4 46 3 53 0 0247 4 03 0 0523 4 45 0 0760 5 02 0 2184 l co 0 \ lI 1 TABLE 4 -continued. Bath Complexing Stabilizing | Sodium Plating Initial Weight Plating NO Agent Ion j Succinate Time p H Gain Rate (moles/liter) I (moles/liter) (Minutes) (Grams) R x 104 56 Morpholine do O 06 10 4 5 0 0594 2 97 ( 0.135) 10 5 0 0 770 3 85 5 5 0 0921 4 60 5 95 0 0925 4 62 4 5 0 1208 5 0 0 1488 5 5 0 1752 5 95 0 1874 57 Semi-carbazide do None 10 5 04 0 0035 0 18 ( 0.0675) 60 5 04 0 0166 58 do do 0 03 10 5 0 0 0636 3 18 5 0 0 0969 59 do do O 06 10 4 53 0 0624 3 12 5 0 0 0722 3 61 4 53 0 1150 5 0 0 1396 do do 0 09 10 5 5 0 0720 3 60 5 03 0 074 3 70 5 5 0 1549 5 03 0 1644 61 Aminoacetic do O 06 10 4 5 0 0833 4 17 acid 10 5 0 0 0940 4 70 (glycine) 10 5 62 0 0924 4 67 ( 0.135) 10 6 05 0 0946 4 73 6 52 0 0985 4 79 7 02 0 0912 4 56 4 5 0 1810 5 0 0 1956 5 62 0 2104 6 05 0 2080 6 52 0 2043 7 02 0 2021 00 \A TABLE 4 -continued. Bath Complexing Stabilizing Sodium Plating Initial Weight Plating No Agent Ion Succinate Time p H Gain Rate (moles/liter) (moles/liter) (Minutes) (Grams) R x 101 62 Beta-Alanine do 0 06 10 4 5 0 0722 3 86 ( 0.135) 10 5 05 0 0952 4 76 5 53 0 0966 4 83 6 03 0 0942 4 71 6 45 0 0922 4 61 4 5 0 1508 5 05 0 1854 5 53 0 1991 _ 6 03 0 1985 _ 6 45 0 1993 _ 00 0 \ \ O o\ 185,696 is For the purpose of establishing a standard 64 were prepared that had the following comof comparison,

simple aqueous citric acid positions: plating Bath 63 and aqueous malic acid Bath Nickel Chloride Sodium Hypophosphite Citric Acid Malic Acid Bath 63 0.0675 mole/liter 0.225 mole/liter 0.0675 mole/liter Bath 64 0.0675 moles/liter 0.225 moles/liter 0.135 moles/liter In a number of portions of Baths 63 and 64 at different p H, adjusted with Na OH and HC 1, each having a volume of 50 cc and at a temperature of about 1000 C, properly Initial p H Bath 63 Bath 64 Plating Rate Rx 104 Bath 63 Bath 64 cleaned steel samples, each of a total area of e I 2, were plated in 10 minute rate tests with the following results: Final p H Bath 63 Bath 64 Bath Appearance (Hot and Cold) Bath 63 Bath 64 4.98 5 08 1 30 2 90 4 18 4 31 Clear Clear green green 5.49 5 53 1 56 3 11 4 20 4 41, 6.02 5 91 1 74 3 16 4 20 4 43 6.53 6 55 2 00 3 50 4 21 4 42, 7.03 7 02 2 00 3 24 4 40 4 50,, turbid green 8.60 3 75 5 50 In all of these tests with Baths 63 and 64, the plating appearance was smooth and bright and there was no evidence of the formation of a black precipitate. Baths 63 and 64 were modified by adding thereto different exaltants, each in the amount of 0 0675 moles/liter, and similar 10 minute plating rate tests were conducted on identical properly cleaned steel samples The results are set forth below and in Table 5. 785,696 en 00 ( N V 4 O cse voun In 00 O m\ m O 0 O O \ O ( 9 M( OMe e t V to N < C( 9 e V 1 f I By R4 N e 9 m m O C 0.V '0 O N Vn XM:N en en uC O i t I O in 00 CIL Wi WI lfC 4; t_ rn 00 >'ti O ( 9 C M: -M t m emn m m V O 10 MD N 1 t 4X S-( C V V V V c SCO CO CO C In all the tests set forth in Table 5, the plating appearance was smooth and bright and there was no evidence of the formation of a black precipitate The color of the plating 5 baths (hot and cold) containing glycine, alphaalanine and aspartic acid, was a clear blue. The color of the plating baths (hot and cold) containing the other exaltants was a clear green 10 Recapitulating, in the continuous plating system, the malic acid-lactic acid-succinate bath, the malic acid-glycine bath and the malic acid-succinate bath are generally preferred both from the standpoint of economy and 15 performance Specifically the malic acid-lactic acid-succinate plating bath, although somewhat slower than the other two last-mentioned plating baths with regard to plating rate is productive of a nickel plating upon steel that 20 exhibits excellent adhesion (even on steel castings) as it may be employed at a p H as low as 4 5 to 5 0, and since this plating bath has a long useful life, as it will retain nickel phosphite in solution even at concentrations up 25 to 1 molar Specifically, the malic acid-glycine plating bath exhibits an exceedingly high plating rate and retains the nickel phosphite in solution over the exceedingly wide p H range 4 5 to 9 5 even in a concentration as high 30 asx 1 molar Specifically, the malic acid

succinate bath has an entirely satisfactory plating range and an optimum p H substantially at neutrality and satisfactorily holds the nickel phosphite in solution even at a con 35 centration as high as 1 molar. A typical malic acid-lactic acid-succinate plating bath comprises; and absolute concentration of hypophosphite ions in the range 0 15 to 1 20 mole/liter; a ratio between nickel 40 ions and hypophosphite ions in the range 0 25 to 1 60; an absolute concentration of malic acid ions in the range 0 04 to 0 20 mole/liter; an absolute concentration of lactic acid ions in the range 0 04 to 1 00 mole/liter; the total 4 c quantity of the malic acid ions and the lactic acid ions are sufficient to complex at least % of the nickel ions; an absolute concentration of succinic acid ions of at least 0 04 mole/liter; and a p H within the range 4 5 tc 50 7.0. A typical malic acid-glycine plating bath comprises: an absolute concentration of hypophosphite ions in the range 0 15 to 1 20 mole/ liter; a ratio between nickel ions and the 55 hypophosphite ions in the range 0 25 to 1 60; an absolute concentration of malic acid ions sufficient to complex at least 100 % of the nickel ions; an absolute concentration of glycine ions of at least 0 04 mole/liter; and a 60 p H within the range 4 5 to 9 5. A typical malic acid-succinate plating bath comprises: an absolute concentration of hypophosphite ions in the range 0 15 to 1 20 mole/ liter; a ratio between nickel ions and hypoin A", f4 A bath according to claim 1, wherein the complexing agent comprises a chelating agent which substantially completely chelates all of the nickel ions in said solution. A nickel plating bath comprising an 70 aqueous solution of a nickel salt and a hypophosphite and a complexing agent and a separate and different exalting additive, said agent substantially completely complexing all of the nickel ions in said solution and comprising a 75 saturated aliphatic hydroxycarboxylic acid and /or a salt thereof, a saturated aliphatic keto acid and/or a salt thereof, an amine, an acid amine, an aminoalcohol, an aminocarbonyl, an amine oxide and/or a polyalcohol, said addi 80 tive substantially exalting the plating rate of said solution and comprising ( 1) a simple short chain saturated aliphatic dicarboxylic acid including from 3 to 6 carbon atoms and/or a salt thereof and/or ( 2) an aliphatic aminocarboxylic 85 acid and/or a salt thereof when the complexing agent is other than an aliphatic aminocarboxylic acid and/or a salt thereof. 6 A bath according to claim 1 or 5, whereinthe complexing agent is monohydroxysuccinic 90 acid, alpha-hydroxypropionic acid and/or a salt thereof. 7 A bath according to any of the preceding claims, wherein the

exalting additive is succinic acid 95 8 A bath according to any of claims 1 to 6, wherein the exalting additive is aminoacetic acid. 9 A nickel plating bath comprising an aqueous solution of nickel ions and hypophos 100 phite ions and a complexing agent and an exalting additive, said agent substantially completely complexing all of the nickel ions in said bath and comprising malic acid and/or a salt thereof or lactic acid and/or a salt thereof, said addi 105 tive substantially exalting the plating rate of said bath and comprising succinic acid and/or a salt thereof. A bath according to claim 9, which contains both malic acid and lactic acid and/or 110 salts thereof as complexing agents. 11 A nickel plating bath comprising an aqueous solution of nickel ions and hypophosphite ions and a complexing agent and an exalting additive, said agent substantially com 115 pletely complexing all of the nickel ions in said bath and comprising malic acid and/or a salt thereof, said additive substantially exalting the plating rate of said bath and comprising glycine and/or a salt thereof 120 12 A bath according to any of the preceding claims, wherein the ratio between nickel ions and hypophosphite ions in said bath is in the range 0 25 to 1 60 and the absolute concentration of hypophosphite ions in said bath is in 125 the range 0 15 to 1 20 mole/liter. 13 A bath according to claim 9 or claims 9 and 12, wherein the complexing agent is malic acid and/or a salt thereof, the absolute concentration of malic acid ions in said bath is su-l 130 phosphite ions in the range 0 25 to 1 60; an absolute concentration of malic acid ions sufficient to complex at least 100 % of the nickel ions; an absolute concentration of hypophosphite ions in the range 0 15 to 1 20 mole/ liter; a ratio between nickel ions and hypophosphite ions in the range 0 25 to 1 60; an absolute concentration of malic acid ions sufficient to complex at least 100 % of the nickel ions; an absolute concentration of succinic acid ions of at least 0 04 mole/liter; and a p H within the range 4 5 to 7 0. In view of the foregoing, it is apparent that there has been provided an improved process of chemical nickel plating, as well as improved plating baths therefor, wherein the baths are of the nickel cation-hypophosphite anion type, also containing a complexing agent substantially completely complexing all of the nickel ions in the bath, and also containing an exalting additive substantially exalting the plating rate of the bath and being selected from the group consisting of simple short chain saturated aliphatic dicarboxylic acids and salts thereof and aliphatic aminocarboxylic acids and salts thereof The plating baths are particularly welladapted for use in a continuous plating system as they exhibit a fast plating rate, have an exceedingly long life, and maintain nickel phosphite in solution in

concentrations as high as one molar. In the appended claims the term " catalytic material " means any material which can be nickel-plated in an aqueous bath of the nickel cation-hypophosphite anion type with the evolution of hydrogen gas at the catalytic surface, and includes a material essentially comprising an element which is catalytic for the oxidation of hypophosphite anions as previously set forth herein, and materials essentially comprising an element which may be nickel-plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect, as previously set forth herein.

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* GB785697 (A)

Description: GB785697 (A) ? 1957-11-06

Improvements in or relating to chemical nickel plating process and apparatus

Description of GB785697 (A)

PATENT SPECIFICATION 785,697 Date of Application and filing Complete Specification: July 9, 1953 No 32470155. Application made in United States of America on July 19, 1952. a (Divided out of No 785,693) Complete Specification Published: Nov 6, 1957. Index at acceptance:-Class 82 ( 2), F( 11 811 B:2 U:2 Z 6), F 4 (A:E:F: J:KW:X), F 5. International Classification:-C 23 c. COMPLETE SPECIFICATION Improvements in or relating to Chemical Nickel Plating Process and

Apparatus We, GENERAL AMERICAN TRANSPORTATION CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 135 South La Salle Street, City of Chicago, State of Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to a chemical nickel plating process and apparatus for chemical nickel plating on a large scale industrial basis rendering it feasible to produce railway tank cars and other large containers having interior linings formed principally of nickel. Heretofore it has not been commercially practical to produce large shipping or storage containers or tanks having satisfactory interior linings formed principally of nickel due to the great expense involved in employing nickel-clad steel sheet in the manufacture thereof and due to the total absence of any known method or apparatus for the satisfactory electrolytic nickel plating of the large interior surfaces embodied in such containers. The present invention provides a process of chemically plating with nickel the interior of a hollow container formed of a catalytic material which comprises providing an aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type having a predetermined composition and characterized by a high plating rate at a temperature within a given range disposed near the boiling point thereof, rotating said container throughout a given time interval about a substantially horizontal axis, maintaining during said rotation and throughout said time interval said container at least partially filled with said solution, and circulating during said rotation and throughout said lPrice 3/6 l time interval said solution from the exterior into said container and therethrough and back to the exterior, wherein said solution when introduced into said container has a temperature within said given range, and 50 wherein the rate of circulation of said solution, through said container' is sufficiently high to maintain the temperature of said fill within said given range and to prevent substantial departure of the composition of said 55 fill from said predetermined composition. The present invention also provides a process as above, wherein the ratio between the nickel ions and the hypophosphite ions in the plating bath is within the first range of 60 from 0 25 to 0 60, the absolute concentration of the hypophosphite ions expressed in mole/litre in said solution is within the second range of from 0 15 to 0 35, and the p H of said solution is within the third range 65 of from 4 5 to 5 6. The aqueous chemical nickel plating solution used in the process of

this invention may also contain a carboxylic acid or salt thereof, the absolute concentration thereof 70 in said solution being at least two carboxyl groups for every nickel ion that can be plated out of said solution Preferably, in such a solution, -the carboxylic acid is a simple short chain saturated aliphatic dicar 75 boxylic acid, the ratio between the nickel ions and the hypophosphite ions is within a first range of from 0 25 to 1 60, the absolute concentration of the hypophosphite ions expressed in mole/litre is within a second 80 range of from 0 15 to 1 20 the absolute ion concentration of the acid in said solution is at least two carboxyl groups for every nickel ion that can be plated out of said solution, and the p H of said solution is within a third 85 range of from 4 3 to 6 8. The present invention further provides apparatus for chemically nickel plating the interior of a tank formed of catalytic material, said apparatus comprising a base, 90 ii: 785,697 means carried by said base for removably supporting said tank with its longitudinal axis in a substantial horizontal position or only slightly inclined with respect to the horizontal so that one end of said tank is only slightly higher than the other end thereof, and for rotating said tank about its longitudinal axis in its supported position, stationary fixture mechanism detachably connectible in liquid-tight relation with said tank and allowing rotation of said tank with respect thereto, and means for circulating an aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type from the cutside through said fixture mechanism into said tank and then from said tank through said fixture mechanism back to the outside during rotation of said tank. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be ur derstood by reference to the following description taken in connection with the accompanying drawings in which Fig 1 is a diagrammatic illustration of apparatus for cheniical nickel plating the interiors of containers or tanks, embodying the present invention, and in which the process of the present invention may be carried out; and Fig 2 is an enlarged fragmentary sectional view of a portion of a container or tank produced in accordance with the present invention. Referring to Figs 1 and 2 of the drawings, the railway tank car 10 there illustrated and produced in accordance with the method of the present invention comprises a substantially horizontal outer body 11 including a number of substantially cylindrical sections 12, 13, 14 and 15, two convex ends or heads 16 and 17, and an upstanding substantially cylindrical and centrally disposed throat 18 that is provided with a removable cover 19 detachably secured in place in liquid-tight relation with the upper end thereof 'by a series of

bolts, or the like, not shown The meeting edges of the several parts 12 to 18, inclusive, of the body 11, are appropriately secured together in liquid-tight relation, as -50 by welding Specifically, as illustrated in Fig 2, the adjacent sections 14 and 15 are secured together by the welding bead 20 The parts 12-18 inclusive of the body 11 are preferably formed of sheet or plate steel in the usual manner, and the welding beads 20, are formed of welding rods consisting principally of steel Further, the tank 10 comprises a smooth, continuous, substantially homogeneous liner 21 intimately bonded to the interior surface of the body 11 and normally having a thickness in the range of 1 to 5 mils and consisting principally of an alloy of nickel and phosphorus, the alloy being composed of 89 O 1 to 97 ' nickel and 11 ,', to 3 %/ phosphorus by weight Finally, the tank 10 comprises suitable fill and drain fixtures, not shown, that are also formed principally of steel and provided with linings of the alloy mentioned Accordingly, the entire interior of the tank 10 is lined with 70 the noncorrosive liner described so that every element thereof in contact with the fluid to be shipped or stored is coated with the alloy Of course, it will be understood that the tank 10 is admirably suited to the 75 shipment of various and sundry liquids such as foods and chemicals, that would normally etch the steel body 11, or would, on the other hand, be contaminated by contact with the steel body 11 However, the non 80 corrosive alloy mentioned as forming the liner 21 is neither etched by a wide variety of the liquids noted, nor are the liquids contaminated by contact with the lining 21. The chemical nickel plating process and 85 apparatus illustrated in Fig 1 of the drawings is employed in the production of the interior lining 21 for the body 11 of thie substantially drum-like tank 10 The apparatus essentially comprises a pair of longitudinally 90 spaced apart roller mechanisms 22 and 23 removably receiving and supporting the tank for rotation about its longitudinal axis disposed in a substantially horizontal position Specifically, the longitudinal axis of 95 the tank 10, indicated by the broken line 24, is disposed at a slight angle with respect to the horizontal, indicated by the broken line 25, the right-hand end of the tank 10 being slightly lower than the left-hand end thereof 100 Also, the system comprises a thrust roller mechanism 26 engaging the lower part of the right-hand convex head 17 of the tank 10, as well as an electric motor 27 for driving the roller mechanism 23 Thus it will 105 be understood that when the electric motor drive 27 is operated, the roller mechanism 23 supports and drives by friction the righthand end of the tank 10, the roller mechanism 22 supports the left-hand end of the 110 tank 10, and the thrust roller mechanism 26 engages the right-hand head 17 in order to prevent longitudinal displacement of the tank 10 as it is rotated

about its longitudinal axis 24 Accordingly, the mechanism 221 115 comprises idler rollers, the mechanism 23 comprises drive rollers, and the mechanism 26 comprises thrust rollers Moreover, in the arrangement, the various rollers of the mechanisms 22, 23 and 26 may be covered 120 with rubber, to prevent undue noise in operation and to afford a better frictional grip upon the exterior surfaces of the tank 10. The left-hand head 16 is provided with a liquid-tight fixture 28, including relatively 125 rotative and stationary parts 29 and 30, the rotative part 29 being secured in liquid-tighit relation with respect to an opening provided in the head 16 adjacent to the centre thereof, and the stationary part 30 being supported 130 785,697 by the base 31 Similarly the right-hand head 17 is provided with what is termed herein a stationary fixture mechanism comprising a fluid-tight fixture 32, including relatively rotative and stationary parts 33 and 34, the rotative part 33 being secured in liquid-tight relation with respect to an opening provided in the head 17 adjacent to the centre thereof, and the stationary part 34 being supported by the base 31 Further, the system comprises a reservoir 35, including a storage compartment 36 and a communicating regeneration compartment 37. The bottom wall of the storage compartment 36 is provided with a drain conduit 38 arranged adjacent to the lowermost portion thereof that is controlled by a manually operable valve 39 and, likewise, the bottom wall of the compartment 37 is provided with a drain conduit 40 arranged adjacent to the lowermost portion thereof that is controlled by a manually operable valve 41 The communicaition between the compartments 36 and 37 is preferably somewhat above the respective bottom walls thereof, as indicated at 42 A series of diffusion baffles 43 are arranged in the storage compartment 36 and a series of mixers or agitators 44 are arranged in the regeneration compartment 37 and carried by a drive shaft 45 that is operated by an electric motor 46 The reservoir 35, as a whole, is adapted to store the bulk of a quantity of aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type, while the tank 10 is adapted to hold, as a bath, a relatively small portion of the solution mentioned The volume of the reservoir 35 may be approximately 15,000 gallons ( 57,000 litres), and the volume of the tank 10 may be approximately 10,000 gallons ( 38,000 litres) In the reservoir 35, the bulk of the solution is stored at a relatively low temperature well below the boiling point thereof, at about 1500 F ( 65 'C) and at a relatively high concentration with respect to the water content thereof, whereas in the tank 10, the small portion of the solution is held at a relatively high temperature slightly below the boiling point thereof, at about 210 RF ( 1000 C), and at a relatively low concentration with

respect to the water content thereof. Any suitable chemical nickel plating solution of the nickel cation-hypophosphite anion type may be employed. Further, the apparatus comprises two motor driven pumps 47 and 48, a filter 49, two condensers 50 and 51, two flash tanks 52 and 53, two steam jet vacuum pumps 54 and 55, and a plating tank 56, as well as various communicating conduit structures and auxiliaries, described more fully hereinafter A "flash tank" is a chamber in which a subatmospheric pressure is maintained with the result that when the solution is introduced therein, there is a very rapid evaporation or "flash" which occurs due to the lower pressure conditions The lower portion of the storage compartment 36 is connected to a conduit 57 that includes a manu 70 ally operable valve 58, the upper portion of the storage compartment 36 is connected to a conduit 59 that includes a manually operable valve 60, and the conduits 57 and 59 are interconnected by a by-pass conduit 61 75 that includes a manually operable valve 62. The conduits 61 and 57 are connected by a conduit 63, including a manually operable valve 64 and a check valve 65, to the inlet of the pump 47; and, likewise, the conduits 80 59 and 61 are connected by a conduit 66, including a manually operable valve 67 and a check valve 68, to the inlet of the filter 49. The outlet of the pump 47 is connected by a conduit 69, including a manually operable 85 valve 70, to the inlet of the filter 49, and the outlet of the filter 49 is connected by a conduit 71, including a manually operable valve 72, to the upper portion of the condenser 50 Also, a liquid flow measuringc 90 device 73, preferably a "Rotameter", is operatively connected to the conduit 71 by an arrangement, including two manually operable valves 74 and 75, and two check valves 76 and 77, so that the flow of the solution 95 through the conduit 71 into the condenser may be appropriately metered. In view of the foregoing, it will be understood that by appropriate manipulation of the valves 58, 60, 62 and 64, the solution 100 may be drawn into the inlet of the pump 47 either from the lower portion of the storage compartment 36 or from the upper portion thereof Also, by appropriate manipulation of the valve 70, the rate of flow of the solu 105 tion from the outlet of the pump 47 may be governed Further, by appropriate manipulation of the valve 67 some of the solution from the outlet of the pump 47 may be bypassed around the filter 49 back into the 110 inlet of the pump 47, whereby the pump 47 may be controlled to pump the solution at its full capacity, while permitting a variable amount of the solution to pass through the filter 49 In any case, the solution is with 115 drawn from the storage compartment 36 by the pump 47 and discharged into the upper portion of the condenser 50, and from

the lower portion of the condenser 50, the solution is conducted via a conduit 78, includ 120 ing a check valve 79, into either or both the tank car 10 and the plating tank 56 More particularly, the conduit 78 is connected to the inlet of the plating tank 56 via a manually operable valve 80 and a check valve 81, 125 and is connected to the stationary part 30 of the fixture 28 via a manually operable valve 82 and a check valve 83 Also the solution in the conduit 78 may be conducted back into the regeneration compartment 37 via a 130 785,697 conduit 84 including a manually operable valve 85 and a check valve 86, which arrangement is utilized for a purpose more fully explained hereinafter Live steam at a presS sure of about 125 pounds per square inch gauge ( 9 kg /cm 2) in a steam supply conduit 87 is conducted via a manually operable valve 88 into the jet mechanism of the steam jet vacuum pump 54, water vapour is drawn from the upper portion of the flash tank 53 via a conduit 89 into the jet mechanism of the steam jet vacuum pump 54, and the steam and the water vapour from the steam jet vacuum pump 54 are injected via a conduit 90 into the upper portion of the condenser In the operation of the steam jet vacuum pump 54, approximately 1,500 pounds ( 700 kg) of steam per hour is conducted through the conduit 87, and approximately 1,500 pounds ( 700 kg) of water vapour per hour is conducted through the conduit 89, whereby the 3,000 pounds ( 1,400 kg.) of steam and water vapour are injected via the conduit 90 into the condenser 50 effecting both heating and dilution of the solution conducted through the conduit 71 into the upper portion of the condenser 50. Specifically, the solution conducted via the conduit 71 into the upper portion of the condenser 50 has a temperature of about 'F ( 65 'C), and is heated to a temperature of about 210 W ( 100 CC), and conducted into the conduit 78, and thence into the plating tank 56 and or the tank car 10 Also the rate of flow of the solution in the conduit 71 is about 94 gallons ( 356 litres) per minute, and the rate of flow of the solution in the conduit 78 is about 100 gallons ( 380 litres) per minute, whereby it is apparent that the solution from the storage compartment 36 is appropriately diluted in the condenser 50 before it is conducted into the plating tank 56 or into the tank car 10. Also an auxiliary live steam injector 91 is arranged in the lower portion of the condenser 50 and is connected by a by-pass conduit 92 to the steam supply conduit 87, the conduit 92 including a manually operable valve 93 and a check valve 94 Thus, it will be under'stood that the valve 93 may be suitably manipulated in order to permit a predetermined by-pass of steam from the steam supply conduit 87 directly via the auxiliary injector 91 into the condenser 50 Furthermore, a conduit 95 is arranged in by-passing relation with respect to the conduit 92 between the steam supply conduit 87 and the

auxiliary steam injector 91, which conduit includes two check valves 96 and 97 and a temperature control valve 98 The temperature control valve 98 is connected by a capillary tube 99 to a temperature control bulb 100 arranged in a casing 101 disposed in the conduit 78, whereby the temperature of the solution in the conduit 78 governs, through the bulb 100 and the capillary tube 99, the position of the temperature control valve 98 so as to govern the amount of steam that passes through the temperature control valve 98 and consequently through the by 7 U pass conduit 95 from the steam supply conduit 87 into the auxiliary steam injector 91. The arrangement above described, including the temperature control valve 98, allows automatic adjustment of the temperature of 75 the solution in the conduit 78 by governing the total amount of live steam that is injected thereinto by the auxiliary steam injector 91 in the condenser 50. The solution from the outlet of the plating 80 tank 56 is conducted via a check valve 102 into a conduit 103 and, likewise, the solution from the tank car 10 is conducted via the fixture 32 and a check valve 104 into the conduit 103, the conduit 103 communicatine 85 with the upper portion of the flash tank 53. The lower portion of the flash tank 53 is connected to the upper portion of the flash tank 52 by a conduit 105, including a check valve 106, and the lower portion of the flash 90 tank 52 communicates via a check valve 107 with a conduit 108, that includes a manually operable valve 109, that is connected to a conduit 110, including a check valve 111 extending to the inlet of the pump 48 The 95 outlet of the pump 48 is connected to a conduit 112 that includes a manually operable valve 113; and the conduits 108 and 112 are interconnected by a by-pass conduit 114 that includes a manually operable valve 115 100 Finally, the conduit i 12 includes a manually operable valve 116 and two check valves 117 and 118 and communicates with the upper portion of the regeneration compartment 37 Also connected to the conduit 112 105 is a liquid flow measuring device 119, preferably a "Rotameter", by an arrangement including two manually operable valves 120 and 121 and two check valves 122 and 123, so that the flow of the solution through the 110 conduit 112 back to the regeneration compartment 37 may be metered. The upper portion of the flash tank 52 is connected to the lower portion of the condenser 51 by a conduit 124, including a 115 manually operable valve 125, the upper portion of the condenser 51 is connected to a cool water supply conduit 126, containing cool water at about 900 F ( 320 C), and including a manually operable valve 127 and 120 a check valve 128, the lower portion of the condenser 51 is connected to a drain conduit 129, and the upper portion of the condenser 51 is

connected via a conduit 130 to the jet mechanism of the steam jet vacuum 125 pump 55 Also, the jet mechanism of the steam jet vacuum pump 55 is connected via a manually operable valve 131 to the steam supply conduit 87 and the outlet of the steam jet vacuum pump 55 is discharged 130 785,697 5 through a conduit 132 and a vent fixture 133 4 to the atmosphere t The solution conducted from the conduit 1 78 into the plating tank 56 and into the tank car 10 may have a temperature of about l 210-F ( 100 C) and the solution conducted from the plating tank 56 and the tank car into the conduit 103 and thence into the upper portion of the flash tank 53 may have a temperature of approximately 210 'F. ( 100-C) Now the operation of the steam jet vacuum pump 54 draws a partial vacuum in the flash tank 53 via the conduit 89 that may correspond to 12 inches to 14 inches ( 30 cm to 35 cm) of 1 Hg whereby the subatmospheric pressure in the flash tank 53 effects evaporation of water vapour from the solution in the flash tank 53 so that it is cooled therein Consequently, the solution conducted from the flash tank 53 may have a temperature of about 180 'F ( 800 C), and is, of course, accordingly more concentrated than the solution conducted thereinto, as a consequence of the evaporation of the water vapour therefrom The solution conducted from the lower portion of the flash tank 53 into the conduit 105 and thence into the upper portion of the flash tank 52 may have a temperature of approximately 180 'F. ( 800 C), as previously noted Now the operation of the steam jet vacuum pump 55 and the condenser 51 draw a partial vacuum in the flash tank 52 via the conduit 124 that may correspond to about 22 inches ( 56 cm) of Hg, whereby the subatmospheric pressure in the flash tank 52 effects evaporation of water vapour from the solution in the flash tank 52 so that it is cooled therein Consequently, the solution conducted from the flash tank 52 may have a temperature of about 1500 F ( 650 C), and is, of course, accordingly more concentrated than the solution conducted thereinto, ias a consequence of the evaporation of the water vapour therefrom. The withdrawal of water vapour from the flash tank 53 and the subsequent injection of this water vapour by the steam jet vacuum pump 54 into the condenser 50 brings about a conversion of heat in the system and effects a corresponding concentration of the solution in the flash tank 53 whereas the withdrawal of water vapour from the flash tank 52 and the subsequent discharge thereof from the condenser 51 to the exterior prevents an overall dilution of the solution in the system and effects a corresponding concentration of the solution in the flash tank 52 In the operation of the system, the total amount of steam that is injected into the condenser 50 from the steam supply conduit 87 per unit time is substantially equal to the total amount of

water vapour withdrawn from the flash tank 52 and discharged by the conlenser 51 to the exterior per unit time, so that during continuous operation of the system, there is no overall and undesired substantial dilution of the solution or substantial expansion of the total volume thereof, 70 provided the exterior heat losses are compensated for or kept to a minimum in accordance with the foregoing method. In the operation of the system, the plating tank 56 may be employed for the purpose 75 of nickel plating the fittings and other accessories of the tank car 10, whereas the portion of the solution held in the tank car 10 brings about the plating of the liner 21 upon the interior surface thereof as the tank car 80 is rotated about ifs longitudinal axis 24 upon the roller mechanisms 22 and 23, in the manner previously explained. The tank car 10 holds a pool of the solution as a bath having a volume of about 85 5,000 gallons ( 19,000 litres), since the tank car 10 is retained only about half full of the solution as it is rotated As the nickel plating reaction proceeds, the solution in the tank car 10 is decomposed bringing about 90 the production of hydrogen gas therein that accumulates in the upper portion thereof In order to prevent gas lock in the tank car 10, the fittings 28 and 32 are provided with substantially U-shaped conduits 134 and 135 95 respectively communicating between the interior of the tank car 10 adjacent to the associated ends thereof and the atmosphere The conduits 134 and 135 are provided with check valves 136 and 137, respectively, in 100 order to prevent the entry of air into the tank car 10. As the tank car 10 is continuously rotated upon the roller mechanisms 22 and 23, the pool of solution remains in the lower por 105 tion thereof, and the upper portion of the tank car 10 disposed above the level of the solution therein, indicated by Ithe broken line 25, is wetted by a film of the solution so that the nickel plating reaction proceeds 110 upon both the upper and lower portions of the interior surface thereof Accordingly, the tank car 10 must be rotated at a suitable speed in order to prevent undue depletion of the film of solution carried by the upper por 115 tion of the interior surface thereof, and it has been found that by rotating the tank car 10 at a speed of about 15 r p m the film of solution carried by the upper portion of the interior surface thereof is not depleted 120 by an amount greater than 50 %, with respect to the normal consistency of the solution contained in the lower portion of the tank car 10. Of course, as the plating operation pro 125 ceeds there is a tendency for the total quantity of solution contained in the system to be depleted somewhat with respect to the normal or standard composition thereof, whereby it is necessary, in order to prevent 130 785,697 785,697 this tendency, periodically to regenerate the plating solution

in the system by the addition of appropriate reagents in the regeneration compartment 37 More particularly, the reagents are added in the regeneration compartment 37 during operation of the motor 46 so that the mixers 44 quickly place the reagents into solution The addition of the reagents should be sufficiently frequent that the composition of the solution does not materially depart from the normal or standard composition previously noted More specifically, the nickel cations and the hypophosphite anions are depleted during the plating operation, whereby appropriate amounts of commercial nickel chloride and sodium hypophosphite are added periodically in the regenerator compartment 37. Also, as the plating operation proceeds, the acidity of the solution is increased, and in order to prevent the undesirable reduction in the p Hl thereof, an appropriate weak alkali, such, for example, as commercial sodium bicarbonate is added in the regeneration compartment 37 The arrangement whereby the reagents mentioned are added in the regeneration compartment 37 is very advantageous in view of the fact that the bulk of the plating solution is retained in the communicating regeneration compartment 37 and storage compartment 36, whereby the consistency of the plating solution that is circulated from the storage compartment 36 into the plating tank 56 and into the tank car 10 does not depart appreciably from the normal or standard consistency thereof. This arrangement is very advantageous in view of the circumstance that the retention of the plating solution in the plating tank 56 and in the tank car 10 substantially at the normal or standard consistency thereof prevents stratification of the laver of nickel that is deposited upon the articles placed in the plating tank 56 and of the liner 21 thatis produced upon the interior surface of the tank car 10 Specifically, the liner 21 is smooth, continuous and substantially homogeneous and totally devoid of stratification or lamination by virtue of the carrying out of the plating operation employing the plating solution in such a manner that the consistency thereof does not depart materially from the normal or standard consistency initially established in the storage compartment 36. In view of the foregoing description, it will be understood that the tank car 10 may be readily placed and removed with respect to the roller mechanism 22 and 23 by an C O appropriate overhead crane, not shown, and that the fixtures 28 and 32 are readilv connectible and disconnectible with respect to -1 te relatively rotative and stationary parts thereof to allow the placement and removal of the tank car 10 After the tank car 10 has been provided with the lining 21 of the character specified and consisting principally of alloy of nickel and phosphorus, consisting of 89 to 97 %o nickel and 3 to 11 lo

phosphorus by weight, the plating solution 70 contained in the tank car 10 is removed therefrom before removal of the tank car 10 from the roller mechanisms 22 and 23, in the manner noted Specifically, the tank car is rotated so that the throat 18 is arraneed 75 at the bottom and a suitable connection is made via a fitting, not shown, carried by the cover 19 to an associated conduit 138 including a manually operable valve 139 At this time, the pump 48 may be operated, 80 with the valve 139 in its open position and the valve 109 in its closed position in order to withdraw the plating solution from the tank car 10 and to discharge it via the conduit 112 and thence into the regeneration 83 compartment 37 for storage therein and in the storage compartment 36 Thereafter the connection between the fixture, not shown. carried by the cover 19 and the conduit 138 is disconnected, and the tank car 10 is re 90 moved by the overhead crane, not shown, from the roller mechanisms 22 and 23, the fixtures 28 and 32 having been previously set for the removal of the tank car 10 Of course, it is apparent that another tank car 95 may be placed upon the roller mechanisms 22 and 23 by the overhead crane, not shown, in a reverse manner, after the relatively rotative parts 29 and 33 of the fixtures 28 and 32 have been secured in the openings 100 provided in the respective heads 16 and 17 thereof Following placement of the new tank car 10 upon the roller mechanisms 22 and 23, the fixtures 28 and 32 are again set for rotation in order to provide Iluid-tight 105 connections with respect to the respective cooperating stationary parts 30 and 34 thereof. When operation of the plating system is first initiated the bulk of the plating solution stored in the storage compartment 36110 and in the regeneration compartment 37 may be substantially below the normal operating temperature of about 150 'F ( 65 C), whereby it is thus necessary to bring about an initial warm-up of the plating solution 115 before circulation thereof through the plating tank 56 and the tank car 10 This may be readily accomplished by closing the valves and 82 in order to cut off the circulation of the plating solution through the plating 120 tank 56 and through the tank car 10 and bv opening the valve 85 in order to accommodate local circulation of the plating solution from the conduit 78 through the conduit 84 back into the regeneration conmartment 37 125 During this warm-up period, the pltting solution is circulated by the pump 47 through the storage comnartment 36 the f Ier 49 and the condenser 5 ( and thus into the conduit 79 and back via the conduit R 4 into 130 785,697 the regeneration compartment 37 In this local circulation of the plating solution, live steam is injected thereinto in the condenser This local circulation is continued until the bulk of the solution is

appropriately preheated to the temperature of about 150 1 F. ( 65 'C) in the storage compartment 36. Thereafter the valve 85 may be closed and the valves 80 and 82 may be opened in order to bring about circulation of the plating solution through the plating tank 56 and the tank car 10, in the manner previously explained. In the foregoing description of the mode of operation of the plating system in carrying out the present method, the tank car 10 has been described as being formed of steel, which, of course, is the normal case, but it is noted that the tank car 10 may be formed of any suitable catalytic material Likewise the articles or fixtures that are plated in the plating tank 56 may be formed of steel or any other suitable catalytic material In this connection, it is noted that the following elements are catalytic and may be readily nickel plated: copper, silver, gold, beryllium, boron, germanium, aluminium, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium, and platinum; whereas the following elements are noncatalytic and may not be nickel plated: bismuth, cadmium, tin, lead and manganese Of the catalytic elements noted, the following are particularly good catalysts in the chemical nickel plating baths mentioned: aluminium, carbon, chromium, cobalt, iron, nickel and palladium Of course, it will be understood that alloys of the catalytic elements mentioned may be readily plated, and that the chemical nickel plating reaction is autocatalytic so that once it is initiated it proceeds automatically Also, such nonconductors as vitreous, ceramic and 4-5 plastic materials are noncatalytic and may not be nickel plated employing the present method. While the layer of plating produced upon a catalytic material is composed principally of nickel, the layer is, in fact, an alloy of nickel and phosphorus, as previously noted, which circumstance brings about several advantages in that the alloy is considerably harder than a corresponding pure nickel layer produced by electrodeposition Furthermore since the chemical nickel plating reaction of the present method is autocatalytic and the plating solution is manipulated so as to prevent material departure thereof from the normal or standard composition thereof, the chemical nickel plating reaction may be carried on for any suitable length of time in order to obtain the lining 21 in the body 11 of the tank car 10 in any appropriate and desired thickness although normally a thickness within the range 1 to 5 mils is entirely appropriate for the lining of railway tank cars. Thus it will be appreciated that a considerable saving is effected by the utilization 70 of the present method since the lining 21 provided upon the interior surface of the body 11 of the tank car 10 is smooth,

continuous and substantially homogeneous and has a thickness normally not in excess of 5 75 mils On the other hand, in the fabrication of railway cars from nickel-clad steel about the thinnest nickel coating that may be employed has a thickness of about 125 mils, and in the production of such railway cars 80 employing the nickel-clad steel mentioned, cracks and crevices are formed in the resulting lining that are most objectionable when the railway car is ultimately placed in use and employed for the purpose of shipping 85 certain foods, such as milk or wine, as it is obvious that the shipped material accumulates in the cracks and crevices mentioned rendering it virtually impossible to clean the tank car after use and before it is again em 90 ployed in the transportation or storage of other material On the other hand, the railway tank car 10 having a smooth continuous and substantially homogeneous lining 21 produced in accordance with the pre 95 sent method is entirely satisfactory for the shipment of foods of the character mentioned by virtue of the circumstances that the interior of the lining 21 may be readily and thoroughly cleaned in a simple manner 100 after use since it is devoid of the cracks and crevices mentioned. Finally, in the system the interior surfaces of the various tanks 35, 50, etc, the various conduits 71, 78, etc, and the various parts 105 73, 119, etc, must be appropriately lined with glass, porcelain, plastic material or other nonconductive and noncatalytic substance in order to prevent chemical plating of nickel thereupon 110 In the above description and the appended claims the term "catalytic material" means any material which can be nickel-plated in an aqueous bath of the nickel cation-hypophosphite anion type with the evolution of 115 hydrogen gas at the catalytic surface, and includes a material comprising an element which is catalytic for the oxidation of hypophosphite ions, and materials comprising an element which may be nickel-plated by 120 virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect. In our copending application No 32471/ (Serial No 785,698) there is described 125 and claimed a container formed of a catalytic material and provided with a smooth. continuous and substantially homogeneous lining intimately bonded to the interior surface thereof and comprising an alloy of 130 8 785,697 nickel and phosphorus, said alloy containing 3 ', to 11 % phosphorus by weight. Our copending application No 19063153 (Serial No 785,693) is concerned with a continuous process of chemically plating with nickel a solid body of catalytic material using an aqueous plating solution of the nickel cation-hypophosphite anion type under specified conditions. In our prior Specification No 761,062 there is described and claimed a

bath for the chemical plating of a catalytic material with nickel which comprises an aqueous solution of nickel ions and hypophosphite ions and an unsubstituted, saturated aliphatic dicarboxylic acid having from 3 to 6 carbon atoms in the aliphatic chain and/or a salt thereof.

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