UK ISSN 0032-1400

PLATINUM METALS REVIEW

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

VOL. 29 JANUARY 19% NO. 1

Contents

The Platinum Metals in Electronics

Improved Iridium Alloy Welds

Rhodium-Iron Thermometers

Hydrogen Diffusion Technology

Hydrogen Storage for Vehicles

Protecting Gas Turbine Components

An Effective Oxygen Evolution Catalyst

A Positive Move Towards Low Lead Petrol

Platinum Group Metals in Catalysis

A Compilation of Catalysts

Richard Knight and His Production of Malleable Platinum

Abstracts

New Patents

2

11

11

12

16

17

26

27

28

29

30

36

43

Communications should be addressed to The Editor, Platinum Metals Review

.lohnson Matthey Public Limited Company, Hatton Garden, London E C l N 8IX

The Platinum Metals in Electronics KEY AREA FOR GROWTH AND NEW TECHNOLOGY

By N. M. Davey and R. J. Seymour Johnson Matthey Group Research Centre

The sophistication possible with modern electronic and microelectronic dwices depends ultimately on the materials from which they are made. The platinum metals have assumed a vital role in electronics at every stage in its evolution. They are found in both thin and thick film dmicm which toRether constitute the backbone of electronic manu,facturing technology and overall this area represents one of their main applications in terms of metal consumption.

The platinum metals have been associated with the electrical and electronics industries for almost as long as the metals themselves have been refined and fabricated. For many years it was their unsurpassed metallurgical properties that accounted for their widespread application, particularly in electrical contacts and in various electrode systems. However the I 970s~ which saw the beginning of the microelectronics revolution, changed the need for the platinum metals but in no way made them redundant. Instead it opened up a range of new applica- tions. For example, the need for low-current contacts gradually diminished as electronic switching progressed, but on the other hand the requirement for materials for the new microelectronic devices produced a high- technology impetus for the platinum metals. It is their use in electronics which is reviewed in this paper and an overview of the total picture is given by taking specific examples of their application; some are shown in Figure I .

Current world demand data for the platinum metals in electronic applications is summarised in Figure 2. It shows that the commercially important metals are ruthenium and palladium, and that in both these cases microelectronics accounts for large percentages of individual demand. If broken down according to geogra- phical region, the data show a bias towards ruthenium in Japan and towards palladium in the USA. Although only 3 per cent of total demand for platinum itself is due to electronic

applications, this still corresponds to several tonnes of metal. In this case the U.S.A. accounts for the majority of sales. Rhodium and iridium are involved mainly in ancillary applications such as crystal growing.

Present and Future Applications The platinum metals are found in practically

every facet of electronic technology and examples of their application are given in Table I. Some of these have been commercially important for nearly twenty years while others are still at the research and development stage. The major electronic applications in terms of absolute metal consumption are undoubtedly thick film resistors, thick film conductors, mul- tilayer ceramic capacitors (MLCCs) and con- nectors. The first accounts for the majority of ruthenium usage and the remainder for the majority of palladium usage. Connector technology-where palladium is used as a cost- effective substitute for gold-has been reviewed recently in this journal ( I ) and is therefore not discussed in this paper. Thin film technology offers the greatest diversity of applications for the platinum metals. They are found in all aspects of the technology from sensing to signal processing and display, and as they give rise to the basic response of the particular devices they are often irreplaceable. They are also widely used during the manufacture of electronic materials. For example, the accurate temperature control of

Platinum Metals Rev., 1985,29, (l), 2-1 1 2

Fig. 1 This diverse collection of hardware illustrates a range of applications of the platinum metals in microelectronics. Among the devices shown are several multilayer ceramic capacitors incorporating palladium buried electrodes and palladium-silver end terrninatiom a resistor network with palladium-silver conductors and ruthenium-based resistors, hybrid structures containing palladium-silver and palladium-gold conductors and ruthenium-based resistors, as well as very large scale integrated circuits with platinum silicide Schottky contacts

Fig. 2 The use of the p l a t i n u m m e t a l s i n electronic applications is shown here as a percentage of the total world demand in the year 1983

Platinum Metals Rev., 1985,29, (1) 3

Table I

Present and Potential Applications of the Platinum Metals in Electronics ~~

THIN FILM TECHNOLOGY Integrated circuits

Data storage Sensors

Displays

THICK FILM TECHNOLOGY Conductors

Resistors Sensors

MULTILAYER CERAMIC CAPACITORS CONNECTORS MANUFACTURING

Platinum silicide ohmic and Schottky contacts, on-chip capacitors Rhodium/RhSi optical media, osmium-doped magnetic tapes Palladium-gated MOSFETs, platinumhirconia oxygen sensors, platinum temperature sensors IrO, electrochromic displays, automatic dipping rear-view mirrors

Palladium-silver, palladium-gold, platinum-gold, platinum- palladium-silver, platinum RuO,, Bi,Ru,O, Platinum resistance thermometer Palladium, palladium-silver Palladium alloys including palladium-nickel Thermocouples, platinum or iridium crucibles for crystal growing, glass melting equipment for manufacture of optical fibres

diffusion furnaces is accomplished using platinum metal thermocouples. High-purity single crystals of many specialised electronic materials including lithium niobate, gadolinium gallium garnet and yttrium aluminium garnet are grown from the melt and non- contaminating, heat resistant containment materials are required. Often the only satisfactory containers are crucibles made from the platinum metals-normally platinum, iridium or alloys thereof depending on the melting point of the particular oxide.

Thin Film Technology Thin film technology involves the fabrication

of circuits by vacuum deposition processes such as evaporation, chemical vapour deposition or sputtering. The process produces thin films of conductive, resistive, insulat ing or semiconducting materials, and allows active semiconductor devices as well as passive com- ponents to be fabricated at a circuit density orders-of-magnitude above any other technology. The main application areas of the platinum metals as thin films are in sensing, display and integrated circuit (IC) technology. This section discusses the advantages of platinum metal silicides for both ICs and

optical storage media and also describes various gas sensors and electrochromic displays.

There is great interest in the use of platinum silicide in silicon IC technology. As a metallisa- tion material-for providing both ohmic low resistance contacts to silicon and rectifying contacts (Schottky diodes)-platinum silicide has low resistance and high stability in subse- quent processing conditions (2). The material is particularly important in the fabrication of bipolar ICs where the metallisation is largely determined by the need to form Schottky diodes with stable and reproducible characteristics. The silicide layer is formed in situ by sputtering a thin platinum layer (-40 nm) onto the silicon surface followed by sintering at 65oOC. Silicides of the platinum metals may be exploited in other ways, for example, exploratory work at I.B.M. has demonstrated that they could be used as long-term archival optical storage media (3); a low power laser being used to induce local silicide formation in a platinum metal-silicon bilayer structure. From the systems studied to date, rhodium-silicon appears to be the most promising due to its relatively low writing power and excellent archival properties. I.B.M. are also working on the use of platinum silicide conductors in complementary metal oxide

Platinum Metals Reo., 1985,29, (1) 4

Pal lad ium t”G I, ,, > p-Si

6 I n

/ /’/

- Fig. 3 The principle of operation of palladium-gated metal oxide semiconductors IS

shown here. Hydrogen molecules from the surrounding atmosphere, which are dissociated and adsorbed at the palladium-gate region, produce variations in the drain current, The operational characteristics of the palladium-MOS device. in a normal and a hydrogen-containing atmosphere. are shown in the response curves

semiconductor (CMOS) structures (4) and thin film on-chip decoupling capacitors whose electrodes are based on platinum-refractory metal intermetallics (5 ) .

Hydrogen-sensitive gas sensors, compatible with integrated circuit technology, can be made using platinum or palladium as the gate metal of a metal oxide semiconductor (MOS) transistor. Hydrogen molecules dissociate on the catalytic metal surface and diffuse through the thin metal film to the metal-insulator interface. Here the hydrogen atoms form a dipolar layer which produces a voltage drop and hence varies the characteristics of the MOS structure, see Figure 3. Lundstrom gives a detailed account of these devices, and shows that there is an equilibrium between the numbers of adsorbed hydrogen atoms on the surface and those at the interface (6). The number at the surface depends on the hydrogen partial pressure in the atmosphere and the pre- sence of other gases. Hence the change in response can be calibrated to indicate the con- centration of hydrogen present in the atmosphere. Detection limits for hydrogen in air are of the order of 0.5 ppm and proposed applications include leak detectors and fire alarm systems.

Several technical problems remain to be solved, particularly those related to long-term stability. These arise due to changes at the metal surface and metal-insulator interface, especially as a result of Contamination and poisoning of the catalytic film. The structure of the film also has a marked effect on gas sensitivity and Lundstrom suggests there may be at least two types of palladium film produced by thermal evaporation. Sensors based on porous gate metals show much better selectivity to different gases with improved selectivity being observed with palladium and platinum themselves. Such developments should ensure an expanding use of the metals in integrated sensing devices.

The rapidly growing need for simple passive displays has created considerable interest in electrochromic displays (ECDs), principally due to their wide angle of view and low power con- sumption in low-switching-rate applications. Operationally an ECD is equivalent to a battery with a visible state of charge. When the display is fully charged, that is to say coloured, it passes no current either with the charging voltage con- nected or under open circuit. It therefore maintains its colour even when the power supply is switched off. ECDs are the only

Platinum Metals Rev., 1985,29, (1) 5

highly developed display technology with non- volatile capabilities.

Tungsten trioxide is probably the leading electrochromic material, but its commercial development has been (and still is) hampered by technical problems. Of these, a low speed of response and time-dependent degradation in aqueous electrolytes are the most serious. Thin film deposited iridium oxide is an alternative electrochromic material which largely over- comes these problems, possessing better speed of response and greater stability than tungsten trioxide. The iridium oxide film is transparent in the “off” state but this quickly changes to blue-black when stimulated by a brief electrical pulse. Response time is reported to be 0.05 seconds, twenty times faster than tungsten trioxide and about the same as liquid crystal displays. A simple seven-segment iridium oxide ECD which can be driven with a simple, low power, battery-operated circuit and which could open the way for their commercial development has been reported from Bell Laboratories (7).

Electrochromic iridium oxide is also being considered for automatically dipping vehicle rear view mirrors to reduce glare during night- time driving. When a sensor in the mirror registers flare of a certain intensity the electrochromic film is switched from colourless to blue-black, thereby reducing the reflectivity of the mirror. If this application were fully exploited, and iridium oxide is currently the material preferred by U.S.A. and Japanese manufacturers, it would open up a major new market for iridium.

Thick Film Technology Thick film technology utilises screen printing

techniques to deposit patterned resistive, con- ductive and insulating films to form miniature electronic components or circuits. The pastes (or inks) used consist of viscous dispersions of finely ground inorganic powders in organic liquids which exhibit pseudoplastic rheological properties under the various shear rates encountered during the screen printing process. In use the inks are deposited through a finely

woven stainless steel mesh, onto which a pattern has been delineated, by the passage of a squeegee across the surface of the screen. The supporting substrate onto which the print is deposited is usually a 96 per cent alumina ceramic chosen primarily for its inertness and ability to withstand the multiple firing stapes which follow paste deposition.

After deposition the print is allowed to settle for a few minutes before being dried at IOO to r50°C and then fired at between 600 and I ooo°C. Although extremely stable devices are produced as a consequence of the firing process the reaction chemistry is extremely complex and in many cases only poorly understood. Hence very careful control of the physical and chemical properties of the starting materials, as well as accurate process control, are required to achieve consistent results.

The use of thick film materials is not restricted to a single segment of the microelectronics industry but rather covers a whole spectrum of applications ranging from simple chip resistors costing a few pence to complex multilayer hybrids costing many hundreds of pounds. Table I1 shows the con- stituents encountered in many of the com- mercial thick film formulations available for this wide range of applications and it can be seen that the platinum metals are of crucial importance as the functional phase of both the conductor and resistor inks.

In nearly every application of thick film technology the resistor material used is based upon a conductive phase of ruthenium in oxide or compound form. Although not unique in their properties, ruthenium(1V) compounds offer an ideal compromise in terms of high temperature oxidation resistance over base metal alternatives such as molybdenum(1V) and titanium(1V) compounds, and significant cost savings over competing conductive phases based upon compounds of iridium, rhodium and osmium.

I t is especially significant that even in an industry such as electronics which is characterised by extremely high rates of technological change the use of ruthenium(1V)

Plathum Metals Rev., 1985, 29, (1) 6

Coml

Gold, platinum, platinum-gold Silver, palladium-silver Platinum-palladium-silver Copper, nickel, aluminium

FUNCTIONAL PHASE Bi,Ru,O, Glass RuO, Glassceramic

Glass/alurnina (filled dielectrics)

BINDER Fritted Reactively bonded Mixed bonded

VEHICLE Volatile phase Non-volatile phase

Table I I Isition of Commercial Thick Film Pastes

Conductor I Resistor I Dielectric

Borosilicate or aluminosilicate glasses CuO, CdO Oxide/glass

Terpineol Ethyl cellulose

compounds has persisted for over I 5 years with little sign of being superseded. Although many base metal materials have been investigated (and in some cases brought to market) none have approached ruthenium(1V) based resistor materials in terms of electrical properties such as temperature coefficient of resistance (TCR) or long term stability.

A cross section through a fired thick film resistor is shown schematically in Figure 4. It can be seen that the ruthenium oxide is con- centrated at the boundaries of the glass particles, forming a conductive chain inside an insulating glass matrix. The final electrical properties of the fired resistor are dependent not only upon the volume fraction of ruthenium dioxide present but also on the

particle size and morphology of the conducting and insulating phases and the chemical nature of the glass matrix itself. In the firing process a complex series of high temperature chemical reactions occur during which the organic liquid burns off and the film sinters to a dense thick film. It is necessary to control rigorously processing parameters such as the firing cycle and firing atmosphere by the use of sophisticated multizone tunnel furnaces. Even so, fired resistance values often vary by as much as k20 per cent in production, necessitating a final adjustment of the resistor value by cutting into the film with a laser or air abrasive trimmer.

For the more sophisticated applications of thick film such as high performance military

Fig. 4 The microstructures of fired thick film resistors and conductors are com- pared here. The ruthenium-based conductive chains built up inside an insulating glass matrix, which, typify resistor systems, are illustrated on the left. Conductors. shown on the right, are thinner than resistors and have a much higher loading of the metallic conducting phase

Platinum Metals Rew., 1985,29, (1) 7

End Termination

Dielectric Buried Electrodes

Fig. 5 Multilayer ceramic capacitors are composed of alternate layers of electrode and dielectric, with a total thickness of approx. 3mm. The electrodes are normally a palladium- rich palladium-silver alloy printed onto BaTiOs dielectric tape. The end ter- minations which provide electrical contact to the external circuit are of silver or a silver-rich palladium-silver alloy

hybrids considerable use is made of minor additives such as niobium pentoxide, which interact with the conductive phase during the firing cycle to counteract any oxygen deficiency that may occur. This has the effect of altering not only the resistivity of the fired film but also improving electrical properties such as the TCR.

In moving from one extreme of the thick film applications spectrum to the other the con- stituents of the resistor pastes vary only marginally. In the case of conductors, however, significant alterations of the functional phase occur depending upon the technical require- ments and price sensitivity of the application. Apart from their obvious function of providing low resistivity interconnections from point to point in a circuit, thick film conductors are also used for a variety of specialised purposes including terminations for screen printed resistors, pads for lead frame and device attach-

ments, and pads for wire bonding connections to silicon circuitry.

Like resistor formulations, fritted conductor pastes consist of a functional phase of conduct- ing particles in a glass matrix which is used to bond the metal particles to the surface of the alumina substrate on firing. As an aid to sinter- ing and adhesion, fluxing agents such as bismuth oxide are often included even though this is now thought to cause problems by reduc- ing conductor adhesion when soldered tracks are stored at elevated temperatures (8).

An alternative technique known as reactive bonding uses very low levels of metal oxides to form an alumina spinel at the metal-substrate interface at a higher than normal firing temperature (980°C). This bonding technique has the advantage of ensuring the highest possible electrical conductivity but occasionally suffers from problems, especially during low

Fig. 6 Palladium powders used in the manufacture of m u l t i l a y e r c e r a m i c c a p a c i t o r s m u s t b e produced to a very high level of purity and to a con- trolled morphology. This s c a n n i n g e l e c t r o n micrograph shows a suit- able powder consisting of spherical, unagglomerated particles of low surface area and with a particle size between 0.5 and 2 microns

Platinum Metals Rev., 1985,29, (1) 8

temperature refire when some of the oxides can migrate to the conductor surface and inhibit wire bonding (9). A third bonding technique, known as mixed bonding, uses a combination of the two techniques outlined above to provide improved conductivities and fewer aged adhe- sion or refire problems and appears to be gaining favour with both paste manufacturers and users.

The structures of fired thick film conductors and resistors are illustrated in Figure 4, which shows that the film thickness of the conductor is much less than that of the resistor and also the use of a very much higher loading of the metallic conducting phase. Although under or over firing will affect film conductivity and adhesion, and poor furnace atmospheres will result in solderability or wire bonding problems, the performance of platinum metal conductor systems is considerably less sensitive to process variations than the resistor materials. Base metal conductor systems such as copper or nickel which, for the most part, rely on neutral (nitrogen) or reducing (nitrogedhydrogen) atmospheres are seriously degraded if the furnace atmosphere is contaminated with oxygen.

A binary composition of a platinum metal and silver, in particular palladium-silver, con- stitutes the basis of the most widely used thick film conductors. These conductors find wide application in the production of chip resistors, resistor networks and hybrids for industrial, automotive, telecommunications and even high- technology consumer applications such as video cassette recorders. The presence of palladium serves to inhibit solder leaching silver out of the conductor and it also reduces silver migration in hot or humid conditions, especially when high electric fields are present between closely adjacent conductor tracks held at different electric potentials.

For less stringent applications where cost is of great importance the ratio of silver to palladium can be as high as I 2: I. For applica- tions where higher reliability is required in adverse environments the ratio of silver to palladium is reduced to 1.85:1. Since any

further decrease in the silver : palladium ratio leads to solderability problems and a reduction in electrical conductivity below acceptable levels, gold has for many years been the functional phase chosen for circuits demanding the highest performance and reliability. With the advent of ever more complex silicon circuitry associated with the move from large scale integration (LSI) to very large scale integration (VLSI) and the consequent difficulties associated with pretesting and burning in of the chip, the concept of a chip carrier surface mounted onto the substrate has arisen. Since gold readily dissolves in the tin- lead solders needed to attach the chip carriers to the top conductors of the circuit the use of special lead-indium solders andor platinum- gold top conductors is becoming of increasing importance to the industry.

Multilayer Ceramic Capacitors The capacitance of a simple discrete

capacitor consisting of two metal electrodes separated by a dielectric is proportional to the electrode area. For a given dielectric material it is necessary to increase the electrode area in order to increase the overall capacitance obtain- able. This is undesirable in microelectronic applications where the large areas required are incompatible with the size reductions associated with LSI and VLSI silicon technology. Multi- layer ceramic capacitors (MLCCs) solve this problem by stacking alternate layers of electrode and dielectric, which are “term- inated” to provide electrical connection to the electrodes. For a given plate area, the capacitance of a MLCC is proportional to the number of laminated dielectric layers. This monolithic multilayer construction, shown in Figure 5 , provides a large electrode area in a small volume package.

The most common dielectric used in MLCC manufacture is barium titanate doped with a variety of oxides in order to alter its sintering characteristics and modify the electrical properties of the finished capacitor. The barium titanate is comminuted to a fine powder (roughly 3 pm diameter) and cast into a flexible

Platinum Metals Rev., 1985,29, (1) 9

tape with the aid of a plasticiser and acrylic binder. The electrodes are then screen printed onto the tape using a paste containing fine metal particles dispersed in an organic vehicle. After drying the layers of tape are laminated together, pressed, cut and fired in air at temperatures in excess of I 3 0 0 T .

Unlike thick film conductor pastes the MLCC electrode materials contain only the metal and an organic vehicle system. The metals utilised for these high sintering temperature dielectric materials are restricted to palladium or a palladium rich palladium- silver alloy. Figure 6 shows a scanning electron micrograph of one such palladium powder used in this application. The powders, manufactured using sophisticated chemical routes, are produced to a very high level of purity and con- trolled morphology in order that they can be screen printed to the minimum possible thickness and will shrink on firing to form a coherent electrode structure at roughly the same rate as the dielectric which surrounds them. If any appreciable difference in the rate of shrinkage occurs then the MLCC will delaminate and must be discarded.

Considerable effort has been expended in a search for high permittivity dielectric materials which will sinter at lower temperatures and so allow the use of low melting point alloys con- taining higher levels of silver. A number of glassseramic materials have been discovered which fulfil this role and some are now being used commercially. While these new materials will undoubtedly supplant the use of high temperature systems in some applications, the performance advantages associated with the use of barium titanate/palladium will ensure their continued use.

The most common end termination materials for MLCCs are silver or silver rich palladium- silver alloys applied using a simple dipping operation and subsequently dried and fired using a tunnel furnace. The pastes used are very similar to fritted thick film palladium- silver inks except that different frit formula- tions are used to match to the ceramic body. Palladium-silver end terminations are generally

preferred. since, in common with conventional thick film materials, they can be fired in air to yield highly conductive layers which can be readily soldered without excessive silver removal by solder leaching.

The trend in MLCC manufacture has been to reduce costs by increasing automation, by thrifting palladium with silver wherever possible and by substitution of base metals. To date the only significant use of base metals has been for end terminations and this trend is likely to continue. While base metal buried electrodes for MLCCs are in existence none has had any appreciable impact on the market, and given the problems associated with their use this situation is unlikely to change in the immediate future.

Summary and Outlook The platinum metals-long associated with

the electrical industry-are now also well established in the microelectronics industry. Because of their unique physical and chemical properties, they are used to fulfil a wide range of the material requirements that are essential to the successful and continued development of microelectronic technology. This is of course supplemented by their ancillary applications involved in the manufacture of the basic microelectronic materials themselves.

Thick film technology accounts for the largest part of platinum metal consumption in the industry, particularly ruthenium for resistors and palladium for MLCCs. Although considerable effort has been expended to develop alternative materials, particularly base metal systems, the continued use of the platinum metals is assured in the near-to- medium-term and also in the long-term for high performance circuits. This is because technical problems associated with these competing systems still limit their use for many applica- tions. Their use is particularly cost effective on the thin film side and a continued expansion of applications is expected, in sensing, display and IC technology itself. Microelectronics indeed represents a key area for growth and new technology for the platinum metals.

Plutiriuni Metals Rev., 1985, 29, (1) 10

Refer I M. Antler, Platinum Metals Rim., 1982, 26, (3),

106 2 “Kirk-Othmer Encyclopedia of Chemical

Technology”, John Wiley, a Wiley-Interscience Publ., New York, Third Edn., Vol. 13, 1981, in section Integrated Circuits, pp. 62 1-48

3 K. Y. Ahn, T. H. Di Stefano, N. J. Mazzeo, S. R. Herd and K. N. Tu, 3. Appl. Phys., 1982, 53, (s),

4 International Business Machines Corporation, 3777; 1982, 53, (6), 4372

US. Parent 4,399,605; 1983

‘ences

5 International Business Machines Corporation, US. Patents 4,423,087; 1983 and 4,471,405; 1984

6 I. Lundstrom, Sens. Actuators, 1981, I, (4), 403;

7 J. L. Shay, L. M. Schiavone, R. W. Epworth and D. W. Taylor,J. Appl. Phys., 1982,53, (9), 6004

8 B. E. Taylor, J. J. Felton and J. R. Larry, Proc. 30th Electronic Components Conf., 1980, 149

9 M. V. Coleman and G. E. Gurnett, Proc. European Hybrid Microelectronic Conference, Bad Homburg, 1977, XVIII, 1-8

198132, (2), 105

Improved Iridium Alloy Welds FOUR-POLE OSCILLATION REDUCES HOT-SHORT CRACKING

The use of platinum group alloys to encapsulate radioactive heat sources in the ther- moelectric generators that are used to provide electric power for instruments on unmanned spacecraft has been reported in this journal pre- viously (1,2). Heat released by the decay of an isotopic fuel, generally plutonium dioxide ( 2 3 8 P ~ 0 2 ) , is converted into electrical power by its action on a collection of thermocouple ele- ments. The plutonium dioxide must be safely contained under both normal operating condi- tions and those that could be encountered in the unlikely event of an aborted launch or later re- entry into the Earth’s atmosphere.

Currently the radioactive pellets are encapsulated by welding together two o.6mm thick iridium alloy cups. In addition to iridium, the alloy contains 0.3wt. per cent tungsten, 60+30ppm thor ium and 5 0 ~ 3 o p p m aluminium, while welding is performed in a protective atmosphere of helium-25 per cent argon. Two-pole magnetic arc oscillation has been used to give the required grain structure. However, it is well known that iridium alloys suffer from hot-short cracking when the thorium concentration approaches rooppm, and in practice approximately one equatorial weld in five exhibits underbead cracking in the arc taper area. Ultrasonic inspection results in a seven per cent rejection rate, although in some batches of alloy this can rise to 26 per cent, an unacceptable level.

Now J. D. Scarbrough of E. I. du Pont’s Savannah River Plant and C. E. Burgan of the Monsanto Research Corporation have reported that the frequency and severity of the weld cracking problem can be significantly reduced by the use of a four-pole magnetic arc oscillator (Welding J., 1984, 63, (6), 54-56). In their paper typical microstructures of the welds

produced by the two methods are shown. Grain growth patterns are very similar but a 17 per cent reduction in grain size results from the use of the four-pole oscillator. Using given parameters, the overall production reject rate fell from 7 to 2 per cent, while batches of alloy that had previously suffered a 26 per cent rejec- tion with the two-pole oscillator also had this rate reduced to 2 per cent when the four-pole oscillator was employed. Two primary causes are postulated for this improvement in the production reject rates.

The two authors suggest that the use of four- pole oscillation may also be beneficial when welding other alloys which are prone to hot- short cracking.

References I Platinum Metals Rev., I 979, 23, (I), I 6 2 H. Inouye, Platinum Metals Rev., I 979,23, (3), I 00

Rhodium-Iron Thermometers Over the past ten years the platinum-

sheathed rhodium-iron resistance thermometer (RIRT) has proved its reliability at temperatures between 0.5 and 20K. Now smaller, more rugged versions of the RIRT have become available. In one, designed for use up to 7ooOC as well as for cryogenic conditions, the resistance coil is mounted in an alumina and glass body. A recent report on the thermometric properties and stability of these ceramic RIRTs by L. M. Besley of CSIRO, Division of Physics, Sydney u. Phy.E: Sci. Instrum., 1984, 17, (9), 778-78 I) concludes that despite small changes in resistance on handling the remarkable stability of these thermometers on thermal cycling together with their low self heating and reasonable sensitivity will make them useful for many low temperature applications.

Platinum Metals Rev., 1985,29, (1) 1 1

Hydrogen Diffusion Technology COMMERCIAL APPLICATIONS OF PALLADIUM MEMBRANES

By J. E. Philpott Johnson Matthey Equipment Limited. Wembley

The technology for extracting pure hydrogen .from hydrogen-rich gas mixtures by dijjusion is now well established. The success 0.f the process and the demand for the product has led to the formalion of

Johnson Matthey Equipment, a company devoted to the supply 0.f

equipment based upon the properties 0.f the platinum group metals, principally hydrogen puri.fication and generation equipment.

The original work on the diffusion of hydrogen through palladium was carried out by Thomas Graham in I 866, when he was Master of the Royal Mint, in London (I). However, for many years the commercial use of palladium as a hydrogen diffusion membrane was seriously inhibited by the fact that at relatively low temperatures the adsorption of hydrogen into palladium induces an (r - p phase transforma- tion, which consequently changes the atom spacing in the metal lattice. This dimensional change is large enough to distort the palladium membrane to such an extent that after only 30 hydrogenation-dehydrogenation cycles very little of the original structure remains. As a con- sequence of this, purification of hydrogen using a palladium membrane was only possible if the mzmbrane was kept above a critical temperature of about 3ooOC throughout its working life, a requirement that did not favour its commercial use.

It was nearly a century after Graham’s discovery that Dr. J. B. Hunter, while working on the diffusion of hydrogen through palladium alloys, found that the maximum rate of hydrogen diffusion through silver-palladium alloys occurred at a composition close to the maximum solubility of silver in palladium (2). Unexpectedly the alloy was found to be stable when thermally cycled through the t r - p phase transition temperature in the presence of hydrogen. Furthermore the addition of silver made metal fabrication easier as well as reduc- ing the intrinsic value of the alloy. This was a

major step forward and led to the development of a range of commercial diffusion cells.

Early hydrogen diffusion equipment was of a simple design. Fabricators of the platinum group metals rarely make a complete product. Generally they are involved in supplying com- ponents which are often intricate and complex in design, but which comprise only a part of the complete product. Thus when fabrication of hydrogen diffusion equipment commenced only the diffusion cells were made; market indica- tions suggesting that potential purchasers would want to construct diffusion plants to their own design, or to incorporate diffusion cells into existing plant. The diffusion cells were of robust construction and had an output of I to 500 standard cubic feet per hour (approx. 0.03 m’/h to 14m3/h). They were designed to operate at temperatures of 500OC and pressures of 500 psi (3); years later some are still in everyday use. Three early models are shown in Figure I . The actual diffusion membrane consists of a number of silver-palladium tubes, which are contained within the cylindrical cell.

Although the supply of diffusion cell com- ponents met the needs of a certain market it soon became apparent that this approach did not satisfy all demands and that there was a requirement for complete purification units. In response to this a series of small laboratory diffusion uni ts were designed and manufactured. Since modified in design, such units still provide the purest form of hydrogen in a great many laboratories.

PZuriizrrni Metals Rev., 1985,29, (l) , 12-16 12

Fig. 1 From left to right, early model A71, A31 and A l l diffusion cells, the hydrogen outputs in standard cubic feet per hour were the same as their reference numbers. The cells were strongly made, and wi~hstood pressures higher than were experienced in even abnormal usage. Pure hydrogen was provided from a single outlet at the far end of each cell. Much the same arrangement of silver-palladium tube membranes is in use in modern hydrogen diffusion equipment

To provide a considerably higher rate of hydrogen output (286 cubic metres of hydrogen per hour) a very few much larger diffusion units were built up from standard difhsion cells but the safeguards against contaminating impurities were less than adequate and these early units did not have satisfactory lifetimes.

The expansion of the electronics industry, which uses hydrogen during the manufacture of silicon chips, resulted in a rapid increase in the demand for hydrogen of a suitable quality. The hydrogen is used to carry doping elements onto the surface of the silicon wafer, and the gas must be of the highest purity. In this high technology industry a reliable supply of high purity gas is regarded as an essential everyday service, and new designs of palladium alloy diffusion units were required to satisfy this demand for hydrogen of near absolute purity. In practice it was found that a moisture meter installed in the gas stream served to monitor the purity of the hydrogen, and once in service dew points below -7oOC are steadily recorded in diffusion units. Two typical purification units

which use silver-palladium diffusion mem- branes are shown in Figure 2.

Many electronics factories are located long distances from traditional sources of com- mercial cylinder hydrogen, making them vul- nerable to delivery delays caused by unusual weather or tr&c conditions. A need for hydrogen self-sufficiency was recognised and led to the development of simple generators for on-site hydrogen production (4). These are fuelled by a methanoywater mixture which is cracked over a catalyst, the resulting hydrogen being extracted by diffusion through a palladium alloy membrane ( 5 ) . The methanoywater mixture and its constituents are cheap and internationally available.

The use of this fuel effectively allows hydrogen to be stored as a liquid, moreover as a liquid which can be contained in thin walled vessels at atmospheric pressure, so providing a safer method of hydrogen storage than when the gas is kept under compression in high pres- sure cylinders.

The first methanoywater hydrogen generator

Platinum Metals Rev., 1985,29, (1) 13

Platinum Metals Rev., 1985,29, (1)

Fig. 2 T w o H M 2 di f fus ion uni ts are shown here prior to despatch. In this range the uni ts are suppl ied as two separate cabinets, one housing the gas pu r i f y ing system a n d the other the electrical controls which therefore can be sited wel l away from the hydrogen gas system. These uni ts provide a s imple and economic means of upgrad- ing commercial ly available hydrogen from a variety of gas sources to the u l t ra high pur i t y requi red during the manufacture of semi- conductor devices

Fig. 3 Th is containerised methanol /water hydrogen generator has been made for the B r i t i sh Antarct ic Survey who w i l l use the hydrogen to f i l l the bal- loons that l i f t sensitive meteorological instruments i n to the high atmosphere. The caboose is sledge mounted so that the whole self-contained unit can hi. moved regular ly. I t is hoped that this w i l l prevent loss of the equipment b y bu r ia l in heavy snowfalls and subsequent incorpora- t ion into the ice cap

14

Fig. 4 T h e G 3 0 ( M a r k I I ) hydrogen generator instal lat ion at the E. 1. Company Ltd., Shannon, Eire. T h e three G I 0 modules each show the i r vertical heat exchangers mounted behind a meta l grid and smal l gas con t ro l panel. T h e uni ts are housed in a building w i t h louvered walls, visible here at the fa r end. The hydrogen is used in the manufacture of electronic products and for the product ion of television tubes. Th is was the most economir and rel iable solu- t ion to the hydrogen re- quirements of E.I.

built by Johnson Matthey was successfully used under many years’ accumulated snowfalls, and in the Antarctic by the British Antarctic a third replacement unit has been supplied. The Survey, who in 1975 installed it in a simple new G2 generator, capable of producing up to shelter built out of its own packing case. This 2 cubic metres of hydrogen per hour at atmos- shelter is now buried deep in the Antarctic ice, pheric pressure, is installed in one section of a

Fig. 5 A G 4 0 ( M a r k I) generator instal led at the Central Electr ic i ty Generating Board power station, Is le of Grain, Kent. T h e Du tch B a r n shelter provides adequate protect ion for [lie f ou r G 1 0 modules. In the foreground are the methanol tanks which hold six months’ supply of fuel. The yellow vert ical pressure vessels are for stor ing hydrogen which is used for rooling t h r a l t r r - nators. Th i s appl icat ion is a m a j o r outlet f o r methanol- fuel led hydrogcsn ycnrrntors; the- wlf- sufficiency they p rov id r to remote power stations has already proved to hr of c.qx.rinl va l~~c .

Platinum Metals Rev., 1985,29, (1) 1s

caboose (Figure 3) where the electrical controls are also housed. However, the low pressure hydrogen store is located in an adjacent section. The whole caboose is sledge mounted and it is hoped that by frequently moving this around burial in the snow will be prevented.

Johnson Matthey Equipment The steady growth in business based upon

the palladium diffusion process led first to the formation of a small business group and more recently to the founding of a commercial company-Johnson Matthey Equipment Limited-whose main business is in on-site hydrogen generators. However, activities include the supply of small laboratory purifica- tion equipment with hydrogen outputs ranging from 28 litres per hour through to modules with outputs up to 56 cubic metres per hour. These may be linked together to form a much larger piece of purification equipment, but generally the modules are installed separately, just prior to the work station in order to reduce the risk of the pure gas becoming contaminated.

The development of on-site hydrogen generators has progressed from the first small units used to fill civil meteorological balloons to military units capable of producing 4.2 cubic metres per hour in almost any climatic con- dition. The market for civil on-site generators has grown steadily and many GIO units (10m3/h) and a smaller number of the newer G25 units (25m3/h) operate in industries as diverse as electronic device manufacture, alternator cooling in power stations, tungsten heat treatment, and in many others where merchant hydrogen has proved too expensive or where the supply is uncertain. Additionally a G5o module (50m3/h) is to be introduced in the near future.

The commercial success of these generators depends largely upon their low operating costs, which enables hydrogen to be produced at a cost significantly below that of gas delivered in cylinders; this accounts for the short payback times for these generators. Compact size and near automatic operation are additional benefits while the purity of the hydrogen produced, at

99.9999 per cent, is a further bonus. Typical installations are shown in Figures 4 and 5.

Extending the Product Range Following on the successful use of silver-

palladium alloy for hydrogen production and purification, the manufacture of a range of equipment using a palladium on alumina catalyst has been started. This equipment removes oxygen from hydrogen gas streams that contain oxygen, or hydrogen from oxygen gas streams. The “Oxygone” range of equip- ment, as these units are called, represents a further broadening in the range of products offered by this new company, which is dedicated to the promotion of equipment utilis- ing the remarkable physical and chemical properties of the platinum group metals.

References T. Graham, Phil. Trans., 1866, 156, 399; see D. McDonald and L. B. Hunt, “A History of Platinum and its Allied Metals”, Johnson Matthey, London, 1982, p.266 I. B. Hunter, Platinum Metals Rev., I 960~4 , (4), I 30 H. Connor, Platinum Metals Rev., 1 9 6 2 ~ 6 , (4), 130 M. J. Cole, Platinum Metals Rev., 1981, 25, (I) , 1 2

J.E.Philpott, PlarinumMetalsRev., 1976,20,(4), I 10

Hydrogen Storage for Vehicles Hydrogen may be used as the fuel in suitable

internal combustion engines and the possibility of using it to power motor vehicles is being con- sidered. However, a major problem is that of storing the hydrogen in a compact, convenient form. A solution may be to use hydrogen to hydrogenate benzene to cyclohexane, which can be distributed in much the same way as petroleum products. The motorist would fill the tank of his vehicle with hydrogenated hydride, from which hydrogen would be released by an onboard catalytic dehydrogenation reactor.

Success could depend upon the dehydrogena- tion step, an endothermic reaction which is reversible. A report of a simulation study for a palladium on alumina catalyst indicates that a dehydrogenation reactor for cyclohexane is feasible, at least in theory (A. Touzani, D. Klvana and G. BClanger, Inr. J . Hydrogen Energv, 1984, 9, (I I), 929-936). Heat normally dissipated by the cooling system could be transferred to the reactor by a system of heat pipes, and would compensate for the endother- micity of the dehydrogenation reaction.

Platinum Metals Rev., 1985,29, (1) 16

Protecting Gas Turbine Components T H E RELATIVE DUHABILITY OF A CONVENTIONAL AND A PLATINUM-MODIFIED ALUMINIDE COATING

By Janis L. Cocking, Graham R. Johnston and Peter G. Richards Materials Research Laboratories, Department of Defence, Maribyrnong, Victoria, Australia

One of the major maintenance problems for gas turbine engine operators i s the degradation of high pressure turbine blades and vanes. The Australian Department of Defence was experiencing unacceptably high rejection rates of these components in one of its high performance engines as a result of severe hot corrosion attack. Accordingly a programme was initiated to find a more durable coating than the con- ventional aluminide coating supplied for the first-stage blades by the engine manufacturer. The coating chosen for the trial was a platinum- modified aluminide coating. Metallographic examination of both coating systems a.fter 750 hours of service i n an operational aircraft clearly established the superiority of the platinum-modified coating. This coating has now been adopted by the Australian Defence Force as the specified coating,for first-stage blades in this engine.

A major problem facing operators of gas turbine engines is the high temperature degradation of the high pressure turbine (HPT) blades and stator vanes. In most engines these components determine the time-between- overhaul periods which, in turn, are a major factor in determining the cost of ownership of the engines. The Australian Defence Force has been experiencing unacceptably high rejection rates of HPT blades and vanes from one of its high performance gas-turbine engines. The major cause of this rejection was a phenomenon known as hot corrosion, which is defined as the combined attack of high temperature combus- tion exhaust gases (which are oxidising and commonly sulphur bearing) and condensed phases (which are commonly salts ingested with the intake air) on the surface of a component.

A component is rejected as unfit for further service when corrosion products have breached the protective surface coating and penetrated the underlying substrate alloy, degrading its mechanical behaviour. Hot corrosion is con- trolled, therefore, for as long as the protective coating is not breached.

The specified coating on the first-stage HPT blades was a conventional diffusion aluminide that was applied by a pack-cementation diffu- sion process. At full overhaul, after approximately 1000 hours of operation, at least 95 per cent of all first-stage blades were rejected because of unacceptable hot corrosion attack.

Accordingly, it was decided to try to identify an alternative coating with superior protective properties. A commercially available platinum- modified aluminide coating was chosen from a number of possibly suitable coatings to undergo engine trials to compare its performance with that of the original coating under identical con- ditions. Platinum-modified aluminide coatings were first developed in Germany in the early 1970s ( I ) . Since then considerable efforts have been made to develop and test commercially viable platinum-modified aluminide coatings (2-5), although much of the work has not been reported in the open literature. Wing and McGill reviewed the development of such protective coatings and described in detail the particular platinum-modified aluminide coat- ings, JML-1 and JML-2, that resulted from a

9 Platinum Merals Rev., 1985,29, (l), 17-26 17

collaborative exercise involving Rolls-Royce and Johnson Matthey (4).

The platinum-modified diffusion aluminide coating used in this trial was produced by electroplating a layer of platinum onto the aerofoil surfaces of the blades prior to a pack- diffusion aluminising process. The “test” wheel, with approximately half of the first-stage turbine blades coated with the original coating and the other half with the platinum-modified coating was fitted to an engine, which was then installed in an operating military aircraft for the trial. To the best of our knowledge, this was the first use of platinum-modified aluminides in a military gas turbine, although such coatings have been used by some commercial airline companies.

Both types of coated blades were removed from the wheel after approximately 520 hours and 750 hours of engine operation for metallographic examination and comparison. The results obtained from the 520 hours inspec tion have been reported elsewhere (6, 7); those

Fig. I First-stage turbine blades from the test engine after 750 hours, Blade A was coated with a diffusion aluminide and shows marked corrosive attack. w h i l e Blade H was coated with a platinum-modified diffusion aluminide and exhibits a significant im- provement in the protection of thc suhstratv a l loy

of the 750 hours examination are presented in this paper. A more complete description of the results obtained at this time is the subject of an Australian Department of Defence report (8).

Metallographic Examination of Blades

A marked difference in the appearance of each type of coating after both 520 hours and 750 hours of engine operation was clearly visible. An example of the appearance of the blades after 750 hours of engine operation is shown in Figure I. The blades coated with the original diffusion aluminide exhibited marked corrosive attack of the leading edge and concave side of the aerofoil. Corrosion pits were evident along the centre of the concave side of the con- ventional diffusion aluminide coated blades, but not on the platinum-modified coated blades. The original diffusion aluminide coated blades showed extensive corrosion of the outer shrouds and some corrosion of the root platforms. The platinum-modified aluminide

Plulinirm Metals Rev., 1985,29, (1) 18

Leading Ed90

Trailing Edge

Fig. 2 Sketch profile of a cross-section through a turbine blade, the areas where greatest hot corrosion attack w a s found w e r e the leading edge and in the concave mid-chord region

blades appeared to have experienced much less corrosion in these areas.

Blades with each type of coating were cut into ten cross-sections of approximately equal

thickness between, and parallel to, the root platforms and the shrouds. After nickel plating, to retain the surface oxide, the sections were then mounted and polished for metallographic examination.

As found previously (6, 7), extensive corro- sion of the leading edges and concave mid- chord regions, delineated in Figure 2, of the original diffusion aluminide coated blades occurred. In these areas the products of hot corrosion were evident at considerable depths into the alloy beneath the coating, see Figure 3. The coating had been breached on each blade examined.

The blades coated with the platinum- modified aluminide similarly exhibited the most severe attack at the leading edge and concave

Fig. 3 a This cross-section taken through the diffusion aluminide coating after 750 hours of operation shows the leading edge of the blade where no intact coating remains

Fig. 3 b This cross-section from the mid-chord region shows, between the arrows, an area where the diffusion aluminide coating is intact after 750 hours of operation

Fig. 4 Cross-section through a platinum- Fig. 5 The platinum-modified aluminide modified aluminide coating in the concave coating in the concave mid-chord region has mid-chord region after 750 hours operation, corroded, after 750 hours forming a series of areas marked A-F are referred to in the tex t wide, shallow pits

Platinum Metals Rev., 1985,29, (1) 19

w

W

N 0

CO

NC

EN

TRA

TIO

N (

wt.

70)

d 8

v

W

a

"8

0 0

0

d

h)

0

P

0

0

0

0

0

0

I

\

Fig. 6 Line scans for nickel, platinum and aluminium along the line a-a in the concave mid-chord region of a blade, the presence of platinum-rich bands within the oxide layer are clearly shown

Plutinum Metals Rev., 1985,29, (1)

Fig. 7 This region of the leading edge of a blade coated with the platinum-modified aluminide shows an area where the coating is in good condition after 750 hours service. The oxide scale shows spallation and/or erosion

mid-chord regions. However, the coating remained intact over the length of the blade, with maximum attack occurring at approximately two-thirds of the aerofoil length up from the root platform. Even in the section where maximum attack of the concave face occurred, more than 50 per cent of the coating remained intact, as can be seen in Figure 4. The attack in this concave mid-chord region of the blades commonly formed a series of wide, shallow pits, as shown in Figure 5 . Electron microprobe analyses of the areas marked in Figure 4 showed the presence of:

(A) a continuous outer oxide rich in aluminium and oxygen

(B) a metallic band, rich in nickel and platinum, which appeared to be near the position of the original surface of the coating

(C) an oxide, which appeared to be porous, in the pit beneath the metallic band, and which was rich in aluminium and contained small amounts of nickel and platinum

(D) a metallic coating zone, which was depleted in aluminium and had the approximate composition Ni,Al

(El a coating zone, which resembled the original, intact, coating

(F) a typical interdiffusion zone

The various zones of corrosion in the pits were further defined by simultaneous line scans

Fig. 8 Near the leading edge of a blade coated with the platinum-modified aluminide extensive internal oxide is present and the diffusion zone of the coating (arrowed) has partially disappeared

for platinum, nickel and aluminium, as shown in Figure 6. The line scans clearly define the presence of bands of platinum-rich metal within the oxide. In some areas the concentration of platinum was close to 70 weight per cent.

Again, in marked contrast to the original diffusion aluminide coating, the remaining thickness of the platinum-modified aluminide coating at the leading edge of the blades was greater than 50 per cent of the original thickness of the coating. The oxidation front, as defined by the oxiddmetal interface, was uniform, in contrast to the pits found on the concave side of the blades. A microstructure typical of a position where the platinum- modified coating was in good condition, at the tip of the leading edge of a blade, is shown in Figure 7. A sharp variation in the thickness of the protective oxide scale, indicative of local spallation and/or erosion, is evident in this micrograph. Some areas of the coating in the vicinity of the leading edge contained extensive internal oxides, such as those shown in Figure 8. Area scans of a similar region, shown in Figure 9, clearly indicate the presence of alumina, both on the surface of the coating and within the coating, as well as the characteristic platinum-enrichment of the outer region of the coating. Quantitative analyses of the various phases present in the coating, marked in Figure I 0, are given in the Table. These analyses show that the bulk of the coating surrounding these

Platinum Metals Rev., 1985,29, (1) 21

Fig. 9 Optical micrograph and electron probe microanalysis back-scattered electron ( BSE:) and element area scans for aluminium, oxygen, platinum and nickel of a region near the leading edge of a blade coated with the platinum-modified aluminide. The back-scattered electron image is a mirror image of the optical micrograph

internal oxides has been depleted of aluminium, for the characteristic enrichment of platinum in producing a phase similar to area D of Figure 4. the outer zone of the coating, there are no Interaction between the particles of oxides and distinctive zones within the coating. The con- the coating has resulted in the partial, or com- centration of aluminium within the metallic plete, removal of the p (NiA1) phase from the part of the coating is uniformly low. coating. Simultaneous line scans for platinum, On the convex side of the blades coated with nickel and aluminium through such an area of the platinum-modified aluminide there was only the coating are illustrated in Figure I I. Except slight coating degradation and the coating

Platinum Metals Rev., 1985,29, (1) 22

appeared to be in very good condition. A typical microstructure is shown as Figure 12.

Discussion Examination and comparison of the

platinum-modified aluminide and original M u - sion aluminide coated blades from the test engine after approximately 520 hours of engine operation revealed significant differences in their protective capabilities (6,7). This examination, after a further 230 hours of engine operation, further illustrates the sig- nificant difference in durability of the two types of coating.

The extensive attack of the conventional diffusion aluminide coating noted at 520 hours had steadily progressed so that, after 750 hours of operation, there was complete breaching of the coating at areas on the concave side of the blade and almost complete degradation and

Ta 0

43.3 (54.0)

Fig. 10 marked A-G. are referred to in the Table

These areas of the internal oxide,

Predominanl Phase

8.7 A1203 (1 4.3)

possibly (PtXNi3,)Al

consumption of the coating at the leading edge. In marked contrast, the platinum-modified

aluminide coating still provided a considerable degree of protection for the substrate alloy of the blade, in that less than 5 0 per cent of the coating was consumed in the vicinity of the

Cr

1.5 (2.1)

Quantitative Analyses of the Areas Labelled in Figure 10, in weight per cent Atomic percentages are given in round brackets

Co Ti

- 7.7 0.1

(9.3) (0.1)

p (0.1)

(53.5)

Al

- 42.9

(31.6)

6.7 ( 1 8.6)

Pt

~~

Distributed as discrete particles within

the oxide

42.8 (16.5)

An inhomogeneous oxide, the major phase present is A1203 I A1203

l l NiAl

(20.8) (41.9)

Platinum Metals Rev., 1985,29, (1) 23

100 -

90

80

70 - js

L 60 z

c

g 50 I- z s

40

30

20

10

0 0

Ni plating

/ \ *-Coating.-* +Alloy Substrate- I

I 1 I --. 20 40 60 80 100 120 140

DISTANCE (prnl

Fig. 1 1 Line scans for the elements nickel, platinum and aluminium along the line a-a, in an area near the leading edge of a platinum-modified aluminide coated blade, show the characteristic enrichment of the outer zone with platinum

Platinum Metals Ree.., 1985,29, (1) 24

Fig. 12 On the convex side of a platinum- modified aluminide coated blade the coating appears to be in a very good condition

concave mid-chord and leading edge regions, that is at the points of greatest attack.

One feature of the corrosion attack that has not been reported before concerns the presence of alumina particles distributed through the platinum-modified coating, particularly in the vicinity of the leading edge. Such particles were also present after 520 hours of engine operation (6,7) and the coating vendor proposed that they were alumina grit-blast particles which were entrained in the surface after the blades were cleaned, prior to the deposition of platinum and the subsequent aluminising process. However, the distribution and size of these particles is dependent on their position around the perimeter of the blade and they also appear to alter substantially with time in the engine. A large network of particles is present around the leading edge of the blades, suggesting that their growth is perhaps catalysed by the presence of mechanical stress, possibly as the result of erosive particles striking the blades in this region. The alloy adjacent to the alumina particles within the coating has become depleted in aluminium to such a large extent that, in some regions, the B (NiAl) phase which should be present, as it is in Figure 7 and area D in Figure 10, has been converted almost entirely to the y’ (Ni3Al) phase, see Figures 8 and 10 and also the Table. This leads to the inference that aluminium within the coating reacts with oxygen ahead of the oxidation front (as defined by the surface oxiddmetal interface) to increase the size of the internal alumina

particles and consequently deplete the metallic part of the coating of aluminium. One conse- quence of this mode of coating degradation is that although 50 per cent of the coating thickness remains, the reservoir of aluminium available to form the protective surface oxide has diminished by a larger factor.

It remains to be seen whether the platinum- modified aluminide coating will remain intact at the full overhaul life of 1000 hours of engine operation, but the present results indicate that a relatively low rejection rate is to be expected.

Conclusions A platinum-modified aluminide coating has

been shown to be superior to a conventional diffusion aluminide coating in the protection it imparts to first-stage turbine blades in a military gas turbine engine operating under conditions conducive to severe hot corrosion attack. After 520 hours of engine operation the original diffusion aluminide coating was breached in some areas whereas, in contrast, after 750 hours of engine operation the platinum-modified aluminide coating remained unbreached. In fact the latter coating still retained 50 per cent of its original thickness in the areas of greatest attack. Near the leading edge, alumina particles situated in the platinum-modified coating below the oxide scale/coating interface have grown substantially in size, presumably by aluminium in the coating reacting with inwardly diffusing oxygen ahead of the oxidation front. This internal oxidation has produced a substantial reduction in the concentration of metallic aluminium in the coating, decreasing the reservoir of aluminium that is available to form the protec- tive alumina scale. These areas, adjacent to the leading edge, are likely sites for subsequent breakdown of the coating with further use.

In the concave mid-chord region of the platinum-modified aluminide, attack has occurred in the form of wide, shallow pits. A distinguishing feature of these corrosion pits is the distinctive metallic band, rich in platinum, which appeared to be at or near the position of the original surface of the coating.

Platinum Metals Rev., 1985,29, (1) 25

The platinum-modified alumnide coated Because of this substantial extension to the life blades are fit for reuse after 750 hours of of the blade, the Australian Defence Force had engine operation and there is a high probability adopted the platinum-modified aluminide that they will be fit for reuse at full overhaul, coating as the specified coating on first-stage that is after 1000 hours of engine operation. blades in this engine.

References

I G. Lehnart and H. Meinhardt, Elecrt.odeposition Surf. Treat., 1972, I, (I), 71 and 189

2 J. A. Goebel, R. H. Barkelow and F. S. Pettit, Proceedings of Tri-service Conference on Corro- sion, MCIC Report No. 7 ~ 4 0 , 1 9 7 9 , p. 165

3 N. R. Lindblad, W. F. Schilling, H. J. Aeschbaker and W. H. Knoll, J. Eng. Power, (Setis A, Trans. ASME), 1980,1oa, 104

4 R. G. Wing and I. R. McGill, Platinum Metak

5 C. Duret and R. Pichoir, in “Coating for High Temperature Applications”, ed. E. Lang, London, Applied Science Publishers, 1983, pp. 33-78

Rev., 1981, I S , (312 94

6 G. R. Johnston and P. G. Richards, Materials Research Laboratories Report R-820, Department of Defence Support, Maribymong, Victoria, Australia, 1981

7 G. R. Johnston and P. G. Richards, “Corrosion in Fossil Fuel Systems”, Proc. Symp. Corros. Fossil Fuel Syst., 1982, New Jersey, The Electrochemical Society, 1983, pp. 456-461

8 P. G. Richards, J. L. Cocking and G. R. Johnston, Materials Research Laboratories Report R-909, Department of Defence Support, Maribyrnong, Victoria, Australia, I 983

9 R. J. Stueber, private communication

An Effective Oxygen Evolution Catalyst In order to expedite the efficient

photocleavage of water into hydrogen and oxygen using solar energy, catalysts must be efficient, stable, specific and fast-acting towards the reduction and oxidation of water. A great deal of progress has been made in the design of hydrogen evolution catalysts using for example colloidal dispersions of platinum, but the search for oxygen generation catalysts has been less successful and results reported on the activity of hydrated ruthenium dioxide (Ru02.xH20) in this regard have been inconsistent and difficult to repeat. Now, however, workers at University College, Swansea have reported that pretreat- ment of hydrated ruthenium dioxide at r44OC for five hours gives an active, stable reproducible catalyst (A. Mills, C. Lawrence and R. Enos, 3. Chem. SOC., Chem. Commun., 1984, (zI), 1436-1438). Yields of 97 to 98 per cent oxygen were obtained from the test re- action represented by the equation: 4Ce” + 2H20 RuOz.xH20 4Ce3+ + 4H+ + 0 2

Conversion of the RuO2 t‘, gaseous RUO4 can compete with the oxygen evolution reaction resulting in loss of ruthenium and low oxygen yields. In a series of experiments Mills found that the oxygen yield was inversely related to ruthenium loss as Ru04 and depended on the temperature previously used for the heat- treatment of the Ru02.xH20. From experiments in which samples of the catalyst were preheated at temperatures from 60 to 900OC it was clear

that optimum yields of oxygen were obtained with the samples heated at about 14o0C (97 to 98 per cent yield). With higher treatment temperatures, the catalytic activity of the samples decreased, probably due to a lowering of the surface area, but no conversion to RuO+ took place. Thermal gravimetric analysis of commercial samples of hydrated ruthenium dioxide indicated water contents of 19 to 24 per cent, but after treatment at 144°C for five hours, the water content was 7 to 10 per cent.

Mills concludes that the ability to catalyse the oxidation of water and the instability to anodic corrosion (that is conversion to Ru04) are both related to the amount of water weakly bound to the powder, and both reactions possibly involve the same reaction sites. The tendency to loss of RuO4 can be removed by the heat treatment. Much of the controversy sur- rounding the use of hydrated ruthenium dioxide as an oxygen catalyst may therefore be rationalised in terms of the degree of hydration, which may vary from one sample to another but heat treatment at about 14oOC for five hours does give a stable, active and reproducible oxygen release catalyst.

These results represent an important step along the pathway towards viable catalyst systems for the water-splitting reaction, and should help to clarify the significance of earlier reports on the use of ruthenium dioxide for oxygen generation. D.T.T.

Platinum Metals Rm., 1985,29, (1) 26

A Posit ive Move Towards Low Lead Petrol NEW PLATFORMER PLANT FOR SHELL U.K. LIMITED

Traditionally lead compounds have been added to petrol to improve the octane rating but forthcoming legislation in the United Kingdom, aimed at improv- ing the environment by reducing the emission of lead from the exhausts of motor vehicles, will necessitate other means of raising the Octane number. In anticipation of this, Shell have just opened a new plant, known as Platformer 111, at Stanlow on Merseyside. Platform- ing is the conversion of low octane feedstock, or naphtha, into a higher octane component which can then be blended with other gasoline fractions to improve their rating, so reducing the need to use lead as an Octane improver.

The feedstock for Platformer I11 is drawn from the refinery's distillation units and after the removal of both sulphur and nitrogen it passes into the stacked reactors that form the heart of the process. Here the gaseous naphtha is subjected to four stages of heating and reaction over a novel platinum on alumina catalyst, produced by Universal Matthey Products Limited under licence from Universal Oil Products Company, before passing through heat exchangers and coolers to yield separate streams of hydrogen and reactor product. The latter, now in liquid form, passes to the platformate stabiliser where liquid petroleum gas and other gases are removed, leaving a liquid high Octane gasoline component suitable for blending into the refinery petrol pool.

Catalyst Regeneration As the gaseous naphtha passes through

the four stacked reactors a very small proportion of the platinum catalyst is withdrawn, regenerated and returned to the system. This continuous recycling of the catalyst will enable the Platformer I11 plant to stay on stream for three years before a major shutdown is required.

Prior to the commissioning of Plat- former 111, two similar plants but without

continuous regeneration already existed at Stanlow, Shell's largest manufacturing location for oil and chemical products in the United Kingdom. The adoption of the very latest technology enables this new P la t fo rmer to p roduce approximately one million tonnes a year of high octane blending components.

Additional information on the process of platforming has been given in two previous articles in this journal (E. L. Pollitzer, Platinum Metals Rev., 1972, 16, (21342-47; 19769 20, (11, 2-61.

Platinum Metals Rev., 1985,29, (l), 27 27

Platinum Group Metals in Catalysis A REPORT FROM THE EIGHTH INTERNATIONAL CONGRESS

The International Congress on Catalysis is held every four years, and the eighth of the series took place at the International Congress Center in West Berlin from 2 to 6 July 1984. It was attended by over a thousand research workers from many countries, including a notable delegation from China. In addition to six plenary lectures and seventy-two orally pre- sented papers, some forty posters were displayed each day. Conscientious participants had their work cut out to do justice to this rich fare. All accepted papers have appeared in four stout volumes, and the texts of the plenary lectures in a slimmer one, all published by Verlag Chemie, Weinheim. A further volume containing the discussion is promised.

As judged simply from the titles, about one- quarter of both the oral and poster presenta- tions made explicit reference to one or other of the platinum group metals, which bearing in mind the state of current interest in zeolites, in selective oxidation and in base metal catalysts for hydrotreating, is an eloquent testimony to the predominant place which these metals con- tinue to occupy on the catalytic scene. It would be pointless to attempt any kind of review of all the relevant papers. However, some of the most popular and important themes are surveyed below, and one or two papers of outstanding quality are highlighted.

Bimetallic Catalysts and Petroleum Reforming

For some thirty-five years, platinum on alumina catalysts have been used to upgrade naphtha fractions by effecting skeletal isomerisation and aromatisation, with a conse- quential increase in Octane number. The discovery that bimetallic systems, such as platinum-rhenium and platinum-tin, deactivated less rapidly has stimulated much research into the role of the second component, but many questions still remain unanswered.

The number of papers presented at the 8th International Congress on Catalysis devoted to bimetallic catalysts and petroleum reforming reflects the continuing interest in this important field.

Work by Russian and East German scientists has greatly extended the range of second com- ponents; elements selected from Groups IB to VIB of the Periodic Classification have been systematically examined, and antimony and bismuth have been found effective in high- temperature operation. Tin, which particularly promotes dehydrocyclisation, does not appear to be completely reduced in the working catalyst, and may play its role through modification of the metal-support interaction.

Much more is now understood about the intermediates existing during the preparation and re-activation of platinum on alumina catalysts. Although sintering occurs more readily in oxidising than in reducing atmospheres, its rate increases as oxygen con- centration decreases, and Pt4+ is implicated in the sintering process. Conversely Pt4+ is formed as a chloro-complex during reactivation, and this is responsible for redispersion of the metal.

Reports were presented on the kinetics of coking, and its effect on product distributions. Other systems have been studied for various reactions; ruthenium-copper and ruthenium- gold for alkane hydrogenolysis, and rhodium-tin for hydrogenation of esters to alcohols.

Reactions of Synthesis Gas A mixture of carbon monoxide and hydrogen

can afford almost any molecule containing carbon, hydrogen and oxygen providing the necessary catalyst is to hand. Current research into the application of the platinum metals as catalysts for these reactions is focused on ruthenium as a possible catalyst for making diesel fuel or alkenes, 'and on palladium and rhodium for the synthesis of methanol or

Plarinum Metals Rev., 1985,29, (l), 28-29 28

higher alcohols including ethylene glycol. Several papers given at this Congress were

concerned with the mechanism of oxygenate formation, and the role of the additives (usually oxides having basic character). The formation of methanol is now definitely associated with ions in positive oxidation states, for example Rh2+, and it is thought that these may play a part in the synthesis of ethanol and acet- aldehyde over rhodium catalysts.

Strong Metal-Support Interactions The discovery by workers at Exxon some

years ago that noble metals supported on titania and other transition metal oxides lost their ability to chemisorb hydrogen when reduced at about 5oo°C has stimulated research into the structural chemistry of supported metals. The effect was named Strong-Metal Support Interaction (SMSI). In a few instances only this is accompanied by an improvement in catalytic performance, the Fischer-Tropsch synthesis being one. The phenomenon continues to excite catalytic chemists, although it is now reasonably certain that it is caused by a simple blocking of the metal surface by the partially- reduced support.

Two of the papers presented highlight the fact that the unexpected in catalysis often occurs. The oxide supports previously found to give SMSI were all more or less easily reducible, and this has been held to be an essential property if SMSI is to take place. However, similar effects have now been discovered with platinum on magnesia, the reduction of which is notoriously difficult. It was also reported that palladium on titania was capable of selectively reducing non-conjugated dienes; palladium on normal supports can only achieve this after prior isomerisation to the conjugated form.

Platinum and Cancer Chemotherapy

There may at first sight be no obvious con- nection between catalysis and cancer, but the link was forged in a masterly paper presented by John Turkevich of Princeton University. He showed that Cisplatin and other therapeutic

complexes react with the component bases of DNA to form adducts having greatly different catalytic activities for decomposition of hydrogen peroxide. From this he was able to conclude that the miscoded DNA responsible for uncontrolled cell growth probably contained a string of cytosine molecules, and he was thus for the first time able to offer an explanation of the phenomenon of cancer in molecular terms. It will be surprising if this work does not have a profound effect on cancer research for many years to come.

In conclusion, the 8th International Con- gress on Catalysis may be said to have been a worthy successor to its antecedents in providing a marked stimulus for all research workers in the field. Excellently organised by Dechema, it will long be remembered by all who attended as a source of great intellectual nourishment and a further demonstration of the key role which the platinum group metals continue to play in catalysis. G.C.B.

A Compilation of Catalysts What is probably the first-ever comprehen-

sive survey of the many catalysts used in the refining industry has recently been published in the U.S.A. (“OGJ Catalyst Report: ’84”, Oil

68-72, 74-82, 84-86). The compilation which identifies some 700 different catalysts will be of considerable benefit to the refiner or design engineer requiring a clear picture of the many catalyst suppliers, manufacturers and licensors.

This interesting and useful survey demons- trates the high degree of specialisation in the catalyst supply and refining industries. The catalysts, many of which contain a platinum group metal, have been categorised into 18 specific process areas and over 20 pages ‘of tables are required to present the assembled information. Legitimate concern about proprietary matters has been respected and where a contributor had reservations about identifying some aspect of a catalyst, most fre- quently the composition of the carrierhpport or the active agents, this has been indicated in the tables. Nevertheless it is clear that platinum group metal-containing catalysts dominate several of the processing categories and make important contributions to others.

Gas J., 1984, 82, (41), 5 5 , 56, 58, 60-65,

Platinum Metals Rev., 1985,29, (1) 29

Richard Knight and His Production of Malleable Platinum THE STORY OF A FORGOTTEN CHEMIST

By L. B. Hunt The Johnson Matthey Group

The outstanding figure in the history of platinum, William Hyde Wollaston, was the first to refine and fabricate the metal on a com- mercial scale and to develop its uses in industry. His first purchase of native platinum, smuggled from South America to Jamaica and made jointly with his partner Smithson Tennant, was effected on Christmas Eve 1800 and by early in 1805 he had not only isolated and identified palladium and rhodium (Tennant having similarly discovered iridium and osmium in the native platinum) but had perfected his produc- tion method and begun to offer chemical apparatus and other products for sale (I).

But almost a year before Wollaston had even bought his initial consignment, on January 9th 1800, a paper was read to the British Mineralogical Society, formed only in the April of the previous year, on “A New and Expeditious Process for Rendering Platina Malleable” (2). This had been prepared by Richard Knight, one of the five founder members of the Society, a man who has so far remained in almost total obscurity apart from being described as “Ironmonger of Foster Lane”. This absence of information on his life and work prompted the writer to undertake an investigation of his career and activities, a study in which he was greatly supported by Dr. Peta D. Buchanan whose genealogical researches first established the details of his life story and then succeeded in locating two of his great- great-granddaughters who had in their keeping quite substantial family records. It is now possible, therefore, to give some account of this almost forgotten pioneer in the long struggle to produce platinum in malleable form.

Richard Knight was born on May 26, 1768, the son of William Knight and his wife

Elizabeth, nke Martin, at 5 Goldsmith Street, close to Foster Lane in the City of London, where her uncle Edward and her father William Martin, both from a Leicestershire family, carried on an ironmongery business that had been taken over by Edward from his master in 1732. In the year of Richard’s birth William Martin’s wife died and the family moved to Holloway but on Martin’s remarriage in 1772 they moved again to Stoke Newington. It was from here that the young Richard attended school at the dissenting academy in Newington Green.

On leaving school in 1783 Knight was apprenticed to his grandfather who was a member of the Worshipful Company of Skin- ners, but four years later, and thus three years short of the apprenticeship being completed, William Martin died, leaving instructions in his will for the trade to be carried on by his daughter and son-in-law “until my grandson shall be properly qualified to undertake the same” (3). Richard’s apprenticeship was therefore transferred to his father William who, in order to carry on the business had hastily to seek membership of one of the City Livery Companies, in his case the Spectacle Makers

Richard was freed from his apprenticeship in December 1791 but he was not taken into partnership by his father until 1795, and it is during these four years that the family records disclose a most interesting association with Joseph Priestley. While still at school Knight had become acquainted with the great dissent- ing minister and mathematician Dr. Richard Price (1723-1791), had attended the services he conducted a t Newington Green and at the famous Gravel Pit Chapel in Hackney and

(4).

Platinum Metals Rev., 1985,29, (l), 30-35 30

Richard Knight 1 768- 1844

Inheriting an ironmongery business established two g e n e r a t i o n s e a r l i e r , Richard Knight was more interested in chemistry and mineralogy and rapidly transformed it into a supply h o u s e f o r c h e m i c a l reagents, apparatus and instruments. Although well known t o many dist- inguished men of science of his time and a founder m e m b e r of s e v e r a l scientific societies he has remained in obscurity apart from brief references to a powder metallurgy process he devised to yield malle- ab le p la t inum before Wollaston had even com- menced his researches. In the inktray there may be seen a platinum knife, one of several made b y Knight’s life long friend W. H. Pepys who presented similar knives to King George 111 and Queen Charlotte as well as to Sir Joseph Banks From P mmature p s m d by his daughter Elizabeth, repduccd by munny of Miss Mcgsn Evans and Mn. Peggy MscKay

became deeply interested in Unitarianism, forsaking the Church of England in which he had been brought up by his parents. As is well known, Price was succeeded in his ministry by Priestley who had found refuge among his many friends in Hackney after the destruction of his home, laboratory and library by the mob in Birmingham. Knight continued to attend the chapel, where he is listed as a subscriber from 1793 onwards (5 ) , and naturally soon discovered that Priestley was the author of a number of scientific books. Now Priestley had been assisted in setting up his new laboratory by Arthur Aikin (1773-1854) the son of his friend John Aikin, until this young man left to enter the ministry in 1793 (6), and it is evident that Knight had either been assisting Priestley in a similar way or that he followed Aikin as laboratory assistant, either living in Priestley’s house or spending considerable time there. The

exact location of the house has recently been identified by Mr. Michael Gray of University College, London, after much research in local records, at the southern corner of Lower Clapton Road and Clapton Passage (7). In this way Knight learnt something of chemistry from Priestley, and would have had the use of the library that Priestley had been able to re- assemble with gifts from his many friends, while the older man befriended him and, in fact, left in his care a number of possessions when he left for America in April I 794. Among these was a sun dial that is still in the keeping of Knight’s descendants. Other relics were later handed over by a member of the Knight family to the Priestley Museum in Northumberland, Pennsylvania.

Clearly Knight continued his studies and in 1798 he was elected a member of the Guy’s Hospital Physical Society, then one of the

Platinum Metals Rev., 1985, 29, (1) 31

The house in Hackney occupied by Joseph Priestley from September 1791 until his departure for America in April 1794, recently identified by Mr. Michael Gray, but no longer in existence. Richard Knight spent considerable time here in working with Priestley who both introduced him to chemistry and converted him to Unitarianism. On Priestley’s departure he left with Knight a number of his possessions, one of which, a sundial, still survives in the family. Later, after his marriage in 1803, Knight took a large house just round the corner in Clapton Passage Photograph by councsy of the London Borough of H P C W Library Services Archives Department and Mr. Michael Gray

leading scientific associations in London in which William Babington, William Allen, George Pearson and Astley Cooper were prominent (8). He was never a member of the Askesian Society founded by William Allen in 1796, but at a meeting held in their rooms at Plough Court in Lombard Street in April I 799 he was one of the five founder members of the British Mineralogical Society together with William Allen, William Hasledine Pepys an ins- trument maker, Alexander Tilloch who had just established the Philosophical Magazine, and the geologist and engraver William Lowry. The rules of the new group stipulated that mem- bership should not exceed twenty and that:

“none to be admitted as members but such as are able and willing to undertake a chemical analysis of a mineral substance” (9). It was felt that the absence in England of any

school or college teaching scientific mineralogy such as the Ecole des Mines that had been set up in Paris in 1783 might be remedied by the

collective activities of the members in applying a little science to mining and metallurgy. Before the end of the year the five founders had been joined by William Phillips, the two Aikin brothers Arthur and Charles, with the former becoming president of the society. Other members included Babington, Richard Phillips, Robert Bingley the Assay Master at the Royal Mint and Theodore and Robert Albion Cox of the gold and silver refining firm of Cox and Merle in Little Britain. Meetings were held fortnightly at Plough Court, reports being read on the analyses of minerals, and on three occa- sions Richard Knight reported analyses of lead and iron ores.

The Platinum Process It may be wondered why Knight should then

turn his mind to the problem of producing the hitherto intractable metal platinum in malle- able form, but the potential value of the metal had formed the subject of a number of papers

Platinum Metals Rev., 1985,29, (1) 32

and articles in the scientific periodicals that had now begun to be published in London, these following upon several reports of but indifferent progress made by workers in Sweden, Germany, France and Spain (10). The Repertory of Arts and Manufactures, for example, founded in I 794, reproduced in I 797 the classic paper, “Observations on Platina”, read by Lavoisier to the AcadCmie des Sciences some seven years earlier in which he described Janety’s process using arsenic ( I I) while John Aikin’s newly established Monthly Magazine reprinted in March 1798 an account of the researches of the Russian metallurgist Count Mussin-Pushkin in compressing a mixture of platinum and mercury and forging it at a white heat (12). In the October and November of the same year Tilloch’s Philosophical Magazine carried a translation of the paper by the AbbC Rochon, “Observations on Platinum and its Utility in the Arts”, from the Journal & Physi- que ( I 3). Earlier sources of information avail- able to Knight would have included William Lewis’ “ C o m m e r c i u m Phi losophico- Technicum” published in parts between 1763 and 1765 and including some 170 pages on platinum, as well of course as Macquer’s “Dictionnaire de Chymie” that had been translated into English by James Keir in 1777, while Priestley’s own “Heads of Lectures on a Course of Experimental Philosophy”, published just prior to his departure for America in 1794, also included two pages on platinum. (Priestley was also sufficiently interested in platinum to purchase a modest amount; his claim for com- pensation after the destruction of his house and laboratory on July 14, 1791 includes the item “Half a pound of platinum E2.8.0”).

Thus the problem of the infusibility of platinum and the numerous attempts to over- come this was much in the air at this time, there was considerable interest in finding a reliable method of rendering it workable, and it was clearly the prospect of commercial success that motivated Knight. His paper opens:

“The many peculiar advantages which platina in a malleable state possesses over every other metal for the fabrication of a variety of instru-

ments and utensils particularly useful for the purposes of chemistry, together with the extreme difficulty of procuring it, being hitherto only to be obtained from Paris, of a very indifferent quality, and at a price equal to that of gold, first induced me to turn my attention to the subject. After having repeated a variety of experiments, from the different writers on this substance, without effect, I at length completed a process, the success of which has fully answered my expectations. By the process, which I follow I am able to reduce any quantity of crude platina to a perfectly malleable state, entirely free from impurity, and capable of being wrought into any form whatever. As this is a circumstance of con- siderable importance to the chemical world, and the advantages which may result from it to society in general are perhaps incalculable, I would consider myself deserving of censure could I allow any motive whatever to induce me to withhold it from the public”. The earlier chemical part of his process,

dissolution in aqua regia and precipitation with sal ammoniac, was not new, but his important innovation was the much more forcible hot compression of his precipitate in a hollow inverted refractory cone to a compact mass that could then be forged into an ingot of malleable metal. This process had the principal advantage of avoiding contact between the platinum and red hot iron that had readily introduced con- tamination in the hands of other workers, but rather curiously there is no indication that he made much practical use of his process or that he made more than one or two articles from his platinum. In fact, in February 1801, scarcely more than a year after his paper was presented, he disposed of the considerable quantity of 800 ounces of native platinum to Wollaston at four shillings an ounce, half of the cost being met by Smithson Tennant (14). His acquaintance with Wollaston undoubtedly arose from the close proximity of the Foster Lane premises to the Church of St. Vedast, exactly opposite and only a few feet away across this narrow lane, where the rector, from 1779 until his death in 1 8 1 5 , was the Rev. Francis Wollaston-father of the scientist-and where members of Knight’s family had attended and had been buried. Why Knight abandoned his platinum work we shall never know, but possibly he foresaw that greater success might be achieved in the hands

Pluritiuin Metals Rev.. 1985,29, ( 1 ) 33

The premises known as Y e White Lyon in Foster Lane, built in 1680 and occupied from 1732 first by Hichard knight’s great uncle and then jointly with his grandfather, Edward and William Martin, as a n ironmongery business. When Knight wee-erded t o the business he rapidly converted it to a supply house for chemicals and apparatus, de5igning a number o f p i w w o f t-qu i pm en t hi mse I f

of a more professional scientist. This purchase was only the second of many such transactions made by Wollaston in the early days of his extensive researches.

Although Knight claimed a high degree of purity for his product it must be remembered that the other five members of the platinum group were then unknown. A recent study by Professor M. C. Usselman and his colleagues, who reproduced Knight’s process starting with native platinum from Colombia provided by Johnson Matthey Inc., has shown that the product would have contained only 94 per cent of platinum with z per cent of iron, z per cent iridium and small amounts of palladium, rhodium and lead ( I 5). These impurities could have caused problems for Knight in the fabrication of his few products.

In the meantime Richard’s father William Knight had died in January 1799 and he became the sole owner of the business, being

Photograph by counay ofthe Guildhall Library

joined two years later by his younger brother George, the firm then becoming known as R. and G. Knight and continuing in this style until 1838. It was now that, with a secure basis for expansion, Richard turned from ironmongery to the devising of apparatus and equipment, an activity in which he progressed and prospered for the remainder of his life, serving his fellow scientists with their needs in the rapidly developing technology of the period.

The isolation of sodium and potassium by Humphry Davy in 1807, employing a rather crude assembly of a platinum spoon to hold the caustic soda and caustic potash and bringing them into contact with a platinum wire con- nected to the negative pole of a battery, aroused of course, considerable excitement in scientific circles, and this classic experiment was repeated on numerous occasions, first before the Askesian Society and the British Mineralogical Society by William Allen and William

l‘larinum Metals Rev., 1985,29, (1) 34

Hasledine Pepys using a more sophisticated platinum apparatus designed by Pepys and made in several versions by Knight ( I 6).

A little earlier Humphry Davy, in one of his lectures for the Board of Agriculture on the analysis of soils, recommended a chemical chest supplied by Knight ( I 7).

By I 8 I I Knight was able to publish an exten- sive catalogue of “Apparatus and Instruments for Philosophical, Experimental and Com- mercial Chemistry” this including furnaces, retorts, stills, blow pipes, electric batteries, thermometers and a range of platinum apparatus.

The British Mineralogical Society was discontinued in 1805, most of the members including Knight then becoming proprietors of the new London Institution, while in 1807 he was one of the eleven founder members of the Geological Society, being chosen as a member of their Committee for Chemical Analysis.

Richard Knight retired in 1838 at the age of seventy, the business being carried on by his brother George and later by the latter’s two sons George and Richard. He had moved from

Clapton in I 830 to a house in Tavistock Square where he died on February 2 I , I 844, leaving a thriving business and the very considerable sum of &~,ooo to his five daughters, his wife having predeceased him by eight months ( I 8). He was buried in the grounds of the New Gravel Pit Chapel in Hackney where he had been for so long a leading member and for some years a trustee.

An obituary notice written by his life long friend William Hasledine Pepys appeared in the journal associated with the Unitarian move- ment ( I 9), but otherwise this industrious chemist, mineralogist and instrument designer, despite his friendship with so many scientists of his time, seems to have left but little record of his achievements other than a brief account of an early method of producing platinum in usable form.

Acknowledgements My great debt to Dr. Peta D. Buchanan has been

mentioned above. I am also most grateful to Richard Knight’s great-great-granddaughters, Dr. Marcia Grant and Miss Megan Evans and their cousin Mrs. Peggy MacKay for making available their family records and for the portrait.

A more detailed account 0.f the career of Richard Knight by Dr. L. B. Hunt and Dr. P. D. Buchanon was published in the July 1984 issue of Ambix, the Journal of the Society for the History of Alchemy a d Chemistry.

References

I D. McDonald and L. B. Hunt, “A History of 1 0 D. McDonald and L. B. Hunt, op. cir., (Ref I), pp.

I I A. L. Lavoisier, Rep. Arts Manuf., 1 7 9 7 ~ 7 ~ 5 9 - 6 2 I 2 A. Mussin-Pushkin, Monthly Mag., 1 7 9 8 , ~ ~ 2 I 6 ‘3 A. Rochony phi’. Mag., ‘79”9, ’,

Platinum and its Allied Metals”, Johnson 55-131 Matthey, London, 1982, pp. 147-177

2 R. Knight, Phil. Mag., 1800,6, 1-3 3 Will of William Martin, Public Record Office

Wills and Probate Division, 1787, February 81,

Chamberlain’s Court Records, Guildhall, 14 WOllastOn Notebook, L, Cambridge University London

PROBI 1 / 1 1 5 0 170-177

Library, Add. MSS. 7736

5 A. R. Ruston, “Unitarianism and Early Presby- terianism in Hackney”, Ruston, Watford, I 980

6 Betsy Rogers, “A Georgian Chronicle”, London, 1958, p. 160

7 Michael Gray, Easr London Record, 1983, October, 32-38

8 Minutes of Guy’s Hospital Physical Society in the Wills Library, Guy’s Hospital Medical School, London

9 Minutes of the British Mineralogical Society, Department of Mineralogy, British Museum (Natural History); P. J. Weindling, in “Metropolis and Provinces”, ed. I. Inkster and J. Morrell, London 1983, 120-150

1 5 B. I. Kronberg, L. L. Coatsworth and M. C. Usselman, Mass Spectrometry as a Historical Probe: Quantitative Answers to Historical Ques- tions in Metallurgy, “Archaeological Chemistry-II”, Advances in Chemistry Series No. 205, Am. Chem. Soc., Washington, 1984, pp. 295-310

16 W. H. Pepys, Phil. Mug., 1808~31 ,241 1 7 Humphry Davy, Communications to Board of

18 Will of Richard Knight, Public Record Office,

I 9 The Christian Reformer or Unirarian Magazine and

Agriculture, I 805,4,-302-3 I 8

PROB.1 I . 1995

Review, 1844~9,261--262

Platinum Metals Rev., 1985,29, (1) 35

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Oxidative Dissolution of Platinum and Ruthenium from Various Base-Metal Binary Alloys R. L. PAUL and M. M. KRUGER, s. Afr. 3. Chem., 1984, 37, (31, 116-120

The preparation of several binary alloys composed of Pt or Ru with a base metal (Al or Fe) and leaching tests on them in HCl acid are described. The poor dissolution observed for Ru is attributed to the strong affinity of this metal for 0, which results in partial passivation of the metal. The almost quantita- tive dissolution of the Pt alloys is ascribed to the lesser affinity of Pt for the adsorption of 0, and to the presence of absorbed H.

The Effect of Various Additional Ele- ments on Properties of Fe-Pt Permanent Magnets Having High Energy Product

1984548, (9)s 930-935 K. WATANABE and H. MASUMOT0,y. 3pn. Inst. Met.,

The effects of Rh, Pd, Ir, Ti, V, Au, Al, Ga and Ge on Fe-Pt alloys were evaluated. The permanent mag- netic properties of Fe-Pt alloys can be improved by adding a small amount of Ti and V. The alloy 6oat.%Fe-39at.%Pt-1 at.%Ti has the highest maximum energy product of 165 kJ/m3, coercive force of 360A/m and residual flux density of I.OT when aged at 823K after water quenching. Alloy 60.~at.%Fe-38.5at.WPt-I at.%V showed the highest coercive force of 41okA/m, maximum energy product 160kJ/m3 and residual flux density of 1.04T when aged at 773K after waterquenching. The per- manent magnetic properties cannot be improved by other additions.

A Photoemission Study of the Oxidation of Platinum in Pt-Based Alloys: Pt-Pd, PI-Ru, Pt-Ir L. HILAIRE, G. DIAZ GUERRERO, P. LEGARE, G. MAIRE and G. K R I L L , ~ ~ ~ ~ . Sci., 1984, 146, (2/3), 569-582 A photoemission technique was used to study the surface composition of Pt-Pd, Pt-Ru and Pt-Ir alloys. The samples were exposed to 0 2 at atmospheric pre- ssure and 20c-6oo0C. 0-induced changes of surface composition were followed. Oxidation properties of Pt, Pd, Ru and Ir changed on alloying. The Pt-based alloys could be oxidised provided the Pd, Ru or Ir surface concentration was higher than a limit between 13% and 20% for all three systems. Above this limit, the impurity and the Pt atoms were both oxidised. Three different Pt oxidation states were detected PtO, cx-Pt02 and P-Pt02. In the low impurity content range, neither impurity nor Pt could be oxidised.

On the Electrical Resistivity , of Pt:SFexMn1-, Alloys in the Exchange Inversion Region

Phys. Lett., 1984,45, (16), L-781-L-784 The electrical resistivity p as a function of temperature is reported for a series of Pt3FeXMn1-. alloys with x = 0, 0.5, 0.6,0.7,0.8 and 1.0. Thep(T) curve for Pt3Feo.sMno.4 shows two panomalies, one is attributed to the Curie temperature and the other to the transition to a heterogeneous non-colinear magnetic structure.

Low Voltage Hydrogen Plasma Interac- tion with Palladium Surface

Nucl. Mater., 1984, 125, (3), 326-329 HZ penetration, distribution and content in Pd under low voltage glow discharge plasma, depending on plasma component structure (Hz, He, Ar and their mixtures), irradiation succession and possible surface structure changes have been investigated by various techniques. The dependence of the H2 permeability through Pd membranes upon the plasma component structure and the preliminary irradiation dose in the inert gas atmosphere has been shown.

On the Friction and Closing Behaviour of Gold and Palladium Alloys. Part 2. The Palladium Alloy System H. AKPOLAT, H. G. FELLER and P. VEILE, Metalloberflaeche, 1984,38, (IO), 448-454 Alloys and sandwich systems based on Pd, with a disc-pin-arrangement were investigated. Friction, rubbing, roughness and surface composition were determined. The results showed a phase, in which the mechanical properties and the dominance of the 4 closing mechanisms changed continuously. All the Pd-Ni layers had selective oxidation of Ni already at 373K3, and Ni enriched the surface as Ni oxide.

Some Properties of Amorphous Pd-Si and Pd-Ni-Si Alloys under Hydrogen Pres- sures of up to 2GPa

Common Met., 1984, 101, 299-304 The electrical resistance and thermoelectric power of amorphous Pd~sSi 15, Pd83Si 17, P d d i 18,

Pd72NiloSil8, Pd63Ni20Sil8 and PdsoNi&ilg were measured as functions of the hydrogen pressure up to 2GPa. Hysteresis was observed during absorption- desorption cycling for all the Pd-Si alloys and for Pd72Ni10Si18. Both PdgsSil~ and Pds3Si17 became saturated with H at H : Pd ratios of 0.45 and 0.36, respectively, and then exhibited superconducting behaviour with T, = 1.6K.

Y. V. YAKHMI, 1. K. GOI'ALAKRISHNAN and R. M. IYER,J.

T. D. RADJABOV, L. YA. ALIMOVA and A. V. SHARUD0,J.

S. M. FILIPEK, A. W. SZAFRANSKI and F. DUHAJ,J. Less-

Platinum Metals Rev., 1985,29, (l), 36-43 36

Formation of Bulk Metallic Glass by Fluxing H. w. KUI, A. L. GREER and D. TURNBULL, Appl. Phys. Lett., 1984, IS, (6),6 I 5-6 I 6 Bulk specimens (0.4-4g) of Pd40Ni40Pzo have been undercooled consistently to the glass state with no detectable superficial crystallinity in a molten flux of dehydrated B oxide. The minimum dimensions of the most massive glass specimen so formed was r.ocm.

On the Structure of Metallic Glasses in the System Palladium with Magnesium, Zinc or Cadmium as Second Component and Phosphorus or Arsenic as Third Com- ponent M. EL-BORAGY, M. ELLNER and B. P R E D E L , ~ . Less- Common Met., 1 9 8 4 ~ 1 0 s ~ (I) , 67-78 The preparation of various metallic glasses was carried out by the splat cooling method. Phase diagrams of the binary and ternary systems are pre- sented. The ranges of good glass-forming ability are outside 80 : 20 stoichiometry.

Magnetic Properties of Intermetallic Compounds RhMnGe, PdMnCe, Pdr.sMn".sSi, Pdl.sMno.5Ge and RhMnSi W. BAZELA, J. Less-Common Met., 1984, 100,

341-346 The magnetic properties of the polycrystalline title compounds were studied using magnetometric measurements. The first four compounds display ferromagnetic properties at low temperatures, whereas RhMnSi is an antiferromagnet. Their Curie (NCel) temperatures are 622K, 576K, 498K, 392K and 400K, respectively and their magnetic moments are 3.56,U~, 3.165,U~, 2.12,Un, 1 . 6 , ~ ~ and 2 . 6 , ~ ~ .

Mobility of Pd and Si in PdzSi

Phys. Rev. B, 1984, 30, (lo), 5916-5922 A diffusion-membrane technique has been developed to determine the mobilities of Pd and Si in PdZSi. A multilayer film structure Pd/Pd2Si/Ge, in which Ge acts as a sink for Pd is used to monitor the flux of Pd through Pd2Si. The Si flux is determined by using the thin film structure Si/PdzSi/Cr in which Cr acts as a sink for Si. Values for the Pd and Si mobilities were calculated and good agreement was found between the calculated Pd mobility values and the parabolic rate constant for PdzSi growth around 200°C.

Profile of Crude Rhodium

1002-1 005

The history of platinum group metals and properties of Rh are explained. Then the geological occurrence of Rh and other platinum group metals is discussed. Present prices of platinum group metals and means of recycling them are given. The recovery of Rh and platinum group metals, the applications and uses of Rh are commented on.

E. C. ZINGU, J. W. MAYER, C. COMPIE and R. PRETORIUS,

H. RENNER and U. TROBS, Metall, 1984, 38, (IO),

Relationship between the Crystal S t r u c t u r e a n d t h e R e e n t r a n t Superconducting Properties of (Sn I - ~ -

Er.) ErlRhsSn 18

s. MIRAGLIA, J. L. HODEAU, M. MAREZIO, H. R. o n and 1. P. REMEIKA, Solid State Commun., 1984, 52, (2), 135-1 37 Single crystals of (Sn1-.Er.)Er4Rh6Snls are superconducting (T, = 1.3K) for x - 0, and are reentrant superconductors (T, = I .24K and T, = o.34K) for x - 0.30 and undergo a single mag- netic transition (T, = o.68K) for x - 0.75. Since the occupancy of the [Sn(r)l-,Er(1).]Er(2)4 sublattice is responsible for the variation of the low temperature properties, predictions can be made as to new reentrant superconductors in the MRh,Sn, series (M = RE). This seems to be the first system of reentrant superconductors where stoichiometry within a sublattice controls both magnetic ordering and superconductivity.

Magnetic Properties of New Ternary Silicides: TbzIrjSis and Both Polymorphic Forms of TbIrzSiz M. HIRJAK, B. CHEVALIER, J. ETOURNEAU and P. HAGEN- MULLER,Mater. Res. Bull., 1984, 19, (6), 727-733 New ternary silicide TbzIr3Sij and two polymorphic forms of TbIrzSi2 have been prepared. The three compounds order antiferromagnetically. A high NeCl temperature is observed for the low-temperature modification (TN = 80K, 8, = 42K). TbzIr3Si5 and the high temperature modification of TbIr2Siz have low TN and 8, values.

Semiconducting Behaviour of RuGaz J. EVERS, G. OEHLINGER and H. MEYER, Mater. Res. Bull., 1984, 19, (9), I 177-1 180 RuGa2, with TiSiz type structure was prepared by inductively heating Ru and Ga in a water cooled Cu boat under Ar. The electrical conductivity of a polycrystalline sample 7 x 5 x 4mm' was measured from 20-400°C by the four point technique. RuGaz is a semiconductor with electrical resistivity of o.zL?crn at room temperature. RuAIz and Os2Si3 were also shown to have semiconducting properties.

Effect of Atmosphere on the Electrical Conductivity of RuOz and Ruthenate Layers

Lett., 1984,3,(11), 1011-1014 The effects of NZ and 0 2 on the electrical con- ductivity of polycrystalline layers of RuOz and BizRuz07 pure and doped with an excess of Bi203 and RuO2 was studied over a broad temperature range. The electrical resistance of BizRu207 layers and ruthenate layers with excess RuOz and Bi203 in the range 20-650°C changes very little, but above 650°C it decreases more steeply. The temperature dependence of resistance of the thick layers of pure RuOz has a similar shape. NZ exposure increases the resistance of the layers, changing to 02 decreases it.

B. REMAK, M. FRUMAR and L. KOUDELKA,J. Mater. SCi.

Platinum Metals Rev., 1985,29, (1) 37

The Micro-Structure of RuOz Thick Film Resistors and the Influence of Glass Particle Size on Their Electrical Properties T. INOKUMA, Y. TAKETA and M. HARADOME, IEEE Tram. Components, Hybrids Manuf. Technol., 1984, CHMT-7, (2), 166-175 The microstructure and electrical properties of Ru02 thick film resistors have been studied with emphasis on the effects of material parameters and processing variables, such as size of glass frit particles, RuO2:glass mixing ratio, firing conditions, etc. A network of Ru02 develops in a glass matrix on firing, and the increase in the glass particle size enlarged the cell in the network without any significant change in the microstructure.

CHEMICAL COMPOUNDS Fluorosulfates of the Noble Metals. 5 . F l u o r o s u l f a t o D e r i v a t i v e s of Platinum( I V ) and the HSOaF- Pt( S0:sF)d Superacid System K. C. LEE and F. AUBKE, Inorg. Chem., 1984, 23, (14), 2 124-21 30 A simple synthetic route to pure Pt(SO,F), is described. This compound was found to be an excellent fluorosulphate ion acceptor forming either [Pt(SO3)F6] or an oligometric anion of the composi- tion [Pt(SO3F)s]-. A number of complexes with the counterions Cs+, C102+, BaZf and Brf were prepared and spectroscopically characterised. The novel dibasic acid H2[Pt(SO3F)6] which undergoes dissociation equilibria was formed in a solution of HSO3F.

Preparation and Characterization of Some Ruthenium (111 ) Porphyrins, Including the Crystal Structure of Bromo( octaethylporphinato) (triphenyl- phosphine)ruthenium( 111 ) B. R. JAMES, D. DOLPHIN, T. W. LEUNG, F. W. B. EINSTEIN and A. C. WILLIS, Can. J . Chem., 1984, 62, (7), I 238-1245 Some Ru(II1) complexes Ru(porpXL)X and [Ru(po'p)Lz]x, (porp = dianion of octaethyl- porphyrin (OEP) or tetraphenylporphyrin (TPP)), (L = PPh3, P"Bu3; X = Br, Cl) were prepared from the precursor complexes Ru(porp)L2 or Ru(porpXC0)L using as oxidant the halogens or air. The X = PFs salts can be made using Et20'Pfi as oxidant, Ru(I1) porphyrin n-cation radical inter- mediates have sometimes been detected.

Preparation and Electrical Conductivity of BizRuzOz Single Crystals

C y s t . Growth, 1984,68, (2), 647-649 Single crystals of Bi~Ru202 have been grown by the flux method from a Bi203/V205 melt. The electrical conductivity of the crystals is of a metallic type, and the major current carriers are electrons.

B.kEHAK, K. HORCIC, M. FRUMAK and L. KOUDELKA,J.

ELECTROCHEMISTRY

The Catalytic Thermal Decomposition of Water and the Production of Hydrogen H. H. G. JELLINEK and H. KACHI, Int. 3. Hydrogen Energy, 1984~9, (8), 677-688 The Pt and Ir catalysed thermal decomposition of H20 has been carried out at I~OC-I~OO~C. The dissociation was very rapid, yielding appreciable quantities of H2 and 0 2 . The great rate of catalytic decomposition compensated for the small degrees of thermal decomposition in this temperature range. Two prototypes for large scale thermal Hz produc- tion are proposed and are described in detail. A reasonable number of these prototypes can replace one year's supply of natural gas by HZ in the U.S.A.

Oxygen Reaction on Titanium Catalysed by Gold, Platinum and Palladium R. ZEJNILOVIC, M. PJEkkIk, M. SLJUKIC and A. R. DESPIe, J. Appl. Electrochem., 1984, 14, (4), 481-488 The electrocatalytic properties of Ti surfaces coated with small amounts (o .ozp~.6mg/cm~) of Pt, Pd and Au and their mixtures, have been investigated during 0 2 evolution and reduction in alkaline solution. All the samples had higher electrochemical activity than the corresponding compact metal surfaces, which may be ascribed to a larger specific surface area of the dispersed catalysts than of smooth metal surfaces. Dispersed Pd gave the best performance, the poten- tial gap between 0 2 evolution and reduction at ImA/cm2 being reduced to 0.66V. No indication of a fast degradation was found.

The State of Pd(1l) in Solutions of Sul- phuric Acid E. s. RUDAKOV, A. P. YAROSHENKO, R. I. RUDAKOVA and v. v. ZAMASHCHIKOV, Ukr. Khim. Zh. (Russ. Ed.),

Spectrophotometric studies of the state of Pd(I1) in H2SO4 solutions showed that Pd(I1) is found either as aqueous-ions or as monobisulphate complexes. Stability constants of the complexes in the solution H2SO4 + HC104 with specific concentration of 8.00 are given at 25 and 8oOC. It is shown that aqueous- ions and monobisulphate Pd(I1) complexes in HzS04 react with H2 at the same rate.

Electrochemical Polarisat ion of Dispersed Palladium Selenide in Caustic Soda Solutions A. BAESHOV, M. z . UGORETS, 0. I. SEMINA and D. N. NAGUMANOV, Zh. Prikl. Khim. (Leningrad), 1984, 57, (71, I52"'524 Electrochemical polarisation studies of dispersed Pd selenide made in 4M NaOH at 25OC showed the solid phase reduction of Pd and the electrochemical decomposition of Se into the solution as selenides. The rate of electrochemical decomposition of Pd selenide into NaOH solution was fast and was com- plete when accompanied by oxidation processes.

1984,509 (7), 680-684

Platinum Metals Rev., 1985,29, (1) 38

Electrochemistry of Coordination Com- pounds. Part XXI. Electrogeneration and Decay of Rh(PPh3)s and Rh(PPh3)r G. ZOrrI, S. ZECCHIN and G. PILLON1,J. Electroanal. Chem. Interfacial Electrochem., 1984, 175, (1/2),

The voltammetric behaviour of Rh(PPh3)3(DMEXC104) was studied in 1,2- dimethoxyethane (DME) at the Pt electrode. The for- mally three-cwrdinate d8 species is reduced in two one-electron reversible processes. The d9 inter- mediate, Rh(PPh3)3, either undergoes a fast second order reaction producing the dimers [Rh(PPh3)& and [Rh(PPh3)& or coordinates one extra phosphine ligand if present, followed by dimerisa- tion.

In-situ Identification of Ru04 as the Corrosion Product during Oxygen Evolu- tion on Ruthenium in Acid Media

Electroanal. Chem. Interfacial Electrochem., 1984, 172, (1/2), 211-219 The corrosion of Ru during 0 2 evolution in o.5MHzSO4 was studied using cyclic voltammetry, the rotating ringdisc electrode technique and differential reflectance spectroscopy. Cyclic voltam- metric curves show a distinct reduction peak at - + 0.80V vs. S.C.E. in the negative scan provided the positive limit is extended beyond - + 1.2V vs. S.C.E. The voltammetric feature observed at - + 0.80V vs. S.C.E. is attributed to the reduction of RU04 in solution. It is concluded that the onset of 0 2

evolution and Ru corrosion takes place at the same potential and thus the reaction pathways of both processes involve a common intermediate.

241-250

R. KOTZ, S. STUCKI, D. SCHIERSON and D. M. KOLB,J.

PHOTOCONVERSION Hydrogen Evolution and Iodine Reduc- tion on an Illuminated n-p Junction Silicon Electrode and Its Application to Efficient Solar Photoelectrolysis of Hydrogen Iodide

Phys. Chem., 1984, 88, (IS), 4218-4222 A p s i electrode, highly doped with P from the surface (n +/psi) generated a photocurrent corresponding to I (or triiodide) reduction in a HVI2 solution at potentials much more positive than those on Pt and p s i electrodes. The kinetics of the Hz photoevolution were improved by depositing a o.5-3nm Pt layer on the surface, but the H2 evolu- tion photocurrent gradually decayed under prolonged illumination, and was restored by keeping the electrode in an oxidative condition. Photo- electrochemical cells, with a Ptdeposited n +/ps i electrode and a Pt counterelectrode electrolysed HI into H and triiodide ions under no externally applied voltage with a high solar to chemical energy conver- sion efficiency of 7.8% under simulated solar AM I radiation.

Y. NAKATO, Y. EGI, M. HIRAMOTO and H. TSUBOMURA,J.

Photoproduction of Hydrogen by Dye- Sensitized Systems Z . C . BI and H. TI TIEN,Int. J. Hydrogen Enera, 1984, 9, (813 7'2-722 Visible light induced production of H Z has been investigated in five different systems. Acridine yellow/EDTA/K2PtCls was shown to be the best system examined, and when Triton X-100, a non- ionic interface agent, was added there was a further enhancement in the rate of H2 evolution.

Photogenerated Catalysis by Transition- Metal Complexes. Photoacceleration of t h e V a l e n c e l s o m e r i z a t i o n o f Quadricyclene to Norbornadiene in the Presence of PdC12( q4-norbonadiene) N. BORSUB and C. KUTAL, 3. Am. Chem. soc., 1984, 106, (17), 4826-4828 Light accelerates the rates at which PdC12(q4- NBDXI) catalyses the valence isomerisation of quadricyclene (Q) to norbornadiene (NBD). The observed quantum yield, defined as (mol of NBD produced/mol of photon absorbed), can exceed xo2 and is dependent upon Q concentration, light intensity and solvent.

Photocatalytic Dehydrogenation of Propan-2-01 Using Rhodium Based Catalysts C. G. GRIGGS and D. J. M. SMITH,J. Organomet. Chem.,

Efficient photogeneration of H2 from propan-2-01 can be achieved with a number of preformed Rh' complexes, as well as RhCI3 in the presence of Ph3PO or Ph3P after exposure to air. The turnovers for the Rh' species are in the range 2ooc-6000 mmol HZ/h.mmoVRh, which are much higher than those claimed for such photolytic systems. RhCI3 systems have lower activity (-1000 turnovers).

Effect of the Ru+++ Treatment on the Electrochemical Hydrogen Evolution Reaction at GaAs Electrodes

953-956 The electrochemical HZ evolution reaction (H.E.R.) both at nGaAs and pGaAs electrodes in the dark was accelerated significantly by dipping treatment in RuCI3 solution; but the photocurrents at pGaAs decreased by the treatment. The Ru+++ treatment introduces a catalytic surface for the H.E.R. and also surface states which act as recombination centres.

Redox Polymeric Film Electrode by Electropolymerization of a Pyrrole- Containing Complex of Ruthenium( 11)

1984,273, (I), 105-109

K. UOSAKI and H. KITA, Chem. Lett. Jpn., 1984, (6),

S. BIDAN, A. DERONZIER and J.C. MOUTET, N O U V . 3. 198498, (8/9), 501-503

A photosensitive electroactive electrode was obtained by anodic electropolymerisation of the [Ru(bpy)~L~]~+ complex on Pt in which L is a pyrrolic groupsubstituted pyridine.

Plariiium Metals Rev., 1985,29, (1) 39

Photoredox Reactions in Water-in-Oil Microemulsions. The Functions of Amphiphilic Viologens in Charge Separa- tion and Electron Transfer across a Water-Oil Boundary

Chem., 1984,88, (IS), 4366-4370 D. MANDLER, Y. DEGANI and 1. WILLNER, 3. P h p .

The photosensitised reduction of a series of dialkyl- 4,41-bipyridinium salts, C,V2+ was examined in water-moil microernulsions, by using Ru(bpy)j+ as sensitiser and (NH&EDTA as electron donor. With the amphiphilic electron acceptors (n = 8-18), these microemulsion media affect the charge separa- tion of the initial encounter cage complex [Ru(bpy)j' . . . C.Vr], and stabilise the photoproducts, C,V: and Ru(bpy):+, against the recombination process. Consequently, enhanced quantum yields for C.Vt formation are observed.

ELECTRODEPOSITION AND SURFACE COATINGS New Platinum Plating Process Ensures Numerous Fields of Application for Platinised Anodes H. HEINER, Galvanotechnik, 1985, 7 5 , (IO),

Platinising by electrolysis in the melt at temperatures >500°C in an inert gas atmosphere gives coatings which are distinguished by high adhesion, ductility and freedom from porosity. This enables platinised refractory metals, such as Ti, Nb and others to be used for manufacturing insoluble anodes for use in acid electrolytes. Their use is particularly good as expanded metal, as the actual anode surface is greater than the geometrical one.

Pulsed Current Electrodeposition of Palladium Y. FUKUMOTO, Y. KAWASHIMA, K. MANDA and Y. HAYASHI, Met. Finish., 1984, 82, (9), 77-80 Electrodeposition of Pd from dinitrodiamine, dibromodiamine and dichlorodiamine baths has been performed by applying pulsed current electrolysis. A close correlation was found between crystallographic features of the Pd deposits and the mode of the pulse current. A decrease in grain size of the deposits was observed by using higher pulse current density, longer pulse on-time and shorter off-time which lead to higher cathodic overpotentials. Although desorp tion of HZ from the Pd deposits was expected during off-time, this did not always occur.

Palladium-Nickel Coating System for High Reliability Connectors S. W. UPDEGRAFF, Electron. Ind., 1984, 10, (9), 43, 45-46948 The properties which make a Pd-Ni alloy system superior to gold for application to connectors are reviewed. The Pd-Ni is plated onto square pin con- nectors, and then plated with gold flash.

I27 1-1 272

HETEROGENEOUS CATALYSIS Study of the Composition of Olefins Formed in Conditions of Dehydrogena- tion of n-Decane on Pt /Alz03

YAKOVLEV, M. A. PANFILOVA, L. K. MASLOVA and N. A. ELISSEV, Izv. Akad. Nauk SSSR, Ser. Khim., 1984,

The effect of catalyst composition and of the reac- tion conditions on the ratio of ndecene (with various positions of the double bond) formed during dehydrogenation of ndecane was studied on PdA1203 catalysts modified by MnO. Amount of a, cis- and transdecene, formed during dehydrogena- tion of ndecane was on average in the ratio of 1:8:11, respectively, and no dependence on the catalyst composition was observed. Decenes with internal double bonds were predominantly formed.

Activity, Yield Patterns, and Coking Behaviour of PI and PtRe Catalysts during Dehydrogenation of Methylcyclo- hexane. I. In the Absence of Sulfur. I I . Influence of Sulfur

1984,88, (I), 150-162; 163-176 The conversion of methylcyclohexane decreased less rapidly while selectivity and aromatic yield increased more rapidly over a 20h period with PtRdAl203 than with PdAI203. Coke deposition was retarded on the PtRe as compared to the Pt catalysts. After HZ treatment selectivity and aromatic yield were lower for PtRe than Pt catalyst. Adding small amounts of S lowers hydrocracking for both Pt and PtRe. S retards deactivation of the dehydroaromatisation activity of PtRe catalysts more significantly than for monometallic Pt catalysts.

Kinetics of the Catalytic Decomposition of Hydrogen Iodide in the Thermo- chemical Hydrogen Production Y. SHINDO, N. ITO, K. HARAYA, T. HAKUTA and H. YOSHITOME, Int, 3. Hydrogen Energy, 1984, 9, (81, 695-700 The decomposition rates of HI over Pt/y-Al203 were measured in the temperature range of 480-700K by a flow method. HI decomposed to H2 and I2 and an overall rate equation was obtained according to the Langmuir-Hinshelwood model, assuming the rate determining step was a surface reaction.

Peculiarities in the Conversion of Naph- thenes on Bifunctional Catalysts 1. WEITKAMP, s. ERNST and H. G. KARGE, Erdoel Kohle Erdgas Petrochem., 1984,37, (IO), 457-462 The differences between the reactions of naphthenes and alkanes on bifunctional catalysts are reviewed and some peculiar results from a bifunctional mordenite catalyst are examined. Ideal bifunctional catalysts are PdSi02-AIz03, PdCaY zeolite, Pt/ultrastable Y zeolite and PdLaY zeolite. (39 Refs.)

G. V. ISAGULYANTS, 0. D. STERLIGOV, A. P. BARKOVA, 1. P.

(9), 2049-2053

R. W. COUGHLIN, K. KAWAKAMI and A. HASAN,y. Catal.,

Platinum Metals Rev., 1985,29, (1) 40

Rapid Determination of Heavy Water Concentration by Isotopic Exchange Reaction between Liquid Water and Hydrogen Using Hydrophobic Platinum Catalyst T. TAKAHASHI, s. OHOKOSHI, N. SHINRIKI and T. SATO, BunsekiKagaku, 1984~33, (s), 233-236 A 2% Pt coated on HD4 type styrendvinyl benzene copolymer was used as catalyst to promote the H2-D2 exchange reaction at room temperature and atmospheric pressure. The catalyst did not lose its activity for a long time after contact with water because it is hydrophobic. On losing its activity it can be easily reactivated. The catalyst was used in a gas chromatographic method for the rapid easy deter- mination of heavy water in light water, in concentra- tions 0.01-99.5%.

Hydrogenation of Acetone to Isopropanol with High Efficiency and Selectivity at 330K over Pt-Ti02 I. CUNNINGHAM and G. H. A. SAWED, Nouv. 3. Chim., 19847 87 (7), 469-474 The preparation of finely dispersed Pt on Ti02 and various pretreatments to confer high activity for selective hydrogenation of acetone vapour to isopropanol at 33oK are described. With optimum values of partial pressures P H ~ and Pmo,, in the Ar carrier gas 75% conversions with selectivites )98% were achieved and maintained. Conversion decreased with the reciprocal of the flow rate. H2 dissociation took place at sites involving Pt and acetone attack occurred on TiO2. Effects of differences in P,,,,, and the temperature of prereduction were examined. This catalyst has enhanced catalytic activity at 330K.

n-Hexane Isomerisation and Toluene Disproportionation in the Presence of Modified Platinated Zeolites

SHCHAINBERG, A. PETERS and K. G. NESTLER, Akad. Nauk SSSR, Neffekhim., 1984~24, (3), 335-339 Studies made of n-hexane isomerisation and toluene disproportionation in the presence of o.swt.% Pdzeolite catalysts modified by addition of REE (REE = mixture of -25% Pry 55% Nd and 20% La) and of Mn2+ cations into CaNaY zeolite showed improved catalytic properties. Zeolites REE CaNaY were found to be active during n-hexane isomerisa- tion and MnCaNaY zeolites during toluene disproportionation.

Kinetic Analysis of Complex Catalytic Reac tions G. F. FROMENT, Bulg. Acad. sci., Commun. Dep. Ckm., 1984, 17, (I) , 28-43 Reaction rate data can be obtained in either differen- tial or integral reactions. Examples are given for hydroisomerisation and hydrocracking of n-paraffins on a Pdultrastable-Y-zeolite, for catalytic cracking of gas oil on zeolites and for naphtha reforming on PdA1203. ( 5 5 Refs.)

KH. DIMITROV, R. DIMITROVA, Z. POPOVA, K.G.

Molecular Clusters. Applications in Homogeneous and Heterogeneous Catalysis M. DORBON,R~V. Inst. Fr. Pet., 1984, (4), 497-515 An overview of the metal cluster catalysts in heterogeneous and homogeneous reactions is pre- sented. Various Pt, Pd, Rh, Os, Ir and Ru clusters and their structures and reactions are examined. A general examination of clusters in catalysis, catalysis mechanisms and Fischer-Tropsch syntheses are pre- sented. Olefin hydrogenations and H2 displacement from H20 are examined. The view is taken that cluster chemistry is new and vast and that the catalytic properties of clusters have shown remark- able activity.

Oxidation of Formic Acid in Aqueous Solution of Palladium Catalysts B. CLAUDEL, M. NUEILATI and 1. ANDRIEU,A~~Z. Cata l . , 1984, 1% (2/3), 217-225 Studies of liquid phase oxidation of formic acid by 02, both dissolved in HzO, were made in the pre- sence of supported and non-supported Pd catalysts at I 00-1 5o°C. Determination of diffusional limitations allows an investigation of the rate law in the chemical regime. Appreciable conversions can be reached with a Pd content as low as 50 ppm.

The Influence of High Methane Con- centration on the Stability of Catalytic Flammable-Gas Sensing Elements S. I. GENTRY and P. T. WALSH, sew. Actuators, 1 9 8 4 ~ 5 , (3), 229-238 Studies were made of the effect of the form of the Pd catalyst used in catalytic flammable-gas sensing ele- ments on their stability following exposure to high methane concentration. Improvement in stability to coking effect was achieved either by depositing Pd on a high surface-area support or by using a co- precipitation of Pd and Th. The apparent H solubilities of a series of Pd+Th02 elements with different Pd:Th02 ratios were determined by a temperatureprogrammed technique. The role of Tho2 as a coke prevention agent is to decrease the Pd particle size which results in a lower rate of methane decomposition.

Reduction of NO by H A 0 Mixtures over Silicon-Supported Rhodium:Infrared and Kinetic Studies W. C. HECKER and A. T. BELL,y. c u f u l . , 1984, 88, (2), 289-299 The kinetics of NO reduction by H2CO mixture was studied over a Rh/Si02 catalyst. The presence of CO retards the rate of NO reduction presumably due to competitive adsorption with H2. The catalyst activity is 50% higher when the catalyst is preoxidised rather than prereduced. NH3 formation is suppressed when the catalyst is preoxidised and a product believed to be HNCO is formed instead of urea. In situ i.r. spectra of the catalyst show that at NO conversion below 70% the surface is dominated by adsorbed NO.

Platinum Metals Rev., 1985,29, (1) 41

Alcohol Synthesis from Syngas on Ruthenium-Based Composite Catalysts M. INOUE, T. MIYAKE, Y. TAKEGAMI and T. INUI, Appl. Catal., 1984, 11, (I), 103-1 16 Hydrogenation of CO on Ru-Mo-Na and related catalysts was studied at z55OC and 86kg/cm2 pres- sure. A series of straight chain primary alcohols, together with hydrocarbons were formed on the catalysts. A Ru-Fe-NdAl203 catalyst had consider- able activity for the formation of higher alcohols, but it gave a low alcohol selectivity. Ru-Mc-Ndactive C and Ru-Mo-LdA1203 had high activity for alcohol synthesis, but 70% of this alcohol was CH3OH. The Ru-Mo-NdA1203 catalyst prepared from RuC13 was preferable to the other catalysts.

HOMOGENEOUS CATALYSIS The Platinum Complex Catalyzed Transformation of Primary Amines to Secondary Amine

Aromatic Hydroxylation: the Direct Oxidation of C-Pd into C-OPd

BANDYOPADHYAY and A. CHAKRAVORTY, J . Chem. Soc., Chem. Commun., I 984, (I 5) , ggg-1000 The C-Pd bond in cyclopalladated azobenzenes can be converted into the C-OPd function in good yield by stoichiometric reactions with m-chloroperbenzoic acid. In effect azobenzene is oxidised to 2-hydroxyazo benzene and z,z ‘dihydroxyazobenzene.

Synthesis of Esters by Rhodium ( I ) Catalyzed Borate Ester-Benzylic Bromide Carbonylation Reactions I. B. WOELL and H. ALPER, Tetrahedron Lett., 1984, 25, (39,3791-3794 Studies of the benzylic halides reaction with trialkyl- borates and CO in the presence of 1,s-hexadiene Rh chloride dimer showed the production of esters in excellent yields. The reaction is applicable to the syn- thesis of primary, secondary and even tertiary esters.

A. K. MAHAPATRA, D. BANDYOPADHYAY, P.

Y. TSUJI, J . SHIDA, R. TAKEUCHI and Y. WATANABE, Chem. Lett. Jpn., 1984, (6) , 889-890 The novel catalysis by a homogeneous Pt catalyst is described. In combination with SnC12.zHZ0 it activates a primary amine and catalyses the transfor- mation to secondarv amine at 180°C. Dibutvlamine Co[zecr. Czech. Chem. Commun.~ 1984, 49,

Hydroformylation of Propene Catalyzed w i t h Carbonylchlorobis( triphenyl- phosphine) Rhodium ( I ) M. A. JEGoRoV, L. UHLAR and v.

was obtained from butylamine in 74% yield. 1677-1679 The effect of amines, amino acids, N heterocyclic

Tetrahedron Report Number 166: compounds and urea derivatives on the rate of the Palladium ( 11) - Assisted Reactions of Rh(CO)CI(PPh3)2 catalysed hydroformylation of Monoolefins propene was studied. A positive effect on the L, S, HEGEDUS, Tetrahedron, 1984, 40, (13), catalytic activity was found with modifying ligands

241 5-2434 of very low basicity.

The two major reaction types of Pd(II>complex- catalysis of olefins, the nucleophilic attack of Pd(I1) complexed olefins, and insertion of olefins into u- alkylpalladium(I1) species are discussed. Nucleophiles reacted include 0, N and C, whilst insertion reac- tions involving oxidative addition, transmetallation and “ortho-palladation” are discussed. (74 Refs.)

Regioselective Synthesis of I-Olefins by Palladium-Catalyzed Hydrogenolysis of Terminal Allylic Compounds with Ammonium Formate J. TSUJI, I. SHIMIZU and I. MINAMI, Chem. Lett. Jpn., 1984, (6), 1017-1026 Various terminal allylic compounds, such as allylic esters, phenyl ethers, carbonates, chlorides and vinyl epoxides react with ammonium on Na formate to give I-olefins with high regioselectivity using Pd tributylphosphine complex as catalyst.

Carbonylation with Homologation Reac- tions of Formic and Higher Molecular Weight Carboxylic Acid Esters with Ruthenium Catalysts G. BRACE, G. GUALNAL, A. M. RASPOLLI, G. SBRANA and G. VALENTIN1,hd. E n g . Chem., Prod. Res. Dev., 1984, 23, (319 409-417 The carbonylation and homologation of formic and higher molecular weight carboxylic acid esters catalysed by Ru carbonyl iodide systems at zoo°C and under a CO/H* pressure of rS-zoMPa was studied. The catalyst was active in the hydrogenation of the formyl moiety of methyl formate to methyl derivatives and in carbonylation and homologation.

Kuthenium-Catalyzed Oxidation of Alcohols and Catechols Using I-Butyl I l ydroperoxide Y. TSUJI, T. OHTA, T. IDO, H. MINBU and Y. WATANABE,J.

Selective Palladium Catalysed Mono- Organomet. Chem., 1984,270, (3), 333-341 hydroesterification of Diols S. B. FERGUSSON and H. ALPER, 3. Chem. SOC.,

Ru complexes catalyse the oxidation of alcohols into the corresnondine ketones or aldehvdes when t-

D

Commun., 1984, (zo), 1349-1351 BuOOH (70% aqueous) is used as an oxidant. The Olefins react with diols under oxidative carbonyla- reactions proceed at room temperature to give the tion and acidic conditions, using Pd and Cu(I1) products in good yields. RuC12(PPh3)3 had the chloride as catalysts, to give hydroxy esters. highest catalytic activity.

Platinum Metals Rev., 1985,29, (1) 42

Water-Gas Shift Reaction over Ruthenium Carbonyl Complexes Anchored to Silica via Phosphine Ligands

Acta, Arric. and Lett., 1984,90, (I), L7-Lg The synthesis of Ru carbonyl complexes, anchored to Si02 via phosphine ligands, Ru(CO)+(PPh2CzH4- SILXI) and H~Ru~(CO)~(PP~~C~H~-SIL)~(~), and their catalytic properties for the water gas shift reac- tion are reported. The i.r.spectra of both of the used catalysts were almost identical with their original complexes. Catalyst (2) could be reused without any loss of catalytic activity. Complex (I) exhibited a high catalytic activity for the water gas shift reaction.

Y. DOI, A. YOKOTA, H. MIYAKE and K. SOGA,InOSg. Chim.

FUEL CELLS Funct ional Metal -Porphyrazine Derivatives and Their Polymers. Part 1 1 . Secondary Fuel Cells based on Oxygen Heduction at a Platinum Electrode Modified by Metal-2,9,16,23-Tetra- carboxyphthalocyanine Covalently Bound to Poly ( 2-vinylpyridine-styrene)

TAKEMOTO and N. HOJO, J. Chem. SOC., Dalton Trans., 1984, (8),1485-'489 A new type of secondary fuel cell is described in which 02 evolved by electrolysis of Hz0 in the charging process is stored in the polymer matrix of metal-2,9,16,23-tetracarboxyphthalocyanine co- valently bound to poly(2-vinylpyridinestyrene) (M = Fe"', CoII, Ni" and Cu") on a Pt electrode and then electrocatalytically reduced in the discharging process in 30% KOH aqueous solution. For this cell, there was no significant decay in its characteristics after over 30 chargedischarge cycles.

0. HIRABARU, T. NAKASE, K. HANABUSA, H. SHIRAI, K.

NEW PATENTS METALS AND ALLOYS High Permeability Alloy FURUKAWA ELECTRIC c o . LTD. U.S. Patent 4,435,~ 12

A high permeability alloy of excellent wear resistance, suitable for use in magnetic heads, con- sists essentially of Fe with 3-10% Al, 4-11% Si and 2.1-20% Ru.

CHEMICAL COMPOUNDS Ruthenium and Iridium Pyrochlores EXXON RESEARCH & ENGINEERING CO.

US. Patent 4,440,670 A procedure is described for preparing electrically conductive compounds of formula M2 (M'2-xM.)07-y which have a high surface area. M is Pb and/or Bi and M' is Ru andor Ir.

ELECTRICAL AND ELECTRONIC ENGINEERING Enhanced Quantum Efficiency of PdnSi Schottky Infrared Diodes on < 1 1 1 > Si R. c . MCKEE, IEEE Trans. Electron Devices, 1984, 31, (71,968-970 A two-fold improvement in the i.r. emission efficiency has been obtained on Pd2SVp-Si Schottky diodes through using < I I I > Si for the substrate orienta- tion. Photo response measurements were taken for < I I I > Si and <roo> Si. Leakage current vs. temperature measurements at 6V reverse bias of the PdlSi/gSi < I I I > diodes with guard ring structures, agreed with thermionic emission leakage current theory, using barrier value 0.35 eV obtained by photo response. These results have implications for detection applications.

TEMPERATURE MEASUREMENT

Search for Thermometers with Low Mag- netoresistive Effects: Platinum-Cobalt Alloy F. PAVESE and P. CRESTO, Cryogenics, 1984, 24, (9), 464-470 A systematic set of measurements on Pt-Co ther- mometers of difference Co concentrations have been performed at 2-28K and up to 6T. Also three com- mercial thermometers with o.gwt% Co were used. Pt- Co alloy, with o.gat.% Co was insensitive to rnag- netic fields within &o.gK down to 4K and up to 4T, or within k0.2K above IOK and below 3T. Among high-stability thermometers presently available PtCo alloy showed the least error in magnetic field at fields of a few teslas.

ELECTROCHEMISTRY Electrolysis Electrodes PERMELEC ELECTRODE LTD. British Appl. 2,134,544A Between the conductive metal substrate and electrode active coating (of a platinum group metal or its oxide) of an electrolytic electrode there is an intermediate layer comprising Pt dispersed in a con- ductive mixed oxide of at least one of Ti (IV) and Sn (IV) and of at least one of Ta (V) and Nb (V).

Tetrafluoroethylene Electrolytic Production IMPERIAL CHEMICAL INDUSTRIES P.L.C.

British Appl. 2,135,669A A Pt cathode and Pt or TiOJRu02 anode may be employed in the production of tetrafluoroethylene by the electrolytic reduction of an electrolyte solution containing dichlorodifluoromethane.

Platinum Metals Rev., 1985,29, (l), 43-48 43

Electrolytic Water Sterilisation HIDOTRONIC DE COLOMBIA S.A.

European Appl. I 14,364 A water sterilisation unit relying on oxidation and the release of Ag ions, using Pt and Ag electrodes, respectively, is controlled by a cell which detects the flow rate.

Rechargeable Lead-Hydrogen Cell YARDNEY CORP. European Appl. I 14,484 A new type of design for these cells uses gas-porous negative electrodes containing Pt and/or Pd catalysts.

Durable Electrolysis Electrode T.D.K.ELECTRONICSCO. LTD. US. Patent 4,443,317 An electrode of improved durability, especially for use in brine electrolysis, consists of a valve metal sub- strate coated with a mixture of 40-90 mol% Pd oxide, 0.1-20 mol % Pt and 5-50 mol% (Ru.Til-x)02, where x is 0.05-0.5.

Oxidation Resistant Electrode DIAMOND SHAMROCK CORP. U.S. Patent 4,444,642 Electrodes for use in electrolytic processes consist of a valve metal substrate, such as Ti, and an adherent active outer coating, such as Mn02. In a process for producing electrodes of increased durability by protecting the substrate from corrosion, its surface is treated with a solution of HCI and a platinum group metal chloride and heated to form a mixed valve metaVplatinum group metal oxide film, prior to the application of the MnO2 coating.

Hydrogen-Bromine Cell SIEMENS A.G. German Offen. 3,241,801 In a H-Br cell of reduced cost, the Br electrode is made of pyrolysed graphite and the H electrode of platinised pyrolytic graphite.

ELECTRODEPOSITION AND SURFACE COATINGS Palladium Electroplating Bath

A high speed bath for the electrodeposition of ductile Pd metal consists of a Pd amine complex, (NH4)2S04, ammonium halide, a Group IA metal pyrophosphate and a stress-reduced agent. It may be used to deposit ductile Pd on Cu, Ni, brass, Fe, Au and alloys thereof.

Electroplating Indium on Palladium

O.M.I. INTERNATIONAL CORP. British Appl. 2, I33,04 I A

INSTITUT ELEKTROKHIMII URALSKOGO NAUCHNOGO TSENTRA AKADEMII NAUK SSR

British Appl. 2,136,447A On a Pd substrate there is deposited, by electroplat- ing from a molten salt bath containing In values, a layer which consists of four sublayers, starting from the substrate, (i) a solid solution of In in Pd, (ii) Pd3In, (iii) Pd2In and (iv) &PdIn. The thickness of layer (iv) constitutes 50-90% of the total thickness of

High Temperature Coatings G. K. SIEVERS U.S. Patent 4,439,470 High performance alloy parts such as turbine vanes and blades are protected from corrosion, erosion and wear by applying an electrodeposited film of Rh, optionally a second platinum group metal, an A1203 slurry and a diffusion pack of Al and A1203.

Recoating of Electrodes DIAMOND SHAMROCK CORP. US. Patent 4,446,245 Used dimensionally stable electrodes having a Ru oxide or other platinum group metal coating on a valve metal base are cleaned and activated. The old coating is then enriched in platinum group metal by impregnation using a dilute solution, and a fresh catalytic coating is applied.

Superalloy Coating Compositions HOWMET TURBINE COMPONENTS CORP.

U.S. Patent 4,447,503 Coatings for Fe-, Ni- and Co-base superalloys, having good high temperature oxidation resistance, include Cr, Al, Ta, Mn, optionally W, Si or Hf, up to 5% La, Y or other lanthanide elements, up to 5% of lanthanide and/or refractory metal oxide particles, up to 5% Ti, up to I 5% Pt, Rh or Pd and the balance chosen from Ni, Co and Fe.

LABORATORYAPPARATUS AND TECHNIQUE Capacitive Humidity Sensor VAISALI OY. British Patent 2,133,161A A capacitive humidity sensor has electrode patterns of a chemically resistant metal such as Pt, Pd or Au on a glass substrate and protected by a thin isolator film which may be of Ta oxide or Si02.

Humidity Sensitive Device MURATA MANUFACTURING CO. LTD.

British Patent 2,135,781A A humidity sensitive film in a humidity sensitive device includes a conductive powder such as Pd, and is formed over interdigitated Au electrodes on an insulating substrate.

Carbon Monoxide Sensing Element NOHMI BOSAI KOGYO CO. LTD.

European Appl. I 14,310 An element able to detect CO more quickly and at lower concentrations is made by mixing stannic oxide, Sb oxychloride and Pt in ratios such that Sb : Sn = 2-8 and Pt : Sn =Z--IO and then calcining the mixture at 600-850°C.

Thermal Air Flow Meter HITACHI LTD. European Appl. I 16,144 A meter consists of a hollow cylindrical support made of an insulating material, a heat sensitive resistor (thin Pt wire) and lead wires bonded together by a fired glass layer. This meter measures the flow rate

the coating layer. from changes- in the resistance with temperature.

Platinum Metals Rev., 1985,29, (1) 44

Gas Sensor Construction HITACHI LTD. US. Patent 4,441,98 I

The gas sensor is used for detecting CO, propane, town gas or H2, and unlike known sensors it has electrodes made of the same material. One electrode is coated with an oxidising catalyst and the other is exposed directly to the gas. In the examples Pt electrodes are deposited on a zirconia-yttria solid electrolyte, and the catalyst layer consists of PdAl203.

Catalytic Gas Sensor

A reference element for a catalytic gas sensor with improved life in the presence of combustible gases comprises a filament such as of a platinum alloy with Ir, Rh, Ru or Au, coated with a layer of TiO2.

BACHARACH INSTRUMENT CO. U.S. Patent 4,447,397

JOINING Nickel Alloy Brazing Filler ALLIED CORP. European Appl. I 17,923 Steels and superalloys may be brazed together, such as in nuclear reactor construction, using a filler alloy containing 25-35 at.% Pd, 15-20 at.% Si and the balance Ni. One alloy contains 5 5 Ni, 30 Pd, I 5 Si.

HETEROGENEOUS CATALYSIS Catalytic Heating Apparatus

A catalyst in a forceddraught space-heating apparatus, suitable for vehicles, boats or caravans, is preferably a Pt-based salt deposited on a corrugated, spirally wound stainless steel support.

Power Storage Battery

ROSS JAMES HEATERS LTD. British Appl. 2,133,522A

SOUTH AFRICAN INVENTIONS DEVELOPMENT CORP. British Appl. 2,134,698A

In a power storage battery at least one heat pipe is provided with a catalytic converter for the flameless catalytic combustion of hydrocarbon fuels. The catalytic converter preferably contains Pt or I'd in the pores of a porous ceramic substrate.

Ruthenium Catalysts BRITISH PETROLEUM CO. P.L.C.

British Appl. 2,136,704A Catalysts, which may be used for NH3 production, are prepared by impregnating a C support with a halogen-containing compound of Ru, reducing this compound to Ru metal with HI, and then depositing an alkali metal and a Ba compound.

Hydrocarbon Hydrodesulphurisation Catalyst SHELL INTERNATIONALE RESEARCH Mij. B.V.

European Appl. I 16,383 Hydrocarbon oil fractions are desulphurised by contact with H in the presence of a catalyst contain- ing Pt whiskers. The whiskers may be formed by burning off C deposited on a Pt wire cloth surface.

Hydrogen Peroxide Synthesis AIR PRODUCTS &CHEMICALS INC.

European Appl. I 17,306 P d C catalysts for peroxide production from H2 and 0 2 are improved by using a non-graphic C support having a surface area greater than 400 m2/g and by hydrogenating the Pd after impregnation.

Methyl Methacrylate Production BASF A.G. European Appl. I 17,496 Carboxylic esters are produced from aldehydes and alcohols in the presence of 0 2 and an active Pd-Pb mixture deposited on a support consisting of Zn oxide. Pd is deposited from a Pd salt.

Catalyst for an External Combustion Engine U.S. SECRETARY OF COMMERCE

European Appl. I I 8,430 Catalytic materials suitable for use in an external combustion engine (to act as both a flameless heat source and heat transfer medium) preferably consist of Pt-Rh alloys and the like applied as a coating to the engine head.

Conversion Catalyst Regeneration STANDARD OIL CO. (INDIANA)

US. Patenr 4,435,282 A coke-containing fluid cracking catalyst, particularly of the molecular sieve type, is regenerated by heating it in an O-containing gas in the presence of finely divided particles of a platinum group metal or Re catalyst, preferably Pt itself.

Catalyst Reactivation STANDARD OIL co. (INDIANA) US. Patent 4,435,3 I I

A catalyst consisting of AMS-IB crystalline borosilicate molecular sieve supporting a platinum group metal, especially Pt, is reactivated by treat- ment with water vapour.

Fibre Packs for Ammonia Oxidation (Process) JOHNSON MATTHEY & CO. LTD. U.S. Patent 4,435,373 In a process for the production of HN03 by the oxidation of NH3, a gas stream containing NH3 and 0 2 is passed over a catalyst assembly. This catalyst assembly includes an agglomeration or assemblage of randomly oriented melt-spun fibres fabricated by melt extracting or melt spinning a platinum group metal or an alloy containing at least one platinum group metal. The agglomeration of fibres may be sandwiched between layers of a platinum group metal gauze.

Alcohols and Esters from Synthesis Gas TEXACO INC. U.S. Patent 4,436,838 Alcohols and esters are produced from a mixture of CO and H2 at 500 psig or greater, and I ~ O O C or above in the presence, as catalyst, of one or more compounds, a compound of Zr, Ti, V or Cr and a quaternary phosphonium salt in the presence of an inert oxygenated solvent.

Platinum Metals Rev., 1985,29, (1) 45

Indole Preparation MlTSUl TOATSU CHEMICALS INC.

U.S. Patents 4,436,916117 Indoles are prepared from anilines and glycols using as catalyst at least one metallic oxide, such as Si02- Y 2 0 3 , SiOz-La203, Si02Ce203 and Si02-ZnO- AgO; a sulphide or selenide of at least one of Pd, Pt and Mo; a chloride, nitrate, sulphate or phosphate of certain metals, including Y; at least one of Ir, 0 s and Ru, or metallic Si02 supported on an Al203 or other carrier.

Propylene and n-Butylene Dimerisation SHELL OIL CO. U.S. Patent 4,436,946 A heterogenous Pd cyanide catalyst, optionally supported on Pt cyanide, is used in the selective dimerisation of propylene, I -butene andor 2-butene.

Automobile Exhaust Catalyst REGIE NATIONALE DES USINES RENAULT

U.S. Patent 4,437,926 In a catalytic converter for an I.C. engine the active material is an alloy of 4c-80% Fe, up to 40% Ni, up to 40% Cr, 0.02-0.1% C, 0.05-2% platinum group metal(s) (preferably a combination of 0.2% Pt, 0.15% Ru and 0.05% Rh) optionally activated or stabilised with up to 3% Ce, Cu, Mo, Ti, La, Ca, Y, Al, W and/or Mn which has been subjected to intergranular corrosion with an acid.

Platinum Group Metal Catalysts MOBIL OIL CORP. U.S. Patent 4,444,909 Catalysts for the conversion of synthesis gas to 1-1 OC hydrocarbons, alcohols, aldehydes and ketones consist of a ZSM zeolite and Pt, Pd, Ir or Rh.

Selective Unsaturated Carboxylic Acid Reduction UOP INC. US. Patent 4,446,073 Unsaturated acids may be reduced to esters or alcohols retaining the unsaturation in the presence of a supported mixture of I-10% Cd and O.I-Z% Ru optionally containing 0.01-2.5s platinum group metal. Typically Pt or Pd is used in a catalyst for the reduction of oleic,-crotonic or erucic acid.

Iridium-Containing Catalyst Reactivation

U.S. Patent 4,447,55 I

Ir-containing catalysts containing agglomerated metallic Ir andor Ir oxides can be efficiently redispersed and reactivated by the use of a halide pretreatment prior to a halogen redispersion step, both steps following decoking and reduction of the Ir oxides if present. The agglomerated catalyst may further contain a Pt, Rh, Re and/or Pd cocatalyst.

Ultrasonically Promoted Hydrosilations

EXXON RESEARCH & ENGINEERING CO.

NORTH DAKOTA STATE UNIVERSITY US. Patent 4,447,633

Ultrasonically promoted hydrosilation of non- aromatic C to C 71 bonds is achieved using a platinum metal catalyst.

1.C. Engine Exhaust Gas Treatment FORD MOTOR CO. U.S. Patent 4,448,756 Finely divided Pd and a Pt-Rh three way catalyst are included in the catalyst system used in a process for treatment of exhaust gases from an I.C. engine.

Olefin Oxidation Catalysts

A composition useful for the Wacker catalytic oxida- tion of olefins to carbonyl compounds contains one or more suitable Pd components, one or more suit- able heteropolyacid or Cu components, one or more surfactants as defined and at least one fluorocarbon compound.

Catalytic Converter DEGUSSA A.G. US. Patent 4,450,244 A catalyst for the oxidation of exhaust gases from an I.C. engine fuelled by alcohol consists of a package of alternating flat and corrugated steel sheets, coated with A1203 and impregnated with Pd.

Gas Purification Catalyst M. 0. OSMANOV Russian Patent 1,088,768 In a process for oxidising CO in gas streams also con- taining SO2 over a PtlAlzO3 catalyst, the working temperature is reduced if the catalyst consists of 0.00014-0.00086 mol Pt, 0.05-0.25 mol each of Co oxide, Cu oxide, Ce oxide and A1203 to make I mol.

Laser Catalysts

PHILLIPS PETROLEUM CO. U.S. Patent 4,448,892

UNIVERSAL M A P H E Y PRODUCTS LTD. South African Appl. 8317689

Catalysts for the oxidation of CO to C02 consist of Pd, one or more of Pt, Ru, Rh and Ir and one or more of Cu, Ni, Co, Fe, Mn, Ag, La, Ce, Pr and Nd on a stannic oxide support.

HOMOGENEOUS CATALYSIS Paper Making Polymers Production W. R. GRACE & CO. British Appls. 2,136,816I17A In the production of polymers having a substantially completely saturated polymeric backbone chain with pendant alkylene amine groups, polymers such as polybutadiene, containing an olefinic bond are aminomethylated in the presence of a Group VIII metal compound as catalyst, preferably a compound of Rh, Ru or Ir. These polymers may be used as retention and drainage aids or wet strength additives in paper making.

Isocyanate Preparation

OF INDIA LTD. European Appl. I I 5,660 Isocyanates are produced by the reaction of nitrobenzene or dinitrotoluene with CO in the pre- sence of an Fe, Ru, Rh or Pt carbonyl. Thus nitrobenzene reacts under a loo psi pressure of CO in the presence of triruthenium dodecacarbonyl to give phenyl isocyanate.

INDIAN EXPLOSIVES LTD. AND CHEMICALS AND FIBRES

Platinum Metals Rev., 1985,29, (1) 46

Bicyclic Olefins FIRMENICH S.A. US. Patent 4,443,632 Bicyclic olefins are made from corresponding aldehydes which are obtained by hydroformylation and ring closure of monocyclic ketoaldehydes in the presence of a catalyst such as HRh(CO)(PPh3)3.

Hydroformylation Catalysts EXXON RESEARCH & ENGINEERS CO.

U.S. Patent 4,450,299 The hydroformylation of olefins to aldehydes is cata- lysed by complexes of Rh with Si-containing phos- phines, especially Rh(CO)H(Me,SiCH2CHzPPh& or Rh(CO)H[Me zSi(CH zCH z P P ~ z ) z ] 3.

FUEL CELLS Ternary Fuel Cell Catalysts UNITED TECHNOLOGIES CORP.

British Appl. 2,133,420A A ternary metal alloy catalyst comprising Pt, Cr and Co dispersed on an electrically conductive C black has a catalytic activity for the electrochemical reduc- tion of 0 of at least 2.5 times that of unalloyed F't on the same C black. Preferably the alloy contains 6 1 2 % Cr, 8-14% Co and the balance Pt.

Fuel Cell Electrode HITACHI LTD. U.S. Patent 4,446,210 Fine cracking in the catalyst layer baked on an electrode from a paste is reduced by forming the paste from a mixture of submicron particles, and materials I O ~ - I O * ~ times larger, both materials being electroconductive. The particles may be platinum metal andor C particles.

Fuel Cell Electrode ELECTROCHEMISCHE ENERGIECONVERSIE N.V.

U.S. Patent 4447,505 A fuel cell electrode has a catalytic layer composed of two separately prepared intimate mixtures of a noble metal (preferably Pt) on C having different specific surface areas.

CHEMICAL TECHNOLOGY Metal Powders UNIVERSITY OF PARIS European Appl. I I 3,281 Metal powders are obtained by heating a suspension of a corresponding oxide, hydroxide or salt in a liquid polyol such as ethylene glycol at a temperature above 85OC. The metals which can be so obtained are Pt, Pd, Ir, Os, Au, Cu, Cd, Pb, Co, Ni and Ag.

Heavy Metal Ion in an Absorbing Agent T. A. LITOVITZ European Appl. I I 8,493 Radioactive I is removed from waste streams by passage over porous silicate glass, silica gel or charcoal carrying a heavy metal ion able to bond the I (or another anion). The metal may be Pt, Pd, Pb, Cu, TI or Ag.

Biodispersions

High dispersion metal crystallites dispersed in a car- bonaceous material matrix are produced by growing living microbes in a growth medium containing dissolved metal which is incorporated by the microbes, harvesting the microbes containing the metal and pyrolysing the harvested microbes in an inert or reducing atmosphere. The metal may be Pt, Rh, Ru, Au or Ag.

DIAMOND SHAMROCK CORP. U.S. Patent 4,448,886

CLASS TECHNOLOGY Glass Fibre Spinneret Production OWENSCORNING FIBERGLAS CORP.

US. Patent 4,447,248 An orificed discharge wall for supplying streams of molten glass is made by inserting orificed elements of Pt, Pd, Ir, Os, Rh, Ru or their base alloys in a laminate member of a layer of refractory metal such as Ti, V, Ta, Cr, Mo, W, Re or their base alloys, and a layer of Pt, Pd, Ir, Os, Rh, Ru or their base alloys. Isostatic pressure and heat are used to seal the elements in the member.

ELECTRICAL AND ELECTRONIC ENGINEERING Cathode Ray Tube R.C.A. CORP. British Appl. 2,136,631A A cathode ray tube includes metallised glass beads each coated with Hanovia Liquid Bright Platinum No. 5 by painting, screening, spraying or print transfer, and then curing at 5oo°C to give a Pt-Au alloy coating.

Zinc-Bromine Battery EXXON RESEARCH & ENGINEERING CO.

European Appl. I I 3, I 59 Ru is used to catalyse the recombination of any liberated HZ with bromide ions in a Zn-Br battery.

Ohmic and/or Barrier Contacts on Semiconductors

Ohmic andor Schottky barrier layers are produced on a semiconductor by applying a fresh layer of Si in a high vacuum, applying a layer of Pt, Pd, Rh, Zr, Hf or Ni, sintering to form a metal silicide and finally applying a layer of Al, Ta, Ti, W or Ti-W.

Stain Resistant Ruthenium Oxide Resistors

I.B.M. DEUTSCHIAND G.m.b.H. European Appl. I 15,550

E. 1. DU PONT DE NEMOURS & CO. European Appl. I 15,798

Thick film resistors are mainly based on Ru oxide but high Ru contents are associated with staining by a dark black residue. This is now avoided by introducing an O-containing non-alkali metal com- pound which is stable at up to 15ooC, such as noble metal oxides, chromates, Ag oxide, Ba nitrate, etc.

Platinum Metals Rev., 1985,29, (1) 47

Solar Cell TELEFUNKEN ELECTRONIC c.m.b.H.

European Appl. I 18,797 A solar cell exposed to radiation on both sides has a semiconductor body with Ti-Pd-Ag conductors.

Magnetic Recording Media INTERNATIONAL BUSINESS MACHINES CORP.

U.S. Patent 4,438,066 Magnetic recording media of high coercivity and saturation magnetisation are alloys Col-,Pt, where x is 1*30 at%.

Platinum Coated Silver Powder G.T.E. PRODUCTS CORP. US. Patent 4,439,468 A procedure is provided for coating finely divided Ag powder (90-99.5% of the final product) with an even layer of Pt, for use in conductive pastes.

Ignition Plug NGK SPARK PLUG co. LTD. US. Patent 4,442,375 A self-cleaning plug has a porcelain body with its electrode of Pt, Pd, etc., in a conical depression.

Printed Circuits J. B. O'HARA U.S. Patent 4,444,6 I 9 In producing printed circuits, track areas are electroplated with a Pd-Ni alloy to which both solder and Au plate are directly bondable to provide a joint.

TEMPERATURE MEASUREMENT Temperature Sensors GENERAL ELECTRIC co. P.L.c.BnZsh Appl. 2,134,7 12A In a temperature sensor a metal contact, for example, of Au is separated from an associated region by a barrier layer of an amorphous Ta-Ir alloy.

High Temperature Thermistor GENERAL ELECTRIC CO. U.S. Patent 4,447,799 A thermistor, suitable for use at above 400°C includes fired quantities of conductive paste consist- ing primarily of Bi ruthenate or Ru oxide.

MEDICAL USES Radiodiagnostic Agents BYK-MALLINCKRODT CIL B.V. European Appl. I I 3,135 Specified radio-labelled metallocene derivatives are useful radiodiagnostic agents, especially for examin- ing the kidneys. The central metal atom is preferably Ru, Os, Fe, Cr, V or Co.

New Anti-Tumour Platinum Complexes INCO RESEARCH & DEVELOPMENT CENTER INC.

European Appl. I 13,508 New hydrophobic anti-tumour materials which can be incorporated into phospholipid vesicles are com- plexesof Pt with aphosphatidic acid, amineor diamine.

Electrical Energy Transfer with Living Tissue BIOSONICS INC. European Appl. I 14,s I I Electrical energy may be transferred to and from living tissue using a thin elastomeric glove in which the fingers are provided with Pt electrodes connected to a supply or a load.

Dental Filling Material ESPE FABRIK PHARMAZEUTISCHER PRAPARATE G.m.b.H.

European Appl. I 15,058 A durable dental filling material is a mixture of a curable resin solution and a powdered sintered mixture of a Ca-A1 fluorosilicate glass, Pd, Pt, Ag, Au or alloy thereof and, optionally, a polycarboxylic acid and/or a chelating agent.

Platinum Complexes for Cancer Treatment TANABE SEIYAKU co. LTD. European Appl. I I 5,929 Complexes LPtXX' are useful in the treatment of cancers. L is a 2-aminomethylpyridine and X, X' are each halogen, NO3 or carboxylate, or XX' is sulphate or phosphate.

Medicinal Bipolar Electrode SIEMENS A.G. European Appl. I I 6,280 A bipolar electrode particularly suitable for heart pacemakers is improved by a surface layer (in the active area) which has a high double layer capacity. This layer consists of a refractory metal carbide, nitride or carbonitride applied to a Pt, Ti or other MY.

Anti-Tumour Complexes DEGUSSA A.G. European Appl. I 16,955 New materials for cancer treatment are the com- plexes LPtX2. L is an optionally substituted 1,2- diphenyl ethylenediamine and X2 is an anion(s) such as C1, Br, phosphate, sulphate or maleate.

Blood Lymphocyte Separation TECHNICON INSTRUMENTS CORP.

European Appl. I 19,692 Lymphocytes are separated from whole blood by centrifuging through a barrier made of Pt, Fe, Au or Ag particles (or particles of their alloys) in a hydro- philic material.

Antivirus Complexes RESEARCH CORP. U.S. Patent 4,440,782 New Pr complexes are intended for treating viral infections (for example in fowls). The general description refers to diamine (such as ethylene diamine) and carboxylate (such as malonate) ligands but all of the examples use Pt(NH3)2C12 or Pt(NH3)z(H20)z.

Platinum Wire Electrode MITSUBISHI RAYON CO. LTD. U.S. Patent 4,442,841 An electrode for use in the living body, for measur- ing the 0 concentration in blood, consists of very fine Pt wire coated with cellulose acetate.

Platinum Metals Rev., 1985,29, (1) 48