The effect of cyanide cadmium plating bath compositions on steel hydrogenation

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<ul><li><p>Electrodeposition and Surface Treatment Elsevier Sequoia S.A., Lausanne - Printed in Switzerland </p><p>213 </p><p>THE EFFECT OF CYANIDE CADMIUM PLATING BATH COMPOSITIONS ON STEEL HYDROGENATION </p><p>V. N. KUDRYAVTSEV, K. S. PEDAN and A. T. VAGRAMYAN </p><p>Institute of Physical Chemistry, Academy of Sciences of the U.S.S.R,, Moscow (U.S.S.R.) </p><p>(Received June 20, 1972) </p><p>SUMMARY * </p><p>The effect of cyanide cadmium electrolyte main components in a wide range of concentrations (Cd 15-40 g/l; NaCN 52-157 g/l; NaOH 10-120 g/l; Ni O-O.3 g/l) on steel hydrogenation has been studied. It is recorded that at high cadmium concentration in the solution the quantity of hydrogen absorbed by the steel sharply decreases. The introduction of nickel brightener (up to 0.3 g/l) in the solu- tion leads to a significant hydrogenation increase. It is shown that a change of NaCN concentration (in most cases) (52-157 g/l) and NaOH (lo-40 g/l) in the conventional limits produces a negligible effect on hydrogen absorption. On the basis of the obtained experimental data a tentative calculation method is suggested, with the help of which it is possible to estimate the relative influence of each component of the electrolyte on hydrogenation. </p><p>INTRODUCTION </p><p>It is well known that significant hydrogenation and a deterioration in the mechanical properties of steel parts may occur when they are electroplated with cadmium from cyanide electrolytes. Many attempts have been made to replace these last-named by less hydrogenating, but equally effective electrochemically non-cyanide electrolytes, but none can be said to have been completely successful. So the problems of hydrogenation and hydrogen embrittlement elimination under cadmium cyanide electroplating are still very acute. In order to solve these prob- lems it is necessary to know how a change in the content of the main components in the solution influences hydrogenation. The available information relating to the influence of separate components of cyanide cadmium electrolyte on hydrogena- tion and the mechanical properties of steel is scarce, and it is contradictory. Thus, Sachs and Melbourne, in a study of bend ductility on spring steel specimens, </p><p>* R&amp;urn&amp; en fran$ais &amp; la fin de larticle. Deutsche Zusammenfassung am Schluss des Artikels. </p><p>Electrodepos. Surface Treat., I (1972173) </p></li><li><p>214 V. N. KUDRYAVTSEV, K. S. PEDAN, A. T. VAGRAMYAN </p><p>discovered that hydrogenation during cadmium electroplating is lower from an </p><p>electrolyte with a small content of free sodium cyanide (2.4 g/l), than from one </p><p>with a large content of sodium cyanide (22.5 g/l). According to Sink2, however, at </p><p>constant cadmium concentration (15, 22.5, 30 and 37.5 g/l) an increase of sodium </p><p>cyanide in the electrolyte of from 50 to 100-125 g/l decreases rather than increases </p><p>hydrogenation, and it is only when the NaCN concentration is raised to over </p><p>125 g/l that hydrogenation increases. At a cadmium concentration of 45 g/l, </p><p>too, an increase in the NaCN content causes the hydrogenation to increase. </p><p>Cotton3 and also Geyer, Lawless and Cohen4 indicate that an increase of </p><p>cadmium concentration in the electrolyte leads to the lowering of hydrogenation. </p><p>The data obtained by Sink2 show that at NaCN concentrations of 100, 125 and </p><p>150 g/l an increase of Cd content in the electrolyte from 15 to 30 g/l results in a </p><p>decrease of hydrogenation, while further increases in concentration lead to an increase of hydrogenation. </p><p>Dingley, Bednar and Roger&amp; present data demonstrating a significant </p><p>influence of alkali on hydrogenation during cadmium electroplating processes. They believe that the origin of hydrogen embrittlement is mainly connected with </p><p>the unstable nature of cyanide electrolytes, which is due to the low alkali concentra- </p><p>tion in conventional cyanide electrolytes. To diminish hydrogenation it is recom- </p><p>mended that the alkali content in cyanide cadmium electrolytes be increased so </p><p>that the OH- and the CN- ion concentrations are equal. However, it should be </p><p>noted that the comparative compositions of stable and unstable electrolytes, </p><p>given by the authors, had unequal cadmium content. In stable electrolytes the </p><p>cadmium concentration was higher5, which as some other authors believe3,4 </p><p>exerted a decisive influence on hydrogenation. </p><p>To improve the quality of the deposit it is recommendeda, ! that a nickel salt </p><p>additive be introduced into the cyanide electrolyte. The effect of such an additive </p><p>on hydrogenation has not been studied. </p><p>The present paper is devoted to the study of the influence of the concentra- </p><p>tion of cyanide cadmium electrolyte main components on steel hydrogenation. </p><p>EXPERIMENTAL PROCEDURE </p><p>To investigate hydrogenation a direct method was used for determining the quantity of hydrogen adsorbed by the steel base during electroplatinglo. </p><p>The procedure used was as follows. Steel specimens were chemically stripped </p><p>of Cd deposit in 40-50% NH,NO, solution, cooled with ice to 5-10C, washed in distilled water, degreased in acetone and then placed in the device for vacuum </p><p>extraction. The content of electrolytic hydrogen in steel was estimated at 400C and residual pressure of 1O-6 mm Hg. </p><p>The specimens used throughout this investigation had been produced from a quenched spring steel Type Y-8A of the following composition (%): C 0.8; Si 0.2; </p><p>Electrodepos. Surface Treat., I (1972173) </p></li><li><p>STEEL HYDROGENATION 215 </p><p>Mn 0.22; P 0.018; S 0.02; Cr 0.15; Ni 0.12. The Rockwell C hardness was 50. </p><p>This steel was chosen on account of its wide use in industry, inclination to hydrogen </p><p>embrittlement, good reproducibility of results (the value of relative error being not </p><p>more than 5-10%) and, also, because of the constant and minimum content of </p><p>metallurgical hydrogen in the steel (at an extraction temperature of 400C it does </p><p>not exceed 0.05 cm3/100 g). The specimens used in the estimation of hydrogen in </p><p>steel after cadmium electrodeposition were 90 x 8 x 0.3 (mm) in size. </p><p>The main plating solutions were prepared from Cd0 and NaCN by way of </p><p>their dissolution in distilled water. NaOH or Ni (in the form of NiS0,.7H,O salt) </p><p>was added to the main solutions in sufficient quantities. All the salts were chemi- </p><p>cally pure. Prior to the experiment the solutions were subjected to pre-electrolysis </p><p>(at c.d. = 0.75 amp/dm2) for a time sufficient to allow the passage of at least 5 </p><p>amp-h per 1 1 of the solution. </p><p>Cadmium electrodeposition was performed in 0.8 I of bath in a thermostatic </p><p>glass cylindrical cell at 20C without agitation, the electroplated area being 15 cm2. </p><p>The anodes were made of cadmium type Cd-00. To avoid anode passivation in </p><p>the process of electrolysis the anodic current density was not more than 1.5 amp/ </p><p>dm2. Cadmium current efficiency was determined with the help of a cupric coulo- </p><p>meter. From time to time the electrolytes were filtered and analysed to detect any </p><p>changes in composition and, where necessary, a content correction was made. </p><p>After each correction the solution was again subjected to pre-electrolysis (cd. = </p><p>0.75 amp/dm2) for a time sufficient to allow the passage of at least 1 amp-h per </p><p>1 1 of solution. </p><p>Prior to the electroplating the specimens were degreased in alkaline solution </p><p>of the following composition (g/l): Na,PO, 30; NaOH 10; Na,CO, 30; OP 7 = 3 </p><p>at 40C in an ultrasonic field. The degreased specimens were thoroughly rinsed in </p><p>hot running water and then in distilled water, and electroplated with cadmium, </p><p>the thickness of the deposit being 0.4 mil in all experiments. Prior to cadmium </p><p>electrodeposition the degreased and rinsed specimens were kept in cyanide electro- </p><p>lyte for 40-60 set in order to improve the adhesion of the deposit. No other pre- </p><p>plating operations which could lead to additional hydrogenation of steel were </p><p>conducted. The influence of sodium cyanide (total and free) on steel hydrogena- </p><p>tion was studied in the solutions with constant cadmium concentration (Table 1). </p><p>Solutions containing 104.8 g/l NaCN and 15 and 30 g/l Cd were used for </p><p>the study of Ni and alkali influence on hydrogenation. </p><p>EXPERIMENTAL RESULTS AND DISCUSSION </p><p>1. E#ect of sodium cyanide </p><p>The dependences of steel hydrogenation on total cyanide concentration </p><p>during electroplating from electrolytes with cadmium contents of 15 and 30 g/l </p><p>Electrodepos. Surface Treat., I (1972/73) </p></li><li><p>@I </p><p>.F </p><p>a </p><p>2 </p><p>TA</p><p>BLE</p><p> 1</p><p>CO</p><p>MP</p><p>OS</p><p>ITIO</p><p>NS</p><p> O</p><p>F E</p><p>LE</p><p>CT</p><p>RO</p><p>LY</p><p>TE</p><p>S </p><p>EX</p><p>AM</p><p>INE</p><p>D </p><p>B </p><p>.: r </p><p>Exp</p><p>t. </p><p>- N</p><p>o. </p><p>5 </p><p>h) </p><p>3 </p><p>Y </p><p>1 </p><p>2 </p><p>3 </p><p>4 </p><p>5 </p><p>6 </p><p>7 </p><p>8 </p><p>9 </p><p>10</p><p>Cad</p><p>miu</p><p>m </p><p>conte</p><p>nt </p><p>(g/l) </p><p>Sod</p><p>ium</p><p> cyan</p><p>ide </p><p>conte</p><p>nt (g</p><p>/l) </p><p>15 </p><p>15</p><p> 1</p><p>5 </p><p>15</p><p> 2</p><p>0 </p><p>20</p><p> 2</p><p>0 </p><p>30</p><p> 3</p><p>0 </p><p>30</p><p>Tota</p><p>l Fr</p><p>ee </p><p>52</p><p>.4 </p><p>26</p><p>.2 </p><p>4 </p><p>12</p><p> 7</p><p>8.6</p><p> 5</p><p>2.4</p><p> 1</p><p>5 </p><p>78</p><p>.6 </p><p>52</p><p>.4 </p><p>6 </p><p>13</p><p> 7</p><p>8.6</p><p> 4</p><p>3.8</p><p> 2</p><p>0 </p><p>10</p><p>4 </p><p>78</p><p>.6 </p><p>8 </p><p>14</p><p> 7</p><p>8.6</p><p> 2</p><p>6.2</p><p> 3</p><p>0 </p><p>13</p><p>1 </p><p>10</p><p>5.6</p><p> 1</p><p>0 </p><p>15</p><p> 1</p><p>04</p><p>.8 </p><p>78</p><p>.6 </p><p>15</p><p> 7</p><p>8.6</p><p> 4</p><p>3.8</p><p> 4</p><p>.5 </p><p>16</p><p> 1</p><p>04</p><p>.8 </p><p>70</p><p>.0 </p><p>20</p><p> 1</p><p>04</p><p>.8 </p><p>70</p><p> 6</p><p> 1</p><p>7 </p><p>10</p><p>4.8</p><p> 5</p><p>2.4</p><p> 3</p><p>0 </p><p>13</p><p>1 </p><p>96</p><p>.2 </p><p>7.5</p><p> 1</p><p>8 </p><p>13</p><p>1 </p><p>10</p><p>5.6</p><p> 1</p><p>5 </p><p>78</p><p>.6 </p><p>26</p><p>.2 </p><p>3.0</p><p> 1</p><p>9 </p><p>13</p><p>1 </p><p>96</p><p>.2 </p><p>20</p><p> 1</p><p>04</p><p>.8 </p><p>52</p><p>.4 </p><p>4.0</p><p> 2</p><p>0 </p><p>13</p><p>1 </p><p>78</p><p>.6 </p><p>30</p><p> 1</p><p>31</p><p> 7</p><p>8.6</p><p> 5</p><p> 2</p><p>1 </p><p>13</p><p>1 </p><p>61</p><p>.5 </p><p>40</p><p>Cad</p><p>miu</p><p>m </p><p>an</p><p>d N</p><p>aC</p><p>N </p><p>con</p><p>cen</p><p>trati</p><p>on</p><p>s ra</p><p>tio </p><p>R=</p><p> g</p><p>-eq</p><p>-NaC</p><p>N </p><p>g-e</p><p>q. C</p><p>d </p><p>Exp</p><p>t. </p><p>Sod</p><p>ium</p><p> cyan</p><p>ide </p><p>No. </p><p>conte</p><p>nt (g</p><p>/l) </p><p>Cad</p><p>miu</p><p>m </p><p>conte</p><p>nt </p><p>(gll)</p><p>Tota</p><p>l Fr</p><p>ee </p><p>_ </p><p>Cad</p><p>miu</p><p>m </p><p>an</p><p>d N</p><p>aC</p><p>N </p><p>con</p><p>cen</p><p>trati</p><p>on</p><p>s ra</p><p>tio </p><p>R=</p><p>6 </p><p>4.5</p><p> 3</p><p>.0 </p><p>8 </p><p>6 </p><p>4 </p><p>g-e</p><p>q.N</p><p>aC</p><p>N </p><p>? g</p><p>-eq</p><p>.Cd</p><p> E </p><p>P </p><p>2 </p><p>2 </p><p>? F </p></li><li><p>STEEL HYDROGENATION 217 </p><p>(a) (b) </p><p>1 </p><p>04 i 50 n 100 150 I 75 I 125 175 C NKtw ) </p><p>Fig. 1. Quantity of hydrogen absorbed by the steel during cadmium electroplating depending on sodium cyanide concentration. (a) Cd concentration = 15 g/l = const. Curve 1, 0.5 amp/dmz; curve 2, 1.0 amp/dm*; curve 3, 1.5 amp/dma; curve 4, 2.0 amp/dm*. (b) Cd concentration = 30 g/l = const. Curve 1,0.5 amp/dme; curve 2, 1.0 amp/dma; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm2. </p><p>are shown in Fig. 1. From the data given (Fig. la) it follows that at low Cd con- </p><p>centration (15 g/l) a simple dependence of steel hydrogenation on cyanide con- </p><p>centration at different current densities is not detected. Thus, at low current density </p><p>(0.5 amp/dm2) with an increase in NaCN concentration of from 52.4 to 131 g/l </p><p>(at the same time the content of free cyanide also increases), hydrogenation grows </p><p>and at 1.5 and 2 amp/dm2 the dependence of hydrogenation on NaCN concentra- </p><p>tion goes through a maximum. The change of NaCN concentration in the solution </p><p>with higher Cd content (30 g/l) at all current densities has little effect on steel </p><p>hydrogenation (Fig. lb). Analogous results were obtained at a cadmium concen- </p><p>tration of 20 g/l. Thus, in the majority of the electrolytes studied the wide range increase of </p><p>both free and total cyanide did not produce a significant effect on the quantity of </p><p>hydrogen absorbed by the steel when electroplated. </p><p>The study of hydrogenation at cathodic polarisation of steel in 0.5 M </p><p>NaOH solution (in the absence of Cd ions) containing different NaCN concentra- </p><p>tions was also conducted. It was found (Fig. 2) that the introduction of relatively </p><p>3.0 </p><p>G </p><p>8 2.0 . %s E </p><p> 1.0 I </p><p>IIfI.I 0 0.5 I.0 1,8 </p><p>C NaCN(M/) Fig. 2. Steel hydrogenation at cathodic polarisation in 0.5 MNaOH solution depending on NaCN concentration. Current density 1.5 amp/dme, time of polarization 15 min. </p><p>Electrodepos. Surface Treat., I (1972/73) </p></li><li><p>218 V. N. KUDRYAVTSEV, K. S. PEDAN, A. T. VAGRAMYAN </p><p>small quantities of NaCN up to 15 g/l (0.3 m/l) results in a significant growth of </p><p>steel hydrogenation, this latter being negligible in the concentration range of </p><p>15-25 g/l (0.3-0.5 m/l). The increase of cyanide concentration upwards of 25 g/l </p><p>has almost no effect on the quantity of hydrogen absorbed by the steel. These data </p><p>also show that at free cyanide concentrations above 25 g/l (0.5 m/l), the hydrogena- </p><p>tion-promoting effect of the CN--anions does not increase. </p><p>2. EfSect of cadmium concentration </p><p>The change of cadmium concentration, unlike that in the case of cyanide, </p><p>produces a significant and simple effect on hydrogenation. The investigation show- </p><p>ed that in the solutions with constant concentration of total cyanide (Figs. 3a and </p><p>3b) at all current densities the increase of Cd concentration resulted in a hydro- </p><p>genation decrease. Thus, the increase of cadmium concentration from 15 to 30 </p><p>g/l led to a 2-5 times decrease in hydrogenation. Analogous dependences were </p><p>obtained in all other solutions. The lowest hydrogenation took place in the solu- </p><p>tion with the highest cadmium content. The data, given in Table 2, confirm the </p><p>predominant effect of Cd concentration on steel hydrogenation as compared with </p><p>the effect produced by free and total cyanide. As can be seen, with the rise of cad- </p><p>mium concentration in the solution, in spite of the simultaneous growth of free and </p><p>total cyanide, hydrogenation falls markedly at all current densities, this fall being </p><p>obviously due to cadmium influence. </p><p>The study of Cd current efficiencies reveals a simple relation between current </p><p>efficiency and concentration of hydrogen absorbed by the steel: an increase of the </p><p>former results in a decrease of the latter, and vice versa. As an example, in Table 2 </p><p>(a) (b) </p><p>- I </p><p>0 15 25 </p><p>CCd k/l ) </p><p>Fig. 3. Quantity of hydrogen absorbed by the steel at cadmium electroplating depending on cad- mium concentration. (a) NaCN concentration = 78.5 g/l = const. Curve 1, 0.5 amp/dm*; curve 2, 1.0 amp/dm2; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm2. (b) NaCN concentration = 104.8 g/l = const. Curve 1, 0.5 amp/dm2; curve 2, 1.0 amp/dmz; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm*. </p><p>Electrodepos. Surface Trent., I (1972/73) </p></li><li><p>STEEL HYDROGENATION 219 </p><p>TABLE 2 </p><p>DEPENDENCE OF STEEL HYDROGENATION ON CYANIDE ELECTROLYTE COMPOSITION </p><p>Electrolyte composition Hydrogen content in steel Cadmium current </p><p>(gll) (cm3/100 g) at c.d. (ampldm=) eficiencies ( %) </p><p>Cd NaCN Total Free </p><p>0.5 1.0 1.5 0.5 1.0 1.5 </p><p>15 18.6 52.4 0.50 0.63 1.02 97 86.3 80.1 30 104.8 52.4 0.25 0.30 0.35 98.3 95.1 93.4 40 131 61.0 0.18 0.14 0.22 98.8 98.3 98.2 </p><p>there are given Cd current efficiencies for three electrolytes. In reality, a current </p><p>efficiency increase, stipulated by the growth of Cd concentration in the solution, </p><p>results in a sharp decrease in hydrogenation. </p><p>The dependence obtained may be explained by taking into account the fact </p><p>that the concentration polarization by ions of discharging metal (Cd) is prevalent </p><p>in cyanide cadmium solutions. It is only natural that an increase of cadmium in the </p><p>solution should lead to a sharp decrease in concentration limitations, to an in- </p><p>crease of Cd current efficiency and, hence, to a reduction of the quota of current </p><p>going for hydrogen discharge. This last-named results in diminishing the degree </p><p>of growing deposit surface coverage by adsorbed hydrogen atoms and produces </p><p>a decisive effect on steel hydrogenation elimination. </p><p>3. The effect of alkali concentration </p><p>No simple dependence of steel hydrogenation on alkali concentration was detected during cadmium electroplating from the solutions with different alkali </p><p>(b) </p><p>Fig. 4. Quantity of hydrogen absorbed b...</p></li></ul>


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