Platinum Metals Review

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PLATINUM METALS REVIEW

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

VOL. 31 JANUARY 1987 NO. 1

Contents

The Role of Platinum Metals in Neurological Prostheses 2

New Dispersion Strengthened Platinum Alloy 8

Commodity Meeting on the Platinum Metals 11

Platinum Reactivity Rationalised 12

The Development and Application of Palladium Contact Materials 13

Pressure Sensitive Palladium Complex 20

Anti-Cancer Platinum Compounds 23

Heterogeneous Catalyst Preparation 24

Corrosion Protection Conference 25 High Temperature Degradation of Nickel Based Alloys 26

A History of Iridium 32

Platinum in Early Instrumentation 41 Abstracts 42 New Patents 48

Communications sbuld be addressed to The Editor, Platinum Metals Review Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE The Role of Platinum Metals in Neurological Pro sthe ses PROGRESS IN BIOMEDICAL APPLICATIONS By P. E. K. Donaldson Medical Research Council, Neurological Prostheses Unit, London

Prostheses are devicesfor restoring artificially somefunction lost through accident or disease. Neurological prostheses, therefore, are surgically implanted microelectronic devices which seek to ameliorate the results of neurological defect. Examples are: implants for treating incontinence, or for recovering some use of paralysed arms and legs following spinal accident; implantsfor patients who are blind as a result of damage to the eye or optic nerve; implants for patients who are deaf as a result of damage to the inner ear. In addition, there are some implanted devices which are not strictly prostheses;for example, implants for relieving pain, and implants for correcting curvature of the spine in children. Despite the variety of purposes for which neurological prostheses are built, they have in common that they are all nerve stimulators and can all be realised using, substantially, the same technology. This article discusses the technology for implant-making which has been worked out at this Unit, and shows the essential role played by noble metals in that technology.

That electric currents have an effect upon the When nerve A is stimulated, by pinching, both nervous system is one of the oldest observations muscles instantly contract. Because the effect in electrical science. Chapter One of practically on B is immediate, the influence can scarcely be any general textbook of electricity has something chemical, but is almost certainly electrical. to say about Aloisio Galvani (1737-1798), and Here was good evidence that the action of or- his experiments with frogs’ legs toward the dinary muscles was indeed, in some way, elec- end of the eighteenth century. At about the trical in nature. same time, people were giving themselves, and Notice the use of preparation B as an instru- each other, shocks from frictional electrical ment for detecting the feeble electrical effects machines and charged Leyden jars; it was clear shown by preparation A. It was to be many that both motor and sensory nerves were af- years before man-made detectors could match fected. An important question arose; were elec- in sensitivity the frog preparation. Eventually trical effects factitious, or were animals- they did, however, and when they did, they including humans-actually some kind of elec- gave quantitative determinations, were stable, trical machine? The shocks one could get from and could be calibrated. They established that electric fishes pointed toward the latter view, nerve fibres also propagate something electrical but electric fishes might be a special case. In in character, the so called “action current”. 1842, Matteucci performed a classic experiment Milestones on the way to these sensitive detec- which first demonstrated “secondary contrac- tors were the capillary electrometer (I872), the tion”: two frog nerve-muscle preparations are string galvanometer (1901) and the valve dissected out, and the nerve of preparation B is amplifier with cathode-ray-tube display (from laid alongside the muscle of preparation A. the year 1919 onwards).

Platinum Metals Rev., 1987, 31, (I), 2-7 2 Over a period of some I 50 years, then, a great Unit, directed by G. S. Brindley, F.R.S., was body of electrophysiological knowledge was ac- founded in 1968. It is not primarily a clinical cumulated. By 1950 the biophysics of nerve unit; its task is to develop implant applications could be said to be understood, and before and implant technology generally. long, many laboratory neurophysiological experiments could be regarded as complex The Nature of Neurological interactive processes between the apparatus- Prostheses perhaps under computer control-stimulating, Ideally, a prosthesis would be a “fit and and recording action currents from, various forget” device, wholly implanted. No training points in the nervous system of the anaesthetis- would be needed to use it, and the patient ed animal under investigation. Very occasional- would not appear disabled. Viewed as a bridge ly, perhaps as a result of the need to carry out for crossing a damaged section of nervous tract, a particular surgical procedure, the nervous the ideal prosthesis would record nervous ac- system could be human. tivity somewhere upstream of the lesion, and The transfer of electrophysiological know- stimulate appropriately healthy nerve fibres how from research environment to clinical ap- somewhere downstream. At present only the plication, in the form of neuroprosthetic im- demand pacemaker has these ideal features. plants, had to await the invention and Most prostheses, though contributing to the development of the transistor. This is not quality of, and possibly extending, the patient’s because such implants contain transistors. life, fall short of the ideal. For example, a They need not; one can make extremely useful paraplegic with an implanted leg-controller has devices without employing transistors. It is at present to manipulate controls on a box, rather that the availability of transistors forced perhaps attached to his belt. The box sends manufacturers of associated electronic com- commands to an implanted radio receiver, ponents to miniaturise their products, so that which decodes them and sends suitable pulses the beneficial reduction in equipment size, of stimulating current along flexible cables to weight and power consumption, which the electrode groups maintained in near contact transistor offered, could be. fully realised. with the relevant motor nerves. This patterned Hermetically encapsulated transistors were stimulation in turn causes muscles in the hips available by the mid 1950s~and the accompany- and legs to contract and relax as required. Con- ing range of companion passive components fining myself henceforward to prostheses soon followed. The first neurological pros- designed and built in this Unit, we see that in thesis, the fmed-rate cardiac pacemaker, was general they divide into an external and an im- announced by two separate groups, one planted part, and that the implanted part Swedish and one North American, in 1959. It divides again into receiver block, cable, and is rather reassuring to find that this important electrode group. In all three implanted parts, medical-technological development could not noble metals find application. have occurred much earlier than it did (I ,2). Other prostheses soon followed: the phrenic Electrode Groups nerve stimulator, for patients who cannot Electrode groups can be monopolar, bipolar breathe on their own, in 1966 (3) and or tripolar. The pattern of the current flow Brindley’s first visual prosthesis in 1967 (4). around each is shown in Figure I. In principle, Since then the subject has grown enormously, the tripolar group is best, since the current is with cardiac pacemakers, phrenic nerve largely confined within the group; thus there is stimulators, cochlear stimulators for the deaf, minimal stray current to disturb neighbouring spinal anterior root stimulators for the inconti- structures such as sensory nerves, whose un- nent and dorsal horn stimulators for those with intended stimulation may be experienced as chronic pain, all commercially available. This pain. On the other hand, tripoles are evidently

Platinum Metals Rev., 1987, 31, (1) 3 - +- +-

(a) (b) (C) Fig. 1 The pattern of current flow about (a) monopolar, (b) bipolar and (c) tripolar electrode groups, indicating the extent of current spread

the most elaborate, and in cases of .difficult lowered. It is then loosely trapped by snapping surgery may be hard or impossible to place cor- onto the trough a silicone-rubber lid. rectly. When access to the nerve is very awkward, it may be that the best that can be Implantable Cable done is to get a monopole in as nearly the right An implantable cable must conform to place as possible. Our electrodes are invariably movements of the patient’s body, and so must of platinum, to which some iridium may have be able to bend, twist, stretch and resist been added where springiness is desirable. The crushing. It should comprise several separate task of the electrode is to convert an electron current in the metal, to an ion current in the ex- tracellular fluid, with acceptably low overvoltage and by redox processes only; while so doing, to dissolve as slowly as possible, forming dissolution products of minimal toxicity; to be convenient in fabrication and easy to join to other materials. Platinum performs these tasks admirably. The redox charge-injection capability is about 300 microcoulombs per real (as op- posed to projected) square centimetre of surface (5,6), which we consider sufficient. The dissolution rate is about 30 nanograms per coulomb if the electrode is properly used (7), which implies a satisfactory life. Pure platinum is easy to handle, platinum-iridium rather less so. Either metal is easily joined by brazing with gold. Figure 2 shows a form of tripolar group devised by Brindley (8); the electrodes are U- Fig. 2 This end view of a tripolar electrode group shaped and line a trough, fabricated from shows the U-shaped platinum electrodes lining a silicone rubber, into which the nerve is silicon rubber trough where the nerve is placed

Platinum Metals Rev., 1987, 31, (1) 4 conductors, to the ends of which temporary or permanent connection can be readily made. A form of cable which meets these requirements has been devised by J. D. Cooper (9). The body of the cable is of silicone rubber, 2 mm in diameter. Through this pass between one and five intercalated helices of 20 per cent iridium- platinum; the wires are 75 microns in diameter and insulated with a polyimide resin. Two short lengths of cable are shown in Figure 3. We usually have one end of the cable permanently attached to its electrode group by gold brazing; the other end terminates in an implantable plug-and-socket assembly, known as a Craggs connector (10). Cooper cable has proved extremely reliable in use, and we attribute much of this to the excellent mechanical properties and resistance to corrosion of the alloy used. Fig. 3 The Cooper multiconductor iridium- platinum cable is able to withstand bending, twisting, stretching and crushing, so conforming Receiver Blocks to the movements of the patient’s body. The Receiver blocks vary greatly in complexity, lower of these two pieces of four-cored cable is an experimental length with colour coded con- from those which are virtually miniature crystal ductors. The sides of the background squares sets, feeding to a single electrode group stimuli measure 1 mm derived by rectifying a simple modulated carrier wave, such as that shown in Figure 4, to Suppose we have been asked to encapsulate a complex demultiplexing receivers supplying cylindrical torch battery, having an insulating several electrode groups from few, possibly on- body and a pole at each end, in some rubbery ly one, radio signal. Whether the receiver is or resinous material so that, upon being thrown simple or elaborate has, however, little in- into the sea, it will not discharge. Water vapour fluence on a fundamental decision in implant will diffuse through the encapsulant and will design, which is, what sort of metal should the condense into any voids at the interface bet- electrical conductors be made of? ween encapsulant and battery, particularly if

Fig. 4 An implantable block of three simple receivers and a triplet of Craggs connectors, on the lefi, shown here at approximately full size. Each of the receivers will supply its own electrode group

Platinum Metals Rev., 1987, 31, (1) S Fig. 5 If a cylindrical torch battery with an insulating body and a pole at each end is encapsulated in a supposedly adhesive but unavoidably water-vapour-permeable material and then immersed in water, a number of things may happen. Of the four situations shown here, only condition (d) is disastrous, the battery having been discharged this interface is contaminated with water- pressure of accumulating corrosion products. soluble soil. If, after a week or two, we go and Secondly, we might use a valve metal such as retrieve our battery, we might find one of four tantalum; it is tempting to use the surface oxide things has happened: (a) The encapsulant is film on tantalum wire as the insulation, and everywhere adherent to the battery; the battery good adhesive bonds can be made to the oxide has not discharged. (b) The encapsulant is surface. However, if nevertheless some local adherent to the poles but has become detached failure of adhesion should occur, there are cir- from the insulating body; the battery has not cumstances in which the oxide layer could be discharged. (c) The encapsulant is adherent to electroreduced, with consequent malfunction the insulating body but has become detached of the implant. The third option is to use a no- from the poles; the battery has not discharged. ble metal, accepting that the encapsulant will (d) The encapsulant is everywhere detached; not bond to it, so the metal will operate per- the battery is discharged. These conditions are manently wet. To minimise the mechanical shown in Figure 5. weakness resulting from the absence of adhe- This illustration brings out an important sion, one uses an insulator to which excellent general principle, which is that it is not adhesion is possible, and lays out circuits so necessary that the encapsulant adhere to both that the area of insulation presented to the en- conductor and insulator surfaces, though clear- capsulant is large compared with the area of the ly the resulting structure is stronger if it does. conductor. If we use a reactive metal such as copper for our In our Unit we have concentrated on the conductors, we should be able to get the encap- third option. Circuits are made by thick film sulant to bond to it. But if, perhaps because of technology; the insulator material is conse- some carelessness in manufacturing technique, quently alumina; an example is shown in that bond fails here and there, the copper sur- Figure 6. For the conductor pattern we use a face will become wet and corrosion will set in. fritted gold-platinum alloy and the terminal Because corrosion products generally take up posts are 18 carat gold, while the coils can be more space than the original metal, we can ex- wound from silver wire. Chip capacitors and pect further adhesion failure caused by the resistors have silver-palladium terminations.

Platinum Metals Rev., 1987, 31, (1) 6 Fig. 6 This simple thick-film receiver for an auditory prosthesis incorporates a number of noble metals. The gold- platinum conductor pattern leaves a significant area of the alumina exposed, where the encapsulant can adhere firm- ly, so providing the required mechanical strength

Diodes and transistors present a slight pro- possible very satisfactory implantable cable, blem: these components can be obtained with while the redox performance of platinum and gold-plated “Kovar” leads, and it is tempting iridium-platinum electrodes in saline allows one to use them. Unfortunately the’amount of gold to stimulate nerves artificially for long periods, used is not really sufficient for implant use, and and as yet we do not know just how long, the smallest pinhole will lead to serious corro- without harming them. sion of the underlying iron alloy. We have found it advisable to switch to option one here, References and use components with tin-plated leads. I R. Elmqvist and A. Senning, “An implantable Manufacturers can afford to be more generous pacemaker for the heart”, in “Medical Elec- with tin, but if one has any reason to suspect tronics”, Proc. 2nd Int. Cod. on Medical Elec- they have not been, one can always add more tronics, Paris, June 1959, Iliffe and Sons, London 2 W. Chardack, A. Gage and W. A. Greatbatch, when soldering the component in. Lastly, there Surgev,w6o, 4% 643 is the matter of the solder itself. We use a tin- 3 W. W. L. Glenn, W. G. Holcomb, J. Hogan, I. lead eutectic solder with 2 per cent added Matano, J. B. L. Gee, E. K. Motoyama, C. S. silver, which works well in practice. We are Kim, R. S. Poirier and G. Forbes,J. Thorac. Car- diovasc. Surg., 1973, 66, 505 careful always to be generous when soldering, 4 G. S. Brindley and W. S. Lewin, 3. Physwl., so that if, by some mischance, there should be 1968, 196, 479 an adhesion failure nearby and corrosion of the 5 S. B. BrummerandM. J. Turner, Trans. IEEE, alloy sets in, there is plenty of sacrificial anode BME-24, 1977. 436 6 N. de N. Donaldson and P. E. K. Donaldson, underneath, to hold the joint together. Med. Bwl. Eng. Cornput., 1986, 24, 41 7 N. de N. Donaldson and P. E. K. Donaldson, Conclusion Med. Bwl. Eng. Cornput., 1986, 24, 431 Noble metals have an essential role to play in 8 G. S. Brindley, J. Neuml. Neurosurg. Psychiutr., neurological prostheses. In all applications their 19773 4% 358 chemical inertness and ease of microjoining are 9 P. E. K. Donaldson, Med. Biol. Eng. Cornput., 19839 213 371 invaluable. In addition, the good fatigue 10 P. E. K. Donaldson, Med. Biol. Eng. Cornput., resistance of iridium-platinum alloy makes 1985, 23, I95

Platinum Metals Rev., 1987, 31, (1) 7 New Dispersion Strengthened Platinum Alloy LOWER RHODIUM CONTENT OFFERS ECONOMIC ADVANTAGES By R. B. McGrath and G. C. Badcock Johnson Matthey Metals Limited

Zirconia grain stabilised platinum alloys developed by Johnson Matthey are widely used to contain molten glass. The high temperature strength of these alloys is well in excess of that of similar conventional rhodium- platinum alloys, and zirconia grain stabilised ten per cent rhodium- platinum, the strongest alloy in the range, is used in the most demanding applications where its excellent creep resistance offers prolonged component life. However the present high cost of rhodium, compared with that of platinum, has generated increased interest in alloys with a lower rhodium content suitable for certain applications where the outstanding properties of the ten per cent alloy are not fully utilised. To meet this demand Johnson Matthey have mw developed zirconia grain stabilised five per cent rhodium-platinum. This alloy offers a useful range of physical properties for applications where economic considerations are a major factor.

Molten glass is one of the most corrosive fine dispersion of zirconium oxide within the materials known to man. However platinum metal/alloy matrix. The effect of this oxide is to and certain of its alloys have excelled as reduce the rate of grain boundary movement, materials used for the manufacture of apparatus resulting in the retention of the fibrous micro- for handling molten glass, primarily because of structure produced during fabrication. High their unique chemical inertness. This property temperature strength and creep resistance are separates them from all other “corrosion resis- significantly improved by the retention of this tant” alloys, and consequently the relatively highly aligned grain structure, even after a low strength of conventional platinum alloys at prolonged period at high temperature. Thus molten glass temperatures was tolerated, and component life is increased, or alternatively it compensated for by careful design including may be manufactured from thinner sectioned the use of refractory supports. When Johnson materials; in either case a considerable cost Matthey introduced zirconia grain stabilised advantage occurs (I, 2). (ZGS) platinum and platinum alloys their The strongest alloy in the ZGS range is ZGS higher strengths and improved creep resistance 10per cent rhodium-platinum. This is widely us- increased considerably the range of possible ed as a constructional material throughout the applications. glass manufacturing industry, and especially for Johnson Matthey manufacture three ZGS baseplates for glass fibre bushings. The materials in significant volume, these being rhodium acts as a solid solution strengthener ZGS platinum, ZGS 10 per cent rhodium- giving superior creep resistance to that of ZGS platinum and ZGS 5 per cent gold-platinum. platinum, which in turn has greater creep All are strengthened by the incorporation. of a resistance than all the conventional alloys up to

Platinum Metals Rev., 1987, 31, (I), 8-11 8 Fig. 1 The stress rupture lC properties at 140OOC of the new ZGS 5 per cent rhodium- platinum alloy lie between those of ZGS platinum and "E ZGS 10 per cent rhodium- platinum. For comparison the * properties of conventional i platinum and 10 per cent El rhodium-platinum are also included w

0.' 1 10 100 10' TIME TO RUPTURE, HOURS

260- I ZGS 10% Rhodium-Platinum

$220. ZGS 5% Rhodium-Platinum w z n qtso. I 0- 140 K ZGS Platinum a m100-

wX p 60.

2012.0 3s L" 1 .o 260 400 660 860 lob0 12bO 1460 TRUE STRAIN, E ANNEALING TEMPERATURE.'C

Fig. 2 Plotting true strain againet hardness shows that the work hardening charac- Fig. 3 Recrystallisation curves are shown teristics of ZGS 5 per cent rhodium- for both conventional and zirconia grain platinum are also between those of ZGS cltabilised platinum, and some of its alloys. platinum and ZGS 10 per cent rhodium- The test samples were held at the anneal- platinum ing temperatures for 30 minutes

and including 40 per cent rhodium-platinum. alloy which none the less is more resistant to In addition rhodium increases the wetting angle creep than ZGS platinum. of molten glass in contact with the alloy, which is advantageous when high quality glass is being Some Properties of manufactured (3). ZGS 5 per cent Rhodium-Platinum The recent rise in the price of rhodium, The manufacturing process used to produce however, has resulted in a demand for high ZGS 5 per cent rhodium-platinum is essentially strength alloys of lower rhodium content. As an that used for the current range of ZGS alloys, alternative to ZGS 10 per cent rhodium- thus its physical and mechanical properties lie platinum Johnson Matthey have developed between those of ZGS platinum and ZGS 10per ZGS 5 per cent rhodium-platinum, a cheaper cent rhodium-platinum.

Platinum Metals Rev., 1987, 31, (1) 9 Fig. 4 The fhrous structure of ZGS 5 per cent Fig 5. Metallographic examination shows that rhodium-platinum is retained after annealing at even after prolonged heat treatment at 140OOC 1100OC, following cold wc$cing to a 90 per cent ZGS 5 per cent rhodium-platinum retains a reduction in cross-sectional area x 150 fibrous grain structure x 150

The comparison is shown in the Table, where lisation behaviour of the new alloy are illus- the properties of some conventional rhodium- trated in Figures z and 3, respectively, where platinum alloys are also included. For glass comparison is again made with the other ZGS manufacture one of the most significant proper- alloys. These properties suggest that ZGS 5 per ties is the high temperature strength and in this cent rhodium-platinum would fabricate as respect it can be seen that, although not match- readily as the other ZGS alloys, and this has ing the excellent creep resistance of ZGS 10per been confirmed during development work. cent rhodium-platinum, ZGS 5 per cent The microstructural behaviour is typical of rhodium-platinum offers considerable improve- the ZGS alloys, the zirconia dispersion retain- ment over both ZGS platinum and the strongest ing the fibrous “as worked” structure; this is conventional rhodium-platinum alloy, namely shown in Figures 4 and 5. 40 per cent rhodium-platinum. This is shown in more detail in Figure I where the stress- Economic Considerations rupture lives of ZGS alloys are plotted against In the past twelve months the ratio of the cost the applied stresses. of rhodium to that of platinum has fluctuated The work hardening response and recrystal- between z : I and 4 : I. In the medium term it

Properties of Selected Platinum Based and ZGS Platinum Based Alloys

Conventional Zirconia Grain Stabilised

5% 10% Pt Pt Rh-Pt Rh-Pt

Specific gravity. glcm’ (at 2OoC) 21.4 21.4 20.6 20.0 Hardness, Hv (arinealed) 40 60 95 110 UTS, kg/mmz (annealed) 12.7 18.6 29.2 36.2 Elongation, per cent (annealed) 40 42 24 30 100 hour Stress rupture life, kg/mmz (at 14OOOC) -0.14 0.36 0.69 -0.91 -1.05 - 1.41

Platinum Metals Rev., 1987, 31, (1) 10 seems probable that the price differential exist- By retaining many of the virtues of the higher ing between these two elements will be main- rhodium content alloy, ZGS 5 per cent tained. Thus the basic material cost of rhodium-platinum offers an attractive eco- rhodium-platinum alloys is considerably in- nomic alternative to ZGS 10per cent rhodium- fluenced by the rhodium content. Every 5 per platinum. cent rhodium addition to platinum increases References the cost of the alloy by approximately 10 per I G. L. Selman, J. G. Day and A. A. Bourne, cent. For those who use large amounts of Platinum Metals Rev., 1974, 18, (2), 46 rhodium-platinum alloys, such as the manufac- 2 G. L. Selman and A. A. Bourne, Platinum Metals turers of high quality glass, the cost savings that Rev., 1976, 20, (3), 86 3 G. L. Selman, M. R. Spender and A. S. Darling, can be made by using alloys of lower rhodium Platinum Metals Rev., 1965,9, (3), 92; 1965,9, (4), content, wherever possible, are significant. 130; ibid., 1966, 10, (2), 54

Commodity Meeting on the Platinum Metals A SURVEY FOR THE INSTITUTION OF MINING AND METALLURGY For some years the Institution of Mining and hydrometallurgical operations and those in use Metallurgy has organised an annual ‘‘Com- at the Inco refinery were outlined by Dr. B. F. modity Meeting” to discuss the whole back- her.The current flow sheet includes leach- ground to a particular metal. The eleventh of ing, precipitation, crystallisation, distillation, these conferences, held on 4th December at the ion exchange and solvent extraction. Geological Society, was devoted to the platinum An informative paper, by B. M. Symes, a group of metals, their history, resources, consulting metallurgist, dealt with the process- mining, refining and applications. ing of the platinum metals from minerals on- After the official opening by the President, wards, particularly those from the primary Dr. A. J. Robinson, a paper on “Platinum: the source in the western world, the Merensky History of One of the World’s Most Strategic Reef. The older conventional procedure was Metals” was presented by Dr. F. D. Collender compared with the newer solvent extraction of Strauss, Turnbull & Co. Outlining the process. By this route the metals are refined to history of its discovery in South America, the a high state of purity, normally 99.95 per cent. first scientific studies of its properties in the Developments in the market for platinum eighteenth century and then its more recent formed the subject of an interesting paper by developments, the author emphasised how vital Mr. Alan Austin, General Manager Platinum platinum has become to meeting man’s greatest Marketing, Johnson Matthey. This emphasised needs-food, fuel, communications, optics and the rather dramatic developments in the range clothing, playing an essential part in the power, and size of its applications that have taken place fertiliser, petrochemical, electronics, glass and over the last thirty-five years and examined the synthetic fibre and automotive industries. key factors that have influenced the market. Professor D. L. Buchanan of the Royal In conclusion trends in the industrial appli- School of Mines described the geology under- cations of the platinum metals were discussed lying the world’s supply of platinum metals, by Dr. G. J. K. Acres, Director, Corporate while the investigation of the so-called UG2 Development (Technology), Johnson Matthey. reef, below the famous Merensky Reef, was In addition to their established uses and their reported by I. M. Hossy and A. A. Saffy. dependence upon the chemical and physical Recently the control of gaseous pollution of properties of these metals and their alloys, the atmosphere has received greatly increased recent applications have resulted from the use attention from all quarters, and the develop- of coatings and dispersions on polymers, base ment of catalytic procedures, based upon the metals and metal oxides. By utilising such com- platinum metals, for this purpose was described binations significant advances have become by Mr. Colin Jaffray of Johnson Matthey’s possible in applications such as magnetic alloys, Catalytic Systems Division. The role of these catalysis, electronics and cancer chemotherapy. metals is now crucial in this connection. The full proceedings of this meeting will be The separation and refining of the six plati- published in July in the Transactions of the num metals involves a highly complex series of Institution. L.B.H.

Platinum Metals Rev., 1987, 31, (1) 11 Platinum Reactivity Rationalised Quantum Chemistry: The Challenge of Transition Metals and Coordination Chemistry EDITED BY A. VEILLARD, Reidel, Dordrecht, 530 pages, Dfl. 210.00/L58.25

Now that developments of ab initio calcula- clusters for the hydrogenation of acetylene im- tion methodologies have turned quantum purities in ethylene streams, a reaction used in chemistry into a predictive tool for molecular commercial processing. In this process, the systems involving light elements, a conference hydrogenation of ethylene does not occur until was sponsored by NATO and the Societi de all the acetylene impurity is converted into Chimie Physique in order to review progress on ethylene, and hardly any ethane is generated the application of similar methods to transition directly from acetylene. These selectivities element systems, including those involving occur despite the fact that palladium is an even platinum group metals. This book consists of better catalyst for the hydrogenation of pure the proceedings of this meeting. ethylene. On the basis of the calculations, it is The carbonyl and olefin insertion (p- proposed that the explanation lies in the larger elimination) reactions in systems relevant to heat of adsorption on a palladium surface for catalytic cycles have been studied by N. Koga acetylene compared with ethylene. Further- and K. Morokuma (Okasaki, Japan). They more, acetylene has active *-bonds all around found that the methyl group migrates in the the carbon-carbon axis, whereas ethylene has x- former reaction and the hydride in the latter. In orbitals only in the plane perpendicular to the all these reactions the activation energy and the molecular plane, giving acetylene a bigger transition state structure are strongly depen- potential for bonding to the palladium surface. dent on the metal as well as on the ligand and The ethylene product generated by the other factors. These authors have also studied hydrogenation of acetylene is coplanar with the the oxidative addition/reductive elimination active palladium atoms and is repelled from the reaction, and claim that with a combination of surface rather than reduced to ethane. all these reactions they will soon be able to The hydrogenation reaction proceeds in a derive a theoretical model for a complete cycle smooth cycle, involving two steps. The first is of homogeneous catalytic reactions, being able the dissociative adsorption of the hydrogen to predict how to change activation energies molecule on the palladium surface and the and heats of reaction. They aim to be able to other is the surface reaction between acetylene provide a theoretical design mechanism for and hydrogen. Palladium shows catalytic acti- homogeneous catalysts. vity in both these steps. Energetically the cata- The relevance of applying the principles of lytic role of the palladium is more important in co-ordination chemistry to elucidate the detail- the first, but the second controls selectivity. ed surface chemistry on small palladium clusters Two French theoretical chemists, B. Bigot was described in a paper given by G. Pacchioni and C. Minot, described their use of the ex- and J. Koutecky (Free University of Berlin). The tended Huckel method to demonstrate the interaction of hydrogen and carbon monoxide adsorption of hydrogen on small platinum with the palladium was investigated, and the clusters. The energy of first adsorption depends spectra predicted using molecular orbital calcula- on cluster size, being a maximum at Pt /Pt, . tions were in excellent agreement with the ex- The conference proceedings show that the perimental photoemission spectra obtained for application of theoretical approaches is helping hydrogen and carbon monoxide on palladium. to elucidate the mechanism of reactions in- Molecular orbital calculations have been used volving platinum group and other transition by H. Nakatsuji and M. Hada (Kyoto, Japan) metal catalyst systems. to explain the selectivity of small palladium D.T.T.

Platinum Metals Rev., 1987, 31, (l), 12 12 The Development and Application of Palladium Contact Materials RECENT WORK ON TELECOMMUNICATIONS CONNECTORS By M. Antler AT&T Bell Laboratories, Columbus, Ohio

Palladium-based contact materials are replacing gold finishes on the contacts of many separable connectors used in telecommunications systems in the United States of America due to their lower cost. Before this was possible, however, methods had to be developed for: inhibiting the corrosive attack of palladium by certain chlorine-containing compounds in the atmosphere, retarding the formation of insulating frictional polymers on palladium, and improving its wear resistance. Also, improved manufacturing techniques for palladium contact materials were necessary. An alloy, clad 60 per cent palladium-40 per cent silver having a small amount of gold dified into its near sugace region, and a new palladium electroplating process which is used with a thin gold overplate, were developed. The technology behind these developments is described, and an example of the application of the new materials in a major connection system is given.

Gold has been the traditional contact material while its sliding wear was relatively unexplored. for high reliability, long lived separable elec- Finally, processes for fabricating palladium- tronic connectors used in telecommunications based contact materials in high volume had to systems. However, escalation in its cost, be developed. together with rapid growth in the use of con- Many organisations have contributed to the nectors and printed circuit boards, spurred a technology of palladium connector contacts. An search for replacement contact materials which historical account of early developments was would be less expensive but equal to gold in published here recently (5). The present paper reliability (I). Palladium was clearly the most focuses primarily on work in the U.S.A. which attractive alternative due to its availability, has led to the growing acceptance of palladium from favourable early results in some telecom- in major products for the telecommunications munications (2) and computer connection pro- industry. An important influence in this work ducts (3), and because of the extensive was the recognition from studies of wire spring experience gained with it on the contacts of relays that the considerably less expensive 60 wire spring relays in older electromechanical palladium-40 silver alloy was comparable to switching systems. There were, however, pure palladium in many of its properties (6). several questions concerning the suitability of palladium for the contacts of separable connec- Environmental Effects tors. Since it is less noble than gold, any suscep- A field study which included many noble tibility to corrode might degrade its behaviour contact materials and base metals was con- in low voltage circuits. In addition insulating ducted by AT&T Bell Laboratories from 1974 frictional polymers were known to contaminate to 1980 to determine the extent to which they palladium surfaces at some conditions (4), were affected by the environment (7, 8).

Platinum Metals Rev., 1987, 31, (l), 13-19 13 Degradation of the bulk materials, corrosion at films containing silver and chlorine, as well as pores in noble metal coatings on non-noble PdCl,.zH,O (7, 10). substrates, and the spreading of tarnish films The greater nobility of 60 palladium-40 silver were all examined. compared to palladium did not make its after- Various materials were exposed in air con- exposure contact resistance more stable because ditioned and non-air conditioned buildings the alloy is both harder and has a higher bulk located in different geographic regions. Visual resistivity; these accentuate the influence of observations for corrosion were supplemented insulating films on contact resistance (7). by analysis with a contact resistance probe, a The effect of chlorine on palladium and method that is very sensitive to the presence of palladium-silver alloys was confirmed by a insulating films on metals (9). The major find- subsequent study of samples that were exposed ing was that palladium and 60 palladium-40 in a multiplicity of indoor environments and in silver are tarnished by traces, that is to say less shelters out-of-doors (8). Contact resistances in than IO-~parts by volume, of certain gaseous excess of 1000 ohms were measured on samples chlorine-containing air pollutants when the after I to I 2 months of exposure in cases where relative humidity exceeds 60 per cent. Below pure gold controls were relatively unaffected. this humidity, there is little or no effect. Further studies of the reaction chemistry (12) The contact resistances at a load of Img for showed that [a1 gaseous chlorine produced the clad palladium, 60 palladium-40 silver and elec- same tarnish fdm as the unidentified chlorine- troplated cobalt-gold controls after 3 to 4 years containing air pollutants, [bl the severity of at- of field exposure are shown in Figure I. The tack increased with both relative humidity and contact resistances increased in all cases from chlorine concentration, [cl gaseous hydro- the initial levels. Small amounts of dust par- chloric acid was unreactive ( I 3), and [dl mated ticles contributed to these changes. Palladium contacts were less susceptible to chemical at- and 60 palladium-40 silver which had been ex- tack due to shielding of their surfaces by the posed in air conditioned locations were prac- connector housing, yet there was still signifi- tically unaffected by corrosion. The tarnish cant risk of contact deterioration when films on 60 palladium-40 silver had slightly palladium and palladium-silver were used. higher contact resistances than the films on In summary, traces of chlorine-containing palladium. compounds that had heretofore not been An Auger surface analysis with sputter depth realised to exist are nearly always present in profiling of palladium and 60 palladium-40 urban and industrial environments, and these silver samples showed that the films contained compounds can rapidly tarnish palladium and chlorine (10). The tarnish subsequently was some of its alloys under humid conditions. If identified as PdCl,.zH,O (11). From the relative humidity cannot be controlled specimens that had been exposed for different below 60 per cent, palladium may not be a lengths of time at a non-air conditioned site in satisfactory contact material. It was therefore an urban industrial location, it was found that evident that palladium-based contacts which the growth of the chloride fdms followed contain some gold might have improved per- parabolic kinetics, and that palladium was more formance; these studies summarise the develop- reactive than 60 palladium-40 silver. The rate ment of low gold-palladium contact materials. constant k in the equation, x2=kt, where x is chloride film thickness and t is exposure time, Contact Materials with is: for palladium, I. I I x 10- cm2/month and Thin Gold Surfaces for the alloy, 5.82 x IO-” cm’/month. A con- Manufacturing Processes current study of 40 palladium-6o silver alloy Two palladium contact materials containing a showed more rapid contact resistance degrada- small amount of gold were studied extensively. tion than palladium due to the formation of These were a clad alloy and an electrodeposited

Platinum Metals Rev., 1987, 31, (1) 14 Fig. 1 Contact resistances of coupons of various Key materials subjected to ex- - posure trials for 3 to 4 years are given. Testing at a load of 1.0 lOOg with hemispherically ended 3.2mm diameter solid gold rod gave: a - initial values; , b - values from air conditioned telephone 0.1 offces; W c - results from a non- g air conditioned loca- 5 - tion in one of the sites from which the g data in b were ob- 0.01 tained V L z- 8

0.001

Co-&I Plate Pd 60W-40Ag

pure palladium with a thin gold coating. One (14). The combined thickness of gold and 60 role of the gold is to attenuate the reactivity of palladium-40 silver in the final contact is in the palladium; but to be cost effective, the amount range of 1.25~to 2.5pm. Multiple passes of that is used must be small by comparison with the composite through the rolls is usually neces- the gold content in the original contact that it sary, depending on the desired thickness and replaces. substrate temper, and the metal is annealed Sheet metal is an especially attractive sub- between each rolling. This causes interdiffusion strate from which to make connector contacts. of the gold and 60 palladium-40 silver so that Strip copper alloy such as CA 725 (88 copper- the composition of DG R-156 at the surface is 10 nickel-2 tin) is stamped and formed to the 55 to 85 per cent gold, the balance being pal- finished part, for example a contact receptacle ladium and silver. The gold content diminishes with integral springs. By inlaying the precious in the body of the palladium-silver alloy; but by metal in the correct location on the sheet, it will concentrating the gold near the surface it is appear selectively at the contact region and in utilised more effectively than if the alloy were this way can be used very efficiently. An inlay homogeneous. DG R-156 has the colour of is made by machining a groove in the substrate palladium. and inserting the metal before rolling it thin. Electroplated palladium has attracted interest Diffused gold, 60 palladium-40 silver cladding, and several commercial processes are now designated DG R-156, is made from a three- available which can give sound deposits with layer material of gold foil on 60 palladium-40 good contact properties. Methods for co- silver and a nickel carrier, with thickness ratios depositing palladium with nickel (I 5) or silver in the range of approximately 1:1o:30to 50 (16) have been developed. A significant

Platinum Metals Rev., 1987, 31, (1) 15 advance in palladium plating technology (17) The migration of corrosion films over the sur- involved the development of a new system faces of selectively coated contact materials is of based upon stable solutions that are easy to interest. The films originate in the copper replenish and to maintain, and which can be based alloy at the edge of the coating. This has prepared inexpensively from simple salts. This not been observed in telephone central offices system will produce crack-free deposits under a (7), but it can occur in highly aggressive en- wide range of conditions of barrel, rack, and vironments. Using dilute mixtures of hydrogen continuous high ,speed strip plating (for sulphide, nitrogen dioxide and chlorine, the example, at current densities from about 0.05 rate of migration of corrosion films on DG to 20 A/dm2). The tendency of palladium R-156 was found to be similar to that over gold deposited from conventional solutions to crack and 75 gold-25 silver alloy (20). Creep is not as originates in co-deposited hydrogen which extensive over less noble materials, such as forms P-PdH; this phase is unstable and looses palladium and 60 palladium-40 silver, because hydrogen spontaneously (I8). Internal stresses the tarnish that forms inhibits this movement. that develop in the deposit cause the cracking. The new process is 100 per cent current effi- Wear and Friction cient, does not generate hydrogen, and is based In general, ductile noble contact materials on a non-ammoniacal bath involving a pal- with a hardness below about 300 kg/mm2 are ladium chelate with an alkaline phosphate not desirable when mated with themselves in buffer (19). A thin gold overplating is applied connectors that are engaged with a wiping or to the palladium deposit, and a nickel subplate sliding action. Such materials experience high is used to improve the wear resistance of the frictional forces, metal transfer, and wear. This finish, similar to practices with thick cobalt- observation assumes that the metals are gold deposits. This plating process is used ex- employed in the usual range of thickness (0.5 to tensively for connector and printed circuit con- sprn), that the normal force of the contact tacts in the telecommunications industry. spring is from 100 to 3008, and that the numbers of engagements is greater than 10. Corrosion Tests Thus, DG R-156, palladium and 60 Laboratory tests and field exposures con- palladium-40 silver, as well as pure gold, are firmed the corrosion resistance of DG R-156 unsatisfactory. This generality excludes most and gold coated palladium plate, compared to cobalt- and nickel-containing gold platings the parent materials without gold. For from cyanide baths; they are relatively brittle, example, in evaluating the inlay, coupons were and asperity junction growth at the interface- placed in laboratory environmental chambers at which contributes to friction and wear-is in- 80 per cent relative humidity, with chlorine at hibited (21). There are a number of ways to im- a concentration of from 70 to 380 x IO-~ prove the sliding performance of DG R-156 and parts by volume in air, or to 380 x IO-~parts of palladium including the use of an opposing of chlorine mixed with 100 x IO-~parts of contact that is thickly plated with cobalt-gold, hydrogen sulphide (12). Exposures were for by using supplementary organic lubricants or a various durations and the characteristics of the metallic film lubricant. In detail, a cobalt-gold resulting films were determined with a contact opposing contact which is less hard than DG resistance probe at a load of sag, as described R-156 or palladium results in superficial metal above. In a typical experiment, the contact transfer, thereby giving a cobalt-gold to cobalt- resistance of a 1.25pm thick DG R-156 inlay gold couple (22). An effective organic lubricant was comparable to that of the widely used con- reduces the asperity welding tendency of the nector contact alloy, 70 gold-30 silver, and was contact metals; and, like a thin metallic film significantly less than that of palladium or of 60 lubricant (such as gold), involves the inter- palladium-40 silver. position of an easily sheared low friction

Platinum Metals Rev., 1987, 31, (1) 16 material at the interface. Boron ion implantation was found to increase the superficial hard- 1.4{ P ness of palladium and 60 palladium-40 silver by ,' Pure Gold from 25 to 45 per cent to values in excess of 300 kg/mm2 (23), which reduced the excessive wear of the parent materials; however, ion implantation is too expensive to be acceptable for general connector applications. Recent work has demonstrated the effective- w ness of a thin gold overplate in lowering the u I .A I 0" 0.05 0.1 0.2 0.5 wear and friction of palladium plate (24). This GOLD OVERPLATE,pm was extended to DG R-156 mated to gold Fig. 2 Relationship between the maxi- coated palladium (25), where it was found that mum values of the coeffcient of friction, both thin pure gold and cobalt-gold platings are in runs with DG R-156 coated contacts versus gold coated palladium coupons effective, as shown in Figure 2. Cobalt-gold is with a nickel subplate is shown. The the preferred material, because if it is in- variable8 were the type of gold plate advertently plated to a thickness greater than (either pure or cobalt-hardened), its thickness, and whether the flats were dry the optimal level of about o.o5pm the perform- or were lubricated with a thin layer of a ance of the system is not seriously degraded, as polyphenylethsr fluid. Test apparatus was is the case with a thick pure gold layer. In addi- a pin on a disc bench tester. Conditions: 200g load, 200 cycles in reciprocation, tion, the benefit of using a supplementary fluid 1 cm long track lubricant is demonstrated in the Figure.

The Effect of Fretting palladium-40 silver alloy is much less sus- Although mated connector contacts are ceptible than palladium to form polymers. An nominally at rest, sometimes small interfacial opposing gold or gold alloy which is softer will movements occur due to variation of the transfer to the palladium, resulting in an all- ambient temperature or to external vibrations. gold system; gold has little tendency to form Adsorbed organic air contaminants polymerise polymers. A thin gold plating on palladium in- on the surface of catalytically active metals, hibits polymer formation until the gold is worn especially palladium, to form insulating solids through. Supplementary organic lubricants, called frictional polymers. It was therefore especially if used in relatively thick layers, can important to evaluate the effect of such move- stabilise contact resistance because the poly- ments on contact materials and new test equip- mers which form are nonadherent. Some of ment was constructed for this work (26). The these findings are illustrated in Figure 3. significant findings are that the levels of organic pollutants in ordinary room ambients are suffi- Thermal Stability cient to cause rapid changes of contact resist- Palladium and its alloys are recognised to be ance, values in excess of ~ooonoccurring with thermally stable. This was verified with DG palladium to palladium contacts in only a few R-156, 60 palladium-40 silver, and electro- thousand cycles under some conditions (27). deposited palladium which were found to have The larger the amplitude of movement and the stable contact resistances, well beyond the lower its frequency, the fewer the numbers of temperatures at which they would be used in cycles required to achieve a given change of practical connector applications. Coupons of contact resistance. However, if the normal these materials were aged in ovens and then force between palladium contacts exceeds about probed with a gold rod at a load of I-. The 200g, the polymers are penetrated and cause contact resistances following 1000 hours of age- only a small rise of contact resistance. The 60 ing in air at 200OC were within I ma of their

Platinum Metals Rev., 1987, 31, (1) 17 100 Fig. 3 The changes in contact resistance during fretting of pure gold flashed 10 palladium mated to itself, both when clean and lubricated with polyphenylether are shown. All results from 2' replicate runs fall within 0 their respective bands. u Wrought palladium without zU Riders and flats were 5 0.1 duplicate runs 0.05pm pure gold or 1.5pm L" Y) palladium, both electro- K deposited. Data for duplicate I- runs with unlubricated pal- ;0.01 ladium, without a gold flash, z are given by the two dashed 8 lines. Here the riders were 0.001 Electroplated palladium solid palladium and the flats Wlth gold flash were 5pm clad palladium. Conditions: 50g load, 20pm wipe distance, 8Hz

roo 10' lo2 10' 10' lo5 106 CYCLES

initial values for 1.25pm thick DG R-156 and incorporated this material on their contacts. 60 palladium-40 silver, for 0.6 and 2.5pm In contrast to these results, 2moC is well electrodeposited palladium on nickel beyond the thermal stability of typical cobalt- underplate on copper, and for 2.5pm of pal- gold (0.I to 0.3 per cent cobalt) electrodeposits ladium plate on copper. Only thin (o.6pm) which cannot be heated for more than a few palladium on copper deteriorated, with contact hours at this temperature (28). Even below resistance rising to 11.5 mi2 from an initial 125OC, the co-deposited elements and base value of I mn. The thermal stability of underplate or substrate materials in gold may palladium electroplate with a 0.05pm thick gold diffuse to the surface and cause the contact coating was verified by product quality control resistance to increase. In summary, palladium, tests carried out using connectors which 60 palladium-40 silver, and palladium alloys that contain a small amount of gold are preferred contact materials for elevated temperature applications.

An Application of Palladium Connector Contact Materials The advances in palladium materials technology have been exploited in a number of telecommunications products. An important DG R-156 inlay example involves the connector contacts of the Fig. 4 An individual pin-socket contact AT&T FastechO packaging system (29). This from an electrical connector consisting of consists of a standard set of printed circuit a pin, plated with palladium and having a thin gold overplate and a socket contact, boards, connectors, and other hardware for which is inlaid with DG R-156 on the mounting and interconnecting electronic com- springs, is shown ponents to build shelves of equipment. The contact pins are pressed into plated through

Platinum Metals Rev., 1987, 31, (1) 18 holes of a printed circuit board backplane. A qualification study of the connector with an compliant section of the pin retains it in the board earlier version of the contact materials has been without solder. The back ends of the pin are ter- reported (31). Exposure to laboratory chamber minated by solderless wrap connectors or by environments involving chlorine and hydrogen pluggable cables. sulphide was used to simulate the effects of The contact system illustrated in Figure 4 aggressive atmospheres; cycling temperature consists of a socket contact and a 0.63mm and mechanical vibrations were used in fretting square pin. The socket is CA 725 alloy inlaid tests; ageing at elevated temperature was used with DG R-156 in the contact springs, and the to induce stress relaxation of the spring CA 725 pin is plated with 0.05j.un of cobalt- materials; and 200 insertions and withdrawals gold and o.6pm palladium on a nickel under- were made to evaluate the durability of the con- plate. The contacts are lubricated by immersion nection. This packaging system has been in or by spraying with a solution of 2 per cent by production since 1980; DG R-156 was intro- weight of a 6-ring polyphenylether lubricant in duced in 1981; gold coated palladium electro- a volatile solvent (30). On evaporation, a resi- plate in 1984; and the present contact dual thin layer of the lubricant remains. A lubrication practices implemented in 1986.

References M. Antler, IEEE Trans., 1975, PHP-XI,216-220 16 F. I. Nobel, op. cit., (Ref. 7), 1985, CHMT-8, F. H. Reid, Plating, 1965, 52, 531-539 (I), 163-172 D. T. Napp, Proc. Fifth plating in the Electron. I7 J. A. Abys and H. S. Trop, “AU That Glitters is Ind. Symp., Am. Electroplaters’ Soc., New not Gold,” AT&T Bell Lab. Rec., Jan., 1985 York, N.Y., 1975, pp. 28-33 I8 H. D. Hedrich and Ch. J. Raub, Metallober- H. W. Hermance and T. F. Egan, Bell Syst. Tech. flaeche., 1977, 31, 512 J.9 1958, 37, 739-777 I9 S. G. Miklus, Met. Finish., 1986, 84, (9,41-43; M. Antler, Platinum Metals Rev., 1982, 26, (9, U.S. Patent 4,468,296; 1984 106-116 20 W. H. Abbott, Proc. 12th Int. Conf. on Electric T. R. Long and K. F. Bradford, Proc. Holm Contact Phenomena, Chicago, 1984, pp. 47-52 Conf. on Electr. Contacts, Chicago, 1975, pp. 21 M. Antler, op. cit., (Ref. 7), 1981, CHMT-4, (I), 145-154 15-29 M. Antler, M. H. Drozdowicz and C. A. Haque, 22 M. Antler and E. T. Ratliff, op. cit., (Ref. 7), IEEE Trans. Components, Hybrids, Manuf. 1983, CHMT-69 (11, 3-7 Technol., 1981, CHMT-4, (4), 482-492 23 M. Antler, C. M. Preece and E. N. Kaufmann, M. Antler, op. cit., (Ref. 7), 1982, CHMTj, (3), op. cit., (Ref. 7), 1982, CHMTj, (I), 81-85 301-307 24 T. Sato, Y. Matsui, M. Okada, K. Murakawaand 9 M. Antler, “Contact Resistance Probing: Z. Henmi, op. cit., (Ref. 7), 1981, CHMT-4, (I), Development of a Standard Practice by the American Society for Testing and Materials”, 10-14 Proc. 10th Int. Conf. on Electr. Contact 25 M. Antler and M. Feder, Proc. Electron. Com- Phenomena, Budapest, Hungary, 1980, pp. ponents Conf., Seattle, WA, 1986, pp. 244-250 13-21 (ASTM B667-80) 26 M. Antler in “Materials Evaluation Under Fret- 10 C. A. Haque and M. Antler, Corns. Sci., 1982, ting Conditions,” Special Technical Publication 22, 939-949 STP 780, ed. S. R. Brown, ASTM, Philadelphia, (a PA, 1982, pp. 68-85 11 S. P. Sharma, Proc. Holm Conf. on Electr. Con- tacts, Chicago, 1981, pp. 191-201 27 M. Antler, op. cit., (Ref. 7), 1985, CHMT-8, (I), 87-104 12 E. S. Sproles, S. P. Sharma and M. H. Droz- dowicz, Proc. 11th Int. Conf. on Electric Contact 28 M. Antler, Plating, 1970, 57, 615-618 Phenomena, West Berlin, Germany, 1982, pp. 29 C. L. Winings, op. cit., (Ref. 7), 1980, CHMT-3, 1 43 -1 47 (41, 601-609 13 E. S. Sproles and S. P. Sharma, op. cit., (Ref. 7), 30 M. Antler, “Electronic Connector Contact 19839 CHMT-6, (9, 343-348 Lubricants: The Polyether Fluids,” Proc. IEEE 14 F. E. Bader, Proc. 11th Int. Conf. on Electric Holm Conf. on Electr. Contacts, Boston, MA, Contact Phenomena, West Berlin, Germany, 26th-qth October, 1986 1982, PP. 133-137 31 E. Guancial, R. W. Kohl, J. J. Dunbar, J. L. 15 P.Wilkinson, Trans. Inst. Met. Finish., 1982, 60, Milton and S. DasGupta, op. cit., (Ref. 7), 1983, 152-155 CHMT-6, (I), 100-107

Platinum Metals Rev., 1987, 31, (1) 19 Pressure Sensitive Palladium Complex By Ichimin Shirotani Applied Science for Energy, Muroran Institute of Technology, Mizumoto, Muroran-shi, Japan

The complex bis(l,2-cyclohexanedionedioximato)palladium(ll) has been prepared and its absorption spectra examined. The preliminary results, which are reported here, show that the colours of thinfilms of this complex are afunction of the applied pressure, a property which may find application as an indicator of pressure and pressure distributions up to perhaps seventy thousand atmospheres.

The development of diamond-anvil pressure Various d8 square complexes are formed cells enables the effect of pressure on various when NiZ+, Pdz+ and Ptz+ react with materials to be observed, in situ, visually. This I ,2-dionedioximes such as dimethylglyoxime. is especially important for the study of The complexes are chemically stable, and have polymorphs and crystal growth. Quantitative various colours at atmospheric pressure. The pressure measurement in a diamond-anvil cell effect of pressure on the absorption spectra of has been carried out by Barnett, Block and these complexes has already been studied Piermarini using ruby as a pressure sensor (I). (3,4,5). The absorption bands show a large red The pressure is determined by measuring the shift with increasing pressure. The colours of pressure shift in the sharp R-line fluorescence the complexes change with pressure shifts of spectrum of ruby. The pressure shift of an op- spectra. For example, the colour of Ni(dmg), tical absorption band in bis(dimethylg1yox- which is initially red turns to green at pressures imato)nickel(II), Ni(dmg) , had already been around 1.7 GPa. It would be convenient if a studied as one approach to pressure measure- semiquantitative value of pressure could be ment in the cell (2). determined visually from a change in the colour

0-- H- - 0 H2 I \ H2 /N /c\c YN, kC \ / \CH2 \ / Pd / '\ H2i \ I H2C \ RC CH2 \c/c ",' N 'c' H2 \ I H2

Fig. 1 The molecular structure of bis( 1,2-cyclohexanedionedioximato)Pd(II), Pd(niox), shows the palladium(I1) ion to be co-ordinately attached to the four nitrogen atoms, of two 1,2-cyclohexanedionedioxime,(nioxime,niox) anions

Plarinum Metals Rev., 1987, 31, (l), 20-23 20 Pd(niox), was prepared from a hot aqueous solution of K,PdCl, and a hot alcoholic solution of nioxime( I ,2-cyclohexanedionedioxime). The diamond-anvil pressure cell was used for the study of optical properties in the complex at high pressures; the optical system consisted of a standard microscope and a monochrometer with an associated photodetection system. The 1 200 400 600 800 pressure was measured by means of the WAVELENGTH, nm pressure shift of the sharp R-line fluorescence Fig. 1The absorption spectrum .of a 1000 thin fdm of Pd(niox)2 at at- spectrum of ruby. Water was used as the mospheric pressure is shown pressure transmitting medium. The absorption spectrum of an evaporated thin film of Pd(niox), at atmospheric pressure of a material with change in pressure. is shown in Figure 2. This spectrum is similar Bis (I ,2-cyclohexanedionedioximato)Pd(II), to that of bis(dimethylglyoximato)Pd(II), Pd(niox),, may be an excellent pressure in- Pd(dmg), , which has already been determined dicator in the range o to 8 GPa. The complex by Ohashi, Hanazaki and Nagakura (6). The turns from yellow to orange and then to suc- band at 294 nm in Pd(niox), may be ascribed cessive colours in the visible spectrum with in- to a metal to ligand charge transfer transition; creasing pressure. In this article we report on the other hand the band at 477 nm is assign- preliminary results for colours and absorption ed to the 4d,2-5pZ transition. Figure 3 exhibits spectra in this complex at high pressures. the absorption spectra of Pd(niox), in the visi- The molecular structure of Pd(niox), is il- ble region at high pressures. The absorption lustrated in Figure I. A palladium(I1) ion is co- band always showed a large red shift with in- ordinated to the four nitrogen atoms of two creasing pressure. Visual observation of the I ,2-cyclohexanedionedioxime(nioxime, niox) sample in the diamond-anvil cell indicated [hat anions. The square planar complex molecules with increasing pressure the colour of stack face to face in parallel columns, linking Pd(niox) turned from yellow to orange (at 0.8 the metal ions in extended linear chains to I .4 GPa), to red (at I .4 to 2.3 GPa), to purple throughout the crystal lattice. (at 2 to 3 GPa), to blue (at 2.7 to 5.5 GPa), to

Fig. 3 Absorption spectra of Pd(niox)2 at various high 400 560 600 700 800 pressures are shown WAVELENGTH, nm

Platinum Metals Rev., 1987, 31, (1) 21 Platinum Metals Rev., 1987, 31, (1) 22 Fig. 4 The series of photographs on the facing page shows the colour of a thin fdm of Pd(niox), at various pressures between 0.2 and 10 GPO:(a) 0.2 GPO,(b) 1 GPO,(c) 2 GPO,(d) 3 GPO, (e) 4 GPO, (0 6 GPOand (g) 10 GPO;the lie drawing identifying the position of the palladium complex and the two reference rubies. The aperture in the gasket measures 0.3 mm from side to side yellow green (at 5.5 to 6.5 GPa), and to pale yellow (above 7 GPa) with increasing pressure. The variation in the colour of Pd(niox), with pressure can be interpreted to show that the absorption band which is ascribed to 4dZ2-5p, shifted toward longer wavelength at high pressures. The relationship between the colour and the pressure is only the preliminary results of our work. The pressure ranges of the colours have not yet been determined in detail. .The thickness of our sample is about I~A.It Fig. 5 A pressure gradient produced under non- should be noted that the tone of a colour depends hydrostatic conditions is displayed visually by the change in the colour of the sample: centre (green) on a number of factors including thickness of about 6 GPO,middle (red) about 2 GPO,outside the sample, the pressure transmitting medium (yellow) 0-1 GPO and the pressure distribution. If the relation- References ship between colour and pressure is studied in J. D. Barnett, S. Block and G.J. Piermarini, detail, a semiquantitative value of pressure Rev.Sci.Instncm., 1973, 4, (I), I could be obtained from the visual observation H. W. Davies, J.Res. Natl.Bur. Stand. (USA), of the change in colour with pressure by a col- 1968, A72, (2), 149 J. C. Zahner and H. G. Drickamer, orimetric method similar to pH testing paper. J.Chem.Phys., I*, 33, (6), 1625 Furthermore, the pressure gradient in a high Y. Hara, I. Shirotani and A. Onodera, Solid State pressure cell can be directly observed in situ. Commun., 1976, 19, (z), 171; I. Shirotani, A. Onodera and Y. Hara,J. Solidstate Chem., 1981, 40, (21, 180 Acknowledgement I. Shirotani and T. Suzuki, Solid State Commun., The present work was partly supported by a Grant- 1986, 59, 533 in-Aid for Scientific Research from the Ministry of Y. Ohashi, I. Hanazaki and S. Nagakura, In- Education, Science and Culture. org.Chem., 1970, 9, (10,2551

Anti-Cancer Platinum Compounds The platinum compound Cisplatin is now prepared by staff at the Johnson Matthey widely used for the treatment of specific Technology Centre (“Second Generation Anti- cancers. However a number of adverse side ef- cancer Platinum Compounds”, c. F. J. Bar- fects are associated with its use, and since the nard, M. J. Cleare and P. C. Hydes, Chem. late 1970s attention has been focused on the Brit., 1986, 22, (XI), 1001-1004). identification of other platinum drugs having Current work is concentrating on Carboplatin less toxicity but with at least equivalent clinical and on Iproplatin, another second generation activity. drug. Particular attention is being paid to the This work has made significant progress and use of these platinum drugs in combination a review of the work carried out between the with radiotherapy, and to varying the mode of discovery of the anti-tumour activity of administration to increase their effectiveness. Cisplatin by B. Rosenberg and L. Van Camp in At the same time the search for third generation 1969 and the launch of Carboplatin, a second platinum complexes with higher anti-tumour generation platinum drug, has recently been activity continues.

Platinum Metals Rev., 1987, 31, (1) 23 Heterogeneous Catalyst Preparation CONTINUING INTEREST IN SUPPORTED PLATINUM METALS

The Fourth International Symposium on P. Gallezot (Institut de Recherches sur la “Scientific Bases for the Preparation of Catalyse, Lyon) studied the effect of oxidising Heterogeneous Catalysts” was held in Louvain- graphite and carbon black with nitric acid, la-Neuve, Belgium, from 1st to 4th September hydrogen peroxide and sodium hypochlorite in 1986 under the chairmanship of Professor Ber- order to provide ion-exchange sites for the nard Delmon. It was attended by some 350 platinous tetrammine ion. High dispersions scientists from many different countries. These were obtained after reduction at 300OC. symposia, which are held at four-yearly inter- It has been known for some time that noble vals, are now well established as occasions for metals may be deposited on photoreactive sup- reviewing progress in the science underlying ports such as titania by photolysis of the metal the preparation and manufacture of technical salt. This technique has been extended to most catalysts. The sixty-seven plenary lectures and of the noble metals, including silver and contributed papers covered the whole range of gold, and to other supports such as zirconia, catalysis, with some emphasis on newer ap- niobia, thoria, zinc oxide and cadmium plications such as amorphous metals and sulphide by J.-M. Herrmann, J. Disdier, P. pillared clays. A significant number of the Pichat and C. Leclercq (Ecole Centrale de papers dealt with catalytic applications of the Lyon). The method can be used to make platinum group metals. bimetallic catalysts. Materials made in this way The ability to control the distribution of the are more active in photocatalysis than those noble metal through a catalyst pellet is a matter made by conventional methods. of great practical importance: picturesque The phenomenon of strong metal-support in- terms such as egg-shell, egg-white and egg-yolk teractions (SMSI) continues to excite interest. structures have been used to describe the Most of the work in this area has employed various possible locations of the metal that can titania as the support, but attention is gradually be produced, and empirical means of achieving turning to the use of other transition metal ox- these structures have been developed. The ides. Y. - J. Lin, R. J. Fenoglio, D. E. Resasco plenary lecture by J. A. Schwan of Syracuse and G. L. Haller of Yale University described University, U.S.A., described systematic work with vanadium(II1) oxide as support: studies of the effect of competitive electrolytes dissolution and re-deposition of vanadyl ions on the adsorption of chloroplatinic acid by during the aqueous impregnation led to the en- alumina pellets. Three types of effect were capsulation of rhodium particles. This system is recognised: (i) on the electrostatics of the solu- far more complex than that based on titania. tion near the support surface; (ii) on the pH of The preparation and use of bimetallic the solution; and (iii) on competition for ad- catalysts attracted considerable attention. sorption sites by the competing electrolyte. Three groups described their work on the in- Several other papers addressed fundamental corporation of the promoter element through questions concerning the preparation of sup- specific chemical reaction either with the metal ported metal catalysts. Controlled-porosity or the support. Thus for example J. Margitfalvi silicas were used as model supports for and colleagues at the Hungarian Academy of platinum by M. A. M. Luengo, P. A. Sermon Sciences showed how tin complexes could be and K. S. W. Sing, of Brunel University, to attached to an alumina surface by first lithiating establish how experimental conditions affected the surface hydroxyl groups and then reacting metal dispersion and location. D. Richard and them with tin(1V) chloride. Yang Yashu and

Platinum Metals Rev., 1987, 31, (I), 24-25 24 her co-workers at the Dalian Institute of industry: it has been in use within Johnson Chemical Physics, China, applied molybdenum Matthey for some twenty years. The second to alumina through the use of a molybdenum paper byG.C. Bond and P.B. Wells (Brunel and *-ally1 compound. In both pieces of work, Hull Universities, respectively) described work platinum was the active component. on EUROPT- 1, a reference platinum on silica It is also a well-established fact that the oxida- catalyst manufactured by Johnson Matthey tion of supported metal particles, followed by Chemicals for the Council of Europe’s Research their re-reduction, frequently leads to improv- Group on Catalysis. Penetrating studies of this ed catalytic behaviour. L. D. Schmidt of the material in a number of European laboratories University of Minnesota has followed the have revealed previously unexpected problems changes that occur during these stages by X-ray in interpreting hydrogen adsorption isotherms photoelectron spectroscopy and by transmis- and have raised important questions which only sion electron microscopy, using rhodium on further research will answer. alumina. Startling changes in alkane In his concluding remarks, J. T. Richardson hydrogenolysis rates were observed, not ade- of the University of Houston, who had attended quately explained by the higher dispersion ob- all the earlier symposia, commented on the tained after the second reduction. Changes in changes he had noticed in the twelve years over particle morphology were invoked to account which the meetings had been held. In the first for the results. meeting, most of the contributions had been made by workers in industry: now they were in Catalyst Normalisation a minority, and academic workers had submit- Particular interest was shown in the ted most of the papers. He was not clear Minisymposium on Catalyst Normalisation whether this represented a growth of academic organised by E. G. Derouane (Namur). Work interest in the subject of catalyst preparation or presented by T. Hattori of Nagoya University, whether industry was now more cautious in the Japan, and carried out under the auspices of the amount of information it revealed. Catalysis Society of Japan, focused on the use of This fourth symposium showed very clearly the carbon monoxide pulse adsorption method however that the platinum group metals con- for supported platinum group metals. This is tinue to play a very important role in the field a simple and rapid method, widely used in of catalysis. G.C.B.

Corrosion Protection Conference Some four hundred corrosion engineers from form of rolls of a wire netting-type material many countries assembled in Birmingham, consisting of a fine titanium mesh coated with England, during November for “UK Corrosion electrocatalyst. The electrocatalysts in use in- ’86”. The conference involved a varied pro- clude ruthenium and iridium. Although the gramme of lectures and an exhibition, and not weight of iridium used per plan square metre surprisingly cathodic protection was featured in may be as little as one gram, the likely area of both. While interest in cathodic protection for concrete that may receive some form of cath- the North Sea oil industry is at a lower level odic protection of the underlying rebars sug- than in previous years, undoubtedly there is an gests that this application is likely to require increased awareness of the opportunities for the significant quantities of ruthenium and iridium. cathodic protection of steel reinforcement bars In spite of the technical difficulties of apply- in concrete. ing cathodic protection to some concrete struc- A paper authored by B. S. Wyatt of Global tures, and the need to prove durability and Cathodic Protection Limited, Telford, and commercial viability of individual systems, D. J. Irvine of Tarmac Construction Limited, there was a general air of optimism that the Wolverhampton included descriptions of many market for cathodic protection systems for rein- of the presently available systems. forcement bars in concrete was just about to Much interest attaches to mesh anodes, in the expand. P.C.S.H.

Platinum Metals Rev., 1987, 31, (1) 25 High Temperature Degradation of Nickel Based Alloys A CONSIDERATION OF THE ROLE OF PLATINUM By G. J. Tatlock, T. J. Hurd and J. S. Punni Department of Materials Science and Engineering, The University of Liverpool

The addition of platinum to nickel-based alloys can have a profound eflect on their oxidation and hot corrosion resistance. lmprovements in gas turbine blade performance in aggressive environments are linked with the protective nature of surface oxides and coatings. However the precise role of platinum in promoting and maintaining this protection is still under active investigation and the results of several recent studies are reviewed here.

Blades within the turbine section of advanced the process is still not without its problems. In gas turbine engines can operate at temperatures particular, the adherence of the coating is para- ranging from 650 to 950°C, under highly stress- mount, since any cracking or loss of coating can ed conditions, and in gas environments which lead to a massive attack on the blade substrate. are generally extremely oxidising and which in Hence improvements in substrate alloys which many cases contain corrosive fuel residues and enhance the oxidation and hot corrosion ingested salts. There is, therefore, a continuing resistance, while maintaining or improving need for both new structural materials and new their mechanical performance, are still being coating compositions having improved sought. One such improvement, made at the mechanical properties and greater resistance to Johnson Matthey Research Centre, was the high temperature oxidation and hot corrosion. production of a range of nickel based super- Major advances have been made in nickel alloy alloys containing platinum group metals ( I). It design over the past thirty years but many of had been known for some time that the addition the improvements in high temperature strength of platinum to alumina coatings improved their have been made at the expense of oxidation and performance (2), and that platinum additions to hot corrosion resistance. The chromium con- nickel alloys had proved beneficial (3), but this tent of early forged blades, for example, was was the first attempt to produce a commercial gradually reduced below 12per cent at the ex- product. However the mechanisms for these pense of resistance to hot corrosion. The switch improvements are still not well understood and to higher strength cast materials produced a this paper reviews the background to these further drop in chromium level, to about 9 per developments and discusses some of the bene- cent, and led to the extensive use of coatings to ficial corrosion resistant properties of nickel provide added protection. This was accom- based superalloys containing platinum. panied by improvements in coating technology and the widespread application of a variety of The Oxidation of Nickel Alloys aluminised coatings and MCrAlY overlays, The effect of platinum additions on the oxi- where M is usually a combination of nickel and dation of pure nickel was first investigated by cobalt. Although the combination of a high Kubaschewski and von Goldbeck (4). Their strength blade and a corrosion resistant coating results could be interpreted as showing that the is now the primary route to blade production, oxidation rate constant decreased as the

Platinum Metals Rev., 1987, 31, (l), 26-31 26 platinum content increased. Thomas also pegs. Short circuit diffusion of oxygen along studied the oxidation of nickel-15 per cent the incoherent interface between matrix and platinum in oxygen at temperatures between dispersoid would enhance oxide formation at 850 and 10ooOC and showed that the resulting certain points and lead to peg formation. subscale consisted of a platinum enriched matrix (5). This system is often cited-for The Effect of Platinum example (6)-as a classic system where oxide on Oxide Formation grows by the outward migration of nickel to Another unusual property of platinum is its form a NiO layer on the surface while the influence on the formation of metal oxides platinum is concentrated at the scale/metal when in close proximity to a sample in an oxi- interface, with a corresponding reduction in the dation furnace. This was first suspected when nickel concentration. For nickel rich alloys the samples suspended from platinum wires be- diffusion of nickel is the rate determining step, haved differently from those on other suspen- and can be analysed theoretically to give good sion systems. Work by Fountain, Golightly, agreement with experiment (7). Stott and Wood showed that the presence of The situation becomes more complex when platinum foil adjacent to alumina forming other elements are added to nickel-platinum alloys altered their oxidation kinetics at high alloys. For example, Felten examined the effect temperatures and led to the incorporation of of platinum on the behaviour of a nickel-8 per platinum into the oxide scale (I0). Increases in cent chromium-6 per cent aluminium alloy in the flow rate of gas through the furnace cyclic oxidation tests carried out between 800 decreased the influence of the platinum, and and 10ooOC (3). The addition of 2.5 weight per hence it was suggested that a gaseous transport cent platinum considerably improved the oxide mechanism involving volatile PtO, was respon- adherence above 10ooOC but was less effective sible for the incorporation of platinum into the at lower temperatures. Increases in the plati- scales. Recent work on nickel-silicon- num level up to 10 weight per cent produced magnesium alloys at IIOOOC has also corresponding improvements in oxidation highlighted the influence of platinum on oxide resistance under cyclic conditions. Nickel-8 formation (I I). However in this case the oxida- chromium-6 aluminium readily forms alumina, tion rate of a nickel-4.4 silicon-o. I magnesium and it was suggested that the presence of alloy was increased by approximately one order platinum in sufficient amounts allowed an of magnitude in the presence of platinum. Once alumina scale to reform even when modest again a gas phase interaction involving PtO, spalling had occurred. was thought to be involved, although rather Similar effects are also observed in other than contributing platinum which was in- alumina forming systems. For example Felten corporated into the growing scale it was sug- and Pettit showed that platinum increased the gested that on this occasion platinum removed adherence of alumina to platinum-2 aluminium magnesium from the scale as volatile platinum- and platinum-6 aluminium alloys (8). An oxide magnesium or platinum-magnesium-oxide. pegging mechanism was suggested in these The change in the magnesium concentration cases. Allam, Akuezue and Whittle also sug- then had a major influence on the formation of gested a pegging mechanism when examining the scale. the oxidation behaviour of cobalt- Io The work carried out at Johnson Matthey on chromium-1 aluminium and also cobalt-Io platinum containing superalloys also showed chromium- I aluminium- I hafnium alloys con- that platinum additions can have a major effect taining I and 3 weight per cent platinum, on oxidation mechanisms at high temperatures. respectively (9). It was speculated that the In a recent study by the authors the behaviour presence of a fine dispersion of PtAl, and/or of one such alloy, designated RJM2012, was HfPt, may be responsible for the growth of the compared with a similar alloy, IN792 + Hf,

Platinum Metals Rev., 1987, 31, (1) 27 platinum which have been deposited on a range of nickel based superalloys. For example early work by Lehnert and Meinhardt was aimed at finding a diffusion barrier to reduce the migration of aluminium from a coating into the substrate (2). However this approach proved unsuccessful in the search for an alumina diffusion barrier, but it did produce a marked improvement in the hot corrosion resistance of the coating, with the platinum remaining concentrated in the outermost region of what was Fig. 1 This cross-section through the surface of a duplex coating. The chemistry and mor- a sample of IN792 + Hf oxidised in air for 500 phology of aluminide coatings on platinum and hours at llOO°C shows the chromia-rich scale1 that exhibits poor adhesion, and a line of platinum coated superalloys were studied by aluminium-rich internal oxides which is always Jackson and Rairden (I 3). They suggested that present below the surface. Further bands of in- the platinum coating inhibits the movement of ternal oxide are formed when the outer scale spalls x 700 refractory metals to the outer region of the coating, thereby improving the hot corrosion which did not contain platinum. It was found resistance, but that platinum should be viewed that the presence of 4.5 weight per cent as a diffusion medium for aluminium rather platinum in RJM2012 changed both the oxi- than as a barrier to it. dation kinetics and the oxide development. The production and properties of platinum- Both alloys exhibited oxide spalling at I IOOOC aluminide coatings have been reviewed by following the growth of aluminium rich oxides Wing and McGill (14). They showed how a below the outer scale. In the case of IN792 + suitable choice of production route can alter the Hf, however, these internal oxides continued to relative amounts of the platinum-aluminium form and led to further attack on the superalloy intermetallics in the coatings. The route also substrate, shown in Figure I. By contrast, in has a major influence on the performance of the RJM2012 the internal oxides eventually joined coated alloys since in some cases volume up to form a continuous layer of alumina which changes, which occur as the coatings degrade, inhibited further attack, see Figure 2. Similar behaviour was observed in certain model alloys which contained nickel-12 chromium-6 aluminium-4.5 platinum. Hence it was concluded that a major role of platinum was to change the growth characteristics of the aluminium oxide. Platinum particles were sometimes observed above the alumina layer in the scales, but these were thought to be formed as a result of the change in oxidation mechanism, rather than its cause.

The Influence of Platinum on Hot Corrosion Fig. 2 This sample of FtJM2012 has been oxidised in air for 800 hours at a temperature of Little work has been done on the hot corro- llOO°C. The original band of aluminium-rich sion of nickel based superalloys containing internal oxides have linked together to form a continuous layer. The outer scale then becomes platinum. Most studies have concentrated on detached, leaving the single protective alumina the behaviour of aluminide coatings containing scale shown here x 700

Platinum Metals Rev., 1987, 31, (1) 28 Platinum containing alloys developed by Coupland and his colleagues at the Johnson Matthey Research Centre also exhibit good hot corrosion resistance (19). Salt shower testing and crucible sulphidation tests conducted at 92s°C with samples immersed in a 90 per cent sodium sulphate/ro per cent sodium chloride mixture both indicated that additions of up to 10 weight per cent platinum had a marked effect on the corrosion resistance. In order to study this further a detailed comparison was Fig. 3 Broadfront penetration of sulphides into made of IN792 + Hf and a similar alloy con- the matrix is shown on this cross-section taken taining platinum (RJM2012) after burner rig through a sample of IN792+ Hf after hot corrosion testing for 200 hours at 8OOOC x450 tests. Although the details of this investigation will be presented elsewhere (20) the results are can lead to void formation and cracking. summarised here. Burner rig and engine tests illustrated the im- Burner rig testing was carried out for up to proved performance of the coatings and further 1000 hours at 800OC on pin samples mounted in successful engine tests have recently been a rotating carousel. After only 200 hours there reported on platinum containing coatings (I 5). were marked differences in the behaviour of the However examples of crack formation in ser- two alloys and by 600 hours the IN792 + Hf vice have also been described (16). samples were heavily spalled compared to the The influence of platinum on Na,SO, in- RJM2012. The degree of attack was also very duced hot corrosion of aluminium diffusion clearly seen in cross-sections taken through the coatings has been examined recently by Wu, centres of the pins. After only 200 hours broad- Rahmel and Schorr (17). Hot corrosion front penetration of sulphides into the matrix mechanisms are often grouped under two head- was often observed in IN792 + Hf, see Figure ings: basic fluxing, where oxides such as 3, while this degree of attack was still not alumina are dissolved in molten salts as present in RJM2012 after 1000 hours, see aluminates, and acid fluxing where aluminium Figure 4. is converted into Al3+ ions; for example see The detailed evolution of the scales on these Goebel and Pettit (18). The results obtained by Wu and colleagues suggest that platinum improves the resistance to basic fluxing, but that there is little difference in the resistance of the platinum containing coatings to acid fluxing. It is suggested that the platinum modifies the structure and composition of the alumina scales or that the platinum rich subsurface layer affords further protection. During the basic fluxing reaction an increase in the oxygen ion activity in species such as Na,SO, adjacent to the alumina layers triggers the conversion of alumina to aluminate, and porosity in the Fig. 4 This sample of RJM2012,a similar alloy alumina then leads to sulphate penetration and containing platinum, has been subjected to hot metal attack. Hence modification of the corrosion testing for 1000 hours at 800'C. Even after a five-fold increase in time (compared alumina or the subscale region by platinum with the sample in Figure 3) sulphide penetra- could inhibit the basic fluxing reaction. tion is only just starting x 750

Platinum Merals Rev., 1987, 31, (1) 29 the alloys after only 2x1 hours, no refractory metals such as tungsten or molybdenum were observed in the scales after these short times. Hence acid fluxing involving MOO, or WO, appears to be precluded at early times, although sulphite enhanced attack could still have occurred. However the major effect of the platinum on the hot corrosion results appeared 200 400 600 BOO to be the promotion of the rapid formation of a DISTANCE, p rn protective alumina + chromia layer, which re- Fig. 5 These aluminium composition profiles across diffusion couples, contain- mained adherent and resistant to corrosion ing (a) 4.5 per cent platinum and (b) no attack without the formation of deleterious platinum, show the similarity in the inter- NiO. In the subscale region chromium and diffusion distance. Each curve represents the average of three traverses across the aluminium levels were also maintained un- centre section of the couples depleted, and hence protective scales could reform if spalling occurred. The Role of Platinum alloys is quite complex and will be reported It is evident from the foregoing discussion elsewhere. However the major differences in that platinum plays a complex role in both the scale formation and development appear, once oxidation and the hot corrosion of nickel based again, to be connected with the protection alloys. It appears to promote the formation of imparted by the alumina scale. The oxides al~mi~scales and it improves their adherence formed on IN792 + Hf were much thicker and to the substrate. It may also be incorporated in- less protective than those on RJM2012 and to scales either directly by platinum/aluminide rapidly became enriched with porous nickel coatings, as particles during oxide growth on oxide. On RJM2012, however, the scale re- platinum containing alloys, or through volatile mained predominantly rich in aluminium and PtO, when samples are heated in the presence chromium, and the sulphides formed after 1000 of the metal. If platinum enhances the for- hours were mainly detected at grain boundaries mation of a continuous alumina scale on alloys with only very isolated areas of more severe which would otherwise suffer from progressive attack. By contrast on IN792 + Hf internal sul- internal oxidation, then, as discussed in ( IZ), phides had formed into broadfront attack after either the platinum speeds up the diffusion of only 200 hours, and after longer times the alloy aluminium through the alloy matrix or it slows adopted the classic hot corrosion morphology of down the diffusion of oxygen through the a voluminous porous nickel rich oxide layer mixed surface scales. Alternatively its presence over massive sulphide penetration. Only slight near the metal/oxide interface changes the reductions in the aluminium and chromium growth morphology as the internal oxides levels occurred below the scale in the platinum develop. containing alloy, while the platinum level itself Any change in the diffusion rate of was increased in this region, presumably by a aluminium through a matrix when platinum is mechanism similar to the case of pure nickel added can be detected simply with appropriate described earlier. In IN792 + Hf, however, diffusion couples. Therefore two couples were below the oxide scale the chromium level had prepared, the first consisting of nickel- dropped to less than 6 per cent, and this had 12 chromiumhickel-Iz chromium-6 alu- seriously impeded any “healing” of the alloy minium and the second of nickel-Iz after oxide spalling. chromium-4.5 platinurnhickel- 12 chromium-6 Although major differences were apparent in aluminium-4.5 platinum. In each case the start-

Platinum Metals Rev., 1987, 31, (1) 30 ing materials were melted in an argon arc fur- platinum is affecting the aluminium diffusion, nace. The matching faces of each half of the the change is small and unlikely to be the main couples were polished to a I micrometre surface factor in accounting for the observed oxidation finish and then they were held together with behaviour. tantalum wire. hecouples were next wrapped The precise role of platinum is still not clear. in tantalum foil and sealed in quartz tubes Both the oxidation and hot corrosion results under a vacuum of 10-5 torr, before being an- could be explained by the platinum modifying nealed for 4 days at IIOOOC.Subsequently, the oxide scales but changes in the scale growth metallographically prepared sections across the mechanisms in the presence of platinum may interface revealed clean oxide free welds, also play a part, especially in view of the although some isolated aluminium rich par- evidence for the strong interfacial interaction ticles, thought to be internal oxides, were between platinum and alumina. observed near the interface. Aluminium con- Platinum is finding an increasing role to play centrations along lines normal to the interface during the design of new cost effective coating were measured by electron probe micro- systems for turbine blades, and has been shown analysis, and typical penetration curves are to have interesting effects on the oxidation and shown in Figure 5. Although the depletion zone hot corrosion of nickel based superalloys. In of the aluminium did appear to be slightly both cases, there is a lack of understanding of greater in the platinum containing alloy with a how platinum is providing these beneficial pro- slightly different profile, the magnitude of the perties. There is certainly a need for further difference was similar to the estimated errors investigation in order to define the exact role of and no firm conclusion could be reached. A platinum, and other platinum group elements. new couple was therefore made containing twice the amount of platinum, with correspon- Acknowledgements dingly lower nickel content. Unfortunately this The financial support of SERC is gratefully increase also had little effect on the diffusion acknowledged, as is the help of Dr. A. Green with the rate. Hence it must be concluded that if diffusion profile measurements.

References

I D. R. Coupland, C. W. Corti and G. L. Selman, 11 G. R. Johnson, J. L. Cocking and W. C. Johnson, “Proceedings of the Petten Conference on the Oxid. Met., 1985,23, 237 Behaviour of High Temperature Alloys in Aggressive Environments”, ed. I. Kirman, J. B. 12 G. J. Tatlock and T. J. Hurd, Oxid. Met., 1984, Marriott, M. Men, P. R. Sahn and D. P. 22, 201 Whittle, Metals Society, London, 1980,p. 525 13 M.R. Jackson and J. R. Rairden, Metall. Trans., 2 G. Lehnen and H. Meinhardt, Electrodeposition 1977, 8A, 1697 Surf. Treat., 1972,I, 71 and 189 14 R. G. Wing and I. R. McGill, Platinum Metals 3 E. J. Felten, Oxid. Met., 1976, 10, 23 Rev., 1981,25, (3L 94 4 0.Kubaschewski and 0. von Goldbeck, J. Inst. 15 J. L. Cocking, G. R. Johnston and P. G. Richards, Platinum Metals Rev., Met., 1949,76, 25s 1985,29, (I), 17 5 D. E. Thomas, Trans. Am. Inst. Min. Metall. 16 R. Bauer, K. Schneider and H. W. Grunling, Ens, 1951,191, 926 High Temp. Technol., 1985,3, 59 6 N. Birks and G. H. Meier, “Introduction to High 17 W. T. Wu, A. Rahmel and M. Schorr, Oxid. Temperature Oxidation of Metals”, Edward Met., 1984,22, 59 Arnold, London, 1983 18 J. A. Goebel and F. S. Pettit, Metall. Trans., 7 C. Wagner, J. Electrochem. Soc., 1952,99, 369 19707 I> I943 8 E. J. Felten and F. S. Pettit, Oxid. Met., 1976, 19 D. R. Coupland, I. R. McGill, C. W. Coni and 10, 189 G. L. Selman, “Proceedings of the International 9 I. M. Allam, H. C. Akuezue and D. P. Whittle, Conference on Environmental Degradation of Oxid. Met., 1980,14, 517 High Temperature Materials”, Inst. of Metal- lurgists, p. 10 I. G. Fountain, F. A. Golightly, F. H. Stott and 1980,2, 126 G. C. Wood, Oxid. Met., 1976, 10, 341 20 T. J. Hurd and G. J. Tatlock, to be published

Platinum Metals Rev., 1987, 31, (1) 31 A History of Iridium OVERCOMING THE DIFFICULTIES OF MELTING AND FABRICATION By L. B. Hunt The Johnson Matthey Group

The use in unmanned space craft of iridium to encapsulate the radioisotope thermoelectric generators, where temperatures of up to 20OO0C have to be withstood over several years of operation, with possible impact velocities of 90 metres per second, has focused greater attention on the remarkable properties of this member of the platinum group of metals. But these same properties of very high melting point and great mechanical strength have been the cause of difficulties in its melting and fabrication over a long period of years. How these problems were tackled and eventually overcome is described in this article.

One of the less well-known members of the For some fifty years after the discovery of platinum group, iridium possesses quite platinum in South America and the early remarkable chemical and physical properties. It investigations of its properties by a number of is not only the most resistant of all metals to English, French, German and Swedish scien- corrosion, insoluble in all mineral acids in- tists, it was not realised that the native platinum cluding aqua regia and unattacked by other they were examining also contained other molten metals or by silicates at high tem- elements. The first to recognise that a small in- peratures, but has a very high melting point soluble residue survived the dissolution of and is the only metal to maintain good native platinum in aqua regia was the French mechanical properties in air at temperatures chemist Joseph Louis Proust, working for a above 1600OC.Its great stability can be gauged time in Madrid under the patronage of King from its physical properties, outlined in the Carlos IV, but he failed to grasp that other Table. Its high modulus of elasticity and members of the platinum group were present modulus of rigidity, together with the very low and in 1799 described his black residue as figure for Poisson’s Ratio (the relationship of “Nothing less than graphite or plumbago” (I). longitudinal to lateral strain), clearly indicate the high degree of stiffness and resistance to Discovery and Characterisation deformation that have rendered its fabrication It was this black residue that greatly into useful components a matter of great dif- intrigued Smithson Tennant shortly after his ficulty over the long period since its discovery, entry into partnership with William Hyde but despite these limitations-and despite its Wollaston in 1800. The object of this famous high cost-a number of applications have de- enterprise was the production and marketing of veloped in more recent years where mechanical platinum in quantity and it was soon decided strength is an essential factor in some of the that while Wollaston should pursue the study of extremely severe conditions nowadays en- the aqua regia solution of native platinum (so countered in modern technology. But before discovering palladium and rhodium) Tennant success could be achieved in either the melting should concentrate on the insoluble matter. By or the fabrication of iridium there lies a long the summer of 1803 he had begun his investi- struggle to be recorded. gation, fortunately mentioning to Sir Joseph

Platinum Metals Rev., 1987, 31, (l), 32-41 32 Smithson Tennant, who had the advantage of Physical and Mechanical Properties a much greater amount of residue from of Iridium Wollaston’s work on platinum, realised that while the Frenchmen suspected the presence of Atomic number ... 77 one new metal in the black powder, there were Atomicweight. .... 192.22 in fact two, namely osmium and iridium, and Crystal structure ... f.c.c. Lattice constant, A ... 3.8392 on 21st June 1804 he presented his paper, a Melting point, OC ... 2443 masterpiece of clarity and conciseness, to the Specific gravity (2OOC) . 22.65 Royal Society. For this he was awarded the Latent heat of fusion, Jlg. 117 Copley Medal for that year, the highest honour Specific heat (O-lOO°C), in their gift, while a little later the French Jlg. OC ..... 0.134 Thermal conductivity workers fully accepted the priority of his (O-lOO°C),Jlcrns. OC. 1.48 discoveries (4). Vapour pressure at 15OOOC Tennant’s comment on iridium was some- torr ...... 10-8 thing of a forecast of the difficulties to come: Specific electrical resistivit at OOC, rnicrohrn. crn. . 4.71 “It appeared of a white colour, and was not Temperature coefficient capable of being melted by any degree of heat I could apply”. of electrical resistivity (O-lOO°C),per OC . 4.27 x 10-3 Electrical conductivity, Oh IACS ..... 36.6 XVI. On two Mrfak,found in tbr black Powder remaining Thermal coefficient of liner after tbe Solution of Platina. By Smithson Tennant, Erq. expansion (O-lOO°C), F. R. S. per OC...... 6.8 x Hardness, HV (annealed), Read June si, 1804. kglrnrn’ ..... 200-240 Modulus of elasticity, E, UPONmaking some experiments, last summer, on the black MNlrn’ ..... 516 x 103 powder which remains after the solution of platina, I observed Modulus of rigidity, G, that it did not, as was generally believed, consist chiefly of MNlrn’ ..... 210 x 103 plumbago, but contained some unknown metallic ingdients. Intending to repeat my experiments with more attention during Bulk modulus, K, MN/rn2 . 371 x 103 the winter, I mentioned the result of thein to Sir JOSEPH BANKS, Poisson’s ratio. .... 0.26 together with my intention of communicating to the Royal Typical tensile strength Society, my examination of this substance, as swn as it should (annealed), 2OoC,MNlm 490-740 appear in any degree satisfactory. Two memoirs were afterwards published in France, on the same subject: one of them by M. DESCOTILS.and the other by Messrs. VAUQUELINand FOURCROY.M. DESCOTILS chiefly directs his attention to the effects produced by this substance on the solutions of platina. Banks, President of the Royal Society, his He remarks, that a small portion of it is always taken up by observation that the black powder “did not, as nitro-muriatic acid, during its action on platina : and, principally was generally believed, consist chiefly of plum- from the observations he is thence enabled to make, he infers, that it contains a new metal, which, among other properties, bag0 but contained some unknown metallic in- has that of giving a deep red dour to the precipitates of platina. gredients”. Fortunately, because work on the M. VAUQUELINattempted a more direct analysis of the sub- same problem was being undertaken almost stance, and obtained from it the same metal as that discovered by M. DESCOTILS.But neitherof these chemists have observed, simultaneously in Paris, first by the director of the Ecole des Mines, Hippolyte Victor Collet- Early in the course of their famous partnership Descotils, and a little later by Antoine Franfois designed to yield malleable platinum in commercial quantities, it was agreed that while Wollaston de Fourcroy and Nicolas Louis Vauquelin at should pursue the investigation of the portion of the Museum d’Histoire Naturelle (2, 3). All the native metal soluble in aqua regia, Smithson three found that the black residue contained a Tennant would study the insoluble portion. The result was the discovery of both iridium and hitherto unknown element but they neither osmium. This shows the opening page of Ten- isolated it nor gave it a name. nant’s paper given to the Royal Society in 1804

Plarinum Metals Rev., 1987, 31, (1) 33 Fourcroy and Vauquelin remarked similarly: On that historic occasion no less than thirty- “This metal has appeared to us to be of a eight distinguished scientists, including Davy, greyish white colour, difficult of fusion, of oxyda- Wollaston, Hatchett, William Allen, W. H. tion, and of solution in acid”. (5) Pepys, W. T. Brande, Henry Warburton and Some years later in Vauquelin wrote of 1814 William Babington, dined together at Ferox iridium: Hall, spent the night there and in the morning “It appears to be brittle and consequently hard. witnessed the melting of a small piece of I cannot give its specific gravity because I have not yet been able to melt it completely”. (6) iridium. This was achieved by means of “the greatest galvanic battery that has ever been con- First Attempts at Melting structed”, consisting of 20 pairs of copper and But by this time a new and powerful method zinc plates, each 6 feet long by 2 feet 8 inches, of obtaining a high temperature was becoming suspended from the ceiling and then lowered available. Following Volta’s news of his dis- into an enormous tank containing 945 gallons of covery of the electric pile in I 800, a number of dilute nitric and sulphuric acids (9). British scientists turned their attention to the Children was not yet satisfied, however, that construction of large batteries to yield a high he had really achieved the melting of a pure voltage. Foremost among them was John specimen of iridium, and early in I 8 I 5 he again George Children, who began to build large bat- set about its fusion, holding the metal in a teries in his private laboratory at Ferox Hall cavity in a piece of charcoal floating on mer- near Tonbridge in Kent in about 1806, while as cury. He had now, acting on a suggestion made is well known Humphry Davy in October 1807 by Wollaston, added a second copper plate to discovered potassium and sodium by means of each cell so that each zinc plate was now faced a discharge from a battery consisting of 250 by two of copper. This materially increased the plates of zinc and of copper each 6 inches by 4 power of the battery, and he then recorded in inches. Davy was friendly with Children and he his paper to the Royal Society, read on 15th was present at Tonbridge when in August 1808 June, 1815: a piece of platinum wire was successfully “Exp. 8. Pure iridium; fused into an imperfect melted by the use of a voltaic battery larger and globule, not quite free from small cavities and more powerful than any hitherto constructed weighing 7.1 grams. The metal is white, very (7). This success encouraged Davy to build a brilliant and in its present state its specific gravity still larger battery at the Royal Institution, but is 18.68,which must be much too low on account of the porous state of the globule”. (10) Children went on to construct an even larger model in 1813. This great occasion was greatly saddened for In that year Smithson Tennant had been those present, however, by the absence of appointed Professor of Chemistry at Cam- Smithson Tennant who, returning from a five- bridge, and while giving his mind to the month tour of France in the February, had met preparation of his lectures in June he wrote to with a fatal accident while on a riding excursion Berzelius, whose friendship with him arose near Boulogne. chiefly from a visit the Swedish chemist had No further attempts to melt iridium are paid to Tennant’s estate in Somerset in 1812, recorded for quite a long period, until, in fact about the choice of a “galvanic machine”. The 1842, when Robert Hare, Professor of letter goes on: Chemistry in the University of Pennsylvania, reported his success in this direction to the “On the 2nd of next month I am going to Mr. American Philosophical Society. Forty years Children’s house to see a machine of which the earlier Hare had devised a hydrogen-oxygen plates are 16square feet. The object is only to pro- blowpipe with which he had melted platinum, duce a very high temperature and I shall try its effect on iridium, which a flame even intensified for the first time in reasonable quantity, and with oxygen will not even touch”. (8) over the years he had gradually brought about

Platinum Metals Rev., 1987, 31, (1) 34 John George Children 1777- 1852 The enthusiasm for building large electric batteries following Volta’s announcement of his discovery infected Children as well as Humphry Davy. In 1831 no less than thirtyeight scientists, including Tennant, were entertainedby Children at his home near Tonbridge and witnessed the first melting of a small globule of iridium by the discharge of a colossal battery he had constructed Phoiopaph hy cmrtcsy of the Wcllcornc Inotilute Uhv. London

improvements in the apparatus. His paper opens: “This communication respects mainly my success in fusing both iridium and rhodium, neither of which in a state of purity had been previously fused. It may be supposed that the globule of iridium, obtained by Children’s colossal battery, forms an exception; but the low specific gravity, and porosity, of that globule, may justify a belief refinery. In any case by 1846, when Michael that it was not pure; and at any rate, the means Faraday was studying the magnetic properties employed were of a nature not to be at command of a wide range of metals and compounds, his for the repetition of the process-so that iridium might as well be infusible, as to be fusible only by records contain the following entry: such a batte y ”. (I I) “2368. Iridium.-Mr. Johnson supplied me Unlike Children’s specimen, Hare’s iridium with several preparations of iridium. The oxide, gave specific gravity values of 21.83 and 21.78, chloride and ammonio-chloride were magnetic; and so was a sample of the metal. One specimen amply confirming his claim to high purity. Of of the metal, which seemed to be very pure, was its physical characteristics he wrote: scarcely at all magnetic, and on the whole I incline to believe that iridium does not stand in the “Although as hard as untempered steel, it is magnetic class”. (12) somewhat sectile, since when split by means of a cold chisel, the edge penetrated about the eighth But the melting of iridium in any appreciable of an inch before a division was effected. By light quantity had to await the work of Henri Sainte- hammering a corner was flattened without frac- Claire Deville and his partner Jules Henri ture, although under heavier blows the mass cracked. I infer that although nearly unmalleable Debray in Paris in the late 1850s. Their design and very hard, iridium may be wrought in the of a furnace constructed from two cylindrical, lathe.” hollowed out blocks of lime and fired by coal- Now Hare had obtained some of his supplies gas and oxygen was first used to melt platinum of iridium from Johnson and Cock (as Johnson on a large scale in 1857 (13), and the British Matthey was known from 1837 until 1845) and rights in their patent were at once acquired by although no published paper exists to support Johnson Matthey. A little later the Russian the contention, it is virtually certain that, as government, impressed with their new pro- will be seen a little later, as early as 1837 cedure for refining native platinum, sponsored iridium had been melted in the Hatton Garden Deville and Debray by setting up for them

Platinum Metals Rev., 1987, 31, (1) 35 pure hydrogen, coal gas being useless for their purpose. Johnson Matthey similarly put the process into effect, and were able to show in the Inter- national Exhibition in London in 1862 a melted ingot of iridium among their numerous other exhibits of the platinum metals. The report of the Juries contains the following item: “An ingot of iridium, hitherto regarded as infusible, now melted into a lump of twenty seven and three quarter ounces.” In I 879 George Matthey presented a detailed account of the refining of the platinum metals in the course of a paper to the Royal Society (I5) of which he was shortly afterwards elected a Fellow. His procedure for the separation, refining and then melting of iridium was “an operation of extreme delicacy” and much too lengthy for reproduction here, but some measure of his achievement may be gained from his statement that while the metal should, if perfectly pure, possess a specific gravity of 22.39, the highest value he had yet been able to attain was 22.38. John Isaac Hawkins 1772- 1865 The Earliest Applications This pictorial tribute appears in a small book, Turning now to the earliest applications of “The Everlasting Gold Pen and How it is Made”, iridium we have to retrace our steps to the published in 1892 by F. Mordan co. A native of Taunton in Somerset he spent hie early years 1830s and to the ingenuity of an extraordinarily in America, inventing among other things the versatile English engineer. This was John Isaac upright piano. Returning to England in 1803 he I followed a successful career as a consulting Hawkins, born in Taunton in Somerset in 772 engineer and patent agent, being elected a the son of a watch and clockmaker. At an early Member of the Institution of Civil Engineers in age he emigrated to America to study at Jersey 1824. He was the first to introduce the iridium pen point College in Pennsylvania-the institution which

Illu-lr.son L PO)YWW ul HI. Wrharl kmlm became Princeton University in I 896-and then turned his mind to mechanical and chemical engineering and also to the improvement of larger furnaces and oxygen plants. From the musical instruments, filing a patent in 1800 for Russian Imperial Mint they were supplied, in the invention of the upright piano, a develop- February 1860, with some eight kilogrammes ment that brought him to the attention of Presi- of crude iridium-containing material among dent Jefferson. In 1803 he returned to England other residues, and “after three and a half in order to claim a legacy and here he embarked months of incessant work” they were able to on a successful career as a patent agent and con- return large quantities of platinum ingots and sultant, his further inventions including a sheet, together with an ingot of iridium weigh- pantograph and then, together with one Samp- ing 1.805 kilogramme (14). To achieve this fu- son Mordan, the use of small particles of “dia- sion they had to consume, for one kilogramme mond, ruby or other hard substances” as pen of iridium, more than 300 litres of oxygen and points, the nibs then being made of horn or

Plarinum Meials Rev., 1987, 31, (1) 36 tortoise-shell (16). The advent of the gold nib Hawkins sold the secret of his technique to an was also due to Hawkins, who spent many years American in 1836, but manufacture of the seeking a suitable material to make a fine and iridium-tipped pens was continued by Francis hard point. Then in 1833 he learned that some Mordan. twelve years earlier Wollaston had provided In the United States several manufacturers samples of rhodium and of the native alloy of entered the gold pen business, but the one that iridium and osmium to Thomas Charles Robin- is remarkable in our present connection was G. son, the famous maker of chemical balances W. Sheppard of Detroit who moved in about and drawing instruments, requesting him to 1842 to Cincinnati. Some ten years or so later prepare pens with each material. (Robinson, of he engaged a boy whom he had noticed working Devonshire Street, off Portland Place in in a neighbouring drug store, one John London, lived quite close to Wollaston and had Holland. Sheppard carried out many experi- provided him with a balance incorporating im- ments with the oxy-hydrogen blowpipe and provements proposed by the purchaser.) Haw- with electric batteries in attempts to melt kins’ information was that Robinson had duly iridium but without success. In 1858 Holland made a few pens with rhodium points (actually became a partner in the business and then, on an alloy of rhodium and tin) but had returned Sheppard’s death in 1862, the sole owner and the iridium alloy as too hard to be wrought into manager (IS). He continued the experimental pen points. This stimulated him to investigate work with no greater degree of success until further, and by 1834 he had succeeded in pro- 1880 or thereabouts, when he was faced with a ducing the first gold pen, this tipped with two demand for much larger pieces of the iridium specks of iridium. Wollaston had died in 1828, alloy for a new type of pen. Simultaneously he and Hawkins had therefore to seek other observed that a specimen of iron ore very high sources of iridium. in phophorus content melted much more In an account of his early efforts, given in readily than other samples and he quickly 1875 by an American pen manufacturer, John heated a small piece of iridium to a white heat Foley, who had received it directly from the and then threw into the crucible a piece of former, the following passage occurs: phosphorus. When the fumes had cleared away he poured out the contents of the crucible and “In the early stage of the business, namely in found “to his joy and amazement a white, com- March, 1834 Mr. Hawkins says, ‘I procured the pact, hard metal” (19). native alloy of Iridium from Mr. Johnson of Hat- ton Garden, London, who allowed me to select For use as pen points this material was from his small stock of a few ounces such particles perfectly satisfactory, but if other uses were to as suited my purpose, at thirty shillings an ounce. be found for the metal it was obviously neces- Mr. Johnson continued to supply me at that price sary to remove the phosphorus. It was at this till July, 1835, when I had picked out all that would suit and he said that he did not expect any point that Holland invoked the help and advice more for some time. I had then only enough to of William Lofland Dudley, Professor of make three dozen Pens, and knew not where to Chemistry at the local medical college in Cin- procure more. I, therefore, went to the British cinnati. Dudley tackled this problem with great Association for the Advancement of Science, which met at Dublin on the 10th of August, 1835, enthusiasm, quickly removing the phosphorus to inquire of the great Chemists of the time, ex- by repeated heatings with lime, but equally pected to be there assembled, where I could be quickly developing an interest in finding new supplied with the precious material. On asking applications for iridium. This enthusiasm led to Dr. Dalton of Manchester, Dr. Thomas Thomson of Glasgow, Dr. Daubeny of Oxford and many the formation of the American Iridium Com- other eminent Chemists, present at the meeting, pany based upon Holland’s activities but with where I could procure the substance, each, without Professor Dudley as general manager. communicating with any of the others, answered The activities of the company received quite that I could obtain it of Mr. Johnson, Hatton Garden, London.’ ” (17) a considerable amount of publicity. John

Platinum Metals Rev., 1987, 31, (1) 37 Holland had filed an American Patent, No. and including a bibliography on iridium (22). 241,216in May 1881for his “Process of Fusing This brought a curt letter from Johnson Mat- and Molding Iridium”, while Dudley had con- they which included these paragraphs: tributed a short account of the process to the “It is only right to record the fact that in the Journal of the American Chemical Society in Great Exhibition of 1851 we exhibited a large the same year, followed by a longer paper given piece of iridium alloy similar to that patented by Mr. Holland, and that the ready fusion of iridium to the Ohio Mechanics Institute that was re- with phosphorus was a matter of metallurgical produced in The Chemical News (20). Then in knowledge long before such exhibit; in fact, some 1883there appeared a further paper by Dudley present members of our staff carry their record of with the rather grand title “The Iridium Indus- its preparation as far back as 1837. . . . For many years past we have succeeded in working pure try” (21). By now several other uses had been iridium into rods and wire, and have the im- found and are described in the paper. These pression that we presented to yourself some pure included draw-plates for the production of iridium wire in a twisted form some years since”. wire, tips for hypodermic needles, the knife (23) edges of chemical balances, and the bearings of In a footnote to this letter the editor of The magnetic compasses. Experiments are also Chemical News, Sir William Crookes, wrote: described with an iridium electrode for the arc “In April, 1882, Mr. Sellon, of the firm of light, while one of the most important appli- Johnson and Matthey, presented us with a beautiful specimen of pure fused and wrought cations was the electrical contact points of iridium in the form of wire 2 inches long and telegraphic apparatus, these being found to about 0.05 inch diameter. It has been bent sharply outlast platinum contacts and not to be subject on itself in the middle, and the two ends are to sticking. Dudley had also carried out ex- twisted together for about half their length. The specimen has been frequently exhibited as a periments on the electroplating of iridium and curiosity, and has been admired by everyone as a claimed that despite the difficulty associated triumph of metallurgical art.” with its insolubility as an anode he had found One other reference to the early applications a suitable electrolyte. In his contribution to the of iridium concerns the work of Thomas Edison chapter on iridium in the 1883 edition of the in developing the incandescent lamp. Before United States Geological Survey’s “Mineral settling for carbon filaments he had ex- Resources of the U.S.” Professor F. W. Clarke perimented with platinum and iridium- of the University of Cincinnati refers to the platinum, and in January 1879he wrote a letter American Iridium Company and adds that to Johnson Matthey, still preserved in their “Professor W. L. Dudley has succeeded in archives: electroplating with iridium, and has obtained “Menlo Park, N. J. January 9th, 1879 excellent results”. The process was later Gentlemen, improved by John Holland, who succeeded Your favour of the 23rd ult. is before me. Can you make iridium in sticks 1/16 in. diameter and Dudley in the management of the Iridium I inch long? Please give me the price for same and Company. also the price of ingots. Dudley thus made for himself a considerable Yours truly, reputation as the leading authority of his time Thomas A. Edison.” on iridium, but his activities in this direction appear to have diminished in 1886when he was Further Applications appointed to the chair of chemistry at the Two or three of the modern uses of iridium Vanderbilt University in Nashville, Tennessee. were first indicated many years ago, but as There is, however, one interesting sidelight might be expected these were slow in develop- to all this activity in America. In 1885 The ment. One reasonably obvious application lay Chemical News published a long article in three in the determination of high temperature by parts by one Nelson W. Perry dealing in some means of thermocouples. The principal couple, detail with the work of Holland and Dudley still in use today, is of course that devised by Le

Platinum Metals Rev., 1987, 31, (1) 38 William Lofland Dudley 1859-1914 Professor of Chemistry in Vanderbilt University in Nashville, Tennessee, from 1886 until his death, Dudley had spent the previous five years teaching chemistry at the Medical College in Cincinnati and it was here that his help and advice were sought by John Holland who had succeeded in melting iridium by adding phosphorus to the charge in the crucible. Dudley plunged into the the metallurgy of iridium with great enthusiasm and contributed a number of papers dealing with its properties and uses PhoioRraph bt couvir.? of the Phoioprmphir Archhe.. Vmierbill Ill,i,rnil,

Chatelier in 1886, platinum versus rhodium- known firm in Hanau. In the closing years of platinum, but clearly this could not be his life he devised an electrical resistance fur- employed to measure temperatures higher than nace in which the main element was a tube of those approaching the melting point of plati- pure iridium, this furnace being used among num. One of the great pioneers in the measure- others by Nernst to determine high tempera- ment of such temperatures was Sir William tures in 1903. It was also supplied to the Chandler Roberts-Austen, Chemist to the Physikalisch-Technische Reichsanstalt for the Royal Mint and Professor of Metallurgy at the same purpose, together with thermocouples Royal School of Mines, and in the course of one consisting of pure iridium against 10per cent of his numerous lectures, given to the Royal mthenium-iridium (25). This combination was Institution in 1892,he referred to other metals found, over the ensuing years, to require fre- with higher melting points being available: quent calibration because of the oxidation of “Thus iridium will only just melt in the flame ruthenium, and numerous couples were tried produced by the combustion of pure and dry based upon combinations of tungsten, molyb- hydrogen and oxygen. By the kindness of Mr. denum and tantalum, all of which are of course Edward Matthey, a thin rod of iridium has been prepared with much labour, and it can be used as subject to severe oxidation. Then, in 1933 Otto a thermo-junction with a similar rod of iridium Feussner, also of the Heraeus company, carried alloyed with 10 per cent of platinum. The iunc- Out a thorough investigation of the iridium- tion be readily melted in the electric ~CYand system and proposed a thermocouple by this means a temperature may be registered which careful laboratory experiments show to be of pure iridium against 4O per cent rhodium- close to 2moC”. (24) iridium, thus enabling temperatures up to This problem of measuring very high 2000OC to be measured in air (26). This com- temperatures was taken up a few years later by bination is still in use at the present time. Wilhelm Carl Heraeus, the founder of the well- Until recently the largest area of growth in

Platinum Metals Rev., 1987, 31, (1) 39 the usage of iridium has been for crucibles for attacked by molten lead, zinc, nickel, iron and growing oxide single crystals for use in com- gold. puter memory devices and in solid state lasers. These crucibles were lovingly prepared by The crystals, such as gadolinium gallium garnet Henry Andrew Kent, a man of near genius in and yttrium gallium garnet, are grown by things mechanical, who had joined the com- Wlting pre-sintered charges of mixed oxides pany in 1875 and who had worked closely with under oxidising conditions at temperatures up John Sellon in developing the fabrication side to 210o~C.However, long before such devices of the business. Nowadays the technique of could be imagined or foreseen, one distinguish- argon arc melting followed by hot rolling makes ed chemist had discovered the valuable proper- it possible to produce ductile and malleable ties of iridium crucibles. This was Sir William iridium in sheet form with a very minimum of Crookes, the founder of The Chemical News and impurities. Such sheet can then readily be President of the Royal Society from 1913 to formed into crucibles of capacities up to 4 or 5 1916, who contributed a paper to that society in litres. 1908, “On the Use of Iridium Crucibles in But the outstanding application of recent Chemical Operations” (27). The paper opened: years, and one that could never have been en- “I should like to draw the attention of chemists visaged in the wildest dreams of those earlier to the great advantages of using crucibles of pure workers, had to await the development of both iridium instead of platinum in laboratory work. nuclear physics and space travel. To provide an Through the kindness of Messrs. Johnson and Matthey I have had an opportunity of experi- independent but reliable source of electric menting with crucibles of wrought iridium, and power for space missions radioisotope thermo- have used one for several months in the usual electric generators have been used since the operations of quantitative analysis in my Voyager probes were launched in 1977, the fuel laboratory. Iridium is as hard as steel, and the crucible is almost unaffected by any mechanical consisting of plutonium-238 dioxide connected treatment that can reasonably be applied to it.” to thermocouples. The fuel is in the form of Crookes, well in advance of his time, went on spheres and these are encapsulated in iridium to to report that his iridium crucibles, one of provide a secure shield of exceptionally high which still survives in the company’s pos- melting point and great strength (28). The session, were resistant to the fusion of many possibility of this spectacular technique finding fluxes, including caustic soda, and were un- other applications is a matter for the future.

Iridium crucibles are now greatly in demand for the growing of oxide single crystals at temperatures around 20OO0C but as long ago as 1908 a number of small crucibles were made in iridium by Johnson Matthey at the request of Sir William Crookes. One of these crucibles still survives in the company’s possession

Platinum Metals Rev., 1987, 31, (1) 40 References I J. L. Proust, An. Hist. Nat., 1799, I, 51-84; 12 M. Faraday, Phil. Trans. Roy. SOC.,1846,136,48 Ann. Chim., 1801, 38, 146-173; 225-247; Phil. 13 H. Sainte-Claire Deville and H. J. Debray, Mag., 1801-2, 11, 44-55; 118-128 Comptes rendus, 1857, 4,1101-1104 2 H. V. Collet-Descotils, Ann. Chim., 1803, 48, 14 H. Sainte-Claire Deville and H. J. Debray, Ann. 153-176; J. Nut. Phil. Chem. Arts (Nicholson), Chim. Phys., 1861, 61, 84-87 1804, 8, 118-125 15 G. Matthey, Proc. Roy. SOC.,1879, 28, 463-471 3 A. F. FourcroY and N. L. VaUqUeh abridged in 16 J. I. Hawkins and S, Mordan, British Patent 4742 Ann. Chim., 1803, 48, 177-183; in full in Ann. of 1822 Chim., 1804, 49, 188-218 17 J. Foley, “History of Foley’s Gold Pens with 4 Smithson Tennant, Phil. Tram., 1804, 94, Illustrations”, New York, 1875, 50-60; see also 411-418; see also D. McDonald, Platinum Metals B. I. Kronberg, L. L. Coatsworth and M. C. Rev., 1961, 5, 146-148. A more detailed account Usselman, Ambix, 1981, 28, 20-32 will be found in D. McDonaldad L. B. Hunt, 18 Information from fi. J. Dembo, Cincinnati “A History of Platinum and its Allied Metals”, ~i~~~~i~alsociety Mat*ey’ 19”’ pp’ 147-152 19 W. L. Dudley, J. Am. Chem. SOC.,1881, 3, 158 A. F. FourcroY and N. L. Vauquelin, Rep. Arts 5 20 W.L. Dudley, Chem. Nus, 1882, 45, 168-169 Mfn. and Ap‘c., 1804, 5, 307; from Ann. Chim., 1804, 50, 5-26 21 W. L. Dudley, Tram. Am. Inst. Min. Eng., 1883, 12, 577-587 6 N. L. Vauquelin, Ann. Phil., 1815~6,444;from 22 N. W.perry, Chem. N~~,Ig85, 51, 19-21; Ann. Chim., 1814, 89, 150 31-33 7 J. G. Children, Phil. Tram. RV. SOC., 18% 99, 23 Chem. brews, 1885, 51, 71 32-38 24 W. C. Roberts-Austen, Pmc. Roy. Imt., 1892,13, 8 Unpublished letter in archives of the Swedish 508-509 Academy Of Sciences, by courtesy Of Dr. A’ E’ 25 W. C. Heraeus, Zeirs. angaoandte Chemie, 1905, Wales 2, 49-53 9 Anon, Ann. Phil., 1813, 2~ 147; “Life of William 26 0. Feussner, Elektrotech. Zeirs., 1933, 54, Allen”, London, 1846, I, 67 155-156 10 J. G. Children, Phil. Trans. Roy. SOC.,1815,105, 27 W. Crookes, Proc. Roy. SOC., 1go8, 80A, 363-374 535-536 II R. Hare, Am. J. Sci., 1846, 2, 365-369; Phil. 28 H. Inouye, Platinum Metals Rev., 1979, 23, Mag,, 18479 31, 147-150 100-108

Platinum in Early Instrumentation The History and Preservation of Chemical Instrumentation EDITED BY JOHN T. STOCK AND MARY VIRGINIA ORNA, Reidel, Dordrecht, 1986, 268 pages, Dfl. 125.00/&9.75 An unusual and intriguing compilation of London, but now with the Royal Scottish papers presented to the History of Chemistry Museum, on “The Use of New Materials in the Symposium of the American Chemical Society Manufacture of Scientific Instruments, c. in September 1985, this publication first 1800-c. 1920”. Among many metals and alloys emphasises the importance of instruments in developed or used for specific purposes, the chemical industry as well as in the laboratory. author mentions Seebeck’s discovery of The eighteen papers, only two of which have to thermoelectricity in 1821, this leading do with platinum, then deal with instruments gradually on to the introduction of the ranging from the very simple and oldest-blow- platinum : rhodium-platinum thermocouple by pipe analysis-all the way to the most modern, Henri Le Chatelier just a hundred years ago. even robotics. In the former case a long paper The first attempt to make a platinum resistance by W. B. Jensen of Rochester, New York, thermometer was made by Sir William Siemens rightly describes Johan Gottlieb Gahn as the in 1871, but its successful use had to await the supreme master of blowpipe analysis and refers researches of Hugh Longbourne Callendar in to his introduction of platinum wire to replace the Cavendish Laboratory in the 1880s. a gold or silver spoon at a time when platinum The other papers discuss a wide range of in- was only just becoming available. One of the struments, and the volume forms a tribute to most fascinating contributions comes from the skill and ingenuity of instrument makers John Burnett, then of the Science Museum, past and present. L.B.H.

Platinum Metals Rev., 1987, 31, (1) 41 ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Effect of Oxygen on the Electronic Pro- perties of Pd An Experimental Test of Various Models H. CLAUS and N. c. KOON, Solid State Commun., 1986, of the Active Site for Nitric Oxide Reduc- 60, (6), 481-484 tion on Platinum Low field magnetisation measurements were taken of R. I. MASEL, Catal. Rev.-Sci. Eng., 1986, 28, (2&3), Pd-Fe alloys obtained by implanting Fe+ into pure 335-369 Pd foils and Pd foils predoped with B+ and O+. Predictions of the reduction of NO have been Oxygen in solid solution in Pd reduces the Pd sus- examined using several models of the active site, ceptibility at a rate of 25% per at.% 0, exactly twice namely the thermodynamic, geometric, atomic site the rate of B. and electronic structure models. Each model predicts which face of a Pt surface will be most active for the The Hydrogenation of CN on Pd(ll1) reduction. Among faces considered were ( IW), (I I I), and Pd(100) (IIO), (~Io),(611) and (210). There is very little M. E. KORDESCH, w. STENZEL and H. CONRAD, surf. agreement between the various models. Experimental Sci., 1986, 175, (I), L687-L692 work on NO reduction was examined, and compared Adsorbed CN may be produced on P~(~II)and with the models. Experimentally Pt(410) is the most Pd(1oo) surfaces at room temperature by dissociative active face, and only the orbital symmetry model of adsorption of cyanogen. HREELS shows that electronic structure was reasonably in agreement with adsorbed CN forms adsorbed HCN or DCN on these the data. (75 Refs.) Pd surfaces by reaction with H adsorbed from the residual gas or by dosing with H, or D, . The reaction Surface Topography of (100)-Type temperature is slightly lower for Pd(I0o) and the Electro-Faceted Platinum from Scanning range of temperatures over which the reaction occurs Tunnelling Microscopy and Electro- is much smaller. chemistry J. G6MEZ, L. VkQUEZ, A. M. BARd, N. GARCIA, C. L. Surface Enrichment of Rhodium in Pd- PERDRIEL, W. E. TRIACA and A. J. ARVIA, Nature, 1986, Rh Alloys after High Temperature Air 323, (b89), 612414 Oxidation The fKst observation on (Ioo)-type Pt electrodes in B. M. JOSHI, H. S. GANDHI and M. SHELEF, surf. real-time by scanning tunnelling microscopy is Coatings Technol., 1986, 29, (3), 131-140 reported. The existence of a faceted surface con- Foils of Pd-Rh alloys containing 85 and 95% Pd were sisting of a flat part surrounded by ridge-type struc- heated in air between 600-1 IWOC and their surface tures was confumed. Initially cluster formation compositions were examined. Surface enrichment of occurs which develops in a preferential orientation, Pd as an oxide was observed for foils heated thus giving direct evidence that faceting occurs <8m0C, whereas Rh enrichment occurred for foils through a selective electrodissolution/electro- heated between 850 and 95Ooc. For foils heated at deposition process which may involve a fast diffusion ~ooo-~~oo~Ca slight enrichment of Rh was of metallic species in the electrolyte or on the surface. observed. These surface changes can be attributed to thermodynamic differences in the formation and Resistivity of the Heavy-Fermion deposition of Pd and Rh oxides and to diffusion in U(Pt,Pd) Alloys thick surface oxides on I'd-rich alloys. R. VERHOEF, A. DE VISSER, A. MENOVSKY, A. J. Kinetics of Phase Transformation from RIEMERSMA and J. J. M. FRANSE, PhySiCa B + c, 1986, to 142, (I), 11-15 PdSi Pd2Si Electrical resistivity measurements were taken on a T. CHIKYOW, I. OHWMARI and s. SUZUKI, Phys. Rev. series of mono- and polycrystalline U(Pt, J'dX), B, 1986, 34, (7), 4807-4811 compounds (x < 0.15) in the temperature range The phase transformation from PdSi to Pd,Si has 1.4-3mK. On alloying with Pd the spin-fluctuation- been investigated. PdSi, initially formed by annealing like resistivity of pure UPt, transforms into a more an epitaxial Pd, Si layer on Si at 850°C, transformed complex curve for x=o.oz and X=O.O~, revealing to Pd, Si by a post annealing below 750% After the transitions at 3.3K and 5.6K, respectively. At higher phase transformation, small grains of Pd,Si and Si I'd concentrations (X=O.IO, O.I~), the resistivity were observed. 9% of the surface of the sample post curves change to a Kando-type of behaviour. A annealed at 65ooC was covered with Pd,Si grains, second phase appears in the X-ray pattern in the same while only 75% of the surface area was covered with concentration range. Pd Si grains for the sample post annealed at 750°C.

Platinum Metals Rev., 1987, 31, (I), 42-47 42 Interdiffusion and Compound Formation First Synthesis of a Nitro Complex of in the MolPdlSi Thin Film Metallization Ruthenium (III), as a Key Intermediate in System the Oxidation of Nitro Ligand to Give R. N. SINGH, Thin Solid Films, 1986, 143, (3), both Nitrosyl and Nitrato Ligands 249-257 H. NAGAO, M. MUKAIDA, K. SHIMIZU, F. S. HOWELL and Interdiffusion and compound formation in Mo/Pd/Si H. KAKIHANA, hog. Chm., 1986, 25, (q), thin fdms were studied between 250-750°C by sheet 43 12-43 I4 resistance measurement, X-ray diffraction, AES and The fust synthesis is reported of Rutherford backscattering spectrometry. Results in- [RuX(NO,)(bpy),]Y where (X=Cl, Y=ClO,), dicated that thermal annealing in the MoiPd/Si thin (X=Cl, Y=PF,), (X=Br, Y=CIO,) or (X=Br, film couples between z50-47s°C leads to Pd-Si in- Y=PF,), by the oxidation of the corresponding teractions, Pd, Si formation and thus a small increase nitrosyl complex with NaClO solution. in sheet resistance. For temperatures >475OC a Mo- Pd, Si interaction, besides the Pd-Si interaction, occurs; MoSi, was formed and a dramatic increase in ELECTROCHEMISTRY sheet resistance occurred. Stabilization of RuO by IrO for Anodic Boiling Points and Ideal Solutions of Oxygen Evolution in Acid Media Ruthenium and Osmium Tetraoxides R. K~TZand s. STUCKI, Electrochim. Acta, 1986, 31, Y. KODA,J. Chem. soc., Chem. Commun., 1986, (17), (10),1311-1316 1347-1348 Anodic 0, evolution on RuxIr,-xO, was investigated The boiling point of RuO, has been directly for x=o, 0.3, 0.5, 0.8 and I usmg electrochemical measured for the first time as 129.6*o.z0C which is and surface physical techniques. The electrochemical identical to that of OsO, namely 12g.7-co.2~C.All behaviour was mainly determined by the Ir compo- mixtures of RuO, and OsO, had practically the same nent for x - 17at.%. The magnetic kidney dialysate concentrations of urea and NaCl susceptibility of these alloys peaked at - 17oK and it (o.sokg/m’ and 1oomol/m3, respectively) the major is suggested that superconductivity co-exists with electrolysis products are N,, C02, 0, and H, and itinerant-electron antiferromagnetism in b.c.c. Cr-Ru the reaction mechanism is solution oxidation of urea alloys. by anodically generated (3,. A N, yielding direct electrode reaction is observed at high urea concentrations (3okg/m’) and low NaCl concentrations CHEMICAL COMPOUNDS (10- Ioomol/m’). Palladium and Platinum Electrocatalytic Synthesis of Methyl For- mate and Methylal from Methanol on a P. A. CHALONER, Coord. Chem. 1986, 72, 1-195 Rev., Platinum-Bonded Solid Polymer Elec- A review of literature on Pt and Pd co-ordination chemistry published in 1983 and some from 1982 in trolyte Membrane Chem. Abs. is presented. Complexes considered in- K. OTSUKA and I. YAMANAKA, Appl. Catal., 1986, 26, clude those of Pt(VI), Pd(VI), Pd(1V) and Pt(1V) (1-2), 401-404 with ligands from Groups IV, V, VI and VII, Pt(II1) The synthesis of methyl formate and methylal from and Pd(III), Pt(I1) and Pd(I1) with similar ligands CH,OH using a Pt-SPE membrane without any sol- and Pd(I), Pt(I), Pd(0) and Pt(0) and those with mix- vent, electrolyte or a divided cell is discussed. The ed oxidation states. Literature on clusters of various electrochemical oxidation of methanol usually yields types is examined, as is catalysis by Pt and Pd com- formaldehyde, formic acid or CO, . The rates of pro- plexes where the amount of literature has increased. duct formation and their selectivities can be controll- Sn-Pt complexes are considered. (787 Refs.) ed by the voltage between the Pt/SPE electrodes.

Platinum Metals Rev., 1987, 31, (1) 43 PHOTOCONVERSION A Glucose Sensor Based on the Adsorp- tion of Glucose on a PalladiumlGold Bipolar Ti0 IPt Semiconductor Modified Carbon Electrode Photoelectrodee and Multielectrode Ar- L. GORTON and G. JdNSSON, 3. Mol. calal., 1986, 38, rays for Unassisted Photocyclic Water (1-2), 157-159 splitting A Pd/Au-modified electrode for detecting glucose, E. S. MOTKIN, A. J. BARD, A. CAMPION, M. A. FOX, T. based on the strong adsorption of glucose oxidase is reported. The electrode allows an extended potential MALLOUK, S. E. WEBBER and J. M. WHITE, PhyS. J. range to be used for examination of potential Chem., 1986, 90, (IS), 4604-4607 behaviour and stability of immobilised oxidase. Bipolar Pt/TiO, photoelectrodes, have been made from a polycrystalline TiO, film with sputter- deposited Pt. The photoelectrodes were assembled into multipanel arrays and vectorial charge transfer HETEROGENEOUS CATALYSIS was observed. Several different multielectrode cells, using KOH and 0, electrolytes, were constructed. In Coke Formation on Platinum Metals series configuration, the open-circuit voltage V, is Studied by Auger Electron Spectroscopy proportional to the number of panels used. With 5 and Secondary Ion Mass Spectroscopy panels in series VW>3.6V is obtained, allowing J. W. NIEMANTSVERDRIET and A. D. VAN LANGEVELD, unassisted photolytic (Xe lamp) water splitting. Fuel, 1986, 65, (IO), 1396-1399 Various techniques were used to distinguish between Efficient Homogeneous Photochemical four types of carbonaceous deposits which may be Hydrogen Generators using Rhodium present on a catalyst: molecular, carbidic, amorphous Compounds as Catalyst Precursors and graphitic C. Differences between Pt, Rh and Ir H. HUKKANEN and T. T. PAKKANEN, J. MOl. calal., for C deposition from C,H, are discussed. 1986, 37, (2-31, 297-307 A homogeneous catalytic system is described which Use of Noble Metals in Automobile Ex- efficiently generates H, by visible light, using haust Catalysts Ru(bipy),CI, as a photosensitiser, Rh carbonyls as J. T. KUMMER, J. Phys. Chem., 1986, 90, (20), catalysts and triethanolamine as an electron donor. 4747-4752 The system is highly active only in organic medium. A review of laboratory work on catalytic reactions for automobile exhaust purification is presented. Pt, Pd and Rh catalysts, oxidation of CO and hydrocarbons, ELECTRODEPOSITION AND NO reduction and the water-gas shift and steam- SURFACE COATINGS reforming reactions are examined. Literature indicating alloy formation between noble metals to be Photoassisted Platinum Deposition on detrimental to catalysis, and segregation beneficial to Ti02 Powder Using Various Platinum catalysis is included. (I 17 Refs.) Complexes J.-M. HERRMANN, 1. DISDIER and P. PICHAT, J. Phys. Sulphur-Induced Faceting of Platinum Chem., 1986, 90, (22), 6028-6034 Catalyst Particles Factors affecting the photoassisted deposition of Pt P. J. F. HARRIS, Nature, 1986, 323, (@I), 792-794 on powder TiO, have been examined in aqueous S poisoning experiments on thin self-supporting solutions containing different complexes. The deposi- Pt/Al,O, catalyst films were examined by TEM. S tion rate was identical for chloroplatinic acid, Na adsorption produced a change in morphology involv- chloroplatinate and hexahydroxyplatinic acid, to a ing the formation of sharp (100) facets. The TEM's detection limit of Ippm. TEM shows Pt deposits Inm of unpoisoned Pt indicated well rounded particles diameter on all the TiO, particles. Longer illumina- with only light faceting and no sharp edges. tion and higher loadings give large agglomerates. Pd, Ag, Rh, Ir and Au have been deposited on TiO,. NO Reduction by CO over Noble-Metal Catalysts under Cycled Feedstreams LABORATORY APPARATUS H. MURAKI and Y. FUJITANI, Ind. Eng. Chem., Prod. AND TECHNIQUE Res. Dev., 1986, 25, (3), 414-419 The reduction of NO with CO was studied over u- Al,O, supported Pt, Pd, Rh, Ru and Ir catalysts. Of Hydrogen The activities were measured using cycled feeds and S.-Y. CHOI, K. TAKAHASHI, M. ESASHI and T. MATSUO, steady non-cycled feeds. The catalyst activity was Sens. Acmarors, 1986, 9, (4), 353-361 Rh>Ru>Ir>Pd>Pt. Under cycled feeding the ac- The drift in Pd-gate MOS sensors for H, detection tivities of Pt and Pd were greater, the cycling affected can be eliminated by using Pd/Pt H, sensing gate and Pt more than Pd. The order of periodic operation cor- Ag/Cu/Pd/Pt reference gate differential-type sensors. responded to susceptibility for CO self-poisoning.

Platinum Metals Rev., 1987, 31, (1) 44 Exhaust-Catalyst Development for The Effect of Various Bimetallics on the Methanol-Fueled Vehicles: 1 .A Com- Graphite-Steam Reaction parative Study of Methanol Oxidation R. T. K. BAKER, J. A. DUMESIC and J. J. CHLUDZINSKI, over Alumina-Supported Catalysts Con- J. Caral., 1986, 101, (I), 169-177 taining Group 9, 10 and 11 Metals Bifunctional Ni-Pt, Pt-Ti, Ni-Ru and Ni-Ti catalysts R. W. MCCABE and P. J. MITCHELL, Appl. catal., 1986, were studied for the Gsteam reaction. One compo- 27, (11, 83-98 nent increases the 0 reactivity and the other ac- Catalysts to be used for the efficient oxidation of ex- celerates the supply of C from the source material to haust products from methanol fuelled vehicles were the catalyst-gas interface. The bimetallic systems ex- investigated. Highly dispersed Pt, Pd, Rh, Ag and hibit a rate of catalytic attack of graphite in steam that Cu-Cr on y-Al,O, were tested. Pt and Pd oxidised is higher than the single components. Introducing a methanol rapidly in the absence of CO and produced second metal can produce changes in the wetting methyl formate below-4mK. With CO present characteristics of the catalyst on graphite. methanol oxidation is strongly inhibited. Rh had much lower activity than Pt or Pd but was not much Heterogeneous Catalytic Hydrogenation affected by CO. of Carola Oil Using Palladium N. HSU, L. L. DIOSADY, N. F. GRAYDON and L. J. RUBIN, Catalytic Wood Liquefaction Using a 3. Am. Oil Chem. Soc., 1986, 63, (8), 1036-1042 Hydrogen Donor Solvent The hydrogenation of carola oil was studied using Pd P. E. ARAYA, S. E. DROGUETT, H. J. NEUBURG and R. black, and compared with a Ni catalyst, for produc- BADILLA-OHLBAUM, Can. 3. Chem. Eng., 1986, 64, ing partially hydrogenated fats with low trans-isomer (51, 775-780 content. Pressure had the largest effect on trans- The direct wood liquefaction of pine sawdust in a H isomer formation. A maximum of 18.7% trans-isomer donor solvent was studied using Ptly-Al,O,, Co- could be obtained, while Ni produces about 50% Moly-Al ,o,, Raney nickel catalysts and uncatalysed trans-isomer. At 250 psig and 5o°C 5% PdlC had runs at 673K and a pressure of xoMPa. The weight twice the activity of Pd black. The oil samples con- ratio of so1vent:solid loaded was 2: I, the gas phase be- tained - ippm Pd residue after filtration. Pd can be ing either N2 or H ,. There was a high conversion to used at 50-1 50 times lower concentration that Ni. liquid and gaseous products. Liquefaction occurred under H, or Nz with and without catalyst. Higher A New Class of Catalysts: Palladium Sup- organic liquid production is favoured under H, in the ported on Phoephinated Inorganic presence of Pt and Co-Mo catalyst. Oxides R. L. AUGUSTINE and L. JIWAN, 3. MOl. catal., 1986, Atomic Structure of Ultrafine Catalyst 37, (2-31, 189-200 Particles Resolved with a 200-keV Modification of SO,, Al ,0 , or SiO, -MgO by the at- Transmission Electron Microscope tachment of pendant organophosphines gave D. A. JEFFERSON, J. M. THOMAS, G. R. MILLWARD, K. phosphinated oxides which on treatment with TSUNO, A. HARRIMAN and R. D. BRYDSON, Nature, Na,PdCl, and heating gave black, catalytically active 1986, 323, (60871, 428-431 species which are metallic Pd supported on these Results of investigations on the ultrastructures of modified oxides. The pendant phosphine groups in- very fine particles using a modified commercial teract with the Pd metal to influence the olefin zcokeV TEM are presented. A new side-entry hydrogenation activity and to markedly decrease the specimen stage in the microscope allows atomic ar- double bond isomerisation capability of these rays to be investigated. Catalysts examined included catalysts. Pt/C and Pt colloidal sols, the sol particles were crystalline, with considerable surface roughness. Experiments on Heterogenization of Homogeneous Rhodium Catalysts, Illus- Dehydrogenation of Methylcyclohexene trated for the Synthesis of Acetic on a PtNaY Catalyst. Study of Kinetics Anhydride and Deactivation G. RITTER and G. LU~,Chem. Ing. Tech., 1986, 58, J. P. GARCfA DE LA BANDA, A. COWand F. V. .MELO, (8), 668-669 Appl. Catal., 1986, 26, (I-2), 103-121 An attempt to combine the advantages of The kinetics of the dehydrogenation of homogeneous co-ordinate catalysts and methylcyclohexene to toluene on a Pt/NaY zeolite heterogeneous catalysts to produce a solid phase and the deactivation of the catalyst have been studied. catalyst is discussed for Rh. Supports studied includ- By comparing dehydrogenation rates for ed SiO,/Al,O,, TiO,/AI,O,, MgO/AI,O, and methylcyclohexane and methylcyclohexene it has Cr,O,/Al,O,, and the effects of pressure and been found with this catalyst that the slowest step in temperature for acetic anhydride syntheses were ex- the overall dehydrogenation is the dehydrogenation amined. The highest activity occurred for Rh on of methylcyclohexane to methylcyclohexene, follow- Al,O, or on Cr,O,/Al,O, with p- ed by the desorption of toluene from the metal. diphenylphosphinoethylbiethoxysilane as fixative.

Platinum Metals Rev., 1987, 31, (1) 45 Effects of the Variation of Electric Pro- Ruthenium Tetroxide Catalysed Oxida- perties of TiO, Support on the tion of Coals. The Formation of Aliphatic Hydrogenation of CO and CO, over Rh and Benzene Carboxylic Acids Catalyst L. M. STOCK and S.-H. WANG, Fuel, 1986, 65, (111, I. TOMBACZ, 1. KOSZTA and F. SOLYMOSI, Mag)). Kem. I 552-1562 Fob., 1986,92, (8), 373-380 RuO, was used as a reagent for the oxidation of The electrical properties of a TiO, support were several different coals. Significant quantities of altered by doping with cations, and the effects on the aliphatic, di-, tri- and tetracarboxylic acids, benzene, catalytic activity of Rh during hydrogenation of CO di-, tri-, tetra-, and pentacarboxylic acids were pro- and CO, were investigated. Changing the electrical duced in these oxidation reactions, and more than 100 conductivity of TiO, affects the catalytic nature of products have been identified. A large number of car- Rh. Incorporating Wb+ ions which increased the boxylic acids were formed in this reaction which electrical conductivity 1-2 orders of magnitude in- selectively preserves the aliphatic portion of the coal. creased the turnover frequency of CH, formation.

Mg * + and Al ’+ hardly affected the electrical conductivity or the activity of Rh. HOMOGENEOUS CATALYSIS Direct Synthesis of Acetic Acid from Syn- “Counter” Phase Transfer Catalysis by thesis Gas over Rh-Mn-Zr-LilSiO, Water-Soluble Phosphine Complexes. Catalyst Catalytic Reduction of Ally1 Chlorides and T. NAKAJO, K.-I. SANO, S. MATSUHIRA and H. ARAKAWA, Acetates with Sodium Formate in Two- Chem. Lett. Jpn., 1986,(9), 1557-1566 Phase Systems The direct synthesis of acetic acid from syngas has T. OKANO, Y. MORIYAMA, H. KONISHI and J. KIJI, been investigated. Acetic acid was produced with > Chem. Lett. Jpn., 1986,(9), 1463-1466 63% selectivity over Rh-Mn-Zr-Li/SiO, catalyst at In the reduction of ally1 chlorides and acetates with 300OC under a pressure of Iookgkrn, of syngas with Na formate in a heptane-water two-phase system, a flow ratio CO:H, =9:1. water soluble Pd complexes function as a novel type of catalyst which transports the substrate into the Hydrogenolysis of Propane, n-Butane aqueous phase and causes it to react with Na formate. and Ieobutane over Variously Pretreated Ru/TiO, Catalysts Colloidal Palladium Supported on C. C. BOND, R. R. RAJARAM and R. BURCH, J. Phys. Chelate Resin Containing Iminodiacetic Chem., 1986, 90, (20), 4877-4887 Acid Groups as Hydrogenation Catalysts The hydrogenolyses of the title compounds were in- H. F. HIRAI, s. KOMATSUZAKI and N. TOSHIMA, J. vestigated over Ru/TiO, containing 0.5 and 5 Macroml. Sci.-Chem., 1986,A23, (8), 933-954 wt.%Ru, pretreated in various ways. Oxidation at Colloidal catalyst Pdkhelate resin containing im- 623K after a first reduction at 758K or 893K, follow- inodiacetic acid was prepared, and cyclopentadiene ed by mild reduction, gives high-activity catalysts was hydrogenated to cyclopentene in 97.I% selectivi- free of in a non-SMSI state. The highly dispersed c1- ty at IOO% conversion of cyclopentadiene under Iatm Ru particles have CH, selectivities, and for n-butane H, in CH,OH at o°C The finely dispersed Pd par- the oxidised catalysts have a marked preference for ’. ticles were 10-60& in diameter. X-ray microanalysis terminal C-C bond breakage. Low activity catalysts and elution analysis showed the existence of large were also produced. amounts of Pd ion complexes in the resin. Pd metal in the resin was - 5% of the total Pd. Since the resin Chemisorption and Catalysis by Metal after removal of most of the ionic Pd had almost the Clusters same catalytic activity as before, it was concluded that R. B. MOYES, P. B. WELLS, S. D. JACKSON and R. the finely dispersed Pd particles are the active species WHYMAN,J. Chem. SOC.,Faraday Trans. I, 1986,8z, in the catalyst. (9), 2719-2727 The properties of clusters derived from Ru(C0) , Oxidation of Alcohols by Transfer of and H,Ru,(CO),, supported on SO,, Al,O, and Hydrogen in the Presence of Saturated TiO, are discussed. The clusters are stable and give Ketones. Application of the Selectivity of highly reproducible activity for ethene hydrogenation and ethane hydrogenolysis. Catalysts freshly Catalyst Transfer by RhH(PPh 3) prepared are initially in a non-steady state, pass D. BEAUPERE, M. MASSOUI, R. RALAINIRINA and R. through a maximum in activity, then decline to a UZAN, Nouv. J. Chim., 1986,10, (8/9),493-498 steady-state value. Hydrocarbons are retained in the A kinetic study of the oxidation of alcohols by H non-steady and steady states. Steady-state catalysts transfer using RhH(PPh,), as catalyst and ketone as had low activity for ethene hydrogenation. Ru cluster H acceptor has been performed under mild condi- catalysts show lower specific activity than correspon- tions. Prochiral enones were reduced by the H, with ding 0s catalysts. an enantiomeric excess reaching 52%.

Platinum Meials Rev., 1987, 31, (1) 46 FUEL CELLS Automated Platinum Resistance Thermo- meter for Determining the Composition Performance Study of a Fuel Cell Pt-on-C of Salt Solutions and Purity of TNT Anode in Presence of CO and C02, and J. M. C. RIDDEN, 3. Hazardous Mater., 1986, 13, (3), Calculation of Adsorption Parameters for 329-336 CO Poisoning A Pt resistance thermometer coupled to a bridge circuit has been used for determining the solidification H. P. DHAR, L. G. CHRISTNER, A. K. KUSH and H. C. point of TNT and the crystallising point of certain MARU, 1986, 133, (8), 3. Electrochem. SOC., aqueous salt solutions. The system can be automated. 1574-1 582 The behaviour of a o.qmg/cmz porous Pt/C fuel cell Thin-Film Platinum Resistance Ther- anode with electrochemically active surface area of mometer for Use at Low Temperatures Isomz/g of Pt was measured to find polarisation losses due to CO, and CO in the H2fuel. The anode and in High Magnetic Fields was tested as a floating electrode in a half-cell T. HARUYAMA and R. YOSHIZAKI, cryogenics, 1986,26, assembly in the presence of 100 wt.% H,PO, at (101, 536-538 1go0C. Among conclusions reached are that the com- A thin film commercially available Pt resistance ther- bined voltage loss for dilution by CO and CO, , and mometer was examined for thermometry from poisoning by CO is the sum of the dilution and 20-3ooK in high magnetic fields up to 5T. It was poisoning voltage losses. found that the thermometer was precise to 2 0.I K within this range. The magnetoresistance of the Pt Glycol/Air Fuel Cells resistance thermometer at 3oK is - 1.5% for a R.-Z. QIU, Int. 3. Hydrogen Energy, 1986, 11, (12), magnetic field of 5T. 817-820 The development of a glycol/air fuel cell is discussed. Resistance Thermometer of Rhodium- The electrode catalyst made of Pt:Pd:Bi = 3:2: I on ac- Ferrum Microwire tive C as carrier was very effective for the elec- S. P. LOGVINENKO and G. F. MIKHINA, Cryogenics, trochemical oxidation of glycol in KOH solution at 1986, 26, (81, 484-485 room temperature. The loading of Pt-Pd can be as Resistance thermometers based on glass insulated low as Img/cmz. A 2W battery consisting of 10cells cast microwire of Rh-o.gat.%Fe have been examined. with a capacity of ~mAhhas been constructed. The alloy cast as a microwire has the same temperature dependence of resistivity as the alloy prepared by the powder metallurgical method. The CORROSION PROTECTION thermometer has a high relative sensitivity in the low temperature region, - I s%/K at I.5 K. Atmospheric Corrosion Test on PdIAg- Thick Film Lead Paths Thick Film Chip Resistors for Use as Low A. H. C. HENDRIKS, Metall, 1986,40, (IO), 1018-1021 Temperature Thermometers The effects of corrosive gases on the solderability of Q. LI, C. H. WATSON, R. G. GOODRICH, D. G. HAASE and Pd-Ag thick film lead paths were examined. Tests H. LUKEFAHR, Cryogenics, 1986, 26, (8), 467-470 simulating atmospheres containing strongly corrosive The resistance and magnetoresistance of a commer- industrial pollutant gases of SO,, H, S, NO,, 0 , and cially produced Bi,Ru,O, thick film resistor have C1, separately, or in different combinations were per- been measured from 8oK-1gmK in fields up to 2oT. formed different Pd-Ag thick film lead paths for on Between 2.5 and 0.I K the resistance of a I kQ resistor 14days. H,S was the only one to have a bad effect. fits R=A exp (B/TR).

TEMPERATURE MEDICAL USES MEASUREMENT Study on Interaction of Antitumor Active Platinum-Point Reference in the Calibra- Platinum(I1) Complexes with DNA and Its tion of the Visual Disappearing-Filament Constituents by Means of High- Optical Pyrometer Performance Liquid Chromatography D. DAS and M. S. CHANDRASEKHARAIAH,High Temp. K. INAGAKI and Y. KIDANI, Nippon Kagaku Kaishi, Sci., 1986, 21, (3), 161-168 1986, (7), 1025-I031 For measuring the brightness temperatures above Selective binding of anti-tumour Pt(I1) complexes I 5m0C the visual disappearing-filament optical with DNA was studied by enzymatic digestion and li- pyrometer needs its range scales to be calibrated quid chromatography. Adjacent guanine bases were before every use; therefore a modified procedure uses the preferred Pt binding sites in DNA. Reaction pro- a Pt-point reference to reduce the work of calibration ducts of d(GpG) with a variety of anti-tumour Pt without losing precision or accuracy. complexes were separated and examined.

Platinum Metals Rev., 1987, 31, (1) 47 NEW PATENTS

PROPERTIES ELECTROCHEMISTRY Corrosion Resistant Pt Alloys Electrochemical Electrode TOKURIKI HONTEN K.K. ORONZIO DE NORA IMPIANTI Japanese Publ. Appl. 61176,634 European Appl. 183,1ooA A high melting point, corrosion- and oxidation- An electrode for electrolytic production of H2 and resistant Pt alloy consists of Pt, Ru, Fe, Cr and Co. alkali metal hydroxide comprises a conductive inert It is used in electrodes, nozzles and medical metal substrate, a pre-coating of ceramic particles in equipment. a metal matrix of Fe, Ni, Ag, etc., and an electrocatalytic ceramic coating of one or more of Pt, Pd, Magnetic Powder for Recording Rh, Ir, Ru, Ti, Zr, Hf, etc. HITACHI MAXELL Japanese Publ. Appl. 61/105,806 Electrode for Electrochemical Cell Ru, Rh, Pd, Ir, Pt andlor Cu are added to y-ferric oxide to produce a magnetic powder which is used as a ORONZIO DE NORA IMPIANTI magnetic recording medium. The noble metal acts as World Patent Appl. 8613,~yA a catalyst for a H reduction reaction to increase the An electrode resistant to Fe and Hg poisoning, com- reduction speed. prises an electroconductive support coated with (a) metal alloy dispersed electrocatalytic material (b) Opto-Magnetic Recording Medium platinum group metal alloy in homogeneous phase. The electrocatalytic material in (a) can be a platinum NEC CORP. Japanese Publ. Appl. 611107,555 group metal, Ti, Zr, Tb as oxides, borides, etc., but The medium has an axis of easy magnetisation is preferably Ru oxides, and for (b) RuCl ,. perpendicular to the fim surface, and has a recording layer of a magnetic alloy containing a rare earth Polymer-Modified Electrode metal, an Fe group transition metal and Pt. JOHNSON MATTHEY P.L.C. World Patent Appl. 86/4,364A Magnetic Recording Medium The manufacture of a PTFE modified electrode with HITACHI METAL K.K.JapaWse Publ. Appl. 611142,525 a Pt, Pd, Ru, or Rh electrocatalyst, and a metal A magnetic recording medium comprises a substrate, substrate is claimed. The electrode has reduced over- a middle layer of Ni-P and a magnetic Co-Ni-Pt alloy potential and is especially used as a chloralkali layer which has a C protective layer on it of ~oooA cathode. The process does not require the polymer to thickness. be fused, and the electrocatalyst is more effective. Ruthenium Electrolysis Electrode CHEMICAL COMPOUNDS L. I. WRKOV U.S. Patent 4,589,969 Luminescent Chelate Labels An electrode for electrolysis consists of a substrate of passivated metal, with a mixed oxide coating of Ru, HYPERION CATALYSIS world Patent Appl. 8612,734A Ti and Sn. The electrode is useful in chloralkali cells, A new chemical moiety containing Ru or 0s can be in a Hg cathode electrolyser, in chlorate production induced to emit electromagnetic radiation by expos- and in waste water treatment. It has low resistance, ing it to chemical or electrochemical energy. It may and is simply made. be used for rapid, efficient and sensitive determination of chemical, biochemical and biological Amorphous Alloy Electrode materials, and act as a chelate label. DAIKI GUM KOGYO K.K. Japanese Publ. Appl. 61167,732 Palladium Co-ordination Complexes A surface activated amorphous alloy for solution elec- RESEARCH CORP. U.S. Patent 4,598,073 trolysis consists of P, Si, and/or B, at least one of Ru, New polycyclo-Pd(I1)-bipyridine complexes are Rh, Ir andlor Pt and at least one of Co,Ni andlor Cu, claimed. They can be used as anti-tumour agents and etc. The alloy is used for electrolysing metal halide are useful as homogeneous or heterogeneous catalysts solution; it has long life, and can save energy. and as intermediates in organic syntheses. Gas Diffusion Electrode Iridium Hexafluoride Prciduction ASAHI GLASS K.K. Japanese Publ. Appl. 611130,497 A. S. SIBE. INORG. CHEM. Russian Palent 1,203,021 The electrode has an electrically conductive porous The pure Ir(V) hexafluoride complex is produced base body of powdered C black with a metal colloid from Ir powder by boiling with B trifluoride, follow- of platinum group metal or alloy, or Ag. It has im- ed by the addition of KCl. proved durability and lower overvoltage.

Platinum Metals Rev., 1987, 31, (l), 48-52 48 Oxide Film Formation Oxygen Sensor HITACHI K.K. German Offen. 3,600,575 MSSAN MOTOR K.K. Japanese Publ. Appl. 61179,i55 A process for oxide film formation on Pt, Pd, Ir, Rh An 0, sensor has a catalyst of I-3:1 of y-Al,O, and or Ru for pH electrodes involves ion implantation Ce oxide on which at least two of Pt, Pd and Rh are with 0 ions. deposited. The sensor is used for controlling air: fuel ratios for I.C.E.; it has improved high temperature Electrochemical Cell durability and the effect of Pb is minimised. J.G.BROWN & ASSOC. INC. swiss Patent Appl. 655,615 Platinised porous Ti is used on tubular electrodes, Multilayer Crucible made from austinitic stainless steel, in an elec- TOKURIKl HONTEN Japanese Patent 86123,472 trochemical cell which has a solid plastomer elec- A multilayer crucible for furnaces is made by draw- trolyte. forming, thin sheets of laminated Pt-Au.

ELECTRODEPOSITION AND Impurity Detector for Water V. E. KAZARINOV Russian Patent I,I 57,940 SURFACE COATINGS Inorganic impurities in industrial water are measured by passing rectangular pulses from a Pt electrode held Electroless Plating at a potential through the water in an electrochemical SHlPLEY CO. INC. European Appl. 187,962A cell. The impurity content is measured from the dif- High activity electroless deposition catalysts of ference between the quantity of electricity between a platinum group metals are produced by reducing first measured pulse and a second. solutions of the platinum metals with an organic suspending agent which forms a complex with the Conductimetric Detector Cell metal. V. E. STEPANENKO Russian Patent 1,203,425 Coated Metal Carbide Boring Tools A cell for chromatography has two sections with plastic spacers to form the measuring channel, and SMITH INTERNATIONAL INC. electrodes covered with Pt black; electrolyte passes Japanese APPl. 61182,959 through the channel and the current through it is Steel tools for boring underground have hard tips of measured. Gas or liquid can be analysed by this. improved durability of metal carbide buried in the steel. The tips are coated with Rh, Ir, Os, Ni, Ti, W, Nb, Mo or Cr and their alloys. JOINING Palladium Deposition Laminated Composite Solder SIEMENS A. G. German Offen. 3,443,420 TANAKA KIKINZOKU KOC'rO A quick precipitating electrolytic bath for producing Japanese Publ. Appl. 61182,996 bright crack-free coatings of Pd alloys does not con- A laminated composite solder material comprises Ti tain a brightening agent, S or C, which leads to a strip coated with Pt, Pd, Au or Ag and lapped with lower contact resistance. There is little increase in and bonded to a brazing strip. The coating protects resistance after corrosion or tempering. The coatings the Ti from oxidation; it is used for brazing ceramic have good ductility. to ceramic or ceramic to metal. Palladium Electrodeposition Bath Joining Ceramics OMI INT. CORP. German Offen. 3,601,698 NGK SPARK PLUG K.K. A Pd or Pd alloy electrodeposition bath contains a Pd Japanese Pu bl. Appl. 611127,676 source, oxalate ions and optionally a source for an Ceramics are joined together or to metal in metallised alloying element, especially Ni, Co or Ag. The Pd salt joining places using a composition of ceramic and Pt, is preferably Pd di- or tetraammino-oxalate or Pd Ir, Rh, Pd or their alloys as metal powder for burning dioxalate salt. in oxidative atmospheres; or Pt, Ir, Rh, Pd, Ru, Os, W,Mo, Fe, etc., or their alloys for joining in vacuum LABORATORY APPARATUS or in a reductive atmosphere. AND TECHNIQUE HETEROGENEOUS CATALYSIS Gas Flow Measurement NIPPON SOKEN K. K. U.S. Patent 4,587,843 Exhaust Catalyst A gas flow apparatus with no hot wires and with high PRO-CATALYSE European Appl. 181,802A resistance to vibration has a sensing circuit with a A Pt catalyst for I.C.E. exhaust purification has at mica plate on which thin Pt and Pt-Rh deposits are least 5owt.% of its filler and binder as Al,O,. After formed by vacuum deposition. 30 minutes use

Platinum Metals Rev., 1987, 31, (1) 49 Deuterated Methyl Methacrylate Selective Hydrogenation Catalyst MITSUBISHI RAYON K.K. European Appl. 186,106A PHILLIPS PETROLEUM CO. U.S. Patent 4,596,783 Deuterated methyl (meth)acrylate is produced by A catalyst for selective hydrogenation of acetylenic direct substitution of D for H present, in the presence compounds consists of Pd, Pb acetate and an of preferably a platinum group metal element or com- aromatic amine oxide on a CaCO, support. pound, using D,O or D,. The deuterated products are used for optical fibre manufacture and give a ma- I. C .E . Purification Catalyst jor improvement in the light transmitting ability. TOYOTA JIDOSHA K.K. Japanese PubLAppl. 61164,337 A catalyst with improved durability and activity can Carboxylic Acid Production remove 93%HC, 89%CO and 91%NO, from engine DU PONT DE NEMOURS co. European Appl. 188,209A exhaust. Catalysts Pt, Pd, Ir, Rh, Os, G,Ni, V or Cu Linear saturated carboxylic acids are produced with are loaded onto a monolithic base material having high selectivity from unsaturated monocarboxylic micropores, in water. The catalyst is added via a acid with CO and H,O in the presence of Rh. slurry. Hydrocarbon Production Heat Resistant Catalyst SHELL INT. RES. Mi. B.V. European Appl. 188,304A CATALER KOGYO K.K. Japanese Publ.App1. 61178,439 Hydrocarbons are produced by passing a CO/H, An I.C.E. catalyst for noxious gas removal from ex- mixture with a hydrocarbon liquid, especially a haust gas includes an inner Al ,0, layer impregnated residue from hydrocracking, over a Co-Ru catalyst with Ce, Y, Nd, etc., and an outer layer impregnated optionally containing Zr, Ti or Cr. with Ce, etc. The catalyst contains Pd-Rh and has improved heat resistance. Catalytic Dewaxing of Hydrocarbons MOBIL OIL CORP. European Appl. 198,898A Hydrocyanic Acid Preparation Hydrocarbon feeds are catalytically dewaxed in 2 MITSUBISHI CHEM. IND. K.K. stages, each with catalysts, which preferably contain Japanese Publ. Appl. 6 I /86,4 I 6 a Group VIII metal, especially Pt or a Group VI, VII HCN acid is prepared over a Pt-Rh alloy catalyst con- andlor VIII non-noble metal, but on different taining 20 wt.% Rh at 5oo-800°C by reacting zeolites. acetonitrile with 0, in the presence of NH,. Production of Higher Carbonyls Combustion Catalyst BRITISH PETROLEUM CO. MATSUSHITA ELEC. IND. K.K. World Patent Appl. 8614,oyA Japanese Publ. Appl. 61/86,944/5 High carbonyls are prepared by the reaction of I-8C A catalyst for detoxifying CO and HC in exhaust from cyclic alcohols using a supported Ru(oxide). An combustion furnaces and domestic ovens contains Ca alcohol with at least one more C than the reactant aluminate and delafossite type composite metal oxide alcohol is also produced. which is composed of Pt, Pd, Rh, Ag, Cu, La, Al, Cr, Ga, etc. Osmium-Cobalt Catalyst EASTMAN KODAK CO. U.S. Patent 4,587,364 Palladium Coke Oven Catalyst An 0s-Co catalyst with 0s:Co=1-1ooo:10-1 is used KAWASAKI STEEL K.K. Japanese Publ.Appl. 61189,294 for olefm hydroformylation to aldehydes. The A Pd catalyst containing almost no C1 is used to catalyst gives aldehyde products with low normal: hydrogenate unsaturated hydrocarbons and 0, in branched molecular ratios in high yields and at low coke oven gas. catalyst concentrations, without complexing agent. Catalytic Combustion Chamber Hydrogen Generation from Water TOYOTA JIDOSHA K.K. Japanese PubLAppl. 61/97,031 CARDINAL E. V. U.S.Patent 4,588,577 Part of a catalytic combustion chamber has a heat A finely divided catalyst of Pt, Pd, Ni, Co, Fe, Cu, resistant inorganic material containing one or more Mg, Mn or their alloys is mixed with H,O at transition metals which is coated with a layer of 60-150OC and a chelating agent to produce H,. platinum group metal catalyst. The assembly is used Fossil fuel may be added to the H, and the mixture in a diesel combustion engine. combusted. Diesel Exhaust Purification Dehydrogenation Catalyst NIPPON SHOKUBAI KAGAKU UOP INC. U.S. Patent 4,595,673 Japanese Publ. Appl. 61/120,640 Li and K are added to a Pt and Sn catalyst on an A catalyst for purifying engine exhaust comprises V Al,O, support which also contains a Group IVA ele- or V compounds and Pt, Pd, Rh or their compounds, ment to improve its performance in hydrocarbon con- possibly with other metals or their compounds. The version processes, especially dehydrogenation. catalyst converts 98%CO and 84% HC at 350°C.

Platinum Metals Rev., 1987, 31, (1) 50 Carbon Monoxide Oxidation Oxide Production KAWASAKI STEEL K.K. German Offen. 3,546,329 SAW0 EmmuCK.K. Japanese Publ. Appl. 611127,865 A catalyst for oxidising low concentrations of CO in Platinum group metal oxide film production involves waste gases, e.g. from furnaces, comprises a introducing the gaseous metal fluoride and 0, andlor honeycomb support with a relatively high Pt loading. 0 compounds into a reaction vessel, followed by The catalyst needs regenerating less often. plasma CVD. The film forms on the base plate and is used as a solar battery transparent electrode. HOMOGENEOUS CATALYSIS GLASS TECHNOLOGY Production of Palladium-Tin Colloidal Catalyst Optical Glass Forming Die I.B.M. INC. U.S.Patent 4,593,016 MATSUSHITA ELEC. IND. K.K. A Pd-Sn colloidal catalyst concentrate is produced Japanese Publ. Appl. 6 I 11 43,s 52 from stannous chloride dissolution in HC1 acid, and An optical glass element press-forming die consists of then mixing this with PdC1, solution. a composite of at least one of Pt, Ir, Os, Pd, Rh and Ru and zirconia. Hydroformylation Catalyst UNION CARBIDE COW. U.S.Patent 4,594,463 Aldehydes are prepared by reacting a primary alcohol ELECTRICAL AND ELECTRONIC with a CO/H, mixture at 1w-30ooC above at- ENGINEERING mospheric pressure in the presence of a catalyst of a soluble Rh compound, an I-containing compound Electrical Contacts and a chelating compound. The catalyst is stable and S.T.C. P.L.C. British Appl. 2,168,381A has high activity and selectivity for aldehydes. Electrical contacts for printed wiring boards comprise a non-corrodible alloy layer preferably of Pd-Ni, Dimerisation of Aliphatic Olefins formed on a base metal surface, with a Au outer layer. SHELL OIL CO. U.S.Patent 4,599,476 The Pd-Ni contains 70-85% Pd and is 2pm thick. A catalyst system of a Pd compound andlor a Ru compound in aprotic organic solvent is used to Conductive dimerise ahhatic 2-12C mono-olefins to dimers. ALPS ELECTRIC K.K. 3aPaneSe Pdl. Appl. 61116,977 Thick film circuit conductive paste for hybrid I.C. is Noble Metal Organo Sol composed of Au resinate, Pt or Au resinate+Pd AGENCY OF IND. SCI. TECH. resinate, and Bi resinate, and Ti or Co resinate mixed Japanese Publ. Appl. 611107,937 with a vehicle. Very fine particles of noble metal are uniformly dispersed in organ0 sol made using Ru, Pd or Pt. The Printed Circuit Board sol has a high catalytic activity for hydrogenation of HITACHI CHEMICAL K. K. unsaturated olefins or nitro compounds. Japanese Publ. Appl. 61166,307 A glass printed circuit board contains o.50-3.00°/~ Pd andlor Pt. The metal transfers the high-frequency FUEL CELLS signal, and the amount of Pd and Pt is reduced as compared with the conventional method. Electricity Generation from Hydrogen M. EMELOCK U.S. Patent 4,597,363 Thin Film Manufacture Electricity is generated by heating oxalic acid to form KUREHA CHEM. IND. K.K. HCOOH, which is then heated to form H, which is Japanese Pu bl. Appl. 61175,s I I /77,3 16 used as a fuel in a fuel cell or I.C.E. The fuel cell Pt, Mn and Sb are simultaneously, sputtered onto a uses H,SO, with C electrodes and a Pt catalyst. substrate, to form a thin film. The material is used for recording, reproducing and erasing information by laser. A temperature of iw0C or more improves CHEMICAL TECHNOLOGY crystallisation. The thin fdm is useful as an op- tomagnetic disc medium. Catchment Packs JOHNSON MATTHEY P.L.C. Electrically Conductive Polyester Fibre World Patent Appl. 8613,479A NIPPON ESTER K.K. Japanese Publ. Appl. 61189,370 An easily installable and removable catchment pack An electrically conductive polyester fibre is prepared to trap oxidised Pt from an NH, oxidation plant com- for plating, then dipped in aqueous solution contain- prises Pd and Au alloy getter wires protected by ing 0.15-15 ppm Pd and kept at 60-95OC. This ac- stainless steel gauze supports. tivated fibre is then plated with Cu, Co,Cr, Ag, etc.

Platinum Metals Rev., 1987, 31, (1) 51 Sliding Contact Device Monomeric Platinum Transferring TANAKA KIKINZOKU KOGYO Complex Japanese Publ. Appl. 61/109,277-84 R.L. STJERNHOLM U.S. Patent 4,590,001 A sliding contact consists of a brush composed of a A monomeric Pt complex is formed by reacting cis- Au-Pt-Ag-Cu alloy with other elements, and a com- diammine-dichloroplatinum(I1) and Fe-free human mutator or slip ring of Ag alloy with Cu, GI,etc., transferrin in the presence of cysteine. The complex added. There is little abrasion wear of the brush and selectively kills breast cancer cells without damaging slip ring and contact resistance is low and stable. Ox- normal cells. ides produced during sliding act as lubricants. New Bone Formation Metallised Glass Fibre UNIV. OF CALIFORNIA U.S. Patent 4,596,574 SIEMENS A.G. German Offen. 3,445,982 A biodegradable porous ceramic system for delivering A glass fibre for optical data transmission line has morphogenic protein to induce new bone formation solderable metal surface layers of Ti, Pd and Au. comprises a novel composition containing a cation of Pt, Na, Ag, K, Ca,etc., and an anion of phosphate, sulphate, carbonate, etc. TEMPERATURE MEASUREMENT Biosensor MATSUSHITA ELEC. IND. K.K. Fast Temperature Probe Japanese Publ. Appl. 61/91,558 G. BARKER & CO. British Appl. 2,167,603A A biosensor for analysis of substances in body fluids, A fast accurate temperature sensing probe has a Pt comprises a base insulator, a Pt electrode system, a resistance coil wound on a ceramic core in a heat con- porous support containing redox enzyme and an elec- ductive compound. The assembly is enclosed in a tron acceptor and filter layer. sealed can, and used in refrigerated display cabinets. Blood Gas Sensor Measuring Temperature Hysteresis SUMITOMO ELEC. IND. K.K. NIPPON TELEG. & TELEPH. Japanese Publ. Appl. 61/128,945 Japanese Publ. Appl. 61186,623 A sensor for simultaneously and accurately determin- The temperature hysteresis of a body is measured by ing 0, and CO, concentrations in the blood com- laminating a Pt fdm to part of one surface of it, prises a pH, a AgIAgC1 and a Pt or Au electrode. laminating a Au fdm to the Pd and then measuring the resistance before and after heating. This can be Platinum Anti-Cancer Agents used at 300-70o0C and for fast moving bodies. CESKOSLOVENSKA AKAD. VED. German Offen. 3,s39,951 New macromolecular Pt complexes are anti-tumour MEDICAL USES agents which gradually decompose in vivo releasing active low molecular weight complexes which give Anti-Cancer Agent long lasting levels of Pt in the blood, and low levels JOHNSON MATTHEY P.L.C. European Appl. 181,166A in the kidneys, liver, spleen and muscles. A new I, I-cyclobutane-di:carboxylate-di:amminePt inclusion compound with a-cyclo-dextrin is an anti- Dental Alloy cancer compound with greater solubility in H,O than K. KORBER Geman Offen. 3,447,413 the parent compound and much lower toxicity than A dental alloy is exclusively made from 0-15%Pt, Cisplatin. The side effects are reduced. I-30% Pd, o.1-15% Ir, the rest Au. No oxide layer is formed on fhgto ceramic; bonding agents may New Platinum Complexes be melted onto the metal. AMERlCAN CYANAMID CO. Eumpean Appl. 185,225A Pt complexes with aliphatic tri-carboxylic acid com- Organism Detoxification pounds are used for inducing regression and/or pallia- A.S. U.S.S.R. ELECTROCHEM. Russian Patent 1,194,425 tion of leukemia and related cancers, lung Organisms poisoned by urea, bilirubin, NH,, carcinomas and mammary tumours, etc. ethanol, CO, medicine overdoses, etc., can be detox- ified more rapidly than current procedures by injec- Transition Metal Complexes ting a NaOCl solution produced by electrolysing JOHNSON MAl-rHEY INC. European Appl. 186,363A NaCl using Pt-promoted Ti electrodes intravenously, A new charged dye transition metal complex with which yields 0 to oxidise the toxins. anti-tumour activity and radiosensitising activity contains as the metal preferably a platinum group metal, especially Pt(I1). The complex formed between The New Patents abstracts have been prepared from rhodamine-123 and Pt(I1) is specifically claimed. material published by Derwent Publications Limited.

Platinum Metals Rev., 1987, 31, (1) 52