PLATINUM METALS REVIEW · important. Alumina, magnesia, zirconia, and thoria have all been employed...

$: PLATINUM METALS REVIEW · important. Alumina, magnesia, zirconia, and thoria have all been employed but of necessity the melting point of the refractory must exceed that of the crystal$
UK ISSN 0032-1400

PLATINUM METALS REVIEW

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

V O L . 18 J U L Y 1 9 7 4

Contents

Czochralski Growth of Oxide Single Crystals

The Detection of Breath Alcohol

Production of Ferrite Memory Cores

Osmium Tetroxide and Its Applications

Ammonia Oxidation Catalysts

New Plants in Three Countries

Platinum Metals in the Development of Analytical Chemistry

Abstracts

New Patents

N O . 3

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey & Co Limited, Hatton Garden, London ECI P 1 AE

Czochralslri Growth of Oxide Single Crystals IRIDIUM CRUCIBLES AND THEIR USE

By B. Cockayne Royal Radar Establishment, Malvern

Iridium is used extensively as a material for crucibles containing oxide melts during single crystal growth because of good chemical compatibility with them in slightly oxidising atmospheres. With care, iridium crucibles can be used in this way for long periods.

During the past decade iridium has been used increasingly as a crucible material for the growth of high melting point oxide and mixed oxide single crystals. These crystals are required mainly as electronic materials and include the compounds listed in the Table.

Examples of uses for these compounds include solid state lasers, magnetic bubble device substrates, insulating substrates for semiconductors, and monolithic crystal filters. In these and similar applications a single crystal with a high degree of structural perfection is required, and device quality crystals are generally grown from the molten state by the Czochralski technique using an iridium crucible to contain the melt.

Single Crystal Materials

Compound

spinel

sapphire

yttrium aluminium

yt t r ium orthoaluminate

gadolinium galliu m

lithium tantalate

garnet

garnet

Formula Melting Point

21 05°C

2050°C 1 1970°C

1875°C

1725°C

1650°C

Platinum Metals Rev., 1974, 18, (3), 86-91 86

Crucible Use The Czochralski technique, as applied to

oxides, has been described fully elsewhere (1-3) but in outline the process consists of slowly withdrawing a rotating single crystal seed from a bath of molten oxide. Melt solidifies on to the seed, which is grown into a crystal of the required diameter by controlling the heat input into the crucible. Both radio- frequency (r.f.) and resistance heating of the iridium crucible are employed but the former is more common. A typical growth apparatus and growing crystal are shown in Figs. I and 2.

Iridium crucibles are available in a wide range of shapes and sizes but are usually cylindrical with capacities varying from around 30 cm3 to several litres. They are cormally manufactured either from hot-rolled iridium sheet by welding or from iridium powder by hot pressing; the respective processes produce coarse- and fine-grained structures.

A typical cycle to which a crucible is subjected during crystal growth is:

(i) charging; (ii) growing the crystal at the particular

oxide melting point; (iii) cooling the crucible and residual

charge after contact between the crystal and melt has been broken.

Fig. 1 Typical apparatus .for single crystal gr0lc.h by the Czochralslzi technique includes this chamber, which contains within a refractory enclosure the iridium crucible heated by the r.f. coil. This and the other photographs in this article are reproduced by per- mission of the Copyright Controller, HBMSO

Charging can take several heating and cooling cycles depending upon the form of the charge, e.g. whether crystalline and compact, or powdered and low density; a reasonable time span for a heating/ cooling cycle is 2 to 6 hours. The time taken for growing the crystal is very dependent upon crystal growth rate and upon the length of crystal required, and can vary from a few hours for a small research-type crystal to a few days or even weeks for commercial-size crystals. Cooling occupies less time than growing the crystal and is typically 5 to 50 hours.

Crucible Failure and Its Avoidance When a crucible fails, the failure is generally

catastrophic and occurs by melting, brittle fracture, reaction between the crucible and oxidising atmosphere/melt, or any combination of these effects. Some new and failed crucibles are compared in Fig. 3. Particular types of failure are often related to particular materials. For instance, it is relatively easy to melt a crucible during the growth of

materials with melting points close to that of iridium, e.g. sapphire and spinel; to fracture a crucible containing materials that cause distortion, e.g. garnets; and to oxidise the crucible when oxygen is required in the gaseous ambient, e.g. lithium tantalate, or when a reactive component forms part of the melt, e.g. gallium oxide in gadolinium gallium garnet, However, considerable interaction occurs between these effects. For example, localised melting can cause cracking on subsequent cooling and preferential oxidation at grain boundaries can lead to intergranular fracture.

With care, failure by melting should only occur in extensively used crucibles that have

Platinum Metals Rev., 1974, 18, (3), 87

Fig. 2 Looking down the side arm of the chamber shown in Fig. I, the growing crystal can be observed through an aperture in the refractory enclosure. The brilliant line just inside the refractory i s the near side of the iridium crucible, the far edge of which, together with the melt level, can just be distinguished beyond the crystal

acquired in-service defects. In a new crucible, melting is frequently a result of making increases in temperature too rapidly in an effort to melt the charge quickly, instead of allowing an approximate equilibrium to be established and maintained between the thermal masses of the crucible, the melt and the surrounding refractory environment. The choice of refractory is, however, also important. Alumina, magnesia, zirconia, and thoria have all been employed but of necessity the melting point of the refractory must exceed that of the crystal being grown, thus excluding the use of alumina at the highest temperatures. Some refractories, such as zirconia, also tend to couple into the r.f. field at high temperatures, producing localised hot spots and crucible melting. Even pure zirconia will act in this way if properties become modified by spillages of the components into the refractory surround during crucible charging.

Failure of crucibles by distortion is a much greater problem, and occurs principally with materials of the garnet type. Several reasons

have been suggested for the distortion. The principal possibilities are:

(i) that the iridium tends to sag under its own weight at high temperatures;

(ii) that garnet materials expand on freezing;

(iii) that relative expansion occurs between the crucible and solidified material.

Little experimental evidence exists to support the two first possibilities as major effects. In fact, possibility (i) is unlikely because for a given size and shape of crucible the sag should be greatest for the high melting point materials, such as sapphire and spinel, rather than for the garnets. For possibility (ii) to apply the solid material must have a lower density than the melt, something negated completely by automated crystal growth procedures using crystal weighing. These have shown conclusively that the buoyancy term is normal for garnets, i.e. the crystal is denser than the melt (4). Possibility (iii) is the most likely explanation but, unfortunately, thermal expansion data are not available for all the relevant materials


Fig. 3 New and used crucibles of 30 cms capacity. From the lefi are shown: a crucible slightly distorted by yttrium aluminium garnet; a crucible which has failed by melting; a new crucible made from welded sheet; a crucible heavily distorted and oxidised by gadolinium gallium garnet

over the whole temperature range from room temperature to melting point.

The thermal expansion coefficient of iridium increases from 6.24 x IO-~/"C at room temperature to 15.19 x IO-~/"C at 2225°C (5) , whereas a typical garnet such as yttrium aluminium garnet (YAG) has an approximately constant coefficient of 8.9 x IO-~//"C from room temperature to 1400OC (6).

Hence, two sources of stress for producing distortion are possible. The crucible can either contract around the solidified charge at high temperatures on cooling or be expanded at low temperature by the charge on heating. Both these mechanisms require the formation of a strong and continuous solidified crust upon solidification and very effective wetting of iridium by the melt; garnet melts fulfil both these criteria. Both high and low temperature distortion have been observed; Fig. 3 shows some of the effects induced.

As distortion occurs during heating and cooling rather than during growth, it can obviously be reduced by minimising the number of heatinglcooling cycles during crucible charging, either by using densified material as the charge or by charging at a temperature slightly in excess of the melting point of the material required. Both these procedures raise difficulties due to possible contamination or preferential loss of a component so a choice must be made between

control of purity/composition and crucible lifetime. There is no unique method for avoiding distortion, although preferential freezing of the melt by crucible base cooling (7, 8) can limit the continuity of the surface crust and the associated distortion at surface level. However, this can sometimes transfer distortion problems to the crucible base. General distortion can be minimised by using slow heating and cooling rates, i.e. hours rather than minutes, so that equilibrium rather than forced distortion occurs. For garnet melts the relatively coarse-grained welded crucibles accommodate distortion better than the fine-grained pressed type by permitting some grain boundary sliding; pressed crucibles initially show little distortion but can fail suddenly by brittle fracture. However, for most materials there is little to choose between the two types of crucible.

Frequent inspection of crucibles after use is advisable. Cracks can easily be detected with a X 10 eyepiece before they lead to catastrophic failure. At this stage, crucible life can be prolonged by 50 to 100 per cent if the surface is melted in a controlled manner using an argon arc welding procedure (see Fig. 4). This process also slightly refines the grain size, thereby increasing the crucible strength for a few growth cycles; it does, however, require a very experienced welder to perform the task successfully.


Fig. 4 ( a ) Typical intergranular fracture in an iridium crucible; (b) the surface of an iridium crucible after localised melting in an argon-arc welding apparatus

Crucible oxidation can be reduced to a minimum by the use of inert atmospheres but, when oxygen is essential for the maintenance of melt stoichiometry, flame-spraying the outside of the crucible with zirconia can increase crucible life by a factor of 1.5 to 2.0,

although if distortion occurs the coating is correspondingly less effective. Reaction of the crucible with particularly reactive components, e.g. Ga,O, in Gd,Ga,O,,, can be reduced by presintering to form the required compound prior to charging rather than by using the component oxides directly. Oxidation and reactivity need careful control. Under particularly adverse conditions, e.g. the growth of Gd,Ga,O,, at 1725°C using 10 vol. per cent oxygen in the gas ambient, iridium losses of 0.5 to 1.0 g/h have been recorded.

Because many oxide materials are hard, the method used for removing residual unwanted charge from the crucible can have a considerable effect upon lifetime. The simplest method is to convert all the charge into crystal but in this case the last part of the crystal to solidify is usually hull of defects caused by segregation phenomena; these defects can cause the whole crystal to crack. Inverting the crucible in the r.f. coil to melt out the charge is an alternative and better solution to the problem. Some oxides are

sufficiently brittle to respond to a few blows with a vibrating percussion instrument, after which the residual charge can be tapped out. However, residual solidified droplets do not respond well to any of these treatments but they can be removed either by chemical etching procedures (phosphoric acid at 300°C is a general oxide solvent) or by grind- ing with a dental drill assembly using diamond-impregnated drill bits. It must be emphasised that unwarranted use of percussion techniques during crucible cleaning can lead to severe distortion and to pre- mature fracture.

Crucible Lifetime In conclusion some typical crucible life-

times are quoted. They represent a general trend rather than a guarantee, as crucible lifetime depends markedly upon the experi- ence of the user. For materials such as sapphire, spinel and yttrium orthoaluminate, which do not cause distortion and which require little or no oxygen in the gas ambient, some 30 to 50 crystal growth cycles can be obtained with a typical 30 cm3 crucible made from welded sheet. For the growth of an undoped crystal some 5 cm long by I cm diameter, this represents some 500 hours containment of molten oxide with a probable


further zoo to 300 hours of heating and cooling. The lifetime is considerably less for materials that cause distortion; 10 to 15 growth cycles could be considered good for yttrium aluminium garnet and a much greater number would be exceptional without some form of repair. Durability does not necessarily decrease with increasing crucible size but increases in wall and base thick- nesses are beneficial for large crucibles, e.g. those of more than IOO cm3.

References I K. Nassau and A. M. Broyer,J. Appl. Phys.,

2 B. Cockayne, Platimm Metals Rev., 1968,12,16 3 B. Cockayne, M. Chesswas and D. B. Gasson,

4 A. E. Zinnes, B. E. Nevis and C. D. Brandle,

5 J. J. Halvorson and R. T. Wimber, J. Appl.

6 T. K. Gupta and J. Valentich,J. Am. Cerum.

7 B. Cockayne, J. G. Plant and A. W. Vere,

8 L. H. Brixner,J. Cryst. Growth, 1973, 18, 297

1962, 331 3064

J. Mater. Sci., 1967, 2, 7

J. Cryst. Growth, 1973, 19, 187

PhYS., 1972,433 2519

sot., 1972, 541 355

J. Cryst. Growth, 1972, 15, 167

The Detection of Breath Alcohol PLATINUM ELECTRODES IN FUEL CELL SENSOR

The development of a fuel cell detector sensitive to alcohol in the breath has led to the production of a small portable instrument as a preliminaty screening test for traffic law enforcement. A similar sensor is incorporated into a more accurate analytical instrument now in use in some countries for final evidence in place of blood and urine analysis.

These instruments are produced by Lion Laboratories Limited of Cardiff following extensive research at Innsbruck University under Professor Gruber and more recently by Dr T. P. Jones at the University of Wales Institute of Science and Technology, Cardiff.

The fuel cell sensor incorporates a phosphoric acid electrolyte and electrodeposited platinum on its electrodes, Breath instruments

The pocket size Alcolmeter produced by Lion Laboratories incorporates a fuel cell sensor with platinum electrodes for the detection of breath alcohol. The more accurate analytical instrument can be seen in the background

with this sensor aspirate alveolar breath directly on to one fuel cell electrode where, as a fuel, it is oxidised catalytically on the platinum. The small current which is gener- ated is amplified and displayed on an analogue or a digital meter or as a printout.

Fuel cell output has been found to vary linearly with blood alcohol concentration over the range of forensic interest. Sensor activity diminishes slowly with time but by occasional calibration checks a sensor can remain in operation for up to 12 months irrespective of the number of samples analysed. The sensor is specific only to alcohol in expired breath but it will respond in other locations to certain other fuels, e.g. alcohols, acetaldehyde and hydrogen.


Production of Ferrite Memory Cores PLATINUM GAUZE BELTS IN SINTERING FURNACES

The growth of the computer industry has led to vast numbers of ferrite cores being manufactured to store information. Even a desk-top computer may contain 16,000 or more of the tiny ring-shaped cores, which are threaded on to the wires that control the write-in, storage or read-out of the single piece of information stored on each core.

Most ferrite cores are about 0.015 to 0.018 inch outside diameter (o.d.), although some now range down to 0.007 inch 0.d. and 0.004 inch inside diameter (i.d.). Cores 0.080 inch 0.d. and 0.050 inch i.d. are now considered large. Ferrite powders are made from combinations of materials which have been calcined to form oxides. The powders of controlled purity and particle size are mixed with a plastic, rolled out into tape or sheet, and are stamped or pressed to produce the core shapes.

Core durability is ensured by subjecting the core shapes to a sintering procedure at up to 15ooOC in a controlled atmosphere furnace. Originally a train of ceramic trays was used to carry the cores through the furnace but quick cooling after emergence from the furnace led to frequent breakages and high losses of cores. Heat-resistant platinum alloy trays were substituted for ceramic trays but they tended to warp in service and block the furnace exit. Next endless belts of platinum

Ferrite memory cores on the 10 per cent rhodium- platinum gauze belt. The largest cores have outside diameters of only 0.080 inch. One square inch of the belt contains 75 warp wires and 150 cross wires. Wire curvature and the apertures provide minimum contact and good circulation of gas

alloy foil were tried. Platinum alloy foil withstood the temperatures without warping, it did not contaminate the cores and the automated system increased productivity. However, cores tended to stick to the foil surface and then either to fall off as the belt doubled back or to re-enter the furnace and suffer from a second heating cycle.

Engineers at Matthey Bishop Inc., Malvern, Pennsylvania have now solved this problem by replacing the platinum alloy foil with a 10 per cent rhodium-platinum gauze belt. The belts have less mass than previous systems and thus encourage more even temperatures and faster firing. Furthermore, the weave improves gas circulation. Ad- herence of cores to the belts is no longer a problem because of the minute contact areas. These advantages have reduced core rejections. In addition, the belts are more flexible and so last longer.

The endless belts are 19 to 22 feet long, depending on furnace size, and up to five inches wide. They are driven by 12 inch pulleys, which eliminate sharp radii that might overstress the belts. Two weaves are


A Harper electric furnace for sintering ferrite cores. passing over the pulleys at each end of the furnace section. weaving the warp wires or by hammer welding

The plat inum alloy belt can be seen The belt is made endless by

produced. The heavier belt for larger cores has a warp of 60 wires per inch of 0.008 inch wire and 75 cross wires per inch of 0.005 inch wire. The apertures are 0.0083 inch x 0.0087 inch. The lighter weave for small cores has a warp of 75 wires per inch of 0.005 inch wire and 150 cross wires per inch of 0.003 inch diameter, giving apertures of only 0.0037 inch x0.0083 inch.

Such belts are gaining increasing accept- ance as their advantages of better cores,

higher production, reduced losses, and easier maintenance become more wideIy appreciated by ferrite core manufacturers.

A reel with a belt of rhodium-platinum gauze produced by Matthey Bishop Ine. Belts up to 5 inches wide are made. Belt length depends upon furnace dimensions. The gauze can withstand the process temperature of u p to 1500°C without deformation, core contamination or core adherence


Osmium Tetroxide and Its Applications By W. P. Griffith Department of Inorganic Chemistry, Imperial College, London

Osmium tetroxide, OsO,, is the most important and most easily prepared compound of osmium. It has a number of specific applications in organic chemistry and in biochemistry, and it is with these that this article is chiefly concerned; it is also a useful source of osmium compounds. It is re- markable in that it is one of the few volatile oxides of a heavy metal and that although the osmium is octavalent (of all elements only osmium and ruthenium reach as high an oxidation state) it is a reasonably controllable oxidising agent. It is from this latter property that most of its applications derive.

Discovery and Preparation The compound was discovered in 1S03 by

Smithson Tennant (1761-1815), and in the same year he isolated metallic osmium from it (I). Fusion with alkali of the black residue remaining after treatment of native platinum with aqua regia followed by extraction and acidification of the melt gave

“a pungent and peculiar smell . . . from the extrication of a very volatile metal oxide; and, as this smell is one of its most distinguishing characters, I should on that account incline to call this metal Osmium” (I) (oopq-smell, odour). Industrially, OsO, is made from crude

platinum concentrates by oxidative acid distillation and is then separated from ruthenium tetroxide. In the laboratory it is best made by direct oxidation of osmium metal (2) or by the acid distillation with chlorate of almost any osmium compound.

Toxicity The solid has an appreciable vapour pres-

sure at room temperature and should be handled with care. The vapour is poisonous

(maximum permitted atmospheric level 2 x 10-6 glm3). It attacks the eyes, causing blurring of vision and, in very severe cases, temporary blindness, and it also attacks and irritates the nose and throat linings and may exacerbate bronchial conditions. Fortunately it has a characteristic, penetrating, rather ozone-like smell and this, together with its irritant effects, makes accidents with it rare. In the event of OsO, vapour attacking the eyes or the skin the remedy is washing with copious quantities of water. Spilled OsO, may be reduced by dissolving it in alkali in 50 per cent water-ethanol solution, and the non-volatile osmate salt may then be washed away.

Physical and Chemical Properties The properties of OsO, have been reviewed

by Griffith (3). The solid forms pale yellow monoclinic crystals (M.P. 40.6”C, B.P. 121.2T, density 4.906). It is fairly soluble in water (7.2 g/Ioo ml at 25°C) and extremely soluble in inert organic solvents (e.g. 350 g/Ioo ml. of carbon tetrachloride). It exists in the gaseous, solid or solution state as discrete molecular tetrahedra (Os-0 distance 1.717 A). The thermodynamic properties of OsO, have been reviewed (4).

In almost all of its chemical reactions, a number of which are summarised in the diagram, OsO, is reduced to compounds containing lower oxidation states. With ammonia, however, the tetrahedral osmiamate ion [OsO,N]- is formed, which is isoelectronic with OsO,.

Applications in Organic Chemistry The valuable function of OsO, in the

oxidation of olefins has been known and applied since 1913, and now constitutes one of


the major industrial and laboratory uses of the compound, particularly for reactions of steroids and sugars. The subject has been well reviewed by Rylander (5) and also by Fieser and Fieser (6). It is used mainly for the cis-hydroxylation of olefinic double bonds to give glycols, for which purpose it is the smoothest and most efficient general reagent known. It tends to react faster with strained olefins, particularly in the presence of pyridine (7). Aromatic hydrocarbons are hydroxylated only at the most reactive aromatic site (e.g. phenanthrene at the 9,10 position (8)).

The reagent may be used either alone in an inert solvent, the resulting osmate (VI) ester being decomposed by bisulphite or hydrogen sulphide (6,7), or, more commonly and economically, in the presence of an additional oxidant such as chlorate, hydrogen peroxide or periodate. These regenerate the OsO, which is therefore functioning as a catalyst. There is little doubt that cyclic osmate (VI) esters are involved in these reactions, and a recent X-ray study showed that mono-esters are dimeric (I) with a dioxo bridge, the osmium having square-based pyramidal coordination (8). The overall reaction is shown below:


Examples of simple hydroxylations with OSO, are the production of glycerol from ally1 alcohol and of ethylene glycol from ethylene. The compound has been used in the synthesis of such species as cortisone, progesterone, and of reserpine-type alkaloids, and also in the degradative investigation of natural products such as columbin (6). The glycol cleavage properties of periodate may be used together with the oxidising properties of OsO, to convert olefins to aldehydes (e.g. trans-stilbene to benzaldehyde, cyclohexene to adipaldehyde), to ketones or to epoxides (10).

In Biochemistry The compound is extensively used (nor-

mally in 2 per cent aqueous solution, often called “osmic acid”) for cell and tissue studies, its unique fixation and staining properties having been recognised and used since 1861. It is used for both visible and electron microscopy of biological materials, but now the latter application is probably the more important.

The purpose of fixation is to “freeze” cells without destruction or disruption of their organisation or structure; staining is necessary for the resolution of cellular structure by increasing the apparent density of some parts of the tissue only. OsO, is unique in that it both fixes and stains biological material. For the electron microscopist its most important functions are the preservation of sub-cellular ultrastructure and its ability to fix and stain membranes. For staining purposes it is often used with polar species such as uranyl or lead ions. The normal method used is to pre-treat the tissue with aldehydes, then to treat it by immersion in a dilute aqueous solution of OsO, (or the tissue is exposed to OsO, vapour) followed by washing, additional staining if required, dehydration with alcohol, em- bedding in resin and cutting into thin sections suitable for microscopy.

The mechanism of tissue fixation and staining by OsO, is far from clear, although it is generally accepted that the first step is the

attack of double bonds in unsaturated lipids to give osmate (VI) esters. There is evidence that mono-esters of type (I) above may be involved, in which case the fixation property may possibly arise from the formation of dioxo bridges (9).

There are still many questions to be answered, however-whether mono- or di- esters are normally formed (12), and whether in the dehydrated tissue the osmium is further reduced to osmium (IV) and perhaps shifted away from the original double-bond sites. The resolution of these problems is important since OsO, is so extensively used, and it is necessary to know to what extent the fixed and stained tissue is representative of the once living organism.

Corrosion Prevention Like some other heavy metal tetra-oxo

species, osmium tetroxide in electrolytes has the property of passifying iron electrodes (13).

I

2

3

4

5

6

7

8 9

I0

I1

I2

13

References D. McDonald, Platinum Metals Rev., 1961, 5, 146; Smithson Tennant, Phil. Trans., 1804, 94, 411 G. Brauer, Handbook of Preparative Chemis- try, Academic Press, New York, 1965, p. 1603 W. P. Griffith, Chemistry of the Rarer Platinum Metals, Interscience, New York, 1967; Quart. Rev., 1965, 19,254 B. N. Goldberg and L. G. Hepler, Chem. Rev., x968,68,229 P. N. Rylander, Engelhard Ind. Tech. Bull., 1968, 9, 90; F. R. Gunstone, Adv. Org. Chem., 1960, I, 103 L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, Wiley, New York, 1967, PP 475,759 R. Criegee, B. Marchand and H. Wannowius, Ann., 1942, 550, 99 G. M. Badger, Qzturt. Rev., 1951,5,160 R. J. Collin, W. P. Griffith, F. Phillips and A. C. Skapski, Biochim. Biophys. Acra, 1973, 320, 745; J . Chem. Soc., Dalton Trans., 1974, I094 R. Pappo, D. S. Allen, R. U. Lemieux and W. S. Johnson, J . Org. Chem., 1956,z1,478 M . A. Hayat, Principles and Techniques of Electron Microscopy, Vol. I, van Nostrand, I970 J. Riemersma, Biochim. Biophyx. Acta, 1968, 152, 718; E. D. Korn,J. Cell Biol., 1967, 34, 627 G. H. Cartledge, Corrosion, 1967,18,316t


Ammonia Oxidation Catalysts DEPOSITS ON SOME RHODIUM-PLATINUM GAUZES

By N. H. Harbord I.C.I. Agricultural Division, Billingham, Teesside

Rhodium-platinum gauzes used as catalysts i n nitric acid plants operating at various pressures have been examined by microscopy and by X-ray diffraction. Some gauzes possess low conversion e@ciency and these are usnully covered with deposits that can frequently be traced to sources of contamination. Gauzes operated at pressures of four or more atmospheres also possess coatings of rhodium oxide that are di#cult to remove by fusion or pickling. The suggested cause of formation of this oxide shows that it cannot be avoided but that methods exist for cleaning gauzes from higher pressure plants.

Over the past few years we have examined a number of unsatisfactory used rhodium- platinum alloy gauzes from catalytic ammonia burners of several nitric acid plants, both British and foreign. The complaints were that the gauzes had low or suspected low efficiencies, although a few gauzes from plants operated at one atmosphere pressure were satisfactory and of long life. The gauzes were taken, as shown in the table, from plants of various designs. Burner operating pressures were one, four or eight atmospheres, and most of the gauzes were of 10 per cent rhodium-platinum alloy; a few were of 5 per cent rhodium-platinum or of platinum only.

Examination of Gauzes On receipt of the gauzes, loose dust was

removed by gentle tapping. In most cases, pieces of gauze were mounted in a cold

Platinum Metals Rev., 1974, 18, (3), 97-102

setting resin and the resultant blocks were then ground and diamond polished to a 4 km finish. These polished mounts were then examined by reflected light microscopy and by electron microprobe analysis. In some instances, selected pieces of the gauzes were examined in the as-received state by scanning electron microscopy.

New gauzes are composed essentially of smooth wires which become roughened during use and which, after a few days’ operation, are found to be covered by alloy excrescences, which with time almost invariably show some well-developed crystal faces. The fully activated gauzes thus have increased surface area. It appeared possible that the active gauze surfaces might in some way be different from the initial gauze in composition as well as form. In some cases, therefore, strands of wire

were extracted carefully and were subjected to X-ray diffraction before and after scraping off the excrescences and also after scraping off the compact surface of wire below the excrescences.

The gauzes examined are listed in the table with brief details of origin, composition, use, and findings of the physical examinations.

Plants Operating at One Atmosphere Ten gauzes were examined, representing

five different sites, six different plants and three types of plant design. Certain samples of good efficiency were fairly clean. Others described as dirty were badly contaminated by iron oxide, principally a-Fe,03, which in some cases (samples 4, 5 and 6) was in the form of fine particles that could be traced to poor air filtration and to sources of iron-

97

Results of Physical Examination Tests on Rhodium-Platinum Gauzes

d z n al - 5 v)

__

1

2

3

4

5

6

7

8

9

10

11

12A

6

13

1 4A

B

15

16

17

18A

6

C

x Y

!2

e V

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.-

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41

92

3

3

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31

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D2

D2

D2

D2

D3

E

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1

1

1

1

1

1

1

1

1

1

4

4

4

4

4 4

4

4

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6m

54m

?

?

?

?

9m

?

?

3m

3m

8m

?

?

?

7m

10

10

10

5

5

10

5

5

10

10

10

10

10

10

10

10

10

10

Microscopy Test after Use

:ez03

nd

nd

n i l

heavy

v. heav)

much

i t t l e

l i tt le

l i t t l e

much

litt le

v. lit.

litt le

fair

fair

n i l

f a i r

fair

heavy

fair

f a i r

fair

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i d

i d

iil

i i l

iil

i i l

;race ji0,

i t t le MoS,

iil

iil

n i l

iil

nil

nil

nil

nil

nil

nil

nil

nil

nil

nil

X-ray Diffraction after Use

nil

nil

nd

nd

nd

nd

nd

nd

nd

ni l

nd

nd

nd

Rh,O:

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nd

nd

nil

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Rh,O

nd

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11.5

11

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nd

nd

nd

nd

nd

nd

10

nd

nd

10-11

nd

8.5

nd

nd

10

1 0-1 '

6

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nd

_ _ - :xcres. Zomp. Rh%

nd

11.5

nd

nd

nd

nd

nd

nd

nd

11

nd

nd

nd

8.5

variabl

nd

nd

nd

nd

6

nd

nd

Efficiency, Appear- lnce andTreatment

good, clean

good, clean

good, clean

dir ty

very dir ty

dir ty

good, clean

good, clean, corroded in places

fairly clean

dirty, corroded

fairly clean

clean

after placing in 1

dir ty

atm plant

after treatment wi th fusion mixture

dir ty gauze

after 2-3 weeks in D1 at 1 atm

after 8 weeks in E a t 1 atm

heated 100 per cent NH,, 50h, 850°C, 1 atm

bearing dust in close proximity to the plant, while in other cases (e.g. sample 10, see Fig. ra, b, c) the texture and microstructure of the iron oxide indicated an origin from plant scale. liberal use of a lubricant.

Quartz sand grains in sample 7 were due to plant siting and to poor air filtration, while in sample 8 the source of M o S , was traced to


heated 11 per cent NHJair, 25h, 850-9OO0C, 1 atm

Plan

t Typ

e

Tim

e in

Use

, m

onth

s or

days

Wir

e Com

posi

tion

, pe

r ce

nt R

h A1

A1

A2

B

B

B

c1

CI

D1

E c 2

D2

D2 D2

D2

D2

D2

D3

K

S

S

S S

S

S

t

E

19

20k

E

21

22

23

24

25

26

27

28

29

30

31

32

331

E

34

35

36

?. u U

aJ

.-

9 U

d - a __

D3

D 4

D4

D4

D 4

D4

D 4

D4

D4

D4

D 4

D5

F

G H

H

J K -

aJ n c U

m h -

S S

S S S S S S S

S

S S U

C

C

C

C

C -

E

E D E

U

z

L -

4

4

4

4

4

4

4

4

4

4

4

4

4

8

8

8

8

8 -

3m

1 Om

3tm 3 i m

34m

2;m

2tm

I m

I m

2d

2d

7m

?

3m

I m

ISIT

?

?

10

10

10

5

0

10

5

10

5

10

5

10

10

10

10

10

10

10

Microscopy Test after Use

Rhi Rh203

Rh

Rh

Rh203

Rh203

Rh203

Rh7.03

Rh203

nil

Rh203

Rh203

Rh203

trace

trace

nil

RhZO,

Rh203

Rh203

trace RhZO,

Rh203

l i t t le Rh203

Rh203

RhZO,

R h P 3

Rh203

fair

fair (Fe?)

trace

some

nil

some

trace

much

nil

nil

nil

nil

n i l

nil

trace

heavy

some

trace

l i t t le

Yes

Yes

Yes

~

Othe

nil

nil

nil

nil

nil

nil

n i l

nil'

nil

nil

nil

nil

n i l

nil

nil

Zn, S

nil

nil

nil

nil

nil

nil

X-ray Diffraction after Use

Rh/ Rh,O

Rh

Rh

nd

Rh,O

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

W i r e Comp Rh%

6-7

6-9

nd

6-5

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

Excres. Comp. Rh%

nd

nd

nd

variabli

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

Efficiency, Appear- ince and Treatment

heated 100 per cent N,, 4h, 850°C 1 atm

heated 100 per cent H,, 4h, 850°C, 1 atm

good efficiency

after treatment w i th fusion mixture

good efficiency

badly corroded

unlit portion

pickled in HCI

lit portion

Plant types: U=Uhde, K=Kuhlmann, D=Dutch State Mines, S=Stamicarbon, C=Chemico nd=not determined

Three samples were examined by X-ray ment in rhodium over the original 10 per cent diffraction, which showed that excrescence in the excrescences and in the compact formation was accompanied by preferential surface of the wire immediately below the platinum loss, with consequent slight enrich- excrescences.


Wir

e Com

posi

tion

, pe

r ce

nt R

h

Tim

e in

Use

, m

onth

s or

days

Sam

ple

No.

l a top, l b middle, I c bottom I d top, l e middle, lf bottom

Fig. 1 Electron and X - r a y images of gauzes f r o m one and four atmosphere nitric acid plants. ( a ) Electron image, Fe-contaminated gauze, 1 atm plant; ( b ) p la t inum X - r a y image of gauze in (a) ; ( c ) iron X - r a y image of gauze in (a). ( d ) EZectron image of gauze f r o m 4 a t m plant; ( e ) pla t inum X - r a y image of gauze in (d); ( f ) rhodium X - r a y image ofgauze in ( d )

Platinum Metals Rev., 1974, 18, (3), 1 00

2a above, 2b below 2c above, 2d below Fig. 2 Scanning electron mir roscop photomicrographs of two gauzes f r o m a 4 a tm plant . ( a ) Gauze ioith freshly actiaated plat inum alloy surface X 500; ( b ) detail of ( a ) X 4000; ( c ) low e$icienry gauze after use X 500: ( d ) detail of ( c ) showing alloy crystal P poking through blanket of porous K h 2 0 3 X 4000

Plants Operating at Four Atmospheres Twenty-one gauzes were examined, repre-

senting three sites, four different plants and two types of plant design. As in the case of plants operating at one atmosphere burner pressure, some gauzes were contaminated by iron oxide (particularly samples 17, 23 and 31), which in most cases could be traced to plant scale and general corrosion. In sample 31 both zinc and sulphur were detected by microprobe analysis. The source of this contamination was found to be zinc-coated wire filters in the air intake that were badly corroded and had disintegrated under attack from

sulphurous effluent from a neighbouring plant.

In addition to the contamination of the gauzes by material from external sources, all of the four atmosphere gauzes (with the exception of sample 17-mknown time on line, sample 23-a platinum gauze: and sample 29-a 5 per cent rhodium-platinum gauze of only two days usage) had further physical contamination as shown in Fig. Id, e, f and in Fig. 2. The platinum excrescences of the active gauze surfaces were masked by blankets of Rh,O,. As shown by results of X-ray diffraction studies, the formation of


Rh,O, leads to depletion of rhodium from the gauze, giving rise to compositions as low as 6 per cent rhodium from an original 10 per cent rhodium-platinum gauze (sample I ~ A ) , whereas in plants operating at one atmosphere burner pressure the rhodium content tends to increase in the alloy with time.

Plants Operating at Eight Atmospheres Six gauzes were examined from four differ-

ent plants, all of the same type of plant design. Again the amount of iron contamination was variable and in some cases attributable to plant scale. All gauzes showed evidence of blanketing of the active alloy surface by a surface covering of Rh,O, and are thus similar to gauzes operating at four atmospheres burner pressure.

Gauze Cleaning Examination of used and Rh,O,-contami-

nated gauzes after plant cleaning procedures showed that the fusion mixture normally used (see samples 14B and zoB) removes iron oxide but has little effect on rhodium oxide. Similarly, pickling in HCl acid (see sample 33) is not very efficient for Rh,O, removal.

However, since the Rh,O, coating arises by oxidation of rhodium in the alloy, the process should be easily reversible. Indeed, it is easily accomplished by heating the gauzes in hydrogen (see sample ISE), when the oxide is reduced to metal, or in nitrogen (see sample I ~ D ) , when it dissociates to metal and oxygen. A like effect is obtained by placing the gauzes in a one atmosphere plant for several weeks (samples 12B, 16 and 17), when they reach equilibrium with the gas compositions and the alloy becomes rhodium-rich and returns to a composition close to the original alloy.

Corrosion of the gauzes used in ammonia burners of nitric acid plants has been shown to occur and has been caused by those contaminants which are expected to attack rhodium-platinum alloys, e.g. zinc, sulphur, molybdenum disulphide, and iron compounds. Contaminants also cause blanketing of the

active gauze surface. In the samples examined the principal extraneous contaminant is iron oxide from plant scale or elsewhere.

In plants operating at one atmosphere burner pressure the alloy at the surface of the wire and in the active excrescences tends to become enriched in rhodium by preferential loss of platinum. Although the vapour pressures of platinum and rhodium are very close, Alcock and Hooper (I) have shown that, in a flowing gas stream containing oxygen, metal loss from platinum and from rhodium is via two volatile oxide species, PtO, and Rho,, and that PtO, is more volatile than Rho,. Therefore, preferential platinum loss probably is due to formation of the more volatile

In plants operating with burner pressures of four atmospheres and above there is preferential oxidation of rhodium to a more stable solid oxide, Rh,O,, under these conditions of increased partial pressure of oxygen. This leads to surface blanketing of the wires by solid Rh,O, and, in contrast to gauzes used at one atmosphere burner pressure, also leads to depletion of rhodium in the alloy of the excrescences and of the wire surface.

The prevention of the oxidation of rhodium at higher pressures is not possible while rhodium-platinum gauzes are used. Traditional cleaning methods, while dealing adequately with iron oxides, do not appear to be particularly efficient in the removal of Rh,O,. However, as shown by our own thermo- gravimetric analyses, since the dissociation temperature of Rh,O, of about 1050°C in air at I atm is lowered in nitrogen to about 790°C, heating Rh,O,-contaminated gauzes in nitrogen at high temperature will convert Rh,O, into rhodium, which can then slowly diffuse back into the alloy surface. Reduc- tion to metal may also be done with hydrogen. Insertion of the Rh,O,-covered gauzes into a one atmosphere plant has a similar effect, with slow disappearance of Rh,O, and diffusion of rhodium back into the alloy.

I C. B. Alcock and G. W. Hooper, Proc. Roy.

PtO,.

SOC. A, 1960,254,551


New Plants in Three Countries EXHAUST CATALYST PRODUCTION AND REFINERY EXPANSION

Two new plants, the first of their kind in the world, have recently been opened by the Johnson Matthey Group for the production of catalyst units for the control of fume emission from car exhausts. The earlier one, at Royston in England, is operated by Johnson Matthey Chemicals, who have already been successful in securing contracts from Rolls Royce and from Volkswagen for the supply of substantial quantities of the specially developed platinum catalysts for incorporation in the exhaust systems of cars to be exported to the United States. The second new plant is at Devon, Pennsylvania, and is operated by Matthey Bishop, who have a contract with Ford to supply catalyst units for their 1975 models.

Exhaust emission control catalysts have been described previously in this journal (I, 2). They consist of elliptical or cylindrical ceramic honeycombs, which act as the supports for dispersions of promoted platinum

metals. Size and shape depend upon the size of the car and its engine, and upon the space available for the exhaust train below the vehicle.

The steady increase in the demand for the platinum metals is responsible for the third new facility, a major extension to the platinum refinery at Wadeville, near Johannesburg, operated by Matthey Rustenburg Refiners, the joint company formed in 1972 by Johnson Matthey and Rustenburg Platinum Mines to absorb all matte treatment and refining into one organisation. The capacity of the Wadeville refinery has now been expanded to process more than one million ounces a year of platinum with proportional amounts of the other platinum metals.

References I G. J. K. Acres and B. J. Cooper, Platinum

z G. J. K. Acres, B. S. Cooper and 6. L. Metals Rev., 1972, 16, (3), 74-86

Matlack, Zbid., 1973, 17, (3), 82-37

Finished honeycomb catalyst pieces being removed from the furnace conveyor belt after $ring at the Royston factory of Johnson Matthey Chemieals Ltd. They ivill be incorporated i n automobile catalyst systems by European manufacturers of motor vehicles


Platinum Metals in the Development of Analytical Chemistry

J

By Frank Greenaway The Science Museum, London

The celebration of the centenary of the foundation of the Society for Analytical Chemistry is an occasion for looking at many features of the history of analytical chemistry. Platinum and, to a lesser extent, the other platinum metals have played a distinctive part in the progress of this branch of science.

A glance at a few of the familiar charac- teristics of platinum show why it has been important. I t is unreactive, which makes it an excellent vehicle for use in contact with a variety of reagents. It has a high melting point, which makes it an excellent vehicle for high temperature reactions. Its electrochemical properties make it an almost unique material for electrode systems.

Against it could at first be set the difficulty of working it, a much greater obstacle than expense (it was comparatively cheap for a long time). The first platinum crucible ever to be made was almost certainly the one described in 1784 by Professor Franz Achard of the Royal Academy of Sciences in Berlin. By using the old arsenic process of rendering

Torbern Olaf Bergman 1735-1784

Professor of Chemistry at the TJniuersity of Uppsala, Bergman laid the foundation of quantitative analysis. He introduced the systematic use of reagents and the concept of determining metals in

the form of their insoluble compounds

J

platinum fusible and a clay mould and former he succeeded in making a crucible “which is hammered a little on a mandrel and is then ready”. This must have been a very fragile article, and there is no further record of Achard’s crucibles.

Guyton de Morveau records in 1786 that:

“I have platinum crucibles which have been very useful in a number of researches, as for example for the decomposition of minerals according to Bergman’s method.”

A year later Guyton de Morveau, refer- ring to the increasing availability of platinum, expressed the hope that “we shall soon be able to make vessels and other apparatus”. But according to Kopp’s History of Chemistry platinum apparatus remained a rarity for chemists at the turn of the eighteenth century.

Platinum Metals Rev., 1974, 18, (3), 1044108 104

CenEenary of the Society for Analytical Chemistry

The Society of Public Analysts, founded in 1874 as a means of exchanging information on methods of analysis, is celebrating its centenary under its modified title of the Society for Analytical Chemistry. The contributions to analytical techniques made by the platinurn metals both before and during the hundred years of existence of the Society are reviewed here.

The history of the perfecting of the method of fabricating platinum at the hands of W. H. Wollaston and others has often been told. Wollaston was the first to use it to make laboratory vessels on any scale, beginning in 1805. Its unreactive nature was now fully appreciated, and by Wollaston’s day the techniques of analysis had been brought to a respectable degree of systematic discipline, as regards theories of composition. The practice had also been refined to such an extent that analysts like Kirwan, working on siliceous minerals, were able to make quantitative estimates of the interference with their results of material derived mechanically or chemically from the glass or earthenware vessels in which their reactions were carried out. The campaign for constancy of conditions and purity af reagents which was led by analysts like Vauquelin was one which benefited from the constancy and un- reactivity of platinum as a material for the construction of crucibles.

The introduction of the platinum crucible for routine use in gravimetric analysis did, however, take time. Apparently there was only one in Sweden in 1808, made for (or by) the foundry-owner Hisinger, who aided and befriended Berzelius. Hisinger lent this to Berzelius, but it was of some size and too heavy for use on the balance that Berzelius

was using at that time. However, in 1823 when Wohler arrived to study with Berzelius he was given a platinum crucible for his own use. Wohler was Berzelius’ only student for some time, so there may not have been many about, but at least there was one to spare.

Berzelius’ Text-book of Chemistry, that monumental summary of the chemical theory and techniques of the third decade of the nineteenth century, tells us a good deal about the use of the platinum crucible. Ignitions and fusions had formerly been carried out in clay crucibles which, while well established for metallurgical wo&, were proving unsatisfactory for much of the more refined chemical work now being done. Platinum thus superseded clay as a favoured crucible medium. Berzelius warned against a number of dangers; for example, metals could not be fused in platinum because of alloy formation which embrittled or destroyed the platinum, and aqua regia, of course, could not be heated in it. Less expected was what was described as the dire effect of a sooty flame, which appeared also to produce embrittlement. (That this is due not to carbon but to the simultaneous effect of undesirable substances being fused was not cleared up until much later. A possible explanation is that some of the low melting point fluxes used, over a low temperature flame, were inimical to the


platinum, so the sooty flame was blamed for the faults of fluxes.)

The familiar porcelain crucible was only just coming into use at this time. Although porcelain manufacture for decorative purposes had been perfected early in the previous century, only in the ISZOS were porcelain crucibles made which would stand even moderate heating. At first one important use for a platinum crucible was as a shield and support for one made of porcelain.

By the time that the Society of Public Analysts was formed platinum ware had, of course, become essential and commonplace. A writer in “The Chemist and Druggist’s Diary” of that very year comments :

“Next in importance to the balance, utensils of platinum must be considered. Of these are required at least one crucible of about an ounce capacity, costing 30s; a capsule holding rather over IOO cc for water residues, a bundle of wire, and if nickel and copper analyses are to be made a platinum knife should be added.”

The rapid development of experimental techniques in the late nineteenth century made it possible for the properties of platinum to be more closely studied than before, with some loss of its reputation as a virtually impregnable material, and some greater understanding of the conditions under which it could behave at its best. No-one has kept, so long after his death, so high a reputation for experimental skill as William Crookes. Towards the end of his career, in 1908, Crookes published several studies of the

properties of the platinum metals. He asserted the virtues of iridium as a material for the construction of crucibles, and one of those made for him by Johnson Matthey survives to this day. In recent years iridium has been used for melting special glasses and for growing the synthetic materials for laser optics.

Electrolytic Methods The processes of gravimetric analysis were

rendered intelligible and self-consistent by the introduction of Dalton’s atomic theory with its universal arithmetic basis. I t required the quantitative laws of Faraday to make electrolysis into a useful analytical method. The qualitative distinction between electropositive and electronegative elements was made quite early after the discoveries of Volta, and Nicholson and Carlisle, and became the basis of important theories of chemical constitution. A link with the qualitative theories of composition was made by the discovery by Faraday that, when metals were deposited at a cathode or a gas

JSns Jacob Berzelius

Among his many great contributions to chemistry, Berzelius carried out analyses of many rare minerals and improved analytical methods. He discovered cerium, selenium and thorium, and also standardised the methods of separuting the constituents oj native plutinum on an analytical scale

1779-1848


Wolcott Gibbs 1822-1908

Born in New York, Gibbs graduated at Columbia and then studied in Germany under Liebig and i n Paris under Dumas and Regnault. In 1849 he became Professor at what i s now the City University of New York, later accepting a chair at Harvard. His researches mere mainly in analytical chemistry; umong other achievements, in 1864 he was the first to introduce quantitative electrochemical analysis

was liberated at an anode, the quantities liberated were related both to the equivalent weights and to the quantity of electricity passed. This could have been, from the outset, the basis of a system of electrolytic or electrogravimetric analysis, but this in fact had to wait until the work of Wolcott Gibbs in 1864.

His apparatus, although simple and soon superseded, set the pattern for most work to follow. The electrolyte was contained in a platinum crucible acting as cathode, the anode being a central platinum wire immersed in the electrolyte. He determined copper and nickel by deposition on the weighed cathode but this was not a coulo- metric method, the current being used solely to effect complete decomposition of the electrolyte. Its logical form was the same as that of traditional dry assay (total extraction of the desired species from a weighed sample), but the factors interfering with rapidity and completion provoked a number of developments in the physical form of the cell used.

Platinum remained the essential material but electrodes became more involved in shape as more was learned about the physical

behaviour of deposits and about the basic electrochemistry.

One of the earliest workers in the field, acting independently of Wolcott Gibbs, was C. Luckow. In 1895 he reviewed the early progress of electrochemical methods and described his own electrodes, a platinum cylinder as cathode with a horizontally mounted platinum disc having a vertical wire stem from its centre. He also introduced the flat spiral anode. He also claimed to have been determining copper and silver by electrolysis in 1860, before Gibbs, and certainly he was responsible for introducing this technique into industrial laboratories.

I t was appreciated early on that current density at different points on the surface of the cathode could have a profound effect not only on the amount of deposition at any point but also on the structure of the deposit. Clemens Winkler, Professor at the Freiberg School of Mines, was one of those who devised novel forms of electrode systems and he was the first to employ a platinum gauze cathode with its advantages in circulation of the electrolyte.

More effective in the releasing of gases was the rotating anode, like that described at the first meeting of the Faraday Society in I903 by F. Mollwo Perkin. He suggested another improvement, the use of an alloy of iridium and platinum in place of platinum. Perkin


Clemens Alexander Winkler 1838-1904

Professor of Chemistry at the Freiberg School of Mines, Winkler was an outstanding inorganic chemist of his time. Among his achievements was the discovery qf germanium, and in 1899 he proposed the use of the cylindrical cathode made of platinum gauze, still in use today, for electro-

chemical analysis

pointed out that although platinum was usually regarded as a metal practically unaffected by any reagent other than aqua regia, it was by no means as resistant as had been thought under some conditions of electrolysis, particularly in the presence of cyanides. Iridium or a platinum-iridium alloy was more resistant, and its use was taken up. Iridium presented great difficulties in working, and Perkin recommended that chemists should not attempt to prepare their own electrodes but should get Johnson Matthey to do it for them.

So far this brief note has dealt only with electrogravimetric methods. Another branch of electrochemistry also developed in the late 19th century. Hydrogen ion concentration has a special place in the theory of electrolytic dissociation, and the measurement of pH is perhaps the most frequently performed electrochemical procedure. Platinum played its part in the development of the theory of hydrogen ion concentration, and thus in the development of analytical techniques. In 1893 Le Blanc found that if a stream of hydrogen is allowed to flow over the surface of a platinum electrode this behaves as a hydrogen electrode, i.e. if immersed in a solution of an acid it behaves like a metal electrode immersed in a solution of that metal ion. The studies of hydrogen ion concentration made possible by this electrode system led to the theory of indicators, to the concept of buffer solutions, and to the pH concept developed by Sorensen and others in their study of enzymes.

The recognition of platinum as a distinct element was slow and uncertain, the metal having been found and used long before the modern concept of chemical purity emerged in the early nineteenth century. Ideas of purity and methods of analysis did in fact develop hand in hand. Wollaston’s separation of the other platinum metals from platinum itself by treatment of crude platinum with aqua regia followed by mercuric cyanide was not an isolated experiment. The stepwise separation of complex mixtures had been initiated by Bergman and in the hands of Kirwan and Klaproth was already very similar to the systems of group separation which were to become the backbone of inorganic analytical chemistry for a century or more. The platinum metals separation is a distinctive example of the discipline of analytical procedure which was to reach its peak in the rare earth separations of William Crookes.

No doubt the history of analytical chemistry could be written without specific mention of platinum and its allied metals but such a history would fail to do justice to an interesting and, in many respects, vital contribution.


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Heat Capacity of Platinum from 350 to 1200K: Experimental Data and an Analysis of Contributions c.-c. YEH and c. R. BROOKS, High Temperature Sci., 19733 51 (61,403-413 The heat capacity of Pt was measured at 350- 12ooK using dynamic adiabatic calorimetry. Results showed that the 161 data points were all within =I"/, of a polynomial fitted to the data, and this polynomial curve was within 19: of the previous measurement.

Study of Crystallisation in Glasses by Means of Electron Microscopy I. GUTZOW and M. MARINOW, Silikattechnik, 1974, 25, (11, 18-23 The morphology of nucleating condensation cores in the glass as well as forms of growth and equilibrium of small Pt, Ir, Rh, Pd, Au metal crystals in the glass melt volume were studied. Experimental details are described.

On the Stoichiometric Chemisorption of Hydrogen on Platinum

TURAKULOVA, Zh. Fiz. Khim., 1974, 48, (2),

A review of the present position in this area (50 refs.).

X-ray Photoemission Spectra of Palladium s. HUFNER, G. K. WERTHEIM and D. N. E. BUCHANAN, Chem. Phyr. Lett., 1974, 24, (4), 527-530 The X-ray photoemission spectra of Pd prepared by vacuum evaporation and by argon ion sputtering were compared; the former shows a close correlation with calculated band structure, while the latter exhibits much less detail, strongly suggesting that the sputtered surface is amor- phous. Narrow core lines of the evaporated samples show the asymmetry predicted to arise from the hole-conduction electron interaction.

Adsorption of Hydrogen on Palladium Single Crystal Surfaces H. CONRAD, G. ERTL and E. E. LATTA, Surface Sci., 1974, 41, (21,435-446 The adsorption of H, on clean Pd(1ro) and Pd(1Ir) surfaces as well as on a Pd(II1) surface with regular step arrays was studied by means of LEED, thermal desorption spectroscopy and contact potential measurements. Maximum work function increases of 0.36,0.18 and 0.23 eV

V. S. BORONIN, 0. hl. POLTORAK and A. 0.

258-264

were determined for Pd(Iro), Pd(II1) and the stepped surface, respectively, being influenced only by absorbed H, under the chosen conditions.

Fe,P-type Phases in the Ternary Alloys of the Rare Earths with Thallium and Pal- ladium

Kunde, 1974,65, (I), 4-41 F. FERRO, R. MAKAZZA and G. RAMBALDI, z. Metall-

The ternary phases of the alloys of the rare earths with TI and Pd in the stoichiometric ratio I :I : I were studied. They are of the Fe,P-type. The results obtained, compared with those of the iso- structural compounds previously known, are briefly discussed.

Equiatomic Ternary Phases in the Alloys of the Rare Earths with Iridium and Nickel or Palladium R. FERRO, R. MAKAZZA and G. RAMBALDI, Z. Metall- kunde, 1974, 65, (I), 37-39. The R.E.-NiIn and R.E.-PdIn compounds were prepared and examined by using the methods of chemical analysis, density measurement, and metallographic and X-ray examinations. These phases are of the Fe,P structural type and their crystallographic constants were determined.

High Field Magnetostriction in a Meta- magnetic FeRh Alloy J. A. R I c o n m u and D. MELVILLE, J. Physique, 1974, 35, (2), 149-152 The parallel and perpendicular magnetostriction of polycrystalline equiatomic FeRh was measured in pulsed magnetic fields up to 15T in the antiferromagnetic phase and at the antiferro-ferromagnetic transition induced by the field. The perpendicular antiferromagnetic magnetostriction is N 3 x I O - ~ at IOT and is temperature dependent. The parallel magnetostriction at IOT is -5 X I O - ~ and is temperature independent. The lattice parameter change at the transition agrees with that established by thermal expansion measurements.

Deformation of Single-crystal Ruthenium D. B. SNOW and J. F. BREEDIS, Acta Metall., 1974, 22, (41, 419-427 Studies of Ru crystals oriented for single slip on (1100) deformed by compression at room temperature showed that the dislocation distribution formed during stage I consisted of bundles containing primary edge dipoles while the stage 2 dislocation structure consisted of primary- secondary prism dislocation tangles lying between


tight edge multipoles. Cross-slip activity on (0001) was detected during stages I and 2.

Thermodynamic Investigations in the Thorium-Ruthenium System H. KLEYKAMP and M. MURABAYASHI, J. Less-common Metals, 1974, 35, ( z ) , 227-233 The Gibbs free energy of formation of the intermetallic phases ThRu,, ThRu, Th3Ru, and Th,Ru, existing in the Th-Ru system was determined by e.m.f. measurements using electrolytic cells with solid CaF, electrolyte. The measurements of the Gibbs free energies of formation are given for the intermetallic phases at 1020-1170 K.

Dependence of Electrical Resistance of Rhodium, Iridium and Platinum on Enthalpy M. M. MARTYNWK and V. I. TSAPKOV, Fiz. Metal.

Temperature coefficients of resistance for Rh and I r at 298-1550K are initially proportional to specific heat C,. a varies linearly with temperature which cannot be explained by the s-d theory of scattering. For these metals from I550K to their melting points and for Pt from 298K up to its melting point the size of C, predominates over the increase of a.

I974, 373 (I), 49-54

CHEMICAL COMPOUNDS Formation of Platinum(II1) Chloride during Thermolysis of Hexachloroplatinic Acid L. K. SHUBOCHKIN, v. I. GUSHCHIN, G. M. LARIN and v. A. KOLOSOv, Zh. Neorg. Khim., 1974, 19, (2), 460-463 Studies of the thermal decomposition of H,PtCl, at zo-SOOT indicated a range of intermediate products. EPR studies on the decomposition of PtCI, at 3oo-330°C showed that PtCl, was formed.

Observations on the Formation of Platinum Silicide M. J. RAND and J. F. ROBERTS, Appl. Phys. Lett., 1974, 24, (21, 49-51 When thin-film Pt and single-crystal Si are inter- diffused, -100 a of SiOz is evident at the PtSi surface. The SiO, can serve to protect the silicide from attack by aqua regia commonly used to remove unreacted Pt. If, however, the SiO, is removed, the PtSi on Si will dissolve in aqua regia even faster than Pt. These findings are particularly applicable to contact technology for Si devices and integrated circuits.

Anisotropy of the Electrical Conductivity of the One-dimensional Conductor

H. R. ZELLER and A. BEcK,J. Phys. Chem. solids, 1974, 35, (1),77-80 The conductivities ull and oL parallel and per-

K ~ c N ) , I B ~ , . 3 a . 3 ( ~ , ~ )

pendicular to the c-axis in single crystals of K2Pt(CN),Br,.3.3(H20) were measured simultaneously by Montgomery's method. The anisotropy is of the order 105 at room temperature but decreases to 3.10~ at 35K.

Ultraviolet to Far Infrared Optical Properties of the One-dimensional Conductor K,Pt(CN),Br,. ,.3H,O J. BERNASCONI, P. BRUESCH, D. KUSE and H. R. ZELLER, J. Phys. Chem. solids, 1974, 35, (21, 145-157 The optical properties of crystals of the quasi-one- dimensional conductor KzPt(CN),Br,.,.3H20 were studied at the special range of 45000 to 10 cm-l. For light polarised perpendicular to the highly conducting direction it behaves as a trans- parent dielectric, as shown by reflection and transmission spectra.

Organoplatinum(1V) Compounds. I. Trim- ethyIplatinum(1V) Azide, Me,PtN, K.-H. VON DAHLEN and J. LORBERTH, J . Organo- metal. Chem., 1974, 65, (2), 267-273 The preparation of trimethylplatinum azide via trimethylplatinum sulphate is reported. The compound is characterised by IH N.M.R., mass and vibrational spectroscopy and its probable structure is suggested.


Dimethylplatinum(1V) Compounds. 111. Acetylacetonatc Complexes J. R. HALL and G. A. SWILE, J . Organometal. Chem.,

The preparation of a number of acetylacetonate complexes of dimethylplatinum(1V) is described and their possible structures are proposed.

1974, 67, (3)1 455-466

Some Cationic Carbonyl Complexes of Rhodium( I) G. K. N. REDDY and B. R. RAMESH, J . Organometal. mem., 1974, 67, (3), 443-447 The preparation of a number of cationic Rh(1) complexes of the type ph(CO),(N-N)]ClO,, [Rh( CO) ,L3] C10 , and [Rh( CO)( N-N)L ,] C10, , where (N-N) :=z,z-bipyridine or 1,Io-phenan- throline and L is a tertiary phosphine or arsine, is described and their structure and assigned. The configuration of the complex ion [Rh(CO),L,]+ is dependent on the size of the ligand L.

Some Adducts of RhCl[P(C,HI1),],, a Rho- dium Compound Spontaneously Coordinating Dinitrogen

J . Organometal. Chem., 1974, 65, (2), C43-C45 Solutions of RhCl(PCy3)2 react with O,, N,, C,H,, CO and H, to give trans-RhCIA(PCy,),, where A=O,, N,, C,H, and CO and Cy=cyclo- hexyl, and to give RhClH,(PCy3),. The spon- taneous formation of the fairly air-stable

H. L. M. VAN GAAL, F. G. MOERS and J. J. STEGGERDA,

Metalloved.,

RhCl(PCy&N, is ascribed to a combination of the steric requirements and electronic properties of the phosphine ligand.

Phase Relations in the Systems Na,O-IrO, and Na,O-PtO, in Air c. L. MCDANIEL, J . Solid State Chem., 1974, 9, (a), 139-146 The equilibrium phase relations for the Na,O- IrO, and Na,O-PtO, systems were determined in air using the quenching technique. The Na,O- IrO, system contains two stable compounds, Na,O-IrO, and zNa,O.jIrO,, which dissociate at 1235 and 1040"C, respectively. TheNa,O-PtO, system contains Na,O.PtO,, metastable zNa,O.jPtO, and Na,Pt,O, (0 <x GI). They dissociate at 890, 710 and 81o"C, respectively. Indexed X-ray diffraction powder patterns for Na,O.IrO, and jNa,O.jIrO, are given.

Mass Spectrometric Observation and Stability of Gaseous RuC,, PtC,, and IrC, K. A. GINGERICH, J. Chern. SOC., Chem. Commun.,

The gaseous molecules RuC,, PtC, and IrC, were detected in a high temperature mass spectrometer and their atomisation energies were determined as I I 19.0~38~1084.1 I 3 8 , < 1088.3 z t 42 kJ/mol.

'974, (6)J 199-2m

ELECTROCHEMISTRY Radiometric and Electrochemical Study of Methanol Adsorption and Oxidation on Platinum A. WIECKOWSKI, J. SOBKOWSKI and I. SZAMKEJ, Roczniki Chem., I974,48, 77-85 The adsorption and oxidation of MeOH on a platinised electrode was studied both by electrochemical and radiochemical methods, used simultaneously, in order to establish the mechanism of this reaction.

Effect of Hydrogen Concentration on Super- conductivity and Clustering in Palladium Hydride J. M. E. HARPER, Phys. Lett. A, 1974, 47A, (I), 69-70 A method of preparing superconducting PdH by electrolysis is described. The relationship of the superconducting transition temperature to H- concentration and the behaviour of the H- clustering temperature at high concentrations are reported.

Dissolution of Palladium in Aminochloride Electrolytes by Asymmetric Alternating Current of Industrial Frequency M. N. POKIN, N. G. MAKAROVA and I. I. MAZURINA,

Oscillographic and gravimetric studies of anodic ZaShChita, 1974, 10, (I), 82-83

dissolution of Pd in aminochloride electrolytes (20 811 Pd, pH=8.5) by asymmetric alternating current of industrial frequency showed that the dissolution rate and the power yield are maximum for anodic current density of 400mA/cma. Maximum dissolution rate of Pd is -0.55 pm/min which compares with practical deposition rate 1-3 pm/min.

ELECTRODEPOSITION AND SURFACE COATINGS Role of Rinsing during the Activation of ABS Plastics Using Mixed SnCl,/PdCl, Catalysts A. RANTELL and A. H O L T Z W , Electroplating Metal Finish., 1974, 27, (z), 15-20 In the plating of plastics involving a mixed SnCl,/PdCl, catalyst system the function and importance of the post-catalyst and the post- accelerator rinse is discussed.

LABORATORY APPARATUS AND TECHNIQUE Protein Coated Electrodes E. E. UZGIRIS and J. H. KAPLAN, Rev. sci. Instrum.,

A simple method for coating platinised Pt electrodes with bovine serum albumin is described. The coating does not alter the electrical properties of the electrodes in dilute salt solutions and prevents a specific type of surface reaction from occurring between the Pt surface and sucrose buffer.

1974, 453 (I), IZC-121

HETEROGENEOUS CATALYSIS Aromatisation of Isoheptanes in the Presence of Platinum/Alumina Catalysts YU. N. usov and v. F. IL'IN, Neftekhimiya, 1974, 149 (111 49-55 Conversions of five isoheptanes and three alkyl- cyclopentanes were studied over acidic and basic samples of Pt/Al,O, at I atm in flowing Hz at 37O-~2Ooc using pulsed microcatalytic conditions. Aromatisation of the isoheptanes occurred by C5- and C,-dehydrocyclisation. The composition of the initial isoheptane affects the relative amounts of C5- and C,-dehydrocyclisation.

Relation of the Directions of Catalytic Demethylation of 2-Methylhexane to Its Electronic Structure I. I. LEVITSKII, KH. M. MINACHEV, I. V. STANKEVICH, E. A. UDAL'TSOVA and A. M. GYLIL'MALIEV, Zzv. Akad. Nauk S.S.S.R., Ser. Khim., 1974, (I), 39-41 The pressure of H, alters the direction of de-


methylation of a-methylhexane over zo:/,Pt/C at 375°C by promoting the splitting of€ of the methyl group bonded to the third atom. Studies of the electronic structure of 2-methylhexane showed that C atom of the CH, groups carry maximum negative charge but minimum electron density is centred on the third atom.

Investigation of the Efficiency of Platinum/ Zeolite Catalysts in the Decomposition of H,O,. IV. Activity of Platinum/Zeolite Catalysts Produced by the Ion Exchange Method on Cay Zeolite

SHEKHOBALOVA and N. I. KOBOZEV, Zh. Fiz. Khim.,

The activity of Pt was related to its content in Cay zeolite (SiO,:A1,0, =4.8) for the decomposition of H,O,. Results for Cay and NaY zeolites are analogous but catalysts supported on Cay zeolite have 4-12 times greater activity. Activation energy is 10.8 kcal jmole.

Acidity and Catalytic Activity of Pt-containing Zeolites K. v. TOPCHIEVA, v. A. D~ROGOCHINSKAYA and KHO SHU TKHOANG, Zh. Fiz.Khim., 1974, 48, (I), 182- 184 The acidity of Pt /zeolite, determined by high temperature NH, adsorption, was compared with catalytic activity for n-C,HI4 isomerisation. Acidities of samples after reduction of Pt by H, are almost equal and are much less than acid than initial Ca-decationised samples. Strong acid centres are unnecessary for n-C6Hlp isomerisation.

Investigation of the Stepwise Mechanism and Selectivity of Hydrogenation of Stable Iminoxyl Radicals on Pt Catalyst

FREIDLIN and E. G. ROZANTSEV, Zzv. Akad. Nauk S.S.S.R., Sw. Khim., 1974, ( I ) , 48-52 Studies of the liquid phase hydrogenation of iminoxyl radicals on Pt black showed that biradicals are reduced selectively through the formation of hydroxylamine radicals. The selectivity is due to more stable adsorption of biradicals on Pt compared to the intermediate formation of nonradicals. Noncatalytic reduction of the biradicals by phenylhydrazine is non- selective, with simultaneous formation of hydroxylamine radicals and of dihydroxylamine.

Exhaustion of Absorption Platinum Catalysts in the Decomposition of H,O, T. G . MARTYNYUK, z. v. LUK’YANOVA, V. I. SHEKHOBALOVA, T. A. POSPELOVA and N. I. KOBOZEV, Zh. Fiz. Khim., 1974, 48, (2), 327-330 The activity of Pt;SiO,, Ptjzeolite, PtiC, PtIZnO, and PtlWO, for H,O, decomposition is stable after reduction by aqueous NaBH, solution but when reduced by electrolytic H, at 3oo-38o0C

T. G. MARTYNYUK, T. A. POSPELOVA, V. I.

1974,48, (3)J 602-604

E. F. LITVIN, L. M. KOZLOVA, A. B. SHAPIRO, L. KH.

or when treated before use with H,O the activity falls, first sharply and then gradually. Pt black reduced by these methods shows no loss of activity. Activation energy remains constant at I I kcal/mole. The loss of activity is suggested as being caused by the action of the solvent on the surface of the catalyst support.

Hydrogenation of Dimethylethynylcarbinol on Palladium/Polymer Catalysts in the Presence of Some Cations 0. A. TYURENKOVA and N. A. TERPUGOVA, Zh. Fix. Khim., I974,48, (I), 67-69 Potentiometric studies of the hydrogenation of dimethylethynylcarbinol on Pd /polymer catalysts in the presence of Zn, Pb and Cd ions showed that ZnSO, reduces the rate of hydrogenation on polyacrylonitrile and anide catalysts, and increases the rate of H, addition on colloidal catalysts by protection by polyvinyl alcohol. The rate of double bond hydrogenation is greatly reduced. Pb acetate and Cd sulphate solutions almost completely suppress the reaction.

Hydrogenation of Dimethylethynylcarbinols on Mechanical Mixtures Containing Pd/CaA Zeolite Catalysts D. V. SOKOL’SKII, N. A. GOGOL’ and N. L. SHLIOMENZON, Zh. Fiz. Khim., 1974, 48, (I), 131-133 Studies of the activity of mechanical mixtures containing Pd/zeolite with 0.1-5.0 wt.:, active component for hydrogenation of dimethylethynylcarbinol showed that their activities are generally similar, variation only occurring for selectivity of hydrogenation of triple bonds.

Activity of Pd Catalysts Produced in an Ultrasonic Field in the Original State I. V. SOLOV’EVA and A. N. MAL’TSEV, Zh. Fiz. Khim.,

The activity of newly formed Pd catalysts during hydrogenation of acrylic acid was compared for those formed from PdCl, using H, in an ultrasonic field and those formed with vibration. Pd catalysts in the crystalline state have higher activity when produced in the ultrasonic field, thus indicating the specific action of an ultrasonic field during catalyst generation.

Kinetics of the Selective Hydrogenation of Dimethylethynylcarbinol on Palladium in the Vapour Phase. 11. Reaction of Di- methylethynylcarbinol with Deuterium and the Kinetic Isotope Effect

KIPERMAN and M. A. BESPROZVANNYI, Kinet. Kataliz, 1974, 15, (I), 98-103 Studies at 153 and 203°C of the reaction of dimethylethynylcarbinol with D in the vapour phase over Pd in a steady system showed that the

19741 4% (I), 194-195

D. Z. LEVIN, E. P. PROKOFIEV, B. S. GUDKOV, S. L.


kinetic isotope effect for H,-D, exchange during the hydrogenation was 1.8-1.9. Theoretical and experimental values were close. The distribution of D, in the reaction products was measured by infra-red spectroscopy, proton magnetic resonance and mass spectroscopy.

On the Mechanism of Reaction of Butyn-2- diol-1,4 with Degasified Rhodium-Zirconium and Zirconium Electrode Catalysts M. V. AVRAMENKO, V. M. TSINTSEVICH, G. l'. KHOMCHENKo and M. B. KATS, Zh. Fiz. Khim., 1974,483 (31, 749-750 Studies of the mechanism of adsorption of butyn-2-diol-1,4 on Rh-Zr and Zr skeleton electrodes showed that the electrooxidation current is hardly affected by the p H of the media (o.INH,SO, ando.1 NKOH), or bythe potentials at which the double layer is formed. The dehydrogenation current is proportional to the initial diol concentration. Adsorption of the diol occurs by a chemical mechanism.

Carbon Dioxide Methanation on a Ruthenium Catalyst P. J. LUNDE and F. L. KESTER, Ind. Engng. Chem., process Des. Dev., 1974, 13, (I), 27-33 The rate of mcthanation of CO with H, was empirically determined at 200-350'F on a 0.576 Ru/Al,O, catalyst according to 4H,(g) +CO,(g)% 2H20(g) 'CH,(g) 4-43 kcal. Various feed ratios of H, :CO, were investigated. Theoretical equilibrium compositions for the feed mixture from 200-8cx1~F are given.

Hydrogenolysis ofgern-Dimethylcyclobutane on Group VIII Noble Metals

ZOTOVA, E. I. VOSTOKOVA and A. L. LIBERMAN, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1974, (2), 363-365 Hydrogenolysis of gem-dimethylcyclobutane on 20wt.% Pt/C, Pd/C, RhIC, Ir/C and Ru/C occurs selectively at the unshielded bonds and produces 2, 2-dimethylbutane.

0. V. BRAGIN, E. G. KHELKOVSKAYA-SERGEEVA, S . V.

HOMOGENEOUS CATALYSIS Homogeneous Hydrogenation of Sulpho- lene-3 into Sulpholane in the Presence of the Reduced Complex of PtCl,(H,O)[P(C,F,),] v. F. ODYAKOV, K. I. MATVEEV, N. N. SUSHILOVA and A. v. MASHKINA, Kiizet. Kataliz, 1974, 15, (I), 76-81 Sulpholene-3 in the presence of PtCl,(H,O) [P(C,F,),1 reduced by H, is converted to sulpholane at 25°C with only partial intermediate isomerisation to sulpholene-2. Rate of hydrogenation is proportional to total Pt concentration, tending to a maximum at increased concentration

of sulpholene-3 and increased pHz. Activation energy is 10.9& 1.3 kca1,hnole. Butadiene activates the catalyst and SO, in low concentration poisons it.

Palladium-catalysed Linear Dimerisation of Conjugated Dienes A. D. JOSEY,J. Org. Chem., 1974, 39, (21, 139-145 The dimerisation of isoprene in the presence of bis(tripheny1phosphine) maleic anhydride palladium(0) occurs in exclusively tail-tail fashion to give 2,7-dimethyl-1,3,7-octatriene. 2-Ethyl- 1,3- butadiene is dimerised similarly to give the corresponding 2,7-diethyl derivate. The isoprene-butadiene codimer is rearranged by catalytic amounts of base to a single conjugated triene or cyclised by stoichiometric base to isomeric dimethylcyclohep tadienes.

Study of the Direction and Selectivity of the Hydrogenation of Acetylene IIydrocarbons in the Presence of the Chloro(dimethy1- su1phoxidc)palladium Complex L. KH. FREIDLIN, YU. A. KOPYTTSEV and N. M. NAZAROVA, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1974, (311 604-60s Hydrogenation of C =C bonds catalysed by chloro(DMS0) Pd complex is zero order with respect to the substrate; the reaction rate is not related to the length of substituted hydrocarbons. Monosubstituted alkyl acetylenes are reduced at a lower rate than disubstituted acetylenes. Reduc- tion of alkyls occurs by stages with high selectivity and stereospecificity. Diphenylacetylene is reduced by a stageless mechanism to form diphenylethane.

Noble Metal Catalysis. 111. Preparation of Dialkyl Oxalates by Oxidative Carbonylation D. M. FENTON and P. J. STEINWAND, J . Org. Chem., 1974, 39, (5)> 701-704 Dialkyl oxalates were prepared by oxidative carbonylation in the presence of alcohols and dehydrating agents using a Pd redox system and 0 2.

Effect of the Nature uf the Oxidiser on the Rate of Oxidation of Ethylene in the Pres- ence of Aquo-complexes of Palladium(I1) N. B. SHITOVA, L. I. KUZNETSOVA and K. I, MATVEEV, Kinet. Kataliz, 1974, 15, (I), 72-75 C,H, was oxidised over aqueous acidic Pd,SO, solutions with n-benzoquinone, Fe,(SO,), and K,Cr,O,. n-C,H,O, is stable up to [n-C,H,O,]/ [Pd] =I. Reaction rate is not related to n-C,H,O, concentration at [n-C,H,O,] /[I'd] ~1.5-8.0. Pd is precipitated when [Fe3T]/[Pd] > 200. n-C,H,02 is better able than Fe3+ to form Pd(0) complexes. Reaction rate is proportional to the square root of Cr,02- concentration. The limiting stage of the reaction is a stage in the oxidation of Pd(0) to Pd(I1) complexes.


Hydrogenation of Unsaturated Hydrocarbons in the Presence of Platinum Group Metals and Phosphorus-containing Polymers R. G. MURATOVA, R. Z. KHAIRULLINA, S . V. SHULYNDIN, B. E. IVANOV and R. I. IZMAILOV, Kiner. Kataliz, 1974, 15, (I), 137-140 Studies of the liquid-phase hydrogenation of isoprene, phenylacetylene and hexyne-1 in C,H,OH solution in the presence of PdCl, or H,PtCl, with P-containing polymers at 10-40°C showed that the polymer increases the rate of hydrogenation by-from 1.5 to 10 times. There was a negative temperature coefficient of hydrogenation of isoprene and phenylacetylene. It is suggested that the hydrogenation occurs in stages and that the thermal effect of intermediate complex formation is larger than the activation energy for conversion of intermediates to the final product.

Mechanism and Kinetics of the Decarbonyla- tion of Para-substituted Benzoyl and Phenyl- acetyl Chlorides by Chlorotris(tripheny1- phosphine) rhodium(1) J. K. STILLE and M. T. REGAN,J. Am. Ckem. soc.,

Mechanism of Decarbonylation of Acid Chlorides by Chlorotris(tripheny1phosphine) rhodium(1). Stereochemistry J. K. STILLE and R. W. FRIES, Zbid., 1514-1518 Mechanism of Acid Chloride Decarbonylation with Chlorotris(tripheny1phosphine) rhodium (I) Stereochemistry and Direction of Elimination

15 18-1522 Studies using RhCl(Ph,P), indicated the mechanism and kinetics for decarbonylation of para- substituted benzoyl and phenylacetyl chlorides, acid chlorides and acid chloride decarbonylation.

Aspects of Catalysis. Part 11. Dimethyl Sulphoxide Complexes of Iridium(II1) including Hydrides Y. M. Y. HADDAD, H. B. HENBEST and J. TROCHA- GRIMSHAW, J. Chem. SOC., Perkin Trans. I., 1974,

The preparation of a number of DMSO Com- plexes of Ir(II1) is described, including the catalytically active dichlorotris(DMS0) hydrido- iridium(1). Structures of these complexes are assigned.

Hydrogen Transfer Reactions Promoted by Iridium Complexes R. Z A ~ L L A , P. CANZIANI, R. ROS and M. GWIANI, J. Oreanometal. Chem., 1974,67, (31,449-454 The use of Ir(1) complexes to promote hydrogen transfer from EtOH to diphenylacetylene to give trans-stilbene is described and a reaction mechanism is proposed.

1974, 941 (5)J 1508-1514

J. K. STILLE, F. HUANG and M. T. REGAN, Ibid.,

(5)J 5g2-595

Reactions of RuCI,(PPh,) with Carbinols: Formation of Ethers, Hydrogen-Deuterium Exchange, and Racemisation of Optically Active Alcohols Y. SASSON and J. BLUM, 3. Ckem. soc., Chem. Commun., 1974, (81, 309-310 Studies of RuC1,(PPh3), catalyst during conversion of tertiary and substituted secondary carbinols into ethers, H-D exchange in primary and secondary alcohols, and racemisation of optically active alcohols showed the intermediacy of Ru alkoxides, and P-H, transfer in the formation of Ru hydrides from carbinols.

CHEMICAL TECHNOLOGY Corrosion Behaviour of Titanium and Its Palladium Alloy during Heat Transfer in Moving Solutions.

Zaschita Met., 1974, 10, (I), 28-32 Corrosion studies of T i and 0.2% Pd/Ti during the heat exchange in moving 5-200//0 HCI showed that the corrosion resistance depends on the temperature of the media, quantity of heat trans- ferred and the direction of the thermal current. Temperature range of corrosion resistance increased in turbulent flow around the disc electrode in the air absorbed HCI.

I. V. RYSHKIN, M. G. KOLOSOV and N. D. TOMASHOV,

ELECTRICAL AND ELECTRONIC ENGINEERING Structure and D.C. Electrical Properties of a Au-Rh-Glass Thick-Film System J. W. M. BIZSTERBOS,~. Appl. Phys., 1974, 45, (I),

The structure and d.c. properties of a metal-glass thick-film system were studied and the influence of the firing treatment, and of the film composition are discussed. Different types of conduction observed in this thick-film system are correlated with film structure.

153-160

TEMPERATURE MEASUREMENT Catalytic Effects on Pt-Pt/Rh Thermocouples in Combustion Systems Involving Hydrogen as the Fuel

3. Phys. E, Sci. Instrum., 1974, 7, (I), 65-66 Extensive tests were carried out to assess the performance of quartz sheathed Pt:139: Rh-Pt thermocouples in a stirred reaction which was fuelled with H,. Observation of thermocouples contamination by SiO, when heated for 50h at IZOOT showed. 196 increase in the indicated temperature of 0.076 mm diameter Pt:13O/o Rh-Pt thermocouples.

M. V. D. 'SOUZA, G. A. KARIM and M. RASHIDI,


N E W P A T E N T S METALS AND ALLOYS Tarnish Resistant Alloy PENNWALT CORP. US. Patent 3,767,391 A tarnish-resistant alloy, especially useful in the presence of S and S-containing environments, contains 39-47V0 Au, 9-1276 Pd and the balance AgandCuwithaAg:Curatioof I:I to 1.5:1.

Radioisotopic Heat Source

U.S. Patent 3,767,930 A radioisotopic heat source includes a core of heat-productive, radioisotopic material, an impact- resistant layer of graphite surrounding the core and a shell of Ir metal between the core and the impact layer.

Bright Cast Alloy

U.S. Patent 3,769,006 An improved Au alloy casting composition has sufficient A1 and/or Si to form a lustrous oxidation- resistant surface coating during and after casting. Typically 0.08-0.327; A1 is added to a Au dental alloy containing 3"/0 Pd, 84; Pt, <1"/0 In and Sn and 0.25% Fe.

U S . ATOMIC ENERGY COMiMISSION

WILLIAMS GOLD REFINING CO.

CHEMICAL COMPOUNDS Organic Palladium Compounds in Organic Synthesis HERCULES INC. U S . Patent 3,783,140 An organic group is introduced into an ethyleni- cally unsaturated carboxylic acid using an organic Pd complex formed in situ. In an example, a mixture of phenyl mercuric chloride, Li Pd chloride and acrylic acid is formed in ace'conitrile as solvent. This results in the formation of an unstable adduct between the acrylic acid and phenyl Pd chloride.

ELECTROCHEMISTRY Rhodium and Molybdenum Mixed Oxide SOLVAY ET CIE. U.S . Patent 3,773,915 An oxidic compound of Rh and Mo of empirical formula Rh,MoO 6, having semiconducting properties, is suitable for coating electrodes.

ELECTRODEPOSITION AND SURFACE COATINGS Rhodium Plating Bath

British Patent 1,346,753 A bright deposit of improved properties is

AMERICAN CHEMICAL & REFINING CO. INC.

obtained from a bath containing 1.030 g/1 Rh ions, 0.05-5.0 g/1 A1 ions, 50-400 g/1 sulphamic acid and 1.0-25 g/1 of a polybasic organic carboxylic acid.

Chemical Plating Sensitiser RCA CORP. British Patent 1,348,793 The chemical deposition of Pt, Pd, Au, Coy Cu, Ni, etc., on non-conducting surfaces, such as plastics materials, may be sensitised by treatment with a solution containing both divalent and tetravalent tin ions. In one example a solution of SnCl, and SnC1, is used to treat a plastics surface before a Pd catalyst for chemical Ni plating is deposited.

Chemical Plating of Polypropylene

British Patent 1,348,842 In order to enable polypropylene to be plated using a conventional SnC1,-PdCI pretreatment, a small amount of a phenolic compound and/or resin compound is added.

Sensitising for Chemical Plating KOLLMORGEN COW. British Patent 1,349,666 A solid sensitising composition that readily dissolves to a clear solution contains a Pt group metal, a Group IV metal and an anion capable of forming a stable compound with both valencies of the Group IV metal. The ratio of the three components varies from I:I:~ to 1:6:24. The preferred metals are Pd and Sn.

Undercoat for Rhodium Plating AMPEX CORP. U.S. Patent 3,767,369 Rh-plated articles are given superior wear qualities by providing an undercoating of a Sn-Ni alloy. The undercoat is particularly applicable for metallic discs having a magnetic coating used for data or TV recording. The amount of Rh used may also be reduced.

Deposition of Metals or Oxides on a Metallic Support by Cathodic Sputtering PROGIL US. Patent 3,773,639 A precious metal or its oxide is deposited on a metallic support by first submitting the metallic support to ionic bombardment in a rare gas atmosphere, then, without cooling below 300"C, depositing the precious metal by cathodic sputtering conducted first in a rare gas atmosphere and then in an atmosphere of mixed 0, and rare gas. Pt can be deposited on T i in this way to provide electrolysis electrodes.

Selectively Depositing a Metal on a Substrate WESTERN ELECTRIC co. U.S. Patent 3,775,121 Selective chemical plating is achieved by sensitis-

DIAMOND SHAMROCK CORP.

Platinum MetaZsRev., 1974, 18, (3), 115-120 115

ing the substrate surface and depositing an activator such as Pd. The activator is poisoned to destroy its activity. UV radiation through a mask or image is used to reactivate the activator only in selected areas. The activator is available to bring about chemical plating of those areas.

Electrodeposition of Rhodium

U.S. Patent 3,775,267 Plating with a soluble Rh electrodc is achieved by maintaining a constant Rh concentration in the electrolyte, the continuous dissolution of the Rh anode being effected by imposing a pulsed signal on to it.

BELL TELEPHONE LABORATORIES INC.

JOINING Titanium Brazing Alloy ALLOY METALS INC. U.S. Patent 3,778,258 A strong, ductile, corrosion-resistant alloy suitable for brazing T i and Ti-based alloys contains about 3-30?; Al, about 3-17o/n Pd and about 55-95?; Ag.

Platinum-based Weldable Material

French Patent 2,171,659 A Pt-based welding material comprises PtO, and 0 . 0 0 5 ~ . 2 0 / ~ (based on the PtO,) of Y ; it may also contain at least one lanthanide oxide.

COMPTOIR LYON-ALEMAND-LOUYOT

HETEROGENEOUS CATALYSIS Catalytic Composite

British Patent 1,345,611 A complex catalyst for hydrocarbon conversion is produced by dissolving GeCl, in an anhydrous alcohol, equilibriating the solution and mixing it with an aqueous Pt metal solution. The product is used to impregnate a porous support, e.g. y-Alz03. After firing, the support should contain o .or-~y~ Ge, O.OI-Z?/~ Pt group metal and 0.5-4% C1,. Pt itself is preferred.

Dehydrogenation Catalyst

British Patent 1,345,612 A dehydrogenation catalyst is formed by mixing an alcoholic Ge tetrahalide solution with aqueous solutions of a Pt group metal compound and an alkali metal compound. The mixture is used to impregnate a porous support such as AlzO,. Preferably the catalyst after calcining contains 0.05-57; Ge, 0.05-596 Pt and 0.01-1.5"/0 Li.

Hydrogenation of Hydrocarbon Resins EASTMAN KODAK co. British Patent 1,345,619 Petroleum resins produced by the polymerisation of unsaturated feedstocks over metal chorides are

UNIVERSAL OIL PRODUCTS CO.

UNIVLRSAL OIL PRODUCTS CO.

improved by hydrogenation, preferably in the presence of a Pd catalyst.

Hydrogen Cyanide Production

British Patent 1,345,785 HCN is produced in the vapour phase by the reaction of 0,, NH, and a hydrocarbon over a Pt group metal catalyst, especially a gauze made from an alloy of Pt with up to 20q/, Rh.

Platinum Metal Catalysts

British Patent 1,348,653 Where Sn accompanies Pt (or another Pt group metal) in a supported hydrocarbon conversion catalyst, a more active catalyst is produced when the Sn is supplied to the support as a stannate ion. For example Al,Os may be impregnated using a Pt salt solution and a Na stannate solution.

Acetic Acid Production

British Patent 1,349,100 C,H, is oxidised to CH,COOH in the presence of added HzO and a supported catalyst containing Pd metal and H,PO,. A1,0, and C supports are mentioned in the examples and they carry 0.01- 5 "6 Pd and at least 2 7; H,PO,.

Ruthenium Catalyst DIAMOND SHAMROCK cow. U.S. Patent 3,766,089 An improved Ru catalyst is prepared by im- pregnating a catalyst support with a RuCl, solution, drying the impregnated support and then partially reducing the dried RuCl, coating on the support. The catalyst is useful in the hydrogenation of the pyrroles. Spent catalyst can be rejuvenated by recoating with RuCl, solution, drying rhe coated spent catalyst and then partially reducing the RuC1, coating.

Auto Emission Catalyst

U.S. Patent 3,770,659 The active catalyst for burning exhaust gases from an internal combustion engine consists essentially of a sorptive A1,0, matrix, 5-180/, MnO, 2-87; Cr,O, and 0.01-0.2% Pd, the unit weight ratio of MnO to Cr,O, being 2-3.5 and the total weight of such oxides being 8-24o/b.

Preparation of a Catalytic Composite

U.S. Patent 3,772,213 A Pt group component and a Ge component are uniformly dispersed throughout a porous high surface area carrier material by treating a GeCl, /anhydrous alcohol solution with an aqueous solution of a H,O-soluble, decomposable compound of a Pt group metal and using this as the impregnation solution.

E.I. DU FONT DE NEMOURS & CO.

SHELL INTERNATIONALE RESEARCH MIJ. N.V.

NATIONAL DISTILLERS & CHEMICAL CORP.

AIR PRODUCTS & CHEMICALS INC.



Hydrocarbon Isomerisation Process

U S . Patent 3,772,397 Hydrocarbons are isomerised using a catalytic composite comprising a combination of a Pt group component and a Sn component with a porous carrier material, e.g. 0.75O/b Pt and 0 . 5 ~ 4 Sn on y-Al,O,.

Hydrocracking Process

U.S. Patent 3,775,297 Fresh gas oils are converted to high quality motor fuels and naphthenic lubricating oils by hydrocracking at 720-750'c in the presence of crystalline zeolite hydrocracking catalyst containing a hydrogenating component, e.g. Pd, the catalyst having been preconditioned to a predetermined state of deactivation. Preconditioning is accomplished by accelerated coking with an aromatic gas oil at 800-900°F. The preferred catalyst consists of o.I-I~* Pd on a Y-zeolite.

Hydrocarbon Conversion with a Catalytic Composite of Platinum, Iron and Germanium

U.S. Patent 3,775,300 Hydrocarbons are converted by contacting them with a catalytic composite of a Pt group metal component, an Fe component and a Group IVA metallic component with a porous carrier material, e.g. 0.3750/0 Pt, 0 . 5 7 ~ Ge and 0.1% Fe on A1203 containing 0.85:); Cl,.

Hydrocarbon Conversion with a Trimetallic Catalytic Composite

U.S. Patent 3,775,301 Hydrocarbons are converted by contacting them with a combination of a Pt group metal component, a Re component and a Ge component with a porous carrier material, e.g. 0.1% Re 0.2% Ge and 0.5% Pt on Al,03 containing 0.85:; C1,.

Dehydrocyclisation of Paraffins

U.S. Patent 3,775,502 A Na zeolite X or Na zeolite Y, is ion-exchanged with from 0.10-1.2"/, Pt. The catalyst is calcined and the Pt then reduced with H, to the free metal to catalyse the dehydrocyclisation of 6-roc paraffins.

Reforming Catalyst CITIES SERVICE OIL co. U.S. Patent 3,776,860 An improved reforming catalyst has an A120, support impregnated with Pt, Re and a rare earth metal. Preferably the catalyst composition comprises Pt, Re and rare earth metals such as Nd, Pz, Sm and Yb each in amounts of from 0.1-5yo.


SUN OIL CO. OF PENNSYLVANIA



SUN RESEARCH & DEVELOPMENT CO.

Platinum and Lead Catalyst ASAHI KASEI K.K.K. U.S. Patent 3,781,221 Selective reforming catalysts contain an Also, carrier, with pores of a diameter distribution having a peak in the range of 2,000-7,000~ supporting Pt and Pb. The pores are obtained by burning out an organic material uscd in shaping the catalyst support.

Hydrocarbon Conversion Catalyst

French Patent 2,164,986 A hydrocarbon conversion catalyst consists of an Al,O,-supported mixture of Pt, I r and Sc, Y , Ac, Ti, Zr, Hf, Thy Ge, Sn or Pb, e.g. 0.2% Pt, 0.05% Ir and 0.5"/~ Th. In French Patent 2,165,056 the third element is 0.59:, of U, Pa, Gay V, or Tc.

Carbon Catalyst Supports

Active C is treated with an aqueous solution of a volatile acid, e.g. HCl, and dried before treatment with a mineral base such as NaOH. This dual treatment is said to improve the catalyst support properties. In one example this support is impregnated with RhCl[P(OPh),],.

Catalyst

German Oflen. 2,229,210

A catalyst for the treatment of exhaust gases and for production of CH, by the steam reforming of naphtha comprises a refractory support coated with a first layer of one or more oxides of Ti, Zr, Hf and T h and a final layer of a mixture or alloy of l't, Rh (1-50:b) and optionally base metal (0.01-25q6). Preferably the base metal is Ni or Cu and the final coating contains 0.01-10;; by weight of the total metal content.

Dehalogenation Catalysts KNAPSACK A.G. German Offen. 2,240,466 The dehalogenation of organic compounds, especially the dechlorination of polychloroacetic acids, is catalysed by a supported Pd catalyst in which the Pd is enriched on the surface.

Zeolitic Catalyst

Dutch Appln. 72. 11,593 Catalysts for selective hydrocracking and other reactions are prepared by a specified system of heat treatment of a cation-exchanged zeolite, such as KS 01, on which a metal, such as Pd, Pt, Ru and Rh (among others), is deposited.

Ketone Production Catalyst

Dutch Appln. 72. 11,914 Ketones are produced by the reaction of mer- captans with H,O in the presence of a supported

STE. FRANCAISE DES PRODUITS POUR CATALYSE

STE. RHONE-PROGIL French Patent 2,165,280

JOHNSON, MATTHEY & CO. LTD.




Group VB, VIB and/or Mn sulphide catalyst promoted by a Group VIII metal such as R h or Ir. In one example butanethiol-z is converted to butanone-z in the presence of a sulphided mixture of Mo and Rh on Ala03.

HOMOGENEOUS CATALYSIS Olefin Production

British Patent 1,344,887 British Patent 1,278,806 describes a process in which 1,6- and/or 1,7-octadienes are produced by contacting one or more acyclic conjugated dienes with metallic Pt, Pd, Rh, Ru, or 0 s in a polar solvent. It has now been found that the process may also be carried out in a non-polar solvent such as C&.

IMPERIAL CHEMICAL INDUSTmES LTD.

Adipic Acid Production

British Patent 1,348,800 Butadiene is reacted with CO and H,O to give adipic acid in the presence of a Rh catalyst activated with an organic halide in the absence of acid. Thus Rh(CO),Cl can be used in the presence of CHJ (used in all the four examples).

Silicon Rubber Production GENERAL ELECTR~C CO. British Patent 1,349,311 New Si rubbers are produced from silyl isocyanurates in whose production Pt catalysts may be used for the silylation reaction.

Platinum Complexes of Unsaturated Siloxanes GENERAL ELECTRIC co. U S . Patent 3,755,452 Pt complexes of unsaturated siloxanes are provided which are useful as hydrosilation catalysts. These Pt-siloxane complexes can contain an average of up to-1 g.atom of halogen per g. atom of Pt, but include complexes which are substantially free of inorganic halogen.

Production of Alcohols

U.S. Patent 3,766,279 Aldehydes are converted to higher molecular weight alcohols by simultaneous aldol condensation and hydrogenation reactions which are catalysed by a Ru-biphyllic ligand catalyst, e.g. RuCI,(PPh,),.

Activator Solutions for Electroless Plating ENTHONE INC. U.S. Patent 3,767,583 Surfaces intended to be elecuolessly metal plated are treated with a colloidal catalyst metal-free acid liquid solution of a soluble, Lewis base- modified noble metal-Sn halide complex until the surface becomes catalytic, e.g. a PdCI2-SnCI,- CHsOH complex.

BADISCHE ANILIN- & SODA-FABRIK A.G.

UNION OIL CO. OF CALIFORNIA

Alcohol Amine Interchange

U.S. Patent 3,767,709 A tertiary amine is reacted with an alcohol or aldehyde in a liquid reaction medium containing a Ru, Os, Re, or T c catalyst which is preferably in complex association with a biphyllic ligand to interchange the hydrocarbyl portions of the reactants. In a typical process tributylamine is contacted with octanol in the presence of RuCl, and Ph,P to produce butanol and octyl dibutyl- amine. Aldehydes can be similarly reacted under H, pressure.

Oxidation of a-Aryl Alcohols

U.S. Patent 3,769,325 Aryl alcohols or their ethers are oxidised to aldehydes, ketones or esters using Group VIII arsine, phosphine, stibine or bismuthine complexes, e.g. a RhCI, or PdCl2-PhsP complex.




Redox Catalyst System for Ethylene-Vinyl Grafted Copolymer Dispersions

K persulphate, a Pd salt and ammonium ferric sulphate are used as a redox system for graft copolymerising EVA emulsions with vinyl chloride or another monomer.

WACKER-CHEMIE G.m.b.H. U.S. Patent 3,773,699

Process for Benzyl Ketones STANDARD OIL CO. U.S. Patent 3,773,837 Benzyl ketones are produced in a one-step process by reacting C,H, with a ketone at elevated temperatures in the presence of a divalent Pd salt of a carboxylic acid and a strongly acidic catalyst.

Preparation of Unsaturated Esters ESSO RESEARCH &! ENGINEERING CO. U.S. Patent 3,77 j 4 6 9 Unsaturated esters are prepared through the reaction of a 4-6C aliphatic conjugated diene with a carboxylic acid in the presence of a Pd catalyst, or organic phosphine or phosphite ligand modifier and a promotor compound such as NaBH, or acetic anhydride. The reaction is carried out in the absence of tertiary arnines and in the substantial absence of 0,. Pd acetylacetonate is used in the examples.

Platinum or Palladium Phosphinite Catalysts

U.S. Patent 3,776,929 Compounds of formula (L),MXY, where L is a phosphinite, phosphonite, thiophosphinite or dithiophosphonite ligand, M is Pd or Pt, and X and Y are alike or different and are selected from C1, Br, I, various substituted and unsubstituted alkyls and aryls, cyano, SnCI,, isocyanate, thiocyanate, aroyl, and 10- perAuoroslky1

E. I. DU PONT DE NEMOURS & CO.

lower

groups are produced by reacting one equivalent of a source of MXY with two or more equivalents of a selected P-containing ligand. The products, e.g. PtCl ,-(dimethyl phenyl phosphinite) are useful in the alkoxycarbonylation of olefins and in the polymerisation of acetylene.

Preparation of Alkadienoic Acid Esters

U.S. Patent 3,780,074 Esters of alkadienoic acids are prepared through the reaction of 4-12C aliphatic, acyclic, conjugated diolefins with a I-zoC monohydroxy alcohol and either gaseous CO or gases containing CO in the presence of a catalyst system including zerovalent Pd, e.g. Pd(PPh,),.

Synthesis of Pyridine Bases

U S . Patent 3,781,292 Pyridine bases are produced by reacting olefins with NH, in the presence of a Pd tetrammine complex whose activity is enhanced by means of a Cu (11) salt and 0,. Thus PdCl,, NH, and CuCl, may be used in picoline production.

Preparation of Aromatic Isocyanates OLIN CORP. U.S. Patent 3,781,321 The complex PdL(CO)X,, where L is a hetero- cyclic N compound such as lutidine and where X is a halogen, is prepared by reacting CO with a Lewis base and a Pd dihalide andlor a mixture of elementary Pd with an acid halide, in the presence of a liquid reaction medium. The resulting cornL- plex is useful as a catalyst in the preparation of organic isocyanates by reacting CO with an organic nitro compound.

Preparation of a-Hydroxyamides

U.S. Patent 3,781,351 Formamide or a substituted formamide is reacted with a 2-IZC carbonyl compound in a liquid reaction medium containing a Ru or 0 s catalyst, preferably complexed with a biphyllic ligand, at 5c-3oo0C to form an whydroxyamide. In a typical process formamide is reacted with an excess of benzaldehyde in the liquid phase in the presence of RuC1, complexed with triphenyl phosphine to produce alpha-hydroxyphenyl aceta- mide.

ESSO RESEARCH & ENGINEERING CO.

YAWATA CHEMICAL INDUSTRY CO. LTD.


FUEL CELLS Fuel Cell Electrode

A fuel cell electrode has an anodic catalyst including Pt and Rh oxides and a Ni, Co, Fe, or Cu oxide together with a component convertible to W oxide to provide high electrical performance at very low noble metal loadings. A typical mixture of oxides contains 2g Pt, o.Ig Rh and 1.9g Ni.

UNITED AIRCRAFT CORP. U.S. Patent 3,755,947

Fuel Cell Electrode

Dutch Appln. 7 ~ 1 4 , 9 0 0 A fuel cell electrode has an electrically conducting metal grid with a catalyst-containing coating which has one or more layers varying in porosity. The catalyst layer, for example, consists of ptfe particles forming a matrix containing Pd, Pt or Ag catalyst.

STUDIECENTRUM VOOR KERNENERGIE

CHEMICAL TECHNOLOGY Preparing Radiation Source Material

U.S. Patent 3,773,295 A uniform dispersion of a radioisotope within a noble metal matrix is provided by chemically plating a noble metal coating on to particles including a dissociable compound of the radioisotope. For example, Pd in the presence of H, can be deposited on Cf oxalate particles containing Cf-252. The coated particles are dried and the oxalate decomposed to Cf oxide.

Diffusion Cell

U.S. Patent 3,782,077 A H, diffusion unit for separating mixtures from gaeous mixtures containing H, has two super- imposed metal foils such as Ag/Pd foils, bonded together at their edges to form an envelope. At least one of the foils is corrugated or undulated and each corrugation or undulation is supported by a helix of stainless steel or like wire.

Fogged, Direct-positive Silver Halide Emul- sion Layer FUJU PHOTO FILM co. LTD. U.S. Patent 3,782,957 Pt group metal compounds such as K,RuCl, are used with methine dyes in photographic sen- sitisation.

U S . ATOMIC ENERGY COMMISSION

JOHNSON, MATTHEY & GO. LTD.

GLASS TECHNOLOGY Glass Feeders

British Patent 1,350,644 New alloys for glass feeders consist of 14-85:/0 Pt, 15-857L Rh and O.I-I% of an additional metal selected from Mo, W, Ir, and Re in an amount only sufficient to increase the ductility of the alloy.

Alloy Glass Fibre Forming Bushing

U.S. Patent 3 ,771 ,728

A high temperature-high strength alloy containing Pt, Rh and one or more of Mo, W, Ir, and Re is fabricated into apparatus adapted to receive and controllably emit molten material for attenuation into glass fibres. One example of the alloy contains 7906 Pt, 20.99~6 Rh and o.oI:/, Mo.

OWENS-CORNING FIBER-GLASS CORP.

J. H . HANSEN 82 R. W. BET2


ELECTRICAL AND ELECTRONIC ENGINEERING Resistors OWENS-ILLINOIS INC. British Patent IJ45,549 PdO and related metal oxide resistors are very sensitive to firing schedules and their stability is low. These problems are now overcome by the use of metallising compositions which contain an organic Pd, Rh, Ir, Ru, or In compound.

Electrically-insulating Seal between a Metal Body and a Semiconductor Device R.C.A. CORP. U.S. Patent 3,769,688 A seal is built up by oxidising the surface of the semiconductor, depositing a layer of Si, evaporat- ing Pd on to the Si and finally covering the Pd with W, Ni and a solder.

Printed Dieleetric/PaIladium-SiIver Struc- tures

U.S. Paten6 3,770,496 In a method for printing multilayer electronic structures on a substrate which minimises degradation at crossovers, at least ZOO;, Ag is incorporated in the metallisation used to print the Au electrode which is used with dielectric crossovers and a Ag or Ag:Pd electrode.

Electrical Resistance Compositions

U.S. Patent 3,776,772 An electrical resistance composition comprises particles of RuOz coated with Nb andlor Nb oxide and a glass frit. In one example the composition contains RuO,/Nb particles (12 parts) with 63 parts glass frit and 25 parts alkyd resin solution.

Electro-conductive Material and RuO,

US. Patent 3,778,389 An electro-conductive material, essentially con- sisting of a double oxide obtained from PbO and RuO, in a molar ratio of 3:1 to I :3, is useful as the fundamental composition for production of a resistor paste, a ceramic resistor or the like.

Tungsten Electrical Switching Contacts ECHLIN MANUFACTURING CORP. U.S. Patent 3,778,576 The contacts consist of a porous body, obtained by leaching Fe from a W, Mo, Re, or Nb alloy, plated with a thin layer of Au, Ag, Pt, I'd, or Rh and then with Ni or Co.

Method of Platinum Diffusion in Semi- conductors T.R.W. INC. U.S. Patent 3,783,049 A controlled degradation of minority carrier

E. I . DU FONT DE NEMOURS & CO.

SHOE1 CHEMICAL INDUSTRIES CO. LTD.

MURATA MANUFACTURING CO. LTD.

lifetime in a Si semi-conductor crystal body uses H,Pt(OH)6 as a source of Pt. One gram of H,Pt(OH), is dissolved in 130 cm' anhydrous acetone and approximately 0.05 cm2 of this solution is placed on the surface of a Si semiconductor crystal body. The solution is dried and the body is then heated to the Pt diffusion temperature for a time sufficient to have Pt atoms uniformly dis- tributed throughout the active portion of the Si crystal.

Process for Making Capacitors

U.S. Putent 3,784,887 An improved process for making multilayer monolithic capacitors uses metallised areas which can be cofired with reactive dielectric materials at elevated temperatures. The metallisation materials contain critical proportionate amounts of Pt and/or Au and Pd and optionally Ag.

Resistance Pastes

German Offen. 2,234,543 Pd, Ru and other noble metal sulphides are used as semiconducting constituents in resistance pastes. Noble metal or metal alloy powders may also be present. In an example PdS is used with B oxides, red Pb, SiO,, and ZnO to form a frit used in screen printing compositions.

Resistance Pastes

German Offen. 2,234,644 Pastes for the production of fired electrical resistances are based on the use, as conductor, of semiconducting mixed crystals of PdO and CuO, optionally accompanied by a noble metal powder, e.g. a Ag-Pd alloy powder.

E.I. DU PONT DE NEMOURS & 60.

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT

TEMPERATURE MEASUREMENT Thermistors

Thermistors are provided in which the thermally sensitive semiconducting material has the formula PbO.PdZO,, where 2 is selected from Cr, Mo, W, and S. The thermistor device can be made by dipping two closely spaced electrical conductors into a melt of the thermally sensitive semiconducting material to form an element of the material between the conductors.

Resistance Thermometer Element

U.S. Patent 3,781,749 A temperature-sensitive element is made from a layer of glass containing conducting particles attached to a non-conducting support. Au, Ag, Pt metals, Fe, Ni, Co, or Cu may form theparticles.

GENERAL ELECTRIC CO. U.S. Patent 3,766,511

JOHNSON, MATTHEY & CO. LTD.


PLATINUM METALS REVIEW · important. Alumina, magnesia, zirconia, and thoria have all been employed...

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Transcript of PLATINUM METALS REVIEW · important. Alumina, magnesia, zirconia, and thoria have all been employed...