PLATINUM METALS REVIEW - Johnson Matthey ... Editor, Platinum Metals Review Johnson, Matthey & Co.,...

PLATINUM METALS REVIEW

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

V O L . 1 2 J U L Y 1 9 6 8

Contents

Rapid Determination of Carbon in Steel-Making

Design of Rhodium-Platinum Furnace Elements

Platinum-clad Isotope Fuel Capsule for Space Applications

Organometallic Chemistry of the Platinum Metals

An Improved Schottky Diode

Platinum-clad Equipment for Handling Molten Glass

Properties and Uses of Palladium

Ruthenium Resistor Glazes for Thick Film Circuits

Periodic Variations in the Catalytic Properties of Metals

High Purity Palladium Brazing Alloys

High Temperature Strain Gauges

Selective Diffusion of Hydrogen Allotropes through Palladium

Abstracts

New Patents

NO. 3

82

86

88

89

91

92

98

99

100

105

106

107

108

11.5

Communications should be addressed to The Editor, Platinum Metals Review

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

Rapid Determination of Carbon in Steel-Making AN EXPENDABLE PLATINUM THERMOCOUPLE CARTRIDGE

By C. R. N. Clark Johnson Matthey Metals Limited

Carbon content is the controlling factor in operating a steel-making furnace, and f m t and accurate carbon determinations can yield fuel and time savings that lower production costs. This article describes an expendable device incorporating a platinum: rhodium- platinum thermocouple which gives carbon contents extremely rapidly by thermal arrest point determination.

The steel-making process at all stages is governed almost entirely by the carbon content of the steel, and a rapid method of analysis for carbon is, therefore, essential to the efficiency of the process in terms of fuel con- sumption and time. A recently introduced method of fast carbon analysis is based on the measurement of the liquidus temperature of molten steels by means of an expendable cartridge containing a platinum : rhodium- platinum thermocouple. All the alloying constituents of a steel or cast iron affect the temperature at which the liquidus phase change occurs, but the element which has the greatest effect on this temperature is carbon.

Liquidus temperatures of molten metals can conveniently be measured by the use of thermocouples which have junctions of low thermal capacity and therefore give rapid response to temperature change. As a method of analysis this has been used for some time in cast iron found-

Fig. 1 The Leeds & Northrup Tectip S cartridge for the rapid determination of carbon in liquid steel. The platinum: rhodium-platinum thermocouple can be seen through the transparent quartz tube fitted into B e bottom of the sand mould

ing (I), where the tolerance on carbon content is less critical and the process less dependent on an accurate knowledge of the level of this element. Steel-making normally involves carbon contents up to 0.6 per cent, and the tolerance on carbon determinations must be of the order of 20.01 to 0.02

per cent. In terms of the change of liquidus temperature this tolerance requires that any temperature measuring system used must read to an accuracy of 11°C over the range 1450 to 1550°C.

Platinum Metals Rev., 1968, 12, (3), 82-85 82

Fig. 2 After a lengthy evaluution of the expendable rartridge terhnique in the electric arc furnaces at Steel, l’eech & Tozer three sets of equipment huoe been installed and substantial

time savings have been made i n routine working

The need for such extreme accuracy in temperature determination has, until recently, precluded the use of thermal arrest measurements as a means of analysing for carbon in steel. However, it is now possible to obtain thermocouples of platinum against 10 or 13 per cent rhodium-platinum that can provide temperature measurement to within +o.s0C in this temperature range. This improved accuracy has led to the introduction by Leeds & Northrup Ltd of a procedure for quick carbon analysis by the use of an expendable cartridge.

The Expendable Cartridge The cartridge, known as the ‘Tectip S’,

consists basically of an expendable sand mould A thermocouple, approximately 2

inches long, made from platinum and 10 per cent rhodium-platinum wires 0.005 inch in diameter, is first spot-welded together at the hot junction, This thermocouple is protected by a fused quartz U tube cemented

inside the sand mould, which has a capacity of 4 to 5 cubic inches. The platinum and 10 per cent rhodium-platinum wires are joined to copper-nickel and copper compensating leads of larger diameter which emerge from the base of the sand mould to form contact points. The cartridge is shown in Fig. I, in which the thermocouple can be seen through the transparent quartz tube fitted into the bottom of the mould. This unit is expendable and inexpensive; it is used for one thermal arrest point determination only.

The cartridge is plugged into a permanent stand, shown in Fig. 3, from which compensating lead cable runs to a rapid response recorder, of the type shown in Fig. 4, calibrated in 0.5”C intervals over the range of interest. The narrow range of chartered temperature is necessary to achieve maximum sensitivity to carbon content, and the recorder must have a high chart speed, in the region of 4 inches per minute.

In order to take a reading, molten steel is

Platinum Metals Rev., 1968, 12, (3) 83

spooned from the bath, deoxidised with aluminium wire, and poured into the mould, as shown in Fig. 5. A certain skill is required in pouring the sample to ensure that the steel is at just the right temperature to give a thermal arrest point in 20 seconds, since if the pouring temperature is too high or too low freak curves may result. The thermal arrest temperature can then be converted to a carbon content by reference to the appropriate calibration graph.

Apart from carbon, the other alloying constituents in steel also depress the liquidus temperature, although to a lesser degree.

Fig. 4 A rapid response type of recorder is used, calibrated over as narrow a temperature range as possible to give maximum sensitivity and to ensure coverage of the carbon range

Fig. 3 I n order to make u determination the cartridge is mounted i n a metal stand to enable the thermocouple to make contact with the compensating cable linking it to a temperature recorder

Each constituent affects the liquidus temperature by an amount proportional to its content and independent of the presence of other alloying constituents. This effect of the alloying constituents is compensated for by prior knowledge of the level of each of these constituents. It is not necessary to know the levels of these elements accurately, because their affect on the liquidus is much less than that of carbon, and compensation can be made by the use, for example, of the depression values given by Roeser & Wensel of the National Bureau of Standards (2).

Field trials of the Tectip S for determining


Fig. 5 In order to take (I reading a sample of molten steel is poured into the Tectip cartridge. l h e thermal arrest point is recorded within twenty seconds, and the carbon content can then

be read from a conversion graph fully corrected for the effects of other elements

the carbon level at all stages of the steel- making process have recently been described by P. B. Dunnill and H. Atkinson (3), of Steel, Peech & Tozer’s Rotherham Works. They found that 96 per cent of results were within k0.03 per cent carbon and 87 per cent within i0.02 per cent carbon when compared with conventional induction heating rapid analyser results.

Comparison with Conventional Techniques

Other methods of carbon analysis at Steel, Pcech & Tozer involve a time lag of five minutes between sampling and availability of results, whereas the Tectip S provides an answer in thirty seconds. Because it is necessary to know the carbon level at a number of stages during steel-making, the total time saved in this plant was 10 to 15 minutes per cast. This time-saving alone justified the introduction of the Tectip S as a regular means of melt control.

The apparatus is well suited to shop floor operation by relatively unskilled personnel. The total cost of the equipment differs by orders of magnitude from that of the direct

Platinum Metals Rev., 1968, 12, ( 3 ) 85

reading instruments, which have usually to be installed away from the melting shop and must bc operated by more highly skilled workers. The accuracy of the method is slightly less than that of the more sophisti- cated methods, but, as a procedure complementary to these more accurate methods, the Tectip undoubtedly offers the steel maker a means of reducing his production costs.

In the United States the Tectip method is now being used as a routine production tool, and some thirty steel works are making a total of about IOO,OOO Tectip carbon determinations per month. Among the users are Bethlehem Steel Corporation, Republic Steel Corporation, Kaisers and Colorado Fuel and Iron.

In the United Kingdom ten companies are carrying out development trials and some are using the method in place of other carbon determination methods for intermediate sampling of heats; a few have used it on tapping samples.

References f Platinum Metals Rev., 1962, 6 , 20 2 W. F. Roeser and H. T. Wensel, -7. Rex. N.B.S.,

1941,26, (April), 273 3 Steel Times, 1968, 196, (January), 13

Design of Rhodium-Platinum Furnace Elements LONG LIFE AT HIGH TEMPERATURES

By w. Gutt, &I&., PLD., F.R.I.C. and B. Hinkins, B.Sc., A.I.Ceram. Building Research Station, Watford

The design of high temperature furnaces incorporating internally wound 20 per cent rhodium-platinum heating elements has been developed and improved over many years at the Building Research Station. The type of construction described here permits a higher furnace temperature to be obtained for a given winding temperature than is possible with other con- structions, and yet enables good working lives to be achieved.

High temperature furnaces are needed in the course of the activities of the Building Research Station for the preparation of experimental cements and synthetic slags and glasses, as well as for research on chemical compounds and phases that occur in building materials during the heat treatment associated with their manufacture. In addition, they are used for the study of high temperature phase equilibria in systems relevant to the con- stitution of cements, slags and ceramics. The furnaces described are the result of continual development over a long period.

Fig. 1 The mould and former for a D-shaped element of internal dimensions 12.5 x 5 x 3.5 em. The paper covering the former is marked ready f o r winding the 20 per cent rhodium- platinum wire.

In the construction of a muffle type furnace a mould and former are used. The former consists of three wedge-shaped pieces of aluminium, the centre piece of which is keyed and tapered to facilitate withdrawal of the former after the element has been wound. Two detachable posts on the former allow the wire to be anchored. A mould and former for a D-shaped element are show in Fig. I.

The paper covering the former is marked ready for winding. Similar moulds are in use for the construction of tubular elements of 2.5 and 5.0 cm internal diameter.


The parts of the former are greased, assembled and wrapped with two layers of filter paper, and the winding posts are inserted. The filter paper is marked to guide the winding of the 0.8 mm diameter 20 per cent rhodium-platinum wire. The wire, at about 25 cm from its free end, is attached to one winding post on the former and the element is carefully wound, an even tension being maintained. On completion of winding the wire is attached to the other winding post and, allowing for 25 cm for the lead, the wire is cut. The former is then fixed in the mould case and the space between the former and the case filled with the alumina refractory, the grading and water ratio of which are given in the table.

Composition of Alumina Refractory for One Element

Material Quantity -10+20 mesh fused alumina -20+60 mesh fused alumina -60+120 mesh fused alumina Morgans Alumina Cement 961 W a t e r 50-60 ml

167 g 111 g

56 g 167 g

This mix has low plasticity and must be compacted on a vibrating table. When the mould has been filled and compacted it is dried in an oven at 80°C for a day. The element is then strong enough to be removed from the mould and the centre of the former is gently drawn out of the element. The remainder of the former and mould can then easily be removed.

The element is fired in a box of alumina powder by passing an a.c. current through the winding. It is raised to 14ooOC in about three hours, and then cooled. A thin slip of alumina cement is run around the inside of the element after firing in order to coat the winding and so to restrict volatilisation of the wire. It is preferable to refire the element and to give it a second thin coating of cement if necessary. This second coat is fired when the clement is installed in its case.

All three designs of element give long lives under different working conditions. The


Fig. 2 A complete mufle furnace with its proportional controller

D-shaped elements are used in closed-ended furnaces, such as that shown in Fig. 2, at temperatures up to 1650°C. The 5 cm bore tubular elements are used in open-ended horizontal furnaces mainly for heating substances having volatile constituents in a controlled atmosphere. Perforated alumina end plugs allow the inlet and outlet of gas.

The 2.5 cm diameter elements are fitted into vertical quench furnaces used for the accurate determination of melting points and for the study of other phenomena by the well-known quenching method, and for the checking and calibration of thermocouples. These 2.5 cm elements are capable of attain- ing 1780'C with a very small temperature variation over the central 5 cm height of the furnace. The spacing of the turns specified below has been found to give optimum results. The winding starts 6 cm from the top end of the element; the turns per 2.5 cm are then respectively: 10, 8, 6, 4, 6, 8, 10, and the winding ends 2.5 cm from the bottom of the element. When the element is removed from

the mould and before it is fired a few extra turns of wire are wound round the outside at each end to ensure that the ends are fired properly. These extra turns are removed before the element is inserted in its furnace.

If cracks develop in an element coating during use they should be covered with more cement slip, as maintenance of an even and impervious coat over the wire is the main factor needed to ensure a long life, but the grading of the refractory used ensures a low shrinkage and it is very rare for cracks to develop in the outer part of the element. The slip coating gives adequate electrical insula- tion to enable samples to be heated in platinum vessels placed on the floor of the mufile and these are invariably used. The temperature variation along the central 5 cm length of an element is less than 20%~ and with proportional controllers the temperature can be maintained to within 2 O C for several hours.

The furnace cases are lined with high temperature insulating bricks and the element is surrounded by about 5 crn of alumina powder. The temperatures of the furnaces are controlled by various proportional controllers. An electromechanical type described by Nurse and Welch in 1950 (I) has been extensively used, and a more precise saturable reactor type gives the very close temperature stability ( f o . ~ " C ) required for quench furnaces. The temperatures of the furnaces are measured by 5 per cent rhodium-platinum : 20 per cent rhodium-platinum thermocouples and read on an electronic recorder.

The work described formed a part of the pro- gramme of the Building Research Station and the paper is published by permission of the Director.

Reference I R. W. Nurse and J. H. Welch,?. Sci. Instrum.,

(Crown copyright reserued) '95'J '7, (41, 97

Platinum-clad Isotope Fuel Capsule for Space Applications

As one of its long term objectives NASA continues to support work on radioactive heat sources and a recent report by Atomics Inter- national (USAEC Rept. NAA-SR-12578) provides some interesting preliminary design data for a proposed test capsule capable of holding a large (undisclosed) heat source and operating in a space environment for more than five years with a surface temperature of approximately 109oOC.

The total assembly, in the form of a cylinder with hemispherical ends is 7.37 inches long and 1.72 inches in diameter. The isotope heat source is centrally disposed, surrounded by a tantalum honeycomb and finally welded into a thick walled tantalum alloy shell which provides the strength for long term helium containment and for impact survival. An external covering of 10 per cent rhodium-platinum alloy, 0.020 inches thick, protects this shell from oxidation. Metallic diffusion between the tantalum and platinum alloys is inhibited by a thin layer of vapour phase deposited alumina. The outer surface of the platinum alloy is coated with a layer of iron titanate to increase heat emmissivity.


Paradoxically enough the design of this capsule was complicated because of its low operating temperature, no reliable creep data on rhodium-platinum alloys tested below 1200°C having yet been published. The designers extrapolated downwards with respect to temperature and outwards by a factor of 45 with respect to time. In con- cluding that hoop stresses in the rhodium- platinum sheath should be kept below 75 pounds per sq. inch they emphasise the uncertainties involved in their assumptions.

The compatibility studies scheduled in this report will be made in vacuum of IO-* Torr for periods up to 2200 hours. In both geometry and environment these test conditions depart from those existing inside the proposed capsule. It will be interesting therefore to read in subsequent reports whether the reactions between tantalum, alumina and rhodium-platinum tested in close association inside the capsule in a helium atmosphere differ significantly from those which occur in vacuum where the reaction products are continuously removed.

A, S. D.

Organometallic Chemistry of the Platinurn Metals A REVIEW OF PAPERS AT THE DUBLIN SYMPOSIUM

By B. L. Shaw, Phm. Department of Inorganic and Structural Chemistry, University of Leeds

At the joint annual meeting of The Chemical Society, The Institute of Chemistry of Ireland and the Royal Institute of Chemistry held in Dublin in April, one of the symposia was on ‘Recent Progress in Organometallic Chemistry’. Several of the plenary lectures and contributed papers given at this symposium were concerned with the chemistry of the platinum metals, and these are summarised and reviewed here.

In recent years there has been enormous interest in organometallic chemistry. One very important interest has been the use of metal complexes, especially of the platinum metals, as homogeneous catalysts. This aspect was hardly touched upon at the recent Dublin meeting, but there is nowadays no shortage of symposia and meetings on homogeneous catalysis and perhaps it was a refreshing change to have a meeting concerned with other aspects of organometallic chemistry.

Metal Carbonyls Interest has been particularly keen in the

field of metal carbonyls, and in his opening lecture on “Recent Progress in Metal Carbonyl Chemistry”, Professor F. G. A. Stone (Univer- sity of Bristol) described some recent developments in methods of synthesising polynuclear carbonyls of ruthenium, osmium, rhodium and iridium, e.g. [RU~(CO),~], [OSdC0)121, [R~~(CO)I,I , [ R ~ L ~ C O ) I ~ ~ I and [Ir4(CO)12]. These carbonyls are readily prepared by reductive carbonylation, i.e. reduction of a metal salt in the presence of carbon monoxide. Their structures have been determined by X-ray diffraction and indicate metal-metal bonds and sometimes bridging carbonyl groups. Carbonyls of the type

[Pd,(CO),] and [Pt,(CO),] are so far un- known. Polynuclear metal carbonyls with two different metals can also be prepared, e.g. [Fe,Ru(CO),,1 and [F~RU,(CO)~,I.

[ R U ~ ( C O ) ~ ~ ] has been used as the starting point for many syntheses. Thus by reduction to [Ru(CO),IZ- and acidification it gives [RuH,(CO),] as an unstable volatile liquid. [Ru,(CO),,] reacts with acetylenes to give products similar to those formed from [Fe,(CO),,] and acetylenes. With halides or hydrides of sub-group B elements it reacts to give compounds containing ruthenium- metal (metalloid) bonds, e.g. with Me,SnH it forms [(Me,Sn),Ru(CO),] but with Me,SiH the product is [Me,SiRu(CO),Ru(CO), SiMe,]. Compounds containing germanium- ruthenium bonds were also described.

Perfluoroalkyl or perfluoroaryl groups form particularly stable and/or inert bonds to transition metals and Professor Stone’s lecture concluded with a discussion of the preparation of a large variety of such compounds.

Allylic and Related Complexes The lecture by B. L. Shaw was concerned

with aspects of the chemistry of allyl deriva- tives of rhodium, iridium and palladium. An allyl (or allylic) group can of course be


a-bonded to a metal but about 1960 it was recognised that the three carbon systems of an allylic group could be sideways, ir- or sand- wich bonded to a metal and thereby act as a four electron donor (if regarded as an ally1 anion). More recently asymmetrically bonded (7~') allylic ligands have been recognised both b y NMR and X-ray studies, the first example being [PdCl( 2-methylallyl)(PPh,)]. In this complex the terminal carbon atom of the allylic group opposite to the phosphine is less strongly bonded to the palladium than the one opposite to chlorine. In solution in the presence of ligands which can coordinate to the palladium the more weakly bonded terminal allylic carbon breaks away from the palladium to give a transient a-allylic complex which can reform the m'-allylic ligand in a different orientation from before. In the presence of [Pd,Cl,(z-methylallyl),] or triphenylphosphine such rapid rate processes occur and they can be conveniently studied by 1H NMR. In the presence of an excess of triphenylphosphine (i.e. PPh,:Pd ratios> I) phosphine exchange also occurs. A large number of systems of this type have been studied by NMR with different allylic ligands, different phosphines or arsines etc. and at various temperatures. Interconversions of ?-(or m'-) and 0-allylic systems are thought to be very important in homogeneous catalysis, e.g. in the oligornerisation of butadiene by metal complexes and probably occur by processes such as described in this lecture.

Also discussed were some interconversion reactions of V-, v'- and u-allylic complexes of iridium (111) and the acid catalysed conversion of a a-2-methylallyliridium (111) complex into a o-isobutenyhidium (111) complex, e. g. [ Ir C1 ,(a-2-methylall yl)( CO) (PMeJh) ,I-+ [IrCl,(a-isobutenyl)(CO)(PMe, Ph),] (a new type of reaction which may be important in some catalytic systems).

A very convenient synthesis of allylic- rhodium complexes was discussed which involves the hydrolysis of coordinated carbon monoxide ligands (to give carbon dioxide) in the presence of an allylic halide. Thus

treatment of [Rh,Cl,(CO),] with an allylic chloride (all-C1) in methanol/water gives carbon dioxide, a hydrocarbon (all-H) and the allylic-rhodium complex [Rh,Cl,(all),]. The reaction is promoted by a base and in the presence of acid the major product from 2-methylallyl chloride is [Rh2Cl,(z,5-di- methylhexa-1,5-diene)J. Mechanisms for these reactions were suggested and supported by deuteration experiments. The reactions now make allylic complexes of the type [Rh,Cl,(all),] very readily available and these are convenient starting materials for the synthesis of many types of allylic-rhodium complexes, e.g. [Rh(~-allyl)(7~-allyl)(C~H~)], [Rh(n-allyl),], [Rh(xi-ailyl>,(dipyridyl)] [BPh,] etc. These conversions and the properties of the products were discussed.

Fluxional Molecules Professor F. A. Cotton (Massachusetts

Institute of Technology) discussed some fluxional molecules which have two or more equivalent nuclear configurations of lowest energy and pass from one to the other quickly at room temperature. The fluxional motions are slowed down and eventually stopped by lowering the temperature and such systems may be studied by variable temperature NMR. Molecules such as these are now fairly commonplace in organometallic chemistry; allylic-metal complexes of the type [M(all)J (M=metal; x=z, 3 or 4) being one example.

Professor Cotton discussed the variable temperature 'H NMR spectrum of [F~(~-C,H,)(T~-C,H,)(CO)~]. At room temperature the spectrum consists of two singlets one due to the ir-cyclopentadienyl protons and the other due to the u-cyclopentadienyl protons. On cooling the first singlet remains sharp but the one due to the m-cyclopentadienyl protons broadens, then splits into broad peaks which gradually sharpen until at or below -1100" a sharp but complex resonance pattern characteristic of an A B B ~ C ' spin system, i.e. a "frozen" u-cyclopentadienyl group is obtained. The equivalence of the five protons at room


temperature is caused by the rapid motion of the iron atom around the ring by a r,~-shift. NMR only "sees" the time arranged environment and if the motion is sufficiently rapid all five protons of the o-cyclopentadienyl group appear to be equivalent.

A similar situation exists for the cyclo- octatetraene (COT) complexes [Fe(CO), (COT) and [Ru(CO),(COT)]. The X-ray structure of [Fe(CO),(COT)] shows the iron atom to be bonded to only four of the carbon atoms yet the lH NMR spectrum at room temperature shows only a sharp singlet resonance. As the temperature is lowered the resonance broadens then splits, but even at --I45" is still broad. The ruthenium complex, however, which also shows a singlet resonance at room temperature shows four well-defined resonances at - 145' inter- pretable in terms of a structure in which the ruthenium is bonded to only four carbon atoms. The computer simulated spectra are only consistent with the ruthenium atom moving around the ring by a r,z-shift and rule out 1,3; 1,4; 1,5 or random shifts. Professor Cotton went on to discuss some more complex fluxional molecules some of which have been investigated by variable temperature NMR; these include [Cr(CO), (1~3,5,7 - tetrarnethylcyclo - octatetraene)], [Fe , (CO) (1 ,3 ,5 ,7 - tetramethylcyclo- octatetraene)], [Ru,(CO),(COT)] and [Ru, (CO),(COT~,1.

Reactions with Rhodium Chloride B. R. James, M. Kastner and G. L. Rempel

(University of British Columbia) studied the kinetics of reactions between RhCl, . 3H,O and ethylene. In non-aqueous solvents such as dimethylacetamide, the anion [Rh'CI, (C2H4),]- is formed but in water the production of small amounts of rhodium(1) species catalyses the formation of [Rh"'Cl,(H,O),]'. Acetylenes are catalytically hydrated by chlororhodate(II1) complexes. The reaction mechanisms all involve insertion of the unsaturated organic molecule (ethylene or acetylene) into a Rh"'-OH bond.

R. Murray and J. Walker (I.C.I. Petro- chemical and Polymer Laboratory) have made a thorough 220 MHz. and IOO MHz. lH NMR study of substituted triphenylphosphine complexes of palladium(I1) and platinum(II), and corresponding 19F studies on P(p-FC,H,), and P(m-FC,H,), complexes. They interpret their results in terms of 0- and r;-electronic effects. Our knowledge and understanding of factors contributing towards chemical shifts and spin-spin coupling constants is still limited and only tentative interpretations can be at present given to such studies.

An Improved Schottky Diode The conventional Schottky barrier diode

(which does not inject minority carriers) is capable of switching times less than 0.1 nanosecond. An improved version has been developed by M. P. Lepselter and S. M. Sze at the Bell Telephone Semiconductor Device Laboratory (Bell Laboratories Record 1967, 45 (Nov.), 340). The introduction of a guard ring eliminates "edge effect", giving a breakdown voltage close to the theoretical limit, while the use of a very clean junction between the n-type silicon semiconductor and a layer of platinum silicide provides an almost ideal forward current-voltage characteristic,

The n-type silicon substrate is cleaned by a glow discharge in which gas ions remove impurities by bombardment. Without removal from the vacuum chamber a smooth layer of platinum is then sputtered on. The result is a layer of uncontaminated platinum silicide with a near-perfect interface to the n-type silicon. Successively, a guard-ring of p-type silicon is formed, a silicon dioxide layer deposited, channels of access etched, and gold beam leads applied.

Platinum silicide is a very stable compound, highly resistant to corrosion and able to form a low-resistance contact. In other related applications the silicide layer receives a deposit of titanium followed by a platinum layer. The titanium layer bonds strongly to the silicon dioxide insulating layer, which it improves by absorbing impurities. The further platinum layer is required to form a strong bond with the gold leads, and also to prevent goldltitanium reactions.

R. J. N.


Platinum-clad Equipment for Handling Molten Glass THE MECHANISM OF FAILURE AT HIGH TEMPERATURES

By A. s. Darling, Ph.D., A.M.I.Mech.E., and G. L. Selman, B.Sc., A.I.M. Research Laboratories, Johnson Matthey & Co Limited

Under normal conditions platinum-clad molybdenum equipment used in the glass industry eventually fails because of a vapour phase reaction in which molybdenum is transferred to the platinum envelope across a partly evacuated void. I n this article, based on a paper recently delivered at the joint meeting of the British Ceramic Society and the Society of Glass Technology in She#eld in April, it is shown that metal transfer can be largely inhibited by keeping the partial pressure of

oxygen in the interfacial volume at a very low level, and practical methods of achieving this objective are discussed.

Platinum-clad molybdenum apparatus is extensively employed for the industrial handling of molten glass, and at temperatures up to IZOO’C can be relied upon for several months of useful service. Increased operating temperatures accelerate the breakdown process, however, and although platinum-clad molybdenum still represents the best combination of metals acceptable to the glass manufacturer for use above 13oo0C, premature failures in this elevated temperature range tend to occur in a rapid and characteristic manner. Large distortions of the sheath occur at an early stage, the component develops a “blistered” appearance, and the eventual cracking and failure of the sheath leads to catastrophic oxidation of the molybdenum core.

Platinum Metals Rev., 1968, 12, (3), 92-98

Various explanations for such behaviour have been advanced. It is said, for example, that oxygen diffuses through heated platinum and that failure is caused because of the oxidation products which form at the platinum-molybdenum interface. A n alternative mechanism involves the diffusion of molybdenum through the platinum so that the final failure process is caused by the weakening effects of internal oxidation on the grain boundaries of the platinum sheath.

An analysis of the gradually accumulating fund of information showed that neither of these postulated mechanisms accounted completely for the characteristics of actual failures. It was known, for example, that components in which the platinum had been metal- lurgically bonded to the molybdenum core tended to resist failure for longer periods at high temperatures than those in which the platinum cladding was not in intimate contact with the molybdenum. The blistering which preceded most failures implied the generation of considerable internal forces or pressures, and it also appeared significant that under industrial conditions sprayed alumina barrier layers, although marginally effective below 12oo0C, had no significant effect on the process of breakdown at higher temperatures.

The investigation described below was undertaken to establish the true mechanism of failure as a preliminary to the development of generally improved techniques for cladding the refractory base metals with platinum.

Some preliminary tests on platinum-clad niobium were made to confirm that platinum was sufficiently impermeable at high tem-

92

perature to ensure effective oxidation protec- tion over long periods of time. Niobium was selected for these tests because at 1400OC it takes oxygen very rapidly into solid solution. The increase in hardness thus caused provides a sensitive index of oxygen content and by this method it was hoped to obtain a quantitative measure of the rate at which oxygen diffused through the platinumenvelope.

It was found, however, that niobium rods, when sealed up in platinum, softened appre- ciably even after the capsules were heated in air at 1400'C for over 300 hours. These results, and many others obtained with other specimens, confirmed that platinum, provided that it did not react with the core material, was for all practical purposes completely impermeable to oxygen at temperatures up to I4 5 0 c .

As a complementary approach to this oxygen diffusion problem, platinum-clad molybdenum rods were heated in air, argon, vacuum and glass at 14ooOC. Regardless of the test environment, the platinum sheath began to show signs of distortion after 20

hours at temperature. After a test period of IOO hours, the sheaths on all four samples were badly misshapen, and metallographic examination revealed extensive grain boundary cracking within the sheaths, and in the case of the specimen tested in air, gross internal oxidation of the intermediate alloy layers in the immediate vicinity of the cracked boundaries.

These preliminary experiments showed quite conclusively that failure was a manifes- tation of internal reactions within the composite itself, which were not affected, except possibly after the sheath had cracked, by the nature of the external environment. All of the subsequent tests were carried out in air, this being the most realistic test atmosphere from the practical point of view, particularly since weight measurements could then be used to determine, quite unambiguously, the point at which complete failure of the sheath had occurred.

Molybdenum rods were encapsulated in platinum envelopes which were evacuated and degassed as fully as possible at 1400°C and finally sealed off with residual gas pressures below IO-~ Torr. To simulate typical production conditions additional specimens were made in which the pressure of the interfacial volume was reduced to 2 Torr at 800°C and held at this level for about ten minutes before the envelope was sealed off by hammer welding. Both types of specimen were tested with and without a sprayed alumina barrier layer between the molybdenum and platinum, and for comparative purposes some of the capsules without alumina barrier layers were lightly hot swaged to bond the sheath to the platinum core.

After preparation as described above, the capsules were annealed in still air in a horizontal tube furnace for long periods at 14oo0C.


(4 SJ) Fig. 2 Surface condition of molybdenum core at the time when increases of weight arejirst being detected. Specimens sealed with internal pressure of 2 Tom. Heated in air at 1400°C

to produce weight increases of (a ) 3 and ( b ) 31 mg. x 200

It soon became apparent that the pressure of gas sealed up in the test capsule had a profound effect upon the rate of failure. Specimens sealed off with an internal pressure of z Torr failed after 400 to 600 hours at 14oo0C and the alumina barrier layer had no beneficial effect,

Changes of Weight and Surface Effects

The dimensional and weight changes suffered by the test capsules during their periods of heat-treatment in air are summarised in Fig. I. During the initial period of test, all specimens showed a steady decrease in weight due to loss of platinum from the sheath in the form of volatile platinum oxide. This period of steady loss was, however, at some stage superseded by a rapid increase in weight, inevitably followed by a rapid loss in weight. The onset of failure in loosely sheathed specimens was indicated first of all by a rapid increase in distortion, followed, after a short in- cubation period, by a similarly rapid change in weight.

Fig. 3 External appearance of platinum-clad moly6denum test capsules afer heating in air for 1091 hours at 1400°C. Lefi, originally sealed at 2 Tow; right, originally sealed at 10-3 Torr. x 4

The first increase in weight was taken to indicate the beginning of failure as it was at this time that the presence of molybdenum oxide could first be detected. The condition of the molybdenum core when examined at this stage is illustratcd in Fig. 2, where the quantity of trapped solid oxides which ac- count for the weight increases can be seen. It can also be observed how this trapped oxide increases in volume with time of heat treatment.

Ultimate catastrophic failure occurs when cracks or grain boundary defects in the platinum sheathing permit the molybdenum oxide to volatilise away as soon as it forms. The alumina interlayer did not retard the incidence of either effect when the capsules were sealed under a vacuum of 2 Torr. The external appearance of the low pressure capsules when


Fig. 4 Diffusion zone on the Fig. 5 Diffusion zone on the Fig. 6 Diffusion zone on the inner surface o f Q pEatinum molybdenum core, obtained by inner platinum surface con- sheath in which molybdenum heat treating a specimen sealed taining only platinurn-rich was sealed with the internal with the internal pressure phases. Sealed at Torr. pressure maintained at 2 Torr. maintained at Torr. with an alumina barrier. x 200 x 200

visually examined after 2300 hours at 1400T suggested that the alumina barrier in these components had delayed ultimate failure by at least 500 hours.

The curves relating to bonded specimens show that the failure mechanism in this type of composite was somewhat different in nature. No dimensional changes were observed, and failure was catastrophic, an- nounced only by a sudden decrease in weight. The most probable explanation of this type of failure is that the molybdenum had diffused completely through the cladding.

The surface condition of two specimens removed from the furnace after approximately 1100 hours at 1400’C is illustrated in Fig. 3. The extensive grain boundary sliding visible on the specimens sealed at 2 Torr is completely absent on the specimens sealed under a hard vacuum, and these illustrations emphasise the importance of sealing pressure on the mode of failure.

Internal Reactions Metallographic studies were largely con-

centrated upon specimens which had been removed from the test furnace before the point of ultimate failure. In all specimens sealed up with an internal pressure of 2 Torr, considerable molybdenum deposits were found

x 200

on the inside of the platinum envelope. The constitutional relationships of the diffusion zones between molybdenum and platinum have already been described in some detail (I). The same range of phases can be detected on the section shown in Fig. 4, which illustrates the appearance of the inner surface of the platinum envelope after 1091 hours at 14ocT. The presence of a thick layer of sprayed alumina between platinum and molybdenum has had, in this instance, no inhibiting effect on the migration of molybdenum to the platinum.

Molybdenum migration was inhibited, however, by the simple expedient of sealing the capsules in a hard vacuum. The specimen shown in Fig. 5 was sealed off below IO-*

Torr and the alloying which has occurred is limited in extent and confined almost entirely to the molybdenum surface. Micro-analysis and micro-hardness measurements confirmed that no molybdenum had diffused into the platinum sheath. The failure which eventually occurred in thin-walled capsules sealed under such conditions was suspected to be a consequence of solid state diffusion in local areas where direct metallic contact occurred.

When high vacuum conditions prevailed in the interfacial volume the presence of the sprayed alumina layer restricted the formation


Fig. 7 Section through the platinum sheath of a specimen which had just begun to increase in weight. x 60

Fig. 8 A grain boundary failure within the sheath of u specimen which was rapidly losing weight. X 25

of the diffusion zone on the inner platinum surface. As shown in Fig. 6, this zone contained none of the molybdenum-rich phases.

Fig. 7 illustrates a section taken through a platinum capsule which was just beginning to increase in weight. The sheath has distorted considerably by grain boundary slip and cracks have formed from both the inner and outer surfaces. Under such conditions oxygen can obviously penetrate the sheath sufficiently rapidly to cause the oxidation effects shown in Fig. 2, where the trapped solid molybdenum oxide has not been free to escape.

After close examination of grain boundary cracking of this sort it becomes almost impossible to discount the possibility of direct although limited oxygen ingress through small cracks or fissures in other parts of the specimen. Oxygen diffusion through rapidly sliding grain boundaries must also be considered as a possible mechanism. Catastrophic failure occurs when the exterior cracks penetrate through to the diffusion zone and

has been incompletely evacuated before sealing.

They indicate that under such conditions molybdenum migrates rapidly to the inside of the platinum envelope and that the dimensional changes and tensile strains resulting from the formation of these reaction layers cause ultimate failure of the sheath. Molyb- denum transfer can be considerably reduced by keeping the pressure within the interfacial volume below I O - ~ Torr. Under such conditions the direction of metal migration is reversed, Platinum diffuses to the molybdenum although the rate of transfer is very slow.

These simple relationships are complicated by the presence of the alumina barrier layer, which has no effect on metal transfer when the gas pressure is high, but appears to encourage the migration of molybdenum to platinum when the gas pressure is low.

This behaviour must obviously be interpreted in terms of vapour phase reactions as

the molybdenum oxide then formed volatilises rapid metal transfer occurs even when the at a great rate. Fig. 8, a section through a molybdenum and platinum surfaces are control test specimen intercepted at this stage, separated by a considerable void. shows the characteristic internal oxidation The metal vapours themselves are obviously behaviour of molybdenum-platinum alloys. not of critical importance within this context

as transport is tremendously reduced under Mechanism of Failure high vacuum conditions. The vapour pressure

The results described above show that of platinum is, moreover, approximately failure occurs most rapidly in those com- twice that of molybdenum at 1400OC and, if ponents where the interfacial volume between any serious transfer occurred via metal the molybdenum core and platinum envelope vapour, we would have expected to find a


deposit of platinum upon the molybdenum core. As shown by our experiments, this occurred only under high vacuum conditions.

The vapour phase reaction most likely to be promoted by the presence of a residual gas pressure is one which involves volatile oxides. Molybdenum trioxide is such a volatile phase and it is interesting to speculate about the quantitative aspects of molybdenum transfer by this oxide.

The partial pressure of molybdenum trioxide within the interfacial volume will be directly related to the partial pressure of oxygen in the residual gases. Assuming the residual gas to be air, the partial pressure of oxygen at 2 Torr would be approximately 5 x 10-4 atmospheres, and molybdenum oxide vapours would be formed at pressures considerably higher than those of any metal vapours present in the system. It is reasonable to postulate, therefore, a mechanism in which oxygen reacts with the molybdenum to form a gaseous oxide from which the molybdenum is, in turn, extracted by the platinum to form intermediate phases and solid solutions in which the activity of the molybdenum is kept at a low level. Such a closed cycle would operate indefinitely on a very small quantity of trapped oxygen.

When the interfacial volume is well evacuated, the partial pressure of oxygen, and consequently that of the molybdenum trioxide produced, will be very low. Only the very dilute solutions of molybdenum in platinum would have sufficient affinity for the metal to extract it from the low pressure oxide vapours, and this would explain the absence of inter-

mediate phases in the envelope reaction layers in capsules containing alumina barriers which resisted failure for long periods of time.

The somewhat anomalous role of the sprayed alumina barrier layer must also be considered. As would be expected, this permeable layer had little effect upon the vapour phase metal transfer process when gas pressures were high. Under hard vacuum conditions it seems evident that the alumina must have acted as an oxygen source, and as mentioned above, limited, although detectable, alloying occurred at the inner platinum surface. The ability of platinum to reduce alumina under vacuum conditions has recently been established (z), and such reduction processes would inevitably release enough oxygen to promote molybdenum transfer.

Under high vacuum conditions with no alumina present, platinum transferred to the molybdenum. This direction agrees with the relative metal vapour pressures of platinum and molybdenum. In spite of the molybdenum transfer and diffusion which occurred in the presence of alumina, the effective molybdenum concentration above the inner surface of the platinum was in- sufficiently high to promote the formation of the molybdenum-rich intermetallic phases, and no distortion of the sheath took place. These experimental findings provide a strong clue to the reason for the more satisfactory behaviour of platinum-clad molybdenum components at lower temperatures, since it is now known that at temperatures below 1325°C the molybdenum rich E phase can no longer exist in the diffusion zone (I).

Molybdenum +0.1 per cent zirconium



Effect of Zirconium Additions upon the Life of Molybdenum clad with 0.020 in. thick layers of Pure Platinum at 1400°C in air

Core Barrier layer Average Life

Effect of Zirconium Additions upon the Life of Molybdenum clad with 0.020 in. thick layers of Pure Platinum at 1400°C in air I

Core 1 Molybdenum Molybdenum +0.1 per cent zirconium


Molybdenum +0.003 in. of sprayed zirconium

Barrier layer

- - -

Stabilised ZrO,

Average Life (hours)

460 1200

2000 > 2300

Non-Volatile Oxides Since the mechanism of failure had been

shown to involve a volatile oxide of molybdenum, experiments were made to confirm that improved results could be obtained by using niobium as a core, this metal having an oxide of low vapour pressure (3).

Specimens sealed with an internal pressure of 2 Torr exhibited lives which were 2 to 3 times as high as those which would be expected from similar specimens containing a molybdenum core. The results obtained on loosely encapsulated specimens did, in fact, confirm the beneficial effects of low vapour pressure oxides as the evidence for vapour transport of niobium to the platinum sheath was very limited indeed. Failures in the main were caused by diffision which occurred where the sheath and core were in direct metallic contact.

The violent bursts caused by the accumu- lation of niobium oxide in the failure area were rather more spectacular than those in platinum-clad molybdenum, however, and niobium was found to have other disadvan- tages which would restrict its application as a core material for platinum-clad apparatus

in the glass industry. Any failure which occurred would have serious effects upon both the glass and the glass tank refractories and few barrier layers can be envisaged which would be completely inert with respect to both niobium and platinum at high temperatures. For this reason attention was concentrated upon the problem of ensuring that the residual gas pressure in the platinum-clad molybdenum apparatus was kept at a very low level. A convenient way of achieving this desirable objective is to use zirconium as a getter (3).

The results of some tests in which the zirconium was added to the molybdenum core as an alloying constituent and as a sprayed deposit are presented in the table. This shows that lives in excess of 2300 hours at 14oocC can be obtained even when the platinum sheath is only half a millimetre thick.

References I G. L. Selrnan, Platinum Metals Rev., 1967,

2 A. S. Darling, Metals and Materials, 1968, 2, 11, (4), 132

(11, 28 3 Johnson Matthey B.P. Application No.

17306 166

Properties and Uses of Palladium Palladium: Recovery, Properties and Uses, by Edmund M. Wise. Pp. xii and 187 Academic Press, New York and London, $I I (102s.)

Although it is probably better known for its catalytic uses and its selective trans- mission of hydrogen, palladium, the cheapest of the platinum metals and the second most abundant, has an unusual ability to form workable alloys with an extremely wide range of other metals. For this reason palladium has a number of commercial uses in the electrical contact field, in special purpose brazing alloys and in dentistry and jewellery, and these applications are all dealt with briefly in the present volume. Perhaps the most valuable part of the book to the metal- lurgist, however, is the lengthy compilation of binary and ternary equilibrium diagrams that forms the longest chapter, in each case full properties of the alloys being given as far as they are established.

Palladium plating is also of growing interest, particularly in the telecommunica- tions field, and several suitable electrolytes are described in a short chapter on this subject, but it is a little unfortunate that the obsolescent tetrammino-palladous nitrate bath (giving matte deposits) is featured and that no reference is made to the diammino-palladous nitrite bath yielding bright deposits.

Although the title of the book includes the word “Recovery”, little or no reference is made to the mineralogy, extraction or refining of palladium, while the substantial output from South Africa also escapes mention.

A final chapter contributed by P. N. Rylander surveys the many types of reactions in which palladium serves as a catalyst.

L. B. H.


Ruthenium Thick Film

It is only two years ago

Resist or Circuits that, during a

conference organised by the Institution of Electronic and Radio Engineers and the Institution of Electrical Engineers on the technology of “thin film” elements and circuits, the first significant references were made to “thick films” in the same context of microelectronics.

The preparation of metal films, notably of silver, gold or platinum, by a process of screen printing a metallic ink on to a ceramic substrate and then firing, has been known and practised for many years in the production of discrete components such as capacitors, but the development of this technique for micro-circuits has been both recent and rapid, stimulated by the relative ease and low cost with which such circuits can be produced. The very considerable interest and importance now attaching to this field were clearly demonstrated during a conference on “Thick Film Technology” held at Imperial College, London, in April, again organised by the IERE and the IEE, and attended by over four hundred engineers from twelve countries.

Among the papers presented during this meeting was one by G. S. Iles of Johnson Matthey Research Laboratories on “Ruthen- ium Resistor Glazes for Thick Film Circuits”. The development of a new type of glaze resistor preparation based on ruthenium dioxide was initially described in this journal some nine months ago (Platinum Metals Rcv., 1967, 11, 126). The objective was to devise an ink based on a chemically inert system that would depend on the firing stage to fulfil two simple functions, namely the burning out of the organic matter in the vehicle and the sintering of the metal oxidelglaze particles. The further requirements that had to be met were the availability of a wide range of resistance values, low temperature coefficients

and

for

the most economical use of ruthenium. These characteristics have all been achieved in the range of preparations now available, and smooth, well defined films may be obtained by screen printing through normal mesh sizes. The prints are fired in the temperature range 600” to 800°C to give films of the order of 0.0005 to 0.001 inch in thickness, the relatively low temperature of 600°C allowing the use of cheaper substrates than has hitherto been possible with thick film resistor pastes.

Since the publication of the first paper on these new glaze preparations the range of resistance values has been extended, and resistances from 5 to 100,ooo ohms/sq/mil can now be provided. Inks with intermediate values, instead of being mixed by the user, are produced during manufacture by the blending in special equipment of a limited number of master batches with established values. This ensures that the inks are homogeneous and possess the required electrical properties.

Temperature coefficients in the range *IOO x IO-~/”C can be expected with sheet resistivities from 50 to 5000 ohms/sq/mil, with animprovement to within &so x IO-~/”C where particular attention is paid to the precision of printing followed by a firing schedule that is controlled and reproducible. At the higher end of the resistance range, from 5000 to IOO,OOO ohms/sq/mil, temperature coefficients from -50 to -zoo x IO-~//”C may be expected, but the technique of preparation of this family of inks makes it possible to adjust temperature coefficients to fulfil a particular requirement.

Measurements carried out so far indicate that resistors produced from these ruthenium oxide glazes possess high stability and give acceptably low noise levels.


Ruthenium Resistor Glazes for Thick Film Circuits

Periodic Variations in the Catalytic Properties of Metals THE INFLUENCE OF SOLID STATE PARAMETERS ON ADSORPTION AND CATALYSIS

By G. C. Bond, D.s~., F.R.I.C. Research Laboratories, Johnson Matthey & Co Limited

Of the one hundred or so elements in the Periodic Table no less than spventy-jive are metals, but of these only the twelve i n Groups V I I l and I B have important catalytic properties. The marked changes in these properties on proceed- ing either certically or horizontally through the groups is discussed i n terns of the periodic variation of the solid-

state properties of the mijtals.

It is now well established that the occur- rence of significant and useful catalytic properties is largely confined to the elements lying in Groups VIII and IB of the Periodic Table. Other elements of the transition series are able to act catalytically, but because of the great thermochemical difficulty of reducing them to the metallic state, and of keeping them reduced, they do not find any practical applications. Metals which have either no d-electrons or which have only filled d- electron shells, while sometimes thermo- chemically suitable, are generally catalytically inactive, and catalysis (particularly of hydrogenation and related reactions) has therefore come to be particularly associated with the presence of unpaired d-electrons in thc metal.

There are, however, many large and important differences between the twelve metals constituting Groups VIII and IB : to facilitate discussion we will subdivide the twelve metals as follows:

( I ) The Group IB metals (coinage metals) : Cu, Ag, Au.

(2) The first row Group VIII metals (base metals): Fe, Co, Ni.

(3) The second and third row Group VIII metals (platinum group metals) : Ru, Rh, Pd, Os, Ir, Pt.

Comparison of Groups VIII and IB There are dramatic differences between the

catalytic properties of the Group IB metals and those metals lying adjacent in Group VIII : these differences are particularly marked with hydrogenation and similar reactions. Silver and gold are totally unable to activate hydrogen and hence to catalyse reactions involving hydrogen, while their immediate neighbours to the left, palladium and platinum, are among the best known hydrogenation catalysts. This simple ob- servation constitutes the most vivid possible demonstration of the existence of an electronic factor in catalysis, since geometrically speak- ing there is very little difference between palladium and silver, or between platinum and gold (see Table I). Their electronic properties (magnetic susceptibility, electrical conductivity, etc.) are of course substantially different; the Group VIII metals having incomplete d-electron bands are paramagnetic, while the Group IB metals having no unpaired d-electrons are diamagnetic (see Table TI). The presence of unfilled d-electrons is essential to hydrogen chemisorption, as they stabilise an intermediate weakly-held form without which dissociation cannot occur.

A similar but less marked difference in catalytic properties exists between nickel


and copper. Although nrckel is generally much superior, copper is not without some modest properties as a hydrogenation catalyst, being particularly attractive for the selective hydrogenation of alkynes and diolefins (I). The reason for the slight activity of copper has been a matter of debate for many years and no firm conclusion has been arrived at. It is possible that the d-electrons in copper are more readily thermally excited to sp-states than those of silver and gold, and that as before the resulting unpaired d-electrons are responsible for catalytic activity.

The Group IB metals are more active than their Group VIII neighbours in the rare cases where the metal is required to act as an electron-donor, as for example in the case of the decomposition of hydrogen peroxide (2). Silver has an important role to play as a controlled oxidation catalyst, and is used on a large scale for the oxidation of ethylene to ethylene oxide and of methanol to formaldehyde. Copper is too easily oxidised to be a possible catalyst, and gold is so noble that it is unable even to chemisorb oxygen. The Group VIII metals usually give only complete oxidation.

Comparison of the Base Metals with the Platinum Group Metals

It is now desirable to compare the differences in physical and catalytic properties observed on moving vertically through each sub-group of Group VIII. The base metals differ from the platinum group metals in many of their physical and chemical properties. The lanthanide contraction is responsible for the close similarity in the atomic and metallic radii of vertically adjacent pairs of the platinum group metals, and this is substantially responsible for other similarities, for example, in latent heats of sublimation and in melting points (see Table 111) and in mechanical properties. All the metals of the second and third sub-groups are face-centred cubic in structure, but those in the first sub- group are either body-centred cubic or close- packed hexagonal (see Table I).


Table I Crystal Structure, Metallic Radius and

Density of the Elements of Groups VIII

b.c.c. = body-centred cubic c.p.h. =close packed hexagonal

f.c.c. =facecentred cubic

Fe c o Ni c u h.c.c. f.c.c. f.c.c. f.c.c. 1.248 1.258 1.248 1.278

7.87 g/cc 8.90 g/cc 8.90 g/cc 8.96 g/cc

Ru Rh Pd Ag c.p.h. f.c.c. f.c.c. f.c.c.

and IB

I'.32lf r.348 1.37A 1.44A 1.90 g/CC 12.44 g/CC 12.02 g/CC 10.49 g/CC

0 s Ir Pt Au c.p.h. f.c.c. f.c.c. f.c.c. 1.338 1.358 1.388 1.448

2.48 g/Cc 22.5 g/CC 21.45 g/CC 19.3 g/CC

There is also a related sharp break between the first and second row elements with regard to electronic properties. The base metals are ferromagnetic while the platinum group metals are paramagnetic (see Table 11): the base metals are readily oxidised and corroded (and their compounds are correspondingly more difficult to reduce to the metallic state), and have lower electrode potentials, than the platinum group metals. This has important practical consequences in catalyst preparation, since for example nickel oxide is not easily reduced to the metal while the oxides of palladium and platinum can be reduced to the corresponding metals by hydrogen under ambient conditions. The significant differences in the chemistry of the elements of Group VIII also have repercussions on pre- parative procedures for catalysts. Thus there are no palladium or platinum analogues of the simple nickel salts such as Ni(NO,), and NiSO,, while hydrated nickel chloride, freely water soluble, contrasts with palladium chloride, which is anhydrous, polymeric in structure and virtually insoluble in water.

The differences between the catalytic properties of the base metals and the platinum group metals are too numerous and well- known to warrant a detailed exposition. The latter are generally superior to the former as

para- para-, para- dia- magnetic magnetic magnetic magnetic

9 +0.50 -+1.11 7 5.4 -0.20

Ir Pt All para- para- para- dia-

magnetic magnetic magnetic magnetic

Catalytic Properties of the Platinum Group Metals

Although the metals of the platinum group distinguish themselves from all others in terms of their catalytic abilities (6, 7 ) there are nevertheless important differences between the various members of the group. Specific points of difference have been described previously (3) and it is only necessary to mention a few examples here. Ruthenium is very much less active than palladium for the reduction of aromatic nitro-groups, while the reverse is true for carbonyl group reduction. The reduction of

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

methylene groups in certain steroids is more stereoselective when iridium is the cataIyst than when platinum is used (4). As a final example, palladium is more active than rhodium for the hydrogenolysis of substituents (for example, alkoxy groups and halogen atoms) from aromatic rings ( 5 ) . Attempts to rationalise effects of this kind have only been made in very limited contexts, the difficulty being the lack of adequate knowledge concern- ing metals other than palladium and platinum.

It is instructive to seek the origin of these differences in catalytic behaviour. The different crystal habits (Table I) may have some effect, but it is probably not large. There has been much discussion over a protracted period on the relation between the catalytic properties and the bulk properties of metals (6, 7 , 8). Although catalytic effects must result from the physico-chemical properties of surface atoms, there are grounds for hoping that these, themselves not easily measurable, will reflect the more easily measurable bulk properties.

An important effect in determining catalytic activity is undoubtedly the strength of adsorption of intermediate species. For optimum catalytic performancc there is required maximum coverage by species of minimum adsorption energy. With metals to the left of Group VIII activity is lower because the adsorption energy is too high; to the right it is lower because the adsorption energy is too small to maintain adequate surface coverage. The precise position of the activity maximum depends on the nature of the reaction, as is demonstrated in Figs I and 2. The view has often been expressed that the strength of chemisorption bonds parallels the strength of the metal-metal bond in the solid, and so correlations have been sought between catalytic activity and latent heat of sublimation (9) or other physical properties (6) which should reflect the metal-metal bond strength and which vary periodically with increasing atomic number. Unfortunately the physical properties in question divide themselves into two groups, one of which indicates maximum

102

Table II Magnetic Character and Mass Magnetic Susceptibility (c.g.s. units x 106) of the

Elements of Groups VIII and 1B

Fe C O Ni cu ferro-. ferro- ferro- dia-

magnetic magnetic magnetic magnetic - -0.09 - -

catalysts for hydrogenation and related reactions, although the cost differential (about 20 between nickel and palladium) sometimes counteracts the activity difference. For this reason also iron is widely used in ammonia synthesis and decomposition, although the more costly ruthenium is in fact more efficient. The superiority of platinum as a hydrogenation-dehydrogenation catalyst, however, deter- mines its selection for petroleum reforming operations, notwithstanding the cost factor. The platinum group metals are the undoubted choice for oxidation processes such as the hydrogen-oxygen reaction, complete hydrocarbon combustion and ammonia oxidation, where base metals would he rapidly oxidised and inactivated.

cohesive strength in Groups V or VI of the Periodic Table, and the other of which indicates maximum cohesive strength in Group VIII (6). The former group of properties involves phase changes (sublimation, melting, etc., see Table 111) while the latter does not (density, metallic radius, etc., see Table I) and is therefore thought to be more reliable as a guide to cohesive strength.

Although these properties vary rationally and periodically with increasing atomic number, because of the difficulties outlined above it may be preferable for the present to seek only to correlate catalytic properties with position in the Periodic Table. In a sense this is avoiding the main issue, but if- some trends can be discerned as the electron/atom ratio changes then some rationalisation of catalytic phenomena may be hoped for.

The limited success that quantitative correlations with physical properties enjoyed is due in part to the different physical forms in which the metals have been used. If, however, attention is concentrated upon those catalytic properties which are substantially indepen-

Table Ill Latent Heat of Sublimation and Melting

Point of the Elements of Groups VIII

Fe co Ni cu gg kcal/g IOZ kcalig IOI kcallg 81 kcalig

atom atom atom atom

and JB I

1540°C 1493°C I455’c 1083°C

R u Rh Pd Ag 155 kcal/g 133 kcal/g 89 kcal/g 68 kcal/g

atom atom atom atom 2400°C 1966°C 1554°C 960°C

0 s Ir Pt Au 187 kcal/g 158 kcal/g 135 kcal/g 84 kcal/g

atom atom atom atom 3045’c 2454°C 1773°C 1063°C

dent of the physical form of the catalyst then some measure of order is apparent. Detailed study of the hydrogenation of olefins, dioleiins and alkynes catalysed by all the Group VIII metals has revealed a consistent pattern of behaviour which correlates qualitatively with the known stabilities of organometallic olefin complexes; this work has been reviewed in detail elsewhere (10). A larger challenge is, however, presented when the hydrogenation of other functional groups is attempted on a comparative basis, because the important and useful selectivity consideration is frequently absent and reliance has to be placed on qualitative rate measurements. Nevertheless certain regularities of behaviour are emerg- ing, and these are worth sketching in outline.

Hydrogenation of the Aromatic Ring

Although all the platinum group metals are in some measure active for the gas-phase reduction of aromatic hydrocarbons, significant differences appear when they are used under mild conditions in liquid-phase reduc-


tion. Palladium is inactive, whereas both rhodium and ruthenium are active: unfortunately it is not possible to quantify this state- ment because of the different kinds of catalyst that have been used. The aromatic ring is expected to adsorb parallel to the surface, and the bond probably involves partial donation of the delocalised 7;-electrons of' the ring to the metal ( I I). Hence nai'vely the lower the electron/atom ratio, the stronger the adsorption is expected to be. We therefore conclude that palladium is inactive because it does not adsorb the aromatic ring sufficiently strongly. I t is significant that compounds such as phenol and aniline, having substituents which donate electrons to the ring and which hence would be expected to adsorb more strongly, are more reactive than benzene when palladium is used as catalyst.

Hydrogenation of the Carbonyl Group

Aromatic aldehydes and ketones are readily hydrogenated in the presence of palladium catalysts while the corresponding aliphatic compounds are unaffected under mild conditions. Now because of electromeric effects, the carbonyl group in aromatic compounds will have a greater electron density than in aliphatic compounds. Hence adsorption of the carbonyl group on palladium would seem to involve electron donation from this group zo the metal, and the low reactivity of aliphatic carbonyl compounds is probably due to in- sufficiently strong adsorption. If this is so, we may predict that on moving to rhodium and thence to ruthenium, that is, with decreasing electron/atom ratio, the adsorption and hence the reactivity of aliphatic carbonyl compounds should increase, and qualitatively this is what is observed.

The activity of the second row metals for hydrogenation of aromatic nitro-compound conversely increases with increasing electron/ atom ratio. We therefore infer that adsorption of the nitro-group is either too strong on ruthenium (which is inactive) or alternatively that adsorption involves electron donation

from the metal to the nitro group, the inactivity of ruthenium being due to too weak adsorption of the reactant. We cannot distinguish these possibilities without further experimental work.

Conclusions On passing along any row of the Group

VIII metals from left to right, the increasing electron/atom ratio has the effect of decreasing the strength of metallic bonding since the number of unpaired electrons is falling. Hence also the concentration of valency electrons at the surface is falling, and this means decreasing strength of adsorption for those species where the metal donates electrons to the adsorbate. Catalytic activity across the row may either increase or decrease depending on where the optimum adsorption strength occurs. A knowledge of the sense of


the activity change with increasing electron/ atom ratio can give valuable clues to the reaction mechanism and can assist the selection of catalysts of optimum activity for particular reactions. For example, binary alloys of metals having activities possibly superior to those of pure metals may be selected on this basis.

References I R. S. Mann and K. C. Khulbe, Indian J.

Technol’., 1967, 5, 65; A. de Jonge, J. W. E. Coenen and C. Okkerse, Nature, 1965, 206, 573

2 See for example D. A. Dowden and P. W. Reynolds, Discuss. Faraday SOC., 1950, 8, 194

3 See for example G. C. Bond and E. J. Sercombe, Platinum Metals Rev., 1965, 9, 74; ‘Platinum Metal Catalysts’, published by Johnson Matthey & Co Ltd

4 G. I. Gregory, J. S. Hunt, P. J. May, F. A. Nice and G. H. Phillips, 3. Chem. Soc., (C), 1666,2201

5 H. A. Smith and R. G. Thompson, Adv. Catalysis, 1967, 9, 727

6 G. C. Bond, ‘Catalysis by Metals’, Academic Press, London, 1962, (see especially Chapters 2 and 21)

7 A. M. Sokol’skaya, S. M. Reshetnikov, A. B. Fasman and D. V. Sokol’skii, Internat. Chem. Engning, 1967, 7, 525

8 G. C. A. Schuit, L. L. van Reijen and W. M. H. Sachtler, in ‘Actes 2me Congres Internat. Catalyse’, Editions Technip, Paris,

g S. M. Reshetnikov and A. M. Sokol’skaya, Zhur. $2 Kham., 1966, 40, 2412

10 G. C. Bond and P. B. Wells, A‘dv. Catalysis, 1964, 15, 92; G. C. Bond, in Kinetics and Catalysis’, ed. P. B. Weisz and W. K. Hall, Amer. Inst. Chem. Eng. Symposium series, 1967,631 3

11 See for example J. L. Garnett and W. A. Sollich-Baumgartner, Adv. Catalysis, 1966, 16, 95

1961, P. 893

High Purity Palladium Brazing Alloys MULTI-STAGE JOINING IN THE MANUFACl’URE OF THERMIONIC VALVES

The manufacture of special purpose thermionic valves operating at relatively high temperatures and under conditions of high vacuum necessitates the use of brazing alloys specifically suited to these requirements. Such alloys must be free from impurities that might hinder wetting and flow of the molten brazing material, must have low vapour pressures at high service temperatures, high melting points and, where needed, good mechanical properties at high temperatures.

While the well known silver-copper eutectic alloy melting at 778°C can satisfy a good many of these requirements when produced under careful conditions, alloys containing palladium show distinct advantages in terms of both vapour pressure requirements and mechanical properties, while also giving improved wetting characteristics on molybdenum, tungsten and nickel alloys. In addition they offer reduced risk of failure of the joints due to intergranular penetration.

~~~~~

Pallabraze High Purity Brazing Alloys

Alloy

Pallabraze 810 Pallabraze 840 Pallabraze 850 Pallabraze 880 Pallabraze 900 Pallabraze 950 Pallabraze 1010 Pallabraze 1090 Pallabraze 1225 Pallabraze 1237

Composition

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

18 Pd-Cu 30 Pd-Ag 60 Pd-Ni

Melting range “C

807- 810 830 - 840 824 - 850 856 - 880 876 - 900 901 - 950 970-1010

1080-1090 1150-1225

1237


The Pallabraze range of high purity palladium brazing alloys developed by Johnson Matthey was described in this journal some years ago by M. H. Sloboda (Platinum Metals Rev., 1963, 7, S), but a revised Data Sheet just published by the company brings up to date the detailed properties and uses of these alloys. As will be seen from the table, a range of brazing materials is available to provide melting points spaced at convenient intervals so that complex assemblies can be fabricated by the step-by- step technique.

High Temperature Strain Gauges ADVANTAGES OF PLATINUM METAL ALLOYS

Electrical resistance strain gauges provide in principle a simple, cheap and sensitive method for measuring and recording small deformations at the surface of almost any structure or engineering component. They usually comprise a grid formed from a length of fine wire and cemented to the surface under study.

In the early years of their development, around 1941, strain gauges were used extensively for measuring strain in aircraft and similar structures at room temperatures, but in recent years the need to study strains in turbo-jet and similar engine components under operating conditions has stimulated the development of gauges capable of measuring steady strains at up to 300°C for periods of 50 to 150 hours and alternating strains at temperatures of 300" to IOOOT for shorter periods-all in oxidising surroundings.

When properly fabricated and installed, a strain gauge instantly and faithfully responds to any extension of the surface to which it is attached, registering the movement by a change in its electrical resistance. It is obviously of prime importance that the basic electrical resistivity of the alloy of which the gauge wire is made shall be stable, unaffected by structural and other changes during the heating cycle, and that the wire shall not be eroded by oxidation during service.

A recent paper by R. Bertodo, Chief Research Engineer of Ruston & Hornsby Limited, Lincoln (presented at a conference in Cambridge on "Recent Developments on the Theory of Electrical Resistance Strain Gauges", organised by the Institute of Physics and the Physical Society), describes the development of platinum metal alloys for this

A typical assembly of eighz strain gauges jitted to a turbo-jet engine

purpose and lists the main requirements as : (I) Metallurgical stability, as in a single

phase alloy, and resistance to oxidation, as in a platinum metal alloy;

(2) Relatively constant temperature coefficient of resistance and a resistivity of more than 40 ohm/crn;

(3) A moderate change of strain sensitivity with temperature (this is affected by the degree of mismatch between the materials of the alloy wire and the basic material in their expansion characteristics);

(4) Adequate mechanical strength. Hitherto, the wire material that has proved

most satisfactory at temperatures up to 300°C is the 9.5 : 90.5 tungsten-platinum alloy developed by the author (Platinum Metals Rev., 1964, 8, (4, 128).

At higher temperatures, howevcr, oxidation and associated resistance drift severely limit its application, and in the present paper the author describes an extensive investigation for an improved alloy. The choice of alloying constituent was based more on conclusions drawn from the periodic table than


on knowledge of phase relationships, but it was implicitly accepted that a platinum metal was needed as a major constituent in order to resist oxidation.

The paper summarises the results of tests on the strain sensitivity, electrical resistivity, temperature coefficient of resistivity, and ultimate tensile strength of the systems of alloys of palladium with silver, ruthenium, osmium and molybdenum, and of platinum with gold, osmium and tungsten. Tests were also made on some alloys in the ternary systems palladium - rhodium - ruthenium, platinum - osmium - iridium, palladium - ruthenium - molybdenum and platinum - osmium - tungsten, as well as on some base metal systems.

From an electrical point of view, the molybdenum-palladium alloys were selected as having the most favourable properties, but their resistance to oxidation was found to be inadequate.

To improve oxidation resistance, platinum was substituted for part of the palladium; and the final conclusion was reached that of all the alloys tested the most suitable for use at high temperatures was the 45 :45 : 10 platinum- palladium-molybdenum alloy. This has a temperature coefficient of resistance of IOO

micohms per ohm per degree C , and a strain sensitivity at room temperature of 4.0. No prediction, however, is attempted of an upper safe temperature for its steady use.

J. C. C.

Selective Diffusion of Hydrogen Allotropes through Palladium

The isotopes of hydrogen diffuse through palladium at different rates, and several processes which utilise this effect for the concentration of deuterium have been established on an industrial scale. Some corresponding effects involving the ortho and para allotropes of hydrogen have recently been reported by L. Fitoussi of CEN Saclay (Compte Rend. Acad. Sci. 1968,266, (C), 164) and, in view of the considerable differences in diffusion rates observed, the experimental findings deserve careful consideration.

The tests were made on a palladium membrane of unspecified thickness which was maintained at 175°C and subjected to an upstream hydrogen pressure of 30 Torr. The downstream side of the membrane was continuously evacuated. Diffusion rates measured with ordinary hydrogen (25 per cent para- hydrogen) increased initially to a peak value of 1.3 arbitrary units and subsequently decreased slowly to a steady state value of I arbitrary unit. Rapid evacuation of the upstream side of the membranc followed by admission of fresh hydrogen momentarily increased the diffusion rate to 1.3 units after which a gradual return to steady state conditions was observed.

These findings were interpreted as an indication that diffusion was being inhibited by the development of an adsorbed layer of

ortho hydrogen on the upstream surface of the palladium membrane. When the proportion of para hydrogen in the feed gas was gradually raised from 25 to 50 per cent the diffusion rate incrcascd by a factor of 6.5.

If para hydrogen diffuses so much faster than ortho hydrogen it is difficult to under- stand why the output of laboratory and commercial diffusion units run from gas cylinders should remain constant over long periods of time. Such units are of course run at temperatures and pressures much higher than those reported in this paper. The effective- ness of the hydrogen/deuterium separation processes can of course easily be correlated with the Y. to p phase changes in the palladium and it is possible therefore that in his selection of experimental conditions L. Fitoussi may have hit upon temperatures and pressures particularly favourable to selective allotrope diffusion.

It seems very significant, however, that the 50 per cent para hydrogen mixture which provided high diffusion rates was continuously circulated over the membrane surface. The ordinary unenriched hydrogen which diffused very slowly was not circulated, nor was any bleed-off provided in the vicinity of the membrane. Such stagnant conditions are well known to inhibit rapid diffusion.

A. S. D.


ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Specific Heat of Platinum from 1.4 to 100°K G. E. SHOEMAKER and J. A. RAYNE, Phys. Lett., 1968, 26A, (6), 222-223 Measurements indicated no anomalous temperature dependence of the lattice heat capacity. The corresponding variation of the Debye temperature was compared to that calculated from elastic data using a central force model.

Measurements of the Thermal Conductivity and Electrical Resistivity of Platinum from 100 to 900°C D. R. FLY" and M. E. O'HAGAN,?. Res. NES, Sect. C, Engng Instrumentation, 1967,71C, (4), 255-284 Results of two methods show good agreement and indicate that thermal conductivity of Pt increases with temperature. Electrical measurements gave results equivalent to those from conventional nonelectrical methods and the thermal conductivity of Pt does not depend significantly on electric current densities. Further work by the same electrical method on samples of different purity are necessary before Pt can be established as a thermal conductivity reference standard.

Quenches of Deformed Platinum J. J. JACKSON, Bull. Am. Phys. soc., r968, 13, (I), 74, abstr. EJ2 More than 10 atomic fraction lattice vacancies can be generated thermally in Pt with indefinite retention of an appreciable number by rapid room-temperature quenching. The number of vacancies lost depends on the number initially present, on the vacancy migration distance, and on the density of effective sinks. Pt deformed at raised temperatures and subsequently quenched has a sink concentration dependent on holding time before quenching.

Vacancies, Divacancies, and Self-diffusion in Platinum D. SCHUMACHER, A. SEEGER and 0. HjiRLIN, Phys. Status Solidi, 1968, 25, (I), 359-371 The electrical resistivity of thin high-purity Pt wires quenched from z IOOO'C by the helium-I1 technique recovers between 380 and 52oOC with activation energy of 1.33rt0.05 eV; quenched from near the melting point recovery occurs between 200 and 460°C by two second-order processes with activation energies 1.0 and 1.34 eV. Self-diffusion data are reanalysed to allow for both mono- and divacancies and are compared with previous work. A consistent set of vacancy parameters for Pt is proposed.

The Interaction between Liquid Platinum and Some Transition Metal Carbides R. WARREN,^. nucl. Muter., r968,25, (I), 117-rrg Studies of the interaction of liquid Pt with plaques of VC, TIC, WC, and mixed refractory carbides by the sessile-drop method confirmed that they react to form graphite plus metallic solutions or intermetallic compounds. Measure- ments were qualitative but mixed carbide solid solutions do not appear more stable towards Pt than single carbides. Wettability of WC-TIC by Pt decreased with increasing Tic content.

Effect of Diffusion Barriers on Interdiffusion between Noble Metals and Refractory Metals at 2000°F

Metals, 1968, 20, (I), IWA Specimens of commercial Mo and Ta alloys were held in contact with Pt, Rh, 20% Rh-Pt and 40"; Rh-Pt at 2000-F for 30 and 120 days, and the extent of interdiffusion was measured by metallographic, microhardness and electron micro- probe methods. It proved to be similar in all cases. Chemical vapour deposition of o.ooi inch films and/or plasma arc spraying of 0.005 inch films of A1,0,, ZrO,, ZrC and TaC were tested as diffusion barriers. Al,08 was most effective, ZrO, less effective, and ZrC and TaC were ineffective in reducing interhffusion.

Thermodynamic Properties of Solid Pal- Iadium-Copper and Platinum-Copper Alloys K. hi. MYLES and J. B. DARBY, Acta Metall., 1968,

Activities and free energies of formation at r35o"K of solid Pd-Cu and Pt-Cu alloys were calculated from vapour pressure data. Enthalpies of formation at 298°K were determined by liquid Sn solution calorimetry for Pt-Cu. Entropies of formation of both systems were computed from free energy and enthalpy values. The systems are compared to Pd-Ag, which has similar electronic structure.

On the Preparation and Electrical Properties of PtSb, c. T. ELLIOTT and s. E. R. HIS COCKS,^. muter. Sci., 1968, 3, (z), 174-177 Single crystals of PtSb,, prepared by a liquid encapsulation technique and pulled by the Czochralski method, consist of n-type material with a carrier concentration x 6 x Iole;cms, a ratio of electron to hole mobility P ~ : &=0.57 at I IO'K, and max. electron mobility 2ioo m Z / V sec at 50°K. Thermal energy gap is 0.1 IZ eV.

H. M. HOFFMAN, R. C. HAM and J. R. OGREN, J.

16, (41, 485-492

Hutinurn MetuZsRev., 1968, 12, (3), 108-115 108

The Low Temperature Thermoelectric Power of Some Palladium and Platinum Alloys

(145),21-35 R. FLETCHER and D. GREIG, Phil. Mag., 1968, 17,

Thermoelectric power S was measured at 2-120'K for Pd-Ag, Pd-Rh, Pd-Pt, Pt-Au and Pt-Ir alloys and it proved possible for alloys of Pd and Pt with their neighbouring elements to correlate the sign of Sd, the diffusion component of thermo- power in the residual resistance temperature range, with the slope of density of states versus concentration curves. Observed values of Sd/T agreed with calculation from the rigid band model for all Pt-Au and Pd-Ag alloys studied apart from that with < I yL Ag. & was not predicted correctly for Pd-Pt. Each specimen had large positive phonon drag component of S, which persisted to high temperatures despite alloying. These phenomena are caused by phonon-induced scattering of either s-d or d-d processes.

The Enthalpies of Formation of the Pal- ladium-Kickel, Platinum-Kickel and Pal- ladium-Platinum Systems J. B. D A R B Y , ~ . Metals, 1968, 20, (I), 74A. Enthalpies of formation of Pd-rich Pd-Ni alloys are negative, i.e. exothermic, and are slightly positive for 70-1000~~, Ni content. Values for Pt-Ni are exothermic with a maximum of -2250 caljg atom at equiatomic composition. Ordered Pt,Ni, has twice the enthalpy of formation of the disordered alloy. Pd-Pt alloys also have negative enthalpies with a maximum of -850 caljg atom at equiatomic composition.

Specific Heat Enhancement in Strongly Paramagnetic Pd-Ni Alloys A. I. SCHINDLER and c . A. MACKLIET, Bull. Am. Phys. SOC., 1968, 13, (r), 124, abstr. HJ9 Low-temperature specific heat measurements on 0-1.95 at.% Ni-Pd alloys show that y, the electronic specific heat coefficient, has strongly linear dependence on Ni content and increases by 18:h per at.'$& Ni addition. No TSlog T dependence occurs in the low temperature heat capacity and data were analysed according to a T +/3T3.

Application of the Electron-donation Model for Hydrogen Absorption to Palladium-rich Alloys Hydrogen-Gold-Palladium K. ALLARD, A. MAELAND, J. w. SIMONS and T. B. FLANAGAN,~. phys. Chew., 1968,72, (I), 136-143 Absorption data for low contents of H , in a-phase Au-Pd alloys give heats of absorption at infinite dilution by extrapolation of the isosteric heats as j980,7000,7 j40,9040, and 9340 caljmole H, for 5 .7 , 15.3, 18.8, 26.5, and 44.70L Au-Pd respectively. Measured entropies of absorption are compared with those calculated from a model of localised protons treated as three-dimensional oscillators. Both Au and H are assumed to donate electrons to the vacant s and d bands of Pd.

Investigation of the Thermodynamic Proper- ties of Solid Solutions of the Ag-Pd System by the Method of Measurement of the Vapour Phase

PRITULA, Zh. $2. Khim., 1968, 42, (3), 657-659 Studies at IOOO"C by measuring the rate of vapori- sation of Ag in the alloys produced isotherms of the thermodynamic activity of both parts and enables the isobaric-isothermal mixing potentials to be calculated. Ag has negative deviation from Raoult's Law at all compositions while for Pd the activity is more ideal in Pd-rich alloys and less ideal in Ag-rich alloys. The extreme value is -3.7 kJiH atom at ~ 6 0 at.",: Ag.

Structural Transformations and Magnetic Properties of Iron-Palladium Alloys L. M. MAGAT, G. M. MKAROVA and YA. A. SHUR, Fiz. Metal. Metalloved., 1968, 25, (3), 431-438 Studies of changes of magnetic properties and phase structure of high-coercivity alloys of ~ 3 0 at.% Pd-Fe during annealing were related to the effect of prior plastic deformation.

The Relative Thermodynamic Properties of Cobalt-Palladium Solid Solutions L. R. BIDWELL, F. E. RIZZO and J. v. SMITH, J. Metals, 1968, 20, (I), 76A EMF studies at 800-1100°C show that the thermodynamic activity of Co in Pd departs positively from ideal solution behaviour in Co- rich alloys and negatively in rd-rich alloys. Heats of mixing were endothermic for Co-rich and exothermic for Pd-rich alloys. A miscibility gap below 600°C may exist for Co-rich alloys. Compositions up to 40y0 Pd-Co were studied in the ferromagnetic state. Relative integral molar excess entropies were all positive.

The Titanium-Palladium Alloys E. RAUB and E. ROSCHEL, Z. Metallkunde, 1968,59, (2), I 12-1 14 The existence was confirmed of Ti,Pd,, TiPdf and TiPd,, the latter with LI, type crystals. Ti,Pd, occurs only between 1280" and 795°C. TiPd shows a transformation at j10--52o0C with orthorhombic crystals below this temperature. Maximum solubilities of Pd are <: 1.176 in a-Ti, x 31 at.O/o in ,&Ti. The disordered solid solution and the L I , phase have similar properties which makes it difficult to find the boundary of the f.c.c. Pd-Ti solid solution.

X-ray Studies of Palladium-Cadmium and Palladium- Antimony Allays J, N. PRATT, K. M. MYLES, J. B. DARBY and M. H. MUELLER, J . less-common Metals, 1968, 14, ( 4 , 427-433 Lattice parameters of Pd-rich f.c.c. and f.c. tetragonal Cd-Pd alloys are tabulated. The solid solubility limit of the cubic phase was determined.

V. N. EREMENKO, G. M. LUKASHENKO, and V. L.


An attempt to characterise the crystal structure of the f.c. tetragonal phases was made. Lattice parameters of Pd-rich f.c.c. Pd-Sb are tabulated. Solid solubility limit of Sb in Pd at 500-1000'C was determined. Lattice parameters of PdSb and PdSb, were measured.

Electronographic Investigation of the Pd-Sb System in Thin Layers T. P. KARPOVA, R. M. IMAMOVA and s. A. SEMILETOV,

Kristallograjiya, 1968, 13, (2), 316-321 Studies of thin films of Pd-Sb revealed PdSb and PdSbz and the new hexagonal compounds Pd,Sb, with a-7.59, c-:13.86& Z-4, and PdSb, with a-7.59, C-43.2AY 2-24.

Pressure Dependence of the Magnetic Tran- sitions in Fe-Rh, Fe-Rh-Pd, and Fe-Rh-Ir Alloys R. c. WAYNE, Bull. Am. Phys. SOC., 1968, 13, (3), 442, abstr. DK15 50-60 at.?(> Rh-Ir alloys exhibit first order antiferromagnetic transitions at temperatures somewhat dependent on the binary alloy composition but the addition of a few :!, of I'd lowers and of I r raises these temperatures considerably. Pressure coefficient of Curie temperature and transition temperature To are constant with pressure up to 25 kbar for the alloys studied. To and dTo/dP depend on the heat treatment. A triple point occurs in the P-T plane at 15 kbar for the 60;; I r alloy. At pressures above this only antiferromagnetic and paramagnetic phases exist.

New A,B, Phases of the Ti-Group Metals with Rh B. C. GIESSEN, R. WANG and N. J. GRANT,J. Metals, 1968, 20, (I), 1o8A The A,B, phase in the Ti-Rh system is iso- morphous with orthorhombic Ge,Rh,5.

The Compound U,Ru, A. F. BERNDT and A. E. DWIGHT, Trans. metall. soc.

U,Ru, formed at 102 j & 5°C by peritectoid transformation of U,Ru,+U,Ru, has f.c.c. structure with a - - I2 .8g~+o.o01~ and density 14.45 g C I T - ~

but it has not been identified with any other known AIB,-type structure.

Magnetic Susceptibilities of the Hexagonal Close-packed Alloys of the Later 4d and 5d Transition Metal Series J. G. BOOTH, Phil. Mag., 1968, 17, (I45), 205-209 Magnetic susceptibilities were measured for 41 alloys of the h.c.p. systems Mo-Ru, Mo-Rh, Ru-Rh, Ru-Pd, Ru-Nb, Re-W, Re-Os, Re-Ir, Re-Pt, 0s-Pt and 0s-Ir from the 4d and 5d series at 77-330°K. Results largely suggest a rigid (or plastic) band model for these h.c.p. alloys. An apparent minimum in the density of states curve occurs at an average group number of

AIME, 1968, 242, (21, 340-341

~ 8 . 1 . Re-Pt is the exception,perhaps because of enhanced exchange contribution to the susceptibility.

Superconductivity, Susceptibility, and Speci- fic Heat in the Noble Transition Elements and Alloys. I. Experimental Results K . ANDRES and M. A. JENSEN, Phys. Rev., 1968, 165, (2) 533-544 Studies of superconductivity and magnetic susceptibility in mostly Ir-rich f.c.c. Ru-Ir, Rh-Ir, Pd-Ir, Re-Ir, 0s-Ir, and Pt-Ir alloys show that filling of the first d band first depresses the superconducting transition temperature T, and then causes a rapid increase of x. Metals with exchange enhanced susceptibilities are not superconducting above 0.015"K. It is predicted that Pd will not superconduct even at 0°K and that superconductivity will occur well below 10-3°K for Pt and Rh, if at all. 11. Comparison with Theory M. A. JENSEN and K . ANDRES, Ibid., 545-555 Spin fluctuations seem to he suppressing T,, since there appears to be correlation between decreasing T, and increasing x / y , where yT is the electronic specific heat.

CHEMICAL COMPOUNDS On Iridium Bromide N. I. KOLBIN and V. M. SAMOILOV,Zh. neorg. Khim., 1968, 13, (31,906-908 IrBr, prepared by bromination of Ir at 8-g atm, 84o',K is an insoluble powder with density 6.45 g/cmY and specific magnetic susceptibility -0.2 x Dissociation to the elements com- mences at =440"C, dissociation pressure is 1 atm at 846"K, and the heat of formation is 50.0 kcalimole. Treatment of IrO2,2H,O by HBr produces IrBr and IrBr, as well as IrBr, with properties somewhat different, which are tabulated.

Thermal Dissociation of Iridium Triiodide

Measurements of the thermal dissociation pressure of IrI, at 585-7a3"C, which dissociates according to IrI, (solid) --Ir + 3j2 I, (gas) without formation of the lower iodides, give dissociation constants according to log Kp,,,- --8975.0/T-l- 12.42. The change of enthalpy for IrI, formation from Ir metal and I, gas is AHa9s. l j - -~83.2x 10-3&5.0X IO-~ J:'mole, the change of entropy is ~S",,,.16=-282.0~1.9.0 J/degC mole and the standard entropy of solid IrI,? is S'?,,.,,=r45.0 J/deg C mole.

The Crystal Structure of Ruthenium (111) Bromide K. BRODERSEN, H.-K. BREITBACH and G. THIELE, Z. anorg. allgem. Chem., 1968,357, (4-6),162-171 RuBr, forms orthorhombic crystals with a 16.47,

Ibid., (4), 915-918


b--11.205, c-5.855A, Z=4, consisting of (RuBr,)Br,;, groups with Ru in approximately octahedral coordination.

Magnetic and Other Studies of Ruthenium Dioxide and its Hydrate

M. J. HOLDWAY and M. H. RAND,^. Chem. Sac., A, inorg. phys. theor., 1968, (3), 653-657 Magnetic behaviour of RuO, up to rooo"K suggests that K is 2 3000 cm-l in dioxo-bridged chains of Ru atoms. High electrical conductivity and structure suggest that the average oxidation state of Ru atoms is & 1 4. The oxide hydrate is R U O , , ~ . ~ H , O , where x is up to 0.12 due to excess chemisorbed O 2 after removal of some H,O and where y is often 1-1.3. Susceptibility, similar to that of RuO,, varies in relation to adsorbed groups and to some Ru atoms behaving like Ru (V), i.e. in the d 3 state.

The Formation of [Ru(NH,)SNz]2+ from Ruthenium Trichloride and Ammonia

J. M. FLETCHER, W. E. GARDNER, B. F. GREENFIELD,

J. CHATT and J. E. FERGUSSON, Chem. commun., 1968, (31, 126 [Ru(NH,)N,]CI, was produced while preparing [Ru(NH,),]Cl, by reductions of RuCl, in NH, by Zn dust. The N, ligand in [Ru(NH3)N,l2' appears to be produced by dehydrogenation of NH, on the Ru ion and indicates great stability of RUN*.

Fixation of Atmospheric Nitrogen by Ru- thenium Compounds

46, (31,469 A. D. ALLEN and F. BOTTLEY, caiz.3. Chem., 1968,

[Ru(NH,),N,12 1 was prepared using atmospheric N, from [Ru(NH,),Cl] Cl,', and this was the first time that such a compound had been prepared from atmospheric N2. [Ru(NH,)&l]CI,+ was alternately reduced with amalgamated Zn and H,SO, under Ar, and exposed to air for 5-7h.

Triphenylphosphine Complexes of Ru- thenium and Rhodium. Reversible Combina- tions of Molecular Nitrogen and Hydrogen with the Ruthenium Complex A. YAMAMOTO, s. KITAZUME and s. IKEDA, J . Am. Chem. SOC., 1968, go, (4, 1089-1090 A triphenylphosphine complex of Ru combines with N, in a C6H6 solution and the coordinated N, ligand can be expelled from the Ru complex simply by passing an Ar stream through the C,H, solution at room temperature. The N, complex has not yet been isolated. A similar combination with H, has been observed. N, is not coordinated to a similar complex of Rh.

Oxide Chlorides of Osmium R. COLTON and R. H. FARTHING, Awt. J . Chem.,

Os,OCI, was prepared from OsO, and HCI. I.R., 1968, 21, (31, 589-593

mass spectroscopic and oxidation state determinations showed its structure to be polymeric with 0x0 bridges. SCI, reduction of OsO, gave OsC1, and OsOCI,. Attempts to prepare Os,OCl, failed.

Thio- and Seleno-compounds of the Plati- num Metals w. RUDORFF, A. STOSSEL and v. SCHMIDT, Z. anorg. allgem. Chem., 1968, 357, (4-6), 264-272 Twelve A,Me:xMelVX, crystalline compounds were prepared. K,Pt,S,, Rb,Pt,S,, Cs2Pt,S,, K ,Pt,SeG, Rb 2Pt4Seo, K,Pt ,IrS,, and K ,Pd,Pt S , had hexagonal rhombohedric structures with Z -3. K,Pt,SnS,, Rb,Pt,SnS, and K,Pd,SnS, were hexagonal with Z - z . K,Pt,TiS, and K,Pd,TiS, were prepared also.

ELECTROCHEMISTRY Enhanced Catalytic Activity of Platinum Electrodes Resulting from Cathode Pre- treatment J. N. HIDDLESTON, Nature, 1968, 217, (5133, Mar. 16), 1047 Potential-current density curves plotted for anodic oxidation of HCOOH in z N solutions of H,SO,, HClO, and HNO, show enhanced oxidation rates, i.e. increased currents at lower potentials, with stability provided that electrode potential was not increased beyond 600 m V for long periods, i.e. (4 min.

The Anodic Bebaviour of Palladium in Aqueous Solutions R. KAMMEL, T. TAKEI, H. WINTERHAGER and H . YAMAMOTO, Metalloberflache, 1968, 22, (4), 107- 111 Rest potential measurements and potentiostatic studies of Pd electrodes in buffer solutions and in aqueous HCl and HzSOl solutions enabled possible reactions and equilibria to be derived from potential-pH and potential-pC1 graphs. Pd dissolves in the divalent state and the dissolution is reversible. Flade potential measurements indicated the stability of the oxide-like surface layers of the electrodes.

ELECTRODEPOSITION AND SURFACE COATINGS Electrocrystallisation of Mercury, Silver and Palladium D. J. ASTLEY, J. A. HARRISON and H. R. THIRSK, Trans. Faraday SOC., 1968, 64, (I), 192-201 Kinetics of electrodeposition of Ag, Hg and Pd on inert C electrodes were studied potentio- statically. Pd formed a three-dimensional crystalline growth with rate constant ~ 3 . 3 x I O - ~ moles/cm2 sec and cr--0.6 for 5.12x10-~ M PdCl, solution.


Electrolytic Deposition of Palladium- Nickel Alloy S. N. VINOGRADOV and N. T. KUDRYAVTSEV, Zashchita Metal., 2968, 4, (2), 145-251 Studied in the electrodeposition of Ni-Pd were composition, yield according to current, resistance, internal stress, microhardness, and wear resistance of cathodic deposits in relation to electrolyte composition and the conditions of electrolysis. As Ni content increases, internal stress of the deposit decreases but microhardness and wear resistance increase. 25% Ni-Pd has 1.5 times the microhardness and 14 times the wear resistance of pure Pd. Wear resistance is related to temperature, acidity and current density but microhardness is not. Discharge of the Pd ions is made more difficult but of the Ni ions more easy during joint deposition. Optimum conditions are given for bright 20-25% Ni-Pd deposits.

Platinum-metal Alloy Deposition from Bro- mide Electrolytes c. J. N. TYRRELL, Synopsis Papers, 7th Internat. Metal Finish. Conf,, Hanover, 1968, (May), paper 21

Aqueous electrolytes based on acid solutions of complex bromides were developed for Ir, Pt, Pd, Rh, and Ru and satisfactory deposits up to 5pm were obtained. Each pair of these metals could be co-deposited to produce true alloys and the ternary Pd-Ru-Rh combination was deposited also. An electrolyte suitable for 5-50% Ir-Pt deposits on etched T i or Au-flashed Cu contained 3.5 g/1 Pt, 1.5 g/1 I r as complex bromides at p H 2-2. 20-80% alloys of Pd-Pt and Rh-Pd were obtained as adherent, reasonably bright deposits, and up to 50% Ru-Pt and Ru-Pd were of the same standard but, for more Ru, "black" non-adherent deposits tended to be formed.

Wear Behaviour of Rhodium Coatings on Variously Hard Underlays A. KEIL and E. MAHLE, Metalloberjlache, 1968, 22,

Effects occurring during dry friction of metals are discussed in terms of the hardness of the loaded faces. The hardness of Rh therefore makes it important as a coating for rubbing contacts and a thicker layer of another metal is usually deposited below it. Tests showed that Rh deposited on Ni directly is more stable than when an intermediate layer of Ag is used. This is true for electrical contacts in almost continuous operation.

(21, 44-48

HETEROGENEOUS CATALYSIS Study of the Adsorption and Energetic Properties of Metallic Catalysts. 11. Catalytic Activity of Blacks v. I. SPITSYN, A. A. BALANDIN and L. I. BARSOVA, Zh. Jiz. Khirn., 2968, 42, (2), 345-350 Specific activities for catalyst blacks for liquid-

phase hydrogenations of cyclohexene decrease in the order Pd>Rh>Pt>Ru for those prepared by Zelinski's method but in order Rh>Pt>Pd> Ru for those prepared radiochemically. Measure- ments of stationary potential against reaction time indicate slight adsorption of cyclohexene on the catalyst surface and show that the surface energy is almost independent of the method of catalyst preparation. The measurements also lead to a theory for the negative activation energy on Rh and to the cause of the induction period on Ru black. A compensation effect bears little relation to the method of catalysr preparation or to the type of catalyst.

The Rates of Hydrogenation of Cycloalkenes from the Liquid on Platinum-Alumina Catalysts A. s. HUSSEY, G. w. KEULKS, G. P. NOWACK and R. H. BAKER,^. org. Chem., 2968, 33, (2), 610-616 Reaction rates were determined for hydrogenations of 18 cycloalkenes in C,H,, solution over Pt/Al,O, at 25"C, % I atm H,. Reactions were first order in pH2 and amount of catalyst; zero order in cycloalkenes. Activation energies for cyclohexene and cycloheptene were 5.7 and 6.5 kcal/mole. Discussion in terms of the Horiuti- Polanyi mechanism leads to the suggestion that Pt surfaces have two types of site, one involved in H, addition and the other in olefin exchange.

On the Conversion of Propylene on Platinum on Alumina Catalyst

Neftekhimiya, 1968, 8, (I), 46-49 Pt/AlaO, possesses appreciable activity for polymerisation of C,H6 at 70 atm, z50-30o"C. I t promotes formation of significant amounts of aromatic hydrocarbons above 350°C. The 75-20Ooc fraction contains up to 90% aromatics, mainly C, and C8 homologues of benzene.

Isotopic Exchange of Oxygen on Platinum Powder Y. L. SANDLER and D. D. DURIGON,J. phys. Chem.,

Kinetic studies on the isotope exchange of 0, on Pt powders at -195 to +300"C showed three different weak modes of chemisorption, all varying with time and temperature. No 0, beyond the equivalent of a monolayer was in or on the powders, which were well annealed and free of C or H,. Previous reports of the uptake of several layers seem due to impurities or defects. N a does not exchange on Pt nor interfere with 0, exchange up to 600°C.

The Relative Specific Activity for Benzene Hydrogenation of Some Supported Group VIII Metals W. F. TAYLOR,J. Catalysis, 1967, 9, (2), 99-103 Specific activity studies of C6He hydrogenation

V. I. KARZHEV, N. V. SHAVOLINA and V. Z. ZLOTNIKOV,

1968, 72, (3), 105~-1057

Platinum Metals Rev., 1968, 12, ( 3 ) 112

on NijSiO,, Co/SiO, and Pt/SiO, at 70-17S”C and at a common set of reactant partial pressures revealed apparent activation energies of 14.0, 5.8 and 2.3 kcal /mole for the respective catalysts. Apparent activation energy increases with pH%. Below 90°C the relative specific activity is Pt>Co>Ni; above 90°C it is Pt>Ni>Co. It is difficult to relate apparent activation energy to the stability of the proposed surface r complexes because of its complexity.

Influence of Hydrogen in the Dehydrogena- tion of Cyclohexane on Platinum B. MENCIER, F. FIGUERAS, L. DE MOURGES and Y.

Activity of Pt/SiO, is affected by reversible deactivation caused by H,, and by permanent fouling on the catalyst which H, reduces.

Heterogeneous Oxidation of Methane over Palladium Catalysts J. G. FIRTH and H. B. HOLLAND, Nature, 1968, 217, (5135, Mar. 30), 1252-1253 Reaction parameters were established for oxidation of CH, on Pd and on Pd/zeolite formed in different u’ays.

The Decomposition of Formic Acid Vapour on Silver-Palladium Alloys G. RIENACKER and H. M ~ ~ L L E R , Z. annrg. allgem. Chem., 1968,357, (44% 255-263 Catalytic activity of l’d for decomposition of HCOOH vapour is unaffected by addition of up to 30 at.yb Ag. A sharp decrease of activity occurs at 30-40 at.?(, Ag. The activity at >40 at.”/, Ag is steady at the lower value for Ag-rich alloys and pure Ag. Activation energy of the catalysts depended on thc experimental conditions and on their pretreatment.

On Changes of Selectivity of the Action of Pd Catalysts by Modification in the Hydrogena- tion of 6-Methylhepta-3,5-dien-2-one L. KH. FREIDLIN, N. v. BORUNOVA, L. I. GVINTER and s. s. DANIELOVA, Zh. fiz. Khim., ~968, 42, (I), 98-100 Hydrogenation of 6-methylhepta-3,5-dien-2-one over s:, Pd/CaCO,, I:/” Pd/A1209 or 10; Pd/TiO, occurs principally by addition of H, at the 5,6 double bond but when the catalysts are modified with Cd the addition of H, occurs principally at the 3,4 double bond, Addition of (CH,COO),Pb to Pd;CaCO, does not change the point of H, addition but initiates deactivation.

Isomerisation of Hexenes in the Presence of Ruthenium, Rhodium, Osmium and Iridium, Supported on Carbon M. ABUBAKER, I. v. GOSTUNSKAYA and B. A. KAZANSKII, Vest. Moskov. Univ., Ser. II, Khim.,

Studies of double bond migration in hexene-I,

TRAMROUZE, c ,r . , [email protected], 1968, 256, (9), 595-598

1968, (I), 105-107

a-methylpentene-I, 3-methylpentene-I, and 2,3-dimethylbutene-r in the presence of Ru,’C, Rh/C, Os/C, and Ir/C at 80’C showed that activity varies in the order Rh>Ru>Os>Ir .

Catalytic Hydrogenation of Allene

(2), r61-166 The order of activity of metal/pumice catalysts is P t > P d > R h > I r>Ni> Co > Fe,Ru> 0 s and their apparent activation energies are 17.4, I3,9.6, 5.3, 7.8, 10.8, 9.4, 3.0, and 4.6 kcal/mole respectively. Pressure-time curves for the reaction showed a dependence on reactant ratios and their order of admission. The reaction was first order, 01 slightly higher, in H2 and zero order in allene. A mechanism similar to hydrogenation of acetylene is suggested.

R. S. MANN and D. E. TO, Cun.J. Chem., 1968, 46,

HOMOGENEOUS CATALYSIS A Comparison of Heterogeneous and Homo- geneous Platinum-catalysed Exchange Pro- cedures for the Isotopic Hydrogen Labelling of Synthetic Hormones and Steroids J. L. GARNETT, J. H. O’KEEFE and P. J. CLARINGBOLD, Tetrahedron Lett., 1968, (22), 2687-2690 K,PtCl, catalyses deuteration and tritiation of synthetic hormones and steroids faster and at lower temperatures than Pt/NaBH, or self- activated PtO,. Homogeneous deuteration of oestrone, cholesterol and testosterone is confined to positions close to the points o€ unsaturation. In hexestrol, trans-stilbene and bibenzyl, both ring and side chain H is exchanged. Homogeneous exchange is simpler than heterogeneous and will probably replace the latter for deuteration and tritiation. The methods are complementary for labelling of other substances.

Initiation of Vinyl Polymerisation hy Tetra- kis(triphenylphosphine)( 0) c. H. BAMFORD, G. c. EASTMOND, and K. HARGREAVES, Trans. Faraday SOC., 1968, 64, (I), 175-184 Pt(PPh,), effectively initiated vinyl polymerisation at 25-8o‘C in the presence of CCl, because of its low activation energy, 11.2 kcal/mole, and the lack of inhibition at high concentration. Ratcs and degrees of polymerisation, solvent effect, and the effect of CO addition are discussed.

The Mechanism of Hydrogenolysis of Cyclopropanes at Platinum and Palladium w. J. IRWIN and F. J. MCQUILLIN, Tetrahedron Lett., 1968, (IS), 2195-2198 The rate of fission of cyclopropanes with single substituents and the nature of the products both depend on the nature of the substituent and on the catalyst uscd, Pd being much more active than Pt. Hydrogenolysis by electrophilic polarisation of the chemisorbed cyclopropane is postulated as the rate-determining step, followed by H, transfer.


Isomerisation of cc-Olefins in Palladium Chloride Solutions I. I. MOISEEV, A. A. GRIGOR’EV and s. v. PESTRIKOV, Zh. org.Khim., 1968,4, (3h 354-359 KMnO,, K,Cr,O,, H,O,, CuCl,, and n-benzo- quinone inhibit positional and geometric isomerisation of butenes, hexene- I , and q-methylpentene-r by PdCI, by oxidising the reduced form of Pd. Anhydrous PdCl, does not cause isomerisation but addition of H,O or alcohol causes reductive decomposition of Pd(I1) --complexes and inhibits isomerisation.

The Isomerisation of n-Phenylbutenes Cata- lysed by Palladium Complexes N. R. DAVIES, A. D. DI MICHIEL and v. A. PICKLES, Aust. J . Chem., 1968, 21, (z), 385-395 Isomerisation of 4-phenylbut-~-ene to a mixture of cis- and trans-I-phenylbut-2-ene and trans-1- phenylbut-I-ene in the presence of bis(benzoni- trile)dichIoropalladium(II) proceeds both by consecutive reactions and by direct conversion. The kinetics of this reaction are similar to those observed for allylbenzene.

Organic Syntheses by Means of Noble Metal Compounds. XXXIV. Carbonylation and Decarbonylation Reactions Catalysed by Palladium J. TSUJI and K. OHNO, J. Am. Chem. soc., 1968, 90, (11, 94-98 PdC1, is more efficient than metallic Pd for decarbonylation of acyl halides to form olefins. Pd(NO,),, PdO, Pd(acetylacetone),, RhCl,, and Rh,O, are also active for this reaction but PtiC, PtCl,, ReCl,, ReCl,, and IrCl, are inactive. Pd/C catalyses decarbonylation of aldehydes in gaseous phase at zoo°C. XXXV. Novel Decarbonylation Reactions of Aldehydes and Acyl Halides Using Rhodium Complexes K. OHNO and J. T~UJI , Ibid., 99-107 Aldehydes are decarbonylated by RhCl(PPh,), under mild conditions and acyl halides are decarbonylated also to give olefins. Five-coordinate acyl-Rh complexes were isolated as intermediates of the latter reaction. RhCl(CO)(PPh,), catalyses decarbonylation of acyl halides and aldehydes, e.g. aromatic acid halides give aromatic halides. The complex also catalyses carbonylation of alkyl to acyl halides.

Dirnerisation of Acrylonitrile to 1,4-Dicyano- 1-butene with Ruthenium Complexes J. D. MCCLURE, R. OWYANG and L. H. SLAUGH,J. organometal. Chem., 2968, 12, (I), P8-Prz. The mechanism of this reaction was studied using RuCl,(CH,-CHCN), and similar Rh complexes. A Rh hydride intermediate was postulated with the insertion of r-bonded acrylonitrile into the 0-2-cyanoethylruthenium bond followed by elimination of the Rh complex.

Conversions of Acetylene Compounds in Solutions of Palladium and Rhodium Salts s. M. BRAILOVSKII, 0. L. KALIYA, 0. N. TEMKIN and R. M. FLID, Kizet. Kataliz, 1968, 9, (I), 177-179 Studies of the reaction of acetylenes, vinylacety- lenes and phenylacetylenes with PdCl, and RhCl, in aqueous and non-aqueous solutions at various temperatures show that in all cases compounds are formed with general formula C1,M- (-CR,zCR,-),-X, where m, n, and X depend on the metal, the solubility and the temperature. Where M is Pd, m = I, n varies from 2 to 14, and X is OH or C1. When M is Rh, n varies from 4 to 20. An organic residue in the reaction of RhC1, with phenylacetylenes is low molecular weight polyphenylacetylene.

Homogeneous Catalytic Hydrogenation of Aldchydes with Rhodium Carbonyl Catalysts. I1 B. HEIL and L. MARK& Acta Chim. Acad. S L HunR., 1968, 55, (I), 107-116 Reaction kinetics at 160”C, pcO28o atm obey the equation d(alcohol)/dt =k[aldehyde][Rh] (pH2)0.5 (P~~)-O.~. Rh,(CO)la was the principal Rh complex in the mixture. CO-deficient HRh(C0)16 was also active. Rh,(CO)* and HRh(CO), were not detected.

Homogeneous Hydrogenation of Olefink Substrates Using Rhodium Complexes Con- taining Sulphur Ligands B. R. JAMES, F. T. T. NG. and G. L. RE‘MFEL, hmg. nucl. chem. Lett., 1968, 4, (4), 197-199 RhCl,( SEt,), catalyses hydrogenation in N,N’- dimethylacetamide solution with excess of the substrate. Kinetics and mechanism of the hydrogenation of maleic acid were studied. The reaction is first order in both Rh and H,.

Kinetic Study of Iridium(1) Complexes as Homogeneous Hydrogenation Catalysts B. R. JAMES and N. A. MEMON, Can.J. Chem., 1968,

Hydrogenations catalysed by IrX(CO)(PPh3),, where X=Cl, Br or I, were found to be between zero and first order in each of the concentrations of Ir, substrate and H,. The reaction rate was enhanced by a co-ordinating solvent and by traces of 0,, and followed the order I>Br>CI for the different halogens.

Osmium Tetroxide-catalysed Oxidation of Olefins J. F. CAIRNS and H. L. ROBERTS, J . Chem. SOC., C, org., 1968, (6), 640-642 The catalytic activity of OsO, in alkaline solution is dependent on pH. A wide range of olefins and partially oxidised compounds were oxidised by 0, at I atm, S O T , pH 8.5-x2.5. The products and the stability of the reaction depended on pH.

46, (2), 2I7-223


FUEL CELLS Ammonia - Oxygen Fuel Cell E. J. CAIRNS, E. L. SIMONS and A. D. TEVEBAUGH, Nature, 1968,217, (5130, Feb. 24), 780-781 An NHB-O, fuel cell uses 54 wt.% aqueous KOH electrolyte and Teflon-bonded Pt black electrodes with 51 mg Pt/cm2. Total cell resistance was 0.03 ohm, the cathode curve showed no limiting current density up to at least 1000 mA/cm2 at 140°C and the anode voltage rose sharply at current density :-700 mA/cm?. For current densities between 20 and 200 mA/cm2 the anode performance improved by almost 75 mV between 109 and 191°C. Performance level of these cells exceeds those of all fuels other than H3 or N,H,.

NEW PATENTS

METALS AND ALLQYS Manufacture of Precious Metal Spheres and Spheroids INTERNATIONAL NICKEL LTD. British Patent 1,103,396 Small spheres or spheroids of alloys of Ru, Rh, 0 s and I r are used for points of moving elements, e.g. in compasses, and fountain pen nibs. They are produced by heating a powder of one of these four metals with a matrix mixture of Pd or Pt with Au or Ag above the melting point of the matrix but below that of the four metals, forming the product into spheres, cooling and leaching out the matrix.

Niobium Alloys BIRMINGHAM SMALL ARMS GO. LTD. British Patent 1,103,724 The strength of Nb-W alloys, with or without Ta, is improved by the addition of one or more of Ru, 0 s and Ir. The range claimed is at least 30:; Nb, 10-250/~ W, o-4o0{, Ta and O.I-IO% Pt metal. Small amounts of Hf and Zr may also be present.

Preparation of FineIy Divided Metals INTERNATIONAL NICKEL LTD. British Patent 1,109,890 Finely divided I r or Ru is produced by thermally decomposing a halogen-free I r or Ru compound at up to 400'C in non-oxidising conditions, the Ir or Ru atom being in a complex with NH, and,/or oxalate groups, the other groups in the compound leaving no residue on decomposition. A typical compound is (NH4),[Ru(CO),(C,0,)].

TEMPERATURE MEASUREMENT Practical Temperature Scales between 11K and 273K H. PRESTON-THOMAS and R. E. BEDFORD, Metrologin,

The reproducibility of proposed scales, which might replace four national scales below go. r8"K, is analysed and the scales are related to best estimates of the thermodynamic scale. Lack of reproducibility below SO'K may be tolerated or the thermometer characteristics must be restricted. The proposed scales have systematic variation in degree size with temperature. All this work is based on the Pt resistance thermometer.

1968, 49 (I), 14-30.

Manufacturing Non-Magnetic, Elastic Metal- lic Materials

Britisla Patent 1,110,045 These materials are produced from metallic Pd or an alloy of 3c-roo wt:; Pd and 7 0 4 wt":, Au by heating the metal or alloy at above 600°C but below its melting point for more than one minute and then slowly cooling it to achieve annealing. It is permissible for 0-5~'~ of a variety of other alloying elements to be present.

Reorientation of Stabilised Platinum

Italian Patent 787,630 French Patent 1,504,716 Mechanical properties of a strengthened metal or alloy are improved by cold-working and annealing. The cold-working causes recrystallisation during annealing with a grain structure elongated in the direction of working. Pt and Rh-Pt are strengthened prior to treatment by the inclusion of a dis- persed carbide.

Platinum Claddings for Refractory Metals

Italian Patent 794,340 Articles comprise refractory metal cores, such as Nb, Ta, Cr, or an alloy thereof, or Mo, which do not form volatile oxides at the operating temperature nor form alloys with the Pt or Pt alloy cladding at melting points below this temperature. A barrier layer between core and cladding consists of a compatible refractory carbide, silicide, boride, sulphide, nitride, or oxide, e.g. a rare

ZAIDAN HOJIN DENKI JIKI ZAIRYO KENKYUSHO

JOHNSON, MATTHEY & CO. LTD.


Platinum Metals Rev., 1968, 12, (3), 115-120 11 5

earth metal oxide, carbide or nitride. This corresponds to Belgian Patent 697,292.

CHEMICAL COMPOUNDS Production of Platinum and Palladium Oxides

U.S. Patent 3,357,904 These oxides are made by electrolysis using an electrode comprising or containing Pt and 'or Pd in a bath of molten alkali metal hydroxide.

MATTHEY BISHOP INC.

ELECTROCHEMISTRY Electrodes for Cells

British Patent 1,104,374 Electrodes for electrolytic cells particularly for the direct electrolysis of sea water to produce hypo- chlorite is based on a cheaper anode material which is covered with a Pt-Ni alloy containing not less than 301;& Pt covered with a pure Pt film.

CENTRAL ELECTRICITY GENERATING BOARD

ELECTRODEPOSITION AND SURFACE COATINGS Surface Treatment of Titanium IMPERIAL METAL INDUSTRIES (KYNOCH) LTD. British Patent 1,105,388 Before plating Pt on to T i surfaces, they are pretreated with an oxalic acid solution at elevated temperature. The adherence of the Pt electro- deposit is improved.

Platinum Plating of Titanium STE UGINE U.S. Patent 3,357,858 A Pt group metal plated deposit adheres well to articles with a Ti or T i alloy surface when the surface is pretreated with a mixture of HCl and HNOs and the deposit is heated at 300°C.

Activation of Glass before Chemical Plating

U.S. Patent 3,370,973 Glass is coated with an organic solution of nickel chloropalladate and then heated at elevated temperature to convert the coating to a Ni-Pd film. This film catalysed subsequent chemical (electroless) plating baths.

INTERNATIONAL BUSINESS MACHINES CORP.

Coatings on Easily Oxidised Metals INTERNATIONAL NICKEL LTD. French Patent 1,500,545 Bodies formed of Ir, Ru, Mo, W or their alloys with noble metals are protected against oxidation at high temperatures by coating with a ternary alloy containing Au and Pt or Pd.

Platinum Metal Plating

German Patent 1,26I,367 Refractory metals are coated by applying a sulphur-free chelate of a Pt metal dissolved in an organic solvent, allowing the solvent to evaporate and then decomposing the metal chelate at a temperature up to 400°C. Aliphatic dinitriles and decarboxylic acids are suitable chelating agents.

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT

JOINING Brazing Methods for Porous Refractory Metals

U.S. Patent 3,363,306 Porous W is bonded to other refractory metals, such as Mo or massive W, using a thin layer of Rh which wets the metal surfaces and forms an alloy on heating.

Refractory Ceramic to Metal Seal

U.S. Patent 3,366,466 Ceramics are metallised with a spongy layer of Mo andlor \XI, the pores of the spongy layer are filled with a Ta-Rh, Rh-Mo or Mo-Ru alloy which also covers the surface and then a braze containing a Ta or Nb alloy is applied. See also British Patent 1,108,764.

T.R.W. INC.

NORTH AMERICAN PHILIPS CO.

HETEROGENEOUS CATALYSIS

Production of Unsaturated Mononitriles

British Patent 1,103,046 Acrylonitrile and related compounds are produced by reacting an olefin with HCN and 0, at an elevated temperature in the presence of a Pt metal catalyst, especially a supported Pd catalyst.

Production of Vinyl Acetate KNAPSACK A.G. British Patent 1,103,125 Vinyl acetate is produced from C,H,, CH,COOH and 0, in the gas phase using a carrier catalyst containing 0.1-6 wt'); (preferably 0.5-2':;) rnetal- lic Pd, 0.01-10 wto/, (preferably o.03-r0&) metallic Au and 1-20 wtu,o (preferably up to 5 wt:;) alkali metal formate or acetate. See also British Patent 1,107,495.

Hydrocracking Process ESSO RESEARCH & ENGINEERING CO. British Patent 1,103,393 The activity of catalysts made by depositing a Pt metal on a base-exchanged zeolite with 6-15A pore openings is maintained and increased by adding halogens or a halogen source to the hydrocarbon feed for hydrocracking. See also British Patent 1,106,338.

FARBWERKE HOECHST A.G.


Preparing Cyclohexane

British Patent 1,104,275 CGHG containing more than 0.5 mg/l of S may be successfully hydrogenated in two stages using Pt metal catalysts: in the first stage all S compounds are converted to H2S but only some CoHG is converted while in the second stage the remaining C,HG is hydrogenated. Pt/Al,O, is a suitable catalyst.

Production of Allyl Chloride FARBWERKE HOECHST A.G. British Patent 1,104,361 Allyl chloride or methallyl chloride is produced by contacting 0, and a mixture of a 3-4C olefin and HC1 and/or a 3-4C monochloroparaffin with Ru, Pd, Ir, Pt, or PtO as catalyst.

STAMICARBON N.V.

Preparation of Piperidine

British Patent 1,106,168 Piperidine is produced by reacting glutaric acid or its anhydride with NH, and H, at elevated temperature and pressure in the presence of a hydrogenation catalyst. The preferred catalyst is based on Ru, e.g. Ru/C.

Production of Vinyl Acetate

British Patent 1,106,236 CH,COOH is reacted with C,H, and 0, in the gaseous phase in the presence of a solid catalyst containing Pd, Pt, Ru, Rh or Ir in elementary form together with a Mn compound on a support.

Production of Metallic Oxide Catalysts

British Patent 1,106,814 Electrolytic production of oxides of Pt and/or Pd or oxides of Pt and/or Pd mixed with oxides of other metals not harmful to the catalytic properties of the Pt and/or Pd oxides by electrolysing the appropriate Pt, Pd, Pt alloy or Pd alloy anode in a molten bath of alkali metal halide and nitrate.

RHONE-POULENC S.A.

FARBWERKE HOECHST A.G.


Catalyst

British Patent 1,107,276 A1,0, is treated with aqueous solutions of fluoboric and H,PtCl, in molar proportions of 3.5- 4.5 mols fluoboric acid per mol H2PtClG. The catalyst is especially for catalytic reforming.

Production of Phenols

British Patent 1,108,256 An aromatic compound is oxidised to a phenol using an 0,-containing gas in a liquid phase containing HCOOH and a transition metal catalyst, especially Pd, Rh, I r or other noble metal.

STE FRANCAISE DES PRODUITS POUR CATALYSE

IMPERIAL CHEMICAL INDUSTRIES LTD.

Catalytic Oxidation of Alcohols

British Patent 1,109,228 Primary and secondary aliphatic alcohols are oxidised to aldehydes, ketones and,'or acids by contact with 0, in the presence of Ir. The I r is preferably unsupported and is best precipitated from an iridate or iridite.

IMFERIAL CHEMICAL INDUSTRIES LTD.

Isomerisation of a Hydrocarbon Fraction

British Patent 1,110,170 Normal paraffins and naphthenes in a 5-7 C hydrocarbon fraction are hydrogenated in the presence of 100-5000 ppm S and a noble metal catalyst composited with a halogenated Si0, cracking component to bring about isomerisation. The catalyst is preferably Pd or Pt on SiO, containing F.

Production of Hydrogen Cyanide

U S Patent 3,360,335 Pt and Pt-Rh gauze catalysts, used in the oxidation of an NHJhydrocarbon mixture, are treated with aqua regia to activate or reactivate the catalyst.

Hydrocracking Process

U S . Patent 3,360,458 Feedstocks containing both polycyclic and non- polycyclic hydrocarbons are cracked using a mixture of crystalline zeolite catalyst and an amorphous cogel catalyst, the zeolite containing a higher proportion of Group VIII noble metal catalyst metal. Pt, Pd, Rh and I r are the preferred metals.

SHELL INTERNATIONALE RESEARCH MIJ. N.V.

E.I. DU PONT DE NEMOURS & CO.

UNION OIL CO. OF CALIFORNIA

Platinum Metal Catalyst Activation

U.S. Patent 3,360,481 A catalyst consisting of a Pt metal, especially Pd, on a zeolite support is activated using dry H, at up to 3 0 0 ° F until activation is partly complete and then with wet H, at a temperature above 300°F.

ESSO RESEARCH & ENGINEERING CO,

Cyclohexylamine Production

U S . Patent 3,364,261 The reaction of C,H,OH, NH, and H2 at low pressure is catalysed by Rh metal.

ABBOTT LABORATORIES

Catalytic Gasoline Reforming

U.S. Patent 3,365,392 A gasoline is reformed to high octane fuel and LPG by mixing it with H, and S and passing it at 800-1100°F over a platinised or palladised zeolite.

UNIVERSAL OIL PRODUCTS CO.


Hydrogenation of Benzylic Compounds

U.S. Patent 3,366,695 Phenyl carbinol, phenyl alkyl carbinol, phenyl alkyl ketone, benzyl alkyl ethers and benzyl alkanoates are reduced to the corresponding cyclohexyl compounds using a catalyst consisting of a porous support carrying Rh or Ru and promoted with an alkali metal base.

Exhaust Gas Combustion Catalyst

U.S. Patent 3,367,888 The catalytic activity of noble metal catalysts, e.g. PtjAl,O,, in burning exhaust gases is promoted by incorporating 0.1-1.5 wtX of thiomalic, thio- glycolic or mercaptopropionic acid.

Acyclic Olefin Isomerisation

U.S. Patent 3,367,988 a-Olefins are isomerised to internal olefins using a Pt metal on an inert support and an alcohol as promoter, e.g. Pd/C and n-octanol.

Cyclododecene Production

U.S. Patent 3,369,052 Cyclododecatriene is selectively reduced to cyclododecene in good yield in the absence of solvent, using H, and Pd catalyst, e.g. Pd black or PdO.

CONTINENTAL OIL CO.


ETHYL CORP.

GEIGY CHEMICAL CORP.

Packaging System

U.S. Patent 3,369,859 Traces of 0, in a package filled with inert gas containing H, are eliminated by catalytic combination on a cylindrical pellet of refractory oxide carrying o.I-IC;/U Pd or Pt.

ATR PRODUCTS & CHEMICALS INC.

Finely Divided Metals

U.S. Patent 3,369,886 Finely divided metals, especially Pt, are obtained by precipitating the metal from its salts while simultaneously precipitating Al(OH),. The Pt is then freed from Al,O, with KOH to give a catalyst of high surface area.

Halogen Exchange Process

U.S. Patent 3,370,096 The exchange of halogen in a hydrocarbon with the halogen of a Friedel-Crafts metal halide in the presence of H, is catalysed by a Group VIII metal, preferably Pt iAl,O,.

EX30 RESEARCH & ENGINEERING CO.


Hydrocarbon Conversion Process

U.S. Patent 3,371,126 Catalytic reforming with a Pt catalyst, and hydro-


dealkylation are used to produce aromatic hydrocarbons and town gas.

Platinum Coating and Impregnating Method

Dutch Appln. 67.02,039 A PtO, or a mixture of such an oxide with up to sov: of oxides of Rh, Ru, Ir and/or Pd is reacted with a dispersing medium containing a 2-5 C aliphatic alcohol to form a Pt dispersion. This dispersion is applied to a support and the Pt salted out on to the support. The organic material present is then oxidised and the water expelled.

Selective Catalytic Reduction JOHNSON, MATTHEY & CO. LTD. Italian Patent 787,791 Reduction of a ketone or of an aromatic aldehyde to the corresponding alcohol uses H, and Pd, char- coal catalyst in the presence of a primary aromatic amine, e.g. C6H,NH,, p-toluidine or benzylamine, or of a heterocyclic tertiary amine, e.g. C,H,N or quinoline.

Mixed Noble/Base Metal Oxide Catalyst

Italian Patent 787,819 The catalyst consists of a 3:1 intimate homogeneous mixture of a Pt metal oxide, e.g. oxides of Pt or Pd, with a base metal oxide, e.g. at least one of Fe, Co, Ni, and Cu. The catalyst mixture is prepared by mixing Pt metal and base metal salts and heating or treating them in the presence of a reactant such as NaNO,.



HOMOGENEOUS CATALYSIS Organosilicon Compositions

British Patent 1,104,117 A liquid curable system consists of a siloxane, a liquid terminal diene and a catalytic amount of Pt, especially H,PtCl,.

Production of Alkyl Vinyl Ethers

British Patent 1,105,293 In this multistage process, the first stage consists of reacting C2H4 with H,O in the presence of a Pd salt or coordination compound and the usual acetate ions, 0,, Cu salt, etc., to give vinyl acetate. In the second stage an identical or similar catalyst (e.g. PdC1,) is used to give the alkyl vinyl ether from the vinyl acetate.

Production of Acetaldehyde

British Patent 1,109,483 CaH4 is contacted with an aqueous oxidising composition, at pH 0.5-3.5, containing CuC1, and a catalytically active Pd compound such as PdC1, to form a complex which is then hydrolysed.

DOW CORNING CORP.

IMPERIAL CHEMICAL INDUSTRIES LTD.

EASTMAN KODAK CO.


Producing Vinyl Acetate ASAHI KASEI K.K.K. British Patent I,I 10,663 C,H,, CH,COOH, O2 and a small amount of HCl are reacted in the presence of a catalyst consisting of (a) Pt, Pd, Rh, Ru, I r or their chlorides or oxides, hydroxides and salts which readily provide the chlorides of these metals and (b) Cu, Ag, Zn, Cd, Sn, Pb, Cr, Mo, W, Fe, Ni or their chlorides or oxides, hydroxides and salts which readily provide these metal chlorides.

Lower Saturated Aliphatic Nitriles

British Patent 1,110,687 Lower saturated aliphatic nitriles (especially propionitrile and normal and iso-butyronitrile) are produced by the reaction of CzHa and/or C,H, and HCN in catalytic addition at 200-450' in the presence of Pd and/or Rh and/or one of their compounds. See Brilish Patent r,i 10,682.

Preparation of Alkenyl Esters SHELL OIL co. US. Patent 3,358,016 Vinyl esters are produced from a 2-4C unsaturated vinylic halide and a Na, Cu or Fe 2-18C mono- carboxylate in the presence of DMF, dimethoxy- ethane and PdCl, but in the absence of free carboxylic acid.

Redox Catalytic Oxidation of Olefins to Aldehydes and Ketones

U S . Patent 3,365,498 The catalyst consists of a Pd, Pt, Ir, Rh, Ru or AU inorganic or organic salt or a diketo complex and a similar compound of a transition metal.

ASAHK KASEI K.K.K.

UNION CARBIDE CORE'.

Oxidation of Olefins to Ketones

US. Patent 3,365,499 A 6-40 C olefin is oxidised by a mixture of a quinone or other oxidising agent and an aprotic solvent with a Pt metal catalyst, e.g. PdCl,.

Hydrogenation of Unsaturated Compounds

US. Patent 3,366,646 Non-aromatic C-C unsaturation is hydrogenated over a trisitertiary phosphine or arsine)rhodium nitrosyl.

Polymerisation of Bicycloheptene Com- pounds

U.S. Patent 3,367,924 Olefins containing a bicyclo (2,2, ~)-hept-~-ene ring system are polymerised in aqueous emulsion using a catalyst based on an I r or Ru compound (e.g. IrCl,) and a reducing agent.

GULF RESEARCH & DEVELOPMENT CO.

SHELL OIL GO.

UNIROYAL INC.

Peroxide-bleaching of Wood Veneers DR. KURT HERBERTS & CO. German Patent 1,259,088 The H,O, bleaching of wood veneers can be activated by a metal colloid sol, e.g. an ammoniacal Pt sol containing 2.27; Pt. The bleached wood is free from traces of peroxide.

Carbonylation of Olefins and Acetylenes

German Patent 1,261,509 Carbonylation is catalysed by a deacidified solution containing Pd salt complexed with organic phosphine, e.g. bis(tritolylphosphine)PdC12.

Hydrogenation of Water-Soluble Compounds

Belgian Patent 701,238 Dutch Appln. 67.09,685 Certain new hydridopentaminorhodium compounds of formula (HRhX&' -, where X is 5 mols of NH, or 4 mols of NH, and I mol H,O, are very suitable hydrogenation catalysts, especially for carboxylic acids and other compounds dissolved in HzO.

BADISCHE ANILIN- & SODA -FABRIK A.G.


FUEL CELLS Catalyst Composition

British Patent 1,108,317 A catalyst for use in electrochemical reaction is made from a mixture of Pt, Re and Ru, each metal being relatively inactive when used alone. The proportions claimed are 40-70% Pt, 1-40% Re and 1-400,6Ru, by weight and especially active catalysts are obtained with an atomic ratio of 68.5:15:16.5 (Pt:Re:Ru) where CH,OH is fuel.

Fuel Cells

British Patent 1,108,776 A fuel cell producing current from fuel anodic oxidation, having hydrophobic portions, e.g. Pt black on ptfe, is operated with a fluorocarbon sulphonic or carboxylic acid electrolyte.

Rhodium Catalyst for Fuel Cells

U.S. Patent 3,357,863 An inexpensive multimetal H, fuel cell electrode consists of a mixture oP0-47.50: Pt, 40-yja,& Rh and 5-20% W oxide, where the amount of Pt is not more than 50% the amount of Rh.

Platinum-Rhodium Fuel Cell Catalyst

US. Patent 3,357,863 A Hz fuel cell used a four-component catalyst mixture of ( a ) 15-35u/u Pt, (b) 15-350/0 Rh, (c) 5- 35yk W oxide and (d ) 5-35?; Mo oxide.

ESSO RESEARCH & ENGINEERING CO.

ESSO RESEARCH AND ENGINEERING CO.

AX!ZRICAN CYAXAMID CO.

AMERICAN CYANAMID CO.


Platinum Metals in Fuel Cell Electrodes

U S . Patent 3,364,074 C-containing electrodes for fuel cells are impreg- nated with Pt, Pd, Rh or I r and simultaneously waterproofed by the application of a complex of one of these metals and a suitable diketone, e.g. Pd or Pt acetylacetonate.

UNION CARBIDE CORP.

CHEMICAL TECHNOLOGY Mounting of Foils Permeable Only to a Specific Gas PROTOTECH CO. British Patent 1,106,876 In order to be able to use thinner, cheaper foils (especially Pd alloy foils permeable to H,), the foil is sinter-bonded to a support of sufficient rigidity which is made of metal at least on the side facing the foil.

Structures Incorporating Thin Metal Mem- branes

British Patent 1,107,81 I H, permeable membranes, for example, are produced from a perforated support which is bonded to a gas permeable metal or alloy which seals off the holes in the support. Thus in an example a Ni disc is indented on one side, plated on this side with Pd and then Ag and finally abrasive used to remove the projecting material from the reverse side. This leaves holes covered with a Pd-Ag membrane.

Hydrogen Purification Apparatus T. EGUCHI et al. U S . Patent 3,368,329 H, is purified by diffusion through a bundle of Pd or Pd alloy tubes in a diffusion chamber.

Hydrogen Diffusion Tubes

German Patent 1 ~ 4 5 ~ 9 2 r A closing plug for sealing the open end of Pd or Pd-Ag alloy H, diffusion tubes consists of material with approximately the same coefficient of thermal expansion and dimensioned to fit tightly with a projecting, threaded spigot of smaller diameter than the tube and used to form a means for attachment of or for stabilising an internal support for the tube. This corresponds to British Patent 1,009,326.

Hydrogen Diffusion Tubes

Dutch Patent 123,628 A diffusion tube used for separation of H, from gaseous mixtures, made of Pd or of 25 wt.g, Ag-Pd, is made more robust and its life is pro- longed by incorporating stainless steel or Ni coil

ENERGY CONVERSION LTD.



springs or metal or ceramic rods as stiffening members to prevent flattening of the tube walls yet permit free passage of gas. This corresponds to British Patent 966,122.

ELECTRICAL AND ELECTRONIC ENGINEERING


Platinum-Platinum Oxide Electrodes

British Patent 1,103,413 Oxide electrodes for detecting corrosive attack are produced by immersing a rod of Pt metal in fused alkali metal nitrate at a temperature of about 400°C and for a period of at least one hour. The oxide layer obtained consists essentially of 3-7 parts monoxide and I part dioxide by weight. See also 1,103,414.

Tailoring of Resistors

British Patent 1,107,788 A film resistor consisting of an oxide semiconductor material with a noble metal additive (e.g. PdO with Au or Ag) is tailored by subjecting a portion of the resistor to electromagnetic radiation to reduce its resistance.

Spark Plugs

British Patent 1,110,255 A spark plug using less 1% in its construction has a Pt head formed as a plate or disc-like flange which is pressed into the insulator bore so that it deforms and seals the opening of the bore. The opening and the bore portion then form a casting chamber for the remainder of the electrode.

Iridium and Rhodium Semiconductors

US. Patent 3,356,464 New semiconductors claimed ate IrAsSb, IrPAs, RhAsSb and RhPAs, although the text covers a slightly larger range of compounds such as RhSb, and IrP. The semiconductors can be used in thermoelectric devices.

Ductile Ruthenium Alloy INTERNATIONAL NICKEL CO. LTD. U.S. Patent 3,362,799 Ru powder is mixed with 0.1-25 wt":, Re powder and processed in the usual way to give a ductile alloy, e.g. for sparking plugs.

Gold-Palladium Alloy with High Specific Resistance

German Patent 1,262,021 The alloys of German Patent 1,236,207 consisting of 1 8 7 5 7 ~ Au, 75-200,; Pd, 2-1s0/0 Fe and 0.4-1 .2'4 A1 are modified by replacing some or all of the A1 by B, Ga and/or In.

CONTINENTAL OIL CO.

INTERNATIONAL BUSINESS MACHINES CORP.

ROBERT BOSCH G.m.b.H.

AMERICAN CYANAMID CO.

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT

PLATINUM METALS REVIEW - Johnson Matthey ... Editor, Platinum Metals Review Johnson, Matthey & Co.,...

Documents

Transcript of PLATINUM METALS REVIEW - Johnson Matthey ... Editor, Platinum Metals Review Johnson, Matthey & Co.,...