PLATINUM METALS REVIEW

A quurterly survey of reseurch o n the platinum metuls urrd of dwelopments in their applications in industry

V O L . 7 J A N U A R Y 1 9 6 3

Contents

Temperature A,-asurement with the Expendable Immersion Thermocouple

Platinum Bubbler Tubes in Glass Melting

High Purity Palladium Brazing Alloys

Co-ordination Chemistry of the Platinum Metals

Production of Hydrogen from Coal

Low Temperature Platinum Resistance Thermometry

The Platinum Metals as Selective Hydrogenation Catalysts

Rhodium Plating in Lighthouse Beacons

Some Properties of Ruthenium (111) and (IV) in Acid Solution

Magnetic Transformations in Iron-Rhodium Alloys

Abstracts

New Patents

NO. 1

2

7

8

I t

14

1.5

18

2 4

25

29

30

38

Communications should be addressed to The Editor, Platinum Metals Review

JohrLson, Mutthey 6% Co., Limited, Hatton Garden, London, E.C.1

Temperature Measurement with the Expendable Immersion Thermocouple A SURVEY OF WORKS EXPERIENCE

By J. A. Stevenson, B.s~. Platinum Development Department, Johnson Matthey & Co Limited

The expendable immersion thermo- couple, developed by Leeds and North- rup to give greater accuracy, speed and convenience in the measurement of molten metal temperatures, has now been in use in a number of steelworks for some time. I t has also begun tojind a place in the melting of non-ferrous metals. This article surveys the results of experiences so far obtained in replac- ing the conventional pladinum rrhodium- platinum immersion thermocouple with

the expendable cartridge type.

For over twenty years the method of measuring molten steel temperatures has remained virtually unchanged. In 1937 Dr. F. H. Schofield of the National Physical Laboratory proposed a “quick immersion” method which allowed accurate noble metal thermocouples to be used to measure steel temperatures in excess of 1600°C. Robust and reliable pyrometer units were soon produced, and apart from minor modifica- tions and improvements in instrumentation, the method is in use in most steelworks to this day.

Recently, expendable cartridge immersion thermocouples have been developed, princi- pally by the Leeds and Nortlrup organisation, and it is claimed that they overcome a number of the disadvantages inherent in the older

design. To appreciate the merit of these claims it is necessary to consider briefly the design of the conventional pyrometer, con- sisting essentially of platinum : rhodium- p la t inu m t h er mo coup 1 e wire s thread e d through a long steel tube which normally has a right-angle bend some three feet from the hot end. The thermocouple is insulated with twin-bore alumina sleeves to within an inch of the hot junction. This hot junction, formed by welding or twisting the thermo- couple wires together, is protectcd by a fused silica sheath which is cemented or plugged with asbestos cord into the end of the steel tube. In many cases the steel tube adjacent to the hot junction is further protected by an outer refractory or graphite sleeve or by a thick mild steel end-block. These prevent corrosive attack when the silica-sheathed hot junction is plunged through the slag layer into the molten steel.

At the cool end of the steel tube a reel-box houses reserve thermocouple wire so that when it is necessary to renew the hot junction fresh wire may be pulled from the reserve spools down through the insulators. Com- pensating wires complete the circuit back to the instrument.

Silica is not normally recommended for use in contact with platinum thermocouples at high temperature; it is chosen, however, as the sheathing material becausc of its out- standing thermal shock resistance but must be renewed after each measurcrnent. The

Platinum Metals Rev., 1963, 7 , (11, 2-6 2

Extensive trials with the expendable cartridge type of immersion thermocouple have proved successful at the Abbey Works of the Steel Company of Wales, and the system hus been adopted in place of the

conventional immersion pyrometer in both open hearth furnaces and Bessemer converters

thermocouple hot junction, although un- touched by molten slag or steel, has to be renewed frequently as it suffers a progressive deterioration with each dip, mainly due to contamination. This not only causes a reduction in the thermal e.m.f. output but also embrittles the wire. With care a junction may survive for thirty dips but in many steelworks the junction and a few inches of wire are cut off and the junction re-made much more frequently.

The response time is approximately 10 to 15 seconds owing to the relatively large thermal mass of the sheath and junction. The speed of response is also affected by the type of recorder used and by the rate of immersion chosen by the operator.

While this procedure has clearly established its reliability over a long period of years, it does have certain drawbacks. It does not present a new and hence an accurate thermo- couple junction for every measurement; the replacement of the silica sheath after every

dip means that there is an appreciable interval of time when a probe is out of circulation and emergency probes must be on hand in case temperature re-checks are required; the response time may be ernbarrass- ingly long especially with the new pneumatic steel-making processes, and skilled, or at least semi-skilled, labour is required to re-make the hot junctions.

The expendable cartridge type of pyro- meter is claimed to overcome these difficulties. I t uses exactly the same principle as the old system, but differs considerably in detail. I t is essentially an assembly in which a new, uncontaminated noble metal thermocouple contained in a sealed plug-in unit is used for one measurement and is then discarded. The compensating leads and connectors form part of a permanent circuit back to the high-speed recorder and are so protected that the accuracy of the reading is unimpaired.

The device has three main components : the expendable thermocouple cartridge, the long

Platinum Metals Rev., 1963, 7 9 (11, 3

steel dipping tube and the expendable card- board sleeve which slips over the cartridge and the hot end of the dipping tube.

The expendable cartridge has a fine gauge platinum : 13 per cent rhodium-platinum thermocouple wire enclosed in a small U-shaped quartz tube so that the junction is in the centre of the U. Thc ends of the tube are mounted in a special cement in a ceramic block so that about 3 inch of tube protrudes. At a point sufficiently far inside the cement not to be affected by excessive heat during the period of recording the thermocouple wires join leads of compensating material. These leads continue to the back face of the plug, where they form non-reversible contacts of the same material. Copper and a nickel- copper alloy, the normal compensating materials for noble metal thermocouples, are used for all leads and contacts.

The protruding quartz tube is covered by a steel cap which gives protection during handling and storage, and also absorbs the physical shock when the cartridge is plunged through the molten slag into the steel.

The long dipping tube is usually of I inch i.d. steel pipe, bent at one end if desired. Fitted into the hot end is a unit capable of accepting the plug-in cartridge. Leading from

this unit a compensating cable runs the length of the tube and then back to the recorder.

The third component is the cardboard sleeve. This is slipped over the cartridge and the hot end of the dipping tube to prevent slag or metal coming into contact with the dipping tube.

In use the assembly is similar to the traditional probe, no preheat is required, and the tip can be plunged directly into the steel. The cap immediately melts and allows molten steel to surround the thin quartz tube. The excellent thermal contact and the low thermal mass allow the maximum temperature to be recorded within four or five seconds and the probe can then be withdrawn. The thermo- couple cartridge together with the charred cardboard sleeve must be stripped off immediately before excessive heat is trans- ferred to the contacts. A new assembly of cardboard sleeve and cartridge can then be fitted.

Normally no attempt is made to recover the scrap thermocouple wires although in a large works it may be found to be worth while.

To deal with the rapid response a high- speed recorder is desirable. One model incorporates special signal lights and an

A sectioned view of the Leeds and Northrup expendable thermocouple cartridge, showing the p1atinum:rhodium-platinum thermocouple wires housed in the U-shaped

quartz tube and protected by the steel rap

Platinum Metals Rev., 1963, 7 , (11, 4

audible warning device, the sequence being a green signal light when the cartridge is plugged in, indicating a closed circuit; a timing device which operates as soon as a certain temperature is achieved, say 13oo0C, and then after four or five seconds have elapsed a red light and warning horn are operated.

Clearly the expendable cartridge system offers the great advantage of presenting a new and uncontaminated thermocouple on each immersion. Provided that this does not increase the cost of temperature measurement, and that the introduction of additional com- ponents into the circuit does not affect accuracy and reliability, there is much to commend the method. It is not to be expected, of course, that it will entirely replace the conventional system, which will retain its usefulness in a number of applica- tions, but where rapid response is essential and automatic recording is installed an appreciable improvement can be secured. The economy achieved by the use of fine diameter platinum and rhodium-platinum alloy wires is to a considerable extent offset by the very much lower-if any-recovery of scrap platinum and rhodium from the spent cartridges, and the net cost per immersion is comparable with the older method.

Experience at the Steel Company of Wales

At the Abbey Works of the Steel Company of Wales extensive trials have been carried out with expendable cartridge thermocouples in open hearth furnaces, in Bessemer con- verters and in ladles. Mr J. T. Davies, Chief Fuel Technologist to the company, reports that they are now convinced of the superior accuracy and reliability of the new method, and would not wish to revert to the previous system of immersion pyrometry.

During check immersions using both procedures readings with the expendable cartridge were almost invariably higher than those obtained with the older method but the differences in temperature were in general

agreement with the fall normally experienced in the e.m.f. of the conventional type of couple. When cross-checks were made using a second expendable cartridge or a new and uncontaminated couple of the old type the readings were all in close agreement. Failures from all causes are now running a t about 55 per cent of those experienced before the adoption of this method.

Maintenance on the dipping rods is also only a fraction of that previously required. There have in fact been periods of several weeks during which thousands of immersions have been made without any repair to the dipping rods being necessary. The life of a connecting receptacle has been found to be about 500 immersions, while only a few minutes are required for a replacement to be fitted. The steel tube has been found to last for over 1500 immersions.

Experience at the Steel Company of Wales also goes to show that the design of the contacts in the cartridge and the connecting receptacle can play a particularly important part in the accuracy and reliability of the system, since any temperature difference existing across the faces of the contacts can cause errors in measurement. The disinte- gration of the cardboard tube during immer- sion is also rather active and can cause some oscillation of the dipping rod, with the possibility of causing contact chatter. On the other hand the ease of assembly of a cartridge into a dipping rod does enable a temperature to be taken within seconds of its fitting, and although this may not be standard practice it can and does happen, particularly when a quick check is required. The use of the cardboard tube was found to prevent excessive temperature rise very effectively, but a cartridge can be fitted into a dipping rod that has a receptacle temperature considerably above that of the tip and it is in these conditions that good heat transfer between the contacts is required. Fitting a cartridge into a well-used receptacle at a temperature higher than that experienced in normal working indicated, however, that

Platinum Metals Rev., 1963, 7 , (11, 5

I n addition to its applications in the steel industry, the ex- pendable immersion thermo- couple has begun to Jind a place in the melting of non- ferrous metals. Here it is being used to check temperature before casting in a copper- alloy foundry

the maximum error from this source would not excced 3" at 1600'C.

The consistency of res- ponse of the cartridges, coupled with the very short immersion period necessary to obtain a reading, makes possible-and requires if the maximum life is to be obtained from the dipping rods-the automatic timing of immersion as described earlier.

Use in Arc Furnaces at Samuel Fox In the Stocksbridge works of Samuel Fox

& Co Limited, the expendable cartridge thermocouple has also been under extensive tests and has now been adopted as a regular procedure on two 60-ton arc furnaces. Dr R. H. Baulk, Instrumentation Officer to the company, reports that this system of immersion pyrometry appears to have several advantages over the conventional method. It is more accurate and always gives a reading either identical with or higher than the older method; it is more reliable, and very few dips have to be repeated because of defective readings, while the instrument is more readily handled since it is much lighter. The cost per dip at Stocksbridge was found to be less with the newer system when all labour charges are included.

Initial difficulties experienced by Dr Baulk were of two types; the design of the support- ing arm and of the contacts made it possible for some overheating to occur, while the re-

education of the furnace operators into the different handling technique took some little time. These initial difficulties have now been overcome and, in addition to using the method exclusively on the two large arc furnaces, steps are being taken to apply the technique on other melting units in the works.

A High Temperature Cartridge A further development of considerable

interest in connection with the use of oxygen in steelmaking is the substitution of an iridium : 40 per cent iridium-rhodium couple for the normal platinum : rhodium-platinum combination. This is capable of measuring temperatures up to zooo°C, and an expend- able cartridge designed by the Amalgams Co Limited, of Sheffield, incorporating this thermocouple has been used successfully during the oxygen blowing period in an arc furnace to record 1960°C. This is a sig- nificant advance in instrumentation, as there has hitherto been no method of measuring such temperatures under industrial conditions.

Platinum Metals Rev., 1963, 7 , (11, 6

Platinum Bubbler Tubes in Glass Melting IMPROVEMENT OF QUALITY AND OUTPUT

Bubbling is now an accepted method of improving the thermal efficiency and output of a glass melting tank. Small bubbles of gas, introduced by way of bubbling tubes inserted in the siege of the melting end of the tank, expand and rise to the surface of the glass. The agitation mixes the lower cold layers of glass with the hotter upper layers. Glass is a poor thermal conductor and this mechanical mixing considerably improves the efficiency of heat utilisation; the glass melting rate is increased and so the output of the furnace improves.

The number and disposition of the bubbler tubes naturally varies with tank design but they are placed so that a curtain of bubbles rises across the full width of the tank. The bubbles bursting on the surface form a barrier to floating scum and prevent it passing into the refining zone. While rising the expanding bubbles also absorb other small pockets of gas or air in the glass and in this way improve the quality of glass produced.

This technique is especially useful for glasses of high density, for example the 30 per

cent lead oxide containing glasses common in the radio and radio valve industry, and for highly viscous glasses such as the boro- silicate heat resisting glasses.

The size of the bubble introduced into the glass is critical, and so the bubbler tubes must be made from material which can operate continuously in molten glass without being attacked. They must also be mechanically strong, be unaffected by the gas used for bubbling, and be capable of lasting the whole life of the furnace.

The illustration shows a typical 10 per cent rhodium-platinum/nickel composite bubbling tube. The bubble emerges from a hole of chosen diameter drilled on the top of the flat face. The length of the rhodium-platinum section is chosen so that the joint with thc nickel is in a position where the temperature does not exceed approximately 700°C. If for any external reason a failure occurs the bubbler tubes may be replaced. Attached to the end of the nickel section, a coupling allows connection with a gas or compressed air line. E.P.

A typical bubbler tube as jitted to a glass melting tank. The smaller diameter portion is in I0 per cent rhodium- platinum, welded to a larger diameter nickel tube

Platinum Metals Rev., 1963, 7 , (11, 7-7 7

High Purity Palladium Brazing Alloys MULTI-STAGE JOINTING IN THE MANUFACTURE OF THERMIONIC VALVES

By M. H. Sloboda, Dipl. Ing.

Research Laboratories, Johnson Matthey & Co Limited

The possibility of using palladium as a component of brazing alloys for high tem- perature service was first explored by Rhodes, working in the laboratories of the Mond Nickel Co Limited, who studied the effect of additions of this metal on the pertinent pro- perties of silver-copper alloys.

This early work was directed towards satis- fying the demand for high-temperature braz- ing alloys suitable for the fabrication of turbine assemblies for jet engines. It resulted in the development of a series of ternary silver- copper-palladium alloys containing between 5 and 25 per cent palladium. All these alloys freeze at temperatures higher than the melting point of the silver-copper eutectic (778°C); they have sufficiently narrow melting ranges, they wet readily nickel-based alloys without causing cracking due to inter-granular pene-

tration and they meet many requirements imposed by high service temperatures in a large number of industrial applications.

The manufacture of special-purpose ther- mionic valves, such as magnetrons and klystrons, represents a relatively recent field of application of palladium-bearing brazing alloys.

Since these devices operate at relatively high temperatures and under conditions of high vacuum, the use of standard cadmium- and,'or zinc-bearing silver brazing alloys is ruled out. Silver-copper eutectic has been widely used in this application, but more satis- factory results can often be obtained with the palladium-bearing alloys because of their better mechanical properties at elevated temperatures, improved wetting characteristics on molybdenum, tungsten, and nickel alloys,

The Pallabraze Range of High Purity Brazing Alloys

Pal lad i u rn A1 I oy percentage Melting

and composition range "C

Pallabraze 810 Pallabraze 840 Pallabraze 850 Pallabraze 880 Pallabraze 900 Pallabraze 950 Pallabraze 1010 Pallabraze 1090 Pallabraze 1237

5 Pd-Ag CU 10 Pd-Ag CU 10 Pd-Ag CU 15 Pd-Ag CU 20 Pd-Ag CU 25 Pd-Ag CU

5 Pd-Ag 18 Pd-Cu 60 Pd-Ni

807 - 810 830 - 840 824 - 850 856 - 880 876 - 900 901 - 950 970- I0 I0

1080- I 090 I237

Platinum Metals Rev., 1963, 7 , (1),8-11 8

Components of a power triode header assembly, by English Electric VaZve Co Limited, together with the inserts of Pallabraze 810 wire that are used in the brazing operation. Brazing is carried out by induction heating, and brazing time i s about thirty seconds

and reduced risk of failure due to intergranular penetration. Gold- copper and gold-nickel alloys are also used in this field.

The manufacture of thermionic valves may entail fabrication of components comprising several joints that cannot be brazed in a single operation. A range of braz- ing alloys is therefore required with the melting points spaced at convenient intervals so that com- plex assemblies can be fabricated

The power triode assembly shown above in position in the induction brazing unit and ready f o r the crarked ammonia bell to be lowered. T h e joints are made between nickel sleeves o n the filament posts and Ni lo K seals o n the ends of the spacers

Platinum Metals Rev., 1963, 7 , (11, 9

The complete English Electric BR109 power triode

by the step-by-step brazing tech- nique. In addition, best results in brazing close-fitting parts are achieved with alloys of the eutectic type - having a single melting point or a narrow melting range - whereas an alloy with a relatively wide melting range may be re- quired to bridge wide joint gaps or to form large fillets.

These requirements are met by a range of palladium-bearing braz- ing alloys, marketed by Johnson Matthey under the name “Palla- braze”. The range includes six ternary silver-copper-palladium alloys and three binary composi- tions : 5 per cent palladium-silver, 18 per cent palladium-copper and 40 per cent palladium-nickel, the last of these alloys constituting a useful addition to the range because of its high single melting point of 1237°C. Particulars of these alloys are set out in the table on page 8. In each case the reference number of the alloy is its liquidus temperature.

Importance of High Purity A feature distinguishing the Pallabraze

alloys from similar materials intended for general engineering applications is their extremely high degree of purity. This con- sideration is of primary importance for several reasons.

First, since the application of brazing fluxes in the fabrication of thermionic valve com- ponents is inadmissible, brazing alloys used for this purpose must be virtually free from impurities that might impair their wetting and spreading characteristics; this group of impurities includes metals forming refractory

Platinum Metals Rev., 1963, 7 , (11, 10

oxides that do not dissociate except at very high temperatures and low pressures and that can only be reduced in reducing atmospheres of purity difficult to obtain in industrial braz- ing practice.

Secondly, efficient functioning of thermionic valves and other similar devices depends on maintaining a high vacuum; this means that all the materials of construction, including the brazing alloys, must be free from volatile constituents. These include not only metals that have high vapour pressures at tempera- tures at which thermionic valves operate, but also carbonaceous surface contaminants (grease, oil, lubricants, etc.) that might affect the vacuum as a result of gradual build-up of carbon monoxide in the valve.

These requirements impose the need both for rigorous control of the purity of the raw materials used in the manufacture of brazing alloys for this application and for special precautions at every stage of the manufactur- ing process.

Based on the extensive experience of Johnson Matthey in the production and application of ultra-pure materials, very low limits of impurities for Pallabraze alloys have been established. These are set out in the table. All the JMC Pallabraze alloys listed in the table on page 8 are made to this specification, and every batch of wire is checked to ensure that these limits are not exceeded.

Brazing Technique Although palladium-bearing alloys can, in

principle, be used for torch brazing, this method is not applicable in the manufacture of thermionic valves because of the complica- tions caused by the necessity of using a brazing flux. For this reason brazing must be carried out either in vacuum or in a neutral or reducing atmosphere. Depending on thc nature of the parent metals, a vacuum of 10 mm Hg, or a protective atmosphere with a dew point lower than -SOT, may be required. Hydrogen and cracked ammonia are both

Impurity Limits in Pallabraze Alloys

Impurity

Aluminium Beryllium Chromium Manganese Titanium Zirconium

Antimony Bismuth Cadmium Calcium Lead Lithium Magnesium Tin Zinc

Phosphorus

Parts per Million, Maximum

5 " 5

10 10 10 5

30 1 I

10 I l o I 30 1

30 I' 101

I00

Total of

these impurities 90 PPm

* 10 ppm in the case of Pallabraze 1237

suitable as protective atmospheres, provided that their moisture content is sufficiently low.

The brazing alloys are supplied ready for use in the form of wire. They can, however, become contaminated during any forming operation or in handling, in which case they should be vapour-phase degreased immediately before brazing. Similar steps should, of course, be taken to ensure cleanliness of the work pieces.

Difficulties encountered in fluxless brazing of components made from alloys containing metals which form refractory oxides can sometimes be overcome by raising the brazing temperature. If this expedient fails, recourse may be taken to nickel plating the com- ponents before brazing.

Part of an assembly of an English Electric power klystron being prepared for furnace brazing. All the components shown are copper and the joints are made with wire rings of Pallahrate 880

Platinum Metals Rev., 1963, 7 , (11, 11

Co-ordination Chemistry J

of the Platinum Metals A REVIEW OF THE SEVENTH INTERNATIONAL CONFERENCE

By R. A. Shaw, Ph.D., F.R.I.C. Birkbeck College, University of London

The Seventh International Conferencc on Co-ordination Chemistry, held at Stockholm and Uppsala during June 1962, was attended by six hundred participants from more than thirty countries. About two hundred and fifty papers were presented, some thirty of which dealt wholly or partly with the chemistry of the platinum metals.

While many of these papers describe work that has at present no obvious application, some of the complexes described have potentialities as homogeneous catalysts. There is a rapidly growing interest in the co-ordination com- pounds formed from platinum and palladium complexes with olefinic or acetylenic ligands; the subsequent reactions of these complexes will undoubtedly assume importance in syn- thetic organic chemistry.

M. R. Truter, Leeds University, discussed the structure of the monomeric complex trimethyl (acetylacetonyl) z,z’-bipyridyl plat- inum and of the related dimeric complex Me,Pt.PrCOCHCOPr, both of which showed the interesting feature of some form of a co-ordination bond from the central carbon atom of the $-diketone to the platinum group metal.

A. J. Edwards, J. H. Holloway, R. D. Peacock and R. W. H. Small, of Birmingham University, showed that tetrameric units exist in the solid state of a number of transition metal penta- fluorides. The refinement of the ruthenium pentafluoride structure had not been completed, but it appears that the metal itself possesses a distorted octahedral co-ordination. Osmium pentafluoride was found to be the isostructural with the ruthenium compound.

C. Berecki-Biedermann, of the Royal Technical High School, Stockholm, mentioned experimental problems in the preparation of solutions of pure rhodium(II1) and palla- dium(I1) perchlorates.

R. G. Hayter, Mellon Institute, Pittsburgh, presented his findings on some palladium(II1) complexes. He reported a series of compounds [PdX(PR,)L], (X-Cl, Br, I, SCN; R=Et, Ph; L =R,PH or R,P), and produced evidence in favour of a phosphorus-bridged structure.

R,

Measurements of a number of physical properties including infra-red spectra, mole- cular weight, d o u r and melting points were presented. These compounds were non- electrolytes and were shown to be dimeric in a number of solvents. A halogen-bridged struc- ture is discarded in favour of a phosphorus- bridged one, in view of the nature of the reaction products with reagents such as mines or thiocyanate ion.

Preliminary X-ray data suggested that the tram structure indicated in the diagram is correct. A number of related ionic compounds were also reported.

G. B. KaufTman, J. H. Tsai, R. M. Kailo, R. C. Fay and C. K. Jargensen, of Fresno State College, University of Illinois and Cyanamid Research Institute, Geneva, investi- gated the iridium complexes of composition [Ir(Et,S),Cl,]. They suggested that the yellow

Platinum Metals Rev., 1963, 7 , (11, 12-14 12

L

x

R, P .

P’ R-2

non-electrolytic isomer possesses the cis structure and that the red isomer was a I:I electrolyte and could be formulated as an e!ectrolytic polymerisation isomer of the yellow form. The latter formed in benzene under the influence of ultra-violet light a brownish- o r a n g e c o m p o u n d f o r m u l a t e d a s

Ally1 alcohol, under conditions of homo- geneous catalysis by means of Pt(I1) ions and acid, was shown by J. Milgrom and W. H. Urry, American Oil Co., Whitney, Indiana, and University of Chicago, to give in suitable circumstances either diallyl ether or a mixture of this with allyl alkyl ether. The overall process can be written as CH, = CHCH,OH + =CHCH,0R+H20 (R-saturated alkyl). If allyl alcohol was the only one present diallyl ether was the sole product, but when a saturated alcohol was added the proportion of the symmetrical to the unsymmetrical ether de- pended on the nature of the saturated alkyl group.

No saturated dialkyl ethers were detected, indicating the essential nature of the complex of allyl alcohol with the platinum metal ion. The mechanism of the above reactions was discussed in some detail.

A most interesting quadrico-ordinate iri- dium(1) complex, [IrCl(CO)P,] (P =Ph,P), was reported by L. Vaska, of the Mellon Institute, Pittsburgh. This can react rever- sibly under moderate conditions with molecular hydrogen and oxygen. The crystalline adducts were isolated and their properties investigated. The reactions of these adducts in the solid state, as well as in benzene solution, are summarised in the scheme below :

[Ir(Et,S) ZC131 2.

ROH+CH, = CHCH20CH,CH =CH + CH,

The two hydrogens were considered to occupy cis positions. The analogous reactions with oxygen were found to be slower, but the overall properties of the resultant oxygen adduct were rather similar. It was suggested that the compound was peroxidic in nature, with both oxygens attached to the same central atom.

Other reactions with hydrogen chloride, or chlorine, and the interconversion of some of these compounds were also reported.

R. J. Mawby and L. M. Venanzi, of the University of Oxford, described complexes of platinum and palladium with tetradentate arsenic ligands, QAS, and compared these with analogous tridentate ligands.

As- 5 QAS l3

A series of complexes such as [MX(QAS)]X (M=Pt, Pd; X=C1, Br, I, SCN) and RhX(QAS) (X=Cl, Br, I) were reported. The platinum(II), and probably also the pallad- ium(I1) and the rhodium(1) compounds possess a trigonal bipyramidal structure. On the other hand, ruthenium(I1) and osmium(I1) com- pounds form complexes of the type MX,(QAS), which are six-co-ordinate. These complexes possess very high thermal stability, as well as considerable resistance to oxidation, which is believed to have a mechanistic origin,

Complex hydrides of iridium and ruthenium were reported by B. L. Shaw and J. Chatt, Leeds University and I.C.I. Limited, Welwyn.

[IrC1(CO)P2]/C6H, -t X z T - [IrX2Cl(CO)P,]/CsH,

S C & 11 - C& + C6H6 11 - C&

[IrCI(CO)P,](cryst.) + X2* [IrX,Cl(CO)P,](cryst.)

When X, is the hydrogen molecule, the Hydride transfer reactions were described using monomeric non-electrolytic, diamagnetic ad- the iridium(II1) complex [IrCl,(PEt,Ph),] as duct was formulated as [Ir(III)H,Cl(CO)P,]. an example. This gave in alcohols, with one,

Platinum Metals Rev., 1963, 7 , (11, 13

two or three moles of potassium hydroxide, several crystalline stable hydrides [IrH,Cl,_, (PEt,Ph),], whose stereo-chemistry was dis- cussed.

A number of other similar iridium com- plexes were also reported. In the “reversed carbonylation” reaction, a ruthenium(I1) complex [Ru,C~, (PE~,P~)~]C~ gave under similar treatment with potassium hydroxide in ethanol, methane and the hydrocarbonyl complex [ RuHCI( CO)(PE t $’h)J.

A. D. Allen and C. D. Cook, of the University of Toronto, reported kinetic and equilibrium measurement for the displacement of some aryl acetylenes by others in platinum complexes [Pt(PPh,),L] (L =aryl acetylene).

F. Zingales, University of Milan, gave a paper on the reactions of palladium (11) chloride with phenyl-ethyl-acetylene (L) from which he obtained three products, 1,2,4- triphenyl-3,5,6-trimethyl-benzene, and two

complex palladium compounds. These were crystalline, diamagnetic, non-electrolytic solids of formulation PdC1L4 and Pd,Cl,L,. By reduction of either of the latter two compounds with sodium borohydride, a cyclooctatetraene derivative was obtained. The first of the two palladium complexes could be converted by thiocyanate or iodide ion to Pd(SCN)L4 and PdIL, respectively.

W. D. Jacobs, J. T. Pyle and R. B. Wilson, of the University of Georgia, described a large number of substituted dithio-oxamides, some symmetric, some unsymmetric, and investi- gated these as reagents for palladium, platinum, osmium, rhodium and ruthenium. The com- plexes are formed in very strong hydrochloric acid solutions. With some, maximum colour is developed almost instantaneously at room temperature, while for others considerable time i s required and heating is sometimes necessary.

Production of Hydrogen from Coal PALLADIUM CATALYSTS IN DEHYDROGENATION OF VITRAIN

The possibility of the economic production of molecular hydrogen by the catalytic dehydrogenation of coal is suggested by the results of work reported recently by R. Raymond, I. Wender and L. Reggel, of the Pittsburgh Coal Research Center, U.S. Bureau of Mines (Science, 1962, 137, (August 31st), 681-682). Surprisingly large yields of hydrogen were obtained in attempts to determine the hydroaromaticity of coal by the dehydrogenation of vitrains and other related materials with the use of polycyclic aromatic solvents and supported palladium catalysts.

In the laboratory-scale process, 0.5 g finely-divided coal (-ZOO mesh), the solvent and 0.55 g palladium-on-calcium carbonate catalyst were refluxed together for five hours in a helium atmosphere. Generally the major part of the gases, consisting of hydrogen with small amounts of carbon monoxide, carbon dioxide and methane, was evolved in the first hour. With phenanthridine as solvent and a 30 per cent palladium-on-calcium carbonate catalyst, 30 per cent of the hydrogen

contained in Pittsburgh vitrain was evolved. Other coals, under the same conditions, gave lower but appreciable yields of hydrogen, depending on their rank. About 50 per cent of the total hydrogen content of Pittsburgh vitrain was evolved when 2-azafluoranthene was used as solvent, but it is thought that some of this hydrogen was due to side re- actions.

Yields of about 30 per cent of the total hy- drogen in Pittsburgh vitrain were also ob- tained when other platinum metal catalysts were used with phenanthridine as solvent. Such catalysts included I and 5 per cent palladium-on-calcium carbonate, 5 per cent palladium-on-alumina, 5 per cent ruthenium- on-alumina, and 5 per cent rhodium-on- alumina. A commercial chromia-on-alumina catalyst was totally ineffective in these conditions.

This catalytic dehydrogenation process, demonstrated so far only on a small scale, has indicated a possible new use for certain coals as a source of hydrogen gas.

B.M.G.

Platinum Metals Rev., 1963, 7 , (11, 14-14 14

Low Temperature Platinum Resistance Thermometry CONSIDERATIONS OF DESIGN AND CALIJ3RATION

By C. R. Barber, B . s ~ . Standards Division, National Physical Laboratory, Teddington

The platinum resistance thermometer has long been recognised as the most precise temperature measuring instrument for the temperature range from - 182.97"C, the boiling point of oxygen, up to 630.5OC, in which range it is the chosen interpolation instrument of the International Practical Scale of Temperature. In the last decade or so its range of usefulness as a precision instru- ment has been extended to both higher and lower temperatures by suitably modifying the design of the thermometer.

At low temperatures the resistance-temper- ature relationship of platinum is by no means ideal, €or in common with other metals there is a considerable departure from linearity and many calibration points are required to define the shape of the curve. Curves typical of platinum of very high purity given in Fig, I

show the relationship between the reduced resistance (RT/Rooc) and the temperature and also the variation of the temperature co- efficient of resistance for the temperature range from 10' to 90°K. We see that the resistance of the thermometer has fallen at 60°K to 0.1 of its value at o°C, to 0.01 at 26°K and to 0.001 at 12°K. The temperature coefficient of resistance, however, does not fall proportionally, and we find that we now have to measure the resistance of the thermometer to only I in 6,000 at 20°K to achieve a pre- cision of o.oo~OK instead of 4 in 1oe as at 0°C. The precise shape of the resistance- temperature curve is critically dependent on the purity of the platinum. Despite these limitations platinum still appears to be the best choice for the purpose, since it can be obtained in a very pure condition and much

Platinum Metals Rev., 1963, 7 , (11, 15-17 15

Fig. 2 A group of capsule-type platinum resistanre thermometers designed jor use at low temperatures. On the left, one of British manufacture; next, one developed at the National Physical Laboratory; in the centre, a thermometer made in the USSR; fourth from the left, one constructed at the Pennsylvania State University, and on

the extreme right one of American manufacture

experience has already been gained in the production of uniformly high-purity wire suitable for resistance thermometer con- struction.

The design of a resistance thermometer for low temperatures is governed by the following considerations. It is obviously an advantage to make the thermometer small but the limit is here set by the minimum diameter of wire that can be used without excessive self- heating by the measuring current. It is common practice for standard thermometers to use wire in the range from 0.07 to 0.1 mm in diameter. I t is necessary to suppress conduction of heat into the thermometer by way of leads and stem, otherwise the ther- mometer may not reach the temperature of the surroundings, for thermal capacities are small and thermal conductivities large at lower temperatures. The method of con- struction therefore permits total immersion and good thermal contact with the surround- ings. In some measurements the platinum

sheath of the thermometer is actually joined to the apparatus by a low-melting point solder. The leads of fine wire are brought to the same temperature as the thermometer before being joined to it.

A group of capsule-type platinum ther- mometers, as they are sometimes known, is shown in Fig. 2. The one on the extreme left of the group is of British manufacture and the one on the extreme right is manufactured in USA. They are contained in thin-walled platinum sheaths about 5 mm in diameter and 45 to 50 mm long, and are filled with a low pressure of helium. The thermometer in the centre of the group was made in the USSR; it has a glass sheath and the coil is mounted on a twisted glass strip.

A type which has recently been used successfully at the National Physical Lab- oratory is the second from the left in the photograph. The sheath is only 2.5 mm in diameter and 70 mm long. The remaining thermometer is somewhat larger than the

Platinum Metals Rev., 1963, 7 , (11, 16

others and was constructed at the Pennsyl- vania State University.

Properly constructed platinum thermom- eters are extremely stable when cycled between room temperature and the lowest temperatures, the Root values remaining constant to within the equivalent of o.oo~"C for long periods. In fact any changes that take place are more likely to be due to mechanical rather than to thermal shocks. We can probably say that from the point of view of the physical dimensions, robustness and stability, the capsule-type platinum resistance thermometer is ideally suited to low tempera- ture measurement but the greatest difficulty in its use is to provide it with an accurate calibration.

At certain of the national standardising laboratories, namely, the National Physical Laboratory in this country, the National Bureau of Standards in the USA and the Physico-technical Radio-technical Measure- ments Institute in the USSR, low tempera- ture scales have been established over the range from 10' to 9ocK and these are recorded in terms of groups of platinum resistance thermometers of the types above- mentioned. It is possible from these to derive accurate calibrations by comparison at many temperatures over the range. I t would be very advantageous, however, to be able to define the practical scale of tempera- ture in terms of the platinum thermometer using only a few fixed points of calibration, just as we do already in the regions defined by the International Practical Scale of Tempera- ture.

There is no simple function relating resistance and temperature in the low temperature range and the only way of dealing with the problem is to use a standard table of resistance (or some function of resistance) and temperature, based on a typical thermometer or group of ther- mometers, and to derive the calibration of a particular thermometer by difference from this table using a few calibration points. A method suggested by the application of

Matthiessen's rule over the range from 20°

to 90°K is to use a standard table of Z RT - RH, Ro, - RH, functions, where Z = and &, RH,

and Rot are the resistances of the thermometer at temperature T and at the boiling points of hydrogen and oxygen respectively. By limiting the thermometers to those having a-coefficients greater than 3.92 x 10-' it is probable that such a table would give a calibration accurate in all cases to 50.02OK and it would only be necessary to calibrate the thermometer at the boiling points of hydrogen and oxygen. To obtain calibrations with smaller errors of interpolation it is clear that more calibration points must be used, and suggestions have been made for using quadratic and cubic equations for the departures from the 2 function table, using one and two additional fixed points.

A method recently considered by the author which appears to have good possi- bilities-because it is generally simpler than others and moreover covers a wider range-is as follows. The particular thermometer is calibrated at the triple point of equilibrium hydrogen (13.82"K), the boiling point of equilibrium hydrogen (20.27"K), the triple point of nitrogen (63.15"K) and the boiling point of oxygen (90.18"K). A curve of difference from a standard table of reduced

resistance isc) and temperature is then

plotted. With thermometers having ci-co- efficients greater than 3.925 x I O - ~ it is found that the calibration is given to within

o.oo5"K over the whole range 14" to 90°K. The particular calibration points are chosen because they are comparatively simple to realise.

The capsule-type platinum resistance ther- mometer is thus capable of giving very high accuracy of temperature measurement down to 14°K and may well eventually be the means of defining an extension of the International Practical Scale of Temperature. The problem is under consideration by the International Committee of Weights and Measures through its Advisory Committee on Thermometry.

Platinum Metals Rev., 1963, 7 , (11, 17

The Platinum Metals as Selective Hydrogenation Catalysts A BASIC APPROACH

By Peter B. Wells, B.s~., PbD. Department of Chemistry, University of Hull

A t the present time the consumption of catalytic materials by industry i s in- creasing rapidly, and the demand i s growing f o r catalysts that are able to promote specijc or selective reactions. In practice, however, the formulation of a catalyst for a particular function i s frequently empirical, at least in part. W e are not yet in the position of being able to design a catalyst “on the drawing- board” for a specijc complex operation with any high degree of conjdence, although this i s a situation which we m a y reasonably hope to achieve at some time in the future.

Recent research at the University of Hull , most of which i s unpublished as yet , has indicated that a considerable rationalisation may soon be possible in the Jield of the metal-catalysed hydro- genation of multiply unsaturated hydro- carbons and the hydroisomerisation of olejns. I t i s the purpose of this paper to

present a preview of this work and to advance some of its tentative conclusions.

The Pattern of Selectivity All of the metals of Group VIII may be

used as catalysts for the hydrogenation of acetylenes and di-olefins, although the extent to which mono-olefin is produced as an initial product varies widely from metal to metal. Metals that produce high yields of mono-

olefin are referred to as highly selective, using the definition:

yield of mono-olefin yield ofmono-olefin + paraffin Selectivity =

Platinum Metals Rev., 1963, 7 , (11, 18-24 18

Results in the literature indicate, and our own work confirms and extends the generalisation, that the selectivity shown by a given metal is characteristic of that metal and is substantially independent of the physical form of the catalyst and of the multiply-unsaturated hydrocarbon that is undergoing hydrogen- ation. A selection of the available results for the noble Group VIII metals is shown in Table I .

Selectivity is found to decrease with increasing hydrogen pressure and decreasing temperature, and the selectivities quoted in the table must be examined with that in mind. It is apparent from the table that the metals may be placed in a sequence of decreasingly selective behaviour thus :

Pd > Rh > Pt > Ru > 0 s > Ir . . . . sequence (i)

It is interesting that this is exactly the series reported recently by Zajcew for the selectivity of these metals (except osmium, which was not studied) in the hydrogenation of tall-oil fatty acids to give selective formation of oleic acid (14).

So different are the conditions of experi- ment, the catalysts, and the molecular species involved, that a sequence such as this demands an explanation.

Unfortunately, the hydrogenation of an acetylene or a di-olefin is not a simple reaction.

Table I

Selectivities Shown by the Noble Metals of Group VIII

Metal

Ru Ru Ru

Rh Rh Rh Rh Rh

Pd Pd Pd Pd Pd Pd Pd Pd Pd Pd Pd Pd Pd

0 s 0 s 0 s

Ir Ir

It-

Ir

Pt Pt Pt Pt Pt Pt P t P t Pt

support

alumina a h mi na alumina

alumina alumina alumina pumice carbon

alumina pumice silica pumice alumina (wire) (film)

pumice alumina carbon carbon

-

- alumina alumina alumina

alumina pumice alumina alumina

alumina pumice alumina pumice alumina - carbon carbon -

Hydrocarbon

acetylene allene butadiene

acetylene allene butadiene acetylene pent-2-yne

acetylene acetylene acetylene allene butadiene bu tad ie ne butad iene butadiene

ProPYne bu t-2-yne pent-2-yne piperylene isoprene

acetylene allene butad iene

acetylene acetylene allene butadiene

acetylene acetylene allene allene butadiene butadiene piperylene pent-2-yne isoprene

Initial PH,/Phc

2.0 3. I 2.0

2.0 3.0 I .o I *

2.0 2.0 3.7 I 2.0 2.0 2.0 *

I .o 2. I * * 41

2.3 6.0 2.0

2.0 I I .8 3.0

2.0 I I .8

I 2.0 * * * *

Temoerature Selectivity '"C

I33 51 0

I32 61 56 85 18

22 36

181 I I6 21

I50 19

-I2 80 20 I8 18 ?

I53 I30 69

62 I75 28 24

97 I63 79 89

I08 -I2

18 18 ?

0.82 0.84 0.73

0.93 0.92 0.92 0.86 0.84

0.95 0.92 0.97 I .oo I .oo I .oo 0.99 0.94 0.97 I .oo 0.99 0.99 0.98

0.67 0.73 0.69

0.22 0.30 0.36 0.25

0.83 0.82 0.89 0.80 0.8 I 0.61 0.82 0.92 0.65

-I__

Reference

1 -2 i

182

1 1 1 3 4

1,5 6 7 8 1 9 9

10 8 II 4 4

12

1,2 1

1,2

1,5 3 1 1

1.5 13

1 8 1

10

4 4

12

* denotes liquid phase hydrogenation

Platinum Metals Rev., 1963, 7 , (11, 19

Let us consider the simplest case, the reaction of acetylene itself with hydrogen; the reaction may be written as follows :

GH, (gas phase) C d , (gas phase) CIH, (gas phase) I 4 c

An asterisk denotes an adsorption site on the

Variants on this mechanism may be written for other acetylenes and di-olefins. It has been well established (I , 5 ) that the paraffin formed in selective hydrogenation is produced during one residence of the hydrocarbon species on the surface, and not by the re- adsorption and reaction of olefin that has been returned to the gas phase. Therefore, to understand selectivity we must pay attention to steps 5, 6, 7 and 8 of the above scheme. Since these are also the steps which operate in ethylene hydrogenation, it is with olefin hydrogenation that we must first be concerned.

Factor One: Activity for Olefin Hydrogenation

Consider two extreme hypothetical cases. First, a catalyst which has no ability to promote the hydrogenation of ethylene would be perfectly selective for the hydrogenation of acetylene to ethylene. Secondly, a catalyst which is extremely active for ethylene hydro- genation would catalyse steps 6 and 8 at the expense of step 5, and the absolute value of the selectivity would then be governed by the amount of ethylene formed by step 3. Thus, the first important factor to assess is the

surface of the catalyst.

relative activities of these metals for ethylene hydrogenation.

Two determinations have been made of the relative activities of rhodium, palladium and platinum for ethylene hydrogenation, one by Beeck who used evaporated metal films (Is)

and the other by Schuit and van Reijen who used silica-supported metals (16). The work by Beeck has been discussed in this journal by Bond (17). In both reports rhodium was found to be more active than palladium, and pal- ladium more active than platinum. More- over, the activities of these metals vary linearly with the percentage d-character of the metallic bond (18). Results from the literature are shown in Table 11.

The metallic bonds in iridium, ruthenium and osmium have either the same or nearly the same d-character as those in rhodium, and it is to be expected, therefore, that their activities in olefin hydrogenation will be similar to that of rhodium. Unfortunately, the measurement for iridium by !jchuit and van Reijen does not support this, although there is fair agreement between the. values for rhodium and ruthenium. Our own qualitative comparison, based merely on measurements of reaction rates, have shown rhodium, ruthenium and iridium to have similar activity for ethylene hydrogenation, at least to within an order of magnitude. Another quantitative comparison of the activities of all of the noble Group VIII metals for this reaction, or indeed for the hydrogenation of any other olefin, would be very valuable in this connection.

Platinum Metals Rev., 1963, 7 , (11, 20

Table II Values of the log of the velocity constant for ethylene hydrogenation and the

percentage d-character of metal-metal bonds as calculated by Pauling

P t Pd Rh lr Ru 0 s

- - - Log 10 (Kc, Ha) (15) - 1.6 - 0.8 0.0

Log 10 (%Ha) (16) - 1.5 - 0.9 0.0 - 2.0 - 0.3 - d-character of metal 44 46 50 49 50 49

For the purpose of this discussion, the order of activity for ethylene hydrogenation will be based on the d-character of the metallic bond. Thus, relative activities may be placed in the following sequence:

Rh = Ru 2 Ir = 0 s > Pd > Pt

This sequence must now be considered in connection with the reaction scheme. It has been shown that the selectivity will be higher the lower the activity for ethylene hydrogen- ation; thus, if this is the only factor operating, the order of selectivity should be the reverse of sequence (ii), that is:

Pt > Pd ;, 0 s = Ir ;a Ru = Rh

. . . . sequence (ii)

, . , . sequence (iii)

However, this bears only a little resemblance to sequence (i) and some other competing factor or factors must be present in the system.

Factor Two: The Reversal of Alkyl Formation

The competing factor is step 7. In this step the ethyl group loses a hydrogen atom to reform diadsorbed ethylene, which has a finite chance of undergoing desorption to give gas phase ethylene. The greater the importance of step 7 the higher will be the ethylene yield, and the higher the selectivity. It is necessary, therefore, to examine experi- mental evidence for the presence or absence of step 7, which will be referred to as the reversal of ethyl formation. The processes which give this information are olefin exchange and olefin isomerisation.

The interaction of an olefin with deuterium will yield deutero-paraffins and also, possibly, deutero-olefins and HD. Deutero-olefins may arise by the reversal of ethyl formation thus:

i D C,H,(g) + HZ$ - $HB ---i HZC - CH,D -

H+H,C - CHD - * C,H,D(g)

This series of steps is termed an olefin exchange reaction.

When an olefin contains four or more carbon atoms, the same series of steps, in

X X

Platinum Metals Rev., 1963, 7 , (11, 21

which a hydrogen atom is first added and then a different hydrogen atom removed, leads to cis-trans isomerisation or to double bond migration. Thus it is expected that a metal that gives olefin exchange would give iso- merisation with the same parent olefin, under the same conditions.

The isomerisation of each of the three normal butenes has been studied over all of the noble Group VIII metals (2, 19) and that of pent-I-ene and pent-2-ene over rhodium, palladium, iridium and platinum (4). The pattern of behaviour that has emerged is that the elements of the second transition metal series in Group VIII are good catalysts for isomerisation reactions, whereas the metals of the third series are poorer catalysts ; indeed, iridium and platinum have shown only the slightest isomerisation ability. Several workers in the United States have studied the iso- merisation and hydrogenation of di-substi- tuted cyclohexenes, exo-olefinic di-subs tituted cyclohexanes and certain octalins (20).

These experiments were carried out in the liquid phase, using palladium supported on charcoal and reduced platinum oxide catalysts. Almost without exception, isomerisation of the parent hydrocarbon was found to be an important reaction over palladium, but to be almost absent over platinum. These results agree with ours, and indicate that this may be a general feature of the catalytic properties of these metals.

The reactions of olefins with deuterium have only been carried out using rhodium, palladium, iridium and platinum, as yet (19). Considerable propylene and butene exchange was observed over the second row metals, but it occurred only to a negligible extent over the third row metals. This repeats the pattern established in isomerisation and lends support to the generally accepted mechanism for these reactions.

In order to discuss the relevance of alkyl reversal to our examination of selective behaviour it is necessary that some numerical comparison be made between the metals regarding their activities for isomerisation and

Table 111 Typical F Values given by the Noble

Metals of Group VIII

Metal Temp. ("C) F

Ruthenium 24 I .05

Rhodium 69 5.70

Palladium 37 I .90

Osmium 25 0.23

Iridium 0 0.0 I

Platinum I07 0.03

exchange. For the purposes of this paper it is sufficient to define two quantities, F and F'. Consider first the reaction of but-I-ene with hydrogen. The quantity F may be defined so that :

pressure of cis- f trans-but-2-ene produced F = pressure of n-butane produced

Secondly, consider the analogous quantity, F', that can be obtained from the reaction of propylene with deuterium.

pressure of exchanged propylenes produced pressure of deutero-propanes produced

F' =

Values of F and F' are given in tables I11 and IV.

Thus, we may write the sequence of activity for these metals as follows :

Rh > Pd > Ru > 0 s > Ir m Pt

These results may be interpreted in one of two ways. It may be that alkyl reversal is efficient over the second row metals but not over those of the third row. A second possi- bility is that the reversal of alkyl formation takes place over all of the metals, but that in the case of the third row metals the equili- brium is so much on the side of the alkyl radical that virtually no adsorbed olefin is present to desorb and appear in the gas phase. An analysis of results published in 1956 by Bond (zI), using an electronic computer, has shown that, for the reaction of ethylene with

. . . . sequence (iv)

Platinum Metals Rev., 1963, 7 , (11, 22

Typical F' Values ghen by some Noble Metals of Group VIII

Metal Temp. ("C) F'

Rhodium

Iridium

Platinum

deuterium over platinum, the second of the two possibilities given above is the true one. A study of the ethylene-deuterium reaction over the other metals is now in progress in order to provide comparable data. If there- fore we define the usual equilibrium constant K, such that :

then the variation of K among the metals is the reverse of that given in sequence (iv):

. . . . sequence (v) Pt x Ir > 0 s > Ru > Pd > Rh

A Synthesis of the Factors It now remains to attempt a synthesis of the

€actors which govern sequences (ii) and (v). Osmium, iridium, ruthenium and rhodium are expected to possess similar activity for ethylene hydrogenation. Thus the selectivity in this quartet will be governed by and will be inversely proportional to K; that is, the selectivity will be expected to decrease in the sequence

Rh > Ru > 0 s > Ir . . . . sequence (vi)

That this is the observed order (see sequence (i)) is very encouraging. Platinum is less active for olefin hydrogenation than rhodium, but K for platinum is higher than that for rhodium. Here there are two opposing factors and the higher selectivities shown by rhodium

I .6

1.1

0.03

0.06

Palladium

must indicate that the latter is of the greater importance. Palladium exhibits a lower activity for ethylene hydrogenation than rhodium and a slightly lower value of K. Thus it is to be expected that the selectivity over palladium will be higher than that over rhodium, as is observed. This synthesis of the two factors, therefore, gives a sequence that is identical to that observed experi- mentally and it would appear that an under- standing of selective behaviour has been achieved.

Some Remaining Problems Several problems remain. Why are the

values of K higher for the third row metals than for the second row metals ? May not the ability of the metals to promote isomerisation be a function of temperature such that no truly fundamental difference in catalytic behaviour exists ?

Another difficulty may be introduced into discussions of olefin isomerisation in the near future. In this paper the mechanism of isomerisation has been assumed to involve the alkyl radical. A report has recently been made that intermediates may be present in certain catalytic reactions which are x-bonded to the surface (22). Such intermediates could be formed by the loss of a hydrogen atom from, say, a but-2-ene to form a x-allylic species in which the x-electrons overlap with the d-orbitals of a metal atom or atoms, with the formation of a chemical bond. The addition of a hydrogen atom to this species could then give but-I-ene or but-z-ene, depending upon the point of addition, that is, isomerisation could thus be achieved. While it is not envisaged that this mechanism would be totally responsible for the observed isomerisa- tion, its possible existence as a contributary mechanism may well serve to cloud the picture. On the other hand, it is a new concept, and as such it offers a challenge to experimen- tation and hypothesis that must be welcomed.

A discussion has not been given here of the isomer distribution obtained in isomerisation reactions or of the principle underlying the

Platinum Metals Rev., 1963, 7 , (11, 23

stereo-determining step. I t is probable that the alkyl radicals will take up those confor- mations which are of lowest energy and thus an estimation of these conformations is all important. A study of the preferred confor- mations of the butyl group CH,CH&HCH, has led to an understanding of the isomerised butenes observed in our studies, while a similar approach, in principle, has been used by Siege1 to understand the paraffinic isomers that arise by the hydrogenation of di-sub- stituted cyclohexenes (20). This approach should allow an understanding of the initial isomer distribution that is obtained both in olefin isomerisation and in the hydrogenation of multiply unsaturated hydrocarbons such as butadiene which give a distribution of isomers.

Another problem concerns the importance of step 3 as an olefin-forming step (see the general mechanism). This step is not present in mechanisms for di-ene hydrogenation and yet such systems fit into the general classifi- cation along with the acetylenes. A complete predominance of step 3 over step 4 could lead to perfectly selective behaviour in which none of the factors discussed above is applicable. No such system has yet been identified.

In Conclusion The value of this discussion of selectivity

and isomerisation is twofold. It has allowed an understanding of experimental results, but also it should furnish a basis on which pre- dictions can be made for systems as yet unstudied. Factors such as the inhercnt activities of the metals, and the energetically favourable conformations of alkyl groups, are sufficiently fundamental, once established, for predictions to be made for a wide range of systems. At the present time these factors and their synthesis present a new approach and they may, as time passes, need revision or amplification. However, it is only by estab- lishing such fundamental factors and by testing their validity over as wide a range of experimental conditions as possible that a rationalisation of catalytic behaviour will eventually be achieved.

References Journal of Catalysis, 1962, I, 74

Platinum Metals Rev., 1962, 6, 12 J . Chem. SOC., 1952,2962 Unpublished work Proc. 2nd Int. Cong. Catalysis (Editions Technip,

Paris), 1961, 1177 J. Chem. Sac., 1945, 470 Rev. Inst. Franc. Petrole, 1959, 14, 214 Tram. Faraday SOC., 1952, 48, 651,658 Unpublished work J . Amm. Chem. SOC., 1947,69, 2046

I G. C. Bond, G. Webb, P. €3. Wells and

2 G. C. Bond and G. Webb . . . . 2 1. Sheridan and W. D. Reid . . . .

J. M. Winterbottom

k.-C. B o n d and L. A. McArd le 5 G. C. Bond, J. Newham and P. B. W e i s

6 J. Sheridan . . .. . . . . 7 A. Grignon-Dumoulin and C. Thonon . . 8 G. C. Bond and J. Sheridan . . . . g P. B. Wells and M. L. Whitehead . .

10 W. G. Young, R. L. Meier, J. Vinograd, H. Bollinger, L. Kaplan and S. L. L inden

11 W. M. Hamil ton and R. L. Burwe l l . .

13 I4

I2 B. A. Kazanskii, I. V. Gostunskaya and

J. Sheridan . . . . . . . . M. Zajcew . . . . .. ..

15 0. Beeck . . 16 G. C. A. Schuit and I,. L. vanRei ien. .

A. M. Granat

17 G. C. Bond . . . . . . . . 18 L. Pauling . . . . . . . . 19 G. C. Bond and J. M. Winterbottom . . 20 S. Siege1 and G. V. Smith . . . .

J-F. Sauvage, R. H. Baker and A. S. Hussey G. V. Smith and R. L. Burwel l . .

21 G. C. Bond 22 J. J. Rooney, F. 6. Gault'and C.'Kcemball

Proc. 2nd Int. Cong. Catalysis (Editions Technip,

Izvest. Akad. Nauk. S.S.S.R., Otdel. Khim. Nauk.. Paris), 1961, 987

1953,670 J . Chem. SOC., 1945,305 J . Amer. Oil Chemists' SOC., 1960, 37, 473 Disc. Faraday SOC., 1950, 8, 118 Advances in Catalysis, 1958, 10, 242 Platinum Metals Rev., 1957, I, 87 Proc. Roy. SOC., 1949, A196,343 Unpublished work J . Amer. Chm. Soc., 1960, 82, 6082, 6087 ibid, 1960,6090; idem. ibid, 1961, 83,3874

ibid, 1962, 84, 925 Trans. Faraday Soc., 1956, 52, 1235 Proc. Chem. Sac., 1960,407; idem, Journal of Catalysis,

196233,255

RHODIUM PLATING IN LIGHTHOUSE BEACONS

An unusual example of the corrosion resistance and reflectivity of electroplated rhodium is found in the AGA Sunvalve manufactured by the lighthouse engineers, Gas Accumulator Co., (U.K.) Limited. This ingenious device controls the operation of lighthouse beacons.

The valve consists of three copper rods, rhodium plated t o give a highly reflective surface, and a fourth copper rod w i th a mat black surface. A t dawn, sunlight falling on the mat black surface warms the copper rod and it expands, while at dusk, when the light intensity falls, the rod cools and contracts. The movement in the rod caused by longitudinal expansion works a valve cut-off mechanism, interrupting the flow of acetylene gas t o the beacon and extinguishing the light during daylight hours.

The high reflectivity of the rhodium plated rods ensures that their expansion is independent of the light intensity and they serve t o compen- sate fc r expansion o r contraction in the mat black rod due t o changes in ambient tempera- ture. In service, Sunvalves are exposed t o the corrosive attack of marine atmospheres in al l climates yet the rhodium plate retains i t s reflectivity for very long periods. The average service life of the valve is fifteen years but some have been in operation for over thirty.

Platinum Metals Rev., 1963, 7 , (11, 24-24 24

Some Properties of Ruthenium (m) and (IV) in Acid Solution A REVIEW OF RECENT RESEARCH

By G. A. Rechnitz and S. C. Goodkin Department of Chemistry, University of Pennsylvania

The solution chemistry of the lower oxidation states of ruthenium has attracted considerable attention in recent years from an applied viewpoint, but remains incompletely understood as far as basic considerations are concerned. Much of the contradictory in- formation in the literature is a result of tendencies to oversimplify the exceedingly complex processes which ruthenium com- pounds can undergo in aqueous media. It is becoming more and more apparent that such phenomena as oxidation-reduction, poly- rnerisation and cornplexation must be taken into account when dealing with ruthenium species in solution, even for seemingly simple overall processes.

The older literature on ruthenium com- pounds is summarised by Mellor (I) and also by Sidgewick (2). The most recent general review in this field seems to be the excellent comprehensive summary of DeFord (3), who has given a critical discussion of the literature up to 1948. Much important work has been reported since 1948, however, because of the interest in ruthenium as a long-lived product of fission wastes.

Reduction Potentials Despite repeated efforts to establish reliable

information on the oxidation-reduction potentials of the lower oxidation states of ruthenium, considerable confusion and am- biguity still exist in the literature on this aspect of ruthenium chemistry. According to DeFord (3), the lack of reproducible experi- mental data on oxidation-reduction potentials

is due to the lack of rapid, reversible reactions suitable for this type of measurement.

Wehner and Hindman (4) have placed limits on the formal potential for the Ru (1V)- Ru (111) couple in perchloric acid solution with values ranging from 0.55 to 1.17 V 0s. the normal hydrogen electrode (NHE) de- pending on whether zero-current potentials were approached by reduction or oxidation, respectively. It is likely, however, that equilibrium was not attained. More recently, Atwood ( 5 ) has given some potential values obtained in perchloric acid media by potentio- metric titration of Ru (IV) with vanadium (11) sulphate:

Ru (IV) 0.56 V m. NHE Ru(3.5)0.42 V _ _ _ ~ + -+

RU (111) -0.11 V RU (TI) -f -~

The potential of the Ru (1V)-Ru (111) couple has also been evaluated polarographic- ally as 0.65 V z's. NHE in IM perchloric acid (6).

Pshenitsyn and Ezeiskaya (7) studied the chloro-complexes of Ru (111) and Ru (IV) and reported the following potentials: K,RuCl,'e---i K,RuCl, 1.oVus.NHE

Ru,0CI,,-4+e-- > Ru(H,O)CI,= 0.67 V

Backhouse and D y e r (8) measured the Ru (1V)-Ru (111) potential in both hydro- chloric and hydrobromic acids, finding de- pression of potentials with increasing halide and hydrogen ion concentrations. Their potential values, extrapolated to zero acid con- centration, were 0.96 V in hydrochloric acid and 0.82 V in hydrobromic acid solutions

Platinum Metals Rev., 1963, 7 , (11, 25-29 25

(presumably VS. NHE). The potential of the Ru (111)-Ru (11) couple in hydrochloric acid medium is given by Backhouse as 0.084 V and stated as being independent of acid con- centration in the 1.5 to 6.8M range.

Polarograph y In 1945 Willis (9) found no published in-

formation on the polarography of ruthenium except for a paper dealing with the effect of ruthenium on catalytic hydrogen discharge waves (10). Willis was unable to obtain reduction waves for K,RuCl, or K,RuCl, in KCNS, KCN, NH,-NH,Cl or pyridine- HCl mixtures. Niedrach and Tevebaugh (6) investigated the polarography of Ru (IV) in perchloric acid media and reported three reduction waves at potentials of 0.57 to 0.65, 0.40 to 0.45, and -0.14 to -0.10 V 'us. NHE respectively. The first two waves were thought to be due to the reduction of two different hydrolysis species of Ru (IV); the third wave due to the reduction of Ru (111) to Ru (11). Chloride ion was found in the polarographic solutions after electrolysis, an indication that perchlorate might have been reduced by the electrolysis products. Susic (11) also found three polarographic waves in perchloric acid solutions of mixtures of Ru (IV) and Ru (111), but concluded that these were actually catalytic hydrogen waves because both wave heights and half-wave potentials were pH dependent.

Recently, Atwood (5) restudied the polaro- graphy of Ru (IV) in perchloric acid. His potential values of 0.59, 0.39, and 0.11 V DS. NHE compare well with those of Niedrach and Tevebaugh (6). The polarographic waves were found to be pH dependent and rate con- trolled. The author proposes an intermediate average oxidation state of 3.5 to explain his polarographic and potentiometric data. Gortsema (12) showed that Ru (IV) in perchloric acid solution can exist as a RuO-- monomer or as polymers of the type [RuO,(OH,),],RuO++. Atwood (5) used this information to propose half reactions for three observed reduction steps:

[RUO,(OH,),]~RUO+++ 2H++ e- + [RuO,(OH& Ruta+H,O

[RUO,(OH,),]~RU+~+ zHf+ e- --+ [RuO(OH,),]Rut4+ H,O

[RuO(OH,),],RU+~+ 2H,O+ 2e- [(H,0)2Ru-O-Ru(0H,)Jx+'

Polarographic studies of ruthenium in hydrochloric acid using a rotating platinum electrode have been carried out by Turk (13) who found variations in half-wave potentials from 0.55 to 0.48 V vs. NHE in 0.03 to 2.0 M acid. A similar study by Simpson (14) yielded only an ill-defined wave. Investigations of the polarographic behaviour of several ruthen- ium complexes containing chloride were reported by Pshenitsyn (7). This author pre- pared the compound K,Ru (OH) C1, which was irreversibly reduced to RuC1, (H,O)= at a stationary platinum electrode with a half- wave potential of about 0.66 V vs. N H E in a 2 M HCl -IM NaCl electrolyte. The fact that the limiting current obtained equalled only one-half of the expected current for a one electron process suggests that K,Ru (OH) C1, exists in solution as a binuclear complex of the type RU,OC~,,,-~.

Spectra and Solution Chemistry Ruthenium (IV) chloro-complexes have

been studied by Wehner and Hindman (16) who gave spectra for Ru (IV) in 10 M HCI with maxima at 460,380 and 360 mp. Mixed aquo, hydroxy and chloro-complexes of Ru (IV) in perchloric acid were also studied by these workers. Ru (IV) was prepared in perchloric acid by reduction of RuO,, at a potential of 1.10 V 0s. NHE on a platinum electrode. Solutions of Ru (IV) in I M HClO, showed no spectral evidence of de- composition after 120 days, but solutions in 6 and 9 M acid were found to be unstable. Gortsema and Cobble (17), however, suggest that Wehner and Hindman were not working with monomenic Ru (IV) species. Atwood (5) transformed polymeric Ru (IV) to mono- meric species by ion exchange techniques and

Platinum Metals Rev., 1963, 7 , (11, 26

attributed an absorption band at 300 mp to the species RuO 1-4 in perchloric acid solution. Spectra of Ru (IV) in 2 M HCl and 2M H,S04 solutions with maxima at 240, 380, 460, and 690 mp and 238, 300, 420 to 480, and 610 to 640 mp, respectively, have been reported by workers at the Argonne National Laboratory (I 3, I 8).

Spectra of Ru (111) complexes in acid solution seem to depend on the source or method of preparation of Ru (111) as well as the nature and concentration of the solvent species. As a result, information con- cerning the nature and properties of Ru (111) in acid solution remains ambiguous and con- tradictory. Interpretation of available data is further complicated by possible polymer formation and oxidation-reduction processes. Jorgensen (19) produced Ru (111) by the oxidation of ruthenium metal to K,RuO,, reduction of this compound with ethanol to Ru(OH),, followed by further reduction with metallic silver in concentrated HC1. In 10 M HC1 maxima were found at 307, 313, 349, 388, and 521 mp, presumably due to RuC1,r. A species presumed to be RuBr,= was pre- pared in an analogous manner in 6 M HBr and yielded absorption maxima at 400, 485, and 655 mp.

Fine (20) investigated the chloro-complexes of Ru (111) by ion-exchange methods and found predominantly cationic and neutral species in solutions less than 2 M in HC1 and anionic complexes in more acid solutions. The author succeeded in determining equilib- rium constants for the various mononuclear forms of Ru (111) present in hydrochloric acid solution. Evidence was presented for the existence of highly charged polymeric species which could not be eluted from the ion exchange resin.

A number of investigators have claimed that commercially available Ru (111) com- pounds contain Ru (IV). Halpern (21)

reported that (NH,),RuCl,H,O, RuC1,-H,O and (NH,),RuCI, all show the same absorp- tion spectra when dissolved in hydrochloric acid. The resulting spectra correspond to

those obtained by Wehner and Hindman (4) for Ru (IV). The presence of Ru (IV) in these solutions was confirmed by titration with stannous chloride and measurement of hydrogen up-take. The spectra of the result- ing reduced solutions agreed with those reported by Jorgensen (19) for Ru (111). Sawyer (22) reported that RuC1, contains 85 per cent Ru (IV) as determined by the method of Crowell and Yost (23).

Connick and Fine (24) investigated the species Rut3, RuC1+2, RuCl,+ by ion exchange techniques and determined the charge per metal ion and charge per species for these three ions. These authors report absorption maxima for RuCl and RuCl,’ between 300 and 320 mp and Rut3 at 220 mp. Two neutral species of the type RuCl,, having absorption maxima at 320 and zgo (360) mp respectively, were also identified. Rehn and Wilson (25) carried out a similar study using trifluoroacetic acid as a non-complexing medium. While these authors agree with Connick and Fine in assigning formulae to the species present, the actual observed spectra show considerable differences.

Analysis Most of the volumetric methods for the

determination of ruthenium depend on the reduction of Ru (IV) to Ru (111). Oxidation- reduction titrations invohing ruthenium are complicated by uncertainties in the oxidation state of the final titration product. Reliable potential data are needed to clarify this prob- lem. Ru (IV) may be titrated with stannous chloride (26) using visual or potentiometric end point detection. Alternately, an excess of iodide may be added and the liberated iodine titrated with thiosulphate. Ru (IV) can also be titrated potentiometrically under nitrogen with TiC1, in dilute hydrochloric acid (27). The titration curve is reported to pass through an intermediate break requiring 0.5 equiva- lents of TiCl,. A review of recent advances in oxidation-reduction methods for the deter- mination of ruthenium has been given by MacDonald (41).

Platinum Metals Rev., 1963, 7 , (11, 27

Many spectrophoto- metric methods for the determination of ruthenium with both inorganic and organic complexing agents have been reported. Most of these methods require a preliminary separation of ruthen- ium as RuO,, a toxic material. Careful con- trol of solution pH is usually required, and traces of ni t ra te or

Spectrophotometric Methods for Determination of Ruthenium

Reagent I , 4-diphenylthio-

Anthranilic acid . . Acetyl acetone . .

semicarbazide

2-nitroso- I -naphthol p-nitrosodimethyl-

Dithiooxamide . , I, 10-phenanthroline

analine

chloride may prevent colour formation. Sandell (28) has evaluated several of the older methods.

Ruthenium can be determined spectro- photometrically using the yellow-green colour of KRuO,, formed by distillation of RuO, into KOH (4, 28, 29). The orange-red colour of K,RuO, has also been used as the basis for a colorimetric method (30, 31). The colour is measured at 465 mp and is reported to be stable for thirty minutes in 2 M NaOH.

Several investigators have used thiocyanate as a colorimetric reagent for ruthenium. In the method of Below (32), ruthenium is

Remarks Reference

CHC1, extraction-colour

pH 5.2 to 6.0, green colour CHCl, extraction - pH

time dependent . . m . 34 35

dependent; 505 mp . . 36

HAc-NaAc buffer; 610 mp 38 HC1-SO, solvent . . * * 37

HC1-alcohol; 650 mp . . 39 NH,OH solution; 448 mw . . 40

oxidised to RuO, with Ago, absorbed in CCl, containing SCN; and determined as Ru(SCN)++, a red complex. Forsythe (33) investigated the nature of the complexes formed in this reaction and found evidence of anionic species. Ru (11) may also be present under these conditions.

Thiourea gives a blue colour with ruthenium compounds in hydrochloric acid, forming the basis of an analytical method studied by DeFord (3). Several other common spectro- photometric methods for the determination of ruthenium are outlined in the table.

References I J. W. Mellor, A Comprehensive Treatise on 10 P. Hcrasymenke and I. Slendyk, Cull. Czech.

Inorganic and Theoretical Chemistry, Chem. Comm., 1936,5,479-496 hndon : LoWmms, 11 M. V. Susic, Bull. Inst. Nuclear Sci., 1958, 8,

Their Compounds, Oxford: Clarendon IZ F. Gortsema, Ph.D. Thesis, Purdue Univer- Press, 1950 sity, January 1960

3 D. D. DeFord, Ph.D. Thesis, University of 13 E. Turk, Argonne National Laboratory Kansas, May 1948

4 P. Wehner and J. C. Hindman,J. Amer. Chem. 14 R. B. Simpson, R. L. Evans, H. A. Saroff, SOC., 1950, 72, 3911

5 D. K. Atwood, Ph.D. Thesis, Purdue Uni- 15 N. K. Pshenitsyn, B u r . Anal. Chem., 1961, versity, August I 960

6 L. W. Niedrach andA. D. Tevebaugh, J. Amer. 16 P. Wehner and J. C. Hindman, J. Phys. Chem.,

7 N. K. Pshenitsyn and N. A. Ezeiskaya, Russ.J. 17 F. l'. Gortsema and J. W. Cobble, J. Amer. Znor. Chem. (in trans.), March 1961, 3, 510

S J. R. Backhouse and F. P. Dwyer, J . Proc. 18 ArgomeNational Lab. Report No. 372, P. 49 Royal SOC., N. S. Wales, 1949,83, 134-137. 19 C. K. Jorgensen, Actu Chem. Scand., 1956,10,

9 J. B. Willis,J. Amer. Chem. Soc., 1945, 67, 20 D. A. Fine, Ph.D. Thesis, University of

Zi co, 1937 2 N. V. Sidgewick, The Chemical Elements and 53-57

Report No. 4292 (March 1949)

J. Amer. Chem. SOL., 1955, 77, 1438

(z), 196-200

Chem. Soc., I951,73,2835 1952,56, 10

Chem. Soc., 1961, 83,4317

C. A . 45:8389 518-534

547-550 California (Berkeley), February 1960

Platinum Metals Rev., 1963, 7 , (11, 28

21 J. F. Harrod, S. Ciccone and J. Halpern, Can.

22 D. Sawyer, R. George, J. Bagger, J . Amer.

23 W. R. Crowell, D. M. Yost, J. Amer. Chem.

24 R. E. Connick, D. A. Fine,?. Amer. Chem. SOC.,

25 I. M. Rehn, A. S. Wilson, private communica-

26 J. L. Howe,J. Amer. Chem. Sac., 1927,49,2393 27 N. K. Pshenitsyn, Iv. Sektora Platiny ION.

Kh. Akad. Nauk U.S.S.R., 1955 (33), 20-30 [ A n d Abstr., 1957, 22141

28 E. B. Sandell, Determination of Traces of Metals, 3rd ed., New York, Interscience, I959

29 F. E. Beamish, W. A. E. McBryde, Anal. Chim. Acta., 1958, 18, 551

30 E. D. Marshall, R. R. Rickard, Anal. Chem.,

J . Chem., 1961,39, I372

Chem. SOC., 1959, 81,5893

SOC., 1928, 50, 374

1961,839 3414

tion

1950>22,79

31 R. Larsen, L. Ross, Anal. Chem., 1959, 31,

32 W. L. Below, G. R. Wilson, L. T. Corbin,

33 J. H. W. Forsythe, R. J. Magee and C. L.

34 T. Hara, E. B. Sandell, Anal. Chim. Acta.,

35 A. K. Majumdar, J. G. Sen Gupta, Z. Anal.

36 A. Brandostetr, COIL Czech. Chem. Comm.,

37 D. L. Manning, 0. Menis, Anal.Chm.,1962,

38 J. E. Curran, A. Fischel, Anal. Chem., 1952,

39 G. H. Ayers, F. Young, Anal. Chem., 1950,

40 C. V. Banks, J. M. O’Laughlin, Anal. Chem.,

41 A.M. G. MacDonald, Ind. Chem., 1959,35,293

1768

Anal. Chem., 1961, 33, 886

Wilson, Talanta, 1960, 3, 324

1960, 23,65

Chem., 1961, 178,401

1961,26, 392

34, 94

24, 1980

22, 1281

1957>29, 1412

Magnetic Transformations in Iron-Rhodium Allovs ANOMALOUS CHANGES AT MODERATE

J

TEMPERATURES

The saturation intensity of ferromagnetic materials generally decreases slightly with heating until at temperatures approaching the Curie point a rapid decline occurs. A notable exception to this rule is afforded by alloys containing approximately equal numbers of iron and rhodium atoms which are non- magnetic at room temperature and become suddenly ferromagnetic when heated to 60’C. Above this temperature they respond as normal ferromagnetic materials, the Curie point being at 400°C. Hocart and Fallot (I, 2) who first reported this behaviour attributed it to a sudden ordering reaction. Recent X-ray (3) and neutron-diffraction (4) measurements have shown that the magnetic transformation is due to a rapid yet uniform expansion of the CsCl type ordered structure which exists above and below critical temperature. The state below this temperature is antiferro- magnetic with the magnetic unit cell doubled in all directions ( 5 , 6). I n the ferromagnetic region above the characteristic temperature the magnetic and crystallographic unit cells coincide.

A field of 5 Koe is sufficient to saturate the 52 atomic per cent rhodium alloy which has a peak magnetic intensity at 77’C of 115 emu’gm. (7). Rhodium has in this region an appreciable magnetic moment, and it is prob- able that the magnetic moment of the iron atoms in this alloy is higher than in alpha iron (6). The temperature hysteresis asso-

ciated with the magnetic and electrical resist- ance changes of this alloy has been interpreted as evidence of a first order phase change (7). Complete confirmation of this hypothesis would require the demonstration of a crys- tallographically discrete phase.

The remarkable magnetic characteristics of the alloy are likely to be of considerable utility. Thermal switching is an obvious application, although more sophisticated devices will undoutedly suggest themselves to the development engineer.

A. S. D.

References I M. Fallot, Ann. Phys., 1938, 10, 291 z M. Fallot and R. Hocart, Rm. Sci., 1939, 77,

3 F. de Bergevin and L. Muldawer, Compt. rend.,

4 F. de Bergevin and L. Muldawer, Bull. Amer. Phys. SOC., 1961, 6, 159

5 E. F. Bertaut, A. Delapalme, F. Forrat, G. Roult, F. de Bergevin and R. Pauthenet, Proceedings of International Conference on Magnetism and Crystallography, 1961, vol. 111. ( J . Phys. SOC. Japan, 1962, 17, Supple- ment B.111)

6 E. F. Bertaut, A. Delapalme, F. Forrat and G. Roult, F. de Bergevin and R. Pauthenet, J. Applied Physics, 1962, Supplement to Vol.

7 J. S. Kouvel and C. C . Hartelius, J. Applied Physics, 1962, Supplement to Vol. 33, No. 3, 1343-1344

498

1961,252, 1347

33, NO. 3, 1123-1124

Platinum Metals Rev., 1963, 7 , (11, 29-29 29

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Constitution Diagrams of Alloys of Rhenium with Platinum Group Metals (Rhodium, Palladium, Iridium) M. A. TYLKINA, I. A. TSYGANOVA and E. M. SAVITSKII, Zhur. Neorg. Khim., 1962, 7, (8), 1917-1927 Constitution diagrams of the three systems were constructed after microscopicexamination, thermal and X-ray analysis, and hardness measurements of a series of Rh-Re, Pd-Re and Ir-Re alloys. Diagrams of the peritectic type with two limited solid solutions were found in each case. There is no evidence of the formation of chemical com- pounds. The bigger the differences of the melting temperatures of Re and the Pt group metal, the lower is the temperature of the peritectic reaction and the greater the extent of the two-phase region. The physico-chemical properties of Re and the Pt metals and the relationships between them are discussed.

The Constitution Diagram of the Magnesium- Palladium System E. M. SAVITSKII, v. F. TEREKHOVA and N. A. BIRUN, Zhzsr. Nemg. Khim., 1962,7, ( 10), 2367-2373 Various methods of physico-chemical analysis were used to construct the diagram. The system is characterised by the formation of the chemical compounds Mg,Pd, MgJ'd, Mg,Pd, MgaPd, and MgPd. Mg,Pd, Mg,Pd and MgJ'd are formed by peritectic reactions at 700* xo0C, 790& 10°C and 1130f IOT, respectively. Mg,Pda melts con- gruently at 1350 f 10°C and MgPd is formed from Mg,Pd and Mg,Pd, at 7003 10°C. Eutectic reac- tions occur at 5401 10°C and -27 wt.?; Pd and at 1280t 10°C and -88-89 wt.76 Pd.

The Constitution Diagram of the System Molybdenum-Osmium A. TAYLOR, N. J. DOYLE and B. 5. KAGLE, 7. Less- Common Metals, 1962, 4, ( s ) , 436-450 X-ray diffraction and micrographic methods were used to examine alloys in the whole range of the system and the constitution diagram was con- structed. The four single-phase fields observed are: (i) the b.c.c. u-Mo primary solid solution, (ii) the cubic intermediate @-phase based on Mo,Os, (iii) the tetragonal 0-phase centred round Mo,Os, and (iv) the terminal solid solution based on 0-0s. Lattice parameters were determined for u, F, o and 0-phase alloys. The Mo-0s and W-0s systems are compared with alloys of Mo and W with other Pt metals.

On the Equilibrium Diagram of the System Bismuth-Rhodium R. G. ROSS and w. HUME-ROTHERY, J. Less-Common Metals, 1962~4, (51, 454-459 The equilibrium diagram was constructed by thermal analysis and X-ray examination of alloys with up to 50 at.0;" Rh. Only one modification of the compound Bi,Rh was found, but two modi- fications of BizRh, with a transition temperature of 425"C, were identified. There was no evidence for the existence of Bi,Rh. The NiAs-type struc- ture of BiRh was confirmed. Lattice spacings of BiRh were measured up to 977-C.

Certain Alloys of Ruthenium with Molyb- denum G. A. GEACH, A. G. KNAPTON and A. A. WOOLE, Powder Metallurgy in the Nuclear Age, Plansee Proc., 1961, 750-758 Alloys over the full range of compositions were prepared by argon-arc melting and their cold working characteristics were studied. Maximum ductility was found with alloys containing 40-50 at.Y, Mo. The work-hardening, hot hardness and corrosion resistance of the 45 at.?;; Mo-Ru solid solution alloy were studied. The alloy may be cold-rolled or swaged, has good mechanical proper- ties up to at least IOOO~C, and is corroded only by alkaline oxidising solutions. A method for analysis of the alloy is given.

The Miscibility Gap in the System Silver- Iron-Palladium at lOOO", 1100", and 1200°C A. MUAN, Trans. Met. SOC. A.I.M.E., 1962, 224, (s), 1080-1081 Phase relations in three isothermal sections ( IOOO", IIOO", IZOO"~) were determined by studying 40 alloys within the Ag-Fe-Pd system by metallo- graphic and X-ray methods. The miscibility gap originating along the Ag-Fe join of the isothermal sections decreases with increasing Pd content, but extends as far as "75 wt.% Pd. All three sections show an area in which an alloy a of low Fe content is in equilibrium with an alloy p of low Ag content.

Tensile Properties of Refractory Metals at High Temperatures c. A. BROOKES and B. HARRIS, Powder Metallurgy in the Nuclear Age, Plansee Proc., 1961, 712122 Mechanical properties of Nb, Ta, W, Mo and Ir were measured in the range o-zzoo3C and their fracture mechanisms were studied. The variation of ultimate tensile strength, yield stress and per- centage elongation as a function of temperature

Platinum Metals Rev., 1963, 7 , (11, 30-38 30

for all the metals is shown in a series of graphs. Above IOOO~C, Ir is stronger than Ta, Mo and Nb. Of the five metals, Ir is the most resistant to contamination in atmospheres containing oxygen and C.

Elevated-Temperature Properties of Rhodium, Iridium, and Ruthenium

print 65, 1962, 11 pp. (Paper presented at the 65th Annual Meeting of the A.S.T.M., June, 1962) The tensile and short-time stress-rupture proper- ties of Rh, Ir, and Ru were studied in vacuum in the temperature range 75O0-I50Ooc. Rh, I r and Ru have high strengths at high temperatures, I r and Ru comparing favourably with W up to 15oo'C. The tensile properties of Rh and Ru are affected by the testing atmosphere at 750" and IOOO'C, respectively, and have higher strengths in vacuum than in air. The properties of Ir are unaffected by the atmosphere. I r and Ru show intergranular failure over the testing temperature range.

The Mechanism of the Solubility of the Phases in the System Gold-Platinum v. v. SANADZE, Proc. Acad. Sci. U.S.S.R., Chem. Section, 1961, 140, (I-6), 889-892 (Transl. of Doklady Akad. Nauk S.S.S.R., 1961, 140, (I), 133-1 36) Alloys containing 10 and 25 at.?/, Pt were studied by the method of successive quenchings. The mechanism of the solubility of the a,-solid solution, based on Pt, and the =,-solid solution, based on Au, is discussed in detail. It is concluded that Pt,Au, PtAu and Au,Pt are ordered states, not phases, arising on the course of the mutual solubility of the phases.

An Investigation of the Supercooling of Molten Metals J. FEHLING and E. SCHEIL, Z. Metallkunde, 1962, 53, (91, 593-600 The supercooling of molten Pd, Fe, Co, Ni, Cu, Au, Ag, Ge, and Ni-Pd, Ni-Cu and Ni-Au alloys was studied. The structures of the supercooled metals were investigated and the influence on their formation of low frequency vibrations and variations in the cooling rate was determined.

The "Invar" Properties of Iron-Palladium Alloys K. JESSEN, Ann. Physik, 1962, 9, (5161, 313-315 Expansion measurements were made on Pd-Fe alloys containing 28-33 at.% Pd. The tempera- ture range of lower thermal linear expansion, obtained by rapidly cooling the test specimens to 250"C, may be extended to 350°C by cold- working. Jnvar properties of the alloys are very unstable and disappear both as a result of heating and partially by cooling at low temperatures.

R. W. DOUGLASS and R. I. JAFFEE, A.S.T.M. Pre-

Magnetic Properties of a Chromium-Platinum Alloy with 30 Chromium A. J. P. MEYER and R. ASFELD, COmpt. rend., 1962, 254, (zs), 4266-4268 The alloy was obtained in the disordered state by quenching in H 2 0 from 1400°C and in the ordered state by annealing for 15 h at 950°C. A study was made, for both states, of the variation of magnetisation as a function of field, and of the paramagnetic behaviour below the ordering tem- peratures. The results are discussed briefly.

Electrical Resistivity and Thermoelectric Power of Palladium after Hydrogen Desorption

Phys. Rev., 1962, 127, (I), 179183 Resistance measurements were made between 4.2 and 300°K on Pd wires in the following conditions : unannealed, annealed, charged with hydrogen, and after hydrogen desorption. Thermoelectric power measurements were made between 77 and 273°K on specimens of Pd wire in the as drawn and annealed conditions and after hydrogen desorp- tion. The desorbed samples showed an increase in the residual resistivity, a decrease in the value of dp/dT, and thermoelectric power values be- tween those of annealed and cold-worked Pd. Experimental results are explained in terms of an observed expanded lattice.

The Effect of Iridium on the Mechanical and Electrical Properties of Palladium A. A. RUDNITSKII and v. P. POLYAKOVA, Zhur. Neorg. Khim., 1962, 7, (10), 2361-2366 The properties of alloys with up to 30 wt."/, I r were studied. Results are given of various heat treatments on the hardness and strength of the alloys. All alloys with up to 25 wt.y(, I r are easily cold-worked after quenching from 1400- I S O O O C without intermediate annealing. Measure- ments of electrical resistivity and its temperature coefficient confirmed that the solubility of Ir decreases from 30 wt.7; above 1300°C to 10 wt.O,, and less below 700'C. Alloying with I r increases the electrical resistivity of Pd and reduces its temperature coefficient.

Self-diffusion in Platinum F. CATTANEO, E. GERMAGNOLI and F. GRASSO, Phil. Mag., 1962,7, (Ax.), 1373-1383 Self-diffusion coefficients in Pt were obtained in the range 12~0°-172~nc by measuring the decrease of activity at the surface of cylindrical specimens during diffusion.

The Effect of the State of the Surface on the Adsorption of Ions by Platinum N. A. BALASCHOVA, Electrochim. Acra, 1962, 7, (Sept.:Oct.), 559-565 Radioactive tracers were used to study the effect of thermal and mechanical pretreatment and of

R. J. SIMITH, A. I. SCHINLILER and E. W. KAMMER,

Platinum Metals Rev., 1963, 7 , (11, 31

oxidation of a Pt surface on its adsorption of ions and on the kinetics of adsorption. The mechanism of the effect is explained in terms of the change in area of the real adsorbing surface and the penetra- tion of ions into the Pt. It was found that oxygen adsorption is retarded by pre-adsorbed anions and vice versa.

A Study of the Mechanism of Carbon Monoxide Adsorption on Platinum by a New Electrochemical Procedure s. GILMAN, Abstracts of Papers, 20T, Div. of Phys. Chem., r42nd Meeting, A.C.S., Atlantic City, N.J., Sept. 1962 The adsorption of CO from solution was studied as a function of the extent of surface coverage. From the information obtained, a lower limit was set on the rate of fast chemisorption of CO from solution and the nature of the CO-Pt bond was determined.

The Preparation and Properties of a Hydrous Ruthenium Oxide c. J. KEATTCH and J. P. RED FERN,^. Less-Common Metals, 1962, 4, (51, 460-465 A method of preparing a compound with the empirical formula R u 0 2 H z 0 is described. Results of a thermogravimetric study of the compound are given. Both the hydrous and the anhydrous material act as catalysts in the decomposition of 300 vol. H,O,.

Xenon Hexafluoroplatinate (V) Xe+[PtF,]- N. BARTLETT, Prac. Chem. Soc., 1962, (Jun.), 218 The formation of XePtF,, an orange-yellow solid, is reported. This charge-transfer compound is stable at room temperatures.

The Molecular and Crystal Structure of OS,(CO),, E. R. COREY and L. F. DAHL, Inorg. Chem., 1962, I, (3), 521-526 The crystal and molecular structure of Os,(CO),,, determined by X-ray diffraction, is described in detail.

Hydrido- and Related Organo-complexes of Transition Metals

Recent developments in the study of the bonding of hydrogen to transition metals and of the proper- ties of hydrogen as an anionic ligand are described. Numerous complexes of the Pt metals are discussed.

J. CHATT, ProC. Chem. SOC., 1962, (Oct.), 318-326

Vaporisation of Ruthenium and Osmium M. B. PANISH and L. RE IF,^. Chem. Phys., 1962, 37, (I), 128-131 Vapour pressures were determined by the use of Knudsen effusion and Langmuir vaporisation techniques. The vapour pressure of Ru over the temperature range 2000°-25000K is given by the

equation log pmm=10.81-333480~T, and that of 0 s over the temperature range 2300"-2800~K by the equation log pmm= 10.85 -40950:T. Heats of vaporisation found by third-law analyses of data are: Ru,AHo,,,=~~4.gf 1.3 kcal/mole, and Os,AHo,,, = r87.4io.9 kcallmole. Estimated boiling points are: Ru, 4350"&1OO0K and OS, 5300'-k 100°K.

The System Iridium-Oxygen I. Measurements on the Volatile Oxide of Iridium E. n. P. CORDFUNKE and G. MEYER, Rec. Trav. Chim., 1962, 81, (6), 495-504 (In English) A transportation method was used to obtain partial pressure measurements of a volatile oxide of Ir. The dependence of the partial pressure of this oxide on the oxygen pressure was determined. Results indicate that the formula of the volatile oxide is I r08, The equilibria: 21r(,j+302Tf 21r03(g) and zIrO,(sl +02a I r0 , (g ) were meas- ured as a function of the temperature.

11. The Dissociation Pressure of IrO, Ibid., (8), 670-678 Results obtained in the determination of the dis- sociation pressure of IrO, are explained by the formation of the non-stoichiometric oxide Ir02-x, The composition of the IrO,-x phase in equilib- rium with Ir was determined as a function of the temperature. For the three-phase equilibrium IrO,--Ir-G, log poz (mm) = -1 1780/T + I 1.487. For stoichiometric IrO,,AH,,,.,,~K := -65.5 (*I.s) kcal/mole.

The Adsorption and Diffusion of Electrolytic Hydrogen in Palladium M. A. V. DEVANATHAN and Z. STACHURSKI, proc, Roy. SOL., Series A, 1962, 270, (1340)~ 90-102 An electrolytic technique for the measurement of the instantaneous rate of permeation of electro- lytic hydrogen through Pd membranes is de- scribed. It was found that the diffusion constant is independent of thickness in the range 0.0035 to 0.054 cm and the permeation is inversely pro- portional to thickness. For hydrogen-poor K-Pd the diffusion constant is 1.30&0.20 x lo-, cm2 sec - l at room temperature. Errors arising from classical time-lag methods are discussed.

A Study of the Kinetics of Heating Palladium- Hydrogen Alloys by the Pulse Heating Method v. M. KUL'GAVCHUK, Zhur. Fiz. Khim., 1962, 36, (8), 1713-1716 (English summary) Results are given of determinations of the energy consumption prior to melting, the resistance at the melting point and the jump in resistance on the pulse heating of pure Pd and Pd saturated with hydrogen (PdH,.,,). Heating was carried out with I sec electric current pulses at peak current densities of 2.4 X 10, Ajcm'. The melting point

Platinum Metals Rev., 1963, 7 , (11, 32

of PdH,.,, was calculated as 1123'C. The tem- perature coefficient of resistance of liquid Pd was estimated.

ELECTROCHEMISTRY Recent Studies of the Action of Inorganic Inhibitors

322t Recent work on the nature of the anodic process to be suppressed is discussed and the influence of adsorption and semiconducting surfaces on the kinetics of the dissolution reaction is shown. The action of corrosion inhibitors of the type X0,"- (x P, Cr, Mo, W, Tc, or 0 s ) is considered. Mechanisms involved in inhibitor action include oxidation-reduction processes, electrochemical polarisation, adsorption and ion exchange, and electrostatic polarisation. (41 references)

A Solid Electrolyte Fuel Cell J. WEISSBART and R. RUKA, .7. Electrochem. soc., 1962, 109, (8), 723-726 A galvanic cell with a solid (Zr02)o.8~(CaO),,.15 electrolyte and two porous Pt electrodes is described. The cell acts as a simple oxygen con- centration cell. Experimental data are given for the reaction of oxygen with hydrogen/H,O and CH,:H,O mixtures. Experimental and theoretical open-circuit voltages for the hydrogen-oxygen reaction are in close agreement, and current- voltage curves show that the cell output is limited essentially by the resistance of the electrolyte. It is possible that such cells may be used as fuel cells with hydrocarbons as fuel and oxygen or air as oxidant.

G. H. CARTLEDGE, Corrosion, 1962, 18, (9), 316t-

Anodic Protection of Austenitic Stainless Steels in Sulphuric Acid-Chloride Media s. J. ACELLO and N. D. GREENE, Corrosion, 1962,18, (8), 286t-29ot Studies on the anodic protection of Types 304 and 310 stainless steels showed that stress-corrosion cracking of 18Cr-8Ni stainless steel in 10 N H,SO, plus 0.j N NaCl may be prevented by maintaining the metal in the passive region by impressed anodic currents. A Pt wire auxiliary electrode was used. The stress-corrosion cracking is potential-dependent and is initiated in the active state. Chloride solutions up to 0.1 N do not greatly affect the passive or transpassive dis- solution behaviour of the steels in H,SO,.

Passivating Effect of Chemisorbed Oxygen on the Anodic Oxidation of Molecular Hydrogen at Platinum M. w. BREITER, Electrochim. Acta, 1962, 7, (Sept.1 Oct.), 601-611 The oxygen coverage of a smooth Pt wire electrode was determined by cathodic charging curves at

Platinum Metals Rev., 1963, 7 , (11, 33

different potentials under the conditions of periodic, low-speed, potentiostatic current:pot- ential curves in IN HClO,, with hydrogen or argon stirring, between t o . 6 V and +1.5V. It was shown that most of the passivation is caused by a small oxygen coverage. (33 references)

Use of a Precious Metal Anode in the Electrowinning of High-Purity Chromium from a Fluoride Bath J. A. WHITTAKER, J. Electrochem. Sac., 1962, 109,

The use of a Pd anode instead of a 77" Sn-Pb anode in the production of electrolytic Cr resulted in a decrease in efficiency of the CrO, bath and an increase in the bath resistance. These disadvantages may be overcome by saturating the bath with PbCrO, and by preforming PbO, anodically on the Pd anode.

Halogen Electrodes on Carbon and Platinum Powders w. TOMASSI and M. JANIKOWNA, Przemysl Chem., 1962, 41, (8), 449-451 (English summary). It was found in an invesngation of the behaviour of C and Pt powder electrodes in the chlorine, bromine and iodine electrode systems that only the iodine electrode always reached the state of equilibrium. A relationship was established be- tween the deviation of the stationary state from the equilibrium state and the value of the dis- sociation energy of halogen molecules, as well as the ability of the powder to adsorb these molecules.

Overvoltage and the Hydrogen Content of Palladium Cathodes J. c. BARTON and F. A. LEWIS, 2. Phys. Chem. (Frankfurt), 1962, 33, (I-4), 99-110 (In English) The relative electrical resistance, R IR, (where R, =the initial resistance of hydrogen-free Pd), and electrode potentials of hydrided Pd wires were measured at z 5°C during and after cathodisa- tion in hydrogen-saturated HCl. The wires had received various pre-activation treatments. It was shown that for current densities <O.I A/cm2, the rate at which hydrogen molecules can diffuse from the electrode surface controls the com- ponent of the overvoltage of static, catalytically active electrodes, itself a function of their hydro- gen content.

The Role of Surface Films in the Kinetics of Oxygen Evolution at Palladium-Gold Alloy Electrodes J. J. M~CDONALD and B. E. CONWAY, Proc. Roy. SOC., Series A, 1962, 269, (1338), 419-440 Anodic oxygen evolution was studied on Pd, Au, and Pd-Aualloys containing 21, 35.1, 40, 45.1, 60 and 75 at.% Pd in ultra-pure H,SO, and KOH solutions. In KOH, with Au and the Au-rich alloys, a transition region in the current-potential relation was observed which probably corresponds

( IO) ,986-987

to a limiting high coverage of the active surface with adsorbed reaction intermediates and to the onset of passive behaviour. Results obtained in H,SO, indicate that the discharge process in- volves H,O rather than OH- ions.

LABORATORY APPARATUS AND TECHNIQUE Susceptor Elements for High Temperature Induction Heating s. HASKO and H. S. PARKER, Bull. Amer. Ceram.

The design and fabrication of susceptors produced from Ir and W powders, and sheet W, Ta, Mo, and 20% Rh-Pt, are described. Advantages and disadvantages of crucible, ring-type and sandwich- type susceptors used for heating small specimens in vacuo, and in oxidising, inert, and reducing atmospheres, are discussed. Temperatures up to 2300°C in air and >2600”C in helium were attained with Ir and W susceptors, respectively

SOC., 1962, 4x9 (7)1 467-469

METAL WORKING A New Brazing Alloy for Age-Hardenable Super Alloys J. F. BARKER, P. R. MOBLEY and T. K. REDDEN, Welding J . (Research Suppl.), 1962, 41, ( g ) ,

J-8600 alloy containing 33y0 Cr, 24Ob Pd, 4(j0 Si, balance Ni has been developed for brazing super alloys such as Renk 41. The brazing alloy shows good wetting and flow properties without eroding or embrittling the base metal when used on Rene 41 in vacuo at 2150°F. J-8600 alloy has high temperature strength comparable to that of other brazing alloys and has been used successfully in prototype jet engines.

409S-412s

CATALYSIS Catalytic Decomposition of Acid Hydrogen Peroxide Solutions on Platinum, Iridium, Palladium and Gold Surfaces G. BIANCHI, F. MAZZA and T. MUSSINI, Electrochim.

The decomposition of H,O, (10-l to 10-1 M) was studied in 0.5 M H,SO, and M HC1 solutions at 25°C using Pt, Ir, Pd and Au disc electrodes as catalysts. I t was found that in H,SO, solution, Pt, I r and Pd catalyse the reaction, but Au is in- active; in HCl solution, none of these metals is catalytically active. The catalytic activity is found only when the metal surface is covered with a film of oxide, and is prevented by the formation of complexes. The reaction mechanism is ex- plained.

Acta, 1962, 7, (Jul.Lhg.1, 457-473

Reaction of Sodium Borohydride with Platinum Metal Salts in the Presence of Decalourising Carbon - A Supported Platinum Catalyst of Markedly Enhanced Activity for Hydrogenations H. c. BROWN and c. A. BROWN, J. Amer. Chem. Soc.,

A method of preparing in situ Ru/C, Rh/C, PdlC, Os/C, Ir/C, and P t C catalysts is described. In the hydrogenation of I-octene, the activities of Rh,’C, PdlC and PtlC are greater than those of the corresponding unsupported metals; however, the activities of Ru, 0 s and Ir are decreased by the presence of the C support. The rate of hydro- genation of several unsaturated hydrocarbons over the Pt:C catalyst is zoo to 400:: greater than that observed with an unsupported Pt catalyst.

Hydrogenation of Nitroaromatics in the Presence of the New Platinum Metal and Carbon-Supported Platinum Metal Catalysts H. c. BROWN and K. SIVASANKARAN, Ibid., 2828 Unsupported and C-supported Ru, Rh, Pd, Os, Ir and Pt catalysts were prepared in situ and evaluated for the hydrogenation of C,H,NO,. Results showed that both supported and un- supported Pd and Pt are the most active catalysts for the reaction. The catalysts prepared in situ are almost twice as active as commercial PdiC and Pt/C. A number of nitroaromatics were con- verted to the corresponding amines using the new Pt, C catalyst.

The Surface Chemistry of Ethylene on Alumina and PlatinumlAlumina v. KEVORKIAN, J. L. CARTER and r. J. LUCCHESI, Abstracts of Papers, 10-1, Div. of Colloid and Surface Chem., IQnd Meeting, A.C.S., Atlantic City, N. J., Sept. 1962 The surface chemistry, adsorption kinetics, and energetics of C,H, on A1,0, and Pt/AI,O, were studied at 250% in a differential isothermal microcalorimeter and infra-red spectrometer. Adsorption heats on both catalysts change from exothermic to endothermic with increasing cover- age because of extensive surface reactions. Infra- red analysis indicates that on A1,0, the chemi- sorbed ethyl group (S-C,H,) appears first, and the sideways-held form (S-CH,-CH,-S) appears second. Over Pt/Al,O,, both forms appear at the onset of adsorption. CzHa self-hydrogenates on Pt /Al,O,.

Deuterium Tracer Studies of the Mechanism of Homogeneous Catalytic Hydrogenation J. HALPERN and B. R. JAMES, Abstracts of Papers, 23N, Div. of Inorg. Chem., r42nd Meeting, A.C.S., Atlantic City, N. J., Sept. 1962 A study of the isotopic exchange of deuterium with aqueous solutions of RuC1, suggested that the principal exchange path involves the hetero- lytic splitting of deuterium by the catalyst, i.e.,

1962, 84, (I4h 2827

Platinum Metals Rev., 1963, 7 , (11, 34

R u l ~ I + D , ~ R u r r l D - t D+. Other reactions Au-Pt alloys had less effect on their catalytic studied include (i) the isotopic exchange between activity than on that of Pt. The lower activity of deuterium and H,O, catalysed by Ru(I1)-olefin the 75 and 90 at.:& Au-Pt alloys and of pure Au complexes and (ii) RuC1,-catalysed homogeneous could not be measured accurately. hydrogenation of fumaric acid to succinic acid. The mechanism of reaction (ii) is discussed. Dehydrogenation of Normal Alcohols

W. ZABLOmy and M. I. SMIRNOW, Przemysl Chem., Reductions with Ruthenium Catalyst 1962, 41, (7), 386-388 (English summary) 111. Hydrogenation of Nuclear Substituted A spiral of Ni-Cr wire covered with Pt was used Anilines as the catalyst in the dehydrogenation of ethyl, M. FREIFELDER and G. R. STONE, Abstracts of n-PropYl, n-butyl and n-amyl alcohols. Reaction papers, 8-0, ~ i ~ . of Medicinal Chem., 142nd constants and activation energies were computed Meeting, A.C.S., Atlantic City, N.J., Sept. 1962 from experimental results. Gas analysis of the The effect of nuclear on conversion reaction products showed that dehydration of the of the benzene ring to the cyclic Structure was alcohols and thermal decomposition of the alde- studied. In addition, the effect of the Ru catalyst hydes Obtained Occurred to Only a extent* on groups that may undergo hydrogenolysis under the reaction conditions (90'C and 70 atm pressure) was investigated. N-Methylaniline and ethyl N-phenylglycinate were hydrogenated to compare the effects of mono- and di-substitution.

On the Mechanism of Thermal Decomposi- tion of Nitrous Oxide at a Platinum Filament N. R. MURTY, Naturwiss., 1962, 49, (IS), 447-448 The thermal decomposition of N,O at a Pt fila- ment at 970°C followed an apparent zero order rate. During the course of the reaction the Joshi effect, &Ai, was studied. The mechanism pro- posed for the reaction involves the chemisorption of oxygen and the formation on the catalyst sur- face of a labile electrogenative radical due to the interaction of the chemisorbed atomic oxygen on the Pt surface and nitrogen in the gas phase.

Decomposition of n-Propane and n-Butane on Clean Rhodium Foils R. w. ROBERTS, J . Phys. Chem., 1962, 66, (9), 1742-1743 The decomposition reactions were carried out at 27" and 100°C on Rh films about 50 a thick deposited by pulse evaporation on the inside of a Pyrex sphere. It was found that both n-C,H, and n-C,Hlo decompose in these conditions to give lower hydrocarbons and an adsorbed hydro- carbon residue. The primary reaction product for both saturated hydrocarbons is CHI. Adsorbed gases reduce the activity of the Rh films.

The Effect of Adsorbed Oxygen on the Cata- lytic Activity of Platinum and Platinum- Gold Alloys in the Conversion of Para- Hydrogen D. MENZEL and L. RIEKERT, Z . Elektrochem., 1962, 66, (51, 432-439

Comparison of Hydrogen Isotope Exchange, Para-Hydrogen Conversion and Oxyhydro- gen Gas Combustion in Aqueous Suspensions of Noble Metal/Activated Charcoal Catalysts u. SCIIINDEWOLF, M. KENAWY and E. G . MAHADEVAN, Z. Elektrochem., 1962, 66, (s), 406-412 Aqueous suspensions of Pt:C and PdjC were used as catalysts for the isotope exchange between hydrogen and water, para-hydrogen conversion, and oxyhydrogen gas combustion at pressures < I atm and at room temperature. A study of the reaction processes leads to the assumptions that the three reactions are initiated by the catalytic activation of hydrogen and that the chemisorption of hydrogen is proportional to the pressure.

Palladium-Catalysed Decarbonylation of trans-&-Substituted Cinnamaldehydes N. E. HOFFMAN, A. T. KANAKKANATT and R. F. SCHN~IDER,J. Org. Chem., 1962,27, (7), 2687-2689 A I o * ~ Pd/C catalyst was used in the decarbonyla- tion of several trans-a-substituted cinnamalde- hydes. It was found that &-olefins predominate if the product is distilled rapidly after formation, but that trans-olefins result from isomerisation of the cis-olefins if the product is distilled only after decarbonylation is complete.

Palladium - Catalysed Hydrogenation of Pyridines G . N. WALKER, 7. Org. Chem., 1962, 27, (S), 2966-2967 It has been found that I O O ~ Pd/C may be used as a catalyst for the reduction of pyridines to the corresponding piperidines at reaction tempera- tures and pressures of 70-80°C and 3-4 atm, respectively. Compounds closely related to known central stimulants have been produced.

The conversion reaction was studied at tempera- tures in the range 170-5oo~K with Pt and 5, 10 and 20 at.*, Au-Pt alloy catalysts, and at > 8 0 0 " ~ with 75 and 90 at.o& Au-Pt catalysts. The depend- ence of the reaction rate on the pretreatmentof the catalysts with oxygen and hydrogen was in- vestigated. Pretreatment of the 5 , 10 and 20 at.',

Hydrogenation-Hydrogenolysis Studies of Symmetrically Substituted 1, 4-Acetylenic (%'COlS

R. J. TEDESCHI, 3. org. Chem., 1962, 27, (7), 2398-2402 Hydrogenation of the I , 4-acetylenic glycols was

Platinum Metals Rev., 1963, 7 , (11, 35

carried out at 55-85°C and 30-55 p.s.i. using a 5Ya PdlC catalyst. The addition of small amounts of base such as KOH, NaOH, or (CH,CH,),N before hydrogenation was found to inhibit hydro- genolysis side reactions, and high yields of olefinic and saturated diols were obtained. A route for the hydrogenolysis is given.

Selective Hydrogenation of Methyl Oleate Ozonolysis Products by Palladium in Pyri- dine-Methanol Solvent E. H. PRYDE, D. E. ANDERS, H. M. TEETER and J. c. cowAN,J. org. Chem., 1962,27, (9), 3055-3059 The presence of C,H,N improved the yield of methyl azelaaldehydate when the ozonolysis pro- ducts were hydrogenated over a PdiC catalyst at room temperature and I atm. C,H,N poisoned the catalyst for hydrogenation of olefinic unsatura- tion. Unused methyl oleate could be recovered.

Stereochemistry and the Mechanism of Hydrogenation of Cyclo-alkenes. IV. 4-tert- Butyl-1-methylcyclohexene and 4-tert-Butyl- 1-methylenecyclohexane on Platinum Oxide and a Palladium Catalyst s. SIEGEL and B. DMUCHOVSKY, J. Amer. Chem.

The hydrogenation reactions were carried out in CHsCOOH using PtO,, 5"4 PtiAl,O, and so0 Pd:A1,0, catalysts. It was found that the ratio of the saturated stereoisomers obtained with reduced PtO, catalyst is a function of the pressure of hydrogen. The extent of isomerisation of the alkene varies with the catalyst used and occurs in the order: Pd:Al,O,>Pt:Al,O,>PtO,. It is assumed that with a Pd catalyst the rate-limiting surface reaction occurs at a later stage than with a Pt catalyst.

The Stereochemistry of the Hydrogenation of the Isomeric Xylenes and y-tert-Butyl- toluene over a Platinum Catalyst S. SIEGEL, G. V. SMITH, B. DMUCHOVSKY, D. DUBBELI. and w. HALPERN, J . Amer. Chem. SOC., 1962, 84, (1% 3136-3139 Hydrogenation over reduced PtO, in CH,COOH at 25°C produced a mixture of czs- and trans- dialkylcyclohexanes. The &:trans ratio is a funcrion of the structure of the substrate and the pressure of hydrogen. Comparison of the experi- mental results with the stereochemistry of the hydrogenation of the related cycloalkenes suggests that the latter are intermediates in the reduction of the aromatic cycle.

Oxidation of Ethylene to Acetaldehyde by the Direct Oxidation Process G. BERGER and R. MITTAG, Erdol u. Kohle, 1962, Is, (9), 699-702 Technical details are given of the one-cycle and two-cycle processes for the production of

SOC., 1962, 84, (16), 3132-3136

CH,CHO in which a PdCl,/'CuCl, oxidation catalyst is used. The yield and quality of the CH,CHO obtained is described.

Ethylene Enters a New Field

2 I 6-22 I The Celanese Chemical Co.'s plant at Bay City, Texas, is described. CH,CHO is produced by the direct oxidation of C,H,, using a PdC1, catalyst, in the two-stage Wacker process. CH,CHO is used as the raw material for the production of z-ethyl hexanol and n-butanol.

The Kinetics of the Oxidation of Cyclohcxene by Palladium Salts in Aqueous Solutions M. N. VARGAFTIK, I. I. MOISEEV and YA. K. SYRKIN, Proc. Acad. Sci. U.S.S.R., Phys. Chem. Section, 1961, 139, (1-6)~ 634-636 (Transl. of Doklady Akud. Nauk S.S.S.R., 1961, 139, (6), 3196-3199) The oxidation reaction was studied in the temperature range 7.0" to 30.3'C in the presence of p-benzoquinone which oxidised the metallic Pd formed from the Pd C1, catalyst. Confirmation of an earlier assumption that the reaction pro- ceeds through the formation of a x-complex is provided by the results of the kinetic study.

The Reactions of Olefins with Aqueous Solutions of Palladium Salts w. HAFNER, R. JIRA, J. SEDLMEIER and J. SMIDT, Chem. Ber., 1962, 95, (7), 1575-1581 Experimental work was carried out to investigate the mechanism of the reactions. The effects of acids and complex ligands upon the course of the reaction were traced to the different polarisa- tion of the unsaturated compounds in the respec- tive Pd complexes. Solutions of K,PdCl, were used in the oxidation of propylene and hept-I-ene.

A Method for the Reactivation of Noble Metal Catalysts H. KOGLER and s. QUECK, Chem. Techn., 1962, 14, (9), 541-545 The method described for reactivating spent Pt /A1,0, catalysts involves treatment with a solu- tion of NH,C1 and NH,NO, followed by heat treatment in an oxidising medium. It appears that spent catalysts may be successfully reactiv- ated several times by this method.

Catalytic Oxidation of Automotive Exhausts w. A. CANNON and c. E. WELLING, Ind. Eng. Chem. (Product Res. & Dev.), 1962, I , (3), 152-156 A laboratory method for evaluating catalysts for the oxidation of simulated exhaust gas mixtures is described in detail. Catalysts found to be satis- factory for complete oxidation of simulated exhausts from unleaded gasolines include Mn-Cu oxides, Cu chromite, Ag,O-BaO,, promoted FeBOB, CuO, V,O,, and supported Pt and Pd. Phase changes and decreased activity of Mn-Cu

H. C. BOZEMAN, oil &' Gas .y., 1962, 60, ( ~ $ 2 ) ~

Platinum Metals Reu., 1963, 7 (11, 36

oxides, Ag,O-BaO,, and Cu-promoted Fe,03 on heating to 760°C for 16 h indicate that these catalysts may be unsuitable under actual operating conditions.

Mechanism of the Transformations of Cyclo- hexene and 1,3-Cyclohexadiene on Platinum Films V. M. GRYAZNOV and v. I. SHIMULIS, Proc. Acad. Sci. U.S.S.R., Chem. Section, 1961, 139, (1-6), 749-752 (Transl. of Doklady Akad. Nauk S.S.S.R., 1961, 139, (4), 870-873) Experimental results show that both cyclohcxene and I, 3-cyclohexadiene exhibit simultaneous hydrogenation and dehydrogenation on Pt films at 20°C. At low pressures the dehydrogenation predominates, but as the hydrogen accumulates, the hydrogenation rate increases. The mechanism of the reactions is discussed.

Refining-Petrochemical Centre G. L. FARRAR, Oil & GasJ., 1962,60, (27), 100-104 The layout and operation of the El Paso Natural Gas Products-Rexall Drug L? Chemical installa- tions at Odessa, Texas, are described. Among the many units are a Platformer operated for the production of aromatic hydrocarbons and a motor- fuel Platformer.

The Refining Hydrogenation and Catalytic Reforming Plant of Homs Refinery (Syria) z. KOPELENT, Chem. Techn., 1962,14, (S), 451-456 The operation of this refinery, which went on stream in 1959, is described in detail. The refinery comprises two main units, a hydrogena- tion plant and a catalytic reforming plant in which a Pt catalyst is used.

An Improved Platinum Catalyst for Hydro- genation of an Olefin R. w. BOTT, c. EABORN, E. R. A. PEELING and D. E. WEBSTEX, Proc. Chem. soc., 1962, (oct.), 337 The catalyst was prepared by adding 0.01 m mole H,PtCl, in 959A aq. C,H,OH to a solution of 0.1 m mole tribenzylsilane in 9500 aq. C,H,OH at 70°C. In the hydrogenation of oct-I-ene at 30°C this catalyst was found to be more active than Adams’ (PtO,) catalyst or Brown and Brown’s catalyst (J . Amer. Chem. SOC., 1962, 84, @), 1493-1495). However, it is less active than Adams’ catalyst in the hydrogenation of C,H,, Tncholoro-; triethyl-, tri-n-butyl-, and triphenyl- silane were also used to reduce H,PtCl, with the formation of catalysts of similar activity to the one dcscribed.

Particle Size Determination of Supported Catalytic Metals: Platinum on Silica Gel c. R. ADAMS, H. A. BENESI, R. M. CURTIS and R. G. MEISENHEIMER, J . Catalysis, 1962, I, (4), 336-344 Results are given of particle size determinations of

a PtISiO, gel catalyst which were obtained by using electron microscope, X-ray diffraction, and adsorption techniques. All three methods give comparable results. Applications and limitations of the methods are discussed.

The Catalytic Properties of Borides of Platinum Group Metals B. D. POLKOVNIKOV, A. A. BALANDIN and A. M. TABER, Doklady Akad. Nauk S.S.S.R., 1962, 145,

Borides of Pd, Pt, and Rh were prepared and their catalytic activity in the liquid-phase hydrogena- tion of various unsaturated organic compounds was compared with that of Pd black, Pt black, and Rh black. Hydrogenations were carried out at 20°C in CH,OH. The boride catalysts showed greater activity and stability than the correspond- ing “black” catalysts in the reactions reported. The activity of the boride catalysts was found to be in the order: Pd-B >Pt-B : Rh-B.

(4), 809-8 I I

CATHODIC PROTECTION The Use of Platinised Titanium in a New Form for Marine Cathodic Protection Instal- lations ANON., Corrosion Prevention & Control, 1962, 9, (101, 51-54 Two forms of strip anode are described and their advantages are pointed out. One type consists of a T i strip platinised on the side exposed to the sea- water and located in a plastic backing. The second type is a $ in. diameter Cu-cored platinised T i rod sheathed with perforated PVC.

CHEMICAL TECHNOLOGY On the Use of Palladium Osmosis Tubes

1962, 39, (91,480-481 R. W. CROMPTON and M. T. ELFORD,?. SCi. Instr.,

Precautions to be observed in the use of Pd diffusion (osmosis) tubes for the purification of hydrogen are discussed. Cracking of the tubes due to the a- to p-phase transition when Pd is heated or cooled in hydrogen, leaking of the seal between the tube and the vacuum system, and reduction of the diffusion rate during operation are avoided by adopting these precautions. The advantages of using Ag-Pd diffusion tubes are mentioned.

ELECTRICAL ENGINEERING Improving Reliability of Microcircuit Con- nectors J. R. ANDERSON and J. B. SAUNDERS, Electro-Technol., 196% 70, (4)1 74-78 The use of monolayer boundary lubricants to

Platinum Metals Rev., 1963, 7 , (11, 37

reduce friction and wear between contact metals is discussed. Data are given for the coefficient of friction, wear track width and contact resistance of several unlubricated metal pairs (Au on Pd, Pt on Pd, Au on Au, k on Au, Au on Rh, Pt on Rh, and Pt on Ag) for loads of 2-50 g. Octadecylam- ine hydrochloride, octadecylamine, stearic acid, and iodide films were evaluated as lubricants for various noble metal pairs.

TEMPERATURE MEASUREMENT Precision Method of Measurement for Testing the Thermal-E.M.F. Temperature Depend- ence of Platinum - Rhodium : Platinum Thermocouples by Comparison with a Standard Thermocouple W. HEYNE, Feingeratetechn., 1962, 11, (9), 400-402 A method of measurement suitable for use with noble metal thermocouples is described and con- trasted with the conventional method. I t is claimed that the new method of comparison of similar thermocouple limbs is the quicker and more accurate of the two.

Effect of Thermal Neutron Irradiation on Thermocouples and Resistance Thermo- meters C. w. ROSS, A.I.E.E. Trans., Part I, Communica- tions & Electronics, 1962, (July), 192-196 The results are given of a study of the effect of

transmutations due to neutron adsorption on the accuracy of Pt:rooj, Rh-Pt thermocouples and of Cu, Pt and Ni resistance thermometers. It was found that the thermal e.m.f. of a 1't:roYb Rh-Pt thermocouple is decreased by thermal neutron irradiation, largely as a result of the transmutation of Rh. Increases in resistance of Cu, Pt and Ni due to transmutations are in the order: Cu>Pt> Ni. Methods for estimating the result- ing errors in temperature measurement are given.

Thermoelectric Instability of Some Noble Metal Thermocouples at High Temperatures

U.S. Naval Research Laboratory Report NRL

The thermoelectric instabilities of Al,O,-sheathed individual thermoelements and thermocouples of Pt, Rh, Ir, 50°& Ir-Rh, and some Rh-Pt alloys were studied in the temperature range 1000"- 1700'C in argon and in air. Compositional changes in the thermal gradient zone of the thermocouple material are the main cause of in- stability. Fe originating in the A1,0, sheathing tubes is the main contaminant of Rh-Pt thermo- couples and the resulting instability is greater in argon than in air. Internal changes are the main cause of instability of pure Rh, Ir, and 50*, Ir-Rh thermoelements; Ir and 5096 Ir-Rh have excellent resistance to Fe contamination. In argon, stability of Rh-Pt thermocouples is increased by increasing the wire size, but in air it is independ- ent of wire size.

B. E. WALKER, C. T. EWING and R. R. MILLER,

5792, June 1962, 19 PP.

NEW PATENTS

Cathodic Protection of Ships alumina and/or silica support with compounds of H. S. PREISER British Patent 902,667 germanium and of platinum and heating the An anodic assembly for use in cathodic protection support at Over 800°F (9Oo0-I800"F) to form a of a ship's hull consists of a rod of platinum or of solid solution comprising germanium and Plat- copper, or a silver-copper alloy, coated with inum and containing at least 5% each of platinum or palladium connected to an insulated germanium and Platinum, the finished catalyst cable so that the rod can trail behind the ship, containing O.I-IO% by wt. of the solid solution.

Production of Aromatic Nitriles CALIFORNIA RESEARCH CORP. British Patent 902,880 Aromatic nitriles are made by contacting in the vapour phase an alkyl substituted aromatic hydrocarbon (7-15 carbon atoms per molecule) with ammonia and air at 30O0-65Ooc in the presence of a composite catalyst consisting of at least 194 of a heavy metal oxide, e.g. vanadium pentoxide and at least 0.01% by wt. of platinum.

Hydrocarbon Conversion Catalyst STANDARD OIL co. British Paten1 903,773 A reforming catalyst is made by impregnating an

Reduction of Pyridine and Salts thereof ABBOTT LABORATORIES British Patent 904,r 17 Piperidine or a salt thereof is made by hydro- genating pyridine or a salt thereof in the presence of rhodium (0.05-2y0 by wt. based on wt. of starting material) at a pressure below 125 p.s.i. and a temperature between room temperature and 150°C.

Hydrogenation of Aromatic Hydrocarbons UNIVERSAL OIL PRODUCTS CO. British Patent 904,732 In the hydrogenation of aromatic hydrocarbons with hydrogen at elevated temperature of not

Platinum Metals Rev., 1963, 7 , (11, 3 8 4 0 38

over 427"C, substantially complete saturation of the aromatic hydrocarbons with hydrogen is effected in the presence of a catalyst consisting of an alumina-containing refractory oxide carrier and containing 0.1-2% by wt. of platinum (or another platinum group metal) and one or more alkali or alkaline earth metals (0.01-0.7% of alkali metal).

Vitreous Enamels E. I. DU FONT DE NEMOURS & CO. British Patent 9°4J936 A vitreous enamel composition intended for firing on to a ceramic dielectric to form an electrical resistor is composed of 8-900/, of finely divided palladium oxide or rhodium oxide and 10-920/~ of finely divided vitreous enamel flux. Up to 50% of gold, silver or platinum may be included with a minimum of 4% of palladium or rhodium oxide.

Electrolytic Cells IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent 905,141 An electrolytic cell for manufacture of chlorine and caustic alkali comprises a non-conducting porous diaphragm held between, and in contact with, a perforated sheet metal cathode and a perforated sheet titanium anode support carrying an anode in the form of a coating thereon of a platinum group metal.

Electrolytic Capacitors THE TELEGRAPH CONDENSER co. LTD. British Patent 905Y323 The negative member of an electrolytic capacitor is made by chemically depositing hydrogen- absorbing material, e.g. palladium or platinum black, on a basis body of conductive material, e.g. silver. For example, a silver body may be boiled in an acidified solution of palladium chloride.

Activating a Catalyst UNIVERSAL OIL PRODUCTS CO. British Patent 905,499 Platinum-and/or palladium-n alumina catalyst composite is activated by passing an oxide of nitrogen at 25"-1000"C through the dry comp- osite, which is then subjected to separate treatments of oxidation with a free oxygen- containing gas and of reduction with a hydrogen- containing gas.

Alloys UNION CARBIDE CORP. British Patent 905,673 An alloy which is resistant to hydrogen embrittle- ment resulting from elcctrochemical action consists of tantalum, a tantalum-titanium alloy or a I O ? ~ chromium stainless steel, and 0.05-5.0~0 by wt. of a platinum group metal, gold, rhenium or alloys thereof. Examples: (I) 99.574 tantalum and 0.5% platinum; (2) 49.57; titanium, 0.50/~ platinum and balance tantalum.

Hydrogenation of Marine Oils ENGELHARD INDUSTRIES INC. British Patent 906,392 Marine oils are hydrogenated by treatment with hydrogen in the presence of a palladium-contain- ing catalyst as sole catalytically active metal. o.o1-100/~ by wt. palladium supported on carbon is used.

Coating a Molybdenum Grid PHILIPS ELECTRICAL INDUSTRIES LTD. British Patent 906,961 A discharge tube grid of molybdenum to be coated with platinum, is first coated with an intermediate layer of iron, cobalt or nickel having a rough surface and a platinum layer is then electrodeposited thereon.

Purification of Propylene ENGELHARD INDUSTRIES INC. British Patent 906,994 A propylene-containing gas is purified by mixing the gas with hydrogen and passing the mixture over a catalyst containing palladium, rhodium or platinum metal or a mixture of two of them at a temperature above I Z O " ~ . Palladium on activated alumina may be used.

Catalytic Reduction of Dinitrotoluenes IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent 907,154 Dinitrotoluenes are reduced to diaminotoluenes by gradually adding the dinitrotoluenes and hydrogen to a suspension of palladium or platinum catalyst in an aqueous solution of the diaminotoluenes at a temperature of I 10"-140°C. The amount of catalyst used is such that from 15-150 parts by wt. of palladium or platinum are present for every I,OOO,OOO parts by wt. of total dinitrotoluenes to be reduced.

Thermocouples ENGELHARD INDUSTRIES INC. British Patent 908,528 A thermocouple has a positive element formed of an alloy of 3-15% gold, 5543% palladium and 14-347" platinum. The negative element consists of an alloy of 60-65:/, gold and 35-40% palladium.

Hydrogenation of Aldehydes and Ketones ENGELHARD INDUSTRIES INC. British Patent 908,639 A saturated or unsaturated aldehyde or ketone (other than an alpha-beta unsaturated aldehyde or ketone) is hydrogenated by treating it in liquid phase with hydrogen in the presence of a rhodium-containing catalyst. A 5% rhodium on carbon powder catalyst is referred to.

Thermoelement Alloy

German Patent 1,127,091 An alloy of 24-4076 palladium, 0.5-7:; nickel and 55-7176 gold is used to form the negative limb of a thermoelement.

DEUTSCHE GOLD-UND SILBER-SCHEIDEANSTALT

Platinum Metals Rev., 1963, 7 , (11, 39

Hydrogenation Process STANDARD OIL co. US. Patent 3,042,197 A hydrogenatable feed stock is contacted with hydrogen gas under hydrogenation conditions with a catalyst composed of 0.05-1% by wt. of platinum, 0.054% by wt. of thiocyanate ion on an alumina support.

Platinum-alumina Catalyst

A platinum-alumina catalyst having a low halogen ion content is prepared by commingling alumina in an aqueous medium with a platinum metal halogen-containing compound (halogen selected from Group VIIB with atomic number from 35-53), drying, heating to calcination temperature of at least 8oo"F in an inert atmosphere and then further calcining the product in an oxidising atmosphere to reduce halogen to a low concen- tration.

Production of 3-amino-propyl Isocyanurates ALLIED CHEMICAL CORP. U.S. Patent 3,042,672 3-aminopropyl isocyanurates are produced by reacting bis-(or tris)-(a-cyanoethyl) isocyanurate in the presence of a platinum or palladium hydrogenation catalyst.

Hydrocracking of Polynuclear Hydrocarbon oils ESSO RESEARCH & ENGINEERING co. U S . Patent 3 3043,770 A hydrocarbon oil feed boiling at about 350°F rich in polynuclear aromatics is hydrocracked at 875"-1o5ooF and a pressure of 200-1000 p.s.i.g. in the presence of platinum on era alumina, produced from aluminium alcoholate, as catalyst and at a feed rate between 0.5 and 3 w/h/w in presence of 1000-5000 s.c.f. of hydrogen per barrel to convert the feed [o high octane gasoline.

Spinnerette ENGELHARD INDUSTRIES INC. US. Patent 3,0~,155 A spinnerette is made of an alloy of 70% gold and 30% platinum by wt., which has been electro- plated with rhodium or ruthenium.

Hydrocracking of Liquid Alkanes PHILLIPS PETROLEUM GO. U S . Patent 3,046,317 A normally liquid normal alkane (at least 5 atoms per molecule) is hydroaacked by contacting it, admixed with hydrogen, and under hydrocracking conditions, with a catalyst composed of 0.1-10 wt. 56 of a platinum metal mixed with boria and zirconia.

Recovery of Rare Metals E. R. WOLCOTT U.S. Patent 3,049,422 Platinum or platinum compounds are recovered from finely divided ore containing them by treating the ore with a gaseous mixture of nitrosyl chloride and chlorine produced from aqua regia at a high enough temperature to cause

ENGELHARD INDUSTRIES INC. U.S. Patent 3,042,627

only these metals to form volatile compounds, which are then separated from the ore.

Thermocouple ENGELHARD INDUSTRIES INC. U.S. Patent 3,049,577 A thermocouple comprises a negative element formed of a platinum group metal core within a sheath also of a platinum group metal. The core consists of a number of compacted interfused elongated bodies in direct contact with the sheath. The positive element is formed of a platinum group metal alloy bonded to the negative element.

Spinnerette ENGLEHAFUI INDUSTRIES INC. U. S. Patent 3,049,753 The material defining the extrusion orifices in a spinnerette plate is composed of a sintered mixture of tungsten carbide powder and I-20q4 of a platinum group metal powder.

Brazing Alloy GENERAL ELECTRIC GO. U S . Patent 3,053,652 A high temperature brazing alloy contains

~o-zoo/b chromium 5-15% palladium 10-40% manganese I- 5 % silicon

Balance nickel.

Deposition of Metal LEESONA CORP. U.S. Patent 3,053,741 A non-porous layer of palladium-silver alloy is electrodeposited on an article from an ammoniacal nitrate solution of palladium and silver having a pH of 7.5-11.

Anode for Electrolysis UNIVERSAL OIL PRODUCTS CO. U.S. Patent

A platinum-plated titanium anode is made by electrodepositing on a titanium base a coating of amorphous platinum and activating the latter by heating at above 600°F in the presence of an air stream containing hydrocarbon vapours, for a long enough period to initiate catalytic oxidation of the vapours on the platinum surface.

Catalyst ENGELHARD INDUSTRIES INC. U.S. Patent 3,055,840 A catalyst consists of a support carrying a deposit of ruthenium and, as a promoter, platinum, rhodium or palladium. The ruthenium con- stitutes at least 20% of the catalytically active metal content of the catalyst.

Catalytic Contact of Gases

The ignition and combustion of a mixture of methane, oxygen and inert gases is effected by contacting the mixture at above its ignition temperature, but not over 400"C, with a catalyst consisting of rhodium or rhodium and another platinum group metal.

3,055,81 I

ENGELHARD INDUSTRIES INC. U.S. Patent 3,056,646

Platinum Metals Rev., 1963, 7 (I), 40