PLATINUM METALS REVIEW - Johnson Matthey...processing and utilisation of soybeans began a few years...

PLATINUM METALS REVIEW

A quurterly survey of reseurch o n the platinum metuls urrd of dwelopments in their applications in industry

V O L . 15 J A N U A R Y 1 9 7 1 N O . 1

Contents

The Homogeneous Hydrogenation of Soybean Oil Methyl Ester

Further Advances in Catalytic Hydrogenation

The Control of Air Pollution

Platinum and the Refractory Oxides

Monolithic Multilayer Ceramic Capacitors for Hybrid Circuits

Zerovalent Complexes of Platinum

The Form of the Interaction between Palladium and Hydrogen

Cubane-type Platinum Metal Complexes

A New Mining Area for Rustenburg

Abstracts

New Patents

2

8

9

13

19

20

21

25

26

29

35

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, h’latthey & Co Limited, Hatton Garden, London EClP 1AE

The Homogeneous Hydrogenation of Soybean Oil Methyl Ester SELECTIVITY OF PLATINUM AND PALLADIUM COMPLEXES

By Johii C. Bailar, .Jr. University of Illinois

The so?bean, a major crop in the LTnited States as zuell as in China and Brazil, yields an oil used widel?. i n the manufacture of margarines, salad oils, shortening, and other food products. Before use, howecer, it must be up- graded by selective hydrogenation of linolenates to linoleates. This paper describes research on platinum complexes that have been found to be highly selective in this reaction. The work was carried out under contract with the U.S. Department of Agriculture arid zuas supervised hy the Northern Utilisation Research and Decelopment Division of the Agricultural Research Service.

Although the soybean has been a major agricultural product in the Orient for more than three thousand years, it was virtuaily unknown in the western world until about forty years ago. Research on the culture, processing and utilisation of soybeans began a few years before that, and was pursued with great vigour, especially in the United States. Through careful plant breeding, the soybean was adapted to American soils and climate, and it soon became a major crop, especially in Illinois, Indiana, Iowa and other mid- western states.

Soybeans contain up to 20 per cent oil, which is pressed or cxtracted from the beans and is used widely in the manufacture of margarines, shortenings, salad oils and other food products. I t also finds wide industrial

Platinum MetalsRev., 1971, 15, (l), 2-8 2

use in the manufacture of alkyd and poly- amide resins and, in modified form, in drying oils. These uses, however, are much less important than its use in foods. The meal which remains after the oil is extracted from the beans is a valuable by-product, finding extensive use in animal feeds, meat sub- stitutes, and special protein concentrates. World production of soybean oil is much greater than that of any other edible vegetable oil.

Soybean oil is a mixture containing chiefly glycerol esters of long chain organic acids. To simplify the study of this mixture, the glycerol esters are usually converted to methyl esters; thus, each alcohol group is attached to a single acid chain instead of three. Samples of the oil differ somewhat in composition, depending upon the strain of the plant from which the oil came, and the soil and climatic conditions in which the plant grew. A typical oil might contain:

linolenate 7.5 per cent linoleate 50 ,, stearate palmitate 10 ,, oleate 27 $9

4 JY

All of the double bonds have the cis configuration, which is desirable from a practical point of view.

In soybean oil which is to be used in the manufacture of foodstuffs, linolenates are highly objectionable because they have a bitter taste, and palmitates and stearates are somewhat undesirable because, if present in too large amounts, they are difficult to digest. Since it is impractical to separate the desired from the objectional esters in this mixture,

The World's most important edible ixgrtnble oil i s extractedfrom soybeans (or soya brans). Annual production of soybean oil now amounts to over f i ve million metrir toranes. The oil is a mixture of glycerol rsters of long-chain organir arids, inrluding undesirable linolenates. pazmitates and st car ate^. These need removal or substantial redurtion brfore consumption.

(Pzctwe c v u v t c y of b'nilerer Limited,

efforts to upgrade soybean oil have depended largely upon converting linolenates to linoleates by selective hydrogenation. The formation of oleate is less desirable, but even this represents an upgrading of the oil.

Hydrogenation of Linolenic Ester Unfortunately, the double bonds in lino-

lenic cster are remarkably alike, and one cannot rely on any difference in chemical reactivity which will allow the hydrogenation of one of them to the exclusion of the others, or even a difference in rate of hydrogenation. If there is to be highly selective hydrogenation, it must rest upon some peculiar property of the hydrogenation catalyst, and the mechanism of catalyst operation.

Apparently, the first specific attempts to hydrogenate soybean oil selectively were made by Zajcew (I), who used a palladium catalyst at 114T and 47 p s i . of hydrogen.

There was some selectivity, but his product contained 19.1 per cent of saturates. Allen (z), using a nickel catalyst at 285'F and 30 p.s.i. of hydrogen, was much more successful, for he was able to reduce the content of linolenic ester to 1.0 per cent and to increase the content of oleic ester to 61.5 per cent, leaving the stearate at 5.7 per cent.

Various catalysts have been tested as replacements for nickel in the hydrogenation of vegetable oils on a commercial scale but hitherto nickel, e.g. as formate, has been the most important. Specific attempts to hydrogenate soybean oil have been made using salts of chromium, cobalt, vanadium, etc.

The catalysts which are the main subject of this paper are platinum complexes. That they are highly selective in the hydrogenation of soybean oil is illustrated by Table I, which gives data from two typical experiments with soybean oil methyl ester (3).

Platinum MetalsRev., 1971, 15, (1) 3

Hydrogenations of Soybean Oil 1 Ester with Platinum Complexes

I After hydrogenation

Palmitate

10.9

11.8

11.5

A sample of methyl linolenate, after hydrogenation, showed 26.0 per cent monoene and 74.0 per cent diene, with no stearate and no unreduced triene. Unfortunately the “monoene” in the product is not all methyl oleate, for the unreduced double bond is chiefly of the trans configuration and it is not exclusively in the 9-position. While most of the material consists of molecules in which the double bond is near the centre of the chain, there are molecules in which it is as close to the carbonyl group as the fourth carbon atom, and as distant from it as the fifteenth (4).

Catalyst Complexes Our concept of the catalysts which are

described in this article grew out of a note by Cramer, Jenner, Lindsey and Stolberg (5) , who reported that, while H,PtC16.6H,0 is only a mild catalyst for the homogeneous hydrogenation of ethylene, and tin(I1) chloride is not a catalyst at all, a mixture of the two is a remarkably good catalyst. The implication that the two have combined to form a complex has been amply confirmed by later work (6).

Although Cramer et al. ( 5 ) had used the Pt-Sn catalyst for the hydrogenation of a compound containing one double bond, we hypothesised that, with a polyolefinic material, it might catalyse the hydrogenation of only a portion of the double bonds in each molecule. Our f is t experiments were performed with this catalyst, in a solvent con-


sisting of benzene (60 per cent) and methanol (40 per cent) (7). van’t Hof and Linsen (8) have also used this catalyst for the hydrogenation of soybean oil. Their results parallel ours. Later, our catalyst was modified by use of bis-triphenyl-phosphine platinum(I1) chloride (9) instead of hexachloroplatinic(1V) acid. This, when treated with tin(I1) chloride, gives a compound which has the structure

/ /

P h i 1’ 51lC1,

We found this catalyst to be slightly more selective than the original one. The reaction by which tin(I1) chloride inserts itself into the Pt-C1 bond is shown to be reversible by the fact that best results are obtained when a tenfold excess of tin(I1) chloride is used. A larger excess reduces the efficiency of the catalyst, supposedly by the formation of Pt(PPh,),(SnCl,), (10).

The catalyst can be varied in a large number of ways without loss of its selective hydrogenation ability toward soybean oil methyl ester. Trialkyl phosphines or mixed alkyl-aryl phosphines can be used; in fact, P(CH,),Ph gives a much more active catalyst than does PPh,. Methyldiphenylphosphine, P(CH,)Ph,, gives a catalyst of intermediate activity. The catalyst made from trirnethyl- phosphine, however, is not very active (11).

Table I Methyl

Before hydrogenation

I After hydrogenation

2 After hvdronenation

composition (%)

Palmitate

10.9

11.8

11.5

Stearate

3.8

4.4

4.4

Monoene

28.3

78.5

84.1

Diene

50.5

5.4

-

Triene or c-t

conjugated td i e m

6.5

0

t-t conjugated

diene

In the catalysts which have been mentioned, the phosphine ligands occupy trans positions in the complex molecule (12, 13), but this is not an essential feature. Bidentate phosphines, R2PCH,CH,PR,, which must coordinate in cis positions, are also effective (12, 13).

Triphenylarsine and triphenylstibine can be used in place of the phosphine. The arsine complex gives a more active catalyst than the phosphine complex, but it is less stable and suffers from the obvious disadvantage of containing a highly toxic material (14). Diphenyl sulphide and selenide can replace the phosphine, also, but do not give highly active catalysts (12). Lead and germanium chlorides can be substituted for tin chloride, but are much inferior (14a).

The palladium complex, Pd(PPh,),Cl, + SnC1,.2H,O is more active than the corresponding platinum complex and shows good selectivity. It has to be used at a lower temperature, however, for it is considerably less stable (14b).

Bis- triphenylphosphine- dicyano-palladate (II), Pd(PPh,),(CN),, (14b) and bis-triphenylphosphine nickel iodide, Ni(PPh,),I,, (15) are selective catalysts, even without the addition of tin chloride, but in the presence of either of these catalysts, the hydrogenation is slow. The ligands CN- and I-, like SnCl,-, are weak G donors and strong r acceptors (6, 10, 16) and are thus able to adjust the electron density around the Group VIII metal so that it can hold both the hydrogen and the olefin in the coordination sphere, but can release them to combine with each other.

For hydrogenation with the platinum catalyst, a temperature of 90" to 110°C is maintained, and a hydrogen pressure of about 500 p.s.i. At lower temperatures and pressures, isomerisation takes place, but not hydrogenation. In certain applications , this may be a useful property. Bond and Hellier (17) have made detailed studies of the isomerisation of I-pentene using a mixture of H,PtCI, and SnC1,.2H,O. They report that, initially, trans-a-pentene is formed in greater

than the equilibrium amount, but within an hour and a half, equilibrium is reached (81 per cent trans-2-, 17.5 per cent cis-2-, 1.5 per cent I-pentene).

The solvent which was used in our first experiments (a mixture of benzene and methanol) was chosen because it readily dissolves both the soybean oil and the catalyst. It soon became evident, however, that in the absence of hydrogen (and probably, to some extent, in its presence) this solvent serves as a hydrogenating agent by converting the chloroplatinum complex to the hydrido complex, which, in turn, transfers its hydrogen atom to the substrate: =Pt-Cl+CH,OH+ ZPt-H + HCHO - HCl(14b)

Platinum(I1) contains ten electrons less than the next rare gas, so it can coordinate with five donor atoms. Normally, it shows a coordination number of only four, but the presence of the fifth coordination position is essential to its catalytic activity, for it is through this that the olefin group is attached.

In the presence of hydrogen and the olefin, the platinum compound is converted to the five coordinate complex [Pt(PPh,),(SnCl,) H(ol)] (12). Several compounds of this general formula have been isolated, including those in which "ol" represents 4-octene and 1,4- cyclohexadiene. 1,s-Cyclooctadiene forms a compound in which each double bond is attached to a molecule of the catalyst. The presence of any strongly coordinating sub- stance blocks the fifth coordination position and destroys the catalytic activity of the platinum. Even the solvent may play this role. It has been found that hydrogenations with the platinum-tin catalyst proceed about five times as fast in methylene chloride as in the benzene-methanol mixture, and that they do not go at all in pyridine (12). Methylene chloride and other chlorinated hydrocarbons are poor solvents for the catalyst, but, even so, they offer a great advantage.

Catalyst Selectivity The selectivity of the platinum-tin catalysts

toward large polyenes apparently rests upon


the fact that only conjugated systems are in E may migrate along the chain until it attacked. If the double bonds are not con- approaches another double bond, whereupon jugated, the molecule must isomerise to the hydrogenation step is repeated, until only conjugation before hydrogenation can take one double bond remains. The presence of D place. In a polyolefinic molecule, isomerisa- or a similar molecule is thought to be neces- tion and hydrogenation take place alternately sary for the hydrogenation of the metal-carbon until only one double bond remains, but the c bond. process must then stop. The following It is not necessary that the double bonds be mechanism is suggested (12): (M represents close together in the original molecule. The the Pt(PPh,),SnCl, fragment of the catalyst. dienoic ester CH,CH,CH =CH(CH,),CH ==

Some of the hydrogen atoms are marked, but CH(CH,),COOCH,, in which the double only so the reader may more easily follow the bonds are separated by six carbon atoms, is discussion. No experiments with labelled readily reduced to the monoene stage (IS). materials have been performed in our work.)

B ? c - c - ? , C $ C -

I ; I? c = c - /h H o I

t M H o - H - C - H * k H o 11-C-H" /

H - C - H *

H H I I c - c -

H I1 I I c - c -

II I1 I t c - c -

Compound A contains a ir bond, which readily converts reversibly to the c bonded compound B. Instead of reverting to A, B may equally well go to the conjugated C, this step also being reversible. The platinum atom in B may, however, attach itself to the adjacent double bond through a r-linkage, forming D. The metal-carbon cs bond in D is broken upon hydrogenation to give E. The double bond

Although soybean oil methyl ester, cyclooctadiene, and other fairly large polyene molecules undergo hydrogenation to the monoene stage, short chain olefins behave quite differently. In such cases, even monoenes may be

hydrogenated easily (19). Those with terminal double bonds are readily hydrogenated


Table II Catalytic Hydrogenation of Some Monoenes

with (PPh,),PtCl(SnCl,) in Benzene-Methanol 34 atm. H p , 90"C, 3 hours

Diene used

15

1.4

1,3

2,4

ethylene

propylene

I-butene

cis-Zbutene

trons-2- bute ne

I-pentene

2-pentene* * I-hexene

2-hexene hexadiene

I-hexene cis trons 3-hexene n-hexane 1,5 1,4 1,3 2,4

0.8 5.8 12.2 1 .o 2.5 0 17.0 2.0 58.7

0 5.0 12.5 0 0 0 5.7 3.6 73.2

0 0 7.5 0 0 0 73.1 19.4

0 0 0 0 0.9

I-isomer yo

66

12.0

0

0

11.6

3.0

12.5

2-isomer yo cis

30.3

71 .I

9.8

30.2

27.7

28.5 -

trans

46.4

27.3

89.6

47.2

67.5

41.6

2-hexene

3-hexene

no observable hydrogenation

no observable hydrogenation

* 97% after 1 hour * * This material was 47.9% cis and 52.1% trans

3-isomer yo Saturated hydrocarbon yo

5.4

100 * 34

11.3

1.6

0.6

11.6

1 .a 12.0

to saturation] but show an even greater tendency to isomerise to those with internal double bonds. Both processes probably proceed through the formation of 5 bonded complexes. When the double bond is internal] hydrogenation takes place very slowly; per- haps there is no hydrogenation except as terminal olefins are formed by isomerisation.

As the chain is lengthened, the hydrogenation becomes progressively slower. Apparently, the light molecules form relatively stable complexes with the catalyst. These are susceptible to hydrogenation, but, because of entropy effects, the heavier molecules and those with internal double bonds form complexes of such low stability


Table Ill Hydrogenation of the Isomeric Hexadienes

with (PPh,),PtCl(SnCl,) in Benzene-Methanol 3 hours, 500 psi

that the c bonded complex does not form. The hydrogenation of some short chain monoenes is illustrated in Table I1 (Igb).

With short chain dienes, rearrangement to the conjugated isomer accompanies hydrogenation and in some cases is much more rapid. Once the conjugated hydrocarbon is formed, it does not hydrogenate to any marked extent (19b). This is seemingly because it forms such a stable complex with the platinum that no further reaction can take place. Evidence for this is found in the fact that the addition of a little butadiene to soybean oil methyl ester completely inhibits the hydrogenation of the latter. Table 111 illustrates the behaviour of the hexadienes (19b). It reveals is a great tendency to form conjugated systems, and that migration of terminal double bonds to interior positions takes place easily. Even when double bonds are terminal, the formation of hexane is overshadowed by the formation of a molecule with internal double bonds (preferably conjugated).

Studies on this system are continuing in attempts to develop more active catalysts as well as heterogeneous catalysts which will show a high degree of specificity.

References I M. Zajcew, J. Am. OilChem. Sac., 1960,37,130

2 R. R. Allen, Ibid., 1962, 39, 457 3 J. C. Bailar and H. Itatani, Zbid., 1966,43,337 4 E. N. Frankel, E. A. Emken, H. Itatani and

J. C. Bailar, J . org. Chem., 1967,32, ~ 4 4 7 5 R. D. Cramer, E. L. Jenner, R. V. Lindsey

and U. G. Stolberg, 3. Am. Chem. Sac., 1963,

6 R. D. Cramer, R. V. Lindsey, C. T. Prewitt and U. G. Stolberg, Zbid., 1965, 87, 658

7 J. C. Bailar and H. Itatani, Prac. Symp. Coordination Chem., Tihany, Hungary, 1964, publ. Hung. Acad. Sci., 1965

8 L. P. van't Hof and B. G. Linsen, J. Catalysis,

9 J. Chatt and B. L. Shaw,J. Chem. SOL., 1962,

10 H. A. Tayim and J. C. Bailar, J . Am. Chem.

I I G. Batley and J. C. Railar, unpublished

IZ H. A. Tayim and J. C. Bailar,?. Am. Chem.

13 R. W. Adams, G. Batley and J. C. Bailar, to

14 a J. C. Bailar, H. Itatani, M. J. Crespi and J. Geldard, Adv. in Chem., 1966,64103

b H. Itatani and J. C. Bailar,J. Am. Oil Chem.

c J. C. Bailar and H. Itatani, J . Am. Chem.

15 H. Itatani and J. C. Bailar, J . Am. Chem. SOL.,

16 G. W. Parshall, Ibid., 1966, 88,704 17 G. C. Bond and M. Hellier, Chem. & Znd.,

18 Unpublished work 19 a R. W. Adams, G. E. Batley and J. C.

Bailar, Inorg. Nucl. Chenz. Lett., 1968,4,455 b Ibid., J. Am. Chem. Soc., 1968,90,6051

8 5 J I6g1

Ig67> 7, 295

5075

Sac., 1967, 89, 3420

results

sac*> Ig67J 433O

be published

Ig67J 44, I47

Ig67> %J 1592

1967, 89, 1600

1965, 35; J. Catalysis, 1967, 7,217

Further Advances in Catalytic Hydrogenation NEW REACTIONS WITH PALLADIUM AND RHODIUM CATALYSTS

Workers from Hoffman-La Roche reported to a recent symposium held by the New York Academy of Sciences that acid chlorides can be converted to aldehydes by a modified Rosenmund reaction using palladium on charcoal catalyst poisoned with quinoline- sulphur inhibitor. The development of this reaction at 50 lb/in2 has reduced catalyst requirements and it opens the way to manufacture of pharmaceutical chemicals from cheaper aldehyde intermedidates by using cheap hydrogen instead of expensive hydrides for hydrogenation of pure acid chlorides. The end point of the reaction was determined by seeing how much hydrogen had been used. The conventional Rosenmund reaction

barium sulphate moderator was not needed. A group from Monsanto showed that

optically active phosphine complexes of rhodium(II1) can catalyse hydrogenation of olefins to optically active products. For example, 28 per cent optical purity, i.e., 64 per cent of one optical isomer and 36 per cent of the other, was obtained during hydrogenation of z-phenylacrylic acid to M- phenylpropionic acid at 300 to 400 lb/in2. The group has not yet finalised the reaction mechanism. The catalyst was formed in situ by reacting the 1,5-hexadiene complex of rhodium(II1) with an optically active phosphine-based ligand such as methyl- phenyl-N-propylphosphine.


The Control of Air Pollution PLATINUM CATALYST SYSTEMS FOR INDUSTRIAL ODOUR CONTROL

By G. J. K. Awes Nesearch Laboratories, Johnson Matthey & Co Limited

lloneycat catalyst systems have been successfully evaluated clnd used in a wide range of industrial processes that emit organic fumes and odours. These include wire enamelling, paint baking, phthirlic anhydride manufucture, puper coating, and nitric acid manufacture. More recently the system has been successfully riialuated for the remobal of odours from the animal, j s h and ,food processing industries.

The development of a new platinised ceramic honeycomb catalyst for the combustion of organic fume offers considerable scope for the control of various types of air pollution (I). These THT catalysts consist of platinum supported on the Du Pont honeycomb ceramic known as Torvex. They possess a low pressure drop, high activity and resistance to attrition, making them suitable for a wide range of industrial processes requiring fume control.

Air pollution takes various forms. I t may consist of toxic emissions or of emissions that offend the eye, the ear or the nose, or a combination of these types. For example, the exhaust gases emitted by diesel engines are frequently both a health hazard and a nuisance to the public. These gases, black smoke and smell included, can be minimised by careful engine design but catalytic combustion constitutes a more effective method of purification (2). Honeycomb catalysts incorporating platinum are suitable for diesel- engined road vehicles and for diesels working in enclosed conditions.

While current legislation on air pollution control is mostly concerned with the toxic emissions, the public often reacts even more to the pollution which offends the senses of sight, hearing and smell. Emissions that pro- voke most public resentment are those which contain some unpleasant characteristic odour.

This is not merely because the odorous materials may be dangerous but because the smells cause immediate public annoyance. The presence of an unpleasant smell does of course often indicate the presence of other and more noxious pollutants.

While several systems have been developed for the elimination of industrial fume, the problem still presents technical and economic difficulties in some industries. Notable arc those processing animal carcases, fish and food. Work carried out by Johnson Matthey to combat these difficulties has resulted in the successful development of Honeycat* catalyst systems to remove both smell and noxious fumes.

Abatement Systems There are five basic methods of fume abate-

ment. They can be classified according to the physical and chemical techniques that are used: dispersion; absorption; masking; oxidation by agents other than air; air oxidation. Generally, odours become less objectionable as their concentration decreases. They arc considered to be eliminated when the concentration drops to the threshold level of perception. However, both the threshold level and the relationship between concentration and odour strength depend upon

*Johnson Matthey Chemicals registered trade name.


ACCESS FOR TUBE CLEANING

CLEAN GAS TO HEAT EXCHANGER

UNTREATED REMOVABLE TOP COVER

EXL1A FAN

CATALYST SECTION

COMBUSTION CHAMBER

BURNER EOUIPME NT

q , / y PRE-HEATED \ \ GAS \

HEAT EXCHANGER

Fig. 1 A typical Honeycat system for industrial odour control comprises the catalytic combustion unit and a heat exchanger to give about 50 per cent heat recovery

the material creating the odour. The dilution required to achieve complete abatement can be determined by sampling techniques (3).

Dilution of an odorous emission is usually achieved by dispersion from a high stack but, although this is usually the most economical method, it is rarely satisfactory because of geographical and climatic effects which prevent complete dispersion of the smell. Odours emitted from the tall stacks of animal, fish and food processing plants have been detected up to ten miles away where in theory their concentration should have been many times lower than the threshold value.

Both solid and liquid absorption systems may be used to remove odours from exhaust gases. A water scrubber system is commonest. While these systems are relatively cheap to operate, they do not always achieve the required degree of abatement because some fume is insoluble in water. In addition, in the food processing industry they create the secondary pollution problem of disposal of the contaminated water from the scrubber.

Masking relics upon the principle that two substances, each with a dis- tinctive smell, can combine to produce another less objectionable smell. This technique is cheap to in- stall but, unfortunately, separation occurs in some climatic conditions, leaving pockets of either the original unpleasant process odour or the odour of the masking agent.

The majority of odours are organic in origin and may be chemically oxidised to other compounds having no odour or one less objectionable than that of the original material. A number of oxidising agents may be used for this purpose, including ozone and

chlorine, but these agents generally do not convert organic substances to their most highly oxidised products, namely carbon dioxide and water, and the presence of objectionable intermediates plus the smell of residual chlorine and ozone may be critical.

While the techniques described above can be designed to remove the main sources of the smells, they do not achieve the objective of the perfect odour abatement system, namely to remove the materials causing the odour without creating another pollution problem and at the same time not to increase the operating costs of the process. Catalytic and direct flame combustion systems are, however, generally recognised to be the ultimate answer to odour abatement, because they destroy completely the organic compounds creating the smells by oxidising them to carbon dioxide and water. Emissions containing sulphur and nitrogen compounds, which are frequently encountered in the animal and fish processing industries, are also oxidised and, although the combustion


CLEAN G A S OUTLET 1

Fig. 2 Catalyst units in Honeycat systems consist of twelve inch square and triangular modules of the platinum on Torvex catalyst. The simplicity of design aids installation of the catalyst and removal for regeneration

products may contain sulphur dioxide and nitric oxide, the treated exhaust gases are odour-free because of their low concentration and the high threshold values of these compounds. With few exceptions the exhaust streams from industrial processes create smells. In particular those in the food processing industry contain organic compounds mixed in air in non-flammable concentrations. For combustion to occur these gases must therefore be heated to between 600 and 1000°C for thermal incineration or, by incorporating a

catalyst into the system, oxidation temperatures may be reduced to between 250 and

While combustion satisfies most of the requirements of the perfect odour abatement system, it suffers from the disadvantages of high capital cost and high operating costs because of fuel requirements.

Incorporation of a catalyst into the system greatly reduces both of these costs as shown in Table I. This table, which was first published by Hardison (4), is often quoted to

450°C.

Platinum MetalsRev., 1971, 15, (1) I 1

Table I Equipment and Fuel Costs for Odour Abatement Systems

Flame

Thermal

Catalytic

Operating

Temperature

"F

Equipment

Cost

$/scfm

Annual

Fuel Cost

$/I000 scfm

2500 i

1000 - 1500

600 - 900

5 -50

1.75- 10

1.75-5

0 - 20

0 - 7.5

0 - 4.5

give an indication of operating temperatures and costs. However, it should be recognised that these costs are only approximate and cannot be used as a basis for determining the cost of a system for a specific problem.

Honeycat Odour Abatement Systems

The incorporation of a catalyst into a combustion system, while significantly reducing the operating costs, can introduce other problems which complicate the system. Notable among these are the pressure drop across the catalyst bed, attrition of the catalyst by vibration or by dust impingement, and catalyst poisoning. As a result most catalytic combustion systems have hitherto been less reliable than thermal systems and more difficult to service. ‘The development of a new platinised honeycomb catalyst (I) has made the construction, reliability and servicing of the equipment very much more practical.

The design of a typical Honeycat system with heat recovery is shown in Fig. I. The burner with its ignition system and flame failure probes is easily removed for cleaning and maintenance and is supplied with clean combustion air from a subsidiary fan to prevent damage to the burner from dirty process gases. The combustion chamber is lined with stainless steel to minimise its size and weight and thc process gases are heated in the combustion chamber and pass directly to the catalyst. This is installed in the catalyst chamber in modular form to simplify installation and removal for cleaning and maintenance as shown in Fig. 2. The catalyst modules are removed through the top of the combustion chamber.

I n the Honeycat system a heat exchanger may be added to the combustion unit to give about 50 per cent heat recovery. This ensures that odour-free outlet gases are above the dew point and thus prevents condensation in the unit. The process gases, prior to catalytic treatment, are passed down the tubes, which are arranged so that the inner walls may be cleaned. The tube bank


may also be removed from the heat exchanger shell to let the outer walls of the tubes be cleaned.

Honeycat System Design The operation of a Honeycat catalyst

system and the factors affecting its performance were described in a previous article (I). Both the operating temperature of the system and the volume of catalyst relative to the volume of air to be treated must be determined to optimise performance. In the majority of odour problems it is possible to specify a range for the temperature and catalyst volume required to eliminate the odour. However, as the composition and concentration of an odour-laden emission are rarely known, it is preferable to make pilot plant tests to find the optimum conditions.

The compactness of a Honeycat system has also made it possible to construct a transport- able pilot unit for on-site evaluations of the system. This unit is designed to treat 200 standard cubic feet per minute of contaminated air at temperatures up to 450‘C and carries its own fuel supply and process air fan. I t may be connected to an exhaust stack without disrupting the process emitting the odours. The pilot plant is fully automatic and incorporates flame-failure devices. It is also fitted with gas sampling points for conventional analysis or odour sampling.

Pilot plant tests enable the optimum size of Honeycat system to be specified for fume elimination in particular industrial plants. Successful installations, as well as those for the elimination of odourless noxious fume, include units for the processing of animal wastes and in fish and meat processing.

References G. J. K. Acres, PZatinum Metals Rtv., 1970, 14,

G. J. K. Acres, Plali,wnz Metals Rev., 1970, 14, (I), 2-10

. .

(3)J-78-85 A. Turk, “Industrial Odour Control and its Problems”,Chem. Engng., 1969,76, (24, Nov. 3), 70-78; “Measurement of Odour in Atmos- phere”, A.S.T.M. Method D 1391-57, 1964, Part No. 23, 612 L. Hardison, “Disposal of Gaseous Wastes”, presented at Seminar on Waste Disposal, Cleveland, May 1967 ’

Platinum and the Refractory Oxides IV - THE PERFORMANCE IN SERVICE OF PLATINUM THERMOCOUPLES

By il. S. Darling, G. L. Selman aiid R. Rushfodi Research Laboratories, Johnson Matthey & Co Limited

The reactions between platinum and the refractory materials in contact with it, described i n earlier articles in this series, account ,for many of the thermocouple failures that occur under practical industrial conditions. Reducing atmospheres accentuate such tendmcies, although several factors usually co- operate to cause completp failure. This urticle examines the way in which platinum :rhodium-platinum thermocouples behave in service under both oxidising and reducing conditions urid

Above the melting point of gold, practical temperature measurements are made with platinum thermocouples which generally provide long and trouble-free service in this temperature region. Under specific conditions, however, environmental reactions can occur, and earlier articles in this series have attempted an analysis of some of the processes which can lead to thermocouple change and deterioration. Against the general back- ground of satisfactory performance the reactions between platinum and the refractory oxides must be viewed in perspective, and it is important therefore to consider the industrial behaviour of thermocouples in relation to the results of the laboratory compatibility experiments previously described.

supported and protected against metallic and vapour contamination satisfactory performance can be obtained for very long periods at temperatures up to 15oooC. An indication of the stability which can be expected under such conditions is provided by Fig. I, where the upper curve indicates the very slow departure from standard calibration of a platinum : 13 per cent rhodium-platinum thermocouple used horizontally in an electrical resistance furnace to which free access of air was available at 1450°C. The fall in EMF, as measured at regular intervals, was

Oxidising and Reducing Conditions Most platinum thermocouples are used in

air and providing that both limbs are properly


also in z'acuum furnaces.

equivalent to about 3 deg C after 1000 hours at temperature. The thermocouple had mm diam. limbs, was insulated with twin bore “Purox” alumina tubes and protected ex- ternally with a loosely fitting “Purox” alumina thermocouple sheath.

The bottom curve on this illustration relates to a similar thermocouple, insulated in exactly the same way, which was run in a flowing atmosphere of dissociated ammonia rather than in air. The thermocouple sheath has obviously provided some degree of protection as mechanical failure of the couple wires has not occurred although a fall in output equivalent to -100 deg C, has taken place after 500 hours at temperature. Subsequent analysis of this thermocouple showed that it had taken up substantial quantities of aluminium, and some silicon which was originally present as silica in the nominally pure alumina.

This type of deterioration can be intensified by changing the orientation of the thermocouple. In one instance rapid thermocouple failure was encountered when the same type of nominally impervious alumina thermocouple sheath was inserted vertically upwards into the hot zone of the furnace. Complete fusion and breakage of the hot junction occurred in dissociated ammonia after about

I 3 per cent rhodium-platinum thermoLoupZe given in Fig. 2. The microstructure of one sheathed zcith ahminu and inserted vprtically area of this failure is shown in l?ig. 3. L~~~~ upwards into a furnace containing an atmosphere

y25 quantities of silicon and aluminium were of dissociated ammonia at 1450°C. found by microprobe analysis, and this type of geometrical arrangement seems very dangerous, as any hydrogen which penetrates the tube is, by virtue of its low density, trapped in concentrated form at the hot junction, thus causing very severe reactions between platinum and the refractory tube and insulators.

Under strongly reducing conditions thermocouples used in contact with magnesia are relatively free from this type of deterioration. The third curve on Fig. I indicates

~ i ~ . 2 ~~~i~~ the hot junction o~ a : 2 hours at 1450‘ C, a typical illustration being

some results obtained when a thermocouple was run in dissociated ammonia at 1450°C

lf’ig. 3 The microstructure of the fused zone on the failed thermocouple illustratd in Fig. 3. x 200


Fig. 4 Intercrystalline cracks associated with oxide in- clusions embedded within the surjace layers o j a rhodium- platinum wire. X 20

Fig. 5 A microssction taken through a defect of the type illustrated in Fig. 4 showing the fused area resulting from reaction between a refructory particle and the rhodium- platinum alloy. X 50

for 450 hours while packed in a bed of fine magnesia powder. The extent of the deterioration which occurred was comparable with that encountered with the alumina insulated thermocouple run in air.

Failure Caused by Superficial Contamination

Premature failures caused by platinum- refractory reactions are occasionally encountered in atmospheres which appear at first glance to be highly oxidising. This behaviour can usually be traced to circumstances in which a fortuitous juxtaposition of platinum and refractory has resulted in a particularly unfavourable geometry.

Small particles of alumino-silicate forced into platinum or rhodium-platinum wires occasionally cause intercrystalline cracking of the type shown on Fig. 4, which occurred on heating in air to 145o'C. Fig. 5 provides another illustration of the way in which intercrystalline failure can proceed at a considerable distance away from the region where the original refractory particle had reacted with the platinum to form low melting point phases in which platinum silicide predominated.

The first attempts to reproduce such effects in the laboratory met with limited success. Mullite particles rolled into sheet normally showed little tendency to react. Some working operations, however, parti-


cularly wire drawing, sometimes gave rise to an inclusion which was almost completely encapsulated by platinum. This type of inclusion tended to react strongly with the platinum when heated in air. As shown in Fig. 6 networks of platinum-platinum silicidc eutectic have penetrated round the grain boundaries for a considerable distance away from the inclusion.

It has recently been shown that this type of failure is usually associated with the presence of sulphur-bearing organic lubricants such as those used for rolling and wire drawing. Traces of these liquids are trapped in the cavity with the refractory particle and the partially sealed conditions obviously facilitate the reaction, based on the formation of volatile silicon sulphide which was first observed twenty-five years ago by Chaston et al. (I).

Reactions at Lower Temperatures At temperatures below rooo"C reactions

do occur between platinum and refractory oxides, although as many investigators have demonstrated (2, 3, 4), contamination of the thermocouple by impurities from the ceramic protection tubes is the most usual cause of instability in this temperature range. Walker et al. (4) have described in detail the way in which iron can be transferred from nominally pure alumina powder into platinum, and suggested mechanisms for this vapour phase transfer process.

Fig. 6 3’etworks of the platinum-platinum silicide eutectirformpd in the vicinity of a siliceous inclusion, encapsulated in rhodium-platinum, on heating in air. Y 1500

The slow changes in thermoelectric output which occur in rhodium-platinum thermocouples heated for long periods in air at moderate temperatures have generally been attributed to contamination processes of this type. Recent investigations in these laboratories have shown, however, that such ex- planations are not always justifiable. In one instance for example a reduced output, equivalent to about 2 deg C, was detected after a 13 per cent rhodium-platinum thermocouple had been used at 625°C for 40,000 hours or 5 years in air in a steel creep testing furnace. Very thorough examination showed little change in the composition of the limbs up to 2 ft from the hot junction. Towards the colder end of the wires changes in alloy homogeneity were, however, detected and micro-examination disclosed the presence of areas which contained substantial quantities of solid rhodium oxide as shown in Fig. 7. The platinum alloy matrix contained only 11 per cent by weight of rhodium, and the presence of this depleted region in the strong temperature gradient between the hot and cold regions of the thermocouple accounted for the change in electrical performance.

A short heat treatment in air at 1200°C dissociated this oxide, returned the rhodium to solid solution in the platinum and restored the thermocouple output. This type of internal oxidation has not, so far as can be ascertained, previously been reported. Very

Fig. 7 Subsurface rhodium oxide in a 13 per cent rhodium-platinum thermocouple wire operated in air for approximately 5 years at nbout 400°C.

/ 750

long periods of time are needed for its development but, since all noble metal thermocouple wires must at some point between hot and cold junctions pass through the temperature range 400-6oo0C, a tendency towards the internal formation of solid particles of rhodium oxide must always exist. The rate at which this internal oxidation proceeds is now being assessed.

Thermocouples in the Vacuum Furnace

Under industrial conditions thermocouple deterioration can usually be ascribed to the operation of various processes and this is particularly true in vacuum metallurgical melting and heat treatment furnaces. The contamination which occurs is usually characteristic of the impurities in the refractory rather than of the refractory itself. Super- imposed on such effects are the changes in composition caused by the selective volatilisation of rhodium under vacuum conditions, and by the absorption of vapours from the material being heated within the furnace.

Premature thermocouple failure was occasionally encountered in a vertical vacuum sintering furnace generally operated at a pressure of about z X I O - ~ Torr. This furnace had molybdenum heaters, and during one series of production runs made at 1500°C adhesion between the components being sintered was prevented by dusting with


Fig. 8 Within the confines of this glass envelope plat inum filaments are heated in contart u i t h refractory oxides under any desired atmospheric conditions. The wire under test and the refractory in contact with it are the only parts of the system maintained at high temperature, and the romplicating effects of spurious contamination are thus avoided. D i f e r - ences between the simplicity of this experimental arrangement and the complex environments in which thermocouples normally operate in industry are discussed in this article.

alumina powder. The thermocouple calibration changed rapidly under such conditions, and useful working lives were limited to about 70 hours. Both limbs of the thermocouple tended to absorb substantial quantities of both silicon and aluminium. Although the precise source of this siliceous contamination was not detected, it and the aluminium have obviously reached the thermocouple via the vapour phase. The thermocouple was in fact at a slightly lower temperature than the furnace heaters and their supports, and this situation obviously encourages contamination by volatile species. It is in this important respect that practical conditions differ greatly from the test cell geometry described in the previous articles, where thermocouples were intentionally run at much

higher temperatures than their environment so as to discourage spurious contamination.

Fairly satisfactory protection against such vapour attack can usually be obtained if the impermeable alumina thermocouple sheaths are prolonged without join into the cold part of the furnace. Thus in a horizontal vacuum resistance furnace the thermocouple was supported within twin-bore alumina insulators and protected entirely by an impervious alumina sheath which continued into the colder part of the furnace where temperatures were below zoo”C.

After about 150 hours of operation at 1475’C in vacuum conditions of about 5 x 10 Torr the output of such thermocouples decreased by the equivalent of about 3 deg C at the gold point. This deterioration was traced


Fig. 9 Traces of the Pt,Al intermetallic compound formed locally on the surface of a plotinurn thesmo- couple mire operated in a vacuum fusnace,for 100 hours at l400’C. x150

to the gradual loss of rhodium from the alloy limb which in some regions nearer the hot junction was reduced to 11.4 per cent by weight. NQ rhodium was detected in the pure platinum limb, and it must be remernbcred that the volatility of rhodium in vacuum is many times higher than that of platinum.

Reactions tetween platinum wires and their alumina insulators are detectable in ordinary vacuum furnace operations, although the areas of contamination are fairly local. Fig. g illustrates such a reacted area which developed where the thermocouple wire passed the junction between two alumina insulators. This region, although rich in aluminium, is not deep enough to weaken the wire seriously, and because of its short length is not able in normal temperature gradients to have a serious effect on the thermal EMF generated by the thermocouple.

Complete and rapid failure of thermocouples in vacuum furnaces is therefore rarely caused by direct reaction between platinum and refractories. Dangerous contamination generally emanates from the more volatile constituents of the materials being heated within the furnace and can usually be avoided by effective sheathing. Although

rhodium does evaporate preferentially and reactions do occur between platinum and alumina refractories the changes thus caused are gradual, continuous, and tolerable under ordinary production conditions.

Conclusions Under practical conditions of operation

thermocouple behaviour cannot always be predicted because of the conflicting factors responsible for the changes in electrical output which occur. Although the best per- formances are generally obtained in air, satisfactory lives are attainable in vacuum and even under fairly strong reducing conditions. Rhodium-platinum thermocouples are most stable, however, when magnesia is used as a refractory, and when the surrounding inert atmosphere inhibits volatilisation of platinum or rhodium in either metallic or oxide form.

The 10 per cent and 13 per cent rhodium- platinum thermocouples perform very well in such conditions and further improvement is attainable by using the 6 per cent rhodium- platinum versus 30 per cent rhodium- platinum combination. Minor losses of rhodium metal vapour from the positive limb of this thermocouple have little effect on the thermal EMF. Any slight tendency for the negative limb to absorb rhodium can be controlled by surrounding the assembly with a 5 per cent rhodium-platinum “reservoir” of suitable capacity.

I n practice it is not always feasible to provide the ideal climatic conditions necessary to ensure extreme stability in refractory sheathed thermocouples. Suitably controlled “micro climates” can, however, be retained within metal sheathed thermocouples, which will feature in a forthcoming article.

References I J. C. Chaston, R. A. Edwards and F. M. Lever,

2 M. Chaussain, Proc. Inst. Brit. Foundrymen,

3 H. Ehringer, Metall. Z . Tech., Ind. Handel,

4 B. E. Walker, C. T. Ewing and R. R. Miller,

J . Iron & Steel Inst., 1947, 155, 229

1951, 91, (I823), 147

1954, (15 /W> 596

Rev. Sci. Instrum., 1962, 33, (IO), 1029


Monolithic Multilayer Ceramic Capacitors for Hybrid Circuits THE EFFECTS OF TEMPERATURE CYCLING ON STABILITY

By R. F. Tindall Matthey Printed Products Limited

The development of miniature circuitry, and particularly of the hybrid film circuit, has demanded more and more capacitance in a smaller volume of capacitor. ‘There are three possible ways in which this can be achieved. One is to produce capacitors without wires or encapsulation or any of the other appendages previously required by equipment designers. Another is to use thinner layers of dielectric, but this is limited by the voltage that the capacitor must withstand. The third is the use of higher dielectric constant materials, but unfortunately it is generally found that the higher the dielectric constant of a material the poorer is its stability.

This last point is illustrated by comparing the change in capacitance with temperature of two typical materials : one having a nominal dielectric constant of 1200 (known as K12oo) will change its value of K

The platinum metals not only provide the most reliable electrodes but also enable an economical production method to be employed in the manufacture of small monolithic capacitors. By screen printing and firing to form a robust integrated structure it is possible to obtain a very high ratio of capacitance to volume. This cross-section, magnijied 50 times, shows the ceramic layers clearly separated by the platinum electrodes.

by as much as 20 per cent when its temperature is raised from -55‘C (the lower limit stipulated by international specification) to room temperature, while a low dielectric constant ceramic having a K of, say, 30 - generally used for capacitors known as NPO for negative-positive-zero - will vary only by at most 0.25 per cent with the same change of temperature.

The monolithic multilayer ceramic capacitor is produced by screen printing on to strips of “green” ceramic of the barium titanate type an ink or paste incorporating finely divided platinum or a mixture of platinum group metals. A stack of these


strips is then assembled and fired at about 1300OC to mature the substrate and fuse the layers into a block or chip. Metallising the ends of the chip with silver-palladium or gold-palladium then completes the contact between alternate electrodes. By this technique very thin dielectrics, which individually would be hopelessly fragile, may be used, while the fused structure is robust, hermetic- ally sealed, and can be immediately incor- porated into a hybrid circuit.

Ceramic substrates of many compositions can be used in monolithic chips, so that very high dielectric constants are available, but the stability of the capacitor clearly cannot be greater than that of the ceramic itself. The desire to use high K materials in the interests of miniaturisation can thus lead to difficulties because of the relatively poor stability of these materials. When subjected to high temperature processes such as soldering, for example, high K capacitors can show a drift in capacitance beyond acceptable limits.

Some recent work in the Electronics Laboratory of Matthey Printed Products was therefore designed to evaluate the change

in capacitance a monolithic chip capacitor is likely to undergo during the assembly and subsequent processing of a hybrid micro- circuit, and to provide the user with information that will allow him to anticipate this behaviour and make allowance for it. The detailed results of this work, reported at the recent Inter-Nepcon 70 Conference at Brighton, showed that, while the variations are predictable and repeatable and in some circumstances reversible, because of the diversity of techniques employed in the industry it would be unrealistic for a manu- facturer of ceramic chips to specify a time by which a chip will recover its original capacitance after a soldering operation or any other heating cycle.

It was found, however, that the application of high voltages can accelerate the ageing and so stabilise the capacitance.

Further development along these lines should result in components having a limited temperature range in which they will operate satisfactorily, but having at the same time an unrivalled combination of stability and capacitance/volume ratio.

Zerovalent Complexes of Platinum The discovery some twelve years ago of

complexes in which platinum exhibits zero valency-that is, in which the platinum atom is associated only with uncharged ligands- has proved of considerable importance for the synthesis of a wide range of compounds, some of which might be of use in homogeneous catalysis. A typical example of such complexes is tetrakistriphenylphosphine platinum [P(C,H,),],Pt. In reactions involving this compound it has been postulated that the coordinatively unsaturated species [P(C,H,),],Pt is a reactive intermediate. This means that there will be released in the reaction two triphenylphosphine groups which will still be available to compete for the vacant coordination sites. If the reactive intermediate could readily be prepared this situation would no longer exist, and the possibility would arise for even further advances to be made in the field of platinum organometallic chemistry.

In view of this, a paper by D. M. Blake and C . J. Nyman, of Washington State University, entitled “Photochemical Reactions of Oxa- latobis(triphenyphosphine)platinum(II) and Related Complexes” (J . Am. Chem. SOC., 1970, 92, (IS), 5359-5364) assumes signific- ance. In an investigation of photochemical reactions of oxalato complexes a route to the co-ordinatively unsaturated compound has been discovered. Photolysis of an ethanol solution of [P(C,H,),] ,C,O,Pt(II) under a nitrogen atmosphere, from which oxygen had been rigorously removed, resulted in the production of this complex in the form of a dimer, [P(CSHj)J4Pt2. Thus a relatively simple route to this reactive species has become available. Although only this one reaction has been noted here, others are described. It is apparent from this work that photolysis of oxalato complexes offers a route to reactive species for the production of cata- lytically active compounds in sku. F. M. L.


The Form of the Interaction between Palladium and Hydrogen By R. Burch

and F. A. Lewis

Chemistry Department, University of Reading

Chemistry Department, The Queen’s University of Belfast

The high di fusibi l i ty of hydrogen in solid phases of the palladium-hydrogen system allows thermodynamic equilib- r ium to be established over a wide range

i of experimental conditions. Evidence has long existed that, in the hydride phases formed, the hydrogen:palEadium ratio is not simple and is a funct ion of equilibrium pressure and of temperature. Theoretical models of the system have often centred on modijications of the palladium electron band structure due to hydrogen absorption but increasing attention has been pa id to the conse- quences of lattice strain. The position i s now reviewed ire the light of recent work.

In the course of the last ten years a number of general reviews (1-6) have appeared con- cerning the palladium-hydrogen system. Within this same period also has occurred (and been marked by a compilation of review articles (7)) the centenary of Thomas Graham’s initial observation (8) of the absorption or “occlusion” of considerable volumes of hydrogen by a palladium membrane or “septum”- prepared for his use by George Matthey.

Some thirty years after Graham’s original observations isothermal studies in the temperature range 10 to 250°C of the variation of the composition of the hydrided solid as a function of the pressure of hydrogen gas in steady-state equilibrium with it had sug-

gested that these relationships were likely to be represented by a family of plots of the form shown in Fig. I. These studies (9) by Roozeboom and Hoitsema might well be claimed to be the first examples of evidence for the non-stoichiometric and temperature- dependent composition of the solid phases represented in such diagrams.

The plots in Fig. I-which represent results subsequently obtained (6, 10, 11) over a wider range of temperature and pressure than those presented by Hoitsema-are clearly representative of a system subject to the existence of critical phenomena. In terms of a physically descriptive correlation in this particular instance, individual isotherms may


be described, or defined, as supercritical, critical or subcritical with respect to the possibility of the co-existence within thc solid of two hydride phases (the s(- and p-phases), which for the cases of the subcritical isotherms can exist together in varying proportions over the ranges of composition corresponding to the horizontal “plateau” regions-the actual composition of each phase over these horizontal pressure-invariant regions corresponding with the break points of the isotherms at the beginning and end of the plateaus.

The subcritical isotherms exhibit a “hysteresis” of pressure-composition (p-c) relationships over the pressure invariant and adjacent regions, in that, for a given hydrogen content, the steady-state “equilibrium” pressures are higher when hydrogen contents are being steadily increased by the admission of successive doses of gas into the equilibrating system rather than decreased by the successive removal of incremental volumes of gas.

Theoretical Models Clearly it is a central requirement of any

theoretical model of the palladium-hydrogen system that it should be possible to be correlated with, and to account for the form of the pressure-composition relationships. In this context there are two main features of these solubility relationships which require an explanation. These are firstly the occur- rencc of critical isothermal behaviour, and secondly the tendency for palladium to have a limiting solubility for hydrogen at a composition which is considerably less than that which would be expected from purely geometrical considerations. This limiting solubility condition is manifested as a rapid rise in equilibrium hydrogen pressure for small changes in hydrogen content above about H/Pd-0.60 at room temperature.

In general the interpretation of critical phenomena has been based on the early postulate of Fowler (12, 13) that an attractive interaction must occur between neighbouring absorbed species, thus resulting in the heat

of solution of hydrogen having a negative dependence on concentration (Le., the heat of solution becomes more negative as the concentration of dissolved hydrogen is increased).

The first significant attempt to apply these concepts to the palladium-hydrogen system was made by Lacher (12, 14) in 1937 using a statistical thermodynamic approach which formcd an extension of an allied treatment (13) of the problem of absorption of hydrogen by transition metals such as iron and platinum in which it is only sparingly soluble.

Recently it has been pointed out ( I S ) that critical behaviour only requires that the heat of solution should become more negative as the hydrogen content is increased and that this does not necessarily require so specific an interaction as that between neighbouring atoms. In this case (IS) the decreasing heat of solution of hydrogen is taken to be a reflection of the continuous filling of the palladium 4d-band by electrons from hydrogen atoms.

Within the more general framework of the Fowler/Smithells (13) concept of pairwise interactions the nature of this interaction has been considered by various authors (16, 17, 18, 19). This interaction has been attributed to the occurrence of electronic coupling of the screening electrons surrounding each proton (17) or more generally to be a consequence of the lower strain energy associatcd with paired as distinct from monoatomic species in an elastic matrix (16, 17, 18, 19). Recently, by considering the volume expansion produced in the palladium lattice due to the absorption of hydrogen, Burch (20) has derived a value for this pairwise interaction energy. The derived value is in good agreement with the experimental data which would seem to support the general view that the critical phenomena occur as a consequence of the release of strain energy associated with the clustering of dissolved hydrogen atoms.

The tendency towards a limiting solubility at about H/Pd=o.gg led Lacher to postulate that this limit corresponded to a completely filled qd-band and therefore that

Platirium MetalsRev., 1971, 15, (1) 22

this represented the maximum hydrogen content which would be possible without some change in mechanism. Consequently his theoretical equation contained a term such that the derived isotherm unavoidably reached a solubility limit at this composition.

The equation derived by Lacher (14) was of the form:

where O=n/s is the ratio of the number of hydrogen atoms “n” to the maximum number of absorption sites “s” where Lacher took a value for “S” of 0.59. Lacher’s apparent success in achieving a good correlation between this theoretical equation and a significant body of the experimental data led to a widespread acceptance of the general correctness of the physical model for the system which he had employed.

Important limitations of the agreement between p-c relationships derived from Lacher’s theoretical equations and those obtained experimentally, especially when the artificial condition whereby “s” is put equal to 0.59 is removed, are revealed by detailed analysis of the existing data. Subsequently, however, attempts have been made to improve the agreement by extending the Lacher model while still assuming a limited number of absorption sites (21, 22, 23, 24). Modified equations have been derived from models which have variously taken account of the effects of lattice expansion (21, 22), made allowance for the occurrence of hysteresis of the subcritical isotherms (23), or considered the pairwise interaction not only of hydrogen atoms but also of vacancies and vacancy- hydrogen atom pairs (24). In all these cases, however, the limiting solubility was explained on the basis of a limited number of absorption sites.

Recently attempts have been made (15, 16, 18, 25, 26) to relate the solubility limit to variations in the energy associated with the donation of electrons by hydrogen to the 4d and 5s bands of palladium. There is as yet still some disagreement as to whether or not

the gradual filling of the qd-band is paralleled by an endothermic (16, IS) or exothermic (15) electron donation energy term. In all cases, however, it has been assumed that, at higher hydrogen contents when the 4d-band is full, the energy required to transfer an electron from hydrogen to the 5s-band of palladium is greater than the energy which would be required, at low hydrogen contents, for a similar electron transfer to the qd-band.

The resulting theoretical equation is of the generalised form :

where E(n) is a positive electronic energy term which is a function of the hydrogen content “n”.

The electronic term in equation (2) has the effect of increasing the equilibrium hydrogen pressure very rapidly at hydrogen contents greater than about H/Pd -0.6, in agreement with experiment. Only Simons and Flanagan (IS) have attempted to evaluate E(n) from basic principles. Using the rigid band model they have derived, from the density of states curve for palladium, an energy relationship which is of the correct form to predict a limit in the solubility at moderate pressures. A detailed analysis of these various “protonic” models has been presented elsewhere (17) and attention has also been drawn (27) to shortcomings in this model when applied to the absorption of hydrogen by palladium alloys.

The Elastic Model Recently Burch (20) has developed the

concepts of the elastic model, which had already been invoked to explain the existence of critical absorption isotherms, to account for the main features of the observed solubility behaviour. In view of the experimental observation that occupation of an interstitial site by a hydrogen atom causes expansion of the palladium lattice and consequently a displacement of adjacent palladium atoms, it was suggested that vacant sites surrounding the occupied site would be modified to varying


extents by this localised expansion. Subse- quently by relating the energy required to place further hydrogen atoms in partially blocked sites to the volume change of each modified site, it was found possible to derive an equation relating the equilibrium hydrogen pressure to the hydrogen content. An error in the original equation (20) has been pointed out by Dr W. A. Oates. A corrected form of the equation is as follows :

z ( (AV+nAV')2 __ 2WRm 1 -GN 3 (Vo-nAV') Vo where W,, represents the attractive interaction between pairs of atoms, G is the modulus of rigidity of the metal, Vo is the initial volume of an interstitial site (assumed spherical), AV is the increase in volume of the site after occupation by a hydrogen atom, and AV' is the reduction in volume of a modified site. In this model the limiting


hydrogen solubility occurs as a consequence of the increasing difficulty associated with the occupation of sites which have been modified by the presence of hydrogen atoms in adjacent, and especially next nearest neighbour, sites.

As compared to the earlier 'protonic' models this latter model has the advantage of a more general applicability to an interpretation of the behaviour of other transition metals towards hydrogen. In addition the phenomena of hysteresis of the isotherms and the peculiar absorption behaviour of palladium- nickel alloys can more readily be explained using the elastic strain model rather than the electronic model. A comparative summary of the various models is presented in Fig. 2.

It is clear that even after a hundred years of research the absorption of hydrogen by palladium still produces considerable con- troversy. It is probable that the isothermal relationships obtained experimentally reflect

a balance between electronic and physical effects. Thus, while there is fairly general agreement that hydrogen donates its electrons to a collective metallic electron band there is still dispute as to the effect that this can have on the energetics of hydrogen absorption. I t will be of future interest to see which of the physical or electronic factors have most relevance not only in the palladium-hydrogen system but in all transition metal-hydrogen systems.

References I F. A. Lewis, Platinum Metals Rev., 1960, 4,

132; 1961, 5,21 2 G. G. Libowitz, Binary Metals Hydrides;

W. A. Benjamin: New York, 1965 3 K. M. Mackay, Hydrogen Compounds of the

Metallic Elements, Spon: London, 1966 4 A. Maeland and T. B. Flanagan, Platinum

Metals Rev., 1966, 10, 20

5 H. J. Goldschmidt, Interstitial Alloys, Butterworth: London, 1967

6 F. A. Lewis, The Palladium Hydrogen System, Academic Press, London and New York, 1967

7 Engelhard Industries Tech. Bull., 1966, 7, ( I )

8 T. Graham, Phil. Trans. Roy. Soc., 1866, 156, and (2)

415

9 C. Hoitsema, 2.Phys.Ckem. Leipzig, 1895,17, I 10 P. L. Levine and K. E. Weale, Tram. Furaduy

11 E. Wicke and G. Nernst, Ber. Bunsen. Phys. Ckem., 1964, 68,224

12 R. H. Fowler and E. A. Guggenheim, Statis- tical Thermodynamics, Cambridge Univ. Press, 1939

13 R. H. Fowler and C. J. Smithells, Proc. Roy. sot., 1937,16oA, 37

14 J. R. Lacher, Proc. Roy. SOC., 1g37,161A, 525 15 Y. Ebisuzaki and M. O’Keefe,J. Phys. Chem.,

16 H. Brodowsky, Z. Phys. Chem., 1965, 44, 129 17 R. Burch, Trans. Faraday Soc., 1970, 66,736 18 J. W. Simons and T. B. Flanagan, Can. J .

19 M. von Stackelberg and P. Ludwig, Z. Natur-

20 R. Burch, Trans. Fmaday SOC., 1970,66,749 21 A. Harashima, T. Tanaka and K. Sakaoku,

22 T. Tanaka, K. Sakaoku and A Harashima,

23 D. H. Everett and P. Nordon, Proc. Roy. Soc.,

24 R. V. Bucur and M. Crisan, J . Phys. Chem.

25 H. Brodowsky and E. Poeschel, Z. Phys. Chem.,

26 H. Brodowsky and H. Husemann, Ber. Bunsen.

27 R. Burch and F. A. Lewis, Trans. Faraduy

SOC., 1960, 56, 357

1968,72,4695

Ckem., 1965,43, 1665

forsch., 1964, 19a, 93

J. Phys. Soc.Japan, 1948, 3, 208

Ibid., 213

1960,259A, 341

Solids, 1967, 28, 905

1965944, I43

Pkys. Chem., 1966,70, 626

SOC., 1970, 66, 727

Cubane-type Platinum Metal Complexes Recent X-ray diffraction studies have Matthey Research Laboratories) point out

shown that the two platinum metal complexes (Nature, 1970, 228, (5272, November 14), [(C,H,),PtCl], and [(CO),OsO], have 648-651) that Pt(IV) and Os(I1) are iso- cubane-type structure. The eight carbon electronic and that similar structures might atoms of cubane, C,H,, are situated at the be expected for other iso-electronic metals, corners of a cube. The structure of e.g. W(O), Re(1) and Ir(II1). In fact

the diagram to resemble rt formally of this type with cubane and that of the os- one NO and two CO

groups on each Mo(0) atom, OH being the nega-

mium compound is similar, the four osmium and four oxygen atoms being at tive group. The NO group alternate corners of a cube is assumed to act as a uni- with the osmium atoms each bound to three terminal carbonyl groups.

I n a joint communication (SR)I4, which have struc- Professor Sir Ronald Et tures with cubic symmetry.

So far, however, no compounds of this type have been reported for the triad

Bt = C ~ H , Co(III),Rh(III)andIr(III).

Nyholm and Professor Mary R. Truter (Univer- sity College, London) and C. W. Bradford (Johnson

[(C,HS),PtCl], is shown in [(CO),(NO)Mo(OH)I, is

Et

Platinum MetalsRev., 1971, 15, (1) 2s

positive radical. Further- more Re(1) and Mn(1) form compounds [(CO),M

A New Mining Area for Rustenburg PRELIMINARY STEPS TO A FURTHER EXPANSION SCHEME

For years by far the largest producer of platinum and its allied metals in the world, Rustenburg Platinum Mines recently an- nounced a programme designed to maintain that position. The current expansion programme has already increased capacity to a level of T,IOO,OOO ounces of platinum pcr annum and, although it has been decided to defer completion of the programme to increase capacity to 1,300,000 ounces by 1973, the preparations to bring the company’s two mining areas, the Rustenburg and Union sections, up to this potential maximum are complete.

Extending for some twenty miles along the platinum bearing Merensky Re$ Rustenburg’s operations in- volve over thirty inclined haulages such as this from which the shallower portions of the deposit are worked. Over 35,000 miners are en- gaged in these and in the vertical shafts from which the deeper areas are worked

But in order to ensure that the next stage of expansion in output can be achieved with a minimum of delay - and the time taken from a decision to expand until refined metal from any such expansion becomes available to industry ranges from two and a half to three years - a completely new mining area has been delineated to the north-east of the Union Section. The extensive exploration work involved has been completed, the planning of the layout of the new mine is well in hand, and arrangements for the supply of essential services have been made. All these steps have been taken to ensure that the new mining

Platinum Metals Rev., 1971, 15, (l), 26-28 26

A train load of p la t inum ore i s transported f r o m one of the nine vertical shafts at Rustenburg to the nearby mill and smelter. Every working day some 20,000 tons of ore are brought to the surface

area can quickly be brought into production, the scale of operations to be determined in the light of future developments in the demand for platinum.

Current developments mean that the supply of platinum to industry has reached an all-time high, and that future supplies can be increased if necessary to keep ahead of

demand. The annual demand for platinum by the Western world is currently around 1,500,ooo ounces, and there is some possibility that the total supplies of platinum available to users might, by 1972, exceed requirements. On the other hand there is the likelihood that platinum may play an in- creasingly significant part in combating atmospheric pollution from many industrial processes and from automobile exhausts. The extent to which platinum may be required for this purpose cannot, however, be predicted until both governmental policies and competing technical developments can be more clearly assessed, but having regard to the time normally required to achieve further substantial increases in platinum production, it is to ensure that a possible shortage of

Ms D. A. B. Watson Chairman of Rustenburg Platinum Mines

" A t Rustenburg we are in no doubt as to the adequary of our reserves of plat inum and as a primary producer we are able quickly to initiate expansion programmes to meet increasing demand"


After smelting in electric furnaces, a copper-nickel-iron matte containing the platinum metals is transferred to a battery of converters and blozcn to a higher grade. Here the con- verter matte is being poured into moulds. After cooling and breaking up it is passed either to Johnson Matthey or to Matte Smelters for the extraction of copper, nickel and the six platinum metals

metal does not affect decisions on the technique to be adopted that Rustenburg has taken these preliminary steps. Thus, if substantial supplies of platinum should be required for the drive against pollution, Rustenburg will be in a good position to satisfy such a demand with a minimum of delay.

The new mining area is of course also located on the Merensky Reef, where rescrves of platinum have been estimated to exceed 200,000,000 ounces that could be exploited economically during the next thirty years - a clear indication that any likely future demand is capable of being met. At its present level of activity Rustenburg constitutes the world’s largest underground mining operation, the workings extending for some twenty miles along the reef and involving the employment of over 35,000 miners. The shallower parts of the mines are worked from about thirty inclined haulages,

while the deeper areas are opened up from nine vertical shafts ranging in depth from 500 to 3,000 feet.

Every working day some zo,ooo tons of ore are brought to the surface, loaded into trains and conveyed to the mill for a long and complex sequence of grinding, ball milling, flotation and preliminary smelting operations, the final product from here being despatched to Johnson Matthey for the extraction and relining of the six individual platinum metals.

It is Rustenburg’s policy to maintain a reasonable and stable price for platinum, and by taking steps to see that all consumers’ needs can be met at such stable prices, to provide users with the assurance of availability they require when deciding to use platinum. During the period of expansion from 1963 to the present, Rustenburg has invested more than A50 million in order to expand its productive capacity by more than five times.


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Homogenisation Quenching of Platinum A. CI~EK, F. PARI~EK, A. 0RLov.k and J. TOU~EK, (3zech.J. Phys., B, 1970, 20, (I), 56-62 Black dots sz roo.& diameter were observed during transmission electron microscopy of the defect structures of thin foils prepared from 99.9 and 99.99'3 Pt samples quenched from 1300°C. The dots are interpreted as vacancy clusters retained in the presence of impurities. They appear to be spherical and w I IOA.

Thermodynamic Properties by Levitation Calorimetry. I. Enthalpy Increments and Heats of Fusion for Copper and Platinum A. K. CHAUDHURI, D. w. BONNELL, L. A. FORD and J, L. MARGRAVE, High Temperature sci, 1970, 2,

(3h 203-212 Electromagnetic levitation heating and isothermal- drop calorimetry shows that AHf,, for liquid Pt at 2202-2631K is 5300*150 ca1;mole.

Investigation of the Decomposition Kinetics of Gold-Platinum Alloys by Means of Electrical Resistivity G. KRALIK,Z. Metallkunde, 1970,61, (IO), 751-756 Resistivity measurements on 15, 25, 55 and 65 at. "6 Au-Pt alloys to study decomposition after homogenising and quenching in a salt bath clearly indicated the influence of quenched-in vacancies at the start of ageing. Annealing-out kinetics were explained by migration of divacancies. Migration energies were derived from the decay times of vacancy supersaturation. Spinodal temperatures and atomic diffusion energies were estimated.

Resistance Minimum Phenomena in Ex- change Enhanced Pd and Pt Alloys H. NAGASAWA, J . Phys. Soc. Japan., 1970, 28, (5), 1171-1180 The magnetic susceptibility and solute resistance of Cr impurity in Pd,-,Rh, (c=o, 0.01, 0.04, 0.05,o.o8, and 0.10) and also in Pt were measured. The addition of Cr brought about a large increase in the magnetic susceptibility of Pdl-,Rhc; below IOK the solute resistivity obeyed a T3 law. Both effects are explained by the negative polarisation of neighbouring Pd atoms.

Preparation of Homogeneous Palladiom- Silver Alloy Films R. L. MOSS, D. H. THO,UAS and L. WHALLEY, Thin Solid Films, 1970, 5, (I), R19-Rzz 21-68 at.<;,; Pd-Ag films were produced by

simultaneous evaporation at 5 x 109-8 x 10-l" Torr of Pd and Ag beads previously outgassed on W heating loops. Their good bulk homogeneity was shown by their small lattice constant devia- tions and symmetrical X-ray diffraction line profiles. The films were relatively unsintered and crystallite size decreased with increasing vacuum.

Low Temperature Heat Capacities of Pal- ladium-Boron Solid Solutions M. MAHNIG and L. E. TOTH, l'hys. Lett. A, 1970,

The heat capacities of a series of Pd-B solid solutions were measured at 1.6-1oK. Results indicate that the B atoms donate essentially all of their three valency electrons to the d-bands of the metal. The Debye temperature of the system remained roughly constant with electron concentration.

The Thermodynamic Properties of Cobalt- Palladium Solid Solutions L. R. BIDWELL, F. E. RIZZO and J. v. SMITH, Acta Metall., 1970, 18, (9), 1013-1019. The thermodynamic activities of Co-Pd solid solutions relative to pure f.c.c. ferromagnetic Co were measured from 800-IIOOT. The activity of Co showed positive departures from ideality in Co-rich alloys, and negative departures in Pd-rich alloys; the activities of Pd showed negative departures at all compositions. Heats of mixing were endothermic for Co-rich compositions and exothermic for Pd-rich compositions. The relative integral molar excess entropies were positive for all compositions. A miscibility gap below 600°C at high Co concentrations is suggested by the experimental results.

Ordered Phase in the Co-Pd Alloy System Y. MATSUO and F. HAYASHI, J. Phys. Sac. Japan, 19709 28, (511 I375 Electron diffraction observations have revealed the existence of a previously unreported ordered state in evaporated films of Co-Pd alloys. The evidence for an order-disorder transformation in CoPd, is discussed. The highest temperature of the transformation is sz 800°C at 75 at.yO Pd.

Antiferromagnetism in Disordered Cr-Pd Alloys T. KANEKO and H. FUJIMORI, Ibid., 1373 The magnetic properties of disordered 28-341h Cr-Pd alloys were studied at 4.2-300K. Results are presented graphically and include susceptibility-temperature curves and values of the Nee1 and Curie temperatures. The effective magneton

32A, (51, 319-320

Platinum Metals Rev., 1971, 15, (l), 29-35 29

number pefflCr ion is calculated to lie betwcen 1.7-2.2 p~ and is in inverse position to Cr content. Antiferromagnetism in this system is thought to originate from the antiferromagnetic coupling between the dwarf moments of Cr atoms.

Magnetic Properties of Amorphous Pd-Si Alloys Containing Iron R. HASEGAWA,~. Appl. Phys., 1970,41, (IO), 4096- 4100 Magnetic properties of amorphous Fe,Pd,,-, Si,,, alloys (X=0.5-7.0) were studied at I.5-300K in fields up to 8.40 kOe. Above the Debye temperature Bd the alloys arc paramagnetic, and below od superparamagnetic clusters exist. Ferromg- netism was found in amorphous Fe,Pd,,Si,, alloys with a Curie temperature of 28K. Results suggest that the d-d spin exchange interaction is weaker for alloys in the amorphous state than for those in the corresponding crystalline state.

Resistance Anomaly of Dilute Co Impurity in Rh H. NAGASAWA, Phys. Lett. A, 1970, 3zA, (4),

The resistivity and magnetic susceptibility of dilute Co impurity in Rh were measured at r.5- 3ooK. Values of observed Co solute resistivities are presented graphically. The residual resistance of the Co is given as 0.34 @/at../, Co; the effective magnetic moment is 5.0 pB/atom Co, and the Weiss temperature is 1200& IOOK.

Some Aspects of Phase Transformations in Near-equiatomic Niobium-Ruthenium Alloys B. K . DAS, M. A. SCHMERLING and D. s. LIEBERMAN, Muter. Sci. Engng., 1970, 6, ( 4 , 248-254 Studies of reversible phase transformations in three near-equiatomic Ru-Nb alloys by electrical measurements, hot stage optical metallography, X-ray diffraction and magnetic susceptibility measurements suggested a two-stage mechanism in which on cooling the high temperature cubic /3 phase transforms to f.c. tetragonal p' phase, which transforms to f.c. orthorhombic S" phase.

271-272

CHEMICAL COMPOUNDS A Survey of Dinitrogen Complexes of Lhe Transition Metals J. E. FERGUSSON and J. L. LOVE, Rev. Pure. Appl. Chem., 1970,20, 33-50 The preparation and properties of dinitrogen complexes of transition metals including Ru, Os, and Ir are surveyed.

Interaction of Ruthenium Trichloride with Zinc A. N. RYABOV, E. N. RYABOV, G. R. VASILENKO and I. I. KOZHINA, Vextnik Leningrad Univ., Ser. Fix. Khim, 1970, (IO), 98-101 The reduction of cr-RuC1, by Zn was studied by

means of thermographic and X-ray methods. The reaction goes as follows: a-RuCl,+$Zn-> RuJ ZZnC1,. AH",,, for a-RuC1, is 47.4h2.6 kcal , mole.

ELECTROCHEMISTRY Kinetics of the Chemical Reduction of Platinum Black Surface Oxides L. D. BURKE and A. MOYNIHAN, Electrochim. Actu, 1970>15> (91,1437-1443 The rate at which anodic oxide films of platinised Pt electrodes react with H, in aqueous H,PO, was investigated by measuring the amount of oxide film remaining after various reaction times, The reaction rate is inversely proportional to the oxide coverage, probably due to inhibition of oxidation of H, by adsorbed oxygen species on the surface. The kinetics of the reaction are given.

A Ring-disc Electrode Study of the Current/ Potential Behaviour of Platinum in 1.OM Sulphuric and 0.1M Perchloric Acids D. c. JOHNSON, D. T. NAPP and s. BRUGKENSTEIN,

The production of small amounts of soluble species during oxidation and reduction of a Pt electrode was established using the rotating ring- disk electrode. Pt(I1) is produced when an oxidised Pt electrode is reduced, and an un- identified species is produced during oxidation.

Polarisation in Molten Oxides

Ibid., 1493-1509

F. TOUSSAINT, M. BOFFE and E. PLUMAT, Silicates Ind.9 1970, 351 (718), 185-191 Analysis of the intensity-potential curves gave the kinetics of the electrochemical processes at the surface of Pt and simple or complex oxides, e.g. stabilised SnO,, ZrO, or calcined kaolin in molten oxides. The method of electrical conduc- tion of the electrode determined the interface where the electrochemical reaction took place.

Adsorption of Anions on Smooth Platinum Electrodes

J. N. PIRTSKKALAYA, J . Elecnoanal. Chem. Inter- facial Electrochem., 1970, 27, (I), 31-46 The effect of the adsorption of H,, 0, and CH,OH on smooth Pt electrodes was investigated. Chemisorbed I- ions cause an overall decrease in the amount of adsorbed H,; and adsorption of anions lowers that of 0, and CH,OH. These effects were used to determine quantitatively the surface coverage with chemisorbed anions.

Hydrogen Adsorption and Methanol Oxida- tion on Electrolytic Mixed Pt-Rh Deposits

BAGOTSKII, Elektrokhimiya, 1970,6, (8), 1133-1 135 Differential curves for absorption of H, by Pt,

V. S. BAGOTSKII, YU. B. VASILIEV, J. WEBER and

A. M. SKUNDIN, E. K. KHODZHAEVA and V. S.


Rh and electrolytic mixed deposits of 2, 12.5, 20, 50 and 759$ Rh-Pt, and polarisation curves for the electroxidation of IM CH,OH in IN H,SO,, on Pt, Rh and the mixed deposits of 12.5, 20, 50 and 87.5('; Rh-Pt show that the absorption properties of the mixed deposits are similar to those of Rh but that the catalytic properties approximate to those of Pt.

Effect of the Structure of Eleetrodeposited Platinum on its Adsorptive Properties and Electrocatalytic Activity 0. A. KHAZOVA, YU. B. VASILIEV and V. S. BAGOTSKII, Ibid., (g), 1367-1370 Variations in the catalytic activity of platinised Pt electrodes produced by electrodeposition at various potentials, are connected not with the change in rate constants, as in the case of increased roughness, but with the surface concentration of the reacting substances.

Investigation of Mixed Platinum-Rhodium Electrode-catalysts. Adsorption of Hydrogen on Alloys in Sulphuric Acid Solutions

CHENKO and G. D. VOVCHENKO, Vest. Moskov. Univ., Ser. 11, Khim., 1970, 25, (4), 427-431 The adsorption of H, and the catalytic activity for hydrogenation of acrylic acid in H,SO, solutions using Rh-Pt electrode catalysts are greatest for 487" Rh-Pt. Surface area of these electrode catalysts was measured by charging curves and chromatography. A new method for Rh content in Rh-Pt is suggested.

The Cathodic Evolution of Hydrogen on Ruthenium and Osmium Electrodes A. R. KUHN and P. M. WRIGHT, J. Electroanal. Chem. Interfacial Electrochem., 1970, 27, (2),

319-323 Current density - potential curves for the Hz evolution reaction in HC1 and NaCl solutions at 25'C on Ru and 0 s electrodes were obtained at different pH values. Kinetics were determined.

G . S. MANANKOVA, T. M. GRISHINA, G. P. KHOM-

ELECTRODEPOSITION AND SURFACE COATINGS Structure of Evaporated PtSi on Si

Vacuum Sci. Technol., 1970, 7, (5 ) , 543-546 A study of thestructure of evaporated or sputtered Pt on Si substrates has conclusively shown that for annealing temperatures up to 700°C the only phases present are Pt and PtSi.

Electrodeposition of Palladium in Amino- hydroxide, Sulphamate, and Bromide Elec- trolytes I. F. KUSHEVICH and N. T. KUDRYANTSEV, Zashchita Metal., 1970, 6, (41, 465-469 Electrolytes based on Pd(NH,),(OH) 2,

G. A. WALKER, R. C. WNUK and J. E. WOODS, J .

Pd(SOJ'JH,) 2, [Pd(NHdJ(SOJ'JHz) 2, pd(NH3) 2

(NO,),, K,PdBr,, and Pd(NH,),Br, were compared. Polarisation curves were obtained at 2o0C at different values of pH. Current densities were varied between 0.1 and 0.8 A!dm2.

LABORATORY APPARATUS AND TECHNIQUE Two Methods for the Fabrication of Self- supporting Osmium Targets R. F. CASTEN, J . s. GREENBERG, G. A. BURGINYON and D. A. BROMLEY, Nucl. Instrum. Methods, 1970, 80, (21,296-298 Thin targets < 1000 pg/cm2 of self-supporting isotopically enriched 0 s suitable for use in nuclear reaction and scattering experiments and robust targets of several mg an2 were fabricated by use of the described apparatus and methods.

JOINING Braze Alloy Investigation L. F. JILLY, NASA Contract Rept. NASA-CR- 66845, I969,II PP Palniro RE brazing alloy of composition 55 wt.7; Au, 30 wt.% Ni, and 15 wt.()k Pd with a nominal braze temperature of I 107'C has been developed for use on the Hypersonic Research Engine. The properties of Palniro RE are compared with those of Palniro I and 4, which for instance are superior in creep rupture resistance. Although Palniro RE cannot be used at the highest engine temperatures it is suitable, for example, for brazing the mani- folds to the shell structure.

HETEROGENEOUS CATALYSIS Platinum Recovery in Nitric Acid Production Nitrogen, 1970, (66), 40-42 The three methods of recovering Pt from Pt-Rh gauzes are described. The Degussa process uses a Pd-Au gauze below the catalyst gauze; the OSW process employs CaO below the catalyst gauze; the Hercules-Baker process uses glass fibre or ceramic filters to remove Pt present in the gas stream. The economics of Pt recovery are discussed.

Platinum Dioxide as a Catalyst in the Reac- tion of Ammonia Oxidation into Nitrogen Oxide during Nitric Acid Production H. SIKORA, Chemik, I970,23, (I), 11

PtO, catalyses oxidation of NH3 to N oxides at as low as 300°C without prior activation being necessary, unlike Pt which requires heating to a high temperature with a H, burner or by burning C,H,OH on its surface to convert it to PtO,.


Hydrocracking with Chlorinated Platinum- Alumina Catalysts for Liquefied Petroleum Gas Production J. P. GIANNETTI, 11. G. MCILVRIED and K. T. SEBULSKY, Ind. Engng. Chem., Process Des. Dev., 1970, 9,

Specially chlorinated Pt/Al,O, catalysts were prepared by reacting Pt/Al,O, with HCl gas, then with a S chloride or SO, and C1, and finally wirh HCl again. Pentane, hexane and a pre- treated light naphtha were hydrocracked at 2oo-29o3C, and gave results usually obtained at -480°C with conventional catalysts.

Chemisorption of Different Gases on Plati- num/Alumina Type Catalysts T. IOST, T. FILOTTO and G. KALMUCHI, Petrol Gaze, 1970, 21, (z), 111-116 Chemisorption data from the dehydrogenation of cyclohexane on various Pt iAl,O, catalysts showed that information on the size of Pt crystals, the surface coverage by Pt and H iPt ratio is not always sufficient to correlate chemisorption characteris- tics and catalytic activity. Heterogeneity of catalyst surface is calculable from Langmuir, Freundlich or Temkin isotherms, and average heat of chemisorption from the Langmuir isotherm helps clarify the chemisorption mechanism.

Texture Study of Catalysts by Adsorption of Gas. 111. Measure of the Adsorption of Hydrogen and Oxygen on Platinum Sup- ported Catalyst v. BARBAUX, B. KOGER, J.-P. BEAUFILS and J. E. GERMAIN, J . Chin. Phys., I970,67, (5), 1035-1040 0, and H, chemisorption on Pt;Al,O, catalysts were performed in an electronic vacuum micro- balance, after in situ outgassing, by the gravi- metric method. The weights of gases irreversibly adsorbed at 2o'C during a cycle: vacuum, 0,, H,, vacuum, 0, agree with: Pt+*O,-PtO;

The metal surface area and intrinsic catalytic activity were calculated.

Selective Catalytic Reduction of Oxides of Nitrogen by Ammonia on a Platinised Catalyst G. A. SKVORTSOV, A. P. ZASOKIN and A. I. PODZHARSKII, Khim. Promyshlennost, 1970, (6), 435-437 The process of reduction of N oxides by NH, over Pt:A1,0, was studied with regard to effects of temperature, concentration of NH, and concentration of 0,.

On the Role of the Support in Platinnm/ Alumina Catalysts I. I. LEVITSKII, KH. M. MINACHEV and v. v. VORONIN, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1970, (9), 2007-201 I

Comparison of the hydrogenolysis of methyl-

(31, 473-478

PtO+qH,-PtH kH,O;PtHt- 90,=PtO-! 1HZO.

cyclopentane using 5':n Pt /A1,0, with earlier work showed sharp differences from tests with 0.30" Pt!A1,0,. Pt /C and SiO, also gave less hydrogenolysis. A1,0, as the support guaran- tees high dispersion of the supported metal and determines the catalytic properties, presumably due to the different electrical state of the atoms adjoining the support surfaces.

Disproportionation of Cyclohexene and Crossed Disproportionation on Platinum/ Alumina R. MAUREL and G. LECLERCQ, C.R., st+. c, 1970, 271, (4), 239-241 The disproportionation of cyclohexene to cyclohexane in benzene in contact with Pt/AI,O, at 116°C is a complex reaction in which dehydrogenation in benzene precedes hydrogenation.

Kinetics of Consecutive Heterogeneous Cata- lytic Reaction: Gas-phase Hydrogenation of Phenol on a Platinum Catalyst v. HANCIL and L. BERANEK, Chem. Engng. Sci., 1970, 25, (7), 1121-1126

The kinetics of consecutive hydrogenation of phenol to cyclohexanol via cyclohexanone on a Pt:'SiO, catalyst at ISO'C were studied. The course of the overall reaction can be described by Langmuir-Hinshclwood type rate equations, which suggests that both composing reactions occur on the same sites of the catalytic surface.

On the Slow Uptake of Hydrogen by Platin- ised Carbon M. BOUDART, A. w. ALDAG and M. A. VANNICE, J . Catalysis, 1970, IS, (I), 46-51 Burning off the C contaminating the Pt surface of Pt/C before adsorption measurements decreases or suppresses uptake of H?. C contamination of Pt appears to provide bridges which allow surface diffusion of H atoms from Pt to the C support.

Catalytic Activity of Platinum Catalyst on Polymeric Supports s. G. FEDORKINA, G. I. EMEL'YANOVA and N. I. KOBOZEV, Vest. Moskov. Univ., Ser. 11, Khim., 197% 25, (3h 350-352 Studies of the adsorption properties of Pt,'polymer catalysts showed no noticeable effect of the polymers on the catalytic activity of the Pt. Adsorp- tion capacity of an A1,0, support was increased by polymer coating. Polymers tested were caprone, polycarbonate and the copolymer of phenol- phthalein and terephthalic acid.

Palladium : Preparation and Catalytic Pro- perties of Particles of Uniform Size J. TURKEYICH and G. KIM, Science, 1970, 169, (39481,873-879 Uniform particles of Pd, diameter 55-45oA were prepared by the hydrothermal treatment of


Al,(OH), sol to form rods of Also, on which Pd was adsorbed from aqueous suspension. The activity and kinetics of C,H, hydrogenation on this catalyst were examined.

Effect of Zinc Cations on the Selectivity of Palladium Catalysts on Supports during the Hydrogenation of Dimethylethynylcarbinols

SKII, Kinet. Kataliz, 1970, 11, (4), 1072-1074 Studies of the effects of adding Zn cations as ZnSO, to stationary Pd catalysts for hydrogenation of aqueous solutions of 5-757” dimethylethynylcarbinols showed that the modification causes a sharply increased yield (98://) of dimethylvinylcarbinols,

Liquid-phase Hydrogenation of Heptene-l on Palladium and Platinum-Palladium Cata- lysts on Alumina

N. M. POPOVA and A. D. DEMBITSKIT, Neftekhimiya, 1970, 10, (4), 489-493 Studies of the liquid-phase hydrogenation of I-C,H,, in 96:;; C,H,OH at 20°C over Pd/Al,O, and Pt-Pd/Al,O,, in relation to catalyst metal content and to the composition of the active phases, showed that it occurs at the expense of weakly bonded H and is accompanied by isomerisation to cis- and tram-z-C,H,, and 3-C7H,,. Maximum yields on 4% metal/AlpOs occurs with Pd. Yield decreases as Pt content increases.

V. A. NAIDIN, G. D. ZAKUMBAEVA and D. V. SOKOL’

D. V. SOKOL’SKII, M. I. GORYAEV, G. A. SAVEL’EVA,

X-Ray Studies on Supported Palladium Catalysts

1970>73, is), 852-855 M. UEHARA and S . SUZUKI, Kogyo Kagaku Zasski,

Absorbed amounts of H, are proportional to the increase in lattice constant caused by the dissolved Ei,. Dehydrogenation of n-C,H,,, on PdiC was investigated, also the a-B phase transition in PdjC which occurred under a wide range of conditions. The lattice constant of 3.97a suggested a new type of solid solution of H, and Pd.

Hydrogen Absorption Isotherm of Supported Palladium Catalysts

H, absorption isotherms of various supported Ind catalysts were studied and fall into 3 types: {i) perfect step type, in which the Pd exists as uniform crystallites, (ii) imperfect step type, in which the Pd occurs as continuously size- distributed crystallites, (iii) non-step type, Pd as non-crystalline particles. They tcnd towards the non-step type with increasing specific surface area.

Activity of Various Types of Palladium Catalysts Supported on Polyacrylonitrile 0. A. TYURENKOVA and L. A. CHIMAROVA, Zh. Fiz.

Kkim., 1970,44, (91, 2278-2282 Potentiometric studies of the activity of Pd ,poly-

Ibid., 855-859

acrylonitrile catalysts in relation to the conditions of Pd reduction show that those reduced in alco- holic media are more active and stable for the hydrogenation of dimethylethynylcarbinols, whereas those produced using dioxanc have little activity. Optimum reduction occurs at 4 0 T but catalyst produced in those conditions is less selective for hydrogenation of dimethylethynyl- carbinol.

Investigation of the Step Mechanism and Selectivity of Reduction of ,.Aceto- and Propiophenone on Rh-Alto,

S . S . DANIELOVA and R. N. BADAKH, Izv. Akad. Nauk S.S.S.R., Ser. Kkim., 1970, (S), 1797-1803 Rh:Al,O, catalyses addition of H, to aliphatic- aromatic ketones to form alkylphenylcarbinols and alkylcyclohexylketones, depending on the availability of CO groups for hydrogenation. Further reduction depends on the likelihood of either hydrogenolysis of C-OH bonds or of hydrogenation of alkylphenylcarbinol aromatic rings. In mild conditions the former predomi- nates but in severe conditions the latter, forming mainly alkylcyclohexylcarbinols. Partial poisoning of Rh/A1203 by Cd showed that reduction of the aromatic rings occurs at various parts of the catalyst surface at various rates unrelated to the process conditions.

Mixed Adsorption Catalysts for Hydrogena- tion. XVI. Rhodium-Platinum and Rhodium- Palladium Catalysts on Silica Gel

MANTIKYAN, Arm. Kkim. Zh., 1970, 23, (I), 3-8 0.5 wt.% RhSiO, catalysts with additions of Pt and Pd were compared with RhiSiO,, PtjSiO, and PdlSiO, catalysts for hydrogenation of C,H, at 9oCC, volume ratio H,:C,H, ~ 4 : 1 , H, gas flow 1.5-2.5 l/h, activity being expressed as (2, conversion to cyclohexane. Activity increased proportional to Pt content. Activity of concur- rently deposited Rh-Pt:SiO, was greater than the total activity of Rh/Si02 and Pt;SiO, catalysts with the same total content of metals. Pd additions tended to decrease catalytic activity, possibly due to its different electronic structure or to an effect of the SO,.

The Hydrogenation of Alkadienes. Part IV. The Reaction of Buta-1,3-diene with Deu- terium Catalysed by Rhodium, Palladium, and Platinum

P. B. WELLS, and G . R. WILSON, J. Chem. SOC., A, Inorg. Pkys. Tkeor., 1970, (14), 2435-2441 Reactions of buta-1,3-diene with Rh:AI,O,, Pd/Al,O, and Pt/A1,0, as catalysts were studied. Butene isomerisation occurs only after desorption although absorbed butyl groups were formcd at the Rh and Pt surfaces.

L. KH. PREIDLIN, N. V. BORUNOVA, L. I. GVINTER,

A. A. ALCHUDZHAN, N. 2. EDIGARYAN and M. A.

A. J. BATES, Z. K. LESZCZYNSKI, J. J . PHILLIPSON,


Part V. The Hydrogenation of trans- and cis-Penta-1,3-diene catalysed by Cobalt, Nickel, Copper, Palladium and Platinum P. B. WELLS and G. R. WILSON, Ibid., 2442-2447 Gas phase hydrogenation of the pentadienes was investigated using Pd iAl,O, and Pt/Al,O, catalysts amongst others. The reaction was relatively slow; all isomers of n-pentene were formed with little or no pentane.

Measurements of Active Site Concentrations at Rhodium, Osmium, Iridium, and Plati- num Surfaces by l,l-Diphenyl-2-picrylhydrazine Oxidation in the Liquid Phase, and Carbon Monoxide Chemisorption from the Gas Phase

J. GRANT and R. HESELDEN, J. Catalysis, 1970, 18, (21, 224-227 0 atoms chemisorbed at the surface of pre- reduced Rh, Ir and Pt powders with diphenyl- picrylhydrazine to yield H,O and the stable diphenylpicrylhydrazyl free radical. The number of active sites present per gram of powder was calculated from concordance determinations of the free radical concentration by e.s.r. and optical spectroscopy.

Hydrogenolysis of Cyclobutane Hydrocar- bons on Platinum, Palladium, Rhodium, and Iridium Catalysts M. YU. LUKINA, T. G. OLPER’EVA, 0. v. BRAGIN, A. L. LIBERMAN and B. A. KAZANSKII, Dokl. Akad. Nauk

Hydrogenolyses of ethylcyclobutane and of other cyclobutane derivatives over PtlC, Pd jC, Rh iC and Ir /C was studied in constant flow and pulsed flow conditions. With PtjC and PdjC the prin- cipal products were n-hexane and 3-methyl- pentane. With RhIC and Ir/C there were also quantities of other pentanes and lower alkanes.

R. B. MOYES, P. B. WELLS, K. BARON, K. COMPSON,

S.S.S.R., 1970, 193,(1), 106-109

HOMOGENEOUS CATALYSIS Production of Linear Acids or Esters by the Platinum-Tin Catalysed Carbonyktion of Olefins L. J. KEHOE and R. A. SCHELL, J. org. Chem., 1970, 35. (S), 2846-2848 A H,PtCl,-SnCl, couple was used to catalyse the carbonylation of olefins such as dodecene-1 in the presence of methanol to linear esters in Ih at 200 atm.; in the presence of water, acids are formed. K,PtCI, with SnC1,alsoshowedreactivity.

The Palladium(I1) Chloride and Copper(I1) Chloride Catalysed Oxychlorination of Ethy- lene to Ethylene Chlorhydrin H. STANGL and R. JIRA, Tetrahedron Letters, 1970, (41),3589-3592 The reaction of C,H, with 0% in the presence of


PdC1,-CuCI, to produce HO-CH,-CH,-CI is discussed.

Aromatic Substitution of Olefins. The Reaction of Ferrocene with Styrene in the Presence of Palladium(I1) Acetate

s. TERANISHI, J. Chem. SOC., D, Chem. Commun.,

An example of a very convenient direct synthesis of alkenylferrocenes is the reaction of ferrocene with styrene to produce t ~ a n s - sr-styrylferrocene in the presence of Pd(OAc),.

Activation of Molecular Oxygen, Hydrogen, Carbon Monoxide, and Olefins by a Rho- dium(1) Complex in Nonaqueous Media

The complex [(C,H,,),RhCI,],, dissolved in dimethylacetamide containing LiCl, reacts with 0,, H,, CO and some olefins, e.g., maleic acid (MA) to give complexes such as Rh(I)(MA) which have catalytic properties.

Dimeric Metal Acetates for the Homogeneous Hydrogenation of Olefins

Rh,(OCOMe), and Ru,(OCOMe), were shown to catalyse hydrogenation of various olefms in a number of organic solvents.

Homogeneous Catalytic Hydrogenation of Organic Compounds using Rhodiumtriaryl- phosphine Complexes J. L. PARSONS, Diss. Abstr, B, 1970, 30, (9), 4057 Trichlorotris(4-biphenyl-I -naphthylphenyl-phosphine)rhodium(III) has been developed as a homogeneous hydrogenation catalyst and has been used for the catalytic reduction of sr, ,8- unsaturated acids and esters. It is superior in performance to other Rh(II1) phosphine complexes.

Oxidation by Transition Metal Complexes. I. Oxidation of Styrene and Triphenylphos- phine Catalysed by 02-Ir Complex K. TAKAO, Y. FUJIWARA, T. IMANAKA and s. TERANISHI, Bull. Chem. SOC. Japan, 1970, 43, (41, IIS3-IIS7 The oxidation reactions of styrene and PPh, catalysed by various Ir complexes were studied. The complexes IrX(CO)(PPh,), and Ir[(Ph,CH, CH,Ph,),Cl] were effective oxidation catalysts. Oxidation with Pd salts was compared with the Ir complexes.

On the Catalytic Decomposition of Per- chloric Acid in the Presence of Complex Compounds of Iridium S. I. GINZBURG and M. I. YUZ’KO, zh. Neorg. Khim., 197% 15, (91, 2441-2444 I r complexes catalyse decomposition of HCIOI

R. ASANO, I. MORITANI, Y. FUJIWARA and

197% (20), I293

B. R. JAMES and F. T. T. NG, Ibid., (IS), 908-909

B. C. H U I and G. L. RBMPEL, Ibid., (IS), 1195-1196

in the presence of HBSO, at 197-200~C. The formation of polymeric Ir(1V) compounds reduces the catalytic activity. Unstable intermediate compounds, probably of Ir(VI), form initially and are strongly oxidising. Small amounts of Ir evaporate during oxidation of Ir perchlorate due to formation of the higher oxide IrO?

Catalytic Oxidation of Triphenylphosphine Using a Ruthenium-Oxygen Complex B. W. GRAHAM, K. R. LAING, C. J. O'CONNOR and W. R. ROPER,J. Chem. SOC., D, Chem. Commun,, 197% (IS), 1272 Ru(O,)(NCS)(NO)(PPh,), efficiently catalyses oxidation by 0, of PPh, to the oxide.

Hydrogenation of Olefins by p-Dichloro-x- benzene-ruthenium(I1) I. OGATA, R. IWATA and Y. IKEDA, Tetrahedron Letters, 1970, (34), 301 1-3014 The hydrogenation of pentenes by [Ru(C,H,)C1,], was studied in various solvents. The catalytic activity and reaction products depended on the solvent used. The mechanism of hydrogenation and the species produced in coordinating solvents, e.g. DMSO, are discussed.

FUEL CELLS A Fuel-Cell that Operates on Human Blood Chemical Week, 1970, 107, (2), 40 A fuel cell which could power an artificial heart has electrodes of a noble metal substrate to which selective catalysts of Au-Pd alloys are bonded. Placed directly in the blood, one electrode reacts preferentially with glucose in the blood, the other with 0,. 20 !Lw/cm2 of electrode

NEW PATENTS METALS AND ALLOYS Alloys of Variable Transition Temperature F. E. WANG & W. J. BUEHLER British Patent 1,202,404

were obtained; about 10 w would be needed to power an artificial heart,

CHEMICAL TECHNOLOGY Influence of Palladium on the Corrosion and Electrochemical Behaviour of Steel OX25H6T

Zaschita Metal., 1970, 6, (4), 45-427 Studies on the steel oX2gH6T, which contains 60/:, Ni and 25u4, Cr, showed that passivation using o.1-0.5"6 Pd occurs in two stages. The corrosion rates for various Pd additions were: 0.17, Pd, 26.8 g,/m2h; o.zq, Pd, 18 g:m2h; 0 . 5 " ~ Pd, 24.5 g/m2h, in 2o0:, H2S0, at roo'C for 5 h testing,

N. D. TOMASHOV, G. P. CHERNOVA, L. N . VOLKOV,

TEMPERATURE MEASUREMENT On the Control of the Temperature Regime of Glass Masses Delivered for Moulding

PAVLOV and V. V. FOKIN, Stekla Keram., 1970, (8),

Studies of the variations with depth of temperature of molten sheet glass in cooling tanks were carried out using high temperature thermocouples above the surface, Pt-cased thermocouples pro- jecting from the tank walls into the glass and open junction low-inertia Pt :Rh-Pt thermocouples dipped into the glass to various depths. Fluctua- tions and variations at these points indicate that one temperature-measuring point is insufficient and that the thermal processes are complex.

V. M. BUDOV, YU. V. SESKUTOV, V. SH. YAKUPOV, V. S.

6-8

drawn to wire contains about 60-gooh Ru, 5-407{~ Cu, up to about 35:0 Pd and up to 10% Ni. It is produced by liquid-phase sintering, preferably by infiltration of Cu or Cu alloy, into a Ru compact at a temperature between 1083°C and 1500°C.

The alloy JL,M,-, has a martensitic transition

a Group VIA metal, and makes up 50 at.?, of the alloy, the remaining 50", being L I M, where

~ i ~ ~ ~ ~ ~ i ~Noble ~~~~l~

Cu, Au, Ag, Pt, Pd and their alloys are strength- ''Pending the ratio ' M. J is p, R . MALLORY & CO. INC. U.S. Patent 3,515,542

is greater than 0 and less than I. Typically, J is zr, L is Rh and M is R~ oT J is zr, L is pd and

e n d or hardened by introducing UP to 10"" of a compound of Cr, Ti, Th, u, Zr, B Or si Or alloys thereof. A melt is formed of the noble metal and the hardening element and gas bubbled through the melt to form the compound, usually an oxide.

M is Rh.

Workable Duplex Structured Ruthenium Alloys Hardening of Platinum Metals INTERNATIONAL NICKEL CO. INC. U.S. Patent 3,498,763 A cold-workable Ru alloy capable of being cold

JOHNSON, MATTHEY & CO. LTD German Appl. I ,53 3,275 Pt, Pd, Rh and their alloys with one or more

Platinum Metals Rev., 1971, 15, (l), 3 5 4 0 35

temperature depending on

other Pt metals are hardened by the addition of a small amount of one or more base metals. These metals, such as Cr, must form compounds stable at high temperatures.

Dispersion-strengthened Metals

German A P P ~ . 1,935,329 A molten metal (Ag, Au or a Pt metal) is sprayed, together with a disperse-phase component (oxide, carbide, nitride, or sulphide) on to a cooled former. The product may be suitable for, e.g., electric contacts, thermoelements or resistors; or for use as a catalyst, diffusion membrane or spinneret.

JOHNSON, MATTHEY & CO. LTD

CHEMICAL COMPOUNDS Electrically Conductive Oxides Containing Palladium

U.S. Patent 3,498,931 New electrically conductive oxides have the formula PdMO,, in which M is Co, Cr, Rh or CriRh, but may vary slightly in stoichiometry from the formula. They are prepared by the reaction of a Pd dihalide, optionally mixed with Pd, and an appropriate oxide containing M.

Organometallic Polymers

U.S. Patent 3,504,052 A novel class of polymers contains ruthenocene or osmocene units which are inrerlinked to form polymeric products having high heat stability and other advantageous properties. They are produced by reacting ruthenocene or osmocene with an aldehyde or ketone in the melt phase and in the presence of a Lewis acid catalyst.

E. I. DU PONT DE NEMOURS & CO.

MCDONNELL DOUGLAS CORP.

ELECTRODEPOSITION AND SURFACE COATINGS Metallising of Ceramics E. I. DU PONT DE NEMOURS & CO. British Patent 1,202,999 A ceramic is metallised by applying to its surface a finely divided granular noble metal powder. This powder comprises at least 60 wt.O of Pt and optionally a further metal selected from Pd, Rh and for Ru. At least 50 wt.Oo of the Pt must have a surface area of 0.01-1 mL/g. The coated surface is fired, preferably at 1400-2000”C, to give a tightly adherent conductive metal film.

Oxidation-resistant Coated Article Contain- ing Iridium, Ruthenium, Molybdenum or Tungsten

U S . Patent 3,499,740 A coated metal article has a body and a coating of

INTERNATIONAL NICKEL CO. INC.

different compositions which are resistant to interdiffusion at elevated temperatures. They are single-phase conjugate compositions falling at opposite terminals of an alloy tie line on a ternary metallurgical system diagram having Au at one apex, Pd at a second; Ru, Ir, W or Mo at the third.

Palladium Coated Electric Contacts

U.S. Patent 3,500,537 Corrosion-resistant electrical contacts are made coated with Pd. The Pd is electrodeposited from an aqueous ammoniacal bath comprising tetrammino-palladous bromide and having a pH of about 8-10. The deposit is highly ductile thus permitting deformation to form electrical contacts.

Plating Solutions for Rhodium K. OHKUEO et al. U.S. Patent 3,515,651 An electrolyte for electroplating low stress Rh and Rh alloy deposits comprises a Rh salt, optionally a salt of another metal capable of alloying with Rh and at least one of hexameta- phosphoric acid and alkali metal or ammonium hexametaphosphates.

INTERNATIONAL NICKEL CO. INC.

JOINING Brazing Alloy for Joining Graphite to Graphite and to Refractory Metals

U S . Patent 3,497,332 The joining of graphite to graphite and to refractory metals such as Mo, W and their alloys is effected with a brazing alloy consisting essentially of Ni, Pd and 2-12‘;; Cr.

Solderable Stainless Steel P. R. MALLORY & GO. INC. U.S. Patent 3,515,950 A method for rendering solderable a stainless steel body resistant to corrosive attack from common electrolytes includes covering one layer of a stainless steel body with layers of metal. A first metal layer serves as a barrier layer to the diffusion of a subsequent metal layer through to the stainless steel body. The subsequent metal layer is resistant to corrosive attack from common electrolytes, is solderable and consists of Ag alloyed with Au, Pd, Pt, Re or 0 s . The alloy layer may be formed by covering the barrier layer with a layer of Ag and Au or one of the other metals. The layered stainless steel body is heated to a temperature below the melting point temperature of the metal layer having the lowest melting point so that the layers (except the barrier layer) diffuse into one another, forming an alloy layer overlaying the barrier layer.

Solder for Thermoelements

The solder is an alloy of composition:

U S . ATOMIC ENERGY COMMISSION

German ApPl. 1,533,547 SIEMENS A.G.

Pdx(Me,Si,-,) I-x


where Me is Fe or a metal of Group IV, V or VI, other than Cr and Zr, and y is >o.

Soldering Semiconductors

German Appl. 1,564,901 A diode or transistor is attached to a Mo or W base by two layers of a noble metal, preferably Rh.

Solder for Steel and Refractory AUoys L. A. MARKOVICH et d. U.S.S.R. Patent 261,887 The solder has the composition 3~-34')(~ Pd, 22-25";, Ni, I 1-13 5: Cr and the remainder Cu.

TELEFUNKEN PATENTVERWERTUNGS-G.m.b. H ,

HETEROGENEOUS CATALYSIS Self-cleaning Gas Ovens

British Patent 1,200,087 Cooking fumes in a gas oven are oxidised by an oven liner coated with a Pt catalyst.

Dehydrogenation Catalyst

British Patent 1,200,651 Normal alkanes are dehydrogenated to normal alkenes in the presence of a Pt group metal exchanged on to a molecular sieve.

Oxidation Catalyst

British Patent 1,200,952 Concentrated NO is formed by the oxidation of NH, with 0, and water vapour in the presence of a Pt catalyst.

Acrylonitrile Dimerisation Catalyst

British Patent 1,205,285 Adiponitrile is prepared by the dimerisation of acrylonitrile in the presence of a catalyst which is a mixture of a water-soluble salt of a carboxylic acid and a water-soluble Ru salt, supported on C or AI,O,.

Catalyst IMPERIAL CHEMICAL INDUSTRIES LTD British Patent 1,205,521 Aromatic isocyanares are prepared by the action of nitro or nitroso compounds with CO in the presence of a catalyst which is a mixture of at least one of the noble metals Ru, Rh, Pd, Os, Ir and Pt with two or more heavy metal oxides, hydroxides, carbonates, basic carbonates or basic phosphates.

Isomerisation Catalyst IMPERIAL CHEMICAL INDUSTRIES LTD British Patent 1,205,677 The isomerisation of olefines is effected in the

GENERAL ELECTRIC CO.

BRITISH PETROLEUM GO. LTD

INSTYTUT NAWOZOW SZTYCZNYCW



presence of noble metals, preferably Pt, Ru or Pd. Pd gives best results.

Two-stage Hydrocarbon Hydrogenation

U S . Patent 3,494,859 An aromatic hydrocarbon feedstock containing diolefines, mono-olefines and sulphur con- taminants is hydrogenated at a relatively low temperature of 200-500'F with a composite catalyst of Li in Pd ( 1 ) ( A l ~ 0 , to convert the diolefines to mono-olefines. Conventional de- sulphurisation is then carried out.

Production of Acrylonitrile and Meth- acrylonitrile SUN OIL co. U.S. Patent 3,499,025 Acrylonitrile and methacrylonitrile are prepared by reacting C,H, and iso-C,HB respectively with air or 0, in the presence of a slight excess of NH, over a Pt catalyst. The catalyst is in the form of a metallic gauze. Temperatures of from 750- 10oo"C and contact times of less than 0.1 second are used.

Hydrogenation of Aromatic Nitro Compound

U.S. Patent 3,499,034 A new process is described for the hydrogenation of aromatic nitro compounds. It is a continuous, one stage process producing a yield of about 99" , of theory of substantially pure aromatic amine. Pd/C is a preferred catalyst.

Apparatus for Treating an Exhaust Gas Stream with Different Catalyst Beds

U S . Patent 3,503,715 A unitary apparatus for effecting the catalytic oxidation of engine exhaust gases, where there may be both high and low quantities of hydrocarbon emissions with such gases, has one catalyst layer comprising Pt:Al,O, particles containing a Ba, Ca or Sr component.

Catalytic Reforming Process

U S . Patent 3,515,665 A continuous low pressure reforming process is described using a Pt catalyst.

Catalytic Hydrocarbon Conversion

US. Patent 3,516,925 A new conversion catalyst for waxy petroleum feedstocks consists of a Group VI or Group VIII metal deposited on a decationised mordenite containing up to z", of non-catalytic metal cations. The mordenite must have pore openings of 5A or more. A Pt catalyst deposited on decationised mordenite is described in several examples.

UNIVERSAL OIL PRODUCTS CO.




BRITISH PETROLEUM GO. LTD

Naphtha Reforming Process

French Patent 1,583,982 Reforming with a Pt-Re supported catalyst is effected in specified process conditions.

Hydrogenation Catalyst

German Appl. 1,542,089 Liquid-phase hydrogenation can be achieved at comparatively low temperatures and pressures in the presence of a Pt group metal catalyst in SUS- pension, e.g. finely divided Pd.

Catalysts

German App l . 1,542~2 I 4 Catalysts which are active in oxidation, reduction, hydrogenation and dehydrogenation reactions consist of homogeneous mixtures of two or more noble metal (except 0s) oxides. They are not just physical mixtures but are formed, e.g. by CO- precipitation from a mixed salt solution.

Catalyst

German App l . 1,542,216 A catalyst which is useful for, e.g. oxidation and hydrogenation reactions, consists of a coprecipi- tated mixture of l't and Ru oxides, with the weight ratio of the two metals being approximately: Pt from 20 to almost 90; Ru from just over 10 to 80.

Catalyst

German App l . 1,542,239 A catalyst which is active in oxidation and reduction reactions, for example, consists of a mixture, in the proportions of at least 3 : I, of a noble metal oxide (excluding oxides of 0 s ) with at least one oxide of Fe, Co, Ni or Cu.

Keduction Catalyst

VERWERTUNG German App l . 1,567,596 NO may be reacted with hydrogen in H,SO,, in the presence of a Pt catalyst (e.g., 2(:,, PtC) , to give hydroxylamine sulphate.

Oxidation Catalyst

Geman App l . 1,568,364 The partial oxidation of organic compounds, e.g., alcohols, aldehydes, ketones, by an alkali metal or alkaline earth metal hypochlorite is catalysed by the presence of Ru.

Reforming Catalyst CHEVRON RESEARCH CO. German App l . 1,932,339 The catalyst consists of a porous inorganic oxide combined with 0.01-3 wt.Oj0 of Pt, 0.01-5 wt.4" of Re and u.1-3 wt.O<, of a halide.

CHEVRON RESEARCH CO.

DEUTSCHE GOLD- UND SILBER-SCHEIDEANSTALT

JOHNSON MATTHEY & CO. LTD



INVENTA A.G. FUR FORSCHUNG UND PATENT-

CELANESE CORP.

Hydrocracking Catalyst CHEVRON RESEARCH CO. German APPl- 1,947,979 The catalyst is a crystalline zeolite molecular sieve supporting 0.01 to 2.0 wt.76 of Pt, Pd or Ir and 0.01 to 2.0 wt.o/, Re or their compounds.

Vinyl Acetate Production

Dutch Appl . 69.15,305 Vinyl acetate and other esters are produced from olefines, acids and 0, by passage over a catalyst comprising supported Pt metal. The support, e.g. SiO,, has a particle size of 0.1-1.5 ~llfn, preferably 0.1-0.5 mm. It may be hollow.

KNAPSACK A.G.

HOMOGENEOUS CATALYSIS OX0 Catalyst

British Patent 1,202,507 The reaction between an olefinic compound, CO and H, can be carried out continuously in the presence of a solution of a Rh compound in a polar organic solvent, e.g. Rh nitrate, acetate or chloride in methanol.

Polymerisation Catalysts CELANESE CORP. British Patent 1,202,681 The polymerisation of oxymethylene and/or thiomethylene units is catalysed by hydrated trihalides of Ru, Rh, Pd, Gs, Ir and Pt.

OX0 Catalyst

British Patent 1,202,779 Olefines are conveniently hydroformylated in the presence of a catalyst which is a complex of Ir with one carbonyl ligand, one hydride ligand and three other neutral ligands. A typical I r complex is IrHCO(Ph,P),.

Oxidation Catalysts BRITISH PETROLEUM CO. LTD British Patent 1,206,166 Olefines are oxidised by an 0,-containing gas in the presence of a complex of a Group VIII metal, especially Ir(PPh,),COCl, Rh(PPh,),I and Rh(PPh,),Cl.

Rhodium Complex Carbonylation Catalysts ETHYL CORP. US. Patent 3,515,757 Aldehydes are produced from olefines, CO and H, using a complex of formula RhHX,(CO) (TI>,)*, where X is halogen (except F), L is the same or different H atom, 6-12 C aryl, 7-12 C alkaryl or 1-12 C alkyl group, and T is P, As or Sb. Typical catalysts are Rh hydridocarbonyl- bis(tripheny1 arsine) dichloride and Rh hydrido- carbonylbis(n-heptyldi-2- naphthylphosp hine) di- bromide.

MITSUBISHI CHEMICAL INDUSTRIES LTD

BRITISH PETROLEUM CO. LTD


Hydroquinone Production

French Patent 2,014,219 Hydroquinone is produced from C,H,, CO and H2 in the presence of a trimeric Ru tetracarbonyl.

Hydrogenation Catalyst

German Appl. 1,542,380 The catalyst is made by mixing and heating together finely-divided A1 ,03, Ru chloride or nitrosonitrate and (NH,),CO, or bicarbonate.

Hydrogenation Catalysts IMPERIAL CHEMICAL INDUSTRIES LTD German Appl. 1,568,817 Olefinic and acetylenic compounds are hydrogenated in the presence of specified Rh complexes, especially RhX(Ph,P),, where X is an anionic group such as halide.

Hydroformylation Catalyst JOHNSON MATTHEY & CO. LTD. German Appl. 1,939,322 A catalyst for hydroformylation is a Rh hydridocarbonyl phosphine complex, e.g. RhH(C0)

LONZA S.A.

E. I. DU PONT DE NEMOURS 82 CO.

(PPh313.

FUEL CELLS Fuel Cell UNITED AIRCRAFT CORP. British Patent I,200,022

In a fuel cell system capable of operating at full load in the temperature range -40” to ;-5o”C, the catalyst is Pt black.

Fuel Cells GENERAL ELECTRIC co. British Patent 1,204,540 In such a cell the fuel electrode consists of a support material of a metal silicide, Ta boride, Ti boride or B carbide on which is dispersed a catalyst. The latter consists of a Pt-Ku alloy containing 20 to 80 wt.:: of Ru.

Palladium Hydrogen Diffusion Fuel Cell Electrode U.S. SECRETARY OF THE AIR FORCE U.S. Patent 3,497,390 A fuel cell has an electrolyte positioned in a container between a porous oxygen electrode to which oxygen is supplied and a non-porous Pd anode to which gaseous H, is supplied. The Pd anode is produced by heating a Pd strip in air to a temperature between 500% and 875°C.

Fuel Cell Cathode LEESONA CORP. U.S. Patent 3,5r4,336 A fuel cell cathode is a lightweight structure consisting of a mixture of Pt black or another catalytic metal and a hydrophobic polymer such as ptfe.

CHEMICAL TECHNOLOGY Hydrogen Release for a Heat Pipe

U.S. Patent 3,503,438 A heat pipe system, particularly for a railway car, using water which may dissociate and develop a dangerously high pressure of H,, is provided with a H, release device located outside the car. The release device is a Pd or Pd alloy tube sealed to a wall of the heat pipe system and having a closed inner end and an open outer end.

Dispersion-strengthened Metals

French Patent 2,012,909 A mixture of a “host” metal (e.g. a Group VIII noble metal) and a smaller proportion of at least one more reactive metal, in the form of a powder, is projected at high temperature through an atmosphere which will react with the more reactive metal (to form, e.g. oxide, sulphide, nitride), and collected on a cooled surface.

A.C.P. INDUSTRIES INC.


GLASS TECHNOLOGY Method of Forming Jets in Bushing Base- plates

U S . Patent 3,514,84r A method of forming jets in bushing base-plates made of Pt or Pt alloy is described. Pt-Rh and Pt-Ir containing from 1-10 wt.‘:, of gold (especially 2--6O, Au) are preferred. The metal is formed into a body having solid raised portions on one surface, further metal is joined to each of these portions and passage ways are formed through them by the application of dies under pressure. Further metal joined may be of a different alloy.

OWENS-CORNING FIBERGLASS CORP.

ELECTRICAL AND ELECTRONIC ENGINEERING Electrical Heaters for Glass

British Patent 1,202,522

An “ink” containing metal particles or a chemical which will produce such particles on firing, is applied to the glass by silk-screen printing. The metal may be Ag, Au, Pt or Pd.

Electrodes

British Patent 1,206,863 Electrodes, e.g., for the electrolysis of alkali metal chlorides, are obtained by coating T i with an operative electrode material. This consists of oxides of at least one Pt group metal or mixtures thereof with at Ieast one Pt group metal. The preferred composition is RuO,.

TRIPLEX SAFETY GLASS CO. LTD

IMPERIAL CHEMICAL INDUSTRIES LTD


Alloy for Electrical Leads

U.S. Patent 3,495,978 A new alloy for electrical leads normally embedded in a ceramic base constituting a portion of an electrical component, such as a potentiometer, is described. The alloy consists of from 64-90O,~, Au, 10-359, Pd and 0.5-2:o Ru. The proportions are selected so that a greatly improved lead wire is provided in which oxidation is substantially avoided even at the firing temperatures of the ceramic base in which the lead is embedded.

Metallising Ceramics

U.S. Patent 3,497,384 A process for metallising a ceramic substrate by applying a noble metal powder consisting of 6o-r00[~(, Pt (having a surface area within the range of 0.1-1 m"g) and optionally Pd, Rh, Ru and their alloys or mixtures and firing the powder at a temperature within the range of r400-2cmo"C is described. The metal powder forms a tightly adherent conductive metal coating on the ceramic substrate. The process does not use the conventional inorganic binders.

Manufacture of Electrodes NIPPON CARBIDE K.K. U S . Patent 3,497,426 Electrodes are made by mechanically cleaning a T i surface in the absence of O 3 or N, (e.g., by buffing with sandpaper in benzene). They are immediately transferred to a vacuum container, avoiding contact with 0, or N,, and a first Pt group metal coat is then vapour plated on to the cleaned surface to a thickness of 1oo-3cmo A. A second coating of Pt or Rh is subsequently electroplated on to the surface to a thickness of 0.1-5 p. The electrode is suitable for the electrolysis of chlorides and sulphates.

Tungsten Dispenser Cathode

An improved coated dispenser-type cathode consisting of a metal matrix of W or W-LILo in reactive relationship with an alkaline earth metal compound which will supply Ba or BaO to the emitting surface of the matrix is described. The matrix emitting surface is coated with a thin porous layer of an alloy of 0 s and Ir, or 0 s and Ru, to provide longer cathode lifetime. There is also less danger during the manufacture of the cathode than with prior art coated cathodes.

Electrically Conducting Platinum Cobalt Oxides

U.S. Patent 3,514,414 An electrically conductive PtCo oxide is described having the formula Pt&o,O,, where x and y are 0.85=0.15, and a crystal structure based on the rhombohedra1 space group R3m. It is prepared at

WILKINSON DENTAL MANUTACTWRING CO. INC.

B. 1. DU PONT DE NEMOURS & CO.

U.S. PHILIPS CORP. U.S. Patent 3,497,757


elevated temperature and pressure from Co,O, and PtO,. The compound, which may be slightly modified with Mn, is useful in electrical resistors.

Current Collectors for Cells with Hot Acid Electrolytes GENERAL ELECTRIC co. U S . Patent 3,515,595 Current collectors comprise ternary alloys consisting of Ni, Pd and Au. For cells using a hot phosphoric acid electrolyte the alloy preferably consists of 50-80n,; Ni, 5 ' ; ~ Pd and 21; Au on a weight basis. For cells using hot H,S04 or sulphonic acid polymer electrolyte the alloy preferably consists of 30-50"d Ni, at least 30°;, Pd and at least 51:, Au, on a weight basis.

Electrodes

French Patent 1,586,120 Electrodes, particularly anodes for the electrolysis of alkali metal chlorides, consist of T i coated with a noble metal, e.g., Pt.

Electric Resistor

German Appl. 1,640,561 The resistor consists of an insulating body with a resistive surface layer of a mixture of 10-80 wt.qi, (esp. 46-65 WT.';~) of finely divided RuO,, the remainder being glass. Alternative compositions include finely divided Ag and compositions of matter formed by heating RuO, with a Group V metal oxide, such as Nb06.

Electrode Coating Process PPG INDUSTRIES INC. Dutch Appl. 69.14899 An anode for brine electrolysis is coated with Ti and a noble metal oxide. An organic Ti compound and a decomposable noble metal compound are applied to the base anode and heated to produce the oxide coating. T i resinate and Ru resinate are suitable compounds.

Electrode for Electrochemical Processes

Dutch Appl. 69.17586 The electrode has a body of refractory coated with a layer of active catalyst. The layer consists of a Pt metal containing a small amount of a Sn, Sb and/or Ge oxide. In an example a Ti body is coated with a mixture deposited from a solution of a Sn alkoxy compound and RuCI,.

PRODUITS CHIMIQUES PECHINEY-ST. GOBAIN


IMPERIAL CHEMICAL INDUSTRIES LTD

TEMPERATURE MEASUREMENT Resistance Thermometer

British Patent 1,199,878 A Pt resistance thermometer is designed for use in conditions of high vibration.

ROSEMOUNT ENGINEERING CO. LTD


PLATINUM METALS REVIEW - Johnson Matthey...processing and utilisation of soybeans began a few years...

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Transcript of PLATINUM METALS REVIEW - Johnson Matthey...processing and utilisation of soybeans began a few years...