PLATINUM METALS REVIEW · PLATINUM METALS REVIEW ... cheaper electricity and lower environmental...

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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. 30 JANUARY 1986 Contents Platinum-Clad Electrodes for Magnetohydrodynamic Generators Light-Assisted Oxidation of Cyanide Wastes Increasing Applications for Iridium Platinum Metals in Biomedical Engineering Catalysis by Osmium Metal Clusters Transparent Platinum Films Low Reflectance Coatings Platinum-Zirconium Alloy Catalysts Supported on Carbon or Zirconia The Fabrication of Ultrafine Platinum Wire Catalysis by Metal Complexes Platinum and the Greenwich System of Time-Signals in Britain Abstracts New Patents NO. 1 2 11 12 13 14 20 21 23 27 28 29 38 46 Communications should be addressed to The Editor, Platinum Metals Review Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE

Transcript of PLATINUM METALS REVIEW · PLATINUM METALS REVIEW ... cheaper electricity and lower environmental...

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. 30 JANUARY 1986

Contents

Platinum-Clad Electrodes for Magnetohydrodynamic Generators

Light-Assisted Oxidation of Cyanide Wastes

Increasing Applications for Iridium

Platinum Metals in Biomedical Engineering

Catalysis by Osmium Metal Clusters

Transparent Platinum Films

Low Reflectance Coatings

Platinum-Zirconium Alloy Catalysts Supported on Carbon or Zirconia

The Fabrication of Ultrafine Platinum Wire

Catalysis by Metal Complexes

Platinum and the Greenwich System of Time-Signals in Britain

Abstracts

New Patents

NO. 1

2

11

12

13

14

20

21

23

27

28

29

38

46

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE

Platinum-Clad Electrodes for Magnetohydrodynamic Generators INDICATED LIFETIME WOULD AID COMMERCIALISATION

By V. Hruby, S. Petty and R. Kessler Avco Everett Research Laboratory, Inc., Everett, Massachusetts, U.S.A.

The cornbination of a coal $red magnetohydrodynamic generator and a conventional steam-driven turbo-generator promises greater eficiency, cheaper electricity and lower environmental pollution than conventional power stations. Until recently, the unacceptably short lifetime of the anode electrodes has prevented this promise being fulfilled. Based upon tests described in this paper, it is predicted that the use of platinum-clad electrodes will dramatically increase the expected generator lvetime, thus paving the way to the commercialisation of magnetohydrodynamic energy converters. Approximately I300 hours of electrode operation has now been achieved and an extrapolation of the results suggests a lifetime of 6000 to 8000 hours.

The principle of operation of a magnetohydrodynamic (MHD) generator is elegantly and deceptively simple. An electrical- ly conductive gas, liquid or a combination of both is forced to flow through an applied magnetic field, which produces electromagnetic induction according to Ohm’s law. The concept was first demonstrated by Michael Faraday in 1832 in an experiment conducted near Waterloo Bridge over the river Thames in Lon- don, England. Faraday submerged two copper plates connected by a wire on the opposite sides of the river and observed a slight electric cur- rent flowing through the wire. The expression below is a simplified form of Ohm’s law which explains what occurred in the river:

where J is the induced electric current density within the water, u is the electrical conductivity of the river moving with velocity u, B is the earth’s magnetic field and E represents the in- duced electric field. The same law is of course applicable to any kinetic to electrical energy conversion method. Early electricity generators used large piston engines to rotate solid copper conductors through a magnetic field and later

J ili u (E + uB)

the technology was improved by using turbines to rotate the conductors. However, in a MHD generator it is not a solid metal conductor but a gaseous conductor-in fact a high temperature ionised gas-that passes across the magnetic field created by a powerful magnet.

There are many different MHD generator geometries and many different working fluids (I). The first successful generator was built by R. J. Rosa at Avco Everett Research Laboratory in 1959 (2). It produced about I IkW and used argon as the working fluid. For a variety of reasons, most MHD research being carried out in the United States of America at the present time concentrates on linear generators with the combustion products of coal as the working fluid, the electrical conduc- tivity of which is enhanced by the addition of potassium carbonate “seed”. A typical coal- fired, commercially viable MHD generator converts about 20 per cent of the thermal input power to direct current electricity. Hence, at the exit of the generator most of the thermal energy is still in the gas but it is no longer usable for MHD power production due to its low electrical conductivity. However it is more

Plarinum Metals Rev., 1986, 30, (l), 2-11 2

E LECT R I C I T Y ELECTRICITY

Fig. 1 Coal is burned in a combustor to produce an electrically conducting gas which passes through the magnetic field in the MHD section to generate electric power. The re- maining heat is then used to operate a steam turbine, which produces additional electricity

, i ~ in a conventional way

than adequate to produce steam which is then used to power conventional turbo-generators. The combined MHD/steam cycle, shown in Figure I, is thermodynamically in series and electrically in parallel. It has a potential for con- verting up to 60 per cent of the coal's energy in- to electricity, compared with 35 to 40 per cent for a conventional power plant. In addition the MHD generator removes most of the sulphur from the effluent due to a sulphur/potassium reaction inherent in the process, while at the same time nitrogen oxides are reduced to a level

significantly lower than the U. S. Environmen- tal Protection Agency's New Source Perfor- mance Standard (NSPS). Furthermore, the requirement for cooling water at a MHD power plant would be considerably less than that of a conventional power station, leading to reduced thermal pollution. The economic and some of the environmental advantages of a combined MHD/steam power plant over a conventional steam-only-plant are shown in Figures 2 and 3, respectively.

Because of its promise, MHD has been the

1

Fig. 2 The Energy Conversion Alter- native Study has determined that MHD power plants will give higher operating ef- ficiencies and cheaper electricity than modern base load steam plants (6). A com- bined MHDlsteam bottoming cycle plant will be capable of producing 50 per cent more power from a given amount of coal than a modern steam plant (1 mill = 0.001 U.S. dollar)

Fig. 3 The sulphur oxides and nitrogen oxides produced in a MHD plant will be appreciably less than those produced in a modern steam plant of the same power generating capacity and will be well below the U.S. Environmental Protection Agen- cy's New Source Performance Standard (NSPS)

Platinum Metals Rev., 1986, 30, (1) 3

STEAM POWER PLANT

CLEAN EFFLUENT

MUD CHANNEL

ELECTRIC FIELD

I

I 0.M

1000

100

10

4 c I----------?

PAMIR I 1972 r r U R A L 1976

r K H I B I N Y 1977

COMMERCIAL^ I BASELOAD I RETROFIT I

MAY 1965 M K P L _ _ _ _ _ _ _ _ _ _ J

1982 0

\ 1968

V I K I N G 0 I M K l l 1964 0 C D l ? l 9 3 MK 1978

1973 0

E T L M K P ,ETL M K m 1975 1982 0

UTSI 1970 M K m 1982

10 1 10 1 100 1 3 1 s e x hours m x h s ye;r?r

0 001

OPERATING T I M E

Fig. 4 This map of achieved power output and operating times demonstrates the pro- gress made in MHD technology. For commercial viability the performance would have to fall within the indicated target area.

MK I, MK 11, MK V, MK VI, MK VII, LDTE, VIKING, Avco Everett Research Laboratory Inc. (AERL Inc.) Everett, Massachusetts, U.S.A.

LORHO, Tested at Arnold Engineering Development Center, Tennessee, U.S.A. Designed and built by AERL Inc. CDIF, Tested at Component Development and Integration Facility, Butte, Montana, U.S.A. Built by AERL Inc.

ETL MK V, ETL MK VII, Electrotechnical Laboratory, Ibaraki, Japan. PAMIR 1, URAL, KHIBINY, Portable fired by solid fuel rocket, U.S.S.R. U25, High Temperature Institute, Moscow, U.S.S.R. UTSI, University of Tennessee Space Institute, Tullahoma, U.S.A. AEDC, Arnold Engineering Developing Center, Tennessee, U.S.A.

subject of active research for almost three decades in many countries all over the world (3). The efforts intensified in the early seventies and since that time many problems which then seemed insurmountable have been solved.

The chosen strategy, illustrated in Figure 4, was to follow what became known as the two axis approach. Briefly stated this meant perfor- ming two types of experiments: the first, high power but short duration experiments aimed at investigating flow and plasma effects, and the second, small, lower power experiments aimed at investigating channel life-ldting effects. This dual approach reduced developmental risk and was less expensive than a programme that addressed all the issues in one experiment. Figure 4 identifies the boundaries of progress achieved to date. While raising the power boun- dary was not hard to achieve, extending the lifetime boundary was very difficult due to the extremely harsh operating environment in the generator channel.

Currently the Soviet Union is the closest to commercial MHD generation. A 500 MW MHD plant is being constructed about 100

miles east of Moscow. Several other countries including the U.S.A. are considering the so- called MHD Retrofit, which is the addition of a MHD topping cycle to an existing conven- tional steam plant.

A typical commercially viable coal-fired MHD generator, shown schematically in Figure 5, may be 10 to 20 metres long, with a I m2 flow cross-section and will have hundreds of pairs of current collecting electrodes. The generator walls are subjected to a heat flux reaching 400 W/cm2 , to corrosion/erosion resulting from the hot (2500 K) high speed (1000 m/s) slag, sulphur and potassium laden gas flow, and also to electric fields that locally reach 10 kV/m. About 50 per cent of the inter- nal surface of the generator is formed by elec- trodes, shown in Figure 6. Their operating conditions are further complicated by the

Platinum Metals Rev., 1986, 30, (1) 4

Fig. 5 A typical coal fired MHD generator could be 10 to 20 metres long and con- tain hundreds of pairs of electrodes. The electrically conducting gas produced by the combustion of coal enters the MHD generator at 3000 K, 10 atmospheres of pressure and a speed of 1000 metres per second; it leaves for the steam boiler at 2400 K and 1 atmosphere

Fig. 6 Only three anodes are shown in this assembly but hundreds would be m- quired in a commercial MHD generator. The upstream edge of each water cooled electrode is protected by an electrochemical resistant metal cladding and the elec- trodes are separated by boron nitride insulators

Electrode walls-, Anode (top) Cathode (bottom)

t ing wa l ls on

superconducting magnet coal combus oroducts with

/' beed and slag 1

:&y f

EL. cur rent

4 Magnetic field

'lag layer I Axial (Hall) \ 1- EL. f ie ld

E lec t r ic a1 connect ion and mounting

t e r connections

Insulator

transport of current which can be either diffus- ed or constricted (arcing). Of the two types of electrodes, namely anodes and cathodes (defin- ed as electron emitters), the anodes have proved to be the life-limiting component of the generator and a major design challenge.

Anode Development Severe corrosion is caused by the elec-

trochemical attack on anode surfaces by negatively charged ions of oxygen and sulphur oxide radicals. These ions are liberated from the coal slag by arc current transport through the slag layer, and are driven to the anode sur- face by the electric field. Oxidation and sulphidation of the anodic surfaces, along with arc melting, were the major barriers to the development of long duration electrodes.

Early electrode designs consisted of various configurations of castable ceramics in metallic holders. To keep the ceramic hot and to reduce boundary layer joule dissipation, the gas-side metal surfaces operated at high temperatures and served as the current lead-out. Electrode voltage drop and heat transfer losses were minimised with this design. However, rapid ox- idation of the metallic holders and slag fluxing of the ceramic resulted in short lifetimes. In order to achieve the durations required for cen- tral power stations, electrode designs evolved to progressively colder metal temperatures and minimal ceramic surfaces consistent with the development and retention of a continuous slag layer.

In 1978 a significant milestone was achieved. A 500 hour test had been undertaken in two

Platinum Metals Rev., 1986, 30, (1) 5

Etectmc he6 caI resistant metal clad 1

water cwled electrude body

Fig. 7 In 1978 a significant improvement in anode life was achieved by cladding the upstream edge and anodic surfaces with platinum. These results of a 250 hour test show that the electrode erosion suffered by the earlier design of anode (left) was avoided on the platinum clad modifica- tion (right). Plasma flow is leR to right

parts, with a complete tear-down inspection at the 250 hour midpoint. At this inspection the weak points of each electrode design were fairly obvious. Clearly the nickel alloy cladding used for anodic protection in the interelectrode gaps did not have sufficient oxidation resistance. Design modifications were therefore made to a small number of anodes and cathodes which were then incorporated in the second 250 hour test segment. The modified anodes used 0.010 inch thick platinum cladding on anodic surfaces and the upstream corner was reinforced with a 0.62 inch square platinum bar. Comparison of the 250 hour corrosion results for the initial and

the modified designs are shown in Figure 7. A dramatic improvement is clearly evident in the platinum modified design.

Neither of these duration tests was made with sulphur in the plasma, which would be the case with coal combustion. Therefore a series of shorter duration tests (30 to 50 hours) were then conducted using sulphur additions, in amounts similar to those present in the combus- tion products of typical coals, with sulphur con- tents of 0.5 and 5 per cent, simulating Montana Rosebud and Illinois No. 6 coals, respectively. In the search for electrodes and in particular anodes, with adequate reliability and durability to satisfy the requirements of commercial operation a large number of configurations and candidate materials were evaluated. The noble metals tested for use as cladding materials were platinum, platinum-rhodium-iridium alloys, palladium and gold. The following basic elec- trode design criteria were established:

[i] A massive, well-cooled electrode body of high thermal diffusivity (copper) to retard elec- trolytic activity and quench electric arcs;

[ii] Anodic surfaces protected with a thin cladding of oxidation- and sulphur-resistant material;

[iii] Well-cooled inter-electrode insulators of good thermal conductivity to reduce current leakage and/or voltage breakdown;

o 1oo"square plat inum 0 125"square p la t i num

I , O.02O"plat inum /0.030" €8 26-1 / jstainles5 steel 8 1 F l o w ' / 0 0 6 0 " E B 2 6 - 1

- passage

Channel wall

CONFIGURATION No 1

CONFIGURATION No 2

Fig. 8 Two configurations of MHD anode design have recently been tested for over 1000 hours in the Avco Mark VII power train. The water cooled copper elec- trodes are protected from oxidation and sulphidation by platinum in conf i iat ion No. 1 and by platinum plus stainless steel in configura- tion No. 2

Platinum Metals Rev. , 1986, 30, (1) 6

E iec t r I c a I connect ion

Boron n i t r i d e 0.075"

Fig. 9 The major components of the Avco Mark VII MHD power train are indicated, the 5 6 pairs of electrodes being located within the one metre long channel which produces a nominal 55kW

[iv] A slag-covered surface to protect the metallic electrodes from mechanical erosion by particle impact and to reduce their operating temperature as well as to minimise heat loss to the cooling water.

Various anode designs meeting these criteria were recently tested for over 1000 hours of operation (4). Two of the most successful con- figurations are shown in Figure 8. These repre- sent the current state-of-the-art anode design, and are made of water-cooled copper with ox- idation and sulphur-resistant cladding attach- ed. Both designs have the upstream edges reinforced with platinum because the axial Hall field produces current concentrations along this edge. In configuration No. I the remainder of the anodic surfaces are clad with platinum foil while in configuration No. z a nickel-free stainless steel is used. The other anodes tested were variations of these two primary designs and cladding was accomplished by vacuum fur- nace brazing with a gold-nickel alloy.

The 1000 hour test was performed in the

Avco Everett facility shown in Figure 9. Coal combustion was simulated by injecting fly ash and sulphur dioxide into the oil-fired com- bustor, the weight fraction of sulphur being 0.18 per cent of the total mass flow. The generator is one metre long and has 56 pairs of electrodes. Figure 10 shows the averages of cur- rent density, Hall (axial) electric field and elec- trical power density as a function of electrode number. The locations of the two primary anode configurations (Figure 8) are also shown.

Results and Discussion Upon completion of the test, visual observa-

tions and a complete photographic record were made of each channel wall. The walls were carefully cleaned of attached slag and dismantl- ed for individual weight measurements and photographic documentation. Slag samples were subjected to detailed analysis.

The general appearance of the anodes after the 1000 hour test was excellent. Figures I I and IZ show the post-test condition of anodes of

Platinum Metals Rev., 1986, 30, (1) 7

Fig. 10 The positions at which the two designs of elec- trode were used are shown here, together with the three average electrical parameters generated during the 1000 hour duration test

8- 357 16-

7. 3.0. 14.

ELECTRODE MMBER

Fig. 11 Magnetohydrodyn- amic anodes of configuration No. 1 after 100 hours of power generation show that protecting the leading edge and the anodic surfaces with platinum has reduced ero- sionlcorrosion of the anode lo levels which suggest that platinum clad anodes could be used under the particular- ly harsh conditions prevailing in the first (upstream) third of a MHD channel (plasma flowing left to right)

Platinum Metals Rev., 1986, 30, (1) 8

Fig. 12 ARer tests lasting 100 hours the satisfactory condition of these platinum and stainless steel clad anodes of configuration No. 2 enabled testing to con- tinue. On the basis of pre- sent results it is suggested that this configuration of anode could be used in the middle third of a commercial MHD channel

design configurations No. I and No. 2 after removal of the slag layer.

Each anode was weighed at the start of the test, after 500 hours and at the completion of 1000 power hours. The mass loss for all the electrodes in the channel is given in Figure 13. Except for the extreme ends of the generator- Electrodes I to 7 and 46 to 56-the loss distribution resembles the current density pro- file shown in Figure 10. This indicates that the primary variable is the total charge that the electrode transports, as is shown by Figure 14. The slopes of the lines fitted through the two sets of data correspond to an erosion rate of 0. I I pg/coulomb for platinum electrodes and 0.24 pglcoulomb for the platinum/stainless steel electrodes. Furthermore the data indicate zero mass loss at zero current for the platinum electrodes but for the platinum/stainless steel electrodes there is a finite mass loss even at zero current. Thus it is evident that all, or nearly all

of the platinum loss is due to electrical arcing or electrochemical attack whereas the stainless steel loss is partly mechanical and/or chemical erosion.

Detailed analysis of selected anodes suggests that the major cause of mass loss is melting and vaporisation caused by arcing. Figure 15, a scanning electron micrograph, shows an arc track on the surface of a platinum electrode (s), while Figure 16 shows the termination point of an arc on the platinum surface of the same elec- trode. Both clearly reveal melting. Further analysis of the surface of similar electrodes found no platinum/sulphur compounds ( 5 ) . Thus all the evidence indicates melting and vaporisation to be the mzjor cause of platinum loss. However other experiments suggest that the level of sulphur concentration does affect the rate of platinum loss, by reacting with local- ly molten metal.

Extrapolation of the 1000 hour erosion

Platinum Metals Rev., 1986, 30, (1) 9

A A ,

A

Iatinurn 6 Staidless Steel -IgatinurnA I

#- uw 4.0 w

2.

A

A

A

A A

A," o.".""o O O &A A M i l o o 0 0

00"" 00 0% O

-0 od3°000

12

0

0

24 )r GRAMS/COULOMB % O A

A

\ 0.11 p GRAMS/COULOMB

I ' I

10 M 30 4 0 TOTAL TRANSPORTED CHAROE.CWLOMBSXI~~

Fig. 14 These plots of mass loss versus electrical charge transported indicate that platinum clad anodes are eroded at a rate of 0.1 lpg/coulomh, while those protected by platinum and stainless steel lose metal at a rate of O.24pglcoulomh

o platinum and stainless steel, configura-

0 platinum and stainless steel, configura- tion No. 2, at 1000 hours

tion No. 2, 500 hours A platinum and stainless steel, configura-

A platinum and stainless steel, configura- tion No. 1, at 1000 hours

tion No. 1 at 500 hours

Fig. 13 Except for the two ends of the MHD channel, the mass loss distribution during the 1000 hour test resembles the current densi- ty profile, shown previously in Figure 10

measurements made on the platinum clad anode design indicates an electrode life of ap- proximately 7500 hours. This assumes a uniform recession of the metal and is based on a current density of 0.6 A/cm2. In an optimised 500 MW baseload MHD-steam power plant the MHD channel would have the following cur- rent density profie:

front third: middle third: 0.5 to 0.25 A/cm2 rear third:

0.8 to 0.5 A/cm2

0.25 to 0.10 A/cm2 thus, based on the recent test results, the recommended anode configurations to yield a life of 6000 to 7000 hours would be:

front third: platinum upstream corner +

middle third: platinum upstream corner +

rear third: The platinum required for the electrodes in a

5 0 0 MW generator would total 4500 troy ounces representing about 0.1 per cent of the world annual production and would cost around U.S. $1.2 million at today's prices. This represents less than 0.5 per cent of the estimated plant cost and would add at most 0.05 cents per kWh to the estimated cost of electricity. This cost could be reduced by re- claiming the platinum remaining on discarded

platinum anodic surface

stainless steel anodic surface stainless steel anodic surface.

Platinum Metals Rev., 1986, 30, (1) 10

Fig. 15 This arc track across a platinum clad electrode surface, as seen under the scanning electron microscope, indicates melting of the platinum; the evidence suggests that melting and vaporisation are the major causes of platinum loss. The directions of plasma flow and arc move- ment are from top to bottom on the micrograph, which is reproduced here at a magnification of x 600 approximately. Reprinted from Reference (5)

electrodes or captured in the slag. However the amount is difficult to estimate, and therefore zero platinum recovery has been assumed. Thus neither the cost nor the availability would prevent the use of platinum for this potentially important application.

Testing anodes clad with platinum and with platinum plus stainless steel continues, with the objective to demonstrate 2000 operating hours. To date the electrodes have accumulated about 1300 hours. Basic studies of arcing and arc ero- sion on platinum electrodes are proceeding con- currently.

Light-Assisted Oxidation Many industrial processes including the case

hardening of steel, electroplating and ore refin- ing can result in waste waters that contain toxic concentrations of cyanide. These may be destroyed by alkaline chlorination or direct electrolytic oxidation, but the former produces considerable volumes of sludge for disposal while the latter incurs high energy costs.

However, recent work by C. E. Byvik of the National Aeronautics and Space Administra- tion’s Langley Research Center and A. Miles of Southern University has demonstrated another oxidation techniaue. and this is effective in

Fig. 16 An arc termination point on a platinum clad electrode surface again shows melting of the platinum, indicating that this is a cause of platinum loss during power generation. The magnification here is approximately x 1200. Reprinted from Reference (5)

References I R. J. Rosa, “Magnetohydrodynamic Energy

Conversion”, McGraw-Hill, New York, 1968 2 R. J. Rosa, Phys. Fluids, 1961, 4, (z) , 182 3 Proc. 8th Int. Symp., Moscow, U.S.S.R.,

September 1983 4 V. J. Hruby, R. Kessler, S. W. Petty and P.

Weiss, “1000 Hour MHD Anode Test”, 17th Intersociety Energy Conversion Engineering Conference, Los Angeles, August 1982, 3, 1223-1228

5 D. A. Brosnan, “Microscopic Examination of Electrode Surfaces after Avco’s Sulfur Test No. 6”, UTSI-81-7, Report No. FE-10815-66

6 NASA Lewis Research Center, Document No. NASA TM X-73515, “Evaluation of Phase 2 Conceptual Designs and Implementation Assess- ment Resulting from the Energy Conversion Alternatives Study (ECAS)” prepared for Energy Research & Development Administration and Na- tional Science Foundation, 1977

of Cyanide Wastes are significantly below those achieved by established methods (“ Solar-Assisted Oxida- tion of Toxic Cyanide”, LAR-I317I/TN, NTZS Tech. Notes, October 1985).

In their solar-assisted oxidation technique, oxygen-containing air is bubbled through the waste cyanide solution, in which platinised titania powder is suspended, while it is sub- jected to either artificial or M t U d sunlight. The platinised semiconducting powders can be recovered and reused, and the results suggest that the process could become an effective and inexpensive method of treating cyanide- . ,

reducing cyanide concentrations to levels which containing industrial waste water.

Platinum Metals Rev., 1986, 30, (1) 11

Increasing Applications for Iridium By J. R. Handley Johnson Matthey Metals Limited

In recent years the rapid development of computer and telecommunication technology, together with North Sea oil rigs and deep space probes, has resulted in a demand for new iridium products. Iridium is unique in having a high melting point (2443OC) coupled with significant oxidation resistance, and is the only metal with good mechanical properties in air at temperatures above 1 6 o o O C .

The largest growth area has been for iridium crucibles suitable for growing oxide single crystals such as gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG). GGG and YAG are used for computer memory devices and solid state lasers, respectively. The crystals are grown by melting presintered burdens of mixed oxides in an iridium crucible under oxidising conditions at temperatures up to ZIOO~C, using the Czochralski technique. The increasing demand for larger sizes of these crystals has caused the size of crucibles required to increase from a volume of 80 cc to 6280 cc necessitating a corresponding increase

in wall thickness from 1.5rnm to 4.omm. Various techniques have been used to manufac- ture iridium crucibles such as fabrication from hot rolled sheet, hot spinning, fused salt plating on to a mandril, powder metallurgy and, in more recent times, the latter followed by hot isostatic pressing. Fabrication from hot rolled sheet is the only technique which consistently produces crucibles meeting the stringent re- quirements of dimensional tolerances together with a structure which contains a minimum number of defects.

The Noble Metals Group of Johnson Matthey Metals Limited has developed soft and ductile iridium sheet with a maximum metallic impuri- ty content of tm ppm. The production pro- cess used can control the principle impurity elements of tungsten and iron and reduce all other non platinum group metals content to a level of I to 30 ppm. This sheet can be satisfac- torily formed in one operation into cylinders for flat bottom crucibles, or hot pressed to produce the bases for round bottomed crucibles with

Used for melting the mixed oxides from which gadolinium gallium garnet single crystals are grown, this flat bottomed iridium cruci- ble is one of the larger sizes, having a diameter of 180mm and a capacity of 4330 cc

Platinum Metals Rev., 1986, 30, (11, 12-13 12

diameters up to 200mm. All welds in the finish- ed crucibles are X-rayed to check that they have no significant porosity, and are crack free.

A smaller, but growing market exists for the radioactive isotope iridium 192, used as a port- able gamma ray source. These are typically us- ed for radiographing pipe lines, rigs, and other civil engineering structures, and for radiation therapy treatment of cancers. The iridium is sup- plied to radiochemical companies generally as finewires oras discso.5 to3.oomm in diameter, with a thickness of 0.1mm up to 3mm. Even larger slugs of iridium, 6mm in diameter and romm thick, may be supplied. The isotope 192 is produced by irradiating the iridium wires, discs or slugs consisting of the natural isotopes of iridium, namely 191 and 193, in a nuclear reactor. However of the two isotopes only 30 per cent of the natural iridium occurs as 191 which produces the useful isotope 192.

A thorium-iridium alloy has been developed

by Oak Ridge National Laboratory in the United States of America. Tests carried out at Johnson Matthey Metals, Wembley have shown that the addition of 60 ppm of thorium to iridium halves the rate of oxidation and in- creases its stress rupture life by 50 per cent at 15oo~C. This alloy has been used by NASA as a containment vessel for plutonium in the ther- moelectric generators used on deep space pro- bes, while a similar alloy with a higher thorium content has been used as long life spark plug electrodes for aero piston engines. The addition of 1000 ppm of thorium to iridium prevents grain growth in the heat affected zone of welded iridium electrodes and improves the erosion resistance. Indeed the erosion resistance of iridium surpasses that of all other materials in this electrode application.

The unique combination of properties of iridium suggests that its use will increase as other new applications emerge.

Platinum Metals in Biomedical Engineering Pacemaker Leads, Progress in Biomedical Engineering, Volume 2

EDITED BY A. E. AUBERT AND H. ECTOR, Elsevier, Amsterdam, 1985, 420 pages, Dfl. 235,00/u.s. $87

Over the past quarter of a century notable ad- vances have been made in the performance and reliability of the electronic systems that are us- ed to provide cardiac pacing. Problems remain, however, and to seek solutions to some of these an International Symposium on Pacemaker Leads and electrodes was held from the 5th to the 7th September 1984 at the Catholic Univer- sity of Leuven, Belgium. Now fifty-nine of the invited lectures and contributed papers have been published in the Proceedings which pro- vide a clear picture of the present state of the art. They also serve as a useful introductory guide to the subject.

Pacemaker leads have two main functions: to conduct electrical pulses to the heart and to sense intra-cardiac signals and transmit these to the pulse generator. The performance of the electrode at its interface with the cardiac tissue is crucial to the satisfactory functioning of the pacing system and many of the papers con- sidered the size and geometrical configuration of the electrode tip, the material of construction and the condition of the surface.

On account of their biocompatibility and cor-

rosion resistance, coupled with their electrical properties, platinum and platinum alloys became the preferred materials for electrodes during the I ~ ~ O S , although carbons, titanium and multi-component base metal alloys also find application. In order to improve further the results obtained with these materials, engineering modifications to the electrodes con- tinue. In earlier years, lead dislodgement was a problem but now this may be overcome by the use of hooked, screw-in or tined electrode tips. To improve sensing amplitudes and achieve the lowest possible threshold values a variety of electrodes have been constructed. Platinum tips may be in the form of ball-tips, discs, half domes or rings, and the surfaces may be polish- ed, etched, porous or even laser drilled.

Amply supported by references, this book is likely to become a standard source of informa- tion on pacemaker leads. Collaboration bet- ween people from many different disciplines has enabled cardiac pacing to achieve very con- siderable success. This evolution must be con- tinued, and therefore these Proceedings are commended to the readers of this journal.

Platinum Metals Rev., 1986, 30, (1) 13

Catalysis by Osmium Metal Clusters

Lossia’ per cent

By S. David Jackson

and Peter B. Wells I.C.I. New Science Group, The Heath, Runcorn, Cheshire

Department of Chemistry, The University, Hull

Products of T.P.D. per cent CO CO, C,H,+C,H,

Recent studies of catalysis by supported metal cluster compounds have shown that these systems exhibit novel behaviour. Although diffzcult to characterise, by using a combination of analytical techniques an overall picture can be developed of the cluster nuclearity and the number and type of ligands present. Chemisorption and catalytic studies have both shown behaviour fundamentally different from that obtained with con- ventional metal catalysts.

Over the last decade the interest in the use of metal cluster compounds, especially the car- bonyls, as catalysts has grown steadily ( I). This area of research has many attractions, state-of- the-art preparative inorganic chemistry coupled to catalysis using defined molecular species, sounds too good to be true; and it is. The ob- vious attractions are well balanced initially by often difficult preparations with low yields but may be heavily counter-balanced by the dif- ficulties of characterising the catalytically active species when it is a small metal cluster com- pound. In the last five years we have been in- volved in a major study of catalysts prepared from supporting osmium carbonyl cluster com- pounds on materials such as silica, alumina,

and titania. In this review we will briefly ex- amine the characterisation, chemisorptive behaviour, and catalysis of these systems and give a biased view on where cluster catalysis may go in the future.

Characterisation Without doubt unequivocal characterisation

of supported cluster compounds is a difficult, if not impossible, task. In our attempts to characterise these species we have used infra- red and ultraviolet-visible spectroscopies, temperature programmed decomposition, elec- tron microscopy and Extended X-ray Absorp- tion Fine Structure (EXAFS) analyses; none of these techniques on their own was definitive

Table I

Characteristics of Temperature Programmed Decomposition of Osmium Cluster Catalysts

Catalyst

Os, (CO),,/AI,O, Os,(CO),,/SiO, Os,(CO),,/SiO, Os,(COl,,/TiO, H,Os, (CO),,/TiO, H, Os, (CO 1 ,, /A1 , 0,

40 27

5 27 18 13

aa 9 3 92 8 0 0 100 0

82 16 2 45 50 5 39 60 1

CO-ligands retained per 0 s

2.2 2.8 2.8 2.0 2.2 2.4

la’ Total carbon loss expressed as the percentage of CO-ligands converted to products

Platinum Metals Rev., 1986, 30, (l) , 14-20 14

but taken together a consistent description of the systems can be achieved. Catalysts prepared

and H, 0 s ,,C(CO) 24 supported on silica, alumina, and titania were characterised after impregnation of the cluster onto the support and after temperature programmed decomposi- tion (heating to 523K) (2). Immediately after impregnation both infrared and ultraviolet- visible spectroscopies indicated that the majori- ty of the starting cluster was intact on the sup- port although bands not attributable to the starting cluster were apparent. On heating the samples both carbon monoxide and carbon dioxide were produced and by 473K the bands

from (CO) , Os, KO) , H, Os, (CO) 12 ,

not attributable to the starting cluster were the dominant features in the spectra; by 523K they were the only features of the spectra. Table I and Figure I show typical results; there is significant ligand retention and the three band infrared spectrum is common to all the samples. However we needed to know whether the species formed after heating was a cluster. To answer this question we turned to ultraviolet-visible diffuse reflectance spec- troscopy and EXAFS. A study by Tyler, Leverson and Gray (3) on the ultraviolet-visible absorbance spectra of Os,(CO) ,, assigned bands at 330 and 385nm to u-a* and a*' -u*

transitions, that is transitions involving orbitals

4

1 I I 2000 1 BOO 2 000 1800 - ' 2dOO 1sbo

Fig. 1 Typical infrared spectra measured on conversion from starting cluster to one giving three bands: (a) initial spectrum of Os, (CO) /alumina; (b) spectrum of (a) after heating to 523K; (c) initial epectrum of Os, (CO) I Ititania; (a) spec- trum of (c) after heating to 5238; (e) initial spectrum of H40s,(CO)12/titania; (0 spectrum of (e) after heating to 523K

Platinum Metals Rev., 1986, 30, (1) 15

Tabla II

Peak Maxima in UltravioletNisible Absorbance and Reflectance Spectra

355,394 320 394

352,397 317 394

Sample

442.463.530.595 540.61 3,870

476 597,869 540,6 1 3

Os,(CO),,'a'

os, (CO) 18'a)

OS,(CO),,/AI,O,'~' H,Os,(CO),,/SiO,'b' Os, (COI ,JAI2 Oltb)

u - u* and

transitions ,J*' - g'

244 209,242 223.233 220 226,231

Unassigned

Band maxima (nm) I 289 296

273,286 279

269,283

Unassigned

18) In solution in cyclohexane Ib) Reflectance spectra after samples had been heated to 523K Icl M.L.C.T. = metal-ligand charge transfer

associated with 0 s - 0 s bonds. Table I1 shows the bands in this region of the spectrum for various clusters and catalysts, clearly the bands are present on the samples after heating, in- dicating a retention of 0 s - 0 s bonding. However a more definitive answer was given by EXAFS. Figure 2 shows the EXAFS spectra of Os,(CO),,/alumina after heating to 523K (4) and that of a conventional osmium/silica catalyst; clearly interpretation of the spectra is not simple, but the important points are (i) Os- 0 s bonding was retained, (ii) the cluster species did not have the same spectra as bulk metal, and (iii) the average co-ordination number for nearest neighbour osmium atoms was 4. Therefore the species on the support was a cluster. A full analysis of an H 0 s , ,C(CO) ,/alumina catalyst has shown that the tetra-capped octahedral skeleton is in- tact after activation ( 5 ) .

The infrared spectra obtained exhibited three bands, shown in Figure I . The band at 203ocm-' is typical of carbon monoxide linear- ly bonded to zero valent osmium, while we have assigned the low frequency band to carbon monoxide linearly bonded to osmium in a 6- negative valence state and the high frequency band to carbon monoxide bonded to osmium in a 6-positive valence state.

From the temperature programmed decom- position experiments, the number of carbonyl ligands retained during the heating process was

known; however for catalysis to occur some degree of co-ordinative unsaturation must be present. We investigated this via the chemi- sorption behaviour of the cluster catalysts.

Chemisorption The chemisorptive properties of the sup-

ported osmium clusters were investigated using carbon monoxide and oxygen as adsorbates (6). Typical adsorption isotherms are shown in Figure 3. Although the carbon monoxide isotherms are typical for the cluster catalysts they are not typical for carbon monoxide ad- sorption on conventional metal catalysts; the difference lies in the slowly rising part of the isotherm above 0.2 Torr. Below 0.2 Torr there is rapid adsorption of the gas on free metal sites, above there is slow adsorption on sites which have been produced during the thermal activation. These sites we have designated "ligand-C"; they are produced when two carbonyl ligands react to give carbon diox- ide, 2CO - CO, + C. The adsorption on ligand-C by carbon monoxide is reversible at zg3K whereas adsorption on the metal is not. The carbon monoxide can be desorbed from the metal sites by heating to 523K. By this method the adsorption/desorption cycle can be repeated time and time again. When carbon monoxide is adsorbed, carbonyl ligands are still present on the cluster and by adsorbing labelled [ ISO] car- bon monoxide it was possible to show that only

Platinum Metals Rev., 1986, 30, (1) 16

0 .

- 1 .

1

w t 2 0 3

> a 4 - 1

t a: -l W-

t

I 0

5 ' -I

- 1

100 300 500 700 PHOTON ENERGY.ev

Fq. 2 EXAFS spectra of (a) a conven- tional silica-supported osmium catalyst prepared from the trichloride; (h) an Os6 (CO) , /alumina catalyst after heating to 523K; (c) freshly impregnated 0s (CO) , /alumina

0.1 a2 0.3 0.4 0.5 0.6 0.7 0.8 0 9 PRESSURE, Torr

I

Fig. 3 Carbon monoxide and oxygen ad- sorption isotherms: (a) CO adsorption on H, 0 8 , (CO) Ititanin; (b) 0 adsorption on H, 0 8 , (CO) ,z Ititanin; (c) CO adsorption on 0 8 , (CO) /alumina; (d) O2 adsorption on Os6 (CO) ,,/alumina

labelled carbon monoxide was desorbed; no isotopic scrambling took place even at a temperature of 523K (6, 7).

Oxygen adsorption looked at fust sight similar to adsorption on conventional metal catalysts, however the energetics of the adsorp- tion were fundamentally different from conven- tional metal catalysts. On heating to 5 q K all the oxygen was desorbed from the surface without any reaction with the carbonyl ligands. This weak bonding (for oxygen) was found to have interesting consequences when the catalytic behaviour of these systems was sub- jected to a thorough examination.

Catalysis Four reactions were studied in detail over the

osmium cluster catalysts; the hydrogenation of ethene, carbon monoxide and carbon dioxide, and the hydrogenolysis of ethane (7,8). We will consider each of the reactions in turn and com- pare them with results from conventional catalysts. However certain aspects of the catalysis were common to all the reactions and their implications will be considered first.

One aspect of the novel chemistry en- countered with cluster catalysts, which was common to all, was their insensitivity to poison- ing by &/oxygen (9). An active cluster catalyst could be removed from a reactor, exposed to air, replaced in the reactor and reaction con- tinued at the same rate as before without any in- duction period. The process was repeatable and the length of time the catalyst was exposed to air made no difference (Table 111). The reason for this insensitivity is related to the strength of oxygen adsorption on the osmium clusters. Because the osmium is already engaged in bon- ding to the carbonyl ligands, to other osmium, to the support, and to ligand-C, the bonding to adsorbed oxygen is weak. As a consequence oxygen does not dissociate on adsorption, con- trary to the behaviour on osmium metal. Another general aspect of the catalytic chemistry of these systems was the non steady- state. When any of the reactant mixtures were passed over the catalysts there occurred a period of non steady-state behaviour (8). The

Platinum Metals Rev., 1986, 30, (1) 17

Table 111

Activities of Cluster-Derived Catalysts Before and After Exposure to Air at 2 9 3 K (a)

Catalyst Initial rate before Duration of Initial rate after exposure to airlbl exposure, hours exposure to air

1 .1

2.8

0.2 2.0

24.0 0.2

1 . 1 1 . 1 1 . 1 2.8

la1 Reaction, C,H. + H, - C,H. at 435K and a pressure of lOOTori (bl Rates pmol/rnin/g catalyst

form this behaviour took is shown in Figure 4; initially the activity increased to a maximum then decreased to the steady-state value. Dur- ing this behaviour carbonaceous material was deposited on the catalyst and the maximum in activity was reached when the amount deposited was equal to the number of sites. Our interpretation of this behaviour is that the deposited material acts as a hydrogen-transfer agent which is more efficient for hydrogen transfer than the osmium metal sites. As the amount deposited increases so does the rate un- til every site has a deposit, at this point a max- imum is reached. The decrease in activity is due to site blocking effects and steric hindrance as deposition continues. One other general aspect of the catalytic behaviour of these osmium cluster catalysts, which is specific to them, was the variation in activity which follows the shift in frequency of the low frequency infrared band (Figure 5 ) . The variation in position of this band is caused by differing amounts of electron-density being transferred from the support to the osmium. Therefore when there is the largest transfer of electron-density the 0s-C bond is strengthened and the C = 0 bond weakened due to increased back-bonding from the osmium into the anti-bonding orbitals of the carbon monoxide. The effect this has on the catalytic activity can be explained by changes in the strength of adsorption brought about by the varying electron-density. When there is a large amount of transfer the chemisorptive bond is strong and hence activity low; as the amount transferred decreases the activity increases with

I I

1 2 3 4 5 6 7 8 9 1 0 PULSE NUMBER

Fig. 4 Typical non-steady state behaviour, showing an increase in rate to a maximum followed by a decrease to the steady state value. Carbon monoxide hydrogenation to methane over an 0 s (CO) I /silica catalyst

31

1980 1960 1% 5 V, crn-l

Fig. 5 Volcano relationship for CO hydrogenation. Rates, r (mollslg) divided by that for H 0 s (CO) /silica (H2S).

Codes, 3 = Os,(CO), *, 4 = H,Os,(CO)I,, 6 = O S ~ ( C O ) I ~ , 10 = HzOs I oC(C0) 2 4 9 H 2 = H 2 0 s 3 (CO) i o 9

S = silica, A = alumina, T = titania, C = ceria

Platinum Metah Rev., 1986, 30, (1) 18

Table IV

A Comparison of Activation Energies'.' and Ratedb)

Reaction Catalyst

H, Os, (CO),,/SiO,

Os, (CO),,/TiO, Os, (CO),,/SiO, Os, (CO),,/TiO, H,Os,C(CO),,/AI,O, Os/Al,03

o S 3 (CO)i,/AI,O,

C,H, + H, - C2Hs'C1 CO + 3H, - CH, + H,O'd' Ea ~ w m r 3 9 0 Ea I 0 g 1 O r 6 0 5

42(378-406K) 0.25 50(390-500K) - 1.65 44(355-390K) - 0.15 41(385-425K) -0.09 45(325-425K) -0.54 53(520-590K) -2.25 35(290-320K) Ie'

1 1 4(485-561 K ) 0.03 951540-645K) -3.21 931485-570K) -0.62 73(590-665K) -0.32 80(465-605K) - 2.00

1221520-590K) - 1.07 1 19(500-560K) - 0.09")

~~

la) €a in kJ/mol lbl Rates in rmol/s/g catalyst IcI C,H,:H, ratio, 1:l

Id) CO:H, ratio, 1:3 le) Instantaneous reaction, see Reference 1 0 ( f I For experimental details see Reference 1 1

reducing strength of adsorption until a max- imum is reached. Further reduction in the strength of adsorption causes a reduction in the

tained throughout the hydrogenation reaction these results may suggest that on a conventional catalyst there is a significant proportion of

concentration of reactive species and a subse- quent reduction in activity.

The hydrogenation of ethene over the osmium cluster catalysts required a significant- ly higher temperature than that required over a conventional metal catalyst, similarly the activa- tion energies were also higher than those found with a conventional osmium catalyst (Table IV). Positive orders of reaction in ethene for the cluster catalysts compared with zero order for conventional catalysts suggested that ethene ad- sorption on the cluster catalysts is weak. Hence higher temperatures are required to obtain measurable rates from low steady-state concen- trations of adsorbed ethene. Therefore for this reaction the behaviour of the cluster catalyst is similar to that of a carbon monoxide poisoned conventional osmium catalyst.

Carbon monoxide hydrogenation over the cluster catalysts was, for the most part, similar to carbon monoxide hydrogenation over con- ventional catalysts: the activation energies were similar and the products (methane and carbon dioxide) were similar. However, generally the cluster catalysts were significantly less active than their conventional counterparts, although some (notably the silica supported) were as ac- tive (Table IV). As the carbonyl ligands are re-

-e

-7

P 0 0, -8

-Q

-1 0

I

1.6 2 .o 2.4 10' KIT

Fig. 6 Variation of rate with reciprocal temperature (log,,rT = -Eapp/2.303RT + C) for ethane hydrogenolysis (C2H6 + H, - 2CH,), r has units mol/.s/g I

Platinum Metals Rev., 1986, 30, (1) 19

inactive carbon monoxide present on the sur- face during hydrogenation.

The hydrogenolysis of ethane to methane was the one structure sensitive reaction studied and again there were differences between the cluster catalysts and conventional catalysts. For this reaction the activation energies were lower and the activities significantly higher than conven- tional osmium catalyst, see Figure 6. This was the first indication that cluster catalysts could outperform conventional systems. The reason for this superior activity comes about, we believe, due to a change in reaction mechanism when osmium cluster catalysts are used. Because the cluster has a limited number of sites the ethane may not fully dissociate (that is C,H, -+ C-C + 6H), as is the case with conventional osmium catalysts, but retains most of its hydrogen prior to C-C bond rupture.

The Future Research is continuing and will continue into

heterogeneous catalysis by supported metal cluster compounds but the era of them being the “great white hope” for catalysis, if it ever existed, is now dead. These catalysts should be studied for their own sake and for the insight they can give into conventional catalysis but not as the wonder catalysts of the future. Only in the area of structure sensitive reactions do cluster catalysts hold any promise in terms of “applied catalysis” and even here the activity and/or selectivity enhancement would have to be spectacular to overcome the negative aspect of cluster production on a large scale. Even so, cluster catalysts do exhibit novel behaviour, an understanding of which may lead to a question- ing of long held beliefs in catalysis or greater in- sight into areas which are ill understood. Support interactions is one area where we believe cluster catalysts may give us informa- tion not readily available from conventional catalysts. Site interactions, which are ex- ceedingly difficult to study in conventional catalysts, are far more open for study when the number of atoms in a cluster is limited, the ligands specified and the geometry known. None of these answers will be easy to obtain but

the possibilities are there for using cluster catalysts to help our understanding of fun- damental aspects of catalytic chemistry.

References I D. C. Bailey and S. H. Langer, Chem. Rev . ,

1981, 81, 109; S . D. Jackson, P. B. Wells, R. Whyman and P. Worthmgton, “Catalysis, Volume 4”, a Specialist Periodical Report, Royal Society of Chemistry, London, 1981

2 G. Collier, D. J. Hunt, S. D. Jackson, R. B. Moyes, P. B. Wells, A. F. Simpson, and R. Whyman, 3. Catal., 1983, 80, 154

3 D. R. Tyler, R. A. Leverson and H. B. Gray, J. Am. Chem. SOC., 1978, 100, 7888

4 D. J. Hunt, S. D. Jackson, R. B. Moyes, P. B. Wells, P. Worthington and R. Whyman, J. Mol. Catal., 1983, 20, 289

5 S. D. Jackson, S. R. Morris, R. B. Moyes, P. B. Wells, R. Whyman and P. Worthington, paper submitted to Journal of Caralysis

6 D. J. Hunt, S. D. Jackson, R. B. Moyes, P. B. Wells and R. Whyman, 3. Catal., 1984, 86, 333

7 D. J. Hunt, S. D. Jackson, R. B. Moyes, P. B. Wells and R. Whyman, Proc. VIIIth Interna- tional Congress on Catalysis, Vol. 5 , Verlag Chemie, Basel, 1984

8 S. D. Jackson, R. B. Moyes, P. B. Wells and R. Whyman, 3. Catal., 1984, 86, 342

9 D. J. Hunt, S. D. Jackson, R. B. Moyes, P. B. Wells and R. Whyman, J . Chem. SOC., Chem. Commun., 1982, (I), 85

10 G. C. Bond, G. Webb and P. B. Wells, Trans. Faraday SOC., 1965, 61, 999

1 1 S. R. Morris, Ph.D. Thesis, Univ. Hull, 1982

Transparent Platinum Films When prepared by a conventional evapora-

tion technique, a film of platinum 33 nanometres thick will transmit only about 3 per cent of light. However, workers at two Bell establishments in Murray Hill, New Jersey have reported that the same thickness of film prepared by photoelectrodeposition onto in- dium phosphide can transmit as much as 92 per cent of light at wavelengths between 210 and 750 nm (A. Heller, D. E. Aspnes, J. D. Porter, T. T. Sheng and R. G. Vadimsky, J. Phys. Chem., 1985, 89, (21)~ 4444-4452).

Although this high transparency is due par- tially to porosity in the film, it is achieved main- ly by controlling the microstructure of the deposit so that the particles which make up the film are small, compared with the wavelength of the light, and are not well connected.

The work reported may lead to several new areas of research.

Platinum Metals Rev. , 1986, 30, (1) 20

Low Reflectance Coatings PLATINUM BLACK FOR INFRARED TECHNOLOGY

By F. J. J. Clarke and J. A. Larkin National Physical Laboratory, Teddington, Middlesex, England

In recent years, the infrared region of the spectrum has acquired a new importance due to rapidly developing technology which has divers applications, many of which are concerned with energy conservation, space, or the military. Coatings with a very low reflectance over the thermal infrared region, that is which absorb nearly all the incident radiation, are valuable for the components and screens which make up the optical systems used in sensing, measuring or imaging infrared radiation. This is especially true of the actual detectors of radiation used, many of which are thermal detectors which need a coating of uniformly high absorptance over the infrared spectrum.

The National Physical Laboratory (NPL) has recently set up new measuring capabilities to cover the infrared region, and an investigation of coatings for detectors was carried out as part of this endeavour (I). The measuring technique involved the use of a novel NPL hemispherical reflectometer/transmissometer(2,3,4), the prin- ciple of which is illustrated in Figure I. This facility allows the complete set of radiometric properties of a surface to be evaluated over the whole thermal infrared spectrum, from 2.5 to 55 micrometres. Another aspect of the in- vestigation was the angular scattering characteristics, which were measured at Sira Ltd. (I) and which complemented and confm- ed the conclusions of the spectral reflectance measurements at NPL.

The coating for a detector needs to be fully absorbing yet thin enough not to add significantly to the thermal heat capacity, and at the same time it needs as high a thermal con- ductivity and thermal diffusivity as possible. This combination of properties suggests finely divided metals as the best solution, but not as powder adhering by means of a bonding agent:

the metal must be spongy or dendritic and directly “grown” on the metal substrate.

Chemical, electrochemical, or sputtering techniques are preferred, and examples of a number of finely divided metal black coatings were prepared and investigated. Preparations of nickel black, aluminium black and platinum black were made by various techniques (I), but gold black was excluded because it had been ex- tensively investigated elsewhere ( 5 ) and also was known to be difficult to prepare re- producibly. A characteristic of all such coatings is that beyond a certain wavelength, determin- ed by the thickness and metal, the coating ceases to be opaque. The best known of the special purpose black paints for radiometric ap- plications, Nextel IOI - CIO manufactured by the Minnesota Mining and Manufacturing Company, was also included to give a standard of performance for comparison purposes.

Optical axis of Spect rophotorneter -*- - - _ - - -

-- Optical axis - - _ _ - -

Water jacket

Measurement of hemisphere radiance L h ( h )

Fig. 1 The NPL hemispherical reflec- tometer/transmissometer when used as reflectometer. L,(A)/L,(X) gives the dif- fuse reflectance of the sample

Platinum Metals Rev., 1986, 30, ( l) , 21-22 21

Sample

Measurement of sample radiance L s ( h )

Hemisphere mirror

WAVELENGTH, pm [ log.scale1

Fig. 2 Spectral reflectances 3 ? ? 6 8 ’? ’ 5 ‘? 25 3’ . 4’. ?O

over the whole thermal in- frared spect- for four preparations of platinum e0 black, which are suitable for radiometer coatings W

;

n W‘

2 40- I

I .. . .... 40- 2600 lsbo lob0 860 660 a-60 Z ( M

WAVENUMBER. an-‘ (log.scale)

- For sensitive pyroelectric _ _ - - - directors --- For laser power meters -.-

Results showed that platinum black had the best properties of the materials investigated. Figure 2 shows the spectral reflectance data over the whole thermal infrared spectrum for four preparations of platinum black. The substrates were of polished copper, chosen because of its high reflectance to reveal any deficiencies of opacity. Curve A shows ex- cellently low and non-selective values for a coating of 6.8 mg/cmz, which is less than would be required for any known black paint to achieve comparable performance. The other curves shown in Figure z are preparations of only around 0.6 mg/cm* , chosen to be as thin as is compatible with achieving low reflectance up to around 10 micrometres. This is the re- quirement for high-performance detectors sens- ing through the atmospheric transmission band from 8 to IZ micrometres; the water and carbon dioxide in the atmosphere cut down at- mospheric transmission severely in most other parts of the infrared spectrum. Curves B and C are the results of attempts to prepare identical coatings, and indicate that reproducibility is a problem for platinum black when grown on a substrate.

Organisations with special expertise in preparing these platinum black surfaces are:

AWRE at Aldermaston, Plessey Research (Caswell) Ltd. and Thorn-EM1 Ltd. Applica- tions other than detector coatings are: black reference plates and targets for radiometric calibration of infrared systems; coatings on reference black body cavities (specially critical when the cavity has to be rather flattened in shape, as with some satellite or spacecraft ap- plications); non-reflecting coatings around the edges of diffraction gratings, lenses and mir- rors, and their supports; and small heat ex- changers or external skin radiators in aerospace applications. In all these cases the cost of platinum is not a problem, but for other larger- scale applications, like commercial solar heat exchangers, other coatings would be more cost- effective.

References I D. B. Betts, F. J . J. Clarke, L. J. Cox and J. A.

Larkin, J. Phys. E: Sci. Instrum., 1985, 18, 689 2 F. J . J. Clarke, Proc. Soc. Photo-Opt. Instrum.

Eng., 1980, 243, 40 3 F. J. J. Clarke and J. A. Larkin, Infrared Phys.,

1985, 259 359 4 F. J. J. Clarke and J. A. Larkin, High

Temp.-High Pressures, 1985, 17, 89 5 L. Harris, “The Optical Properties of Metal

Blacks and Carbon Blacks, Monograph Series No. I”, Massachusetts Institute of Technology and the Eppley Foundation for Research, 1967

Platinum Metals Rev . , 1986, 30, (1) 22

Platinum-Zirconium Alloy Catalysts Supported on Carbon or Zirconia By R. Szymanski and H. Charcosset Institut de Recherches sur la Catalyse du CNRS, Villeurbanne, France

The preparation of platinum-zirconium alloy catalyst systems is described and their characterisation reveals interesting structures. Studies on a number of catalytic reactions indicate that these alloy systems have catalytic properties significantly different from platinum on zirconia systems. In addition these catalysts do not segregate into platinum and zirconia or zirconium carbide either in air at atmospheric pressure or under conditions used in catalytic processes.

There are only a small number of elements that may be used in the metallic state under catalytic reaction conditions. It is therefore often useful to combine two metals in the form of an alloy catalyst. This is readily achieved in the case of two elements easily obtained by reduction, but very few studies have been per- formed on the preparation, characterisation and catalytic activity of supported alloy catalysts in which a metal such as platinum is alloyed with a Group IV element like zirconium, which by itself would be very difficult to reduce to the metallic state. This type of alloy has been in- vestigated previously mainly in the form of electrocatalysts for phosphoric acid fuel cells (I, 2). The studies described here deal with the preparation of platinum and zirconium (Pt,-,Zr,) supported alloys and their catalytic properties, especially for the gas phase conver- sion of hydrocarbons. The effect of alloy forma- tion on the catalytic behaviour of platinum can be rationalised in terms of dilution and/or elec- tronic effects.

Preparation and Characterisation of the Carbon Supported Catalysts

The method used to prepare these alloy catalysts can be represented by the following equation:

( I -x)R + xZr0, + ZXC + Pt1-,Zrx + zxC0 The carbon acts both as the reducing agent and as the support for the metallic phase. The driv-

ing force for alloy formation could be the high free energy of formation for the well defined in- termetallic compound Pt,Zr. Ott and h u b , who studied this reaction with reference to cor- rosion phenomena, found that alloying started at about gooK via the formation of a face cen- tred cubic solid solution Pt,-,Zr,, up to the limiting value of 25 atomic per cent zirconium at higher temperatures, where there was evidence of the intermetallic compound Pt Zr being formed (3). In the previous works, the starting materials used for alloy formation were mixtures of zirconia with platinum and carbon (3) or platinum on carbon (I), or the precipita- tion of zirconia on platinum on carbon (2).

The originality of our preparative procedure is in applying the conventional co-impregnation methods, used for the preparation of heterogeneous catalysts, to support precursor salts of the dloy components. These salts are further decomposed to obtain intimate mix- tures of platinum and zirconia on the carbon support. Preparative details and other data for the catalysts are indicated in Table I (4).

Alloy formation was followed by X-ray dif- fraction (XRD) measurements. Figure I shows the variation in the percentage of zirconium alloyed as a function of temperature. The same results were obtained for the two supports. The limiting value of 25 atomic per cent zirconium alloyed is in good agreement with that reported by Ott and Raub (3). The profile of the XRD

Platinum Merals Rev., 1986, 30, (l) , 23-27 23

Tabla I

Platinum + Zirconia Supported on Carbon Catalysts, Heat Treated in Vacuum in the Temperature Range 673 to 1273K, for 2 hours

Temperature, K

6 7 3

7 7 3 to 8 7 3

8 7 3 to 1 2 7 3

1 2 7 3

T = 1273K. Pto75 Zr,,,/C After a long time in contact with air at room temperature Conditions to restore the initial state.

State of the catalyst

R + ZrO,/C

Onset of formation of Pt, ~x Zr,/C

Increase of x from 0 up to 0 .25

Pt,,, Zr,,,/C . Per cent dispersion of the alloy phase (Pts + Zr,: Pt + Zr ratio) is 1 3 per cent (C Merck), or 4 . 5 per cent (C Vulcan 6) Heterogeneity of particle size distribution

. Constant Zr : Pt ratio, in all alloy particles

. ZrO and PtO are both present in the alloy particles

. Surface composition is close to Pt, Zr,

Surface segregation into Pt and ZrO,. Alloy preserved inside the metallic particles Heat treatment in hydrogen at temperatures 2 973K

lines suggested a broad particle size distribution and this conclusion was confirmed by electron microscopy.

X-ray emission analysis performed on Pt, Zr/C catalyst using Scanning Transmission Electron Microscopy (STEM) showed that this alloy catalyst has a very uniform composition from one particle to another (5). Electron Spec- troscopy for Chemical Analysis (ESCA) ex- periments on the same catalyst, kept in air at room temperature after preparation, indicated the presence of both zerovalent platinum, and zerovalent zirconium. At least in the metallic particles the zirconium is present in the metallic state and not as a platinum-zirconium-oxygen solid solution.

The re-oxidation which takes place in air under atmospheric conditions is confined to the surface of the alloy particles. In fact no segrega- tion into platinum and zirconia could be detected by XRD. Ion Scattering Spectroscopy (ISS) and Auger Electron Spectroscopy (AES) both confirmed these conclusions (6). AES pro- ved in addition that reactivation in hydrogen at 673K did not restore the alloy surface to its in- itial state, but that reactivation at 973K or

Platinum Metals Rev., 1986, 30, (1)

above did achieve this (6), when the surface composition is then close to Pt0,5Zr,,5, a figure which was confirmed by hydrogen/oxygen chemisorption data (6). The oxidation state of zirconium in the outer layer of the alloy surface directly exposed to the gas phase could not be established unambiguously but ‘‘ZrsO” is among the species likely to be present.

Preparation and Characterisation of the Zirconia Supported Catalysts

The reducing agent used for these prepara- tions was hydrogen and the reaction can be represented as follows: (r-x)Pt + xZrO, + zxHI - Pt- ,Zr , + 2xH,O This reaction has been studied previously but not with the objective of preparing catalysts (7, 8). Approximately 10 weight per cent platinum catalysts supported on zirconia were prepared (6) and reduced by hydrogen for 2

hours in the temperature range 623 to 1273K. The same temperature dependency of the ex-

tent of zirconium alloying was observed for both the (Pt/ZrO, , H,) and the (Pt + ZrO,/C, vacuum) systems. The limit of solubility of zir- conium in platinum (Pt3Zr) was also found to

24

I- z r I

Reaction

(a) Hydrogenation of benzene

(b) Competitive hydrogenation of benzene and toluene

(c) Hydrogenolysis of ethane

(d) Hydrogenation of carbon monoxide

Fig. 1 The variation in the amount of zir- conium alloyed to platinum is shown as a function of the temperature at which platinum + zirconia supported on carbon, or platinum supported on zirconia were heat treated in vacuum or in hydrogen. A Merck active carbon A Vulcan 6 carbon black v Degussa aerosol

Catalytic properties

No effect of the support (C; ZrO,) or of alloying (Pt,_,Zr,) on the TON (per Pt,). Once poisoned by H,S, Pto,75Zro,,5 is more easily reactivated by heat treatment in hydrogen than platinum

KT,B (Relative coefficient of adsorption of toluene and benzene) increases almost linearly with the at.% Zr alloyed

Whatever the support (C; ZrO,) TON decreases due to Pt-Zr alloying

. TON (Pt) (CH,; CH,OH) is much greater for Pt/ZrO, than for

. Pto,75Zro,,5/Zr0, or C, reactivated in H, at only 673K,

. Pto,75Zr,,,5/Zr0, or C, reactivated in H, at 1023K, have

greater selectivity to methanol formation)

Pt/AI,O, or SiO, or C

behaves like PtlZrO,

catalytic behaviour different from PtlZrO, (in particular a

be the same. The particle size distribution of platinum in Pt/ZrO, reduced at both 673K and 1 q 3 K was very broad. The variation in disper- sion of the Pt,-,Zr, as a function of the temperature of reduction has been studied us- ing hydrogen and oxygen chemisorption (9) and

for example, the metal dispersion decreased from 11 to 12 per cent to 4 to 5 per cent as the temperature was varied from 673 to 1240K, with most of the change occurring between 873 and 973K. The surface concentration of zir- conium was about twice its mean concentration over the entire range of x values in Pt,-,Zr, (which is the same as that described above for pto.75z~0.2s~c)~

Catalytic Properties of Platinum- Zirconium Alloy Catalysts

The reactions studied were (a) the hydrogenation of benzene including resistance to poisoning by hydrogen sulphide, (b) the competitive hydrogenation of benzene and toluene, (c) the hydrogenolysis of ethane and (d) the hydrogenation of carbon monoxide (6, 11, 12). The results are summarised in Table 11. The alloy effects may be rationalised in terms of the following factors:

Dilution of Platinum Surface Atoms (Pt,) The platinum atoms are surrounded by inac-

tive zirconium surface atoms probably oxidised or carbided (Zr,O or Zr,C).

In fact, no significant variation of turnover

Platinum Metals Rev., 1986, 30, (1) 25

Table II

Comparison of Some Catalytic Properties of Platinum and Pt, -"ZrX Supported by Carbon or Zirconia

numbers (TON) was detected in reaction (a) whereas a decrease was observed (about one order of magnitude) from platinum to Pto,,5Zro.25 whatever the support, in reaction (c). It is generally assumed that the active sites are composed of a low number of contiguous Pt, in reaction (a) and a larger number in reac- tion (c). Accordingly, a simple dilution effect of Pt, by inactive Zr, could account for the ex- perimental results .in these reactions.

Electronic Modifications of Platinum Due to Alloying

Reaction (b) allows the determination of the relative strengths of adsorption of toluene and benzene (KT,* = bT/b,, the ratio of the ad- sorption coefficients), by using the kinetic analysis proposed by Tri and colleagues (10). These authors showed that KT/B may be related to the electron density of states of platinum in supported platinum catalysts, the larger the KT/B value, the more electrophilic the platinum metal (10).

On platinum-zirconium alloys, the increase of the KT/e value observed from platinum to Pt0,75Zr0,,5 whatever the support (I I) suggests a modification of the electron density of states of alloyed platinum, and this confers on it an electrophilic character. This was corroborated by poisoning experiments performed over platinum and Pto.75Zro.25 supported catalysts in reaction (a). In fact, alloyed platinum was found to be more resistant to hydrogen sulphide poisoning than platinum alone and was more easily reactivated by heat treatment in hydrogen; weakening of the Pt-S bond on the alloy catalyst being due to platinum electro- deficiency.

Dilution of Pt, by Active “ZrgO” Species Evidence was obtained for a zirconia support

effect on platinum in reaction (d): the methana- tion turnover numbers on Pt/ZrO, catalysts were found to be about 20 fold higher than those for platinum supported by alumina, silica or carbon, depending on the heat treatment of the zirconia support (12). The lower the calcination temperature of that support, the

higher was the zirconia support effect. It was further shown that the zirconia support effect needed a direct contact between platinum and zirconia since no such effect was found for mechanical mixtures of platinum on silica catalyst and zirconia support.

In the case of Pt0,,5Zr0~,5 alloy catalyst, reac- tivated in hydrogen at 1023K, an enhanced ac- tivity and a higher selectivity for methanol formation was found for both zirconia and car- bon supported systems. These same catalysts behaved like platinum on zirconia when reac- tivated at only 673K. These results, cor- roborated by the ESCA, Auger, and chemisorption (H,, 0,) characterisation methods account for an insufficient restoration of the alloy surface in hydrogen at 673K. The surface is then presumably composed of Pt, atoms and Zr,02 “patches”. Over the alloy catalysts reactivated at higher temperatures, the specific alloy effect could then be accounted for by dilution of Pt, by Zr,(O) atomic species par- ticipating in reaction (d).

The exact mechanism of action of ZrO, (Pt/ZrO,) or(and) of “Zr,O” (Pt0,,5Zr0,25 reac- tivated at high temperature) in the (carbon monoxide, hydrogen) reaction cannot be deduced from our investigations. It seems also that it cannot be unambiguously deducible from the published scientific literature which is relevant to similar effects (11).

Conclusion It can be said that our alloy catalysts have

shown some interesting effects. For all four reactions studied the X-ray diffraction patterns were found to be the same at the end of the catalytic run as at the beginning. This strongly suggests that the Pt, -xZrx supported catlaysts could be used without any segregation of the alloy components under conditions used in catalytic processes.

Acknowledgement Raymond Szymanski gratefully acknowledges

financial support of the work leading to his doctorate from the French Institute of Petroleum, where he is now working.

Platinum Metals Rev., 1986, 30, (1) 26

References I V. M. Jalan, D. A. Landsman and J. M. Lee,

U.S. Patent 4,19z,go7; 1980 z P. N. Ross, Final Report for Contract RP 1200-5, Lawrence Berkeley Lab., CA, 1980

3 D. Ott and Ch. J. Raub, Metal1 (Berlin), 1978,32, (2), 140

4 R. Szymanski and H. Charcosset, C. R . Acad. Sci. Paris, 1983, 296, Ser. 11, 1485

5 R. Szymanski and H. Charcosset, 3. Mol. Catal.,

6 R. Szymanski, Thesis, Lyon, January 1985 7 W. Bronger, Z. Anorg. Allg. Ckem., 1962,319,58 8 A. S. Darling, G. L. Selman and R. Rushforth,

1984, 253 337

Platinum Metals Rev., 1970, 14, 54

9 L. Tournayan, A. Auroux, H. Charcosset and R. Szymanski, in press in Adsorption Science and Technology

10 T. M. Tri, Thesis, Lyon, 1982; T. M. Tri, J. Massardier, P. Gallezot and B. Imelik, C. R. Acad. Sci. Paris, 1981, 293, 35

11 R. Szymanski, H. Charcosset, P. Gallezot, J. Massardier and L. Tournayan, in press in Yournal of Catalysis

12 R. Szymanski, H. Charcosset and V. Perrichon, Proc. 8th Int. Congr. on Catalysis, Berlin, 1984, Vol. 11, p.151

13 E. K. Poels and V. Ponec, “Catalysis, Volume 4”, a Specialist Periodical Report, Royal Society of Chemistry, London, 1982, p.196

The Fabrication of Ultrafine Platinum Wire WOLLASTON’S HISTORIC TECHNIQUE FURTHER DEVELOPED

In February 1813 William Hyde Wollaston read a paper to the Royal Society describing a method that he had developed for making ex- tremely fine wire. Initially he had been con- cerned to produce fine gold wires, for use as crosswires in the eyepiece of astronomical in- struments. This he did by drilling a hole along the centre of a silver rod into which a length of gold wire was inserted. When the diameter of this composite had been reduced sufficiently by drawing through dies, the silver was dissolved to yield the fine gold wire. However Wollaston found it very difficult to drill the central hole in the silver so he substituted platinum for the gold and modified the technique to make use of the higher melting point of platinum. He ar- ranged a platinum wire with a diameter of r / r o o of an inch along the longitudinal axis of a cylin- drical mould which was then filled with molten silver. Following successive reductions of the composite ingot, the silver was dissolved to give a platinum wire 1/5000 of an inch in diameter. This was excellent for his intended use, but by exercising the utmost care both with the quality of the platinum and during the wire drawing operation he was able to produce platinum wire as small as 1/30,000 of an inch in diameter (approximately 8500 a).

Wollaston’s technique for producing fine wire has remained in use, and modified pro- cedures that enable both single and multiple ultrathin platinum filaments to be produced with diameters as small as 80 a have recently been reported by A. C. Sacharoff and R. M. Westervelt of Harvard University and J. Bevk of A T & T Bell Laboratories, Murray Hill

(Rev. Sci. Instrum., 1985, 56, (7), 134-1346), A preliminary treatment of the ultrahigh

purity metals to remove any surface con- taminants is followed by vacuum annealing before a piece of the 0.5- diameter platinum wire is fitted into a hole drilled along the centre of a 3.2mm diameter silver rod. Next this com- posite rod is slowly drawn through some seven- ty progressively finer dies, to an overall diameter of o.smm. Following a further vacuum anneal the silver:platinum composite is inserted into another annealed silver rod and the drawing continued. Although it is not possi- ble to repeat the annealing stage again without the wire breaking up into short pieces, the other operations can be carried out as often as is necessary to reduce the platinum core to the ultrathin diameters required to test the theory of quasi-one-dimensional electronic localisation and interaction effects, at liquid helium temperatures.

Techniques have been developed that enable these ultrathin wires to be positioned for ex- amination before the supportive silver cladding is etched off.

Multifilament Platinum Yarn In another procedure ten platinum wires are

inserted into separate holes again drilled longitudinally into a silver rod. During repeated reductions, lengths of the resulting composite wires are bundled together, re- inserted in another silver rod and the sequence repeated. When finally the silver is etched away, a fine multifilament platinum yarn is obtained. I.E.C.

Platinum Metals Rev., 1986, 30, (1) 27

Catalysis by Metal Complexes Homogeneous Catalysis with Compounds of Rhodium and Iridium BY RONALD S. DICKSON, Reidel, Dordrecht, 1985, 278 pages, Dfl. 135,00/&7.50

Rhodium, and to a lesser extent iridium, systems are particularly effective at fulfilling the necessary requirements for homogeneous catalysis; reactions such as co-ordinative addi- tion, oxidative addition, reductive elimination and cis-migration all take place readily at these metal centres. Although these metals are intrin- sically valuable, the high activity and specificity often obtained make them cost effective and at- tractive for use in a number of commercial syn- theses. This monograph provides information useful to organic and organometallic preparative chemists in both industrial and academic research laboratories. Most of the reactions considered are homogeneous but the relationship of these to heterogeneous systems supported on both inorganic and polymeric materials is also described.

The activation of C-H and C-C bonds, in- cluding both saturated and unsaturated systems, is described in detail, and this is followed by a chapter on the many hydrogena- tion‘ reactions used to form C-H bonds. RhCl(PPh,) , Wilkinson’s catalyst, is probably the most extensively studied of all the known homogeneous hydrogenation systems and can be used at room temperature and atmospheric pressure. The rate of hydrogenation is increas- ed by the presence of polar co-solvents, and the reaction often occurs with high stereoselectivi- ty. Thus in the hydrogenation of steroids, selec- tive reduction of the least hindered double bond in the presence of other double bonds can be achieved more cleanly than when using heterogeneous catalysts.

Asymmetric homogeneous hydrogenation has been achieved using chiral rhodium complexes as catalysts. A synthesis of L-dopa (3,4-dihydroxyphenylalanine), which is used for treating Parkinson’s disease, has been developed by Monsanto. Up to 90 per cent op- tical purity has been achieved in this synthesis using a rhodium catalyst. Many soluble

rhodium and iridium species also catalyse the hydrosilylation reaction, and the asymmetric reduction of prochiral ketones can be achieved v h hydrosilylation in the presence of prochiral rhodium complexes.

In the chapter on carbonylation and hydroformylation , there is discussion of the many reactions catalysed by soluble and sup- ported rhodium and iridium species. These in- clude the water-gas shift reaction, the hydrogenation of carbon monoxide, and the catalytic reduction of nitric oxide by carbon monoxide, as well as the large variety of methods available for incorporating carbon monoxide into organic molecules via carbonyla- tion or hydroformylation. Some of these reac- tions have already achieved considerable commercial significance, notably the hydrofor- mylation of propylene (Johnson Matthey/Davy McKeeAJnion Carbide), and the carbonylation of methanol (Monsanto). Both of these reac- tions achieve high selectivities for the desired products, n-butyraldehyde and acetic acid, respectively. However, the most significant ap- plication of all for rhodium catalysts is their use to control emissions of nitrogen oxides from car exhausts. Mixtures of platinum metals adsorb- ed on ceramic supports, either monoliths or pellets, are used and one function of the rhodium is to catalyse the decomposition of nitric oxide. The high pressure reaction between hydrogen and carbon monoxide to give ethylene glycol and methanol is pro- moted by soluble rhodium carbonyl catalysts.

The book thus provides a very readable and useful review of the present state of knowledge on catalysis involving rhodium and iridium species. Literature up to 1982 is comprehen- sively covered and very clear mechanistic schemes are provided, while in addition a helpful tabulation of homogeneous catalysts and their applications is presented as an Appendix. D.T.T.

Platinum Metals Rev., 1986, 30, ( l ) , 28 28

Platinum and the Greenwich System of Time-Signals in Britain THE WORK OF GEORGE BIDDELL AIRY AND CHARLES VINCENT WALKER FROM 1849 TO 1870

By John A. Chaldecott The Science Museum, London

The establishment of regular time-signals and their distribution throughout Britain by means of galvanic telegraphy was largely the out- come of collaboration between G. B. Airy and C. V . Walker, with some assistance from the brothers E. and L. Clark. The early history of this development, and the role which platinum occupied in its successful operation, is traced largely from records preserved in the archives of the Royal Greenwich Observatory at Herstmonceux Castle.

A broad historical survey of Greenwich time is to be found in a recent book by Howse (I) , and for anyone having a particular interest in the introduction and development of the Green- wich time-signal service from a horological standpoint there are excellent accounts sup- plied more than a century ago by Ellis (2), who was then employed as an Assistant at the Royal Observatory, Greenwich, and had day-to-day responsibility for overseeing the time-signal service.

The service only became feasible following the extensive development of the electric telegraph, the current for which came from numbers of galvanic cells connected together in series to form batteries. In one respect Ellis’s account was not explicit about the type of bat- tery used at Greenwich, for he referred only to a battery consisting of cells in which the two poles were of copper and zinc, and we know that several types of copper-zinc cells existed at that period, some of which were certainly employed for telegraphic purposes (3).

A recent study of documents preserved in the archives of the Royal Greenwich Observatory (4) has served to clarify the position however, and it can now be said that from the start of the service a variety of galvanic batteries were in use at Greenwich, though within a few years

preference was given almost entirely to bat- teries having metallic platinum present in one form or another.

The service whereby time-signals were made available throughout the country by way of the electric telegraph came about mainly through the efforts of two men: George Biddell Airy who in 1835 was appointed Astronomer Royal (9, and Charles Vincent Walker who ten years later became Telegraph Superintendent to the South Eastern Railway Company (6).

Ary had no practical experience in galvanic telegraphy (7) but he recognised that possible advantages might accrue from the introduction of galvanic systems in the Royal Observatory. As a starting point he wondered whether with the assistance of a galvanic battery it would be possible to make the going of two or more clocks at the Observatory depend on that of the transit-clock. With this in mind he consulted an eminent London chronometer maker, Edward John Dent, mentioning that ideally the galvanic battery should not require frequent renewal but be competent to operate for at least a week and if possible a month (8). Dent replied that there would be no difficulty in putting Airy’s pro- position into effect, but mentioned that in trials made at an earlier date he had encountered dif- ficulty from oxidation of the metallic surfaces

Platinum Metals Rev., 1986, 30, (l), 29-37 29

George Biddell Airy 180 1 - 1892

A distinguished mathematician, author and ad- ministrator, Airy was often called upon by Government for advice on scientific matters dur- ing the forty-six years that he was Astronomer Royal. One of many honours bestowed on him was the Honorary Freedom of the City of London in recognition of his eminent services which had “ s o materially benefited the cause of commerce and civilisation”

where the electrical circuit was made and broken. His own experience had revealed that by using a battery of Smee cells and having platinum and pure gold as the metals where electrical contact was made and broken, such a battery would last for months (9).

Airy’s Plan Having received that assurance as regards the

existence of a suitable galvanic battery, Airy realised that it should be possible to send elec- trical impulses every second to control the movement of “sympathetic” (or slave) clocks situated outside the Observatory; and if he could have a telegraph line connected from the Observatory to one of the existing telegraph systems, he could also make his galvanic time- signals available at designated hours throughout a large area of the country (10).

His opportunity came when he heard that the South Eastern Railway Company proposed to install a telegraph line that would pass within nine furlongs (approx. 1.8 km) of the Obser- vatory. He realised that if he could get permis- sion for a telegraph connection to be made from the Observatory to one of the stations on the South Eastern Railway (SER), he might be

allowed to transmit his time-signals along the railway’s telegraph lines to London Bridge Sta- tion. From there the time-signals might be distributed to stations already on the SER’s telegraph system, and also perhaps to the English Telegraph Company (ETC) whose cen- tral telegraph station was situated at Founder’s Court, Lothbury, in the City of London. That being so, distribution throughout the country could then be made over the telegraph network operated commercially by the ETC, to serve other railway companies, and any public in- stitutions or private firms who might wish to display Greenwich time.

An approach was made to Walker in 1849 in- forming him of Airy’s wish to have a telegraph line laid down from the Observatory to Lewisham Station ( I I). Walker responded at once, promising his cordial co-operation; and after consulting with the Directors of the SER he was able to inform Airy that in giving their assent to his plan they regretted that it would not be possible for them to bear the cost of in- stalling the proposed telegraph line (12).

Financial constraints probably precluded Airy from taking any immediate action to im- plement his plan and it was not until the year 1851 that he felt able to proceed. His first act was to go with Walker to look at some examples of sympathetic clock systems already operating in London, all of which were the work of Charles Shepherd, a well-known London clockmaker. He also went to see the clock

Platinum Metals Rev., 1986, 30, (1) 30

Charles Vincent Walker 1812-1882

Inventor, author, editor, and translator of works on electricity and its applications, Walker took an active part in the newly formed London Elec- trical Society. He has been described as the “father” of the profession of electrical engineers, and for thirty-seven years he served as Engineer and Telegraph Superintendent to the South Eastern Railway, in which capacity he assisted Airy greatly in the establishment of the Greenwich system of time-signals

system which had been installed by Shepherd at the Great Exhibition building in Hyde Park, being accompanied on that occasion by Shepherd’s son (13). Airy then consulted Shepherd and asked him to provide an estimate of the cost of a sympathetic clock system for the Observatory, including some arrangement for operating the Greenwich Time-Ball electrically, and also whatever batteries would be required to operate the entire system (14).

The SER was informed that Au-y now wished to have six or more telegraph lines installed from the Observatory to Lewisham Station, some to go through to London and others to provide a means of communication between the Royal Observatory and the principal European Observatories, once the submarine line from England to France was completed (I 5 ) . A draft agreement was submitted to Ary by the SER, and he then wrote to the Board of Admiralty setting out his reasons for wishing to proceed (16). The Board’s approval was given shortly afterwards and Airy immediately instructed Shepherd to start work on the clock system, and Walker was requested to have the installa- tion of the telegraph lines put in hand.

Clock and Telegraph Batteries The Smee battery, in the form of one or more

cells, was the one generally favoured for operating electric clocks, as it required little maintenance and was capable of producing a strong current provided it was not required to

operate continuously. The Smee cell was in- troduced in 1840 by Alfred Smee and im- mediately became available commercially ( I 7). It was of the single-fluid type, the electrolyte being sulphuric acid diluted in the proportion of one part acid to seven parts water. A sheet of pure rolled zinc, well amalgamated, formed the negative plate, and the positive plate could be platinum, palladium, or pure silver. Before use the positive plate had to undergo special treat- ment, the surface being first roughened all over and then platinised by electrolysis for a short time to acquire a thin coating of platinum black. Sandpaper was used to roughen plates of platinum or palladium, but in the case of silver the surface was etched with strong nitric acid and then washed clean with water (18). The function of this platinising treatment was to promote the easy disengagement of hydrogen bubbles which Smee had observed always tend- ed to adhere more readily to a smooth surface than they did to one that was irregular; it had the desired effect of considerably reducing polarisation when the cell was in operation, and thereby increased its efficiency. The e.m.f. of the cell was about I. I volts (IS), and its internal resistance around one ohm.

Platinum Metals Rev., 1986, 30, (1) 31

Perspective view of Shepherd’s clock, as fitted up in the Royal Observatory at Greenwich, and employed in connec- tion with the distribution of time- signals. It shows the pendulum, its remontoir escapement, and the ar- rangements by which electro- magnetism was made to be its main- taining power. To the left is shown the arrangement by which a dial and its Smee batteries were connected with the pendulum. The illustration is reproduced from an English transla- tion made by C. V. Walker from A. de la Rive’s “Trait6 d’ElectricitC” (3 1)

The position with regard to telegraph bat- teries was much more complex. In the late 1840s the SER and the ETC both employed batteries consisting of large numbers of cells of the type introduced by William F. Cooke. Each cell consisted of a copper and an amalgamated zinc plate, both plunged into a trough of siliceous sand moistened with sulphuric acid diluted with fifteen parts of water (20). The e.m.f. of such a cell was 1.05 volts, and cells were generally connected in series in blocks of 24, 48, 72 or even 96 cells, when they were

usually referred to as “sand-batteries”. These batteries were not at all popular with Walker, who described them as being “good enough when fresh: bad enough when stale; at best variable” (21).

Information which reached Airy early in 1849 indicated that Grove batteries were employed in the American telegraph system, and had been used in some experiments involving the transmission of time-signals over a distance of some 500 miles (22). These batteries were in- vented by William R. Grove, and were of the two-fluid type. An amalgamated plate of com- mon rolled zinc was suspended inside a porous pot containing sulphuric acid diluted with four to five parts water, and the pot stood in a vessel of concentrated nitric acid in which a thin sheet of platinum was partially immersed (23). When such a cell is in operation the hydrogen liberated at the zinc plate passes through the pores of the pot and is then oxidised by the nitric acid before reaching the platinum sheet, and polarisation of the cell is thereby eliminated.

A serious disadvantage of the Grove cell is its production of poisonous fumes of nitrogen peroxide, and to absorb this gas Grove advised that the battery should be provided with a cover containing lime. There are other features associated with the Grove cell, however, which it might be thought would have militated against its use: the current was not constant for any length of time; the materials were intrin- sically dear and difficult to handle; the battery needed daily attention; and it had to be dismantled when not required for active service (24). One can only assume that the Grove bat- tery was preferred at that time in America as being more suitable for operating telegraphs over considerable distances, the Grove cell hav- ing a low internal resistance and also an e.m.f. of I .9 volts which far exceeded that of any other galvanic battery then available.

The same reason may also have accounted for the use of Grove batteries in the South Australian telegraph system although Smee bat- teries were also used there, probably only for local telegraph circuits, in a commercial form

Plafinum Metals Rev . , 1986, 30, (1) 5L

known as the “Chester” battery (25), such bat- teries being manufactured by the New York firm C. T. & J. N. Chester (26).

In Britain in the mid-1850s the sand-battery was replaced for telegraph use either by the ‘‘sulphate battery” invented by John Fuller (27), a battery which needed monthly attention, or by the so-called “gravity” battery invented by Cromwell F. Varley (28), the latter battery only operating successfully provided it was not subjected to any kind of movement.

In April 1849 Walker produced his first “graphite” battery, a modification of the Cooke sand-battery in which the negative cop- per plate was replaced by slices of graphite ob- tained from the corrosion deposited in the interior of old gas retorts. A graphite plate was first pickled for a few days in sulphuric acid and water, and then drilled and electrotyped with copper at the top; this copper was then tinned, a connecting metal strap rivetted tokit with tinn- ed rivets, and then soldered. A small slipper of gutta-percha was fured to the bottom of the zinc plate, to contain a little mercury for the purpose

of amalgamation by capillary action. When the containing vessel was considerably deeper than the zinc plate, so that the solution of zinc sulphate could fall to the bottom as it formed, the graphite cell lasted a long time (29). Walker exhibited his battery at the Great Exhibition of 1851, claiming that its working life was much longer than that of any other copper-zinc bat- tery, because there was no copper present in the electrolyte to produce local action on the zinc plate when the battery was not in use (30).

Galvanic Batteries at Greenwich In mid-July 1852 preparations were almost

complete for the launch of Airy’s time-signal service. Shepherd had already installed his Normal Mean Time Clock, which was kept constantly adjusted to Greenwich mean solar time, together with the associated slave clocks, all operated by twenty-eight large Smee bat- teries provided by Shepherd (31). A few days later Walker suggested that a trial transmission be made by sending a time-signal automatically over the telegraph line from the Observatory

Platinum Meials Rev., 1986, 30, (1) 33

Chearer'M battery in which each Smee cell wam houaed in its own glass jar. Airy's battery wan similnr in d e s i v but the jars were replaced by n bnttery box of vtta-percha. moulded in one pimp without any joinla, to pro- vide twelve e d r e l y aeparaie compartments each houainp one Smre cell 126)

through Lewisham Station to the SER switch- room at London Bridge and thence on to Dover. On discovering that Airy had no bat- teries available for such a trial, Walker lent him three +plate sand-batteries belonging to the SER (32), and the trial proving satisfactory, Airy’s time-signal service came into operation over the SER network using those same bat- teries on 19 August 1852 (33). A few days after- wards the telegraph connection was completed from London Bridge to the ETC’s office in the Strand, where Edwin Clark had arranged for a time-ball to be erected above the roof of the building, and the ball was then dropped each day at I p.m. by means of an electric signal sent from Greenwich (34).

Walker intended to replace the sand-batteries

at Greenwich by graphite batteries of his own construction, and to that end he began cutting graphite plates; however he found this no easy task and over a year passed before he was able to deliver any graphite batteries (35).

In the meantime Airy must have decided to use Smee batteries as a replacement for the sand-batteries belonging to the SER. From Walker he learnt that platinised silver could be obtained from Johnson & Matthey of Hatton Garden (36). It is probable that the fine silver used was prepared by Edward Cock in his home workshop in Rodney Street, Pentonville, and was then platinised at Hatton Garden by Ed- ward Matthey who at the time was serving his apprenticeship to Percival Johnson. This was certainly the procedure being carried out in

Platinum Metals Rev., 1986, 30, (1) 34

An engraving frem 'The Illuitrsied London Newn" of 11 September 1852. shciwing the Time-Ball which Edwin Clark cauned to be erected above the roof of #he Electric TeFeRraph Company'fi Qi%ce in the Mrmd. It wan operated by an electric current sent from Greenwich Obsewatory at 1 p.m. esch day, and Clark reparwd: "the public msnemblr in C ~ O W ~ E ' ' to nee it in action %nd the chronometer mnksra think it B #rent boon"

Invoice relating to the supply by Johnson & Matthey of sixty platinised silver plates required by Airy in the manufacture of Smee batteries to be used for transmitting his Greenwich time-signals. The plates measured five by three inches, and were about 0.0026 inches thick Rcpruduced by counay of rhc Royal Cmnwich Observatory

1857 by Johnson & Matthey (37), to meet an order for large platinised silver plates required by Edward 0. W. Whitehouse for the construc- tion of his modified form of Smee battery, the “Whitehouse Laminated or Perpetual Maintenance Battery”, for use in conjunction with the first Atlantic telegraph cable (38).

Airy’s first order was invoiced as 4 oz. 15 dwt. at 8s. an ounce; his second order involved a strip nine feet long by three inches wide and weighing 8 oz. 2 dwt., so the thickness of the silver must have been about 0.0045 inch (39). Zinc plates 0.25 inch thick were obtained from Henry Treggon & Company, of Jewin Street, Cripplegate (40); the West Ham Gutta Percha Company provided battery boxes, each having twelve individual cells in a single moulding (41); and Joseph Liddon, a metal worker of Royal Hill, Greenwich, was employed by Airy to assemble the batteries from components sup- plied to him, and to make all the fastenings and galvanic connections required between the zinc and platinised silver plates (42).

Further orders for platinised silver plates were placed with Johnson & Matthey each year until 1857 (43), the thickness of those plates be- ing between 0.0016 and 0.0037 inch; but at the end of that year Airy began using some graphite batteries which he purchased from George Knight & Company, of Foster Lane, Cheapside (4). A further development took place early in

1858 after Airy had received an account of some experiments carried out by Walker which clear- ly demonstrated the superior value of platinised graphite over both plain graphite and platinised silver plates (45). A few months later Airy began using “platinised graphite” batteries, having purchased platinised graphite plates with amalgamated zinc plates attached by cop- per straps, as manufactured by William Reid & Company at their works in University Street, London. These were priced at 613.16s. a gross

In 1859 the telegraph lines which ran underground from the Observatory to Lewisham Station became defective, and they were replaced with overhead lines installed by the London District Telegraph Company (LDTC) who were interested in providing time-signals to chronometer makers working in London. The work was carried out free of charge on the understanding that the LDTC be permitted also to run its own special wire in communication with the Observatory’s regulator clock, over which wire the time- signals would be sent to the LDTC on the hour once or twice a day (47). Airy was not expected to provide batteries for this purpose, as Edward Tyer, the LDTC’s Engineer, intended to use twelve of his own modified Smee batteries sited at the London end of the wire and to employ an earth return (48).

(46).

Platinum Metals Rev., 1986, 30, (1) 35

In Tyer’s cell some scraps of zinc were laid in a saucer containing mercury, placed at the bot- tom of a glass jar, and a plate of platinised silver was suspended immediately above. The jar was fdled with dilute sulphuric acid and a piece of gutta-percha covered wire, bared for 0.25 inch at its lower end, dipped into the mercury to provide the zinc connection (49).

By 1862 Airy had replaced all his Smee bat- teries with platinised graphite batteries (so), and in 1865 he sold back to Johnson & Matthey his stock of old used platinised silver plates, amounting to thirty-one ounces troy (51).

In view of the details given above concerning the various galvanic batteries employed by Airy in connection with his time-signal service, one might wonder how it was that Ellis should only have mentioned the use of copper-zinc batteries at Greenwich when he delivered his lecture in the year 1865 (52). The reason must surely be that he was then referring specifically to the use of sulphate batteries which had been employed at Greenwich from 1859 onwards for the sole purpose of sending signals direct to the central telegraph station at Lothbury. This station was then operated by the Electric and International Telegraph Company (E&ITC), following the merging of two telegraph companies, but was moved soon afterwards to Telegraph Street, in the City (53).

Earlier the E&ITC had offered to lend 12-cell sulphate batteries to Airy, or to sell them to him at 25s. each (54), and in 1861 Latimer Clark assisted Airy by providing from the Company’s own stock twelve sulphate batteries in porcelain chambers of Io-pint capacity (55).

Airy was still responsible for providing his own batteries for driving the electric clocks within the Observatory, and he still required batteries for sending time-signals to the SER and for operating the time-ball at Deal. To meet those needs he continued to acquire platinised graphite batteries, but he appears to have had some trouble in obtaining deliveries. In 1861 and 1862 he placed orders with Knight & Co., of Foster Lane (56), and in 1864 he ap- pealed successfully to Walker for help (57). After that he obtained his supplies from the In- dia Rubber Gutta Percha & Telegraph Works Co. Ltd at Silvertown, Essex, the first order be- ing met in I 867 (58) and other orders following until the mid-1870s (59).

All the electric telegraph companies in the country were taken over in 1870 by the General Post Office (GPO) to whom time signals con- tinued to be provided as hitherto by the Royal Observatory. However it was not until 1889 that the GPO became responsible for the maintenance of the telegraph wires and of all the batteries used for the transmission of time- signals from the Observatory to the GPO’s cen- tral telegraph station located at Telegraph Street (60).

Acknowledgemente My thanks go to Miss Janet Dudley, archivist at the

Royal Greenwich Observatory, for enabling me to make full use of the Airy Papers, and for drawing my attention to documents in the Observatory’s library which otherwise might have escaped my notice. The portrait of G. B. Airy is reproduced by courtesy of the Trustees of the Science Museum, and that of C. V. Walker by courtesy of the Institution of Electrical Engineers.

References

Documents identified by the letters RGO are preserved in the archives of the Royal Greenwich Observatory, Herstmonceux Castle, East Sussex I D. Howse, “Greenwich Time and the Discovery

of the Longitude”, Oxford, 1980, pp. 81-115 2 W. Ellis, ‘‘Lecture on the Greenwich System of

Time Signals”, H o d . J., 1865, 7, 85-91, 97-102, 109-114, 121-124; Nature, r876, 14, 50-52, 110-113

3 J. Sivewright, “Batteries, and their Employment in Telegraphy”, 3. SOC. Telegr. Eng., 1875, 4, (XI), 120-146

4 Particularly the Airy Papers in the archives of the Royal Greenwich Observatory

5 “Dictionary of National Biography”, 1901, Sup- plement, I, 22-25. Obituary notices: Proc. Roy. SOC., 1892, 51. i-Xxi; Mon. Not. Roy. Asmm. SOC., 1892, 52, (4), 212-229; Corporation of Lon- don, “London’s Roll of Fame 1757-1884”, Lon- don, 1884, pp. 305-308

6 “Dictionary of National Biography”, 1899, 59, 46-47; C. V. Walker, “President’s Inaugural Ad- dress”, 3. SOC. Telegr. Eng., 1876, 5, (13), 3-22 (especially 11)

Platinum Metals Rev., 1986, 30, (1) 36

7 RGO 6/610, sect. 3: letter Auy to Walker, 12 June 1849

8 RGO 6/721, sect. 12: letter Airy to Dent, 20 November 1848

9 Ibid.: letter Dent to Airy, 21 November 1848 10 RGO 17/1: “Report of the Astronomer Royal to

the Board of Visitors”, read 2 June 1849, pp. 15-16

11 RGO 6/610, sect. 3: report Glaisher to Airy, 19

12 Ibid.: letters Walker to Airy, 23 May and I I June

13 RGO 6/612, sect. 16*: letters Walker to Airy, 9 June 1851, and Shepherd to Airy, 21 June 1851; Great Exhibition of I 85 I, ‘ ‘Official Descriptive and Illustrated Catalogue”, London, 1851, I,

14 RGO 6/724, sect. 37: letter Airy to Shepherd, 7 October 1851

15 RGO 6/610, sect. 3: letter Airy to Herbert, 19 September 1851

16 Ibid., sect. I: letter Airy to Baring, 26 November 1851

17 E. Palmer, “New Catalogue . . . of apparatus, il- lustrative of . . . Voltaic Electricity . . . &c”., London, 1840, p. 41. Copy in British Library:

18 A. Smee, “On . . . a new Chemico-Mechanical Battery”, Phil. Mag., 1840, 16, 3157332; “On a Galvanic Battery of a new Construction”, Trans. Roy. SOC. Am, 1840, 53, 21-29; “Elements of Electro-Metallurgy”, London, 2nd Edn., 1843, pp. 23-26

19 J. T. Sprague, “Electricity: Its Theory, Sources, and Applications”, London, 1875, pp. 222-224; not 0.47 volt as has often been stated

20 C. V. Walker, “Electric Telegraph Manipula- tion”, London, 1850, pp. 7-8

21 RGO 61635, sect. 19: letter Walker to Airy, 17 May I854

22 RGO 6/160, sect. 6: “Documents relative to the Electro-Chronograph invented by John h k e . . . in the Year 1848”, Newark (New Jersey), 1849, pp. 1-38 (especially 21-22)

23 W. R. Grove, “On a small Voltaic Battery of ex- traordinary energy”, Rep. Brit. Assoc. Adv. Sci., Ninth meeting (Birmingham, 1839, 1840, 36-38; Phil. Mag., 1839, 15, 287-293

May I849

1849

Sect. 2, pp. 419-422

787.f. 20( I -2)

24 Op. cit., Ref. 3, 138-139 25 RGO 6/628, sect. 59: report by Todd, 15 October

26 G. B. Prescott, “History, Theory, and Practice of the Electric Telegraph”, Boston (Massachusetts) and London, 1860, pp. 27, 33

1857

27 British Patent 944; 1853 28 Brirish Patent 2555; 1854 29 Op. cit., Ref. 3, 151; R. S. Culley, “A Handbook

of Practical Telegraphy”, London, 2nd Edn., 1867, pp. 20-21

30 Great Exhibition of 1851, “Reports by the Juries”, London, 1852, class x, pp. 291-292

31 RGO 6/725, sect. 49: invoice, 29 September 1852. For a description of the clock see A. de la Rive, “A Treatise on Electricity”, translated by C. V. Walker, London, 1858, 3, pp. 479-484

32 RGO 6/611, sect. I: letters Walker to Airy, 30 Ju- ly, 6 and 16 August 1852

33 “Greenwich Time Signals”, The Times, 23 August 1852, 6, col. 6

34 RGO 6/611, sect. 2: letter E. Clark to Airy, 28 August 1852; The Times, 8 September 1852, 5 , col. 4: letter E. Clark to Editor

35 RGO 61611, sect. I: letter Walker to Airy, 20 September 1852; RGO 6/633, sect. I: letter Walker to Airy, 30 May 1853; RGO 6/25: journal entry 6 October 1853

36 RGO 6/611, sect. I and RGO 6/627, sect. 32: let- ter Walker to Airy, 22 July 1853

37 Unpublished memoirs of Colonel Edward Mat- they (1836-1918), 1918, pp. 40-41. The Johnson Matthey Group holds the only copy printed

38 For details of this battery see “The Atlantic Telegraph. A History . . . of the Undertaking”, London, 1857, pp. 58-60

39 RGO 6/726, sect. 26: invoice, 23 July 1853; order and invoice, 12 August 1853

40 Ibid., sect. 49: invoices, 7 July and 18 Oct. 1853 41 RGO 6/727, sect. 17: order, 19 January 1854 42 RGO 61726, sect. 29: orders, 21 October and 22

43 RGO 6/732, sect. 2 6 invoice, 22 May 1857 44 Ibid., sect. 28: invoice, 4 December 1857 45 RGO 61628, sect. 23: letter Walker to Airy, 18

February 1858 46 RGO 6/629, sect. 8: letter Walker to h y , 24 July

1858; RGO 6/735, sect. 9: letter Main to Reid & Co., 27 July 1858

47 RGO 6/629, sect. 6: letter Tyer to Amy, 20 December 1859

48 Ibid., letter Ellis to Airy, 4 February 1860 49 Culley, op. cit., Ref. 29, p. 21

50 RGO 6/630, sect. 9: MS. description by Ellis of apparatus at Greenwich, April 1862, p. 3

51 RGO 6/743, sect. 22: receipt, 19 May 1865 52 Ellis, 1865, op. cit., Ref. 2, especially 100-101

53 Op. cit., Ref. I , p. IW

54 RGO 6/732, sect. 16: letter L. Clark to Airy, 19 November 1857

55 RGO 6/741, sect. 10: notes, 15 and 17 August 1863; probably the same design as described in “The Electric and International Telegraph Com- pany’’, Electrician, 1862, I, (ID, 147-148

56 RGO 6/739, sect. 25: order, 9 July 1861; RGO 6/740, sect. 24: order, 14 February 1862

57 RGO 6/742, sect. 44: letter Ellis to Walker, 9 June 1864

58 RGO 6/745, sect. 41: order, 27 April 1867 59 RGO 61754, sect. 8: fmal letter, Bishop to Airy,

18 July 1876 60 RGO 17/4: “Report of the Astronomer Royal to

the Board of Visitors”, read I June 1889, p. 19

December 1853

Plarinum Metals Rev., 1986, 30, (1) 37

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Optical Behavior of Sputter-Deposited Platinum-Oxide Films

A series of Pt-0 alloys were grown by reactive sputter deposition on water-cooled Si and glass substrates. Optical behaviour in thenear u.v.-visibleand near i.r. regions was studied by spectrophotometry. Changes in reflection and transmission behaviour were cor- related with changes in film chemistry and structure, especially oxide formation and loss of long-range crystallographic order.

Pt-Co Magnets Produced by DC Triode Sputtering E. w. HILL, G . R. HOFFMAN and A. M. MCCULLOUGH,

Thin permanent magnetic films of equiatomic PtCo have been produced by DC triode sputtering. Films up to 6pm thick have been deposited onto sapphire substrates and give (BH)max products of 72kJ/m3 when optimally heat treated.

Shape Memory Effect in an Ordered Fe,Pt Alloy Associated with the FCC-FCT Thermoelastic Marteneite Transformation

andF. E. FUJITA, Trans. Jpn. Inst. Met., 1985,26, (7), 523-524 The shape memory effect in an ordered Fe-24.9 at.%Pt alloy associated with a f.c.c.-f.c.t. thermoelastic martensitic transformation was examin- ed. The Fe,Pt alloy was manufactured and electrical resistance/temperature curves at different transfor- mation temperatures were plotted. Fe,Pt (Ms <77K) with order parameter, S=0.78, has a martensitic transformation independent of the f.c.c.-b.c.t. or f.c.c.-b.c.c. transformation and is associated with a remarkable shape memory effect.

Magnetic and Superconducting Proper- ties of UPt,

FRINGS, J. Magn. t3 Magn. Muter., 1985, 52, (I -4), 61-69 Results of experimental studies on the ther- modynamic and transport properties of the heavy fer- mion superconductor Upt, are reviewed. The studies include high magnetic field and high pressure ex- periments in the normal and superconducting states and alloying effects on the normal and superconduc- ting state properties.

C. R. AITA, J. &PI. Phys., 1985, 58, (8), 3169-3173

J. Phys. (Paris), Colloq. NO. 6, C6-291-C6-294

R. OSHIMA, S. SUGIMOTO, M. SUGIYAMA, T. HAMADA

J . J. M. FRANSE, A. DE VISSER, A. MENOVSKY and P . H.

A New One-Dimensional Long Period Superstructure in Pd,Ce

EGUCHI, Jpn. J . Appl. Phys. Lett., 1985, 24, (8),

An ingot of Pd-Ce containing about 17at.%Ce was prepared and its structure analysed by X-ray diffrac- tion and electron microscopy. Pd, Ce has two phases, one stable at low temperature and the other stable at high temperature.

The Au-Pd (Gold-Palladium) System H. OKAMOTO and T. B. MASSALSKI, Bull. Alloy Phase

An assessed Au-Pd phase diagram for 0-16oo~C which includes a liquid phase is presented and backed by several references. Liquidus and solidus temperatures are given for various compositions. Long range order for Au,Pd, AuPd, and AuPd is discussed, as is short range order.

Hydrogen in Deformed and Amorphous Pd,,Si,, Compared to Hydrogen in Deformed and Crystalline Palladium

SPEITLING, scr. Metall., 1985, 19, (7), 843-846 H, diffusivity, e.m.f. and resistivity increments in amorphous Pd Si before and after cold rolling were measured and compared with the corresponding quantities in crystalline Pd. Amorphous Pd,,Si,, samples show a different concentration dependence compared to crystalline Pd.

Effects of Implanted Hydrogen on Pd,Si Formation

DELLA MEA, Appl. Phys. Lett., 1985~47, (8), 806-808 Preliminary results on Pd,Si formation in the presence of H implanted in a (111) Si substate near the Pd/Si interface after Pd deposition are reported. The implantation energy was chosen so that most of the H atoms stopped near the Pd/Si interface. Changes in H distribution in annealed samples were investigated.

Electrical Resistivities of Iridium, Palladium, Rhodium and Tungsten at Temperatures between 295 and 1 lOOK E. Y. GARCIA and D. C . L~FFLER, 3. Chem. Eng. Data,

Using thin wire samples, the relationships between electrical resistance and temperature have been established for Pd, Rh, Ir and W in the range 295 to I I ~ K . A polynomial expression is given which fits these and other data with < I % deviations. The elec- trical resistivity of Ir at 295K is given as 9.01 pncm.

N . KUWANO, S. HIGO, K. YAMAMOTO, K. OK1 and T.

L663-L665

Diagram, 1985, 6, (3L 229-235, 283

R. KIRCHHEIM, A. SZ6KEFALVI-NAGY, U . STOLZ and A.

A. PACCAGNELLA, G . MAJNI, G. OTTAVIANI and G.

19853 30, (31, 304-305

Platinum Metah Rm., 1986, 30, (l), 38-46 38

Adsorption and Desorption of NO from Rh{ l l l } and Rh{331} Surfaces

159, (I) , 1 9 9 - 2 1 3 The adsorption and desorption of NO on clean R ~ { I I I ) and Rh{331} single crystal surfaces was followed by various techniques. At saturation coverage there was -10 times more dissociated species on the Rh(331) surface at 3ooK than on the Rh{ I I I } surface. The molecular states of NOad, were /3, and /3, which possess different chemical reactivity, and are present in different proportions on the two surfaces. The populations are coverage and temperature dependent.

Growth of a Bicrystal Superlattice: Ru-Ir

1985, 15, (9) , L221-L226 The growth of a high quality bicrystal superlattice formed from alternating layers of h.c.p. Ru and f.c.c. Ir metals is reported. Ir layers, which are thick com- pared with the Ru do grow in the f.c.c. structure, whereas thin Ir layers take the h.c.p. structure, pro- bably due to strain effects.

Lifetimes of the Lowest Excited State of Tris(2,2 ’ -Bipyridine)Ruthenium(II) and Its Amphipathic Derivative in Micellar Systems

TAKUMA and T. MATSUO, J. Photochem., 1985,80, (I),

9 3 - 1 0 3 The luminescence decay lifetimes of ([Ru(bpy), ] +) and its amphipathic derivative ([RuC I , B] ’ +) were measured in H,O, D,O, CHIOH, CD,OH and CH , OD solutions, as well as in micellar solutions of Na dodecylsulphate in H,O and D,O. They reveal the role of the protic solvent molecules in the deac- tivation of the excited Ru(I1) complexes. The lifetimes of the complexes reduce with increasing size of the waterpool in the inverted micellar solution. ([Ru(bpy),]? +) is present in the waterpool, but ([RUC,,B]~ +) is buried inside the anionic interface with its aliphatic sidechains penetrating deep into the hydrophobic domain.

L. A. DELOUISE and N. WINOGRAD, surf SCl., 1985 ,

J. E. CUNNINGHAM and C. P. FLY“, J. PhyS. F,

Y. KAIZU, H. OHTA, K. KOBAYASHI, H. KOBAYASHI, K.

CHEMICAL COMPOUNDS The Preparation and Properties of Com- pounds Containing Pt(II1) 1. D. wOOLLINS and P. F. KELLY, coord. Chem. Rev.,

Information on compounds with an average Pt oxida- tion number of (111) is presented. The material is divided into mixed valance Pt(II1)-Pt(IV) systems, binuclear compounds, such as sulphate-, phosphate-, hydroxide-, peroxide- and carboxylate-bridged species and Pt blues and related systems, which in- clude binuclear compounds containing biologically relevant ligands. (108 Refs.)

1985 , 659 1 1 5 - 1 4 0

Synthesis and Structure of the [Ni,,Pt6- (CO),,H,J- (n=5,4) Ions: Ni-Pt Clust- ers as Models for “Chemy” Crystallites

MANASSERO, M. MARCHIONNA, G. PIVA and M. SAN- SONI, Angew. Chem., Znt. Ed. Engl., 1985, 24, (8), 697-698 The syntheses and structures of a series of title clusters is discussed. These compounds have been isolated in a crystalline form and two of the structures have been determined by XRD. They constitute the highest nuclearity carbonyl clusters fully characteris- ed, so far. Preliminary measurements suggest unusual magnetic behaviour.

Homoleptic Isocyanide Complexes of Ruthenium(I1) and Osmium(I1)

A. CERIOTII, F. DEMARTIN, G. LONGONI, M.

S. M. TETRICK and R. A. WALTON, h r g . Chem., 1985, 24, (211, 3363-3366 A fmt general synthetic route to the homoleptic metal (11) complexes [M(CNR),](PF,), M=Ru or 0s is reported. The complexes are made by reaction of di-Ru(I1, 111) and di-Os(II1) acetates Ru,(O,C- CH,),Cl and Os,(O,CCH,),Cl, with alkyl iso- cyanides, RNC (R=CHMe,, CMe, or C,H,,).

ELECTROCHEMISTRY Square Wave Voltammetry on Platinum Microdisk Electrodes Using Synchronous Remodulation S. A. SCHUElTE and R. L. MCCREERY, 3. Electmanal. Chem. Interfacial Electmchem., 1985, 191, (z) , 329-342 Pt microdisk electrodes were manufactured and used in one form of square wave voltammetry for analytical measurements. The benefits of using microdisk elec- trodes are examined, as is the square wave voltam- metry used. A detection limit of Z X I O - ’ M was obtained for ferrocene in acetonitrile. The rapid charging current decay allows the use of high modula- tion frequencies and fast voltammetric scans.

Electrochemical Permeability Control through a Bilayer-Immobilized Film Con- taining Redox Sites

Am. Chem. SOC., 1985, 107, (IS), 5300-5301

The reversible permeability control through a viologen (4,4 I -bipyridinium)-containing bilayer-fdm deposited on a Pt minigrid sheet by electrochemical redox reaction is reported. The Pt minigrid was sup- ported on a polyethylene tube. With different poten- tials varying from -0.50V vs. SCE to OV permeability changes occurred, and could be reproduced repeatedly. The changes may be at- tributed to the fluidity change of the bilayer film on the Pt grid because of the T, transitions of bilayers by redox reactions.

Y. OKAHATA, G.-I . ENNA, K. TAGUCHI and T. SEKI, 3.

Platinum Metals Rev. , 1986, 30, (1) 39

Effect of Platinisation on the Elec- trochemical Behavior of the TiOl Elec- trode in Aqueous Solutions K. UOSAKI, R . YONEDA and H. KITA, 3. Phys. Chem., 1985,89, (I9), 4042-4046 The electrochemical behaviour of platinised TiO, electrodes was investigated and was found to increase the H, evolution reaction rate but not to affect the kinetics of 0, evolution at TiO, single-crystal elec- trodes. At polycrystalline TiO, electrodes H, evolu- tion and 0, evolution were accelerated by platinisation.

Electrocatalytic Reduction of C 0 2 at a Chemically Modified Electrode

WESTMORELAND, w. J. VINING, R. w. MURRAY and T. I. MEYER, 3. Chem. SOC., Chem. Commun., 1985,

Electropolymerised complex Re(eviny1-4 ’ - methyl-2,zi-bipyridine)(C0,)Cl as a polymeric film on a Pt electrode, electrocatalytically reduces CO, to CO with turnover numbers greatly exceeding those observed for the analogous electrocatalytic reduction of CO, by Re(bpy)(CO),Cl on Pt gauze electrode.

Removal of Colloidal Silicon in Simulated Seawater by a Dynamic Multi-Short- Circuited Galvanic Cell

Ind. Eng. Chem., Prod. Res. Dev., 1985, 24, (3), 468-473 An inexpensive dynamic multi-short-circuited galvanic cell with Pt-Al electrodes was used to study the removal of colloidal SiO, from seawater, as a pretreatment step for the desalination of seawater by reverse osmosis. The rate of SiO, removal was af- fected by the flowrate of the solution through the cell, the dissolved 0 content of the solution, the nature of the Al electrode surface and the number of contact points between the Al and Pt. The SiO, content was reduced by 95% by this cell. The Pt is not consumed, but the Al is, and a module made of Pt with replaceable Al is suggested as a first step in purifying brackish water or seawater.

T. R. O’TOOLE, L. D. MARCERUM, T. D.

(20), 1416-1417

J.-E. OSTERHOLM, P. W . KRAMER and H. K. YASUDA,

Clay Modified Electrodes. Elec- trochemical and Electron Spin Resonance Studies of Montmorillonite Layers

A. J. BARD, 3. Am. Chem. Soc., 1985, 107, (zo), 564-5652 Montmorillonite films (3onm-3wm thick) with and without added poly(vinylalcoho1) were cast onto Pt, glassy C and SnO,/glass and used as electrodes. The electrochemistry of cationic species incorporated in the fims, Ru(bpy):+, Os(bpy):+ and Fe(bpy):+ is described. The effective diffusion coefficients of the 0 s and Fe species in these films were - 10- ” cmz 1s.

D. ECE, P. K. CHOSH, J. R. WHITE, J.-F. EQUEY and

The Direct Electrochemistry of Redox Proteins at Metal Oxide Electrodes M. A. HARMER and H. A. 0. HILL, 3. Electroanal. Chem. Interfacial Electrochem., 1985, 189, (2),

The DC cyclic voltammetry of several redox proteins at thin film RuO, electrodes is described. Responses on varying pH and solution ionic strengths were observed. The results highlight the importance of electrostatics at the electrodelsolution interface. Preliminary results using IrO,, N a , , W O , and single crystal RuO, electrodes are reported. Subtle differences in behaviour are found at single crystal and thin film RuO, electrodes.

229-246

PHOTOCONVERSION Rate Enhancement of Photooxidation of CN- with TiOl Particles T. L. ROSE and c. NANJUNDIAH, 3. Phys. Chem., 1985,

The rate of photooxidation of CN- by platinised anatase particles was investigated as a function of par- ticle size, platinisation and pH. The reaction rate con- stants increased on increasing the surface area of the particles, platinising the TiO, and lowering the pH from 14 to 11. The fastest rate constant was >500 times faster than any previously reported.

Photochemical Water Cleavage in Suspensions in Pt-Loaded Titania Par- ticles with 0.790 Overall Light to Chemical Conversion Efficiency B. GU, J. KIWI and M. GRATZEL, Nouv. 3. Chim., 1985,

Band gap irradiation of alkaline aqueous TiO, suspensions loaded with ultrafine Pt particles via ion exchange with Pt(NH,):+, and subsequent reduc- tion, produces H, with an overall light to chemical conversion efficiency of 0.1%. The anodic reaction is H,O oxidation to peroxide. Addition of Ba” ion to the suspension increases the overall conversion to 0.7% and the Baz+ also drastically decreases the rate of recombination of H , with 0, and that for the photo-uptake of 0, . Cyclic performance is achieved by decomposing the peroxide at 200-300~C.

Photoelectrochemical Measurements on Thermally Grown Platinum Containing Iron Oxide Photoanodes

MELLS, 3. Electrochem. SOC., 1985, 132, @),

Pt was found to be an effective electrocatalyst when incorporated into the bulk of thermally grown a- Fe,O, during its preparation. When the a-Fe,O, was used as photoanodes for the photodecomposition of alkaline aqueous solutions into H , and O , , the ad- dition of Pt increased the carrier density and gave a more negative flatband potential.

89, (17)s 3766-3771

93 (8/9), 539-543

M. R. ST. JOHN, A. J . TILLER, R. L. COOK and A. F. S A M -

I 859-1 864

Platinum Metals Rev. , 1986, 30, (1) 40

Photoactivated Oxidation of Alcohols by Oxygen

SOC., 1985, 107, (zI), 6116-6117 Primary and secondary alcohols can be converted to the corresponding aldehyde or ketone by using 0, and visible light. The process is catalysed by the presence of H , PtCl, and CuCl, . The reaction occurs at room temperature and ~ a t m 0, in neat alcohol. The catalytic cycle is stable for several days when using primary or secondary substrate alcohols.

In Situ Generation of Catalyst-Coated CdS Particles in Polymerized and Un- polymerized Surfactant Vesicles and Their Utilization for Efficient Visible- Light-Induced Hydrogen Production Y.-M. TRICOT, 8. EMEREN and 1. H. FENDLER, J. Phys. Chem., 1985, 89, (22), 4721-4726 Colloidal CdS particles were in situ generated and coated by Rh or Pt in vesicles formed from dihex- adecyl phosphate, (DHP), dioctadecyldimethylam- monium chloride, and from a surfactant containing a polymerisable styrene moiety (A). A clearly detec- table fluorescence emission was found only for CdS in DHP vesicles. Photosensitised H, generation by visi- ble light was measured and electron donors were tested. EDTA was efficient in polymerised (A) vesicles. Benzyl alcohol was a very efficient electron donor in cationic vesicle systems, but not in negative- ly charged systems. With I% benzyl alcohol at 4ooC in vesicles prepared from polymerised (A), a max- imum rate of - 2mpmol/h of H, was achieved, using only o.8zmg CdS/Rh catalyst. The overall quantum yield of H, generated at 4oonm was 10%.

Characteristics of Photoelectrochemical Cells with Iron-Oxideh-Si Heterojunc- tion Photoanodes T. OSAKA, N. HIROTA, T. HAYASHI and s. s. ESKILOSEN, Electmchim. Acta, 1985, 30, (9), 1209-1212

The Fe oxideh-Si heterojunction electrode was studied as a photoanode for a regenerative photoelec- trochemical (PEC) cell. Modifying the top layer of the electrode with Pd or RuO, enhanced the optical-to- electrical conversion efficiency. A stable PEC had conversion efficiencies of I . 34% and I .6o% for a Pd- and a RuO, -modified electrode, respectively.

Preparation of Active CdSIRuO, Par- ticles for the Photogeneration of H 2

R. E . CAMERON and A. B. BOCARSLY, J. Am. Chem.

D. H. M. W. THEWISSEN, K. TIMMER, E. A. VAN DER ZOUWEN-ASSINK, A. H . A. TINNEMANS and A. MACKOR, J . Chem. SOC., Chem. Commun., 1985, (zI), 1485-1487 The preparation of RuO, from RuO, and in situ generated Ru hydroxide or ruthenate ions, followed by calcination at 4moC gives active catalysts without noxious oxidation of the C d S support. The nature and activity for the photogeneration of H, by various CdSIRuO, powders are given.

Photoelectrochemical Behaviour of RuS Semiconducting Electrodes A. M. REDON, Solar Cells, 1985, 15, (I), 27-37 Various parameters of sintered and single crystal RuS, photoelectrodes are examined. Estimated band gap values for the sintered electrode were I . 5eV for the direct transition, I.8eV for the indirect transition and 2.3eV for the single crystal. RuS, appears to be a good semiconductor for 0, evolution and solar energy conversion due to its great stability. The shape and time evolution of the photocurrent are examined.

Quantum Yield of Formation of Methylviologen Radical Cation from the Photolysis of the Ru(bpz)f + /Methyl- viologenlEDTA System

Phys. Lett., 1985, 121, (I, z), 61-64 Values for the quantum yield of formation of MV'as a function of pH, [MV"] and (EDTA) are given, and Ru(bpz):+/MV*+/EDTA is evaluated as a model system for the photochemical storage of radiant energy, since it has been suggested that Ru(bpz):+ is a superior catalyst to Ru(bpy):+ for water splitting reactions.

D. R. PRASAD, D. HESSLER and M. Z . HOFFMAN, Chem.

ELECTRODEPOSITION AND SURFACE COATINGS Pt-Al,O, Selective Cermet Coatings on Superalloy Substrates for Photothermal Conversion up to 600 O C

THIER, Thin Solid Films, 1985, 126, (xh), 17-22 Pt-Al ,O , cermet coatings deposited by r.f. cosputter- ing on stainless steel and superalloy substances were manufactured and tested. Optical properties were measured before and after annealing procedures and optimisation of the absorber selectivity was attemp- ted. The cermet proved to be a good coating for high temperature photothermal selective absorbers and selectivity could be improved. High temperature selective absorbers for industrial applications can therefore be made.

Plating Process for the High Speed Deposition of Palladium for Contact Devices J. VANHUMBEECK, Siemens Forsch.-Entwicklungsber., 1985, 14, (9, 140-146 A new high speed Pd plating process with an elec- trolyte of Pd chloride, using NH, as complexing agent and phosphate as buffer is described. The cur- rent density and electrolyte movement determine operating conditions to give smooth, semi-bright, crackfree deposits. The contact resistance of the deposits are low and stable even after corrosion testing. Pd layers with an upper Au flash have good wear resistance and a low coefficient of friction.

TRAN KHANH VIEN, C. SELLA, J. LAFAIT and S. BER-

Platinum Metals Rev. , 1986, 30, (1) 41

Electrodeposition of Palladium-Nickel Coatings from a Hydrochloric Acid Elec- trolyte I. P. NENOV and L. TEBAI, Metalloberflaeche, 1985, 39, (1 I), 405-410 A new HC1 electrolyte for electrodeposition of Pd-Ni alloy coatings has been developed. The pH of the electrolyte for optimum conditions is 4.5. The thickness of the deposit, temperature of the solution and current density for deposition are discussed. The electrolyte has a simple synthesis and besides the salts of both metals and the organic ligands contains no other additions.

Electrodeposition of Ruthenium from a LiCI-KCI Melt A BETTELHEIM, F. BROITMAN, u. MOR and R . HARTH, 3 . Electrochem. SOL., 1985, 132, (7), 1775-1776 Thick adherent and compact electrodeposits of Ru were obtained from a LiC1-KCI melt at temperatures as low as 400OC, provided that the melt was saturated with HC1. Coatings up to 4 . 4 m thick, with a cathodic current efficiency of 77% were produced in a bath containing a Ru ion concentration of 0.26 w/o on ap- plying a current density of 5 .qA/cm2.

LABORATORY APPARATUS AND TECHNIQUE New Platinum Silicide Formation Method Using Reaction between Platinum and Silane

PhYs.9 19859 58, (8), 3190-3194 A new method for the formation of Pt silicide is pro- posed. l’t film reacts with SiH, at z50-400°C form- ing Pt silicide. This formation with SiH, is less influenced by 0 contamination than the reaction bet- ween Pt and substrate Si. Pt silicide formation was not influenced by Si-Pt interface contamination, and erosion of Si from the substrate can be reduced without limiting l’t silicide thickness, since Si used for the silicide formation comes from SiH, . Thus this Pt silicide will be useful for the contact electrode on shallow diffused layer of fme pattern Si integrated cir- cuits and for gate and interconnect metallisations.

Performance of Carbon Monoxide- Sensitive MOSFET’s with Metal-Oxide Semiconductor Gates K. DOBOS and G . ZIMMER, IEEE Trans. Electron Devices, 1985, 32, (7), 1165-1169 A multilayer PdO-Pd gate metallisation was in- vestigated as a MOS-CO sensor. The sensor had high sensitivity to CO and good electrical control of the transistor. By comparison with a SnOl commercial CO sensor it has lower cross sensitivity for CH,, butane and C,H,OH. The MOSFET was less in- fluenced by humidity than the commercial sensor.

Y. TAKAHASHI, H. ISHII and J . MUROTA, 3.

MOS Hydrogen Sensors with Ultrathin Layers of Palladium G. J. MACLAY, IEEE Trans. Electron Devices, 1985,

MOS gas sensors were fabricated on n- and p-type Si(5-7S2cm) with thermal oxide layers from 66-269A thick. A 3oAPd layer was deposited through an evaporation melt and covered by a 350 A thick Au layer. The devices were sensitive to H , at room temperature. They also had faster response and recovery at room temperature, and reduced magnitude of response than ones with a 300K thick Pd layer. Devices on p-Si were faster than on n-Si.

3% (71, 1158-1164

HETEROGENEOUS CATALYSIS Effect of Pellet Mobility on the Poisoning Behavior of Packed-Bed Catalytic Con- verters B. K. en0 and s. H. OH, Ind. Eng. Chem., Process Des.

A unique method for analysing the effect of pellet mobility on the poisoning behaviour of packed-bed catalytic converters under pore-mouth poisoning con- ditions is used to examine the oxidation of CO, C,H,, CH, and H, over Pt/Al,O,. Warm up times and steady-state conversions could be simultaneously examined, and the effects of several variables are ex- amined. A single-compartment converter provides the best overall performance, and catalysts with large effective diffusivity have smaller performance deterioration than those with small effective diffusivi- ty, also an increase in impregnation depth up to 200 - 300pm would improve warm up performance without affecting the warmed up performance.

Oxidation of Tritium in Packed Bed of Noble Metal Catalyst for Detritiation from System Gases

and M. ENOEDA,3. Nucl. Muter., 1985, 135, (I), 1-10

Catalytic oxidation rates of tritium over the catalyst beds Pt/Al,O, or Pd/Al,O, are discussed. These catalysts give effective oxidation rates of tritium in the ambient temperature range. The adsorption per- formance of tritiated water in the catalyst bed is also discussed.

Oxidation of Ethanol on Silica Supported Noble Metal and Bimetallic Catalysts

Dev., 19853 24, ( 4 , 897-906

M. NISHIKAWA, T. TAKEISHI, K. MUNAKATA, K. KOTOH

R. D. GONZALEZ and M. NAGAI, Appl. catal., 1985,18, (I), 57-70 The oxidation of C,H,OH was studied over SiO, supported Pt, Ru, Pt-Ru, Pd and Rh catalysts. Pt was the most active catalyst for CO, formation. Ru was highly selective for acetaldehyde formation at 40-10o0C. Infrared studies suggest the presence of an acetate intermediate in addition to an adsorbed ethoxy species and chemisorbed CO. The ethoxy species are adsorbed both on Pt and SO, .

Platinum Metals Rev. , 1986, 30, (1) 42

Dynamic Behaviour of Automotive Catalysts. 4. Impact of AirlFuel Ratio Ex- cursions during Driving R. K. H E W and E. J. SHINOUSKIS, Ind. Eng. Chem., Prod. Res. Dev., 1985, 24, (3), 385-390 The analyses of emissions from automobiles over Pt/Pd/Rh/Al,O, and Pt/Pd/Rh/Ce/Al,O, catalysts during the warmed up portion of the Federal test pro- cedure are compared. The 0 storage capacity obtain- ed by adding Ce to the catalysts gave dramatically increased CO conversion following lean-to-rich step changes. Near lean A/F ratios, near the stoichiometric point, and during the as cycled A/F tests the two catalysts were in reasonably good agree- ment. It is concluded that large amplitude low fre- quency components of A/F fluctuations must be considered in future studies.

A Prototype Truck Powered by Hydrogen from Organic Liquid Hydrides M. TAUBE, D. RIPPIN, W. KNECHT, D. HAKIMIFARD, B. MILISAVLJEVIC and N. CRUENENFELDER, Znt. 3. Hrdrogn E ~ w , 1985, 10, (91, 595-599 A prototype truck has been constructed to use a H,- burning engine with H, injection under 10 bar pressure. The engine efficiency is -32%, with ex- haust gas temperature of -7ooOC and power of - 150 kW. The H, at 10 bar is produced continuous- ly by catalytic splitting of methylcyclohexane on o.25Pt-0.25Re/~,03 on board the truck. The reac- tion occurred at 10 bar pressure, 4woC, efficiency -0.80 and lifetime several hundred hours, without H, recycling.

Behaviour of Hydrogenation Catalysts. 1. Hydrogenation of Soybean Oil with Palladium 1. D. RAY, 3. Am. Oil Chem. SOC., 1985, 62, (8),

A statistical method for evaluating catalysts was used in determining the behaviour of 5% Pd/C catalysts for soybean oil hydrogenation. Pd had very high activity, but offered no special advantage in trans-isomer for- mation or selectivity. Pd could substitute for Ni catalysts at greatly reduced temperature and catalyst concentration, for production of salad oil or margarine basestock from soybean oil.

Water Production on Palladium in Hydrogen-Oxygen Atmospheres

Surf.Sci., 1985, 163, (I), 273-284 Water production on a Pd-Si0,-Si structure in various 0,-H, atmospheres was measured together with work function, photoelectron spectroscopies and H sensitive measurements. A critical 0, :H, pressure ratio is confmed, above which water production rate decreases with increasing 0, pressure, and increases with increasing H, pressure. Below the critical ratio the H,O production rate is proportional to 0, pressure and independent of H, pressure.

1213-1217

L.-G. PETERSSON, H. M. DANNETUN and I. LUNDSTRbM,

Methanol and Methane Formation over PalladiumIRare Earth Oxide Catalysts C. SUDHAKAR and M. A. VANNICE, 3. catal., 1985, 95, (I) , 227-247 Lanthanide rare earth oxide supports for Pd systems provide very good CO hydrogenation catalysts, especially for CH,OH formation. At low temperatures and 1 atm pressure the major product was CH,OH, but selectivity shifted to CH, at higher temperatures. Turnover frequency values for CH, varied more than tenfold, and all catalysts except PdEu , 0 , had an order of magnitude higher activity than on Pd/SiO, or pure Pd metal. Activation energies for CH, were consistently around 32 kcal/mole. Pd/La,O, and Pd/Nd,O, were the most active CH,OH catalysts, and Pd/CeO, was the least active. (4 Refs.)

Polybenzimidazole-Supported Hetero- geneous Palladium Catalysts N.-H. LI and J. M. J. d C H E T , 3. Chem. soc., Chem.Commun., 1985, 16, (16), 1100-1101

The polybenzimidazole.PdC1 , was prepared easily and the loading of PdCl, onto the PBI could be readily controlled by varying the Pd:PBI ratio. The catalyst with only Pdo was extremely stable, and could be heated to 3woC for several hours without decomposition, and showed excellent activity in reducing various nitro compounds. The catalyst was easy to recycle and showed no loss of activity or Pd content after more than 20 cycles, or after heating in air to 3woC for 6h.

The Oxidation of Carbon Monoxide on Polycrystalline Rhodium under Knudsen Conditions. I. Reaction with Oxygen. 11. Reaction with Nitrogen Monoxide. 111. Simultaneous Reaction with Oxygen and Nitrogen Monoxide H . 4 . LINTZ and T. WEISKER, Appl. surf. sci., 1985,

The reaction between 0, and CO on polycrystalline Rh ribbon was observed at 300-1 I ooK and pressures between 10-' and 10-' torr. The reaction on Rh has similar features to that on Pt. The reaction between CO and NO on polycrystalline Rh ribbon was also observed. In the temperature range 300-1oooK the partial pressures of the two reactants varied o.~<p,,Jp,,<~oo at pressures I@-10-5 torr in the reactor. The CO oxidation using mixtures of 0, and NO was studied. At high temperatures the amount of NO reduced is directly proportional to its fraction in the oxidising gas. At low temperatures NO may be reduced with high selectivity.

Surface Conversion of Benzene to Acetylene W. L. PARKER, R. M. HEXTER and A. R. SIEDLE, 3. Am. G e m . sot., 1985, 107, (IS), 494-4585 Using a 10% Rh/a-Al,O, catalyst, benzene was converted to acetylene under UHV conditions.

24, (2), 251-258; 259-267; 268-273

Platinum Metals Rev., 1986, 30, (1) 43

Selective Synthesis of Ethanol over Rh- Ti-Fe-IrlSiO Catalyst and High Pressure Syngas Conversion

SUSHITA, K. TAKEUCHI, T. MATSUZAKI and Y. SUGI, Chem. Lett. Jpn., 1985, (7) , 881-884 A high performance Rh-Ti-Fe-Ir/SiO I catalyst for ethanol production has been developed. Ethanol was produced with > 50% selectivity from syngas at 50 atm and 260OC.

Postcrosslinking of Rhodium Catalysts Bound to Polyacrylic Acid: A Useful Technique to Enhance and Preserve Catalytic Activity G. VALENTINI, G. SBRANA, G. BRACA and P. DA PRATO, 3. Catal., 1985, 96, (I) , 41-50 A significant improvement in catalytic performance of triphenylphosphine polyacrylate Rh(1) complexes was obtained on optimising the preparation condi- tions and by adding a crosslinking agent (hex- amethylenediamine). The crosslinked systems, insoluble in organic solvents, were obtained in high yields and had catalytic activity for pent-I-ene hydrogenation and isomerisation higher than that of a low molecular weight analog working in solution. The systems had remarkable catalytic stability and very constant selectivity upon recycling.

Water Gas Shift Reaction Catalyzed by Osmium Compounds Supported on Zeolites. Evidences for Formation in the Presence of a Base of a Trapped Hydrido- Carbonyl Catalyst

SPOLIARICH, 3. Organomet. Chem., 1985, 290, (z), 213-218 Thermal treatment of 0 s , (CO) , /zeolite gives a new species which in the presence of base is an active catalyst for the water gas shift reaction. When NaOH is used the hydrido-carbonyl anion [H,Os, (CO) ," I - is formed and trapped in the zeolite framework. This compound is also an active catalyst for the water gas shift reaction.

Effect of Potassium and Phosphorus on the Hydrogenation of CO over Alumina- Supported Ruthenium Catalyst

1985, 95, (11, 41-48 The effects of additives K, B and P on Ru/AI,O, were investigated for the adsorption and catalytic hydrogenation of CO. Addition of K increased the strength of CO adsorption by enhancing the back donation from Ru to CO. K also significantly increas- ed the o1efin:paraffin ratios in product hydrocarbons and suppressed CH, formation, while catalytic activi- ty was decreased by the addition. Addition of P or B brought about opposite changes in both CO adsorp- tion and CO hydrogenation.

H. ARAKAWA, T. FUKUSHIMA, M. ICHIKAWA, S. NAT-

M. LENARDA, R. GANZERIA, M. GRAZIANI and R.

T. OKUHARA, H. TAMURA and M. MISONO, J. catal . ,

Metal Cluster Catalysis: Preparation and Catalytic Properties of Anionic Triruthenium Clusters Anchored to Func- tionalized Silica Y. DOI, H. MIYAKE, A. YOKOTA and K . SOGA, Inorg. Chim. Acta, 1985, 105, ( I ) , 69-73 The anionic cluster [ Ru , H(C0) I I 1- was anchored onto a SiO, surface, modified with ammonium and pyridinium functions and used as a catalyst for the water gas shift reaction and for ethylene and CO hydrogenations. The $40, anchored clusters were stable up to 15ooC and exhibited higher catalytic ac- tivities for C , H, hydrogenation (7oOC) and the water gas shift reaction (150OC) than those of SiO, an- chored Na[Ru,H(CO),

HOMOGENEOUS CATALYSIS Catalytic Properties of the Platinum and Palladium Blacks Obtained from Vaporized Metals as Revealed in the Hydrogenation of 4-Methylcyclo- hexanone in Ethanol

and M . UDA, Chem. Lett. Jpn., 1 9 8 5 , (8), 1275-1278 Pt and Pd blacks were obtained from vapourised metals and catalysed the formation of acetal efficiently during the hydrogenation of 4-methylcyclohexanone in ethanol. Pt(NRIM) was the most active of the Pt blacks investigated, and had a much smaller surface area than the others.

Colloidal Platinum Catalysts Prepared by Hydrogen- and Photo-Reduction in the Presence of Surfactant

3 ~ n . , 1985, (81, 1245-1248

S. NISHIMURA, S.-I. IWAFUNE, T. NAGURA, Y. AKIMOTO

N. TOSHIMA, T. TAKAHASHI and H . HIRAI, Chem. Lett.

Chloroplatinic acid in an aqueous solution was reduc- ed by H, molecules or photo irradiation in the presence of surfactants to produce colloidal disper- sions of Pt protected by the surfactants. Particles pro- duced by photoreduction were smaller and more narrowly dispersed than those prepared by H , reduc- tion. They were highly active catalysts for olefin hydrogenation.

Stability of the Structure of Polynuclear Cluster Compounds and Their Reaction Activity for Olefm Hydroformylation

LI, 3. Catal. (Dalian, China), 1985, 6, ( z ) , 172-178 RhC1,.3H,O was used as starting material for the synthesis of Rh, (CO) I , and Rh (CO) I These two polynuclear clusters were very good catalysts for the hydroformylation of olefms, such as hexene-1, heptene- I and cyclohexene. The catalytic activities for hexene- I hydroformylation of these two Rh clusters were compared to those of RhCI(CO)(PPh,),, RhCo,(CO),, and ClCCo ,(CO), .

W.-J. XIE, F.-Y. JIAO, S.-K. YANG, Y.-Q. YIN and D . 4 .

Platinum Metals Rev., 1986, 30, (1) 44

Synergistic Behavior of Homogeneous Ruthenium-Rhodium Catalysts for Hydrogenation of Carbon Monoxide B. D. DOMBEK, &ga?WmetalkS, 1985, 4, (IO), I 707-1 71 2

Homogeneous solutions containing complexes of both Ru and Rh exhibit good selectivity for the catalytic hydrogenation of CO to ethylene glycol. Reactions were studied at pressures from 400-850 atm and 190-24ooC. Iodide ion was an effective promoter. Metal complexes observed in solutions included [HRu,(CO),,]-, [RU(CO)~I,~- and [WCO) 2 1 2 I-.

Water Gas Shift Reaction, Development and Study of Eftkient Homogeneous Catalysts Based on Iridium-Diimiie Com- plexes

Chim., 1985, 9, (61, 395-404 J . P. COLLIN, R. RUPPERT and J. P. SAUVAGE, NOUV. J .

A detailed study of the water gas shift reaction catalysed by several Ir (I) complexes under a range of experimental conditions is presented. The most effi- cient catalytic system was obtained from Ir(dmp- S)(COD) + (dmp-S = sulphonated derivative of 2,9-dimethyl I ,Io-phenanthroline; COD = I ,5-cyclo- octadiene). Turnover frequencies close to 10’ /h have been observed at IOOOC and under xatm CO, making this system one of the most efficient catalysts ever reported. The chemical stability of the homogeneous catalyst is good, even after several thousand cycles; and activity remains unchanged. (85 Refs.)

The Chemistry and Catalytic Properties of Ruthenium and Osmium Complexes. Part 1. Homogeneous Catalysis of Organic Reactions by Bromo(car- bony1)hy dridotris(tripheny1phosphine)os- mium(I1) R. A. SANCHEZ-DELGADO, A. ANDRIOLLO, E. GONZALEZ, N. VALENCIA, V. LE6N and J. ESPIDEL, J. Chem. SOC., Dalton Trans., 1985, (9), 1859-1863 The complex [OsH(Br)(CO)(PPh,) , ] catalyses C=C bond migration, isomerisation of ally1 alcohol, hydrogenation of acyclic and cyclic olefms, dienes, acetylenes, aldehydes, ketones, a, &unsaturated aldehydes and ketones, and hydroformylation of alkenes under moderate reaction conditions. This catalyst combines high activity and selectivity under mild conditions with ease of preparation, handling and recycling.

The Generation of N-Alkylformamides from Synthesis Gas and Ammonia J. F. KNIFTON, J . Chem. soc., Chem. Commun., 1985,

N, N-dimethylformamide and N-methylformamide have been prepared from syngas with NH, by Ru melt catalysis. Several different catalyst precursors were used, but mostly employing Ru , (CO) I , .

(ZO), 1412-1414

(Cyclopentadienone) Ruthenium Car- bony1 Complexes-A New Class of Homogeneous Hydrogenation Catalysts Y. BLUM, P. CZARKIE, Y. RAHAMIM and Y . SHVO, Organometallics, 1985, 4, (8), 1459-1461 [(v4 -Ph, C , CO)(CO) , Ru] I and [(v’-Ph Me, C, C0)- (CO),Ru], represent a new class of efficient precatalysts for homogeneous hydrogenation of alkenes, alkynes, etc., under moderate conditions.

FUEL CELLS Application of Carbon Fiber Felts to Air Electrodes for Fuel Cells. 11. The Effects of Stacking of Felts, Temperature, and Oxygen Partial Pressure on Discharge Properties Y. KERA and M. YOKOTA, Denki Kagaku, 198553, (8), 601-605 A Zn-air cell was constructed, in which KF-1000 felt with a Pt deposit was applied to the air electrode. Electrode potential was measured under discharge at various constant currents. The drop in terminal voltage was due to the air electrode. The maximum power, evaluated from the p.d. between the two elec- trodes could be increased up to three-fold by stacking up to 4 felt sheets on top of each other. At 50°C the maximum power increased by 250% over that at 17OC, and replacing air with 0, gave a further 150% improvement. With 4 sheets of stacked Pt-KF felt in an 0, stream at 5o°C temperature, the maximum power reached ~xgmW/cm’ at i= 17omA/cm’.

Oxygen-Reducing Electrodes for Acid Fuel Cells K. V. RAMESH and A. K. SHUKLA, 7. Power SOUTCeS, 1985, 15, (2&3), 201-205 Electrochemical data for 0, reduction on platinised coconut-shell charcoal electrodes with various Pt loadings in 2.5M H,SO, and 7M H,PO, are reported. The electrodes in both media had good ac- tivity and could sustain currents up to b m A / c m 2 at a polarisation of - 4oomV from their rest potentials.

Electrocatalysis by Ad-Atoms. Part XIII. Preparation of Ad-Electrodes with Tin Ad-Atoms for Methanol, Formaldehyde and Formic Acid Fuel Cells M. WATANABE, Y. FURUUCHI and s. MOTOO, J . Elec- troanal, Chem. Interfacial Electrochem., 1985, 191,

A high specific area Pt electrode with well defined Sn coverage has been developed for use in organic fuel cells. The resulting electrode has enhancement effects in the specific activity over a pure Pt black electrode by a factor of 100 for methanol oxidation, >loo0 for formaldehyde oxidation and of 250 for formic acid ox- idation. A much higher specific surface area of catalyst is obtained by this simplified preparation.

(2), 367-375

Platinum Metals Rev. , 1986, 30, (1) 45

ELECTRICAL AND ELECTRONIC TEMPERATURE ENGINEERING MEASUREMENT

160 x 244 Element PtSi Schottky- Barrier IR-CCD Image Sensor w . F. KOSONOCKY, F. v . SHALLCROSS, T. s. VILLANI and J. v. GROPPE, IEEE Trans. Electron Devices, 1985, ED-32, (8), 1564-1573 A 16ox 244 element i.r. charge coupled device image sensor was developed with 80x40 Fm2 pixels for operation at 30 framesls with standard TV face inter- face. The sensor was developed with PtSi Schottky barrier detectors for 3.0-5.opm thermal imaging.

Novel Method of Producing Ultrasmall Platinum Silicide Gate Electrodes

and 1. F. c. M. VERHOEVEN, Appl. Phys. Lett., 1985, 472 (7), 700-702 To produce Pt silicide gate electrodes a novel method using a lateral chemical reaction of Pt with polycrystalline Si at a step edge was developed. The width of the wire is determined by the thickness of a sputtered metal layer. Wires with widths between 35 and 300nm have been produced.

In/Pt Ohmic Contacts to GaAs D. C. MARVIN, N . A. IVES and M. S. LEUNG, J . Appl. PhYs., 1985, 58, (7A 2659-2661 Graded heterojunction InGaAs ohmic contacts to GaAs with improved electrical and mechanical pro- perties have men produced. The improvements result from thc use of a thin Pt layer between the In layer and the ~m(GaAs) substrate. This layer moderates the reaction of the In and GaAs producing a uniform contact with lower electrical resistivity.

P. H. WOERLEE, G. A. M. HURKX, W. 1. M. J. JOSQUIN

Properties of Industrial-Grade Platinum- Cobalt Resistance Thermometer between 1 and 27K n. SAKURAI and L. M. BESLEY, Rev. Sci. Instrum., 1985, 56, (61, 1232-1235 The stability at 20K of five industrial type Pt-Co resistance thermometers undergoing thermal cycling has been studied, together with their resistance- temperature (WT) characteristics between I and 27K, and their self-heating. The stability at 20K on cycling between room temperature and 20K is - romK, and on cycling between 1 0 0 and 20K it is a few mK. Differences in the R/T relationship between thermometers were very small, but the self-heating effects are relatively large, particularly at temperatures below 4K.

A Reference Function for Platinum Resistance Thermometer Interpolation between 13.8K and 273.15K R. c. KEMP, L. M. BESLEY and w. R. G. KEMP, Metrologia, 1985, 21, (3), 139-146 Recent accurate thermodynamic data are combined to provide a basis for a reference function for Pt resistance thermometer interpolation between 13.81K and 273.15K. The values of thermodynamic temperature for defining the fixed points of the IPTS and also for a number of secondary points are more accurately assigned than previously. A temperature scale based on this reference function and these defin- ing fixed points would give thermodynamic temperatures to f 2mK. This system is proposed for use in the revision of the IPTS.

NEW PATENTS METALS AND ALLOYS CHEMICAL COMPOUNDS

Creep Resistant Platinum Alloys OWENS-CORNING FIBERGLAS CORP.

U. S. Patent 4 , 5 0 7 ~ 56 The creep resistance of a thermomechanical process- ed Pt-based alloy, for example yttria dispersion- strengthened Pt, is improved by heating the alloy to at least 2800OF for at least 6 hours.

Resistance Alloy

ALLOYS U.S. Patent 4,518,439 An electrical resistance alloy having a very low temperature coefficient of resistance over a wide range of temperatures contains 59-88% Pd and 12-41% Fe and is produced by working the material in a specified manner.

RESEARCH INSTITUTE OF ELECTRIC & MAGNETIC

Tetrarhodium Dodecacarbonyl W W CHEMICAL CO. U. S. Patent 4,514,380 Rh,(CO),, is made in less than two hours by reacting RhCI, with CO in the presence of activated Cu and a Group IA metal halide and at 25-75OC and a pressure of 3.52-35.2 kglcm’.

ELECTROCHEMISTRY Electrode Manufacture

A liquid composition containing electrode component metal (such as Ru, Pd or Ir) ions and an organic com- pound capable of forming a complex with the metal ions is thermally decomposed to form an electrode.

PERMELEC ELECTRODE LTD. British Appl. 2 , I 54,248A

Platinum Metals Rev., 1986, 30, (l), 46-52 46

Electrode for Electrolysis T.D.K. CORP. European Appl. I 53,586 Electrodes for use, for example, in the electrolysis of brine and providing increased 0 overvoltage, reduced 0 evolution and improved anodic current efficiency consist of a valve metal substrate coated with a mix- ture of 10-30 mol% Ru oxide, 5-15 mol% Pt, Pt ox- ide and/or Ir oxide and 55-85 mol% Sn oxide.

Cryoelectrodeposition Electrode R. M. ROSE and D. R. SADOWAY European Appl. 155,749 Amorphous metals and semiconductors may be elec- trodeposited in a cryogenic environment using Pt foil electrodes.

Ruthenium-Coated Electrodes DOW CHEMICAL CO. U.S. Patent 4,507,183 An electrode is produced by electroplating Ru metal on to a substrate from a nonacidic Ru-containing elec- troplating solution which includes a salt of the com- plex [Ru,N(H,O),X,]’- where X i s c1 or Br.

Anode for Electrolysis R. C. LANGLEY U.S. Patent 4,512,866 An improved anode for use in electrolytic processes with an electrolyte containing H, SO, acid consists of a valve metal substrate coated with a Pb antipassiva- tion layer and then with a Pb ruthenate or Pb iridate catalyst.

Anode Electrocatalyst BBC BROWN BOVERI co. LTD. U.S. Patent 4,513,102 A catalyst for coating anodes for electrolysis is a rutile crystal containing (in mols) 10-96% SnO,, 2-45% IrO, and 2-45% RuO,.

Photoelectrode UNION OIL co. OF CALIFORNIA U.S. Patent 4,521,499 A specified photoelectrode consists of a substrate con- taining a semiconductor material and a thin conduc- tive coating which may be RuS,, PtCoO,, PdCoO,, PdCrO, or PdRhO,, among others.

Water Electrolysis UNITED TECHNOLOGIES CORP. U.S. Patent 4,528,083 The generation of 0, from a membrane electrolytic cell having a conventional catalytic cathode is improv- ed by using a catalytic anode which is a ternary com- position of at least two platinum group metals and one valve metal or their oxides. The preferred com- position is 50% Ru, 25% Ir and 25% Ta.

Anode for the Electrolysis of Sea Water

TSENTRA AN SSSR Russian Patent 1,139,770 An anode of improved stability for use in the elec- trolysis of sea water consists of a Ti substrate coated with a mixture of 2 5 9 1 % Co, 3-15% Ru and 6-60°/0 Ti in the form of their oxides, such that the ratio Ru oxide:TiO, is 1:2-4.

INSTITUT KHIMII DALNEVOSTOCHNOGO NAUCHNOGO

ELECTRODEPOSITION AND SURFACE COATINGS Palladium Electroplating A. T. & T. BELL LABORATORIES U.S. Patent 4,512,963 In an improved Pd electroplating process the metal is supplied as a Pd diammine hydroxide.

Corrosion-Resistant Coating NASA U.S. Patent 4,522,844 A uniform thin metal fdm free from pinholes is deposited on a substrate by bombarding the amor- phous metal or alloy with ions of an inert gas in the presence of a magnetic field and depositing the vapour so formed. Platinum group and/or lanthanide metals may be used in the process, and specific alloys include (MOO.~RU~.~)~ZB~~.

Thermally Stable Coatings TURBINE COMPONENTS CORP. U.S. Patent 4,526,814 Procedures for protecting the surface of Ni-, Co- or Fe-based alloys from high-temperature oxidation by forming a protective diffusion layer of combined Al, Cr and Pt are claimed.

Palladium Electroplating Bath INOVAN-STROEBE c.m.b.H. & CO. K.G.

Geman Offen. 3,347,384 Uniform, bright, ductile Pd coatings are obtained by electrodeposition from a bath containing a Pd salt, a complexing agent which is a pyridine derivative such as pyridine acetic acid and Na K tartrate.

LABORATORY APPARATUS AND TECHNIQUE Toxic Gas Detection U.S. DEPARTMENT OF ENERGY

British Appl. 2,155,184A An instrument for detecting low concentrations of a pollutant or other component in air or other gas, in- cludes a heating filament having a catalytic surface of a noble metal (such as Pt, Ir, Pd, Rh, Au, or a mix- ture of Pd and Ag), for exposure to the gas and pro- ducing a derivative product from the component, and an electrochemical sensor.

Force Detector SHIMADZU CORP. European Appl. I 50,584 In a high-precision, vibration-type force detector of good stability the vibration string is made of a Pt- based Ni-containing alloy such as 92.5%Pt-7.5%Ni.

Analytical Apparatus ANATEL INSTRUMENT CORP. European Appl. I 50,923 An instrument for measuring the organic C content of water samples incorporates two concentric circular electrodes, preferably of Pt, Pd, Rh, Ir or Ti.

Platinum Metals Rev., 1986, 30, (1) 47

Oxygen Sensor TOYOTA CHOUO KENKYUSHO K.K.

U.S. Patent 4,510,036 A limiting electric current type 0 concentration detector of simple construction incorporates a ZrO, solid electrolyte, for example, stabilised with Y ,01, a Pt film electrode and a Pt f im heater.

Radiation Pyrometer SMITHS INDUSTRIES P.L.C. U.S. Patent 4,521,088 A radiation pyrometer for a gas-turbine engine has a sapphire lens which focuses radiation from the tur- bine blades on to the end of a fibre-optic cable. The exposed front surface of the lens is coated, by vapour- phase deposition, with a mixture of AI,O, and Pt to catdyse the oxidation of soot.

Carbon Monoxide Sensor HONEYWELL INC. U.S. Patent 4,523,690 A sensor for toxic gases such as CO incorporates a Pt sensing electrode, a Pt counter electrode and a Ag- AgCl reference electrode.

Gas Sensor ALLIED CORP. U.S. Patent 4,525,266 An electrochemical cell, particularly suitable for detecting H , S, includes a C counter electrode, a Pt or Au sensing electrode and a Pt reference electrode.

JOINING Brazing Alloy ALLIED CORP. U.S. Patent 4,508,257 An alloy, which is free from B and P and is suitable for brazing at less than IOOOOC, consists of Ni with 15-20 at.% Si and 25-35 at.% Pd.

Glass-to-Metal Seal HONEYWELL INC. U.S. Patent 4,509,880 In a procedure for sealing a glass rod or tube into a narrow tube of metal, such as steel, the inserted end of the glass is first metallised for better bonding with the solder. According to the claims the metallisation consists of successive thin films of Ti-W alloy, Ni and Au but in the text a double coat of Pt-Ag is best.

HETEROGENEOUS CATALYSIS Hydrocarbon Reforming

Hydrocarbon Conversion CHEVRON RESEARCH co. British Appl. 2,153,840A A hydrocarbon feed having a S concentration < 500 ppb is reformed over a dehydrocyclisation catalyst with a large-bore zeolite of at least one Group VIII metal, preferably Pt, to produce aromatics and H, .

Coal Liquefaction COAL INDUSTRY (PATENTS) LTD.

British Appl. 2,156,841A In a method of coal liquefaction using a liquid H donor solvent, at least part of the solvent is catalytically dehydrogenated using Pt and/or Pd on AI,O,, SiO, or C, to reduce the cyclic saturates.

Heating Apparatus NAKAJIMA DOKOSHO c o . LTD. British Appl. 2,156,964A A heating apparatus, such as a soldering iron, using liquefied gas as a heat source, employs a combustion catalyst which is preferably 90-98Yo Pt and 2-10% Rh on AI,O, and/or SiO, coated with y-Al,O,.

Nitrogen Oxide Reduction in Stack Gases UHDE c.m.b.a. European Appl. I 52,907 NO, in the stack gases from coal-fired power stations is reduced in two catalytic stages. In the first stage the reducing agent is the COhydrocarbon component of the gases, and in the second stage the N,O so formed is reacted with an additive such as NH,. In both stages a washable catalyst such as Pt is used.

Hydrocarbon Reforming INSTITUT FRANCAIS DU PETROLE

European Appl. I 53,891 In a process for reforming a hydrocarbon stream by passage through multiple catalyst beds, the first bed, which contains 8-40% of the total amount of catalyst, consists of an AI,O, carrier supporting 0.05-0.6% Pt, 0.005-3% Re and 0.1-15% halogen. The second and any subsequent beds consist of an Al , 0, carrier with 0.05-0.6% Pt, Sn, TI and/or In and halogen.

Diesel Exhaust Gas Purification DEGUSSA A.C. European Appl. 154,145 The filter and converter for diesel engine exhaust gases contains a number of filter layers of two dif- ferent types: (a) a layer carrying a catalyst for pro- moting C black combustion and (b) a layer carrying a catalyst for burning off gaseous contaminants. The catalysts specified mostly contain base metals for (a) and platinum metals for (b).

CHEVRON RESEARCH c o . British Appl. 2, I 53,384A In a method of reforming hydrocarbons, in particular of dehydrocyclising alkanes containing at least 6 C atoms to form aromatic hydrocarbons, the hydrocar-

Catalytic Combustion of Fuel in an I.C. Engine Cylinder

COUNCIL European APPl. 156,543 bons are contacted with a catalyst containing a large- pore zeolite (preferably of type L, X or Y), a Group VIII metal such as Pt, Pd, Rh, Ir or Ru, and one of Ba, Sr and Ca, under conditions so adjusted that the selectivity for n-hexane dehydrocyclisation is > 50%.

An I.C. engine has two cylinders connected at their head ends by a combustion chamber containing a catalyst. The cylinders undergo a four stroke opera- tion but the purpose of the Pt or mixed platinum metal catalyst is low temperature combustion.

Platinum Metals Rev., 1986, 30, (1) 48

Oxidation Catalyst

A catalyst for the adiabatic oxidation of HCN to iso- cyanic acid consists of Pd-plated Ag crystdites.

Reduction Device BECTON, DICKINSON & co. Eumpean Appl. I 58,728 A rupturable package provides means for reducing the 0, in a given volume of air, such as a sealed gas jar, for growing anaerobic bacteria. The package con- tains a H,-generating material and a catalyst such as a supported platinum group metal, preferably Pd.

Chimney Catalytic Reactor FONDIS S.A. European Appl. I 59,955 Pt or Pd catalyst units fitted in a domestic chimney, for example, are provided with a secondary air supply.

Olefm Oxidation Catalyst PHILLIPS PETROLEUM CO. U.S. Patent 4,507,507 A Pdheteropolyacidlsurfactant catalyst system, used with suitable diluents, improves the oxidation of olefins to ketones while reducing corrosive effects.

Catalysts for Olefm Production

AMERICAN CYANAMID CO. Eumpean Appl. 1 5 8 , 1 1 9

AIR PRODUCTS & CHEMICALS INC. U.S. Patent 4,510,267

The conversion of synthesis gas to 2-6C olefins is catalysed by a Ru carbonyl complex such as Ru,(CO),, supported on a carrier consisting of or containing Ce oxide.

Synthesis Gas Conversion Catalyst STANDARD OIL co. (OHIO) US. Patent 4,510,320 A catalyst for the production of alkanes and alkyl acetates from synthesis gas and acetic acid consists of a carrier such as Al 0, -SiO supporting a mixed ox- ide of Ru, Ni and a Group IA metal, preferably Na.

Catalyst for Methanol Conversion EXXON RESEARCH & ENGINEERING CO.

U.S. Patent 4,513,161 A catalyst for the conversion of methanol to higher paraffins and olefins consists of Ru on TiO, . Synthesis Gas Conversion Catalyst EASTMAN KODAK CO. U.S. Patent 4,518,714 A catalyst for the conversion of synthesis gas to olefins consists of a Zn oxide carrier supporting about I% each of Pd and Fe.

Dehydrogenation Catalyst PHILLIPS PETROLEUM c o . U.S. Patent 4,520,223 A catalyst for the conversion of paraffms to olefms or dienes is obtained by depositing a platinum group metal, preferably Pt, on the surface of a pelletised refractory support, using an aqueous solution of an inorganic complex such as (NH,),Pt(SO,),.

Fischer-Tropsch Synthesis MOBIL OIL CO. U.S. Patent 4,523,047 A specified procedure for the conversion of synthesis gas to liquid hydrocarbons incorporates, as catalyst, Pt or Pd supported on ZSM-45 zeolite.

Automobile Exhaust Catalyst UOP INC. U.S. Patent 4,526,886 An improved three-way catalyst consists of an Al,O, carrier supporting a mixture of 60-gooh U, 4 .5 -35% Pt and 0.5-5% Rh.

Sea Water Deoxygenation CONOCO INC. US. Patent 4,527,626 Injection-quality water for use in oil wells is obtained by (a) electrolysing sea water to obtain H,, (b) mixing the H with a mass of sea water containing dissolved 0, and passing the mixture through a catalyst bed. The catalyst preferably consists of anion exchange resin beads coated with Pd.

Automotive Catalyst TOYOTO JIWSHA KOGYO K.K. and CATALER INDUSTRIAL co. LTD. U.S. Patent 4,528,279 A durable catalyst for the purification of I.C. engine exhaust gases consists of a ceramic monolithic substrate coated with a fhn of Al,O, containing 17.5-50% lanthanide metals of which more than goyo are oxides of Ce and La and the atomic ratio Ce:La is O . O ~ - O . ~ : I , and impregnated with Pt and Rh.

Lanthanide Catalyst for Carbonylation Reactions HOECHST A.G. German Offen. 3,340, I I 5 The formation of acetic acid and acetaldehyde from synthesis gas is catalysed by supported Rh, a pro- moter such as Y and a Group IA metal activator, such as Li.

Catalyst for Methanol Conversion SUD-CHEMIE A.G. German Offen. 3,340,569 A catalyst for the conversion of aqueous methanol to synthesis gas consists of a carrier, based on TiO, or GO,, impregnated with o . I ~ - o . ~ % Pt, Pd or Rh.

Oxidation Catalyst DRAGERWERK A.G. German Offen. 3,405,100 A catalyst for the oxidation of CO in industrial ef- fluent gases to CO, consists of an activated C carrier impregnated with an ammine-forming metal such as Zn and then with Pt or Pd.

Purification of Flue Gases SUD-CHEMIE A.G. German Offen. 3,428,231 NO, in flue gases, especially those containing S ox- ides, is reduced by H, and C oxide(s) over a catalyst consisting of an Al , 0, and/or SiOl carrier containing lanthanide metal oxide(s), supporting Pt, Pd, Rh and/or Ru.

Platinum Metals Rev., 1986, 30, (1) 49

Wires for Catalytic Gauzes VEB MANSFELD-KOMBINAT WILHELM PIECK

East German Patent 222,474 Wires for making catalytic gauzes consist of (a) a core which may contain base metal(s) but is preferably an alloy of Pt with 5% Rh and (b) sheath which is preferably made of 75% Pd, 24% Pt and I% Rh alloy.

HOMOGENEOUS CATALYSIS

Platinum- or Palladium-Siloxane Catalysts DEGUSSA A.G. European Appl. I 5 I ,991 New catalysts for hydrosilylation and hydrogenation reactions are polymeric organosiloxane ammonium compounds of formula (NR,) YX- where Y is a Pt or Pd hexahalide or tetrahalide’ion of valance x and R is an organic group of which at least one contains a siloxane group, such as [N(CH,CH,CH, SiO, ,,I, 1 PtQ.

Rhodium Catalyst for Ester Production BP CHEMICALS LTD. European Appl. I 5 5 , I 2 2

A second ester is produced by reacting a fmt carbox- ylic ester, an olefin, CO and H, in the presence of a Rh source, a Ru source and Co or Zn iodide. Thus methyl acetate can be converted to propyl acetate with ethylene in the presence of Rh and Ru trichlorides, Zn iodide and picoline.

Rhodium Complex Catalyst EXXON RESEARCH & ENGINEERING CO.

European Appl. I 59,460 In a process for olefin hydroformylation the catalyst is a Rh complex of formula Rh(L),(CO)H where L is a diary1 (higher alkyl) phosphine.

Platinum Complex Catalysts MINNESOTA MINING & MANUFACTURING CO.

U.S. Patent 4,511,715 Olefm hydrosilylation is catalysed by a complex PtCI,(C,H,)(L) where L is pyridine or phenazine.

Catalyst for Acetaldehyde Production NATIONAL. DISTILLERS & CHEMICAL CORP.

U. S. Patent 4 4 1 4 5 2 1

A catalyst for the production of acetaldehyde and/or ethanol from synthesis gas is preferably [RuCI, (CO) , 1 , promoted with HX, LiX or a halide of a lanthanide metal.

Ruthenium Complex Catalyst STANDARD OIL CO. U. S. Patent 4 , 5 1 9 , 9 5 4

A catalyst for the liquid-phase dimerisation of acrylic monomers consists of an oxide carrier such as SO, , functionalised preferably with a P ligand such as (EtO),SiCH,CH,PPh, to which is bonded a Ru complex such as Ru dichloride tris(acry1onitrile).

Anti-Adhesive Composition RHONE-POULENC SPECIALITES CHIMIQUES

French Appls. 2 ,554 ,117 /18

An anti-adhesive composition curable at elevated temperature consists of an organopolysiloxane con- taining vinyl groups, an organohydropolysilox, a catalyst which is a complex of a platinum group metal, such as bis(ethy1ene) Rh acetylacetonate, and a specified inhibitor.

Rhodium Complex Catalyst RUHRCHEMIE A.G. German Offen. 3,341,035 In a specified procedure for making aldehydes by the reaction of olefins with synthesis gas the catalyst is a Rh phosphine complex such as Rh triphenyl phosphine trisulphonate.

FUEL CELLS Oxygen Permeable Membrane TOSHIBA K.K. European Appl. I 54,468 A composite membrane and air electrode for H,-O, fuel cells, etc., consists of a porous membrane and a thin layer of metal oxide in a C matrix. The metal of the oxide may be Pt, Rh, Ir, 0 s or Ru.

Graphite Fuel Cell Electrode HITACHI LTD. European Appl. 157,385 The performance of a fuel cell is improved by using electrodes made from lamellar graphite with a Group IB and/or Group VIII noble metal deposited on the surface and between the lamellae of the graphite. This may be achieved electrochemically, for example by using chloroplatinic acid.

Fuel Cell PRUTEC LTD U.S. Patent 4,513,066 In a thin fdm, high pressure fuel cell of specified design, the electrodes are hydrophobic porous mem- branes coated with a thin film of precious metal catalyst, such as Pt.

CHEMICAL TECHNOLOGY

Diffusion Transfer Film Units POLAROID CORP. European A P P ~ . 154,377 Particularly useful image-receiving layers in a photographic product for Ag transfer images com- prise colloidal Pd dispersed in colloidal SiO, . The Production of Metal Particles from Molten Metal JOHNSON MAlTHEY P.L.C. European Appl. 156,629 A thin film of molten metal is formed on an angled portion of a surface wetted by the metal and the film is then broken up by a gas flow. The metal may be R, Pd, Ru, Au, Cu, Co, Ni, etc.

Platinum Metals Rev., 1986, 30, (1) 50

Infrared Absorbers MITSUI TOATSU CHEMICALS INC.

U.S. Patent 4,508,655 Useful i.r. absorbers for incorporating into plastics are quaternary ammonium salts of specified halobenzene-o-dithiolates of Pt, Pd or Ni.

Metal Fibre Catchment Systems JOHNSON MA’ITHEY P.L.C. U.S. Patent 4,511,539 A getter for the recovery of precious metals, for ex- ample from the off-gases from a nitric acid plant, con- sists of an assembly of randomly oriented irregular 0.5-4 inch fibres of Pt, Pd, Rh, Ru, Ir, Ag, Au and/or their alloys, produced by a melt-extraction or melt-spun process.

Magnetic Transducer HITACHI LTD. European Appl. 152,000 A Co-Pt hard magnetic alloy may be used as the fdm in a magnetic transducer using magnetoresistance.

MESFET Transistors

APPLIQUEE LEP European Appl. 152,126 Ti-Pt-Au or Cr-Pt-Au multilayer contacts may be us- ed in a MESFET field effect transistor for hyperfre- quency applications.

Small Diameter Radiant Tube Heater

LABORATOIRES D’ELECTRONIQUE ET DE PHYSIQUE

WESTINGHOUSE ELECTRIC CORP. European Appl. I 52,734

Local high temperature heating of the inside of tube bores is achieved using an insulating rod wound with bare Pt-Rh wires.

Solid State Electrolytic Battery SHARP K.K. European Appl. 156,241 A novel battery has a transition metal cathode capable of storing H, such as a Ti-Ni alloy, a solid hetero- polyacid electrolyte and a Pt plate-Pt wire anode.

Thermionic Electron Emitter THORN EMI-VARIAN LTD. European Appl. I 56,454 The electron emissive layer of the emitter is formed of an alloy containing 32-34 at.% 0s and the balance as W and a porous refractory activated with a Group IIA metal, such as Ba oxide in Al,O,.

Tungsten-Iridium Impregnated Cathode VARIAN ASSOCIATES INC. European Appl. 157,634 Pure W agglomerates are formed by sintering fme particles and then they are comminuted to coarse par- ticles. The particles are mixed with fme Ir particles and then sintered. The cathode shapes formed are im- pregnated with a Group IIA aluminate.

Connections for Semiconductors TEXAS INSTRUMENTS INC. U.S. Patent 4,507,851 Electrical interconnections on a semiconductor device are prepared by (a) sputter etching a SiO, or Si nitride surface having windows on to a Si substrate and coating the entire surface consecutively with (b) Pt, (c) a barrier metal such as Ti-W alloy and (d) a conductive metal such as Al.

Metallised Ceramic INTERNATIONAL BUSINESS MACHINES CORP.

U.S. Patent 4,510,000 In a process for making multilayer ceramic modules for the electronics industry, a green dielectric ceramic sheet bearing a Mo or W pattern is laminated with the metallised side of a plastic fdm, the backing is peeled away and the resulting composite is fired. The metallising metal, Pt, Rh, Ni or preferably Pd, doys with the Mo or W to form a densified structure.

GLASS TECHNOLOGY Terminals for Glass-Melting Feeder OWENS-CORNING FIBERGLAS CORP.

U.S. Patent 4,516,995 Terminals for supplying current to a feeder in a fibre- glass spinning plant consist of a core of refractory base metal sheathed in a platinum metal or alloy.

ZGS-Pd Sandwich

Composite materials of good strength, ductility and electrical conductivity (particularly suitable for use in the manufacture of bushings for glass-fibre produc- tion) consist of (a) a layer of Pd or Pd alloy, optionally dispersion strengthened sandwiched between (b) two layers of Pt or a Pt alloy, optionally dispersion strengthened.

Glass Film D. BOTTGER German Offen. 3,507,852 Glass fdm is made by drawing molten glass through an electrically heated spinning plate of Pt or Pt alloy.

JOHNSON MATTHEY P.L.C. U.S. Patent 4,525,433

ELECTRICAL AND ELECTRONIC ENGINEERING CMOS Structure Production NATIONAL SEMICONDUCTOR CORP.

British Appl. 2,157,885A In a process for producing CMOS structures with bipolar transistors, a layer of Pt is deposited over a wafer surface and sintered to create Pt silicide within contact holes.

Semiconductor Device Fabrication FERRANTI P.L.C. British Appl. 2,158,639A An initially continuous Pt layer is deposited on a Si oxide passivating material during the production of a semiconductor device, in which Pt silicide is selec- tively formed.

Platinum Metals Rev., 1986, 30, (1) 51

Solar Collector INCO SELECTIVE SURFACES LTD.

U. S. Patent 4 , 5 1 8 , 4 6 7

A solar collector for use at high temperatures is pro- duced by forming a porous oxide fdm on a stainless steel surface and electrolytically depositing Pd or Ni in the pores.

Merged Fuse and Schottky Diode ADVANCED MICRO DEVICES INC.

U.S. Patent 4,518,981 A merged Pt silicide fuse and Schottky diode struc- ture especially for use in integrated circuits is claim- ed. It is compact and shows improved reverse-biased electrical characteristics.

Variable Resistor MURATA MANUFACTURING CO. LTD.

U.S. Patent 4,527,147 A variable resistor device consists of an insulating substrate; a conductive electrode formed from Ag- Pd, Ag-Pt or Ag, and optionally a glass frit, and resistors formed from glass frit; a fdler such as Al,O,, TiO, or Bi,O,; and an electrically conduc- tive material which is Rh, Ru or Ag-Pd.

Noble Metal Dental Alloy DEGUSSA A.G. European Appl. I 54 ,123

An alloy for fving on to ceramics for dental purposes contains 20-65% Au, 25-65% Pd, 0-7% Cia, 0.2-11% In and/or Sn, 0-2% Cu, 0.05-1% Ru, Ir and/or Re, V, Fe and Co but base metal content <5%.

Detectable Molecules ENZO BIOCHEM INC. European Appl. I 54,788 Detectable organic molecules useful for in vitro or in vivo assays or therapy include a radioactive or non- radioactive metal capable of detection in a diagnostic procedure, such as an isotope of Pt, Pd, Ir, Os, Ru, Au, Ag, Ce, Er, Eu, Gd, Nd, Pr, Tb, Yb or Y.

Biodegradable Implant UNIVERSITY OF STRATHCLYDE European Appl. 155,288 A biodegradable implant is made from a degradable glass containing a chemotherapeutic material which may be Pt, Au, Ag, Cu or Zn.

Silicone Compositions

Curable silicone compositions for use in dentistry in- corporate a Pt catalyst such as a product of reaction of chloroplatinic acid with a divinyltetrame- thyldisiloxane.

Cardiac Lead A. E. ASTRINSKI

Electrodes of Pt, Pt-Ir or the like are used in a new design of cardiac sensing and pacing lead.

Dental Alloy JENERIC INDUSTRIES INC. U.S. Patent 4,518,564 A dental alloy for porcelain-fused-to-metal restora- tions preferably contains 65-75% Pd, 8-16% Cu, 3.5-6% In, 2-6% Sn, 0.5-1% Ru, 2-5.5% Zn and

WACKER-CHEMIE G.m.b.H. European Appl. 1 5 8 , 1 4 1

European A P P ~ . 159,753

0 .05 -0 .15% B.

Carcinostatic Platinum Complexes NIPPON KAYAKU K.K.

Twenty-three complexes of Pt with aliphatic diamines are claimed. They are more water-soluble and less toxic than cis-platin.

Platinum Complexes in Tumour Treat- ment

French APPl. 2,553,777

NATEC INSTITUT FUR NATURWISSENSCHAFTLICH- TECHNISCHE DIENSTE c.m.b.H.

Gennan Offen. 3,340,806 Complexes of formula L[Pt(NH,)Cl,-,], are claim- ed, L is a 5,8-dihydroxy- I ,4-naphthoquinone.

Implantable Electrode SIEMENS A.G. German Offen. 3,345,990 In a specified implantable electrode device, such as for a cardiac pacemaker, the active electrode is preferably made of Pt or Pt-Ir alloy.

TEMPERATURE MEASUREMENT Well Tool Sensors OTIS ENGINEERING CORP. Brizish Appls. 2, I 53,536/37A Pt resistors are used for sensing temperature in a col- lar locator sensor and a flow sensor for use in a well tool.

Heating Apparatus Temperature Control

British Appl. 2,153,555A A Pt temperature sensor is used in the temperature control of heating apparatus, such as i.r. heating ap- paratus.

Temperature Sensor TRW INC. U.S. Patent 4,517,545 A temperature sensor of high resistivity and positive temperature coefficient of resistance is a fired thick fdm of a composition containing 35-85% glass frit and 15-65Oh of a mixture of Fe and Pd particles.

THORN EM1 DOMESTIC APPLIANCES LTD.

MEDICAL USES Intravascular Catheter M. MIROWSKI British Appl. 2,157,954A The distal tip of an electrode in an intravascular multiple electrode unitary catheter is made of a Pt-Ir alloy. An intermediate electrode includes lead fittings and spring wire of Pt-coated Ti. Ag wire is also employed in the device.

Platinum Metals Rev. , 1986, 30, (1) 52