PLATINUM METALS REVIEW · fume eliminators operate with no visible “plume”. In addition, the...

PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of developments in their applications in industry

V O L . 12 J A N U A R Y 1 9 6 8 N O . 1

Contents

Platinum Catalysts for the Control of Air Pollution

Self-heating in Platinum Resistance Thermometry

Dispersion Strengthened Platinum

Platinum in Austenitic Stainless Steel

Palladium Telephone Contacts

Ultra-pure Hydrogen from Water

The Platinum Metals in the Production of Laser Crystals

Ruthenium as a Methanation Catalyst

Platinum and Palladium Electrodeposits on Refractory Metals

Effectiveness of Platinum Fuel Cell Catalysts

Fifty Years of Research on the Platinum Metals

Abstracts

New Patents

2

6

7

13

14

15

16

19

20

21

22

29

36

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Matthey & Co., Limited, Hatton Garden, London, E.C.1

Platinum Catalysts for the Control of Air Pollution A TAIL GAS REDUCTION SYSTEM FOR NITRIC ACID PLANTS

By J. B. Hunter, P m . Matthey Bishop Inc., Malvern, Pennsylvania

The problems of air pollution are in- creasingly the subject of public attention. Pressures, and ultimately legislation by governments, will undoubtedly result in a rapid increase in demand for effective low- cost catalytic pollution control systems. Although some catalytic systems have existed for several years, more severe restrictions on permissible atmospheric pollutants in the future will require new equipment and techniques to meet them.

Until recently most air pollution problems were solved by direct flame combustion methods in specially designed reaction cham- bers. Although catalytic oxidation has long been well recognised as an effective technique, the high pressure drop through dense beds of granular or pelleted catalysts has

limited the development of commercially acceptable systems.

This situation has recently changed as a result of the introduction of a new group of ceramic catalyst supports in the form of a honeycomb-like structure. One major advantage of this open type of substrate is its exceptionally low pressure drop. This is an important operating advantage, resulting in lower power and/or compression costs.

Fig. I shows a comparison of pressure drop through a commercially available + inch cell size honeycomb material known as Torvex, produced by du Pont, with the drop through a bed of standard 4 inch pellets. For a gas flow of 10 s.c.f.m. per square inch of reactor bed, the honeycomb shows a pressure drop of only one inch of water per inch of bed

Platinum Metals Rev., 1968, 12, (l), 2-6 2

Fig. 2 The pilot plant reactor in which the Matthey Bishop tail gas reduction catalyst was developed

depth, compared with 24 inches of water through the pellet bed.

Other important advantages for honeycomb catalysts include more uniform gas distribution, greater structural strength, no at- trition or loss of fines, and no channelling or hot spots. When platinum is used as the catalytic metal, a honeycomb catalyst structure is particularly attractive since there is no loss in effective area such as is found in pellet beds. From the standpoint of system design, the rigid structure also provides greater process flexibility. Horizontal as well as vertical reactors may thus be used.

The development of this unique honeycomb material indeed represents a significant breakthrough in the field of industrial catalysis.

Platinum Honeycomb Catalysts Matthey Bishop has recently developed a

series of metallised ceramic honeycomb catalysts for use in a wide variety of atmospheric pollution control systems and other chemical process applications. Because of its unrivalled resistance to oxidation at high temperatures and to corrosive chemical attack, as well as its unique catalytic properties, platinum is the preferred catalytic metal. Palladium has also been used for certain air pollution applications but, although it is catalytically highly active, it oxidises too readily at high temperatures and is susceptible to poisoning by sulphur.

The Matthey Bishop T H T catalysts differ from other commercially available platinum catalysts in two important respects; a highly active platinum is tightly anchored to the ceramic base by a new proprietary technique, while the introduction of a different concept in catalyst packaging not only protects the ceramic structure against breakage but also

Platinum Metals Rev., 1968, 12, (1) 3

allows for catalyst interchangeability. De- pending on the system requirements two, three or more units may be packaged together to form a bed having any desired pressure drop for a particular catalytic performance that may be needed.

Elimination of Nitrogen Oxide Fumes

In the synthesis of nitric acid a mixture of ammonia and air at high temperature is passed over a platinum gauze catalyst to form nitric oxide (NO). This is followed by oxidation to the dioxide (NO,) and subsequent absorption of the latter in water to produce aqueous nitric acid. Nitrogen together with small amounts of oxygen and unabsorbed nitric oxides are discharged into the atmosphere as a tail gas. This discharge represents a major source of air pollution. In a typical tail gas, nitrogen oxide concentrations may range from 0.1 to 0.6 per cent by volume. Oxides of nitrogen are also discharged into the atmosphere from some

Fig. 3 Four tail gas stacks emitting nitrogen oxide fumes at the Cooperative Farm Chemical Association nitric acid plant at Lawrence, Kansas

chemical operations, from acid concentrators, and from acid storage systems.

Nitric oxide (NO) is a colourless gas, while nitrogen dioxide (NO,) is intensely reddish brown. Decolourisation of a tail gas occurs when NO, is catalytically reduced on a platinum/honeycomb catalyst to NO in the presence of an added fuel (reducing agent) such as hydrogen or methane.

NO, t- H, wr:+ NO + H,O

4NO, + CHI %+ 4NO 4- CO, -t 2H,O

Fume abatement requires conversion of all nitrogen oxides to nitrogen and is achieved when additional fuel is used and the nitrogen oxide concentration is lowered to below IOO p.p.m.

2N0, 4- 4H, E%L, N, + 4H,O

zNO, + CH, N, + CO, -1 aH,O

Although various systems have been devised for controlling nitrogen oxide air pollution, the recently improved technique of catalytic combustion using platinum catalysts on ceramic honeycomb is becoming increas-

ingly popular. Plants equipped with catalytic fume eliminators operate with no visible “plume”. In addition, the heat energy generated by the oxidation of the added fuel (hydrogen, carbon monoxide, natural gas or other hydrocarbons) is profitably extracted by high temperature gas turbines or expanders mechanically connected to the air compressor of the ammonia oxidation system. Heat exchangers and waste heat boilers are also used in combination with the expander to augment further the recovery of energy liberated in the catalytic reactors.

In systems where the reactor is placed in front of the expander, the vessel must be designed for operating pressures in the range of roo p.s.i.g. and for temperatures up to 760°C (1400OF). Catalyst volume is generally based conservatively on an hourly space velocity of IOO,OOO.

When natural gas is used as a fuel, the temperature rise (AT) across a catalytic bed is approximately 130°C (234°F) for every one per cent oxygen consumed. Using the new highly active Matthey Bishop catalyst,


the reduction of nitrogen oxides begins at 370" to 385°C (700" to 725°F) compared with 425" to 480°C (800" to 900°F) for other, older, systems. When hydrogen is employed as the reducing gas the reaction starts at 150°C (300°F) and the temperature rise is somewhat greater, A T = 150°C (270°F). Con- servative system design assumes an initial reaction temperature of 454°C (850°F). Since a reactor temperature above 760°C (1400@F) is undesirable, the maximum A T across the bed is limited to 300°C (550°F). A system operating on natural gas could therefore burn a maximum of

- or 2.40; oxygen per reactor 234

For higher oxygen contents, two-stage reactors have been used.

For tail gas decolourisation it is generally not necessary to reduce the free oxygen content in the system completely. For total elimination of pollution, however, the amount

of fuel used must be in excess of the stoichio- metric requirement.

Nitrogen oxide reduction catalysts for the Matthey Bishop system were developed in the pilot unit shown in Fig. 2. Both natural gas and purge gas (approximately 55 per cent H2) were used as fuels with equal success. Exam- ination of the catalyst after six months of operation showed no sign of deterioration.

The Matthey Bishop Apparatus and Systems Division have already installed the new catalytic tail gas reduction unit in several nitric acid plants having a combined capacity exceeding 1200 tons of acid per day.

The effectiveness of the installation is well illustrated in the photographs. Fig. 3 shows four stacks at the Lawrence, Kansas, plant of Cooperative Farm Chemical Association, each stack handling tail gas from one 120

tons per day nitric acid unit. In Fig. 4, the centre stack has had a Matthey Bishop THT catalyst unit installed and is free from fume. Since this photograph was taken

Fig. 4 .4fier a Matthey Bishop THT catalysl system had been installed at the base of the centre stack this is free.from fume. The other three stacks s d l emitting fume have since been

equipped with similar units and are now all completely clear


all four stacks have been equipped with catalyst units and are all completely clear.

Hydrocarbon and Organic Vapour Abatement

Unburned hydrocarbons and carbon monoxide, as well as a wide variety of organic solvents, present even broader air contamination problems than do the nitric acid tail gases. These include the effluents from engines, industrial paint baking ovens, print- ing presses, wire enamelling, solvent cleaning operations, solvent storage tanks, and from chemical reactions such as the manufacture of ethylene and ethylene oxide.

Miller and Wilhoyte (I) have recently compared the relative effectiveness of plati- nised spherical pellets, metal foils and ceramic honeycomb. The data reported cover hourly space velocities from 30,000 to 175,000 and temperatures from 150" to 450°C. Toluene and n-heptane were used as an experimental pollutants in concentrations up to 10 per cent of that corresponding to the lower explosive limit. This work clearly demonstrates the high catalytic efficiency and low resistance to gas flow of the honeycomb catalysts.

Matthey Bishop THT catalysts were eval- uated and have been found to be effective for completely oxidising these organic contami- nants. Other solvents such as xylene, methyl ethyl ketone and alcohols are also easily oxidised.

The chemical industry provides a large and diverse market for catalytic atmospheric pollution control systems. The production of floor tiles, asphalt, rubber, petrochemicals, wax, varnish, insecticides, comprise only a few of the industries where odour and smoke abatement problems may be effectively and economically controlled by the use of platinum honeycomb catalysts.

Hydrogen-Oxygen Recombination In nuclear power installations, intense

radiation causes the decomposition of water and the gradual rise in concentration of a

Platirzum Metals Reu., 1968, 12, (1) 6

hydrogen/oxygen mixture in a closed loop system. Safety considerations require that this should be prevented by continuously passing the gas through a hydrogen-oxygen recombiner. Platinum honeycomb catalyst has been found to be very effective for this conversion. Pellet beds have been used in the past for this purpose but their high pressure drop and the formation of fine dust in the presence of steam make them unattractive by comparison with the new platinum honeycomb catalyst.

Reference I A Study of Catalyst Support Systems for

Fume Abatement of Hydrocarbon Solvents, M. R. Miller and A. J. Wilhoyte, E. I. du Pont de Nemours & Company Inc., In- dustrial and Biochemical Department, Wil- mington, Delaware

Self-heating in Platinum Resistance Thermometry

Routine measurements of temperatures between -zoo and +850"C are carried out with high accuracy using platinum resistance thermometers, However, the measuring current itself causes heating in the platinum element by an amount proportional to the square of the current. Measurements re- quiring extreme accuracy or those where the measuring current is larger than the usual few milliamperes thus require correction for the self-heating effect.

Dr W. Diehl, of Degussa, Hanau, has now shown (ETZ-B, 1967, 19, (zz), 637-640) that the self-heating coefficient can be calculated by applying results of his tests on sealed platinum resistance elements. These tests measured the self-heating effect of such elements in still air, still water and running water. Using a test current of 3 milliamperes, results then were correct to within 0.008 to o.oz4"C in still water and to within 0.06 to O.II'C in still air at 20%. Self-heating due to other currents can be calculated from the self-heating coefficients in the tables which Dr Diehl has produced.

None the less, for the greatest accuracy, it is recommended that the platinum element should have the lowest possible resistance and that its self-heating coefficient should be determined under conditions similar to those which it will meet in practice.

F. J. S.

Dispersion Strengthened Platinum IMPROVED HIGH TEMPERATURE CREEP PROPERTIES

By A. S. Darling, P h n , G. L. Selman, B.s~. , and A. A. Bourne Research Laboratories, Johnson Matthey & Co Limited

Platinum containing small quantities of a dispersed carbide phase is stronger at high temperatures than many of the rhodium-platinum alloys produced by conventional techniques. It is stable under oxidising conditions and its valuable increments of strength are achieved without sacrijcing any of the desirable characteristics traditionally associated with the use of platinum as a structural element. The physical and mechanical properties of this new material are described in this article and some possible applications briefly reviewed.

Because platinum is the only metallic structural material capable of operating for long periods under strongly oxidising conditions at high temperatures, it is important to consider how these attractive characteristics can be still further improved. The range of elements suitable for solid solution strengthening at high temperatures is very restricted indeed. Poor oxidation resistance rules out all the base metal transition elements, and within the platinum group itself osmium, ruthenium and iridium-platinum alloys are unsuitable for high temperature applications

I500

z 2 1000 . m

Ln m W U

w 5 0 0 Ln

_I

m z w t-

-

0 REFERENCE I o REFERENCE 2

15OO0C 100 h

2 0 40 6 0 WEIGHT PER CENT RHODIUM

Fig. 1 Effect of composition on the ability of rhodium-platinum alloys to resist failure for periods of 100 and 1000 hours at high temperatures

because the oxides formed by these metals are extremely volatile. Severe surface erosion occurs in air and the intercrystalline failure caused by grain boundary oxygen penetration causes catastrophic failure after very short exposure to oxidation.

The natural tendency of pure rhodium to intercrystalline oxidation and failure at high temperatures can, however, be brought within manageable proportions by dilution. This, in essence, was the conclusion arrived at by Le Chatelier when he invented the 10 per cent rhodium-platinum : platinum thermocouple. It has since been established that the optimum creep properties of the rhodium- platinum solid solutions are exhibited by the alloy containing approximately 25 per cent by weight of rhodium.

The effect of composition on the ability of rhodium-platinum alloys to resist failure in air at high temperatures is illustrated by the curves in Fig. I (I, 2) which provide a good example of the law of diminishing returns so far as solid solution strengthening is concerned. Many experiments have shown that the prospects of obtaining, by alloying, high temperature properties superior to those of the 25 per cent rhodium-platinum alloy are rather limited. Ternary additions to the binary solid solutions have met with limited


THORIATED PLATINUM

. m

Lo Lo w

4 Lo 10 I00 I000

TIME HOURS (LOG SCALE 1

Fig. 2 Stress rupture data on thoriated platinum wires compared with those of pure platinum and rhodium-platinum wires produced by conventional

methods

success, and it has been found that marginal improvements tend to disappear in air temperatures above 1250°C.

Considerations of this sort lead naturally, therefore, to the idea of platinum strengthened, not by alloying, but by a finely dispersed non-metallic phase.

Dispersed Phase Strengthening General interest in the possibilities of dis-

persion strengthening was first aroused by the development of oxide-strengthened aluminium products such as SAP (3) which displayed remarkably high mechanical properties at temperatures approaching the melting point of aluminium. Subsequent work on dispersion strengthened copper and nickel has so far met with little commercial success largely because the mechanical properties of these materials become superior to those of conventional alloys only at temperature levels where catastrophic oxidation precludes their employment.

Platinum, however, being the only metal which is immune from these oxidation diffi- culties, becomes the logical candidate for dispersed phase strengthening and the results now being obtained suggest that considerable applications exist for this type of material.

Oxides, which when considered in isola- tion, appear to be the stablest type of compound have been extensively employed in dispersion strengthening studies. Thoriated platinum was introduced as long ago as 1942


(4) as a logical extrapolation of techniques well established in the lamp industry. As shown by the curves in Fig. 2 it provides pure platinum with a substantial increment of high temperature strength although the properties of conventionally produced rhodium-platinum alloys are not exceeded (5). Many other oxide dispersants for the Strengthening of platinum have since been proposed (6).

Carbide Dispersants Basic studies in the Johnson Matthey

Research Laboratories showcd several years ago that the free energy of formation of a compound provided little indication of what its stability would be when completely sur- rounded by a matrix of platinum. A rather surprising result of this investigation was the finding that carbides strengthened platinum more effectively than oxides (7) and that this strengthening effect could be achieved with concentrations of dispersant so low that the ductility, workin characteristics and elec-

not seriously impaired. This was a conclusion of great practical importance as some of the oxide strengthened platinum com- posites described in the literature contained up to 12 volume per cent of dispersant (8) and it seemed most unlikely that these cermet- like materials would satisfy many of the industrial requirements for platinum.

trical properties '1 of the platinum were

0 3 5 r I I

2 0 10 10°/o RHODIUM PLATINUM

0 0 5 DISPERSION STRENGTHENED PLATINUM

I 10 100 I000 TIME HOURS (LOG SCALF!

Fig.. 3 Creep curve of dispersion strengthened platinum stabilised with a rejractory carbide compared with those of pure platinum and 10 per cent rhodium-platinum produced by conventional meth-

ods. Temperature 14OO"C, stress 750 lblin?

Fig. 4 This microstructure of Fig. 5 Microstructure of plat- Fig. 6 Platinum wire contain- a pure platinurn wire affrer inum wire with a titanium ing 0.2per cent of thoria which heating at 1400'C shows the carbide dispersion which has has recrystalliscd at 1400°C very large grain structure recrystnllised at 1400°C after after being subjected to a reduc- developed i n the material being subjected to a 95 per cent tion in area of 95 per cent by

drawing ( x 150) ( x 150) reduction in area by cold cold drawing ( X 150)

Titanium carbide when dispersed in platinum to the extent of 0.04 to 0.08 per cent by weight was found to confer very interesting properties. Fig. 3 shows some typical creep curves obtained on + inch diameter wires, tested in air at 140oCC. Under a tensile stress of 700 p.s.i. pure platinum wire obtained by drawing down a conventionally cast ingot endures for 30 to 60 minutes before failure. The life of the comparable 10 per cent rhodium-platinum wire, approximately 50 hours, is rather higher than that of the thoriated platinum wires produced from powder, whereas the carbide stabilised platinum wires last for about 1000 hours in the same stress and temperature conditions.

Discrepancies between the creep test results provided by sheet and wire specimens prompted a detailed microstructural examination of many dispersion strengthened platinum test pieces which had failed at high temperature. The vast majority of such failures, it was found, originated at grain boundaries, particularly those disposed transversely to the tensile stress axis. Although the reasons for this high temperature grain boundary weakness are still imperfectly understood, it was concluded that all transversely disposed boundaries should be re- garded as potential sources of weakness, and a method was sought which would develop a grain structure having the lowest proportion

of grain boundary area in the direction most likely to be normal to the tensile stress axis.

Working and Reerystallisation Textures

Suitable grain structures were obtained by cold working and annealing procedures designed to produce highly developed recrystallisation textures (9). Platinum wires containing 0.04 per cent of titanium carbide, when subjected to a cold reduction of 95 per cent in area by drawing through a die, invariably recrystallised at 1400OC to produce a highly orientated grain structure in which only one- tenth to one-twentieth of the total boundary area was transversely disposed to the axis of the wire. Fig. 5 illustrates such a microstructure having highly elongated grains in which little evidence of a dispersed phase can be detected with the optical microscope. A correspondingly treated platinum wire containing 0.2 per cent of thoria is shown in Fig. 6. In spite of the higher proportion of dispersed phase this material has not developed such strong recrystallisation textures and the tendency of the thoria to agglomerate reflects itself in the inclusions present in the microstructure. Fig. 4 shows for comparison, the microstructure of pure platinum wire after similar treatment.

The effect upon the resultant creep properties of this working plus recrystallisation


Fig. 7 Microstructure of sheet, recrystatlised at 1400°C afier the ingot f r o m which it had been produced ‘IL’US cold simged before cold rolling. The total reduction imposed by cold

working was 90 per cent ( X 150)

Ingot No.

procedure can be observed from the test results given in Table I obtained from small powder metallurgy ingots containing 0.04 per cent of titanium carbide. After sintering for three hours at 1400’C these ingots were hot forged and finally reduced to sheet by cold rolling. The carefully machined sheet test pieces were stressed in tension at 1400°C in air.

Micro-examination of the sheet after creep testing showed a highly elongated grain structure in material from ingot 3, significant elongation in sheet from ingot 2 and a little if any elongation in sheet from ingot I.

Processes such as swaging and wire drawing which deform the metal simultaneously in two directions are particularly effective in inducing those working textures which en-

Method of fabrication

Table I

I

2

3

Directly cold rolled after hot forging

Directly cold rolled after hot forging

Ingot cold swaged before cold rolling

Zold work total

reduction per cent

5 8

86

86

Platinum Metals Rev., 1968, 12, (1)

Life in hours a! 700 p.s.1. 1400°C

I00

200

620

10

Fig. 8 Microstructure cf sheet, recrystallised at 1400°C after the ingot from which it had been produced was directly cold rolled. The total reduction imposed by cold ivorlring zuas

90 per cent ( x 150)

courage the development of a highly aligned recrystallisation texture. Fig. 7 shows the pronounced recrystallisation texture of sheet from an ingot which has been cold swaged before rolling, the total cold reduction being 90 per cent in area. Although swaging and drawing are not appropriate working procedures in sheet production, flat cold rolling alone does not result in such an elongated grain structure when the sheet is finally annealed. As shown in Fig. 8, sheet which has merely been reduced go per cent in thickness by flat cold rolling recrystallises to produce grains, which, although elongated, are not so completely aligned as those of the partly swaged material. Although not so outstanding as those of wire the creep properties of dispersion strengthenedplatinum sheet, as shown in Table 11, represent a very considerable improvement over those of conventionally produced 10 per cent rhodium-platinum sheet, being comparable to those of the alloy containing 25 per cent rhodium.

Dispersion Strengthened Alloys Although dispersion strengthened pure

platinum has mechanical properties superior to those of the rhodium-platinum alloys many applications can be envisaged where the alloy characteristics are necessary for reasons other than strength. Furnace windings provide a typical illustration, in which the electrical

r

Table II Stress/Rupture Characteristics of Dispersion Strengthened Platinum Wire and

Sheet Compared with Pure Platinum

strengthened Pt,

700 1400 2800

Tensile stress, 1b/ine2

Minimum life, hours

Dispersion strengthcned Pt, 1 sheet

700 1400 2800 700 1400 2800

50 10 1 1000 lo00 100

1 700 1400

150 30

resistivity and low temperature coefficient of rhodium-platinum alloys are necessary for successful heating and current control although any improvement in strength at high temperature is obviously very valuable.

For this reason the dispersion strengthening technique has been applied to the 10 per cent rhodium-platinum alloys. As shown by the typical properties given in Table 111, this material exhibits an outstandingly high resistance to creep.

Mechanical and Electrical Properties

Metals and alloys of this type, which contain only a small quantity of a dispersed phase, display greatly improved mechanical properties and resistance to creep with no significant change or sacrifice of the other properties. This valuable and important characteristic is illustrated by the physical properties given in Table IV. Although the dispersion strengthened materials commence to soften at much the same tempcrature as their conventionally produced counterparts they retain a much higher level of hardness to

much higher annealing temperatures and display a pronounced “hardness/temperature” plateau. The electrical properties of platinum containing small quantities of carbide are similar to those of pure platinum.

Applications Where improved high temperature proper-

ties are required dispersion strengthened platinum or platinum alloys could offer considerable advantages over conventionally produced materials. In many instances they could be strong enough to be used in place of a more expensive rhodium alloy with conse- quent economy. In other applications dispersion strengthened platinum components could be run at higher temperatures with con- sequent savings in time and increased output.

Dispersion strengthened 10 per cent rhodium-platinum wire could function effectively as a furnace winding and reduce considerably the incidence of premature failure. Although high tensile stresses are not usually associated with the operation of resistance furnace elements appreciable creep occurs during heating and cooling because of the

Table Ill Stress/Rupture Characteristics of Dispersion Strengthened and

Conventional 10 % Rhodium-Platinum Wire

I Conventional Dispersion strengthened alloy alloy


Pure Pt, wire

Pure Pt, wire

Dispersion strengthened Pt,

wire

Tensile stress,

Minimum life,

I b / h 2

hours

Tensile stress,

Minimum life,

I b / h 2

hours

Table IV Fhysical Properties of Dispersion Strengthened Platinum and a

Rhodium-Platinum Alloy

Specific resistance

Temperature coefficient

U.T.S. (annealed)

Elongation (annealed)

Melted Pt

21.4 gms/cc

10.6 ILkm

.0039z per "C

10 tons/in.

40 % 22 x 106 lb/in.2

Dispersion strengthened

Pt

21.288 gms/cc

12.0 p*ncm

.0036 per "C

13.8 tons/in.l

35%

23 x 1o6 lb/in.z

differential thermal expansion between the winding and its refractory support. The electrical properties are so close to those of the conventional alloy that the improvement obtained with the dispersion strengthened wire in this application would be attributable to the high stability of the recrystallised grain structure and its increased mechanical strength at high temperatures.

Another possible application for dispersion strengthened 10 per cent rhodium-platinum is as the gauzes used for the oxidation of ammonia to nitric acid. There is no reason to suppose that the catalytic activity is not at least as high as that of gauzes made from the conventional melted and cast alloy. There are indications that less distortion occurs and that the rate of metal loss observed at about 850°C is lower than that of either pure platinum or 10 per cent rhodium-platinum, but this subject needs closer study.

The electrically heated wires used for igniting gas burners represent another application where catalytic activity and strength at high temperatures are required; promising results have been obtained with dispersion strengthened 10 per cent rhodium-platinum.

Although the pure platinum crucibles in which optical glass is currently melted yield a product of satisfactory quality they would


Melted 10% Rh-Pt

20 gms/cc

18.4 pncm

.m17 per "C

21 tons/in.2

35 yo

27 x I O ~ 1b/h2

Dispersion strengthened 10% Rh-Pt

I

19.862 gms/cc

21.22 pfkm

I .0016 per "C

I 28 x 106 1b/hz

perform more effectively and economically if they were stronger at high temperature. Dis- persion strengthened platinum offers the possibility of high temperature properties comparable to those of the higher rhodium- platinum alloys with no danger of glass dis- coloration. The extent to which these advantages can be utilised will depend upon the glass/metal wetting characteristics which are found to obtain and also on the availability of wide sheets of metal.

The applications so far described have been those in which the platinum works at a temperature level where its high strength can be attributed to the development of a well- defined recrystallisation texture. In this range the possible use of dispersion strengthened platinum for the manufacture of thermocouples and of resistance thermometer elements must also be considered although more work will be required before its suitabil- ity for such purposes can be properly assessed.

The welding and joining of dispersion strengthened platinum is a subject currently receiving a great deal of attention. Con- ventional fusion welding destroys the uniform array of fine carbide particles upon which the high temperature properties of this material depend, and any joints made in this way should be situated in the low-stress, low-

Specific gravity

Specific resistance

Temperature coefficient

U.T.S. (annealed)

Elongation (annealed)

Modulus of elasticity

at 20°C

0-r0o"C

(annealed)

temperature regions ofthe apparatus involved this respect dispersion strengthened platinum Where the ~ ~ c h a n i c a l d m m ~ d s imposed behaves like the more conventional materials will be less severe. Alternative methods of of engineering construction. joining such as resistance welding, electron

References beam welding and high temperature brazing I G. Reinacher, Metall, 1963, 17, 699

are now being assessed On a laboratory basis. z H. Albert, D. Accinno and J. S. Hill, Refractory During most of its working life high Metals and Alloys, New York, 1961, p. 465 - . .

temperature platinum and rhodium-platinum apparatus of the normal type operates in the tertiary stages of creep and within such a

3 R- Irmann, MetallW?ia, 1952~46, (275) r25

5 Unpublished data, Johnson Matthey Research B'P. 5783956

Laboratories context it is natural to expect and to tolerate 6 B.P. 645,681 645,682, 646,002, 646,003,

7 B.P. 830~628 persion strengthened 8 A. S. Bufferd, K. M. Zwilsky, J. T. Blucher, distort to the same extent. The linear N. J. Grant, Internat..Y. Powder Metall., 1967.

considerable sagging and distortion. Dis- 646,004J 645,541, 755,835

does not - ~ ..

elongations which occur before failure at 3> (Ix r7-26

15973164 9 B.P. Application Nos 10239/64, 11886/64,

1400'C are usually about 13 per cent and in

Platinum in Austenitic Stainless Steel The effects of adding 0. I to 3.0 per cent of

platinum to 18-12 austenitic stainless steel on the corrosion behaviour of the steel in superheated steam, normal sulphuric acid, and boiling magnesium chloride solutions have been studied in the course of a U.S./Euratom research and development programme carried out in Paris under the direction of Professor G. Chaudron (I).

Electropolished samples were maintained in an autoclave for 1000 hours in superheated steam at 500°C and 50 kg/cm2 (710 lb/in.2). Addition of 3 per cent of platinum to a high purity steel containing 20 p.p.m. of carbon reduced the amount of oxide formation in these circumstances dramatically, the gain in weight being reduced from 122 to 9 mg/dm2. In subsequent tests on an industrial vacuum- cast steel containing 90 to IOO p.p.m. of carbon, maintained for six days in superheated steam at 600°C and 70 kg/cmz (995 Ib/in.2), the corrosion rate of 125 mg/dm was reduced about 20 per cent by the addition of I per cent of platinum.

The corrosion of platinum-containing stainless steels in sulphuric acid has been the subject of several studies in the past and the results of these are broadly confirmed by potentiokinetic observations here reported in air-free normal sulphuric acid at 25°C. The hydrogen overvoltage, although unaffected by the addition of 0. I per cent of platinum to the steel, is considerably reduced by 1.0 per cent of platinum.

In these environments the increased corrosion resistance of the platinum-bearing steels is accompanied by changes in the character of the surface films. On commercial stainless steels, the films consist of two layers of nearly equal thickness, the outer one being crystallised and relatively soft and the inner being much more compact, harder, and more corrosion resistant. In steels of low carbon content, the inner layer becomes subject to intergranular oxidation, but platinum additions yield a thinner and perhaps tougher and more protective inner film, quite free from a tendency to intergranular oxidation.

In boiling magnesium chloride, the film formation due to platinum additions induces passivation (presumably reducing overall corrosion) but increases the tendency to stress corrosion (perhaps at grain-boundary dis- continuities). In samples stressed at 35 kg/mm2, the life was reduced from six hours to three hours by 0.1 per cent, and to one hour by 1.0 per cent of platinum.

It should perhaps be recorded that a brief note in the report disclaims the implication that the effects of platinum additions are confined to improving the protective nature of the surface films-the possibility that they may also improve the inherent corrosion resistance of austenite is not excluded.

I G. Chaudron, U.S./EURATOM R & D Prog- ram, Project No. 293. EURAEC Reports 1749 and 1804

J. C. C.


platinum

Palladium Telephone Contacts A NEW SERIES OF MINIATURE WIRE SPRING RELAYS

Relays have been called the building blocks of telephone systems, and in spite of the liberal use of semiconductor devices in the exchanges now building, very large numbers are still needed both for circuit functions as well as for making connections to existing equipment.

The relays for the central offices of the future will, however, need to be smaller than in the past-not only on account of the increasing pressure on space in telephone plant but especially so that they may be suitable for mounting on the printed wiring boards which carry the small diodes and transistors.

To meet these demands a new family of miniature wire spring relays has been designed by the Bell Telephone System and the Western Electric Company of America. Their development and characteristics are described by C. B. Brown (Bell System TechnicalJ., 1967, 46, (I), 117-147)~ who provides a fascinating account of the efficient way in which the many special requirements have been fulfilled. The method of ensuring constancy of contact pressure, independent of inevitable variations in the angle between the spring wires during assembly, is particularly noteworthy.

The small size of the new miniature wire spring relay designed by Bell Telephone Laboratories can be appre- ciated by comparison with the established type of older wire spring relay

In choosing a contact material the long experience of the telephone industry in the use of all the common contact materials in many shapes and sizes was available, and provided firm evidence that palladium has always given the best all-round performance in their switching devices. It has further been established that a thin layer of gold on one only of each set of opposing contacts is completely effective in suppressing polymerisa- tion effects.

The detailed design of the contacts is shown in the diagram. Each circuit is controlled by two independent spring-supported movable contacts operating as a pair against one fixed contact. With twin contacts the risk of “open circuit” failure is virtually negligible. The fixed contact is formed with a cylindrical surface to reduce the possibility of dust particles lodging between the operating faces and is made from a sandwich material. This has a nickel core coated on each side with palladium with thin outer layers of gold. At the centre, the combined thickness of palladium and gold amounts to 0.009 inch.

The movable contacts are made from solid palladium strips, o.mo inch wide and 0.010


The contact arrangement in the miniature wire spring relay

inch thick, welded longitudinally to the phosphor-bronze spring wires.

Adjustment and maintenance of the contact assemblies have been made simple and straightforward and the contacts are readily cleaned by moving a strip of lint-free parch- ment paper, moistened with a solvent, between the surfaces.

With a non-inductive load or with proper protection on inductive loads, the life of these contacts is confidently expected to be equal to or greater than the mechanical life of the relay-at least 200 million operations.

J. C. C.

0 14-

PHOSPHOR BRONZE SPRING WIRE

'\ OPERATING CARD

FIXED / CONTACT i

M O V I N G CONTA C T

Ultra-pure Hydrogen from Water AN ELECTROLYTIC DIFFUSION CELL

Hydrogen of high purity is frequently needed for specialised laboratory processes where the total demand does not justify the installation of hydrogen cylinders, thermal diffusion cells and their associated control gear.

Such requirements, it was suggested by A. S. Darling in 1963 (PZutinum Met& Rev., 1963, 7, 126), might well be satisfied by the use of small electrolytic diffusion cells fitted with silver-palladium alloy cathodes. Metals Research Limited, of Cambridge, have now engineered such a self-contained portable electrolytic cell, known as the GASPAK-H, based on Johnson Matthey's British Patent

In developing a commercial unit from the laboratory prototype, numerous improvements have been introduced. The cell is thermostatically controlled and the cathode is an assembly of silver-palladium tubes. An internal de-ioniser protects the cell itself from water-borne contamination and fully automatic pressure switches, level controls and safety devices make it suitable for permanent

973,810.

The portable electrolytic hydrogen generator developed by Metals Research Limited

connection, if required, to water and electrical supplies.

The GASPAK sits comfortably on any bench and will produce up to 150 ml per minute of hydrogen at pressures up to 100 p.s.i. When operated as a portable unit its reserve capacity of two litres of water permits five days' continuous operation at full capacity. Its controlled output is very suitable for gas chromatography, small sintering furnaces, or for hydrogenation experiments in organic chemistry.


The Platinum Metals in the Production of Laser Crystals By B. Cockayne, B.SC., Ph.D., A.1nst.P.

Royal Radar Establishment, Great Malvern

Because of their high melting points and lack of chemical reactivity with oxide materials at high temperatures, several of the platinum metals are very useful as container materials for molten oxides. This article describes the use of platinum, rhodium and iridium in the vertical pulling of oxide crystals from the melt. Such crystals form the basis of many solid state lasers and other electronic devices.

Platinum has been used for many years as a crucible material in the solution growth of oxide crystals from solvents such as motlen PbF,/PbO mixtures in the temperature range 900" to 1400°C. These crystals are often small (maximum dimension < I cm) and contain trapped solvent which makes them impure and optically imperfect. With the advent of

demanded solutions to the problems of growing at temperatures in the region of 200o0C under oxidising conditions, and the platinum metals have played a substantial role in the success achieved.

An illustration of the apparatus used for oxide single crystal growth is given in Fig. I

and the actual growth of a calcium tungstate the solid state laser, the requirement arose for larger oxide crystals (typically 5 cm long by I cm diameter) with a very high degree of optical perfection and chemical purity. As a consequence, considerable effort has been devoted to the vertical pulling of oxide crystals from their own melts, because this technique had been used successfully to grow large perfect crystals of semiconducting materials such as silicon, germanium and indium antimonide. The development of the vertical pulling technique for oxides has

Jp

F-

Fig. 1 Schematic representation of the apparatus used for the vertical pulling of oxide single crystals:

-

A iridium crucible - B iridium heat shield C rhodium-platinum heat shield D r.J coil

F refractories G direction of gas j l o i o H direction of pull I direction of rotation

\T E Y

E melt F-

J silira envelope [z!

r* G

-- C

Platinum Metals Rev., 1968, 12, (l), 16-19 I 6

Fig. 2. A single crystal qf calcium tungstate being vertically pulled from an iridium crucible at approximately 1600°C

crystal from an iridium crucible is shown in Fig. 2. Essentially, a seed crystal of the same composition as the melt, or an inert material such as an iridium rod, is dipped into the melt. At the optimum temperature, solidification can be made to occur by slowly with- drawing and rotating the seed under carefully controlled conditions, thereby growing a crystal. If an inert rod is used, polycrystalline growth generally occurs, but single crystal growth can be achieved by reducing the diameter of the polycrystalline aggregate until only one crystal is growing. The process of reducing the crystal diameter is also often employed when a single crystal seed is used in order to minimise the propagation of defects from the seed into the crystal. The crystal diameter is controlled mainly by adjusting the heat input to the melt, and the seed crystal can be made to grow out to the required diameter after the necking procedure by reducing the power supplied to the crucible.

As radio-frequency heating is the most commonly used source of power and since oxide materials are generally insulators, the crucible used to contain the melt must also act as a susceptor. Because of the insulating nature of the melt, steep radial temperature gradients exist and the crucible wall is therefore at a higher temperature than the melt centre, which is required to be at or slightly above the melting point of the oxide material. The crucible material chosen for a particular oxide must therefore have a considerably higher melting point than the oxide. The oxides of major optical interest are listed in the table together with their uses and the most suitable crucible materials.

With the higher melting point materials such as sapphire and spinel, the radial temperature gradients can reach 300°C cm-I, and radiation shields or afterheater assemblies are therefore required to minimise the gradients so as to avoid crucible failure before the oxide


is fully molten. These shields are also made of iridium and are shown in the general photograph of platinum metal ware used in the growth of oxide crystals, Fig. 3. The reduction in temperature gradients achieved with the shields and with afterheaters also reduces the thermal stresses to which the growing crystals are subjected, thereby minimising strain (I) . This is particularly important in the growth of anisotropic materials such as calcium tungstate and sapphire because dis- location generation readily occurs if the thermal stresses are allowed to exceed the yield stress of the material. Subsequent polygonisation leads to the formation of low angle boundaries, which impair the optical perfection of the crystal by presenting small changes in refractive index to a light beam passing through the crystal.

In the growth of oxides the oxidation resistant properties of the platinum metals are particularly useful. For instance, lithium niobate must be grown in an atmosphere of IOO per cent 0, to avoid decomposition and platinum is therefore the only suitable crucible material. For the same reason, calcium tungstate and sapphire require small concentrations of oxygen (0.1 to 4 vol. per cent) in an otherwise inert atmosphere. In these cases the iridium crucible is slightly oxidised but

the gas flow can be arranged so as to sweep any iridium oxide formed away from the melt surface. If no such precaution is taken, iridium platelets become entrapped within the crystal and act as light scattering centres.

Float Zoning Oxide single crystals can also be grown by

a modified floating zone recrystallisation technique (2). In this method growth is achieved by moving a resistance heated strip, made of the platinum metal appropriate to the melting temperature of the crystal required, in a controlled manner up into a sintered charge rod. The melt thus formed flows through a hole in the strip on to the seed crystal below, where solidification takes place. The seed crystal is maintained at a temperature slightly lower than that of the strip by either a rhodium-platinum or an iridium wound resistance furnace, according to the temperature required. Crystals with melting points up to and including that of sapphire have been grown by this method (3).

Ancillary Uses In addition to their direct use in crystal

growth, the platinum metals also play an important role in ancillary studies leading to the growth of either new or more perfect

1 M

1 Oxides of Major Optical Interest and their Most Suitable Crucible Materials 7 Material

Lithium Niobate (LiNbOJ

Calcium Tungstate

Yttrium Aluminium Garnet (Y,AI,O,,)

1 .

M.P. ("C)

I250

1566

1970

2050

2105 --

Crucible

Platinum or rhodium- platinum

Rhodium or iridium

Iridium

Iridium

Iridium

Material Use P Electro-op tics

Laser host for Nd3+

Laser host for NdS+

1

I Possible laser host I

Sapphire and spinel are also used as insulating substrates for the epitaxial deposition of silicon


Sapphire (AlzOs)

Spinel (MgA1,0,)

Laser host for Cr3’ Laser host for Cr3’

Laser host for Cr3’

Fig. 3. Platinum metal ware used in the growth of oxide single crystals a) Iridium and platinum crucibles b) Iridium heut shields

single crystals. For example, certain impuri- The metals platinum, rhodium and iri- ties in calcium tungstate can be removed by dium thus play an important part in the zone-refining this compound in an iridium major growth techniques now used For boat, again using radio-frequency heating as forming single crystals of high melting point the source of power. The high temperature oxides, many of which act as host lattices for thermocouple materials such as iridium: laser ions.

c ) Iridium rod d ) Iridium boat e ) Iridium strips forfloat zoning

iridium-rhodium have also been useful in determining the phase relationships in mixed garnet systems such as Y3A15012 - Gd~'%Oiz and Y,AI,O,, - Dy3A15012, where the melt-

1850" to 1970°C.

References I W. Bardsley and B. Cockayne, Conf. Proc.

I.C.C.G. Boston (1966) Published as Suppl. toy. PhYS- Chem sol-, 'g67J P. I09

ing points lie within the temperature range 2 D* B. GassonJ.7. SCi. Immum., 1965, 4'J 114 3 B. Cockayne, M. Chesswas and D. B. Gasson, 3. Mater. Sci., 1967, 2, 7

Ruthenium as a Methanation Catalyst The value of natural gas for domestic

heating and for industrial power has long been recognised, but in areas of the world not endowed with a convenient supply some alternative economic source of methane is required. The steam-reforming of higher hydrocarbons (for example, "light petroleum distillate" obtained from mineral oil), or the reaction of steam with carbon, yields a mixture of carbon monoxide and hydrogen from which methane may be produced by catalytic hydrogenation. What is then required is a catalyst that will perform this hydrogenation economically, and this must be a catalyst which is not particularly susceptible to poisoning by carbon monoxide.

A recent report from the United States Bureau of Mines (J. F. Shultz, F. S. Karn and R. B. Anderson, U.S. Dept of the In- terior, Bureau of Mines, R.I. 6974, July 1967) has re-emphasised the outstanding catalytic

properties of ruthenium for carbon monoxide hydrogenation. The authors compare catalysts containing ruthenium, rhodium, platinum, palladium and osmium, but of all the catalysts examined only the ruthenium on alumina catalyst was adequately active. I t achieved complete reaction at 220 to 24ooC, whereas palladium and platinum failed to do this even at -joo"C. The kinetics of the reaction using the ruthenium catalysts were examined in some detail : the rate increases with increasing hydrogen pressure and is slightly decreased by increasing carbon monoxide pressure. High molecular weight products appeared only when the H,/CO ratio in the feed gas fell below two; catalyst poisoning only became important when this ratio fell below unity. The authors concluded that the use of ruthenium For carbon monoxide methanation was economically feasible.

G. C. B.


Platinum and Palladium Electrodeposits on Refractory Metals AQUEOUS ELECTROLYTES TO YIELD THICK COATINGS

The platinum metals are well known for their resistance to oxidation and chemical corrosion over a wide range of temperatures, these properties being exhibited to a higher degree than for any other metal. However, economic considerations prohibit the total construction in these metals of large parts for arduous duty at high temperatures and it has been the practice to utilise the mechanical properties of the refractory metals and to protect the surfaces against oxidation by cladding with platinum or its alloys. It is difficult to construct complex parts in this manner, and thus there is a need for electrodeposition systems capable of yielding substantial thicknesses.

Platinum group metal plating baths have been in use for many years in the jewellery industry and more recently in the production of contact surfaces in electronic and com- munication equipment. Here, however, the coatings are thin (for jewellery less than 50

micro-inches and for contacts from 50 to 300 micro-inches) and the solutions in use generally give cracked deposits at thicknesses in excess of 500 micro-inches.

A recent study at the U.S. Bureau of Mines by S. D. Cramer, C. B. Kenahan, R. L. Andrews and D. Schlain (R.I. 7016, September 1967) has examined the use of the previously available proprietary electrolytes for deposition on refractory metals such as niobium, molybdenum, tantalum, titanium, tungsten, vanadium and zirconium at thicknesses in excess of 2000 micro-inches. In almost every case they were found to be inadequate in the sense of producing either non-adherent or heavily cracked plates. Three platinum and two palladium formulations were, however, found to be more successful, and these solutions are set out in the table. Deposits of 0.010 to 0.020 inch were produced, but the platinum electrolyte No. 2 was chemically unstable and was not finally recommended.

Electrolyte designation

Platinum electrolyte No. I

Platinum electrolyte No. 2

Platinum electrolyte No. 3

Palladium electrolyte No. I

Palladium electrolyte hTo. 2

Platinum Group Metal Electrolytes

Constituents Concentration

6-40 811 20-100 g/1 6-40 g/l 10-100 ml/l 10-100 ml/l 8 4 1 1.25 g KOHlg Pt

Tem- perature "C

65-100

75-100

70-80

25-85

85-100

Cathode xrrent density A/ft2

5-100

5-30

7.5

5-50

20-30 __

Anode

Platinum

J,

Palladium


The authors point out that the pre-treatment of the refractory metal is of the utmost importance, total failures occurring when an inadequate procedure was employkd. Indeed a considerable part of the report is concerned with this aspect of the problem, and a table of procedures found to be satisfactory is included. Thick, adherent deposits of platinum and palladium could be formed on some metals after a cathodic pre-treatment in an alkali cyanide fused salt mixture containing platinum ions.

Stress measurements of the deposits were taken in a number of instances, and electron probe studies on the effect of high temperature anneals on interdiffusion are reported; little diffusion of the deposit into the substrate took place but diffusion of substrate into deposit was extensive.

This investigation adds a great deal to our knowledge of heavy platinum metal deposition and is to be commended to those working in this field.

J. H.

Effectiveness of Platinum Fuel Cell Catalysts POSSIBLE ROUTES TO IMPROVEMENTS IN ECONOMICS

Throughout the massive literature on fuel cell research and development run two con- sistently recurring but conflicting strains ; one, the acceptance of platinum as the most effective electrocatalyst, and the other the need to increase its effectiveness-and thus to reduce the amount of metal required- on economic grounds. This problem has been discussed at almost innumerable conferences, and will doubtless remain a lively issue for a long time.

A useful restatement of the position, together with some attempts towards a solution, are contained in three papers recently emanating from the General Electric Research and Development Center, Schenectady. In one of these E. J. Cairns and E. J. McInerney (J. Electrochem. SOC., 1967, 114, (IO), 980) set out the possible routes towards improving the economics of an otherwise feasible fuel cell system operating by the direct anodic oxidation of saturated hydrocarbons as :

‘(1) Make more effective use of the platinum by preparing higher area blacks.

(2) Prepare very high-area platinum on a support which can act as a current col- lector and perhaps also as an enhancement to the platinum activity.

(3) Alloy the platinum with other metals in such a way that more activity per unit weight of platinum is obtained.

(4) Replace the platinum with a less costly, but effective, electrocatalyst.’

These authors discount the fourth method, primarily on grounds of resistance to corrosion, and go on to report their work along

approaches (I) and (2). Both the use of higher activity forms of unsupported platinum, particularly one reduced from Adams’ catalyst, and the use of carbon-supported platinum were found to be more effective in reducing the amount of platinum required for a given amount of power. In the case of a propane-oxygen fuel cell, a carbon-supported platinum electrocatalyst was able to reduce the amount of platinum required by a factor of around 10 and the view is taken that further improvements are likely. In the two other papers from General

Electric, L. W. Niedrach, D. W. McKee, J. Paynter and I. F. Danzig (Electrochem. Tech., 1967, 5, 318 and 419), adopting approach (3), are concerned more with fuel cells operating on reformer hydrogen in which resistance to catalyst poisoning by the carbon monoxide impurity in the gas is of major importance. Ruthenium-platinum catalysts prepared by a modified Adams’ procedure were found to be markedly more resistant to poisoning than platinum, particularly in the temperature range 65 to 85”C, optimum performance being obtained with catalysts containing about 30 weight per cent ruthenium. The second paper reports similar work on iridium-platinum and rhodium- platinum catalysts, these also showing an exceptional tolerance for carbon monoxide in hydrogen. Such binary mixed oxides were first prepared, and found to have exceptional catalytic properties, by G. C. Bond and D. E. Webster (Platinum Metals Rev., 1965, 9, 12; 1966, 10, 10) in the Johnson Matthey Re- search Laboratories.

L. B. H.


Fifty Years of Research J

on the Platinum Metals By A. R. Powell, F.R.S.

Among the industrial concerns who were quick to appreciate the value of research to their business and future prosperity must be numbered the firm of Johnson Matthey. Before the end of World War I, and just after achieving the centenary of their foundation, the then directors of the company decided to establish a small Research Department and the present writer was invited to organise and develop it.

At this time industrial research in Great Britain was on a very small scale, and it was not until the early nineteen-twenties that a real impetus was given by the initial steps taken by government and industry in colla- boration to establish the early Research Associations.

At this time too the output of platinum and its allied metals was by today’s standards extremely small and their industrial uses were few. The greater part of the world’s supplies still came from Russia, although increasing amounts were becoming available from the

The very early Ajax- Northrup high frequency induction furnuce acquired i n 1919 for research into the melting of platinum. The problem of suitable crucible material mas solved by the use, for thejrst time, of zircon

Mond process of recovering nickel from the nickel-copper ores of Sudbury, Ontario, and for some years these had been refined by Johnson Matthey.

The production of nitric acid by the oxidation of ammonia over platinum gauze catalysts was yet to be established at Billingham; viscose rayon production by Courtaulds and others, needing platinum alloy spinnerets, was in its infancy, and the use of thermocouples was virtually confined to heat treatment processes and laboratory work. The melting of glass in platinum, originating with Faraday’s studies, had not yet been adopted in industry, while the demand for electrical contacts in the platinum metals was chiefly represented by the automobile magneto. In 1918 the methods used for refining,

melting and working platinum differed very little from those used in the middle of the nineteenth century. Repeated precipitation of ammonium chloroplatinate with intermediate calcination and re-dissolution of the


m a n of23, was invited by the directors of Johnson Matthey to j o i n the company and to establish a Research Department. From small beginnings the department grew over the years, and M Y Powell remained at i ts head until 1954, when he became Consulting Research Chemist to the company. l i e retired f r o m active duties in 1960 but is still associated with the laboratories on a consulting basis. H e was elected a Fellow of the Rqyal Society in 1953 f o r his work on the chemistry of

the plnt inum metals. I n this article M Y Powell looks back on $fly years of research in this $eld and contrasts some of the methods and equipment

crude metal in aqua regia formed the basis of the method for obtaining the pure metal, which was then prepared for working either by melting with an oxy-hydrogen flame in a furnace made from two blocks of calcined marble, or by consolidation of platinum powder by heating and forging into an ingot. Lime-melting was used chiefly for making platinum alloys for electrical contacts and scientific apparatus, while powder metallurgy ingots were used for making pure platinum sheet for crucibles, dishes, electrodes, large vessels for chemical manufacturers and for making pure platinum wire for thermocouples and resistance thermometers.

The Beginning of Induction Melting

With the invention of the Ajax-Northrup high-frequency induction furnace just after the end of the war, Johnson Matthey were attracted to the feasibility of its use for melting platinum and a furnace was purchased

Today the research metallurgists have available to them modern vacuum melting furnaces for investigations on ihe platinum metals and their alloys

late in 1919, the first to be used in this country. The question of what kind of crucible to use for the melting operation was the first major problem put to the young Research Department and was solved in a relatively short time by the use of purified zircon sand which was carefully ground and graded into different grain sizes, which were re-blended in suitable proportions with a temporary binder and water to give a paste which was shaped on a potter’s wheel; after drying and


On February 11th, 1918, A. R. Powell, a young

of the early days with modern research facilities.

The Hilger medium spectrograph purchased in 1920, initially for the determination of iron in rhodium. Since that time a wide range of spectrographic instruments has been inssdled

firing at the full heat of an oxy-gas burner, crucibles were produced in which up to 50 melts each of IOO oz of pure platinum were made before failure. These were the first zircon crucibles ever made and they were used for the first melting of platinum on a commercial scale in an electric furnace.

The First Spectrograph Investigations on the accurate measurement

of high temperatures with platinum : rhodium- platinum thermocouples in 1920 showed that many couples gradually altered in calibration during long use. The presence of iron in the rhodium used for alloying was suspected but chemical methods of analysis did not yield convincing results. In that year the company therefore purchased its first spectrograph- one of the first batch produced by Adam Hilger-and the determination and thence the elimination of the iron impurity were quickly achieved.

The remarkable improvement in purity of rhodium produced by the new process incited a thorough investigation of the older processes of refining all the platinum metals and during the next four years the Research Department was engaged on this work. New methods for refining ruthenium, osmium and iridium to spectrographic purity were first developed and attention then turned to a study of platinum refining. A number of improvements were made to the processes, and the resulting platinum had an CL value


of 0.003922, higher than that of any platinum available commercially at the time and indicating a very high degree of purity.

At about this time the Research Laboratory made its first move, taking over two more rooms in the Hatton Garden premises, and increasing its small staff. Among these were E. C. Deering-later to become a director and eventually chairman of the company-and E. li. Box, later to become general manager of the company’s factories in thc Stoke-on- Trent area.

Refining of South African Platinum

The next major problem to be tackled by the Research Department was the treatment of the South African platinum ores. During the years 1924 to 1928 large deposits of platinum-bearing rocks had been discovered all over the Transvaal, but containing payable amounts of platinum only in certain areas mainly in the neighbourhoods of Lydenburg, Potgietersrust and Rustenburg. In these ores the platinum metals were associated with the sulphides of nickel, copper and iron and to that extent resembled those of the Sudbury district in Canada, but were much poorer in copper and nickel and much richer in the platinum metals. Considerable technical problems arose in devising suitable methods of treatment, while the proportion of values recovered compared very unfavourably with that obtained in the working of alluvial de-

posits. Large samples of the concentrates were therefore sent by the mining companies concerned to the Krupp Grusonwerk at Magdeburg, to various American refiners, to the Chemical and Metallurgical Corporation at Runcorn and to Johnson Matthey.

In 1926 work started in the Research Laboratory to develop a process for treating these sulphide concentrates, and by the following year a successful and economic route had been worked out by a team comprising E. C. Deering, E. R. Box and the writer. This was the only workable process developed, and led to Johnson Matthey becoming the sole refiner of South African platinum.

Electroplating Investigations As the hopes of an increasing output of

platinum metals from South Africa began to materialise in the late nineteen-twenties attention was turned to investigating possible new uses for the metals. One of the first problems tackled was the development of commercial electrolytes particularly for plating with rhodium and platinum, the main contributor to this work being E. C. Davies,

who had joined us in 1929. Amminonitrite baths had been proposed in the United States for plating thin deposits of rhodium on articles of cheap jewellery to produce a silver- like finish but these proved to be inefficient during prolonged use. Baths based on rhodium sulphate or phosphate, or mixtures of these compounds, were then developed both in this country and in the United States. The sulphate bath produced by Johnson Matthey by a new process proved very satisfactory not only for depositing thin bright films of rhodium but also for building up heavy deposits on relatively large and com- plicated surfaces. Since the latter years of the last century it was known that thin platinum deposits could be obtained from a complex amminophosphate bath but these required much burnishing to give a satisfactory finish. A new bath based on sodium hexahydroxy- platinate developed in the Research Labora- tory was found capable of plating bright fairly thick platinum deposits and this was used for this purpose for many years. Re- cently, however, it has been replaced by a more stable bath based on a sulphatonitrite derivative of platinum.

One of the modern spectrographs, a 3.4 metre Ebert grating instrument, which facilitates the detection and accurate determination of trace impurities in the platinum metals


A process for palladium plating was also developed but no success was achieved in attempts to deposit iridium and ruthenium.

Another move took place in I929 to more roomy laboratories, and about this time several staff changes also occurred. E. C. Deering left the Research Department to become manager of the platinum refineries erected at Brimsdown, F. E. Kerridge arrived to assist with ceramic research activities, while a little later H. E. Bennett joined us from the National Physical Laboratory to strengthen the metallurgical section. A few years later F. M. Lever joined the chemical section, while in 1938 J. C. Chaston came to us as head of the metallurgical section.

Alloys for Spinnerets Artificial silk made by the viscose process

used iridium-platinum spinnerets in its early days but with increasing scarcity of iridium and rising prices for platinum attention was turned to the use of hard platinum-gold alloys. As a result of a later re-investigation in the laboratory of the platinum-gold system by J. C. Chaston, A. S . Darling and R. A.


Research on the electrodeposition of the platinum metals began in 1929 with very simple equipment. Today research i n this jield is aided by precise electrical control equipment

Mintern the optimum composition for this alloy and the correct conditions for working and heat-treatment to obtain the desired structure and hardness were established. Later it was found possible to reduce the cost of the alloy and improve its properties by adding a small proportion of palladium. In later years this was replaced by a small addition of rhodium.

High Temperature Properties

About this time fibre glass was being developed and an extensive

research was undertaken to find the most suitable platinum alloy for making the forehearths or bushings required to produce the glass fibres. These bushings operated at temperatures in the region of 1400°C, where appreciable loss of platinum may occur by volatilisation. The most satisfactory alloy for this purpose was found to be rhodium-platinum, all other alloys being less satisfactory because of oxidation of the alloying metal, excessive loss by volatilisation, or hot-shortness of the welds. Heated electrically at 14so'C in a brick flue allowing a continuous uprising current of air, both platinum and 10 per cent rhodium-platinum alloy lost 10 per cent of their weight in six weeks, most of the precious metal lost condensing on the brick nearest the hot metal in the form of continuously growing crystals while the remainder collected on the cooler brick surfaces as a black powdery deposit containing about 3 per cent of oxygen; there was little difference in the amount of metal lost by the pure platinum and the rhodium alloy, and the condensate from the alloy contained about the same percentage of rhodium as the original alloy. In a steam

The study of the distribution and identification of phases in an alloy system was formerly a lengthy and tedious process. The electron probe micro-analyser makes it possible to

establish the structure of an alloy accurately and rapidly

atmosphere, as used in making glass fibres, metal loss by evaporation over the same period was very small. These experiments showed that volatilisation of platinum at high temperatures was due to the presence of oxygen and was not appreciably diminished by alloying with rhodium; the alloy, however, had the greater mechanical strength when hot.

The knowledge gained in these experiments on the behaviour of platinum at high temperatures was later put to good use in designing wire-wound furnaces to operate up to 1600'C.

The long standing question of finding an adequate and permanent home for the Research Laboratories was finally settled in 1938, when a completely new building, with ample space for expansion, was erected at Wembley. A great deal of new equipment was acquired to enlarge the scope of the work, and the department was able to embark on a great many more research projects.

With the rapid development in the early forties of the immersion thermocouple in the steel industry it was found that in continuous use the wires, especially the pure platinum

wire, tended to become brittle. This was established in the laboratories to be due to the presence of sulphur-bearing oil in the protective sheaths. This caused the formation of silicon sulphide vapour which lost its silicon to the platinum and so liberated sulphur to continue the reaction.

A great deal of effort also went into the whole field of thermocouples, both on the score of refinements in methods of calibration and in the development of new alloy com- binations such as iridium-platinum against gold-palladium for accurate measurement in the medium temperature range.

Many investigations were also made during and after the war years on the properties, and particularly the creep properties, of a number of binary and ternary platinum alloys.

In 1954 the writer was succeeded as Research Manager by Dr J. C. Chaston but continued to function as the company's Consulting Research Chemist.

Constitutional work carried out included the investigation of the gold-piatinum diagram already mentioned (an essential foundation


for the development of improved spinneret alloys), the ruthenium-palladium system and in more recent years parts of the molybdenum-platinum system (of importance to the life and performance of platinum-clad molybdenum in the glass industry) and also parts of the ternary gold-rhodium-platinum system.

Other projects in the metallurgical field included the development of new contact alloys, and considerable work on the equiatomic per cent cobalt-platinum alloy that has such outstanding properties as a permanent magnet material. In the chemical section of the department,

considerable improvements in the methods of analysis of the platinum metals aided the refining activities of the company, and work on complexes of the platinum metals, particularly that by Dr F. M. Lever on the ammino-compounds of ruthenium, and later work by the writer and others on the hydrido- compounds of rhodium and organometallic compounds of all the platinum metals,

Research into the mechanism of chemical reactions involving platinum group metal catalysts, and into the variables that need to be controlled, i s rarriecl out in apparatus of this typo

led to the study of their potential uses in the field of homogeneous catalysis.

The company’s activities on the heterogeneous catalysis front were greatly expanded to meet the rapidly growing demand for such catalysts from the chemical industry and are now in the charge of Dr G. C. Bond who joined the department in 1962.

In 1965 the services of Dr Chaston were lost by his retire- ment, and he was succeeded as Research Manager by Dr Lever.

A project of interest to the glass industry, recently completed and published in this journal, concerned the wetting properties of a number of platinum alloys in contact with molten glass, while a further major study- also reported on in this issue of Platinum Metals Review by Dr Darling and his colleagues-has been the successful search for a dispersion-hardened platinum that would retain greatly enhanced strength properties at very high temperatures.

To look back over a continuous span of half a century of association with research on such fascinating metals as those comprising the platinum group is both a sobering and stimulating experience given probably to few men. Progress in research facilities- particularly in instrumentation-has of course been enormous by comparison with the limited resources available in 1918, but the costs of research have naturally risen pro- portionately and one needs today to give long and careful thought to the selection of new projects and their likely benefits.


ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES On the Temperature Dependence of the Atom Susceptibility of Ruthenium, Rhodium and Palladium as well as Osmium, Iridium and Platinum between 80 and 1850°K W. D. WEISS and R. KOHLHAAS, z. angew. Phys.,

Specific magnetic susceptibilities of the Pt metals were determined at 80-1850°K by a modified Faraday technique. The temperature dependence of the susceptibility of Pd above its m.p. was also observed. Results for Rh, Pd and Pt are compared with those of M. SHIMIZU et al. but no earlier work on Ir, Ru and 0 s was known.

'g671 23J (31, '75-I79

Kinetics of Quenched-in Vacancies in Pure Platinum J. POLM, Phys. Status Solidi, 1967, 21, (2),

581-591 Isothermal annealing curves of pure Pt quenched in H 2 0 show the characteristic "S' shape indicative of second order kinetics which is explained, together with the low values of effective energy of migration obtained, by as- suming the existence of a thermal equilibrium between single vacancies and di-vacancies at temperatures >260"C. The binding energy of a di-vacancy is estimated as (o.18fo.og)eV and the difference in the energies of migration of single and di-vacancies is (0.34+0.05)eV.

Thermal Diffusivity of Platinum fiom 300" to 1200°K J. J. MARTIN, P. s. SIDLES and G. c. DANIELSON,

7. aPPl. PhYS., 1967, 3 8 J (8h 3075-3078 Thermal diffusivity measurements on five Pt samples with R,,,/R4.2 of 12, 34, 100, 900 and 5000 at 300-1200°K suggest that pure Pt would be suitable for a thermal conductivity standard but that measurements by other absolute methods are desirable also. Only the least pure sample (Rzi3/R4.2=~2) showed more than 3% deviation from the average thermal diffusivity of the two purest samples. Comparison with previous work agrees well at room temperature but agreement is poor at high temperatures.

Uniform Microcrystals of Platinum and Gold R. M. WILENZICK, D. c. RUSSELL, R. H. MORRISS and s. w. MARSHALL, J. chem. Phys., 1967, 47, (z), 533-536 'To study physical properties dependent on crystal size, three methods for preparing Pt hydrosols were used and two for Au hydrosols.

Optimum conditions of preparation were established for uniform sized crystals and sizes from 40 to SOOA were obtained.

The Lattice Thermal Conductivity of Some Palladium and Platinum Alloys R. FLETCHER and D. GREIG, Phil. Mug., 1967, 16,

Measurements on some Pd-Ag, Pt-Ir alloys at 2-120'K showed that the lattice thermal conductivity below -30°K is an order of magnitude less than in noble metal alloys of similar concentrations. This is explained by strong electron- phonon scattering but at present it cannot be decided whether the electronic transitions are s to d, or d to d. At higher temperatures measurements are largely independent of solute concentration. At IOO'K, lattice resistance is mainly due to phonon-phonon U-processes.

(I39)J 3O3-3I.5

Growth of Modulated Structure in Gold- Platinum Alloys R. W. CARPENTER, Acta Metall., 1967, 15, (IO), 1567-1572 X-ray studies of the growth of structural modula- tions during early stages of precipitation in 20, 40 and 60% Au-Pt alloys at 500-600°C indicated a nearly constant modulation wavelength for short ageing times with a uniform increase to a maximum value upon further ageing. 40ojO Au-Pt has a smaller maximum wavelength than the other alloys, caused by a maximum in elastic strain energy due to coherency strains.

Experimental Investigation on Exchange Interaction in Platinum-Iron Alloys R. SEGNAN, Phys. Rev., 1967, 160, (2), 404-408 Measuring using the Mbssbauer effect of the temperature dependence of the hyperfine magnetic field Hi at Fe nuclei and of the concentration dependence of the transition temperature T, was carried out on 1-15 at.O/, Fe-Pt alloys and showed that, when TQT,, Hi is nearly the same at each Fe nucleus but that as T increases, the Mossbauer spectral lines broaden, due perhaps to a wide range of Hi values.

Ordered Pt,-Co Alloy Studied in the Field- ion Microscope T. T. TSONG and E. w. MULLER, J . appl. Phys., 1967,

Images of the {III) planes of ordered Pt,-Co confirmed the invisibility of the Co atom species. Layer by layer field evaporation confirmed that the composition of (110) and (100) planes alternates in subsequent layers of pure Pt and

3 8 J (91, 3531-3536


equiatomic Pt-Co. Antiphase domains are clear only where the domain boundary passes through these planes. No sharp boundary exists in the partially ordered state between the ordered and disordered phases.

The Ageing Mechanism of the Cold Work Peak of Hydrogen in Palladium R. R. ARONS, c. TUYN and G. DE VRIES, Acta Metall.,

The cold work peak of P-PdH occurs at -15o"K and decreases considerably after ageing at room temperature and above. Its behaviour is related to the pinning of dislocations by interstitial impurities.

Reactions with Hydrogen of the Alloy

A. A. RODINA, M. A. GUREVICH and N. T. DORONICHEVA, Zh.Fz.Khim., 1967~41, (9), 2382-2383 Unlike <20 wt.y/, Ag-Pd alloys, 40 wt.74 Ag-Pd does not become deformed during heating and cooling cycles in H,. This is due in part to formation of P-Pd-Ag-H. The permeability of 40 wt.o/, Ag-Pd for H, is nearly equal to that of pure Pd but is less than that of 18.5 wt.04 Ag-Pd.

The Transformations in the Solid Chromium- Palladium Alloys E. RAUB, R. GOHLE and E. ROSCHEL, 2. Metallkunde,

Studies of the phase diagram at low temperatures on 10-49 at.% Cr-Pd alloys show that an ordered LI, structure exists at 24-46 at.:;; Cr-Pd and a tetragonal LI, structure at -50 at.% Cr-Pd. The LI , phase is formed by a peritectoid transformation at -505°C.

The Constitution of Cerium-Palladium Alloys Containing 50-10004 Palladium J. R. THOMSON, J . Less-common Metals, 1967, 13, (31, 307-312 Metallographic and X-ray studies of 48-100 at.yo Pd-Ce alloys between 800°C and the melting points indicated four intermetallic compounds, which were compared with Th-Pd alloys. Solubility of' Ce in Pd at 800 and 1050°C is 13f I%, CePd and CePd, crystallise directly from the melt at 1137512 and 1437112'C respectively; compounds containing 571 1 and 62.511 at.% Pd form peritectically at 1137.t12 and r037k 12°C respectively. Eutectics occur at 987f12'C and 1075&12"c.

On the Effects of Cold-working and Anneal- ing, and of Cycles of Absorption and Desorp- tion of Hydrogen, on the Electrical Resistance of Some Palladium-Boron Alloys F. A. LEWIS, R. BURCH, A. s. DARLING and G. SELMAN, solid State Commun., 1967, 5, (8),

The electrical resistance of work-hardened 16

r967~ 15, (lo), 1673-1675

Pd-40 Wt.o/* Ag

1967, 58, (81, 567-568

61 3-614

at.::, B-Pd wire falls rapidly above 80°C and there are irregularities in the curve indicating that thermally activated changes occur at higher temperatures. The variation of resistance during thermal cycling indicates that a metallurgical equilibrium does not exist although there is no evidence for phase changes. Isothermal cycles of charge and discharge of Hz at 25°C have little effect on the annealed resistance value.

Concentration Dependence of Electrical Resistance of Liquid Alloys Pd-Ag, Pd-Cr, Pd-Si, Ag-Si N. A. VATOLIN, 0. A. ESIN and E. L. DUBININ, Zh. Jiz.Khim., 1967, 41, (7), 1813-1815 A correlation between the variation of specific electrical resistance with composition and the composition diagram is shown for Pd-Ag, Pd-Si, Pd-Cr and Ag-Si at temperatures up to 1600"C, e.g. the maximum on the I'd-Si isotherm corresponds to the formation of the compound PdSi. Minimal superheating above the liquidus shows a correspondence between the character of the isotherm of p and the alloy composition Z represented by the equation.

where A and B are constants, c is the at.y4 addition of Z, to the major alloy constituent Z .

Crystal Lattice Parameters and Structural Deformation in Fe-Rh Alloys during Phase Conversions A. I. ZAKHAROV, Fiz. Meial. Metalloved., 1967, 24, (I), 84-90 The antiferromagnetic-ferromagnetic transformation of Fe-Rh alloys occurs at 353-44o"K. Both the initial cubic phase and the new crystal formed are deformed during the process, depending on the initial composition of the alloy, and hysteresis for direct and reverse transformation may amount to from 3 to 14°C.

The Preparation and Some Properties of Tungsten-Rhenium-Osmium Alloys A. LEACH and D. J. JONES, Powder Metall., 1967, 10, (201, 174-191 W-Re-0s alloys were fabricated by powder metallurgical techniques and were studied to learn the effect of 0 s in thermocouples of Re-W alloy. 5% Re-<2.250i;, 0s-W alloys contain a single- phase CL solid solution. 26% Re-<11.3% 0s-W alloys contain r* up to -1.67:L Os, and both CL

and brittle o phase at greater 0 s content, Alloys of -26% Re-W with --0.69-4.5% 0 s are very prone to deformation twinning, especially at -1.67:h 0s .

Thermionic Work Function of Polycrystal- line Ruthenium J. PSAROUTHAKIS and R. D. HUNTINGTON, Surface

Measurements in variable spacing, relatively

ApC/c =A+B (2, -Z)'

sci., 1967, 7, (31, 279-292


large electrode area thermionic converters showed that the thermionic electron work function of Ru under high vacuum is (pm-4.55&0.05 eV. Measurements in a Cs vapour environment corresponded to qm= 4.57+0,05 eV. The process of applying Ru powder to achieve large and dense area electrode coatings is detailed.

The Effect of Noble Metal Additions on the Toughness of Iron-Carbon Alloys S. FLOREEN and H. W. HAYDEN, Trans. Metall. Soc. AIME, 1967,239, (9), 1405-1407 Additions of Ir, Rh, Ru, and Pt all improve the toughness of Fe-C alloys. This supports the proposition that substitutional alloying elements which stabilise austenite do improve toughness although the reason for this behaviour is not clear.

CHEMICAL COMPOUNDS n-Ally1 Complexes of the Transition Metals M. I. LOBACH, B. D. BABITSKII and v. A. KORMER, Uspekhi Khim., 1967,36, (7), 1158-1199 The structure of n-ally1 complexes of the transition metals, including Rh, Ru, Ir, Pd and Pt, were studied by NMR, IR, UV and dipole moment measurements. The preparation and properties of the complexes are discussed together with their use in a wide range of synthetic organic reactions. (318 references.)

Ole fin Coordination Compounds of Rhodium. V. The Relative Stabilities and Rates of Exchange of Olefin Complexes of Rhodium (I) R. CRAMER, J . Am. Chem. SOC., 1967, 89, (18),

Comparisons of stabilities of various olefin complexes of Rh(1) show that alkyl substituents on olefin Cs destabilise Rh(1) complexes much more than the corresponding Ag compounds but that coordination is enhanced by electronegative substituents due to stronger x- or back-bonding. Strongly-coordinating C,F, displaces C,H, from Rh(1) far more slowly than do C,H, or C,H,, which coordinate weakly, which suggests that n-bond formation plays little part in development of the transition state for nucleophilic olefin exchange.

X-ray, Infrared, and Magnetic Studies of a-and P-Ruthenium Trichloride J. M. FLETCHER, w. E. GARDNER, A. c. FOX and G. TOPPING, J. Chem. Soc., A , inorg. phys. theor.,

X-ray, magnetic susceptibility, IR and neutron diffraction measurements of E- and p-RuC1, indicate that the former has a distorted octahedral structure and belongs to the space group P3112(D33), and the latter contains linear chains in a trigonal structure belonging to the space

462i-4626

1967, (7), 1038-1045

group P3c, (C3,3.

New Transition Metal Tetrafluorides N. BARTLETT and P. R. RAO, Abstr. Papers, 154th Mtg, Am. Chem. SOC., 1967, (Sept.), K I ~ PdF,, RhF, and IrF, have been prepared and possess low-spin electron configuration. PdF, has undistorted UC1,-structure and IrF, and PtF, are monoclinic relatives of its tetragonal cell. Each Pd atom is coordinated to four F atoms. RhF,, IrF, and PtF, are more similar to NbF,, where each metal atom is six-coordinated by F ligands.

Carhonyl Halide Complexes of Platinum Group Metals M. J. CLEARE and w. P. GRIFFITH, Chem. and Ind.,

Careful control of reaction conditions and reactants enabled eleven new carbonyl halide salts of Os, Ru and Ir to be isolated and these are tabulated. See also Platinum Metals Rev.,

1967, (40, Oct. 7)> 1705-1706

1967, 11, (4)> 148-149-

ELECTROCHEMISTRY Instability of Supported-platinum Surface Area in the Presence of Electrolytes J. F. CONNOLLY, R. J. FLANNERY, B. L. MEYERS and R. F. WATERS, Abstr. Papers, 154th Mtg, Am. Chem. SOC., 1967, (Sept.), L14 A study of the growth of supported Pt crystallites at <2oo0C in electrolytes indicated that the growth rate depended on the support type, the solution, the Pt concentration, and the initial crystallite size. High support areas and low conductivity solutions reduced growth rates but the best dispersions showed Pt area loss rates up to 90% because their small initial crystallites possessed a high tendency to recrystallise. Electrorecrystallisation is B possible mechanism of the results, with cells formed between large and small Pt crystallites and the small acting as anodes because their surface energies are higher.

The Kinetics of Propane Adsorption on Platinum in Hydrofluoric Acid E. J. CAIRNS and A. M. BREITENSTEIN, J . Electro- chem. SOC., 1967, 114, (8), 764-772 The rate of adsorption of C,H, on smooth Pt at 90°C in 37 mole yo HF was studied by single linear voltage sweep techniques in all-PTFE apparatus with surface coverage of C,H, measured as a function of adsorption time and potential. Steady-state coverage reached a maximum at 0.2 V and the amount of the most electro- chemically active species was highest at 0.3 V. Rate constants were measured at these values.

Oxygen Reduction at Pt-Au and Pd-Au Alloy Electrodes in Acid Solution A. DAMJANOVIk and v. BRUSIC, Electrochim. Acta,

Kinetic studies of 0,-reduction in 0.1 N HClO., 1967, 12, (9), 1171-1184


at room temperature showed that at Pt, Pd, Pt-rich Pt-Au, and Pd-rich Pd-Au electrodes Tafel relationships with SV/S log ix - R T / F occur at w o - * to -IO-~ A/cm2, while at Au and Au-rich alloys the slope is close to -zRT/F. The change of slope from -RT/F to -2RT/F, which occurs at >SO at.% Au, is related to the electronic structure of the alloys, for at -60 at.?& Au there are no longer unpaired d-electrons and the 0,-reduction mechanism changes. Exchange current density for Pt- and Pd-rich alloys changes exponentially with alloy composition; it decreases as Au yo increases. .4t a given potential the linear change in log(activity) with Au yo in Pd-rich Pd-Au is due to the change of heat adsorption of reaction intermediates with alloy composition.

Oxygen Reduction on Gold Alloys of Platinum, Palladium and Silver J. GINER, J. M. PARRY and L. SWETTE, Abstr. Papers, 154th Mtg, Am. Chem. SOL, 1967, (Sept.), L I ~ 10-g00:6 Au alloys of Pt, Pd and Ag were used as rotating electrodes in the cathodic reduction of 0, in 2 N KOH at 25°C. Activity of Au-Ag decreased with increasing Ag content; Au-Pt alloys possessed almost constant activity; Au-Pd alloys showed a maximum activity greater than that of Au-Pt for 207oS.6 Au-Pd. Order of activity of pure metals at low polarisation was Pd>Pt=Au>Ag. Results at 75°C were similar to those at 25°C.

Preparation and Characterisation of Pt- black for Anodic Hydrocarbon Oxidation

Pt-blacks were prepared by reduction of H,PtCl, with HCHO in a basic medium under various nucleation and growth conditions. They were characterised by surface area, pore size, etc., and their activity for anodic oxidation of C,H, at 150°C in 85% H,PO, was measured using a Pt-Teflon structure. Effects of conditions of preparation on the physical characteristics and activity of the blacks were determined.

J. GINER, J. M. PARRY and S. M. SMITH, Ibid., L18

ELECTRODEPOSITION AND SURFACE COATINGS Radioisotope Powered Cardiac Pacemaker Project. Platinum Plating on Component Parts A. RECCHIA, USAEC Rept NUMEC 3731-4. 5-4,

Pt was successfully plated on Hastelloy “C” either with or without a prior Ni flash plating and a good mechanical bond was shown to exist in both cases. Hardnesses of the Pt plated surface and of the Pt anode were compared. Post- plating treatment at ZOOT expelled gases and moisture trapped in the plating. Thermal shock

1967, (Mar.), 13 PP

tests caused micro-blisters to form between Pt and Hastelloy “C” but not between Pt and the Ni-flashed alloy. Barrel plating was shown to be suitable for this work.

The Electrolytic Deposition of Platinum and Platinum Alloys with Respect to the Increase of Hardness G. HANSEL, Metalloberflache, 1967, 21, (8), 238-242 Pt and 5 :/o Re-Pt, deposited electrolytically from sulphamic or fluorboric acid electrolytes containing complex Pt, and Pt and Re salts, have a hardness approaching that of thermally melted metals and alloys. The hardness of 5% Re-Pt is similar to that of Pt-Ir which is used in the manufacture of laboratory apparatus.

Investigation of Processes of Electro- chemical Deposition of Silver-Palladium Alloys in Cyanide Electrolytes N. P. FEDOT’EV, P. M. VYACHESLAVOV, B. SH. K W R and V. v. IVANOVA, Zh. prikladnoi Khim.,

X-ray analysis and physico-chemical studies showed that electrodeposited Ag-Pd alloys form a continuous series of solid solutions. Increases in specific electrical resistance and microhardness occur as the Pd content increases. When deposition occurs from cyanide electrolytes, Ag is deposited with overpolarisation but Pd with depolarisation.

1967, 40, (7)1 1474-1478

LABORATORY APPARATUS AND TECHNIQUE An Investigation into the Use of Platinum Ware for Silicate Analysis B. G. RUSSELL, J. D. SPANGENBERG and T. w. STEELE, NIM rcs. Rept. No. 193, 1967, (Aug.), 32 PP Tests to determine the amount of Pt that dis- solves from crucibles used for fusing samples in silicate analysis showed that alkaline fluxes dissolve more Pt than do acid fluxes and that, if the sample contains ferrous iron, considerable amounts may be absorbed by the Pt. The preferred technique is sintering at 440°C with a mixture of Na,02 and NaOH. Where Fe is to be determined an acid flux should be used and separate crucibles should be reserved for this purpose. Alternate ignitions and pyrosulphate fusions can be used to remove Fe from con- taminated crucibles. Pt crucibles are attacked least when they possess a fine crystal structure. 5’34 Au-Pt crucibles, whilst at least as resistant to attack and to Fe absorption, are less deform- able than Pt. The interference of dissolved Pt on the subsequent determinations of SO,, Al,O,, Fey Ti, Cay and Mg was investigated.


HETEROGENEOUS CATALYSIS The Mechanism of Isomerisation of Aliphatic Hydrocarbons at a Platinum Surface J. R. ANDERSON and N. R. AVERY, J. Catalysis, 1967, 7, (4), 315-323 A model for C, and C, alkane isomerisation on Pt provides more detailed interpretation of C13- labelled n-butane results by proposing that the surface precursor is 1,ydiadsorbed with a double bond to the surface of a C atom and that isomerisation occurs by its transformation to a bridged structure. Energy considerations show that isomerisation will occur when there is partial electron transfer from the hydrocarbon residue to the surface metal atom.

On the Activation Energy of Adsorption Catalysts T. v. PARYICHAK, A. N. MAL'TSEV and N. I. KOBOZEV, Zh.fiz. Khim., 1967, 41, (8), 2048-2050 Pt atoms in Pt black have 130 times the activity of those on A1,0, and 140 times the activity of those on SiO,. Active centres on SiO, are 22 a apart and Pt atoms therefore transmit energy rather better during highly exothermic reactions. Active centres on AI,03 are 51 a apart, energy transmission is weaker and the activity of Pt on it is less. When only small amounts of Pt are present on the supports, their specific activities are similar because the active centrcs are far apart.

Deuterium Exchange between n-Hydro- carbons on a Pt/A1,0, Catalyst D. GELBIN and E. WILDE, Chem. Tech., 1967, 19,

Rapid deuteration of n-C,H, and n-C,H,, occurs on Pt:A1,0, at 60'C but no exchange occurs between deuterated and non-deuterated hydrocarbons at this temperature. Exchange is apparent between deuterated butane and both n-C,H,, and n-C,HIB at 300°C. The rate of exchange increases with the pressure of hydrocarbon. y-Al,O, alone cannot activate the exchange under these conditions. The dissocia- tive adsorption model of the exchange reaction is confirmed.

The Dehydrogenation of Decalin. Effect of Reaction Variables on Selectivity and Catalyst Stability A. w. RITCHIE and A. c. NIXON, Abstr. Papers, 154th Mtg, Am. Chem. SOL., 1967, (Sept.), U20 Good stability of Pt :A120, catalyst in the vapour phase dehydrogenation of decalin was favoured by high pressure, high conversion and low temperature. Practical grade decalin gave better stability than pure grade. The two-stage process had tetralin as an intermediate product. Select- ivity for naphthalene occurred at high temperature, high conversion and low pressure. cis-

(8) J 480-483


Decalin was more reactive than the trans species and cis -+trans isomerisation occurred during dehydrogenation, but no trans+& conversion.

Isomerisation and Transmethylation over Platinum-on-Silica Catalyst S . M. CSICSERY and R. L. BURNETT, J. Catalysis,

Isomerisation of I-methyl-2-ethylbenzene and n-C,H,, over Pt/SiO, proceeded via cyclic intermediates to give n-propylbenzene and 3- methylhexane respectively. A new type of transmethylation equivalent to the reverse of hydrogenolysis formed small amounts of di- methylbenzenes, cymenes, methyl-n-propyl- benzenes, and diethylbenzenes from methyl- ethylbenzene.

The Structure and Activity of Supported Metal Catalysts. 11. Crystallite Size and CO Chemisorption on PlatinumlSilica Catalysts T. A. DORLING and R. L. MOSS, Ibid., 7, (4), 378-385 X-ray and micrographic measurements on the structure of G11.5 wt.O& PtiSiO, catalysts gave results for crystallite size and proportionality of Pt area to (weight Pt) 213 which suggest that a fixed number of crystallites increase in size with Pt content -this number depending on the pore structure of the SO,. Ratios of (Pt atoms ex- posed)/(CO molecules adsorbed) vary from -I to -2. CO coverage of Pt depends on crystallite size and the number of CO molecules adsorbed, calculated from Pt crystallite size distribution, agrees with experiment.

Modification of Raney Nickel Catalysts by Additions of the Transition Metals. VII. Electrooxidation of Hydrogen and Catalytic Hydrogenation on Raney Nickel-Palladium Alloys A. ISABEKOV, A. B. FASMAN and B. K. ALMASHEV, Zh. fiz.Khim., 1967, 41, (81, 1890-1897 Raney catalysts were prepared from Ni-Pd-A1 alloys containing 50 wt."/, Al. Isothermal annealing of the original alloys increased the activity of the catalysts and altered the relation of the reaction rate to the promoter content. Studies of the composition and kinetics of the catalysts indicated that Pd increased their lattice parameters. The effect of electron structure on catalytic activity was studied for the Ni-Pd alloys.

The Parahydrogen Conversion on Pal- ladium-Silver Alloy Films D. R. Ross iNGToN and R. B. RUNK, J. Catalysis, 1967, 7, (41,365-377 Studies of the para-ortho H, conversion on evaporated films of 50, 70, 80 and 10ou/0 Ag-Pd at 273-413"K indicated that activation energy for the process increased with Ag content, especially between the 50 and 70% Ag-Pd alloys.

1967, 8, (1),75-81

The Oxidation of Ethylene over Evaporated Palladium-Silver Alloy Filnis. I. Film Structure and Stability under Reaction Con- ditions R. L. MOSS and D. H. THOMAS, Ibid., 8, (2), 151-161 Electron micrographs of evaporated Ag-Pd films showed extensive coalescence of crystallites in Ag-rich films but a compact mass of small crystallites in Pd-rich films. After use in C,H4 oxidation, Ag-rich films remained homogeneous but Pd-rich films behaved like Pd-Ag-H alloys with 01 and @ phases apparently present. The deviation of the lattice constant from expected values then correlated with the 0, used from the reaction mixture. Pure Pd films always gave the bulk lattice constant but films with as little as I % Ag were apparently well charged with Hz after reaction. At 250"C, 0, can cause some separation of the alloy into its component metals.

Active Centres in Cyclohexene Dispropor- tionation on Supported Palladium S. CARRA, V. RAGAINI and F. GUELLA, Ibid., (3), 261-271 Kinetic studies of the disproportionation of cyclohexene to C,H,, and CGHs at 30-50°C by feeding cyclohexene in He over samples of highly dispersed Pd on Alsos showed that catalyst activity maxima correspond to particular values of :h Pd on the support. Statistics on Pd atom distribution on the catalyst surface indicate that these maxima are related to the probability of formation of particular atomic clusters as active centres.

The Low Temperature Oxidation of Ammonia over a Supported Ruthenium Catalyst T. J. SCHRIBER and G. PARRAVANO, Chem. Engng

Oxidation kinetics of NH, and 0, over 0.5 wt.:/, Ru/AI,O, as 0.318 cm pellets were studied in a stirred flow reactor at 246-365"Cy 176-280 cm Hg. Rates of formation of N, and N,O depend on pNHz, po, and pHZO but are independent of pN2 and pNzO. Equations are developed for both these rates and the stages of reaction are discussed.

SC~. , 1967, 22, (8), 1067-1078

Polymethylene Synthesis from Carbon Mon- oxide and Hydrogen on Ruthenium Cat- alysts. Part 10. On the Importance of Catalyst Pretreatment and Carbonyl For- mation for the Conversions H. PICHLER, H. MEIER zu KOCKER, w. GABLER, R. GARTNER and D. KIOUSSIS, Brennstoff-chem., 1967,

The sizes of polymolecular paraffins are greater when the synthesis temperature is lower, but at low temperature and high pressure, besides the alkylruthenium carbonyls, which have possible importance as reaction intermediates, both

q 8 J (g), 266-272

volatile and heavier Ru carbonyls are formed, which deactivate the RuO, catalyst for reduction. T o reduce Ru carbonyl formation and improve catalyst activity, reduction by H, is recommended. The Ru carbonyls were isolated and identified as containing Rug(CO), e, Ru carbonyl hydride and alkylruthenium carbonyl.

The Oxidation of Cyclobutanok and Aromatic Rings with Ruthenium Tetroxide J. A. CAPUTO and R. PuCHS, Tetrahedron Lett., 1967, (471,4729-4731 The first oxidations by RuO, of cyclobutanols to cyclobutanones and of benzene rings to carboxylic acid groups are reported. 3-Phenyl- cyclobutanecarboxylic acid was oxidised to cis-I,3-cyclobutanedicarboxylic acid, and 135-2- phenylcyclobutanecarboxylic acid to cis- I ,2-cyclobutanedicarboxylic acid. Ethyl j-hydroxycyclo- butanecarboxylate was oxidised to ethyl 3- ketocyclobutanecarboxylate with 78 '$'(, yield. p-tert-Butylphenol was oxidised to pivalic acid, and phenylcyclohexane to cyclohexanecarboxylic acid.

Interaction of Hydrogen and Carbon Mon- oxide on Platinum Group Metals

Studies of CO-Ha mixtures on unsupported metals at IOO-ZOO~C showed that CO is adsorbed on Pt and that the chemisorbed CO could not be removed completely by reduction and evacuation at 150°C. On Rh or Ir the gases interacted somewhat and some CH, was detected at zoo0C. On Ru, chemisorbed CO was removed completely by reduction and evacuation at I~o'C, H, adsorption was enhanced by COY and CH, formed appreciably above 100°C; activation energies for reactions between CO and H, or D, were -9 kca1,'mole. Higher specificity of Ru for the methanation reaction is due to its lower affinity for CO.

Catalytic Hydrogenolysis of Ethane over the Noble Metals of Group VIII J. H. SINFELT and D. J. c. YATBS, Ibid., (I), 82-90 Kinetic studies of hydrogenolysis of C,H, over 5-10 wt.% Ru, Rh, Pd, and Ir on S O z show that the order of catalytic activities is Ru>Rh>Ir% Pd=Pt. The rate of hydrogenolysis decreased strongly with increasing H, pressure. Extensive dissociation of C-H bonds in the C,H, molecule occurs during the initial chemisorption step. Catalytic activities are compared with those of Fe, Co and Ni.

The Role of Hydrogen in the Configurational Isomerisation of Dialkylcyclanes in the Presence of the Noble Group VIII Metals 0. v. BRAGIN, TAO LUN-SYAN and A. L. LIBERMAN, Kinetika Kataliz, 1967, 8, (4), 931-933 Configurational isomerisation of ~,z-dialkyl-

D. W. MCKEE, 3. catalysis, 1967, 8, (3), 240-249


cyclopentanes and of 1,3-dimethylcyclohexanes on C-supported Pt metals does not proceed without free H,. The activity of Pt,'C and Pd;C decreases steadily in He-H, mixtures up to high He concentrations; Os,C, Rh/C, IriC and Ru:C lose considerable activity even at low He concentrations. Activity is restored only after heating in a stream of H,.

Group MI1 Metal Catalysed Reactions of Organosilicon Hydrides with Amines, Hydrogen Halides, and Hydrogen Sulphide L. H. SOMMER and J. D. CITRON, J . org. Chem.,

The reactions of Si-H bonds with nonhydroxylic compounds containing active H were studied over Pd/A1,0,, Rh:Al,O,, Pd,C, Pt/C, Rh/C, RulC and Raney Ni, and provide quick, convenient preparations of silylamines, silanethiols and halosilanes.

'g673 32J (8), 2470-2472

HOMOGENEOUS CATALYSIS Homogeneous Catalysis by Noble Metal Salts. II. Isomerisation of 1-Pentene by a Platiniun(I1) - Tin(I1) Complex G. C. BOND and M. HELLIER, J . Cata~sis , 1967,

In the presence of H, and a Pt(1I) - Sn(I1) complex at room temperature, f-C5HlU isomerises to a z-C,H,, mixture containing 85y; trans isomer and more at lower temperature. The slow rate of hydrogenation is proportional to 1-C5Hlo concentration; virtually no hydrogenation occurs with cis-2-C,Hlo. Styrene is hydrogenated slowly. Isomerisation and hydrogenation rates are maximum when Sn:Pt is -12. The mechanism is l-C,Hlo addition to a hydride formed from H, and trans-[Pt(SnCl,),Cl,].

Homogeneous Hydrogenation Using Plat- inum-Tin Complexes H. VAN BEKKUM, J. VAN GOGH and G. VAN MINNEN- FATHUIS, Ibid., 292-294 Complexes prepared from H,PtCl, and SnCl, are efficient catalysts for the hydrogenation of cyclohexene provided that the Sn:Pt ratio is right, that extra C1 or Br is added, and that solvents other than CH,OH are applied. Results are tabulated and discussed.

Homogeneous Hydrogenation with Plat- inum-Tin Chloride Complexes as Catalysts L. P. VAN'T HOF and B. G. LINSEN, Ibid., 295-297 In solvents other than CH,OH or its homologues, the complex of H,PtClS.6H,O and SnCI,.zH,O catalyses homogeneous hydrogenations at atm. pressure and room temperature. Alphatic carboxylic acids and their esters are suitable solvents, e.g. 1-hexene is hydrogenated in glacial CH,COOH. The effects of reaction temperature,

7, (3), 217-222


Sn:Pt ratio, and substrate and catalyst concentrations have been studied. Unsaturated edible oils can also be hydrogenated with this catalyst system, e.g. soyabean oil has been hydrogenated in CH,COOH and shows preferential hydrogenation of linoleic acid.

Homogeneous Catalysis in the Reactions of Olefinic Substances. IX. Homogeneous Cata- lysis of Specific Hydrogenation of Poly- olefins by Some Platinum and Palladium Complexes H. A. TAYIM and J. C. BAILAR,J. Am. Chem. SOC., 1967, 89, (I7), 4330-4338 The mechanism of hydrogenation of nonaromatic polyolefins catalysed by [MX,(QPh,) ,] or [PtX,(Ol)], (where M=Pt or Pd, X=halide, Q=P or As when n=3 and S or Se when n=2, Ph=phenyl, Ol=bidentate diene), is described. The double bonds migrate stepwise to con- jugation, the conjugated diene is then hydrogenated to the monoene, and the monoene when catalysed causes isomerisation by double bond migration. Reaction intermediates are reported. Effects of solvent, natures of the olefin and the catalysts, and other related effects were studied.

Oxidation of Olefins by Palladium(I1). III. Oxidation of Olefins by a Combination of Palladium(I1) Chloride and Copper(I1) Chlor- ide in Acetic Acid P. M. HENRY,J. org. Chew?., 1967, 32, (8), 2575- 2580 PdC1,-CuC1, in CH,COOH oxidises olefins to acetate esters of glycol and chloro alcohols. C,H, oxidised in solutions with high Cu(I1) content forms 2-chloroethyl acetate, and ethylene glycol mono- and di-acetates, rather than vinyl acetate. Distributions of products of CJls and I- and 2-C,H8 are reported. Oxypalladation adducts act as intermediates in these reactions and decompose by reaction with CuC1,. Product distribution is explained by isomerisation of the oxypalladation addua before reacting with Cu(I1).

Oxidation of Cyclohexene by a Mixture of PdCl, and CuCI, in Acetic Acid P. M. HENRY, Abstr. Papers, 154th Mtg, Am. Chem. SOL., 1967, (Sept.), S78 Experiments showed that saturated disubstituted cyclohexanes (esters) were formed by oxidation only when both PdCl, and CuCI, were present in the reaction mixture; 2- and 3-cyclohexenyl-~- acetate were found in the absence of Cu(I1). Saturated esters were mainly 1,2 isomers, chloroacetates were both cis and trans isomers, I,Z and 1,3 diacetates were the cis isomers. The mechanism involves an oxypalladation adduct as intermediate which eliminates Pt(1I) hydride to give unsaturated esters and which reacts with CuC1, to give saturated esters. Isomerisation of the intermediate leads to the product isomers.

A Catalyst for the Homogeneous Hydro- genation of Aldehydes under Mild Con- ditions

Whereas RhC1(PPh3), is deactivated by aldehydes, IrN,(PPh,), catalyses homogeneous hydrogenation of aldehydes and some olefins at SOT, I atm, e.g. n-butyraldehyde to n-butanol, in C€i&OOH solution. Ir hydrido-acetates are assumed to be the true catalysts in this reaction.

The Decomposition of Formic Acid Catalysed by Soluble Metal Complexes Ibid., 923-924 Many phosphine-stabilised complexes of transition metals, particularly of Ir and Ru, are ex- cellent homogeneous catalysts for decomposition of HCOOH to H, and CO, and functional groups can also be reduced. Results for six catalysts are tabulated and discussed.

R. S. COFFEY, chem. comnzun., 1967, (Is), 923

GLASS TECHNOLOGY Wetting Behaviour of Glasses on Pt and Pt Alloys

211-214

Dynamic methods were used to study the wetting behaviour of Pt, 5% Au-Pt, 5 % Ir-Pt, 5 % Rh-Pt, and a Be-Pt alloy at 40c-1400°c with a heating rate of Io”C/min, on five types of glass. Contact angles are plotted and the results are discussed.

R. KATZSCHMANN, Silikat Tech., 1967, 18, (7),

TEMPERATURE MEASUREMENT Platinum Resistance Thermometry below 10°K R. J. BERRY, Metrologia, 1967, 3, (3), 53-57 An assessment of Pt resistance thermometers at Z-IO~K, based on sensitivity, stability and ease of calibration, concludes that their overall accuracy in this range is 0.03-0.05”K, when used in a fairly convenient manner, and o.oI‘K, when great care is taken.

Birdcage Resistance Thermometer D. A. TOENSHOFF and E. D. ZYSK, Instrum. Control Syst., 1967, 4% (s), 109-1 I I A Pt resistance thermometer of “birdcage” construction was tested as a possible instrument for defining the IPTS scale and measured the gold point (1063°C) to rto.oo~”C.

High-temperature High-vacuum Thermo- couple Drift Tests J. w. HENDRICKS and D. L. MCELROY, Environ. Q.,

Stability of & I O T for roooh at I O - ~ - I O - ~ torr, 120O-I45O0C was found for Pt : IOOG Rh-k, 6% Rh-Pt : 30:/0 Rh-Pt, W: 26% Re-W and 576 Re-W : 26% Re-W thermocouples but at 1200°C severe thermal emf changes occurred with Pt : 10% Rh-Pt in Ta and Nb.

1967, 131 (11, 34-38

NEW PATENTS

lMETALS AND ALLOYS Production of Platinum and Palladium Oxides

Italian Patent 767,275 Oxidation of these metals is achieved by elec- trolysis of a Pt or Pd anode in a bath containing molten NaNO, and an alkali metal halide. This corresponds to Belgian Patent 664,526.

Iridium Alloys JOHNSON, MATTHEY & CO. LTD. INTERNATIONAL NICKEL LTD. British Patent 1,082,078 The addition of 0.1-2% Nb to an Ir of commercial Purity Produces easily workable alloys.

CHEMICAL COMPOUNDS Metallacenyl Organapolysiloxanes

U.S. Patent 3,324,157 Highly stablised organopolysiloxanes are produced by the usual cohydrolysis method where one hydrolysable monomer is a metallocenyl silane, where “metallocenyl” is a residue of a cyclopentadienyl derivative of a transition metal. The Pt group metals are specifically mentioned.

GENERAL ELECTRIC CO. (NEW YORK)

ELECTROCHEMISTRY Anodes and Electrolytic Cells having Such Anodes IMPERIAL METAL INDUSTRIES (KYNOCH) LTD. British Patent 1,076,973 A coated anode is formed from a plurality of Ti members placed side-by-side with each member coated with a Pt metal. The members are connected together by at least one transverse rib. At

Platinum Metals Rev., 1968, 12, (l), 3 6 4 0 36

least half the area of the Pt metal coating is perpendicular to the common plane of the coated members.

Electrodes for Electrolytic Cells IMPERIAL METAL INDUSTRIES (KYNOCH) LTD. British Patent 1,078,516 An electrolytic cell electrode has a core of Ni with a coating of I r or a Pt-Ir alloy. The coating which may be painted on from an organic vehicle, reduces the overvoltage of the electrode.

ELECTRODEPOSITION AND SURFACE COATINGS Non-magnetostrictive Magnetic Electrolytic Deposit INTERNATIONAL BUSINESS MACHINES CORP. British Patent 1,081,316 A Ni-Fe alloy with a small amount of Pd is electrodeposited from an aqueous bath, containing Ni and Fe in a so-80:1 ratio, to which 700 mg/l of Na pallidichloride has been added.

Electrically Conductive Compositions

British Patent 1,086,074 Fired-on conductive metal coatings are produced from a mixture of (a) finely divided metallic Pd, PdO or Pd/Ag alloy, (b ) finely divided Ag, (c) finely divided ceramic consisting of Bi,O, with a Cd or Pb borate frit. The component (a) must provide 22-35% Pd and component (b) 48-69% Ag, based on the total composition.

Platinum Coating Method and Material

Itulian l'atent 764,009 Dispersions of PtO, and mixtures of PtO, with oxides of Rh, Ru, Ir, and Pd, in which Pt is at least 50 wt.'X metal content, are present to 1-500 g/1 in a medium of C,-C, aliphatic alcohols with less than 37% HCHO. Pt metal deposits are formed by coating substrates with this dispersion.

Applying Designs to Metallic Bases

Italian Patent 767,740 A metal or alloy differing in colour from the metal base is applied in an organic base and fired to produce slight adherence, the metal or alloy then being embossed with a design. Au, Ag and Pt metals, e.g. in flake form, are suitable decorative materials. This corresponds to French Patent 1,455,917.

Electrodeposition of Palladium

Italian Patent 767,852 The electrolyte is an alkaline or neutral aqueous

E. I. DU FONT DE NEMOURS & CO.

JOHNSON, MATTHEY & CO. LTD.




solution of a Pd compound and an NH, salt of a weak acid which does not form an insoluble product with the Pd compound. This corresponds to French Patent 1,436,451.

HETEROGENEOUS CATALYSIS Production of Hydrogen Cyanide MONSANTO CO. British Patent 1,077,238 A mixture of NH,, natural gas, H, and air or 0, in the vapour phase is passed over a Pt metal or alloy catalyst at high temperature to produce HCN. A gauze made from an alloy of about 90% Pt and I O ~ ~ Rh is a suitable catalyst material.

Carbonylation of Allylic Halides

British Patent 1,077,773 An acyl halide is produced by reacting CO and an ally1 halide in the presence of a Pt metal catalyst. The preferred catalyst is Pd metal, a Pd salt or a Pd complex of an organic compound.

Catalysts for the Isomerisation of Lower Saturated Hydrocarbons SNAM S.P.A. British Patent I , O ~ I , I ~ O A catalyst consisting of Pt/Al,O, is activated by heating with C,Cl, vapour (at 18o-50o0C) before it is used to isomerise I-6C alkane mixtures. A typical A1,0, catalyst contains 0.8 % C1, and 0.6% Pt.

Carboxylic Acid Vinyl Esters

British Patent 1,082,564 C,H,, 0, and carboxylic acids are reacted in a gaseous state over a supported Group VIII noble metal catalyst to give a vinyl carboxylate. Pd/Al,O,-SiO, is a suitable catalyst.

Process for Activating Catalysts ESSO RESEARCH & ENGINEERING CO. British Patent 1,084,354 Finely divided Au, Ag and Pt metal catalysts (and alloys of those metals) are activated by wetting the catalyst with a basic solution having a p H of 8-14. Wetting, e.g. of a fuel cell catalyst, may be carried out with an alkali metal hydroxide, phosphate, metasilicate or carbonate or with IN NH,.

Preparation of Unsaturated Nitriles ASAHI KASEI K.K.K. British Patent 1,084,599 Unsaturated nitriles are produced by the addition of HCN to a 2-4 C olefine in the presence of 0, and Pd, Rh, Ru, Pt, Au or Cu catalyst.

Hydrogenation of Unsaturated Aldehydes

British Patent 1,086,447 The olefinic double bond of an unsaturated

NATIONAL DISTILLERS & CHEMICAL CORP.

FARBWERKE HOECHST A.G.

UNIVERSAL OIL PRODUCTS CO.

37

aldehyde is reduced selectively in the presence of a Pd catalyst and a two-phase liquid system.

Cyclododecene Production GEIGY (U.K.) LTD. British Patent 1,086,639 Cyclododecatriene is hydrogenated until 2 mols of H, are absorbed in the absence of solvent and in the presence of a hydrogenating catalyst, preferably a supported Pt group metal.

Preparation of Vinyl Chloride

British Patent 1,086,785 Vinyl chloride and optionally ethyl chloride are produced from C,H,, 0, and HC1 in the presence of an elementary Group VIII noble metal, especially Pd, Pt, Rh, Ru and Ir.

Activating a Cornposited Catalyst

British Patent 1,087,586 Catalysts consisting of Pt metals on A1,0, are activated by heating at 510-677" in the presence of S,O,XbY,, where X is C1, Y is another halogen, n is I or 2, a is 0-3 or 5, b is 2,4, or 7, c is o or I and b i - c is 2-8.

Hydrogenation of Unsaturated Hydrocarbons

British Patent 1,087,684 The catalysts used consist of one of the six Pt metals deposited on an Al,O, which has a bulk density of less than 0.78 g/ml. Smaller amounts of other refractory oxides may also be present.

FARBWERKE HOECHST A.G.

GULF RESEARCH & DEVELOPMENT CO.

SHELL INTERNATIONALE RESEARCH MIJ. N.V.

Production of Hydrogen Cyanide .MONSANTO CO. British Patent 1,088,903 HCN is produced by the reaction of NH,, natural gas and air in the presence of a metallic Pt or Pt alloy gauze which has been activated by the passage of a reactant mixture with a NH,:gas:air ratio of 0.7-I.O:I :0.170--0.200. A preferred gauze contains I O - ~ O : ~ Rh.

Catalytic Conversion of Hydrocarbons

British Patent 1,088,933 The catalyst for the petroleum conversion process is a crystalline synthetic mordenite having a pore opening of at least 5A which has been decat- ionised by direct treatment with mineral acid to give a metal cation content of not more than 2 wt.7; and on to which a Group VI or VIII metal or oxide hydrogenating component has been deposited. For hydrogenation the preferred catalyst is Pt or Pd.

Hydrogenation of Aminovinyl Ketones

Aminoalcohols can be produced by hydrogenating the keto and vinyl groups of aminovinyl ketones

BRITISH PETROLEUM CO. LTD.

EASTMAN KODAK CO. U.S. Patent 3,325,491

over Ru or Rh catalysts. The amino group is not touched.

Hydrocarbon Conversion Catalyst

U.S. Patent 3,326,797 The catalyst consists of Pt, Pd or another transition metal hydrogenation catalyst deposited on a crystalline, zeolitic, alumino-silicate base, the base having been prepared by digesting a crystalline zeolite, with a SiO,/Al,O, ratio of about 6-12:1, in aqueous caustic.

Catalyst for Hydrocarbon Reforming

U S . Patent 3,328,286 Petroleum feedstocks are upgraded by hydro- reforming over a catalyst comprising Pt /Al,O, having a reversible CsHs chemisorption of up to 5 I* m o m

Hydrocarbon Conversion Catalysts

U.S. Patent 3,329,604 An alumino-silicate zeolite is treated to replace alkali metal ions by Mn cations and then the product is used as a carrier for a Pt group metal catalyst. The catalysts can be used in cracking, hydrocracking, etc.

Platinum Group Metal Catalyst Selectivity MOBIL OIL CO. US. Patent 3,330,761 In reforming naphtha at 100-1000 p.s.i.g., the selectivity of the Pt group metal catalyst is improved by contacting it, before major use, with a feedstock containing 100-2000 p.p.m. S to reduce subsequent undesirable exothermic reactions.

Steam Reforming Process

U.S. Patent 3,334,055 A Co or Ni oxide reforming catalyst is activated with o .o01~.5 wt.x of a Pt group metal or reducible compound, preferably Pt, Pd or Rh.

Hydrogen Peroxide Production

US. Patent 3,336,112 H, and 0, are reacted together in the presence of a Group VIII metal, e.g. Pd:SiO,, and H,O containing a stabiliser and a condensed phosphate activator.

Hydrogenation with Platinum Metal Sul- phide Catalyst UNIROYAL INC. U.S. Patent 3,336,386 Nitro- or N-nitrosoamine groups are reduced to amine groups using a Pt metal sulphide, e.g. a supported PdS. The catalysts can also be used for other reduction processes and some of the products are rubber stabilisers.

UNION OIL CO. OF CALIFORNIA

THE BRITISH PETROLEUM CO.

ESSO RESEARCH & ENGINEERING CO.

IMPERIAL CHEMICAL INDUSTRIES LTD.



Dehydrogenating Hydroxy- and Oxo-cyclo- aliphatic Compounds PROGIL U.S. Patent 3,336,399 cr-Naphthol and the like are produced by dehydrogenation over a finely divided metal catalyst, selected from Pt, Ir, Pd, Rh and other transition metal catalysts.

Hydrogenation of Cinnamaldehyde

Italian Patent 775,456 Selective hydrogenation of unsaturated aldehydes, in particular of cinnamaldehyde to cinnamyl alcohol, is catalysed by supported Pt metals in alcoholic solutions with alkali promoters, e.g 5%) Pt/charcoal, Ru-Pt/charcoal, Pt/A1,0,. This corresponds to Belgian Patent 685,368.

Hydrogenation of Crotonaldehyde by Trickle Column Catalysis JOHNSON, MATTHEY & CO. LTD. Italian Patent 775, 452 Butyraldehyde is produced by hydrogenation of crotonaldehyde with H, over Pd/Al,O,, Pd/C or Pd/ceramic supports in a trickle column reactor.


HOMOGENEOUS CATALYSIS Preparing High Molecular Weight Paraf- finic Hydrocarbons from Carbon Monoxide and Hydrogen H. I'ICHLER British Patent 1,076,848 CO and H, are reacted at 80-135°C and 100- 3,000 atm, to give hydrocarbons with a molecular weight of above 50,000, using a highly active Ru catalyst. This is formed in situ by reacting a highly active RuO, with a hydrocarbon solvent to give a hydrocarbon complex.

Carboxylic Acid Preparation

British Patent 1,080,867 The reaction of an optionally substituted olefine with CO, to produce a carboxylic acid or its derivatives, is catalysed by a halide or n-complex of Pd, Rh or Ru, e.g. PdC1, or an C,H,-Pd complex.

Chemical Compounds

British Patent 1,081,304 Copolymers of an olefine and CO are produced by heating them in the presence of a catalyst comprising an alkyl phosphine complex of a Pd salt, especially (Bu,P),PdCl,.

Preparation of Carboxylic Acid Esters ESSO RESEARCH & ENGINEERING CO. British Patent 1,083,597 A substituted ally1 ester is produced by reacting a tertiary olefine with a source of carboxylate ions

SHELL INTERNATIONALE RESEARCH MIJ. N.V.


in the presence of a Pd salt and a high boiling anhydrous polar solvent at 50-150"C.

Production of E, P-Ethylenically-unsaturated Carboxylic Acids and/or P-Acyloxy Car- boxylic Acids

British Patent 1,083,880 These acids are produced by the oxidative carbonylation of olefines in an anhydrous reaction medium containing an aliphatic carboxylic acid solvent and 0.001-5 wt.% of a Pt metal, preferably of the Pt or Pd subgroups, as a finely divided metal, salt or chelate.

Production of Vinyl Acetate and Acetal- dehyde

British Patent 1,083,959 The oxidative carbonylation of C,H, takes place in an acid solution of a I'd salt, an ionisable metal chloride, cupric acetate and 0-20 wt.(X of H,O.

Production of Acetaldehyde

British Patent 1,086,347 CH,CHO and optionally vinyl acetate are produced from C,H,, 0, and CH,COOH in the presence of O.OOZ-O.Z mols/1 palladous salt and at least 0.5 mols/l of a Zn/Cu redox mixture.

Manufacture of Ethers

C,H, is reacted with a palladous salt and a metal salt able to oxidise Pd metal in an alcohol to form the vinyl ether of the alcohol and then the metal salt is reoxidised and regenerated with 0,.

Production of Vinyl Acetate E. I. DU PONT DE NEMOURS & CO. British Patent 1,087,508 C,H, is reacted with an CH,COOH solution of a palladous salt and a cupric salt at ZOO psig or higher and also in the presence of 0.05-2.6 mol/l KC1.

Palladium Catalysts for Ketone Polymeri- sation SHELL OIL CO. U.S. Patent 3,321,442 The catalysts are PdCl, and (Ar,X)PdCl,, where Ar is Ph and X is P, As or Sb.

UNION OIL CO. OF CALIFORNIA

E. I. DU PONT DE NEMOURS & CO.

E. I. DU FONT DE NEMOURS & CO.

BRITISH CELANESE LTD. British Patent 1,086,351

Hyclrido-iridium and -osmium Complexes in Hydrogenation STANDARD OIL co. (INDIANA) U.S. Patent 3,324,018 Non-aromatic C-C unsaturation is hydrogenated selectively using a number of specified hydrido- iridium and -osmium complexes of triphenyl arsines, stibines and phosphines, e.g. IrHCl,(PPh,),.


Organosilanol Preparation

The conversion of a SiH group to a SiOH group by reaction with H,O is catalysed by either H,PtCl,, Zeise’s salt, Pd, Rh or Ru.

Polybutadiene Isomerisation UNIROYAL INC. U S . Patent 3,330,817 A polybutadienc containing cis, trans and vinyl isomers in a non-equilibrium ratio is isomerised by contacting it with a Rh salt selected from the chloride, bromide, iodide, sulphate, nitrate or acetate at a temperature of 2c-8ooC.

DOW CORNING CORP. U.S. Patent 3,328,448

FUEL CELLS Fuel Cells THE SPERRY GYROSCOPE CO. LTD. British Patent 1,084,238 A fuel cell is provided with a hydrogen-permeable membrane of Pd substantially free from pinholes. Preferably the Pd is alloyed with a minor proportion of one or more metals, such as up to 27:h Ag, to improve its strength.

Plural Coated Fuel Cells STUDEBAKER GORP. U.S. Patent 3,322,576 The electrode consists of a porous metal support in the form of a Ta or T i sheet member, a first coating of graphite in a fluorocarbon polymer and a second coating of Pt black in an amount of 0.1-20 mg/cm2.

Metallised Paper Fuel Cell Electrode

U.S. Patent 3,328,205 A new form of electrode consists of an unfused, fibrillated, substantially hydrophobic paper sheet on which an active metal catalyst (preferably selected from Pt, Pd and Ru) is deposited in an amount of 25-650/, based on the resulting sheet.

AMERICAN CYANAMID CO.

GLASS TECHNOLOGY Alloy Resistant to Wetting by Glass

Italian Patent 764,901 An alloy for use in the glass industry consists of 60-97 wt.yb Pt, 2-25 wt.?L Rh and 1-10 wt.7; Au. This corresponds to Belgian Patent 682,754.


ELECTRICAL AND ELECTRONIC ENGINEERING Electrical Contact Elements and Contact Assemblies JOHNSON, MATTHEY & CO. LTD. British Patent 1,088,541 A series of contact elements are produced on a backing strip of a different metal which is pro-


vided with a plurality of locating members corresponding to the numbers of contact elements. The object of the locating members is to locate the strip in a press tool accurately to that contact members can be pressed out precisely without leaving waste material between them. The contact metals are preferably formed of noble metals, such as Ag, Pt, Pd or Au.

Electrical Resistance Wire

U.S. Patent 3,320,039 The wire consists of an outer tube of Pt group metal or alloy filled with a refractory oxide selected from A1,0,, ZrO, and MgO. A suitable tube is made from Pt with 10-40% Rh.

Cermet Resistance Element

U.S. Patent 3,326,645 A thin resistance layer is produced on a non- conducting base layer from a cermet composition. This contains 5 0 9 5 wt.7; glass and 5-50 wt.26 of a Ru-Rh alloy, such as a I:I alloy (by weight). The composition of the alloy is matched to the glass so that the glass has a lower melting point than the alloy and at least 10 wt.% Ru is present. See also U.S. Patent 3,326,720.

Electrical Resistance Element CTS CORP. U.S. Patent 3,329,526 The resistance element consists of a resistant insulating base coated with a glass film not thicker than 0.0002 inch and containing particles of Ru having hexagonal close-packed crystalline structure and acicular growth.

Sparking Plug Electrodes

U S . Patent 3,331,685 Ru and Ru-Ir alloy powders are compressed and sintered to form an electrode resistant to contamination by Pb. Ranges of preferred particle sizes, sintering temperatures, and compacting conditions are claimed.

Strain Gauge Alloy HITACHI LTD. U S . Patent 3,333,462 A new alloy useful for strain gauge wire of foil consists essentially of 20.0-52.2 at.% Pt, 11.3- 33.5 at.96 Rh and about 14.3-50.0 at.yL Pd.


BECKMAN INSTRUMENTS INC.


TEMPERATURE MEASUREMENT Tungsten-Osmium Thermocouple US. ATOMIC ENERGY U.S . Patent 3,320,098 The thermocouplc consists of a first leg consisting of 0.5-1.0 at.% 0 s and the remainder W and a second leg consisting of 26 at.% Re and the balance W.

40

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