48
UK ISSN 0032-1400 PLATINUM METALS REVIEW A quarterly survey of research on the platinum metals and of developments in their application in industry VOL. 40 APRIL 1996 NO. 2 Contents Ruthenium Enhanced Titanium Alloys Thermodynamic Properties of the Platinum Metals on ITS-90 Random Paramagnetic Platinum-Iridium Compound Flux Pinning by Platinum and Rhodium in High Temperature Superconductors Platinum Electrodes in Choline and Acetylcholine Sensor Alloys in Catalysis Platinum Group Metals Conference The Development of Molecular Wires Preparation of Platinum/Polymer Nanocomposites New Palladium Polymerisation Catalyst Systems Iridium Activation of Carbon-Hydrogen Bonds Platinum Recovery by Palladium Alloy Catchment Gauzes in Nitric Acid Plants Iridium Apparatus for XRF Fusions Rutheniudlatinum in Water Electrooxidation Abstracts New Patents 54 62 63 64 69 70 71 72 77 78 79 80 87 87 88 95 Communications should be addressed to The Editor, Susan V, Ashton, Platinum Metals Review Johnson .Matthq Puhlic Limited Company, Hatton Garden, London ECl N 8EE

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UK ISSN 0032-1400

PLATINUM METALS REVIEW

A quarterly survey of research on the p la t inum metals and of developments in their appl icat ion i n industry

VOL. 40 APRIL 1996 NO. 2

Contents

Ruthenium Enhanced Titanium Alloys

Thermodynamic Properties of the Platinum Metals on ITS-90

Random Paramagnetic Platinum-Iridium Compound

Flux Pinning by Platinum and Rhodium in High Temperature Superconductors

Platinum Electrodes in Choline and Acetylcholine Sensor

Alloys in Catalysis

Platinum Group Metals Conference

The Development of Molecular Wires

Preparation of Platinum/Polymer Nanocomposites

New Palladium Polymerisation Catalyst Systems

Iridium Activation of Carbon-Hydrogen Bonds

Platinum Recovery by Palladium Alloy Catchment Gauzes in Nitric Acid Plants

Iridium Apparatus for XRF Fusions

Rutheniudlatinum in Water Electrooxidation

Abstracts

New Patents

54

62

63

64

69

70

71

72

77

78

79

80

87

87

88

95

Communications should be addressed to The Editor, Susan V, Ashton, Platinum Metals Review

Johnson .Matthq Puhlic Limited Company, Hatton Garden, London ECl N 8EE

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Ruthenium Enhanced Titanium Alloys MINOR RUTHENIUM ADDITIONS PRODUCE COST EFFECTIVE CORROSION RESISTANT COMMERCIAL TITANIUM ALLOYS

By R. W. Schutz RMI Titanium Company, Niles, Ohio, U.S.A.

Several new, more highly corrosion resistant t i tanium alloys containing a nominal 0.1 weight per cent of ruthenium have been developed and evalu- ated fo r industrial service in corrosive environments. These improved ruthe- nium-enhanced a, a-p and p t i t a n i u m alloys are lower in cost t han the corresponding palladium-containing t i tanium alloys, and offer essentiallr the same corrosion performance in dilute reducing acids and hot brine envi- ronments. The titanium-0.1 ruthenium binary alloys can be cost effectively substituted for traditional t i tanium-palladium alloys and should represent a more attractive alternative to nickel-chromium-molybdenum alloys in hot, acidic brine applications. The corrosion database that has been estab- lished for the higher strength ruthenium-enhanced a-p and p t i tanium alloys in high temperature sweet and sour brines provides the basis for their selec- tion for applications in the chemical process, oillgas production, offshore and geothermal energy industries.

Traditionally, the palladium-containing tita- nium alloys, ASTM (American Society for Testing and Materials) Grades 7 and 11 tita- nium (titanium-0.15 weight per cent palladium, Ti-0.15Pd) have been the most corrosion resis- tant titanium alloys commercially available. These titanium-palladium, Ti-Pd, alloys were selected when other common industrial titanium alloys, such as the unalloyed grades, exhibited susceptibility to crevice and pitting corrosion in more aggressive chemical service. Severe service environments include chlorine- saturated brines, wet halogens, acidic metal chlo- ride solutions (such as FeCl,, ZnCl,, AlCl,) and hydrolysable, concentrated brines (such as MgCl,, CaC1,) at temperatures exceeding - 80°C. The Ti-Pd alloys are also corrosion resistant over a much wider range of tempera- tures and/or acid concentrations in hot dilute inorganic and organic reducing acids (1).

Despite their dramatically enhanced corrosion performance, the utilisation of Grades 7 and 1 1 titanium alloys has been severely limited over the past thirty years due to their high relative

cost. As is shown in Table I, the cost of Ti-Pd alloy is almost twice that of unalloyed titanium and is similar to that of common nickel- chromium-molybdenum, Ni-Cr-Mo, alloys on a dimensional (density-normalised) basis. The higher cost of the titanium alloy results solely from its palladium content, based on a nomi- nal addition of 0.15 to 0.18 weight per cent (at a price taken in November 1995 of $144/troy ounce for palladium powder).

Leaner Palladium-Titanium Alloys Over the past five years titanium alloy

producers have critically re-evaluated the minimum palladium content required in the alloy. Following a closer examination of the original corrosion data established by Stem and Wissenberg in the development of the Ti-Pd alloy (2, 3), it was recognised that significant savings could be achieved by reducing the nominal palladium content. Stern’s profiles of corrosion rates in boiling hydrochloric acid, see Figure 1, clearly suggest that the beneficial effect due to palladium is optimised very quickly at

Platinum Metals Rev., 1996, 40, (2), 54-61 54

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Table I

Approximate Mill Product Cost Ratio* (Corrected for Density)

Alloy I ASTM Grade

Unalloyed Ti Ti-0.3Mo-0.8Ni Ti-0.1 5Pd Ti-0.05 Pd Ti-0.1 Ru

2 12 7

16 26

Ti-3AI-2.5V Ti-3AI-2.5V-0.05 Pd Ti-3AI-2.5V-0.1 R u Ti-6AI-4V Ti-6AI-4V-0.05 Pd Ti-6AI-4V-0.1 Ru

Alloy C-276 (Ni-Cr-Mo)

24

cost ratio

1 .oo 1.12 1.90 1.38 1.15

1.25 1.60 1.38 1.22 1.57 1.34

1.90 - * For 6.3 m m plate Ratios are compared to the cost of unalloyed titanium Costings are based on November 1995 figures

low levels, so that only minimal improvements in corrosion occur for alloys containing above - 0.03 weight per cent palladium (2, 3). This behaviour was confirmed in more recent hydrochloric acid corrosion rate profiles devel- oped by Kitayama, Shida and colleagues (4,5), and by the author, as shown in Figure 2 (6). As expected, dramatic improvements in alloy crevice corrosion resistance in hot chloride and other halide-rich aqueous media are also achieved at these lower palladium levels, see Figure 3

Based on these studies, several new lean- palladium alloys, which are described in Table 11, have been incorporated into ASTM product specifications. These alloys are allowed to contain 0.04 to 0.08 weight per cent palladium, with the nominal amount being 0.05 per cent. The resulting reductions in cost of Ti-Pd alloy mill products are significant, and are shown in Table I.

For applications where higher strength alloys are required, similar additions of palladium can be made to a-j3 or j3 titanium alloys to produce the cost effective alloys outlined in Table 11. The

(5, 6).

corrosion performance of these higher strength palladium-enhanced alloys is documented elsewhere (6, 7).

Lean Ruthenium-Titanium Alloys The on-going pursuit of lower cost industrial

titanium alloys at the RMI Titanium Company has led to the development of ruthenium- enhanced titanium alloys. From the standpoint of alloy formulation cost, ruthenium represents the lowest cost platinum group metal addition on a per weight basis. The ruthenium powder price, in November 1995, was approximately $30 per troy ounce, which is a factor of four to five times lower than that of palladium powder. However, profiles of the acid corrosion rates for the titanium-ruthenium, Ti-Ru, binary alloy and for other titanium alloys suggest that at least twice as much ruthenium by weight is required to impart corrosion resistance comparable to that of titanium-0.05 weight per cent palladium, Ti-0.05PdY see Figure 2 (6). Despite the need to double the weight of the ruthenium addition, the titanium alloy containing the nominal 0.1 weight per cent ruthenium st i l l achieves cost savings of approximately 17 per cent compared with the Ti-O.05Pd (titanium Grade 16) alloy and approx- imately 40 per cent compared with the classic Ti-0.15Pd (titanium Grade 7) alloy. Comparative

5% HCI

3% HCI

0

001-

00 01 0 2 03 0 4 0 5 0 6 0 7 PLATINUM OR PALLADIUM, W t %

Fig. 1 Effect of the palladium content on the titanium corrosion rate in b o i i hydrochloric acid solutions (2,3)

Platinum Metals Rev., 1996, 40, ( 2 ) 55

9 18 28

5 24 29

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Table II

New, Improved and Cost-Optimised Ruthenium-Enhanced Titanium Alloys for Corrosive Service

Ti-0.1 5Pd* (R52250)

Ti-3AI-2.5V (R56320)

Ti-6AI4V (R56400)

Traditional Alloy

11

9

5

Alloy

Ti-0.15Pd (R52400)

Ti-3AI-8V-6Cr4Zr-4Mo (Ti-38644 or Ti 8eta-CTM) (R58640)

19

Low interstitiakoft grade UNS Unified Numbering System

New and Improved Alloy I Motivation for New Alloy

Alloy New alloy

Ti-O.05Pd Lower cost Ti-0.1 Ru

Grade

Ti-0.05Pd"

Ti-3AI-2.5V-0.05 Pd

Ti-6AI4V-0.05Pd Ti-6AI-4V-0.1 Ru

17 Lower cost 27

18 Enhanced crevice and 28 reducing acid resistance

24 Enhanced crevice, 29 reducing acid, and

SCC resistance

Ti-38644-0.05Pd 20 Enhanced crevice, Ti-38644-0.1 Ru - reducing acid,

and SCC resistance

alloy costs outlined in Table I for thin plate product suggest that ruthenium-enhanced tita- nium alloys offer substantial cost savings over the corresponding palladium-containing alloys.

Mechanism of Ruthenium Enhancement The basic mechanism of ruthenium addition

to titanium is considered to be very similar to that of palladium and other platinum group

metals, and results from alloy ennoblement. In a similar way to palladium, ruthenium exhibits minimal solubility (less than 0.1 weight per cent) in the a-titanium phase, which results in a fine, uniform dispersion of noble Ti-Ru precipitates withiin the alloy (8).

When exposed to reducing acids, these precipitates, and/or ruthenium-enriched sur- faces produced by selective dissolution, provide

1 1 t TI Grade 2 + T1-0.05Pd -A- Tt-DlSPd -0- T i - 0 1 0 R u

Fig. 2 Corrosion rate proflea for

and titanium-palladium alloys titanium-0.1 percent ruthenium

1 2 3 in boiling hydrochloric acid

[:ye ~ -4 HYDROCHLORIC ACID, W t -1. solutions

fitinurn Metah Rev., 1996,40, (2) 56

ASTM Grade (UNS Number) ASTM Grade

Ti-O.05Pd Ti-0.1 Ru

Ti-0.05Pd" Ti-0.1 Ru"

Ti-3AI-2.5V-0.05 Pd Ti-3AI-2.5V-0.1 Ru

Ti-6AI4V-0.05Pd Ti-6AI-4V-0.1 Ru

Ti-38644-0.05Pd Ti-38644-0.1 Ru

ASTM ASTM

7 16 16

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cathodic sites of low hydrogen overvoltage and accelerated hydrogen ion (H,O+) reduction (9, 10). This depolarisation of the hydrogen ion reduction reaction, or “cathode-modification” phenomenon, produces a substantial shift in the corrosion potential of the titanium alloy in acid towards the noble (positive) direction where the protective surface oxide film, TiO,, is stable (l), and full passivity can be achieved. This has been a highly effective and well-known technique for improving the corrosion performance of tita- nium alloy, due to the well established active- passive behaviour of titanium in reducing acids and its exceptionally high anodic pitting poten- tial in acid solutions.

Ruthenium alloy additions also effectively inhibit titanium crevice corrosion in hot aque- ous halide and sulphate environments. This enhanced crevice corrosion resistance results from the same “cathode modification” mech- anism discussed above for reducing acids. With time, the solution within a tight metal crevice exposed to hot salt solutions often becomes a more aggressive deaerated reducing acid (1). This explains the dual beneficial effects from the ruthenium addition, both in reducing acid exposure and within crevices. Creviced surfaces are ennobled and local passivity is maintained

Minimum Yield Stress,

ksi (MPa)

40 (275) 40 (275)

25 (170) 25 (1 70)

70 (483) 70 (483)

40 90 140 190 240 290 TEMPERATURE. ‘C

Fig. 3 Temperature-pH limits for crevice corrosion of titanium alloys in naturally- aerated sodium chloride-rich brines. (The shaded areas are regions where alloys are susceptible to attack)

Minimum Ultimate Tensile

Strength, ksi (MPa)

50 (345) 50 (345)

35 (240) 35 (240)

90 (620) 90 (620)

within acidic crevices. The enhanced crevice resistance of Ti-Ru alloys is essentially equiva- lent to that of Ti-Pd alloys, as indicated by the guidelines in Figure 3.

1 10 (759) 11 0 (759)

Higher Strength Ruthenium- Enhanced Titanium Alloys

Greater strength in titanium is commonly achieved by the addition of alloying elements, such as aluminium and vanadium, to form

120 (827) 120 (827)

Minimum Tensile Strength Value

Allov Grade I ASTM

Ti-O.15Pd 7 Ti-0.1 Ru I 26

Ti-O.15Pd” Ti-0.1 Ru”

Ti-3AI-2.5V 9 Ti-3AI-2.5V-0.1 Ru

Ti-6AI-4V ELI Ti-6AI-4V-0.1 Ru

Table 111

for New Ruth

Alloy type

a a

a a

a-P a-P

Low interstitiallsoft grade ksi is 1000 Ibhn’ ELI is Extra Low lnterstitials

Platinum Metals Rev., 1996, 40, (2) 57

Table 111

Minimum Tensile Strength Values for New Ruthenium-Enhanced Titanium Alloys

ASTM ASTM

11

276

9

28 23

29 a-P a-P

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3.00-

T I - ~ A I - ~ V

T 1 - 3 A l - 2 5 V E

u' t

Q d 1.00

g

1 5 0

T I - ~ A I - 2 5 V - Ru T I - ~ A I - 4V- Ru 0 5 0

a-P or P-phase alloys. With the exception of molybdenum, most common alloying elements, and especially aluminium, diminish the reduc- ing acid- and hot halide crevice-corrosion resistance of titanium alloys, with increasing content (1 1). The titanium-3 aluminium-2.5 vanadium, Ti-3AI-2.5V, (titanium Grade 9) and titanium-6 aluminium-4 vanadium, Ti-6AI-4V, (titanium Grade 5 ) alloys are two such common a-p alloys which exhibit attractive medium-to- high strength properties, see Table 111, but in certain environments they possess corrosion resistance inferior to that of unalloyed titanium. In fact, the Grade 9 titanium alloy was recently incorporated into the ASME (American Society

Fig. 4 Corrosion rate profiles for a-P titanium alloys in boiling hydrochloric acid solutions showing the benefits of ruthenium additions

of Mechanical Engineers) Pressure Vessel Code for use at temperatures up to 3 15"C, and offers significantly higher design allowables compared with other titanium alloys listed in the Code. Unfortunately, this alloy is susceptible to crevice corrosion in chloride- or other halide-rich ser- vice environments at temperatures above - 80°C (depending upon pH, etc.), thus severely lim- iting application and design opportunities. The higher strength titanium Grade 5 alloy also exhibits susceptibility to stress corrosion in brine and aqueous halides which similarly limits its use at increased temperatures.

The deficiencies in the corrosion performances of these high strength titanium alloys can also

-"" I 4 3 5 0 TI Grades 2.5.9

a T I - R U or TI -Pd

0 Ti-3AI - 2 5 V - Ru

TI- 6AI - 4 V - Ru

TI Grade 12

2 0 % NaCI. pH2 25% NaCI, p H 3 10% FeCI, or

(Nat. aerated1 (deaeratedl 20% NaO, p H 2 (CI ?- sat1

Fig. 5 Approximate tempera- ture thresholds for crevice corrosion of ruthenium- enhanced titanium alloys in acidic chloride brines

Platinum Metah Rev., 1996, 40, (2) 58

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Table IV

- Types of SCC

tests

C-ring Slow strain rate

U-bend C-ring Slow strain rate

9 U-bend Slow strain rate

Results of Stress Corrosion Cracking Tests for Ruthenium-Enhanced Titanium Alloys in High Temperature Brines I

Temperature SCC or of tests, localised

OC attack?

260 No 232, 260, 288 No

302,330 No 330 No

302,330 No

260 No 25, 260, 274 No

I Alloys tested I Test media

Ti-6AI-4V-R u Ti-3AI-2.5V-RU I Ti-3Al-8V-6Cr-4Zr-4Mo-R~

Sour gas well brine

Ti-6AI-4V-RU Ti-3AI-2.5V-Ru I Ti-6AI-4V-Ru Hypersaline

geothermal brine

Sour gas well brine:

Sour geothermal brine:

Hypersaline geothermal brine:

deaerated 25% NaCI, 1000 psig H,S. 500 psig CO,. 1 g/l S. pH 3.5

20,000 ppm CY, 800 ppm SO:-. 4 ppm F-, 12,420 ppm Na’. 1200 ppm K * , 20 psig H,S. 100 psig CO,. pH 2.3 (deaerated)

15.2% NaCI. 2.45% KCI. 6.7% CaCI,. 200 psig CO,. pH 4.0 (deaerated)

be effectively reduced by nominal additions of 0.1 weight per cent ruthenium. Corrosion studies performed upon ruthenium-enhanced a-j3 titanium alloys reveal substantial improve- ments in their resistance to reducing acids, hot chloride crevice corrosion and stress corrosion cracking (6). Alloy corrosion rate profiles in boiling hydrochloric acid, presented in Figure 4, show the obvious benefit of ruthenium addi- tions. The mechanism of corrosion resistance is again the same “cathode modification” (enno- blement) and oxide film stabilisation phenom- enon as discussed previously for the binary Ti-Ru and Ti-Pd alloys.

The dramatic elevation of the threshold temperatures at which crevice corrosion starts in naturally-aerated acidic brines is indicated in Figure 5 for the ruthenium-enhanced a-p alloys. This enhancement has been confirmed via “worst-case” Teflon gasket-to-metal crevice tests in sweet and highly sour concentrated brines and in deaerated hypersaline Salton Sea geo- thermal brines down to pH 2 (6). In more aggressive, severely-oxidising (chlorine satu- rated or FeC1,-rich) acidic brines, the crevice resistance of these higher strength alloys may

be restricted to pH values above 3, when temperatures exceed - 80°C.

Although the Ti-3Al-2.5V alloy is not gener- ally susceptible to stress corrosion cracking (SCC) in aqueous media, it is known that the Ti-6A1-4V alloy can exhibit halide SCC sus- ceptibility, especially when the aluminum and/or interstitial levels increase (1 2). This serious lim- itation can be alleviated during exposure to hot aqueous halide (brine) by ruthenium addition to the ELI (Extra Low Interstitials with a 0.13 per cent oxygen maximum) Ti-6A1-4V alloy base. The SCC test results outlined in Table IV support the selection of these modified a-j3 tita- nium alloys for use in either sweet or sour sodium chloride-rich brines at temperatures as high as 330°C. These hot brine test environments are typical of those in Salton Sea geothermal brine wells in California and in deep sour gas wells in the Gulf of Mexico.

Similar improvements in high temperature corrosion behaviour can be achieved in j3-tita- nium alloys by the addition of ruthenium. Corrosion studies conducted by the author on the Ti-38644 (titanium Grade 19) (Ti Beta- C”) alloy suggest that the mechanism is again

Platinum Metals Rev., 1996, 40, ( 2 ) 59

Sour geothermal

brine

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P w‘3M3. a

250

b

0 Crevice corrosion in sweet brine I Crevice corrosion in sour brine

Stress corrosion

6 n naa

Standard Ru- Enhanced TI - 38644 TI -38644

Fig. 6 Approximate temperature thresholds for crevice and stress corrosion of standard and ruthenium-enhanced Ti-38644 alloys in sweet and sour sodium chloride brines

“cathode-modification”. Of particular engi- neering value are the dramatic increases in the threshold temperatures for crevice corrosion and SCC offered by the ruthenium-enhanced Ti-38644 alloy in sweet and sour sodium chloride-rich brines (13), see Figure 6.

Status and Potential Applications for Ruthenium-Containing Titanium Alloys

Since the minor addition of 0.1 weight per cent ruthenium to these titanium alloys has no sig- n5cant influence on their mechanical and phys- ical properties, the new ruthenium-containing alloys are specified with the same minimum

tensile properties as the corresponding base alloys. Values for the minimum tensile proper- ties required by ASTM product specifications are listed in Table III. The four new ruthenium- containing a and a-j3 alloys, with a permitted ruthenium content of 0.08 to 0.14 per cent, have been assigned the ASTM grade numbers indicated in Table 11. They have recently been incorporated in appropriate ASTM specifica- tions for sheet, strip and plate (B265), forg- ings (B381), bar and billet (B348), seamless and welded pipe (B337, B861 and B862), fittings (B363), tubing (B338) and wire (B863). ASTM Grades 26,27 and 28 titanium alloys will soon be submitted for approval and eventual incor- poration into the ASME Pressure Vessel Code. The ASME Code design allowables specified for these three alloys should mimic those for titanium Grades 7, 11 and 9 alloys, respectively, already in the Code.

Some other possible applications for the tita- nium-0.1 ruthenium alloys (Grades 26 and 27) in the chemical and process industries are listed in Table V. These alloys offer cost effective, direct replacement of titanium Grade 7 and 1 1 alloys. The lower cost of these Ti-Ru alloys should also result in increased use of titanium in traditional Ni-Cr-Mo alloy applications which involve dilute acids and/or halide-rich process streams.

Current candidate applications for the higher strength ruthenium-enhanced titanium alloys

Table V

Candidate Applications for Titanium-0.1 Ruthenium Alloys

Chloralkali and chlorate cell anodes, liners and components

Hot seawatedbrine plate exchangers*

Hot Ca. Mg salt brines

Hot acidic metal halides (FeCI,, CuCI,. AICI,. NiCI, and ZnCI,)

Hot aqueous CI,/Br, (wet halogens) and CI,-saturated brines

Hot dilute organic and inorganic acids

MnO, anodes

FGD (Flue Gas Desulphurisation) scrubber inlets/prescrubbers

Steel tubesheetlvessel explosive cladding*

* Requires softer. lower interstitial grades of these alloys

Platinum Metak Rev., 1996, 40, (2) 60

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Application

I Ti-3AI-2.5V-Ru I Ti-GAI-4V-Ru I Ti-38644-Ru

Applicable Alloys

Wet oxidation processes I x I I

~ ~~ ~~ ~ ~

Hydrometallurgical ore leaching processes

Deep sour gas and geothermal well tubulars

Other waste treatment processes I X I I

X X

X X X

Hiah ternDerature oraanic svnthesis I X I I

Offshore flowlines, export and catenary risers

Coiled tubing

Pressure vessels, heat exchangers

X X

X

X

Downhole tools and accessories I I X I X

Valves, pumps, shafting X

Fasteners X X

Agitators

Seamless piping

Welded piping

are outlined in Table VI. Note that the titanium Grades 28 and 29 alloys are also currently in the final stage of approval for incorporation in the NACE (National Association of Corrosion

Engineers) MR-01-75 Standard for use in sour service; allowing these new alloys to be selected for many deep oil/gas wells and offshore production components.

References

X X

X X X

X

1 R. W. Schutz and D. E. Thomas, “Corrosion of Titanium and Titanium Alloys”, in Metals Handbook-Ninth Edition, Vol. 13 - Corrosion, ASM, Materials Park, OH, 1987, pp. 670-706

2 M. Stern and H. Wissenberg,J. Elecmchem. SOC., 1959, 106, (9), 759

3 M. Stern, US. Patent 3,063,835; 1962 4 S. Kitayama, Y. Shida, M. Ueda and T. Kudo,

“Effect of Small Pd Addition on the Corrosion Resistance of Ti and Ti Alloys in Severe Gas and Oil Environment”, Paper No. 52, Corrosion ‘92 Annual Conf., NACE, Houston, March 1992

5 S. Kitayama, Y. Shida and M. Oshiyama, Sumitorno Search, Sumitomo Metals, Japan, 1990, (41), 23

6 R. W. Schutz, “Recent Titanium Alloy and Product Developments for Corrosive Industrial Service”, Paper No. 244, NACE Corrosion ‘95 Annual Conf., NACE, Houston, 1995

7 R. W. Schutz and M. Xiao, “Optimized Lean-Pd Titanium Alloys for Aggressive Reducing Acid and

Congr., 3 4 Sept. 1993,NACE, Houston, p. 1213 Halide service Emimmem’’: Roc. 1% Int Corrosion

8 E. Van der Lingen and H. de Villiers Steyn, “The Potential of Ruthenium as an Alloying Element in Titanium”, Paper presented at Titanium Applications Conference, October 2-5, 1994, Titanium Development Association, Boulder, Colorado

9 N. D. Tomashov, R. M. Altovsky and G. P. Chernova,J. Elecmchem. SOC., 1961,108, (2), 113

10 H. H. Uhlig, “The Corrosion Handbook”, J. Wiley & Sons, Nu, 1948, pp. 1144-1 145

11 R. W. Schutz and J. S. Grauman, “Fundamental Characterization of High-Strength Titanium Alloys”, Industrial Applications of Titanium and Zirconium, ASTM STP 917,1986, pp. 130-143

12 Stress-Corrosion Cracking-Materials Performance Evaluation, ASM, Materials Park, OH, July 1992,

13 R W. Schutz and M. Xiao, “Enhancing Corrosion Resistance of the Ti-38644 Alloy for Industrial Applications, Titanium ‘92 - Science and Technology, Vol. III, TMS, Warrendale, PA, 1993, p. 2095

pp. 265-297

Platinum Metals Rev., 1996, 40, ( 2 ) 61

Table VI

Candidate Applications and Components for Ruthenium-Enhanced a-P and P Titanium Alloys

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Thermodynamic Properties of the Platinum Metals on ITS-90

Ru Rh Pd 0 s

Superconducting temperature (TJ, K 0.48 0.000325 - 0.64

Electronic specific heat coefficient (y). mJ/mol K2 3.00 4.65 9.42 2.05

Debye temperature (eD), K 550 51 2 272 467

By J. W. Arblaster Rotech Laboratories, Wednesbury, West Midlands, England

Ir Pt

0.1 125 -

3.20 6.54 420 236

Selected properties taken from recent reviews weights (3): ruthenium 10 1.07, rhodium written by the present author of the thermo- 102.90550, palladium 106.42, osmium 190.23, dynamic properties on the International iridium 192.217 and platinum 195.08 (revised Temperature Scale, ITS-90, are listed in the to 195.078 in 1995) (4). Tables below (1,2). Values in these reviews cor- Selected values for solid rhodium and iridium respond to a standard state pressure of one bar at 298.15 K and below are based on the assess- and have been corrected to the 1993 atomic ments of Furukawa, Reilly and Gallagher ( 5 ) .

Specific heat (Cop), J h o l K

Enthalpy (H029815 - Hoe), J/mol Entropy ( S O ) , J/mol K Heat of sublimation (AHo2= 15), kJ/mol

Table I

Ru Rh Pd 0 s Ir Pt

24.05 24.90 25.85 24.69 25.09 25.65

4577 4914 5444 4992 5266 5694 28.50 31.56 37.64 32.56 35.49 41.53

649 558 377 788 670 565

Ru Rh

Specific heat (Cop), J/mol K 21.524 21.014 Enthalpy (Hozwls - Hoe), J/mol 6235.2 6206.6 Entropy ( S O ) , J/mol K 186.509 185.827

Table I1

Properties at 298.15 K (solid)

Pd

20.786 6197.4 167.066

0 s

20.788 6197.4 192.579

Platinum Metals Rev., 1996, 40, (2), 62-63 62

Low Temperature Properties

Table 111

Properties at 298.15 K (gas)

20.788 25.531 6197.4 6576.6 t 193.584 192.409

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* The melting points of al l but 0 s are proposed secondary fixed points on ITS-90 (6)

Pressure, bar

1 x 1 o - I 2

1 x lo-" 1 x 1 0-1° I x I O - ~ I x lo5 I x lo-' 1 x lod I x 10.~ 1 x 10" I x lo-' 1 x 1 x lo-' 1 NBP

Temperature, K

Ru Rh Pd 0 s Ir Pt

1684 1468 1060 2048 1751 1489 1772 1546 1122 2156 1844 1569 1871 1634 1191 2277 1 949 1659 1982 1733 1269 241 1 2065 1759 2107 1845 1359 2563 21 97 1872 2249 1972 1462 2736 2347 2002 241 2 21 19 1582 2934 2520 21 56 2602 2293 1725 31 63 272 1 2339 2842 2508 1899 3435 2976 2556 31 34 2772 21 20 3793 3288 2821 3498 3102 2400 4239 3681 31 49 3965 3530 2765 481 0 41 93 3567 4588 41 10 3259 5571 4894 41 22 4592 41 14 3263 5576 4898 41 25

Platinum MetaLs Rev., 1996,40, (2) 63

Table IV

Melting Point Properties

Melting point, K * Heat of fusion

(AHOs, I ) , kJ/mol Entropy of fusion

(ASOs. I), J/mol K Vapour pressure, bar

Ru Rh Pd 0 s

2606 2236 1828.0 3400

39.0 27.3 16.1 70.0

15.0 12.2 8.8 20.6 1.05 x 5.05 x lod 4.23 x 7.75 x

Ir

2719

41.3

15.2 9.84 X 10"

Pt

2041.3

21.3

10.4 I .go x lo-'

NBP: Normal boiling point at one atmosphere pressure (1.01325 bar)

References 1 J. W. Arblaster, Platinum Metals Rev., 1994, 38,

(31, 119 (PO 2 J. W. Arblaster, Calphad, 1995,19,327 (Pd), 339

(Ru), 349 (Os), 357 (Rh), 365 (Ir) 3 Commission on Atomic Weights and Isotopic

Abundances, f i r e Q Appl. Chem., 1994,66,2423

4

5

6

Commission on Atomic Weights and Isotopic Abundances, Pure QAppl. Chem., to be published G. T. Furukawa, M. L. Reilly and J. S. Gallagher, J. Phys.Chem. Rej Dam, 1974,3, 163 R E. Bedford, G. Bonnier, A. Maas and F. Pavese, Metrologia, to be published

Random Paramagnetic Platinum-Iridium Compound A new class of magnetic behaviour, random

quantum spin chain paramagnetism, is reported in a one-dimensional compound, Sr3CuPt,Jrx0,. Scientists at the Massachusetts Institute of Technology, (T. N. Nguyen, P. A. Lee and H.-C. zur Loye, Science, 1996, 271, (5248), 489-49 1) prepared a solid solution between

antiferromagnetic Sr3CuPt06 and ferromagnetic Sr3CuIr06. They found that the p1atinum:irid- ium ratio determined the magnetic behaviour of the solid solution; at x = 0.5, the system contained randomly distributed platinum and iridium sites having random but equal ferro- magnetic and antiferromagnetic interactions.

Table V

Vapour Pressures

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Flux Pinning by Platinum and Rhodium in High Temperature Superconductors PLATINUM ADDITIONS TO YBCO THICK FILMS IMPROVE CRITICAL CURRENT DENSITIES AND SUPERCONDUCTING PROPERTIES

By J. B. Langhorn School of Metallurgy and Materials, University of Birmingham

Screen printed thick f i l m technology is recognised as a n inexpensive and effective means for the production of superconductors which have potential applications in the electronics and microwave device industries. Additions of the platinum group metals have been made to superconducting thick films of YBazCu307-s, and these have shown significant improvements, relative to melt processed fi lms, in both their superconducting and physical properties, par- ticularly in their critical current densities. A possible mechanism to explain the improvements is discussed.

The field of cryogenic research was begun and greatly advanced in 1908 with the discovery by Hieke Kamerlingh Onnes (1850-1926) of the liquefaction of helium. He used this discovery to investigate the electrical resistance of metal- lic elements and observed that the resistance of many metals fell dramatically to zero as the tem- perature was reduced below the critical tem- perature (T,) of the material. This was to be the criteria for a new state of matter, the super- conducting state. In 1933 another inherent char- acteristic of the superconducting state was dis- covered by W. Meissner and R. Ochenfeld. They found that a material in the superconducting state will act to expel magnetic flux h m its bulk.

Major obstacles, such as the cost of liquid helium and the fact that the presence of any external magnetic field destroys superconduc- tivity in a material, however, hindered research in and development of these materials. The dependence of the superconducting state upon temperature, the applied external magnetic field and the ability of the material to carry electri- cal current is illustrated in Figure 1.

The critical current density a,) of a material is an extremely important parameter for elec- trical applications of superconductors. When a transport current is applied to a supercon-

ducting material, a magnetic field is generated in the superconductor. In Type I supercon- ductors, if this field, coupled with external fields, exceeds the critical field of the material (HJ, then the superconductivity will be destroyed. When a magnetic field is applied to Type I1 superconductors, such as Y13a,Cu,0,4 (YBCO) flux quanta penetrate the material as a regular array of vortices. When transport currents are then applied they act to move these vortices, thus destroying the superconductivity. The devel- opment of microstructures made of YBCO materials has enabled engineers to increase the J, within Type I1 materials by introducing “flux pinning” centres into the material. Many microstructural anomalies, such as oxygen inho- mogeneities, twins, stacking faults, cracks, dis- locations and second phase particles, have been found to inhibit the possible motion of magnetic flux vortices in these materials.

Platinum Group Metal Additions Platinum has already been widely exploited in

the development of superconductors, even though it exhibits no superconducting proper- ties itself. The principal utilisation of platinum has involved the use of its non-reactive prop- erties for the processing and characterisation of

Platinum Metals Rev., 1996, 40, (2), 64-69 64

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C u r r e n t A density, Fig. 1 The ideal critical surface

superconducting states Transition (J-T- HI

between the normal and the J

Normal stale

state

Magnetic flrlrl u

ceramic superconductors in crucibles, substrates and buffer layers, or as electrodes and electri- cal contacts.

More recently, it has been found that pro- cessing YBCO in the presence of platinum can have a dramatic effect on the microstructure and can improve the superconducting proper- ties of the material produced. It has been observed that platinum additions refine the mor- phology and distribution of the inherent precipitates of non-superconducting Y,BaCuO, (21 1) within bulk melt processed YBCO. On refining, the precipitates become greatly reduced in size and are distributed homogeneously throughout the matrix (1). This refinement of the microstructure increases the magnetic hys- teresis properties due to flux pinning, and hence increases Jc to values estimated as 2 x 10‘ Alcm’, at 77 K and a magnetic field of 1 T. Rhodium has also been observed to give the same remark- able effect and it was suggested that the platinum group metal addition inhibits the growth of the 2 1 1 on processing.

Other work has lead to the theory that platinum plays an important part in the het- erogeneous nucleation of 2 1 1, which is formed by peritectic decomposition of YBCO on melt processing (2, 3). The reactions which occur between platinum and the YBCO system have also been investigated, and it was found that platinum reacts to form many com- pounds, including Ba,CuPt,O, (0412) which is considered to act as a possible heterogeneous

nucleation site for 2 1 1 (4). The synthesis of the 041 2 phase and its addition to YBCO have been undertaken and improvements in properties comparable to those caused by platinum were observed (5).

However, other investigators have argued that platinum does not react with the YBCO system on heating, but dissolves into the peritectic liquid phase, thus altering the diffusion rate of yttrium atoms in the system and/or changing the 21 l/liquid interfacial energy (6-9). The precise mechanism for the microstructural refinement which occurs on addition of plat- inum is, therefore, still widely debated.

This paper will present results from the systematic doping of YBCO thick films with platinum group metals, discuss the improve- ments in superconducting properties achieved and suggest the possible mechanism for 21 1 refinement in the YBCO system.

Developments in Superconducting YBCO Thick Films

The application of bulk ceramic supercon- ductors in the microelectronics and microwave industries is expected to be somewhat limited. However, these industries are already beginning to benefit from the introduction of different forms of these materials which have highly desir- able intrinsic properties, such as extremely low resistive loss characteristics. Many research groups and industrial sources have fabricated high quality thin film materials, which have very

Platinum Metals Rev., 1996,40, ( 2 ) 65

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high current densities and T, values that are equivalent to those of the bulk material. However, the processing techniques used are expensive and would be very difficult to incor- porate into the production of integrated circuits, etc. Thick film technology may offer important advantages in the production of large area coat- ings on, for example, magnetic shields andor complex shapes, such as microwave compo- nents. These can be produced economically and with relative ease, but until recently their prop- erties (J, and T,) were inferior to those of their polycrystalline bulk and thin film equivalents.

While material developments have been made in bulk YBCO by improvements in processing and the implementation of many doping addi- tions, similar improvements in YBCO thick i i h s have not been so dramatic. Previous studies of the superconducting properties of YBCO thick films deposited on a variety of substrates have shown that the film characteristics are highly dependant upon the substrate material, the YBCO precursor material and the processing conditions of the film. YBCO films processed on alumina substrates have yielded poor properties with T, values around 90 K and

Fig. 2 A polarised light micro- graph of a polished c r o ~ section of a atandard thick Glm of YBCO showing the textured nature of the film and the irregular dis- persion of large 211 precipitates

Fig. 3 Polarised light micro- graph of a polished crass section of a platinum doped YBCO film showing the more homogeneous nature of refined 211 particles and the larger amount of detrimental second phases, such as CuO

J, values in the region of 100 Ncm* ( 10). The properties of YBCO thick films can be

significantly enhanced, however, by process- ing them on yttria-stabilised zirconia (YSZ) substrates, and values of J, = 1.5 x lo’ Ncm’ and T, = 92 K are easily achieved (1 1). Also, certain additives to YBCO films have led to increased flux pinning characteristics; for exam- ple BaSnO, additions have increased J, values up to 2 x lo’ A/cm2, and controlled amounts of Ag,O have increased J, values up to 3 x lo3 A/cmz. However, these mechanisms are differ- ent to that of platinum group metal additions.

The work reported here was undertaken to gain an increased understanding of the influ- ence of microstructure on the properties of YBCO thick films and the mechanisms by which platinum group metal additions change micro- structure, and to improve the power handling capabilities of YBCO thick films by improving the flux pinning characteristics of the material.

Results of Experimental Work The first series of experiments which were

performed involved the addition of platinum sponge (2-250 p) to YBCO powder prepared

Platinum Metals Rev., 1996, 40, (2) 66

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doped YBCO films showing the effects of increasing platinum ; 8ooo concentrations

a

- 4 -

-4000

0

I 0 I 0 1 0 2 0 3 6.4 0:5 0‘6

PLATINUM CONCENTRATION, wt %

by solid state calcination at 900°C for 24 hours. Previous studies had shown this YBCO pre- cursor material was good for the production of thick films on YSZ substrates (12) and the addition of large particulate platinum sponge was intended as a feasibility study.

The addition of platinum to the YBCO mate- rial was found to have a dramatic effect upon the microstructure and the superconducting properties of the processed films. As the con- centration of platinum in the system was increased from 0 to 5 weight per cent, the mor- phology, size and distribution of the inherent non-superconducting 2 1 1 precipitates were observed to become refined. Increased vo1,umes of CuO were also seen within the films at 123 YBCO grain boundaries, see Figures 2 and 3.

Quantitative analysis of phases by energy dis- persive X-ray analysis (EDX) in the electron microscope has shown that the larger 2 1 1 pre- cipitates were composed of yttrium, barium, copper, platinum and oxygen in proportions consistent with the reported supposition that platinum reacts to form a 0412 compound, which then acts as a heterogeneous nucleation site for 2 1 1 precipitates (4). Electron micro- probe analysis of the same sample section revealed the possible coring of platinum within the largest particles. Coring is the increase in concentration of a particular element towards the centre of a particle.

Additions of rhodium sponge were also observed to increase the superconducting properties by a similar refinement of 21 1

precipitates, although not to the same extent as with platinum. Maximum improvements in superconducting properties occurred for addi- tions of 0.5 weight per cent: J, increased from 1.2 x 10’ A/cmz to 2.2 x 10’ Ncm’ for plat- inum, and from 1.2 x lo’ Ncm’ to 2.0 x lo’ A/cm2 for rhodium, both held at 77 K and zero applied field.

Following these initial developments, addi- tions offiner particulate platinum (0.8-1.2 p) were made to the same YBCO precursor mate- rial, in order to refine further the morphology of the 2 1 1 precipitates and to increase the super- conducting properties. As the concentration of platinum in the system was increased, the tex- ture of the films was observed to diminish considerably and the concentration of non- superconducting second phases increased dramatically. It is thought that the increased surface area of platinum, as platinum is added, and the subsequent increased reaction to form barium-rich Ba,CuPt,O, is responsible for the larger quantity of copper-rich phases seen in the films. Transport J, values measured within these films were not observed to exceed 500 A/cmz. The poor superconducting properties are pri- marily due to the presence of high volumes of these second phases, which inhibit the percolation of supercurrents through the films.

In order to try and prevent the generation of the detrimentally high volumes of copper-rich second phases during processing, a higher purity commercial YBCQ precursor material was utilised (RhGne Poulenc ‘Superamic Y 123’).

Platinum Metals Rev., 1996,40, ( 2 ) 67

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The superconducting properties of control films made of ‘Superamic Y 123’ were found to be comparable to those of films processed from the YBCO precursor described earlier. Platinum additions of size (0.8-2.5 pn) made to this mate- rial were seen to refine dramatically the microstructure of the films - with only limited formation of copper-rich phases - and to improve markedly the J, characteristics of the material. The variation in transport J, with platinum concentration is shown in Figure 4.

The optimised doping level of 0.15 weight per cent coincides with a maximised reduction in 2 1 1 precipitate size, while maintaining relatively large 123 grains and good c-axis texture.

The addition of platinum having smaller par- ticle sizes (0.5-1.2 pm) was observed to increase the J, characteristics even further. Transport J, values up to 6 x 1 O3 Ncm2 were readily achieved with 0.1 weight per cent platinum. Examination of thin film specimens by transmission electron microscopy showed that the presence of increased dislocation densities was associated with refined 21 1 precipitates of greater sur- face curvature, see Figures 5 and 6. This increase in dislocation density is thought to be the main factor contributing to increased flux pinning.

As previous studies have suggested, the refine- ment of 2 1 1 appears to be due to the formation of 04 12 nucleation sites (4); the 04 12 phase was synthesised by a solid state calcination route and

Fig. 5 Far left: TEM micro- graph of a standard YBCO film, showing large irregu- larly shaped 211 particles. The interfaces between the precipitates and the matrix are observed to be relatively defect free

Fig. 6 Left: TEM micro- graph of a platinum doped film, showing refined highly anisotropic and sub-micron spherical precipitates. A high volume of dis- locations are observed at the interfaces

as an addition to YBCO. Films subsequently processed from the doped material were found to contain highly refined and anisotropic 2 1 1 precipitates, as do platinum-doped specimens. Transport critical current densities greater than 7.0 x lo3 A/cmz were readily achieved with the addition of approximately 0.3 weight per cent of the synthesised 0412 nucleation phase.

Conclusions The addition of controlled concentrations of

platinum and/or Ba,Cu,+,Pt,~,O,~, particulates to precursor powders of YBCO, subsequently used for the deposition of thick film supercon- ductors, can effectively improve the critical cur- rent characteristics of the processed films. Microstructural observations have shown that the size, morphology and distribution of Y,BaCuO, precipitates within the films become highly refined on doping with platinum and Ba,CuPt,O, (0412). The smaller precipitates in the doped films are observed to be relatively spherical in form, while the larger ones are acicular. An increased number of defects is observed at the 12312 1 1 interface, associated with increased surface curvature of these precipitates. It is proposed that platinum based additions act as nucleation sites for the depo- sition of refined 2 1 1 particles, which in turn act as nucleation sites for dislocation networks and aid flux pinning in, the films.

Platinum Metals Rev., 1996, 40, (2) 68

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Acknowledgements The author wishes to acknowledge the support of

the School of Metallurgy and Materials at the University of Birmingham, and the financial sup- port of the Engineering and Physical Sciences Research Council and of Johnson Matthey PLC.

References 1 N. Ogawa, I. Hirabayashi and S. Tanaka, Physicu

C, 1991, 177, 101 2 M. Yoshida, N. Ogawa, I. Hirabayashi and S.

Tanaka, Physicu C, 1991,185-189,2409 3 M. Morita, M. Tanaka, S . Takebayashi, K.

Kimura, K. Miyamoto and K. Sawano, 3pn. J. Appl. Phys., 1991,30, (5A), 813

4 Y. Saito, T. Shishido, N. Toyota, K. Ukei and T. Sakai,J. Cryst. Growth, 1991, 109, 426

5 H. J. Park, H. W. Kim and J. T. Song, J. Muter.

6 C. Varanasi and P. McGinn, PhysiCa C, 1993,207,

7 C. Varanasi, P. McGinn, V. Pavate and E. I? Kvam,

8 C. J. Kim, K. B.Kim,H. W. ParkandG. W. Hong,

9 T. Izumi, Y. Nakahara, T. H. Sung and Y.

10 T. C. Shields and J. S . Abell, Supercond. Sci.

1 1 Y. J. Bi, F. Wellhofer, M. J. Day and J. S. Abell,

12 M. J. Day, S. D. Sutton and J. S. Abell, Cryogenics,

Sci.: Muter. Electron., 1993, 4, 77

79

Physicu C, 1994,221,46

Physicu C, 1994, 250, 153

Shiohara, J. Muter. Res., 1992, 7, 801

Echnol., 1992, 5, 627

Muter. Sci. Eng., 1993, B21, 19

1993,33, 113

Platinum Electrodes in Choline and Acetvlcholine Sensor Acetylcholine is one of the substances in mam-

mals that is responsible for the transmission of impulses between nerves, especially in the parasympathetic nervous system (which slows down activity in the glands and smooth mus- cles, but increases digestion) and in the brain. Acetylcholine is released when a nerve cell is stimulated, and this in turn stimulates an adja- cent nerve cell which also releases acetylcholine, and so transmits the nerve impulse. Immediately after acetylcholine has finished stimulating an adjacent nerve cell it must be deactivated by hydrolysis, into choline and acetic acid, by the enzyme acetylcholinesterase. Any interference with this deactivation short-circuits the nerve impulse transmissions and rapidly results in paralysis or death.

Choline is a strong base which is present in bile; in the brain it is combined with fatty acids or lecithin, and it regulates fat deposition in the liver. As both choline and acetylcholine are found in the central and peripheral nervous systems, they have an important role in human neu- ropsychological and neuropsychiatric disorders; therefore a convenient simple detector would assist in the study of diseases such as Alzheimer’s, dementia and other neuro disorders.

However, the detection of these substances within the body is not easy as they are not oxi- disable and do not have attached groups that can be recognised. The most common method of determination has been via high performance liquid chromatography, followed by a post-col- umn enzymatic reaction with acetylcholin- esterase and choline oxidase. Hydrogen per- oxide, released by the enzymatic reaction, is detected electrochemically at a platinum elec- trode, or by chemiluminescence.

Biosensors, which allow the enzymatic con-

J version and the electrochemical detection of hydrogen peroxide to occur in the same physi- cal device, offer a suitable alternative. Such devices use choline oxidase/acetylcholinesterase enzymes immobilised on membranes or trapped in some other way. However, most of these sen- sors are not usable in high performance liquid chromatography as they do not conform to requirements of fast response time or sensitiv- ity, or they are not adaptable to cell geometry.

Now, however, researchers at the Universita della Basilicata and the Universita degli Studi di Bari, Italy, have reported on an amperomet- ric biosensor, in which the enzymatic conver- sion and the electrochemical detection of hydro- gen peroxide occur together in a stable and highly sensitive device (A. Guerrieri, G. E. De Benedetto, F. Palmisano and P. G. Zambonin, “Amperometric Sensor for Choline and Acetylcholine Based on a Platinum Electrode Modified by a Co-crosslinked Bienzymic System”, Analyst, 1995,120, (1 l), 2731-2736). In their detector choline oxidase/acetylcholin- esterase enzymes are immobilised on a platinum electrode by co-crosslinking with the bovine serum albumin (BSA) and glutaraldehyde. The immobilisation can be adapted to the working electrode and cell geometry typical of electro- chemical detectors. The electrochemical cell, of conventional design, has a platinum rod counter electrode, a Ag/AgCl reference elec- trode and a platinum working electrode made by sealing a platinum disc in a glass body. The co-crosslinkage with BSA produced a very thin enzymatic layer which adhered strongly to the platinum surface and was mechanically highly stable. The sensor had detection limits in the sub-micromolecular range and a response time of around 1 second.

Plutinum Metals Rev., 1996,40, (2) 69

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Alloys in Catalysis Catalysis by Metals and Alloys, Studies in Surface Science and Catalysis, Volume 95

Elsevier, Amsterdam, 1995,744 pages, BY V. PONEC AND G. C. BOND, EDITED BY B. DELMON AND Y. T. YATES,

ISBN 0444-89796-8, Dfl.475.00, U.S.$297.00

Catalysis impacts directly on all aspects of our daily life, whether it be enzymatic catalysis, inte- gral to the existence of living things, or the more widely recognised synthetic catalysis of the lab- oratory, chemical plant or motor car. Even within synthetic catalysis there are numerous ways of categorising the body of known information. Thus, we talk of heterogeneous, homogeneous and acid base catalysis, to name but a few, each in itself being a major subject of academic and industrial study.

The phenomenon of heterogeneous catalysis was first noticed at the beginning of the nine- teenth century. Amongst the early observations was that of Humphrey Davy, who in 1817 reported that coal gas laden air continued to generate heat on platinum wires after the flame beneath them had been extinguished. Further experimentation showed that this phenomenon only happened with platinum and palladium; copper, silver, gold and zinc were ineffectual (1). These observations created great interest, and over the next 20 years or so such luminar- ies as Faraday, Dobereiner and Benelius, as well as Humphrey and Edmund Davy, contributed to this young science. To Benelius is attributed the origin of the term “catalysis” for the observed phenomena (1). Since that time, of course, much work has been published on the subject. It is therefore not surprising that this book, which concerns itself primarily with catalysis by alloys (an alloy is defined as “any metallic system con- taining two or more components, irrespective of their intimacy of mixing or the precise man- ner in which their atoms are disposed”) runs into 14 chapters, in excess of 700 pages, and references around 2000 published papers.

The first half of the book covers the chemistry and physics of alloys and alloy surfaces in some detail, starting in the first chapter with a review of the theoretical aspects of solids, in particu-

lar metals and alloys, and of chemisorption of atoms and molecules onto the surfaces of such materials. The next two chapters deal with a selection of the more important experimental techniques which have been used by solid state physicists and surface scientists to generate infor- mation on the nature and structure of catalysts, and of the chemisorbed species thereon. It seems to be the fate of many of these experimental techniques that they are generally known by acronyms, for example X P S , SIMS, EXAFS, AES, HREM; so I found it useful that each of these techniques was briefly explained a t the beginning of the appropriate section!

These first three chapters are the underpin- ning of what is to follow. Thus, chapter four begins to look at the energetics and surface com- position of alloys and discusses surface segre- gation, whereby the composition of the sur- face is different from the bulk composition, and how this surface segregation can be influenced by the presence of chemisorbed molecules and by particle size. The effects of surface segrega- tion in small metal crystallites on a support, which is the most frequently used form for prac- tical catalysis, may be different from those in larger metal particles for several reasons, and the former are often difficult to study by the spectroscopic techniques mentioned above. However, qualitatively, it is often very useful to be aware of the effects that occur with the larger particles, when attempting to understand the results obtained in catalytic reactions using these small supported metal crystallite systems. This chapter also provides some case histories of the battleground for understanding the per- formance of alloy systems between proponents of the rigid electronic band theory and what might be termed the “segregationalists”. Alloys comprising one element from the nickel, pal- ladium, platinum group with one from the

Platinum Metals Rev., 1996, 40, (2), 70-71 70

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copper, silver, gold group should differentiate between the two theories. Accordingly, much work has been done on these systems, and for many years the balance of data seemed some- times to favour one, then the other. However, some of the data, even with sophisticated surface techniques, was subsequently shown to be flawed, and the rigid band theory is now not favoured.

The basic fundamentals of catalysis and cat- alytic reaction theory are the subject of chapter six, and this is followed by a major chapter on the preparation and characterisation of metal and alloy catalysts, together with no less than 465 references. This chapter reviews various techniques for preparing macroscopic materi- als (films, foils, wires, single crystals, etc.), small unsupported metallic particles (metal blacks, colloids, Raney alloys), and supported metal catalysts of many types, and constitutes a very useful source-book in its own right!

The second half of the book is devoted to the use of alloy catalysts in practical catalytic reac- tions, beginning with some general observations in which the authors very sensibly recognise that amongst all of the reasons for studying cataly- sis on alloy systems, the primary ones are the desire to learn more about how catalysis works, and the wish to produce catalysts having bet- ter performance. There is, rightly, a feedback loop from one to the other, but much of the work published in the literature stems from a more empirical approach. Of course, the major- ity of industrial catalysts comprise metals or alloys on an “inert” support: in practice such supports are rarely inert, and thus contribute in one way or another to the reactivity of the catalyst. Also, in many cases such catalysts are not properly characterised (and in some cases not characterised at all, except by reactivity), and so effects observed may not be directly attributable to the presence - or absence - of alloy formation.

The authors have chosen to formulate the chapters in this half of the book on the basis of reaction type. Thus, there are chapters on reac- tions involving hydrogen (including isotopes), hydrogenationldehydrogenation, oxidation,

reforming, etc. While this is probably the most practical approach - and the best fiom the point of view of the practising chemist - it inevitably means that references to individual alloy systems are spread throughout the text, although there are useful summaries of a few individual systems, such as the alloys of nickel, palladium, platinum with copper, silver, gold, referred to above.

Surprising is the very small amount of space devoted to pollution control catalysis - espe- cially for motor vehicles -which has been a major practical use of catalysis for more than twenty years, and which almost invariably has involved multimetal catalysts.

But, I must not complain: this book surely represents several man-years of effort in accu- mulating the references and attempting to sum- marise them, and is a truly laudable effort. Professor Bond’s first major book published almost 35 years ago (2) was a source of inspi- ration to a whole generation of catalyst chemists: hopefully this volume will provide an equal impe- tus to the further study of alloys.

Readers will be pleased to note that a number of citations appearing in “Catalysis by Metals and Alloys” are to articles which have appeared in Platinum Metals Reeriew.

This book is available from Elsevier, P.O. Box 2 1 1 , 1000 AE Amsterdam, The Netherlands, or in the U.S.A. and Canada from Elsevier Science Inc., P.O. Box 945, Madison Square Station, New York, NY 10160-0757. D.E.W.

References 1 D. McDonald and L.B. Hunt, “A History of

Platinum and its Allied Metals”, Johnson Matthey, London, 1982, Chapter 12 G. C. Bond, “Catalysis by Metals”, Academic Press, London, 1962

2

Platinum Group Metals Conference Over 200 offers of contributions have already

been received for presentation at the Sixth International Conference on the Chemistry of the Platinum Group Metals, to be held at the University of York &om 2 1 st to 26th July, 1996. A second circular and application form will be available shortly. Anyone wishing to contribute or attend should contact Dr John F. Gibson, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, U.K., Fax: 0171-7341227, Email: [email protected].

Platinum Metals Rm., 1996,40, (2) 71

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The Development of Molecular Wires PART 11: ROLE OF RUTHENIUM AND OSMIUM POLYPYRIDINE COMPLEXES FOR FAST VECTORIAL ELECTRON TRANSFER

By V. Grosshenny, A. Harriman, M. Hissler and R. Ziessel Ecole Europkenne de Hautes Etudes des Industries Chimique de Strasbourg, Universitk Louis Pasteur, Laboratoire de Chimie d’Electronique et de Photonique Molkculaires, Strasbourg, France

The concludingpart of thispaper on the use of ruthenium(ZI) and osmium( I I ) polypyridyl complexes, as molecular sized terminal subunits that are linked together bypolyyne bridges functioning as molecular girders to retain the stereo- chemical rigidity, deals with the process of electron transfer between the subunits and considers the benefits conferred by the use of polyyne bridges. The ruthe- nium and osmium complexes have properties which aid the selective promo- tion of a n electron from the metal to the bridging ligand, together with amenable absorption and emission spectral pro+, and facile oxidation-reduction processes. Th i s makes them promising candidates fo r vectorial electron transfer. Future work to extend the lengths of the linkages, to ensure unidirectional and long- range electron tunnelling, and to anchor the wires to supports is discussed. These are the necessary requirements f o r the development of molecular wiring made from these materials for future use with molecular-scale electronic devices.

The first part of this paper introduced the sub- ject of molecular wires and considered the struc- ture and chemistry of the complexes that can be used for them, and other materials currently believed to be the best for this purpose (13). Here, the topic is further illustrated by reference to light-induced electron transfer.

The selective population by an electron of the ethynyl-substituted terpyridyl ligand, followed by electron delocalisation over an extended n*- orbital is of extreme importance for the design of effective molecular wires. It gives direction to the electron flow, since, upon excitation of the ruthenium(I1) complex, an electron is pushed along the molecular axis towards the acceptor. In principle, this electron can approach close to the cation that is co-ordinated to the second terpyridyl ligand, so that the actual elec- tron-transfer step might occur over a relatively short distance. However, there is no suggestion that the extended x*-orbital includes the sec- ond terpyridyl ligand bound to the bridge. The corresponding hole transfer, which involves both

metal centres, must occur between more widely- spaced reactants and it displays a more signifi- cant attenuation factor.

Interestingly, the insertion of a platinum(I1) bis-trialkylphosphine complex into the polyyne bridge, see Figure 6 and Panel 6, has the effect of inhibiting through-bond electron-transfer reactions occurring from the terminal ruthe- nium(I1) polypyridine complex (14). This situation arises because the platinun(I1) centre donates charge to the ethynyl-substituted bipyridyl ligand, making its reduction potential more negative than that of the corresponding platinum(I1)-free ligand, see Panel 6. Consequently, excitation of the ruthenium(I1) complex results in selective electron donation from the metal centre to the unsubstituted lig- and. The electron is localised at this ligand and is unable to migrate to an ethynyl-substituted ligand because of the unfavourable thermody- namic position; thus the photophysical proper- ties remain virtually unchanged from those of the unsubstituted complex.

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Fig. 6 Molecular structures of the trinudear tmns-Ru"J't" and trans-Ru"Pt"0s" complexes

The same situation is observed for the anal- ogous osmium(II) complexes, see Figure 6, but not for the rhenium0 bipyridine complex shown in Figure 7. In this latter case, excitation of the rheniumm chromophore results in the trans- fer of an electron from the rhenium(1) centre to the co-ordinated bipyridine ligand. Although the presence of a central platinum@)

complex lowers the reduction potential of the bipyridine ligand because of charge injection, the metal-to-ligand charge-transfer transition still occurs in the platinum(I1)-contaig rhe- nium(I) complexes, with the result that the pro- moted electron resides in an extended n*-orbital. This causes a substantial enhancement in the triplet lifetimes of the platinum(I1)-containing rhenium(1) complexes (- 80 ns) relative to that of the unsubstituted complex (- 40 ns), as mea- sured in acetonitrile solution at room temper- ature. The stabilised triplet state arises because of decreased vibronic coupling between triplet and ground states, and is a common feature of ethynyl-substituted polypyridine ligands.

Symmetrical Binuclear Complexes A special case can be made for binuclear com-

plexes possessing identical ruthenium(I1) polypyridine complexes at opposite ends of a

Platinum Metals Rm., 1996, 40, (2)

polyyne wire (7), as illustrated in Figure 8. Here, excitation of one of the chromophores results in the formation of the corresponding triplet excited state of the metal complex, which is of metal-to-ligand charge-transfer character. These binuclear complexes luminesce at much longer wavelength than do the reference compounds, due to the lower energy of the charge-transfer state. Furthermore, the triplet lifetimes of the binuclear complexes are significantly longer, rel- ative to analogous mononuclear ruthenium(I1) polypyridine complexes of similar energy, at both room temperature and 77 K.

In these polyyne-bridged binuclear complexes it appears that, under illumination, an

Fig. 7 Molecular structure of the trinuclear trans-Re'J't" complex I

73

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Panel 6

The o-alkynyl-bipyridine derivatives of was prepared by a catalytic homo-coupling platinum(II) were stereoselectively prepared reaction of the ethynyl-substitutec from the ethynyl-substituted building blocks bipyridine in the presence of CuCl, and nuns-[Ptn(P"Bu3),C1,], using a CuI catal- tetramethylethylenediamine complexes ysed reaction. The platinum(I1)-free ligand see Chart A, below.

B r 3 (II) KF, MeOH

84%

Chart A 98% NQ)

The parent &compound of the metallo- synthon was similarly prepared (85 per cent yield) from the parent cis-

Selective com- plexation of one of the two bipy- ridine domains with complex ~-rRU(bPY),CU. 2H,O (bpy is 2,2'-bipyridine), afforded either the dinuclear PtnRun or the tri- nuclear Pt1'Ru1lZ complexes.

Further com- plexation of the free bipyridine subunit within the PtnRun com- plex with the

afforded, in a clean reaction,

the heterotrinuclear complex RunPtnOsn, sel Chart B, below.

W"(P "B~,>,Cl,l.

cis- [OS(bPY)2C121

\

U U U L I RuPtOs ' 86%

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Fig. 8 Molecular structures of the ethynyl-substituted, diethynyl-substituted, diphenyl acetylene-substituted and diphenyldiaeetylene-substihrted dinuclear ruthenium(I1) complexes

electron is promoted from one of the ruthe- n iumm centres to a n*-orbital associated with the bridging ligand. As suggested earlier, this n*-orbital is not restricted to the polypyridine ligand but, because of conjugation, it extends over part of the bridging polyyne chain.

Due to the similarity of the terminal groups, photon migration can take place in which simul- taneous electron- and hole-transfer steps serve to alternate the photon between the two termini, see Panel 7. In this manner, the mplet state shut- tles between the terminal metal complexes, each journey taking about 1 ns, and can react with a quencher molecule at either site. This is a remarkable process, made possible by the strong electronic communication provided by the polyyne bridge, and closely resembles the natural light harvesting complexes found in pho- tosynthetic bacteria (1 5).

Decreasing the extent of electronic coupling between the ruthenium(I1) polypyridine com- plexes, by inserting a bridging phenyl ring, see Figure 8, severely inhibits triplet migration and the photophysical properties of such binuclear complexes resemble the photophysical prop-

erties of the mononuclear reference compounds. Overall, it is clear that polyynes provide sev-

eral important benefits when covalently attached to transition metal polypyridine complexes of the type considered here. They can cause a marked increase in triplet lifetime, thereby favouring reactions with adventitious quenchers, and can induce a sense of directionality into intramolecular energy- or electron-transfer steps. Polyynes operate as molecular girders to retain stereochemical rigidity and, at the same time, they provide highly effective electron and hole channels.

Future Work on Molecular Wires It is now necessary to fabricate longer polyyne

bridges and to ensure that the excellent elec- tronic conductivity is not restricted to short chain lengths. In this respect, it is important to realise that the energy of the bridge is likely to decrease with increasing length and, in terms of superexchange theory, the degree of through- bond electronic coupling will increase as the energy of the bridge approaches that of the excited triplet state. Each added ethynyl group,

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Panel 7

According to superexchange theory, the electronic matrix coupling element (V,.,,), a term that quantifies the amount of electronic communication between the terminal metal complexes, can be expressed in the follow- ing form:

V,, = C,CB/6E

where C, and C@ are the atomic orbital coef- ficients describing coupling between the triplet excited state and the bridge, and between the bridge and the final acceptor, respectively; 6E represents the energy gap between appropriate orbitals localised on the triplet state and on the bridge. For electron transfer, 6E refers to the difference in energy between LUMOs associated with bridge and triplet while for hole transfer the appropri-

ate energy gap would be between HOMOS associated with bridge and triplet. The mag- nitudes of C, and Cp are controlled by the nature of the reactants, especially stereo- chemical aspects, and can be estimated by detailed molecular orbital calculations.

For an homologous series of donor-accep- tor compounds, V, is predicted to decrease exponentially with increasing length (R) of the bridge according to:

V,, = VoAo exp [-pR/2]

Here, VDA0 refers to the electronic coupling matrix element when the reactants are in orbital contact. For the polyyne-bridged mol- ecular systems considered in this work, it appears that V,, will decrease with increas- ing R due to the effective decreased overlap

of wavefunctions associated with the

transfer

) +Cz\ electron

hole transfer

reacting species. However, the energy

gap between triplet state and bridge (6E) will also decrease with increasing R (see the Chart) because of conjugation, such that V,, might actu- ally increase with increasing length of the bridge. These offsetting properties give rise to particu- larly small p values, at least over modest separations.

therefore, should act co-operatively to decrease the energy of the bridge and this effect might offset the decrease in the magnitude of elec- tronic coupling that occurs upon increasing the length of the bridge, see Panel 7. Such prop- erties might serve to minimise the attenuation factors for through-bond electron and hole trans- fer. As such, polyynes possess many of the req- uisites for good molecular wires.

It is also instructive to consider the role of the metal complex in such systems and to enquire

if these complexes possess unique properties that make them particularly attractive subunits for molecular-scale electronic devices. The importance of these complexes lies in the fact that their triplet excited states, often long lived and formed in quantitative yield under visible- light illumination, are of metal-to-ligand charge- transfer character. This property facilitates selec- tive promotion of an electron from the metal centre to the bridging ligand, thereby provid- ing the impetus for vectorial electron transfer.

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Other common types of chromophore do not provide this directionality which is inherent in ruthenium(II), osmium(I1) and rhenium(1) polypyridine complexes. Of these complexes, those based on ruthenium(I1) or osmium(I1) look to be the more promising because of their amenable absorption and emission spectral pro- files and their facile oxidation-reduction processes.

We should also consider, at this stage, the fea- sibility of constructing molecular-scale wires that promote unidirectional and long-range elec- tron tunnelling. Several such systems have been described (9) and many more seem certain to emerge in the near future. Perhaps the most effective bridges are those based on polyenes (2), where charge transfer has been observed to occur over distances in excess of 30 A. These spacer moieties are probably too unstable for practical purposes, hence our utilisation of polyynes, although there have been innovative

attempts to provide both protection and inher- ent redundancy.

Other types of bridge, such as those formed from polycondensed aromatic residues (4-6) or DNA (1 6 ) , provide a more stable environment and exhibit interesting properties.

Theoretical models, predicting very small attenuation factors for electron tunnelling through certain materials, are also beginning to appear (17) and major ndvances are taking place in the synthetic practices used to fabricate supramolecular entities (9). These various fac- tors combine to ensure that appropriate mole- cular wires will soon be available. The next step will involve anchoring the wires to a macroscopic support and, by using scanning tunnelling elec- tron microscopy and time-resolved reflectance spectroscopy, the means to study such inter- actions are in place. One might argue, there- fore, that the age of molecular electronic devices is drawing ever closer.

References 13 V. Grosshenny, A. Harriman, M. Hissler and R.

Ziessel, Platinum Metals Review, 1996, 40, (l), 26-35

14 M. Hissler and R Ziessel, 3 Chem. SOC., Ddkm Trans., 1995, 893; A. Harriman, M. Hissler, R. Ziessel, A. De Cian and J. Fisher, 3. Chem. SOC., Dalton Trans., 1995, 4067

15 G. McDermott, S. M. Prince, A. A. Freer, A. M. Hawthornthwaite-Lawless, M. Z. Papiz, R. J. Cogdell and N. W. Isaacs, Nature, 1995,374,5 17

1994,116,10383

J. Phys. Chem., 1995,99,2929

16 A- M- Brun and A. H d a n , 3 Am. Chem.

17 A. K. Felts, W. Thomas Pollard and R A. Friesner,

Preparation of Platinudolvmer NanocomDosites 1

A simple method of producing metaVpolymer composites, in which nanosized metal particles are homogeneously distributed throughout the polymer, would promote the development of a new generation of useful materials and devices. These devices would utilise the specific com- positions and size-dependent electrical, chem- ical and magnetic properties of the composite. Some syntheses for specific applications have been reported, but no general synthesis for such a nanocomposite material has emerged.

Now, however, scientists at the University of Massachusetts, U.S.A., have developed a syrithesis for making platinum/polymer composites a. J. Watkins and T. J. McCarthy, “Polymer/Metal Nanocomposite Synthesis in Supercritical COT, Chem. Mum., 1995,7, (1 l), 1991-1994). Their method involves the use of a supercritical fluid, in this case carbon diox- ide. As a supercritical fluid, carbon dioxide offers great control over composite composition and

J I structure and has a high permeation rate in poly- mers. Carbon dioxide is also a versatile process solvent and it is clean and environmentally friendly.

The precursor, dimethyl(cyc1ooctadiene)plat- inum(II), was dissolved into the carbon diox- ide, and then sequentially impregnated into, and reduced in, thick films of the polymers poly(4- methyl- 1-pentene) and poly(tetrafluoroethy1- ene). The reduction to metallic platinum was by hydrogenolysis and thermolysis. This resulted in platindpolymer composites containing plat- inum clusters, of sizes &om 15 to over 100 nm (depending upon preparation) being dispersed throughout the films. The sizes and distribu- tions of the platinum clusters were measured by SEM and TEM.

In general, adjusting the permeation and reduc- tion rates controls the size and distribution of the platinum clusters, and h t h e r work is being done to produce gradient structures.

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New Palladium Polymerisation Catalyst Systems By D. T. Thompson Consulting Chemist, Reading, England

There has been considerable interest in the use of early transition metal do - and lanthanide dof -based catalysts for the polymerisation of ethylene and a-olefins. These systems act as mechanistic models for Ziegler-Natta stereo- orienting catalysts used in olefin polymerisa- tion. Structural variations in these homogeneous catalysts allow the resulting polymer microstruc- tures and molecular weights to be controlled.

However, catalyst systems based on the “late” transition metals usually dimerise or oligomerise olefins (rather than form high molar mass poly- mers) due to competing Phydride elimination.

Now, researchers at the University of North Carolina at Chapel Hill have published two papers describing new catalyst systems based on palladium(I1) or nickel(I1) for olefin poly- merisation, which polymerise ethylene and a- olefins (l), and new copolymerisation catalysts based on palladium(II) for copolymerising eth- ylene and propylene with alkyl acrylates (2).

These new highly active palladium(I1) and nickel(I1) catalyst systems, which are based on cationic initiators of general formula:

[(kN=C (R1-C (R)=NAr)M(CH3 ( 0 E b ) l ” B ~ J ~ (0 where M = Pd or Ni; Ar = 2,6-C6H3(i-Pr)*, etc; R = H, Me, etc; Ar’ = 3,5-C,H,(CF,),

incorporate bulky diimine ligands which effec- tively retard chain transfer, and thus promote the conversion of ethylene and a-olefins to high molar mass polymers with varied and unique microstructures.

The new catalysts are the first reported that allow the production of ethylene homopolymers with structures varying from highly branched, completely amorphous materials, through to linear, semicrystalline, high-density materials, by a simple variation of pressure, temperature and ligand substituents. Once the palladium

catalysts have been activated, exposure to ethylene, propylene or 1-hexene produces high molecular weight polymers. These polyolefins are amorphous materials and have extensive chain-branching along the backbone of the mol- ecules, with the branches being randomly dis- tributed and of variable length. The amorphous polyethylene produced by this process is claimed to constitute a new class of polyethylene far more highly branched than low density polyethylene.

Collaboration between Dupont and the researchers at the University of North Carolina is now leading towards a definition of applica- tions for this new polyolefin technology (3).

Mechanistic studies have shown that the ‘rest- ing state’ of the catalyst - the state that the cat- alyst exists in for most of the time - during the polymerisation of ethylene is an alkyl ethylene complex. Following the migratory insertion of this species, a new metal alkyl cation is formed that may be immediately trapped by the ethyl- ene, and after insertion this leads to a linear chain segment. Alternatively, the metal alkyl cation may undergo chain migration before being trapped by ethylene, resulting in chain branch- ing. The extent of the chain migration, and thus the extent of the branching, can be controlled via the parameters of the physical process. The steric hindrance caused by the bulky diimine ligands leads to higher rates of chain propaga- tion than of chain transfer, giving rise to high molecular weight polymers.

The second paper reports on the first exam- ples of metal-catalysed copolymerisations of non-polar olefins (ethylene and propylene) with alkyl acrylates resulting in high molar mass poly- mers via a co-ordination-type mechanism (2). These copolymerisation reactions were initiated by diethyl ether adducts (I), (when M is Pd), or by the more stable chelate complexes 0, which

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0q +

( N‘Ftl’Me + @C(O)OR + N a B A r 4 ’ - Et2O 25.c (:>’3 B A r l - N’ ‘CI

(I I )

are prepared as indicated in the above Equation. The treatment of complexes (I) or (11) with

ethylene or propylene in the presence of alkyl acrylates resulted in the formation of high molar mass random copolymers. These products are amorphous and highly branched polymeric materials. The ester groups are predominantly located at the ends of the branches, and the rates of polymerisation obtained are considerably less than those for the homopolymerisation of eth-

sition-metal catalysts capable of polymerising ethylene and propylene with functionalised vinyl monomers to high molecular weight polymers by a co-ordination-type mechanism. Dupont has filed a broadly-based patent application on this technology.

References 1

2

L. K. Johnson, C. M. Killian and M. Brookhart, J Am. Chem. Soc., 1995,117,6414 L. K. Johnson, S. Mecking and M. Brookhart, ibid, 1996,118,267

ylene. It is claimed that these are the first tran- 3 J. Haggin, Chem. Eng. News, February 5, 1996,6

Iridium Activation of Carbon-Hydrogen Bonds The establishment of a straightforward method

of activating the strong inert carbon-hydrogen bond in the alkyl groups of organic molecules and hydrocarbon fuels would increase the num- ber of chemical reactions that can be performed and expand the usefulness of hydrocarbons. Several methods have been used to break the C-H bond, all use transition metal complexes. Among these is adding a “late” transition metal (on the right of the transition metals in the periodic table) to a C-H bond to form (hydrid0)- (alkyl) metal complexes; also, o-bond metathe- sis where the C-H bond is added across a bond to an electropositive metal, usually an “early” transition metal, lanthanide or actinide, giving a different hydrocarbon and a new metal alkyl complex. The latter reaction proceeds under milder conditions and shows greater selectivity. It can activate methane and terminal alkanes at temperatures as low as 45°C.

However, the preparation of a “late” iridium complex, with behaviour closer to “early” metal o-bond metathesis processes has now been reported (B. A. Arndtsen and R. G. Bergman, Science, 1995, 270, (5244), 1970-1973). This iridium complex:

Cp’(P(CH,),)Ir(CH,) (ClCH,Cl)+ BAri Cp‘=q5-C,(CH,),, BArf=B(3,5-C6H,(CF3),),

shows unequalled C-H bond activation in organic compounds below room temperature and significant selectivity in the C-H bond that

it activates. The<omplex contains two CH,Cl, molecules per iridium complex, one of which is weakly bound to the metal centre. The high activity of the complex is thought to be due to these labile CH,Cl, ligands. Their dissociation allows low-temperature access to the iridium cation. This complex is considered to be the first structurally characterised example of a q’-bound CH,Cl, unit to a transition metal.

Among C-H reactions that have been inves- tigated was the addition of benzene to a CH,Cl, solution of the Ir complex; methane was imme- diately lost, and a phenyl-substituted complex was generated at -30°C. The iridium complex also activates methane at 1 O”C, and activates terminal alkanes at room temperature to gen- erate terminal olefin complexes.

Preliminary experiments with more compli- cated molecules show that even when other func- tionalities are present the complex reacts cleanly at ambient temperatures to break specific C- H bonds, followed rapidly by rearrangement or secondary co-ordination to the metal centre to form saturated 18-electron complexes.

The activation of hydrocarbons by this irid- ium complex is the simplest, general C-H acti- vation by a metal complex observed to-date. As its exceptional reactivity is due to the labile CH,CI, unit, it it suggested that more weakly solvated forms of [Cp’(L)Ir(CH,)]+, should demonstrate even higher reactivity toward organic compounds.

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Platinum Recovery by Palladium Alloy Catchment Gauzes in Nitric Acid Plants THE MECHANISM OF PLATINUM RECOVERY

By Yuantao Ning, Zhengfen Yang and Huaizhi Zhao Institute of Precious Metals, Kunming, Yunnan, l? R. China

Since the introduction of palladium-gold catchment gauzes for the recovery of the plat inum lost f rom the catalyst gauzes used in the manufacture of nitric acid, the mechanism by which these high palladium content alloys catch and recover the plat inum has been of interest to both researchers and manufactur- ers, alike. Using analyses of the surface chemical species which fo rm on pal- ladium, both in flowing oxygen and during the ammonia oxidation reaction, this paper describes how the surface of the palladium, at temperatures above 800"C, i s a multilayer structure with the bright palladium metal surface being covered by a thin layer of palladium metal vapour and then by a layer of pal- ladium oxide vapour. The mechanism of theplatinum recovery is related to the sugace state of thepalladium, and the high recovery rate by the palladium alloy catchment gauze is attributed to this unique multilayer structure and to the ability of palladium to reduce plat inum oxide. Damage to either the surface multilayer structure or the oxidation characteristics of palladium decreases the platinum recovery rate. Thus, catchment gauzes made frompalladium alloys containing high concentrations of base metal solutes, such as nickel, cannot be expected to have such a high plat inum recovery rate.

The platinum-rhodium or platinum-rhodium- palladium catalyst gauzes used in the produc- tion of nitric acid lose weight due to the for- mation of volatile platinum oxide (PtO,). Previously, the lost platinum was recovered by such methods as entrapment by a glass wool filter or a marble bed, as well as Raschig rings. In the 1960s, a new platinum recovery technique using palladium-gold catchment gauzes was introduced into ammonia oxidation apparatus (1). Since then, palladium-gold catch- ment gauzes have become widely used in nitric acid production plants (2,3).

More recently, metals from Groups VIII and IB have been suggested as substitutes for the gold (4). This has led to the development of high content palladium alloys containing cop- per, nickel, etc., and their use in catchment gauzes (5,6). It has been confirmed that catch- ment gauzes made of high content palladium

alloy have a large platinum recovery rate during nitric acid production; this has caused interest in their recovery mechanism.

We suggest that the recovery mechanism is related to the surface states of the palladium or the high palladium content alloys at the oper- ating temperatures. Therefore, the surface chem- ical species of palladium in a flowing oxygen atmosphere and of palladium in palladium-5 per cent nickel alloy catchment gauzes used in ammonia oxidation apparatus have been studied, and the mechanism by which they recover platinum is discussed here.

Surface Chemical Species of Palladium

Changes in the relative weight and heat absorp- tion-heat release curves of palladium metal in oxygen flowing at a rate of 50 to 60 mllminute have been determined by analysis of thermal

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gravimetry and differential scanning calorime- try, see Figure 1. In the temperature range from 0 to 348"C, it can be seen that the palladium lost weight. This was the result of the volatili- sation of any volatile material it contained and was an endothermal process which continued until the temperature reached 260"C, after which exothermal palladium oxidation occurred. However, the small weight gain which took place on palladium oxidation was not sufficient to compensate for the weight loss caused by the volatilisation, until the temperature reached 348°C.

In prior literature, 348°C is thought to be the temperature at which palladium oxide starts to form. In fact, palladium oxidation begins at 260°C, and a gain in weight first becomes detectable at 348°C. Weight gain occurs over the temperature range 348 to 750°C with increasing thickness of the palladium oxide film; this was identified as PdO by X-ray diffraction analysis (7). However, the curve of the weight gain was clearly hysteretic, corresponding to the curve of the heat changes.

In the region corresponding to 720 to 790°C on the heat change curve, and to 750 to 800°C on the weight change m e , the strong endother- mal reaction and the notable weight loss should be attributed to the decomposition of the oxi- dised palladium, which proceeds as the following reversible reaction (8):

PdO = Pd + 11202

Above 820"C, the exothermal palladium oxi- dation reaction resulted in a relative gain in weight by the sample. However, above 877°C the palladium oxide and palladium metal evap- orated. The decomposition pressure of PdO was 101.325 kPa (8) and the vapour pressure of pal- ladium metal rapidly increased, due to the quite low sublimation enthalpy (340 kJ/mol (9)) of palladium; this resulted in a weight loss in the system. Hence, the oxidation of palladium and the evaporation of palladium and its oxide showed that gain and loss of weight exist simul- taneously, and result finally in complete loss of weight at high temperatures.

In brief, palladium gains weight because it is

770 -790.C I

N

0 X

E E a

- 2 .I 0 400 800 1200

TEMPERATURE, OC

Fig. 1 Heat and weight change occurring in palladium of 99.99 per cent purity during in- creasing tempera- (a, u) are arbitrary units

oxidised at temperatures below 750"C, and loses weight because its oxide decomposes at temperatures above 750°C.

X-ray photoelectron spectroscopic (XPS) analysis has been used to determine the surface chemical species of two kinds of palladium sam- ples. Sample [l] was heated at 850°C for 2 hours in air and then quenched in ice water. Sample [2] was also heated for 2 hours at 850°C but was cooled slowly in the furnace. In the XPS analysis, the magnesium K, ray (h,, = 1253.6 eV) and the carbon 1s line at 284.8 eV were used as the excitation source and as the charge ref- erence, respectively, to determine the binding energies accurately. The XPS for Pd 3d and 0 1s are shown in Figure 2, and the cor- responding values of the binding energy are listed in Table I. It is clear that the surface of Sample [ 11 consists of palladium metal (Pd') simply

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ye 534 53 0 526 BINDING ENERGY, eV

Sample

Sample [ I ] Sample [2] Refs. (10, 11)

Fig. 2 XPS curves of palladium 3d and oxygen 1s for (a) the rapidly quenched sample, [l]; (a) the slowly eooled sample, [2]

Pd 3d3n Pd 3dsn 0 1s

Pd' PdO Pd' PdO Bonded state Absorbed state

340.3 - 335.2 - - 532.2 - 342.3 335.1 (weak) 337.1 530.3 533.6

340 - 335.1-335.4 336.3-336.9 529.3 (PdO) -

as metal, with the binding energy of Pd 3~f, ,~ = 335.2 eV, accompanied by absorbed oxygen; no palladium oxide was observed. Thus, Sample [l] retains its bright metal surface.

However, the surface of Sample [2] is covered by palladium oxide with binding energy of Pd 3& = 337.1 eV; this was identified as PdO, as mentioned above, and only a minute quantity of palladium metal (Pd') was found on the surface.

The experimental results shown in Figures 1

and 2 clearly indicate that the oxidation of pal- ladium at temperatures above 800°C should produce a multilayer surface structure: with the bright palladium metal surface being covered (directly) by a thin layer of palladium metal vapour that is itself covered by a layer of pal- ladium oxide (PdO) vapour, which is in contact with air or oxygen. This conclusion agrees fully with the view of Chaston (12).

Precisely because of this the palladium will retain a bright metal surface when it is either

Table I

Surface States and Binding Energies for Rapidly Cooled Palladium [l] and Slowly Cooled Palladium [2], from 85OoC, eV

Platinum MetaLF Rev., 1996, 40, (2) 82

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held at, or quenched from, temperatures above 800"C, but will retain a tarnished surface covered by a palladium oxide film when it is either held at, or quenched from, temperatures below 800°C.

Surface of gauze

(G-5)lal (G-5)lbl (G-~NcI (G-5)ldl

(G-8Nal ( G W b l (G-8)lcI (G-8)ldl

Palladium Chemical Species in Palladium-Nickel Catchment Gauzes

XPS was used to determine the chemical species of palladium that are present in the pal- ladium-5 per cent nickel catchment gauzes used in ammonia oxidation apparatus operating at a pressure of 4 atmospheres and a tempera- ture of 850°C. The gauzes, used for 5 and 8 months, were named (G-5) and (G-8), respec- tively. In the downstream direction, the surfaces of two sheets of gauzes were marked [a], [b], [c] and [d] from the front surface of the top gauze to the back surface of the bottom gauze. Details of the ammonia oxidation and the palladium- 5 per cent nickel gauzes have been described here before (1 2). The X P S curves of palladium 3d are shown in Figure 3. The distinct shoul- der peaks can be observed on the XPS trace of all the gauze surfaces, except for (G-5) [a] and (G-5) [d]. Binding energy values for palladium 3d5,, and 34, are listed in Table 11. The bind- ing energies for palladium 3d5,,, in the range 335.15 to 335.29 eV, are in agreement with binding energy values of Pd', although bind-

Pdo PdO

3d%, eV at.% Pd 3dm. eV at.% Pd"

0 335.15 50 335.29 45 337.0 23 335.24 48 337.05 28 - 0 337.10 88

-

335.27 40.36 337.08 7.70 335.28 35.88 337.05 34.3 335.27 48.63 336.94 20.71 335.22 42.40 337.05 37.19

j 340 335

G- 8 ) 3d512

3 (a ) BINDING ENERGY. eV (b) BINDING ENERGY, CV

Fig. 3 XPS curvea of Pd 3d on various surfaces of (G-5) and (6-8) gauzes

ing energies for PdO in the range 336.94 to 337.10 eV, listed in Table 11, are higher than those reported in References 10 and 1 1 in Table I. The diffraction peaks of PdO were found in

Table I I

Binding Energies of Palladium 3d, and Concentration Distributions of Pd' and PdO on the Surfaces of (G-5) and (6-8) Gauzes

Platinum Metals Rev., 1996,40, (2) 83

"The values in this column are the palladium concentrations in palladium oxide (PdOl

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12k

B Es 0.6 m W

-

I

0

0 PdO I O P d I

1 60 00 100 120 140 156

DIFFRACTION, 28

Fig. 4 XRD pattern of the gauze (G-5)[d] surface, showing the palladium, Pd', and the palladium oxide (PdO) species present

the X-ray diffraction pattern of the (G-5) [d] gauze, see Figure 4. These results show that there are clearly two palladium chemical species, Pd' and PdO, present on the various surfaces of palladium-5 per cent nickel gauzes.

The concentrations of palladium (PdO) and palladium oxide (PdO) calculated from indi- vidual peak areas are listed in Table 11. Two single chemical species, PdO, on the (G-5) [a] surface and PdO on the (G-5)[d] surface were observed. It is clear that the concentrations of Pd' on the [a] and [c] surfaces facing the gas stream are higher than those on the [b] and [d] surfaces, whereas the concentrations of pal- ladium oxide (PdO) on the [a] and [c] surfaces are lower than those on the [b] and [d] surfaces for both (G-5) and (G-8) gauzes. On removing the (G-5) [d] surface layer by argon ion bom- bardment for 3 minutes, the PdO spectrum seen by X P S disappears. This indicated that the PdO species existed only in the surface to a depth of less than 6 nm. Clearly, the surface state of palladium in palladium-5 per cent nickel alloy

catchment gauzes during the ammonia oxida- tion reaction is the same as that of palladium in a flowing oxygen atmosphere, as mentioned above. Hence, the surface states of high palla- dium content alloys, which are operated at the temperatures of the ammonia oxidation reac- tion, consist of a similar multilayer structure: bright palladium metal surface is covered by palladium metal vapour and palladium oxide (PdO) vapour.

Mechanism of Platinum Recovery by High Palladium Content Alloys

The p1atinum:palladium ratios on various sur- faces of the (G-8) gauzes were determined by electron probe microarea analysis (EPMA) and are listed in Table 111. The p1atinum:palladium ratios of the [a] and [c] surfaces are higher than those of the [b] and [d] surfaces; in other words, the front surfaces facing the gas stream recover more platinum than the back surfaces.

This is due to the platinum, which is lost from the catalyst gauzes, being deposited by gas

Table I l l

Platinum:Palladium Ratios on Various Surfaces of (6-8) Gauze

Positions la1 [bl [cl [dl Platinum: palladium ratios* 1.5 1 .o 1.3 0.6

*The ratio values were calculated using weight percentages

Platinum Metals Rw., 1996,40, (2) 84

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Fig. 5 The surface multilayer structure of palladium and the reduction of platinum oxide (PtO,) to platinum on the surface is shown. Platinum then alloys with palladium

PdO vapour

2Pd0 2Pd + 0 2

ZPd + PtO2 = Pt( + 2PdO _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - - - - Pd vapour deposit

transportation preferentially on the b n t surfaces. The recovery of platinum by palladium alloy

catchment gauzes is a process in which the volatile platinum oxide, PtO,, that forms in the catalytic gauzes, is transported by the gas stream to the catchment gauzes where it is reduced to plat- inum metal. The platinum is deposited on the surfaces of the catchment gauzes and then alloys with palladium to form new palladium@latinum) solid solutions (1 3, 14).

When the platinum oxide (PtO,) vapour is transported to the catchment gauze surfaces, it first comes into contact with palladium oxide (PdO) vapour in the multilayer structure on the surfaces of the high palladium content alloys. Since the affinity of palladium to oxygen is stronger than that of platinum, the palladium released by the decomposition of palladium oxide (PdO) could remove the oxygen from the platinum oxide and reduce it to platinum:

2Pd0 = 2Pd + O,? 6) (ii) 2Pd + PtO, = Pt& + 2Pd0

Palladium metal vapour is also likely to par- ticipate directly in the reaction.

The reduced platinum immediately deposits on the bright surface of the palladium metal and alloys with the palladium, forming a solid solu- tion. The process is shown schematically in Figure 5. It can be seen, on comparing the data in Tables II and III, that the p1atinum:palladium ratios are inversely proportional to the con- centrations of palladium oxide on the various surfaces of (G-8) gauzes, see Figure 6. The same

tendency to inverse proportion is also found on (G-5) gauzes. This indicates that the palladium oxide participates in the platinum recovery reac- tion, which leads to the decrease in the palla- dium oxide concentrations, especially on the front [a] and [c] surfaces of both catchment gauzes. On the other hand, the porous struc- ture in the palladium alloy gauzes that formed during the operating period was caused mainly by oxygen released from the decomposition of PdO; this was used for the reduction of PtO,.

The platinum recovery mechanism is related to the surface state of the palladium in the catch- ment gauzes. As a result of the reduction effect of palladium towards platinum oxide (PtO,) and because palladium retains its bright metal sur- face at high temperatures, catchment gauzes

I

I 10 3 0 50

PdO, a t . %

Fig. 6 P1atinum:palladium ratios depend inversely on eoncentrations of PdO on various surfaces of (6-8) gauzes

Platinum Metals Rev., 1996, 40, (2) 85

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made of palladium or high palladium content alloys can recover large amounts of platinum. Platinum and gold also retain bright metal sur- faces at high temperature, but the surface state of gold does not have the ability to reduce plat- inum oxide. Platinum, however, is still oxidised to PtO, at the operating temperatures of the catchment gauzes, so the platinum recovery rate for palladium-gold gauzes is lower than that of palladium gauzes ( 2 ) . Other metals, such as nickel, copper and iron, are not suitable for use as catchment gauze because they are quickly oxidised and are eventually lost under the con- ditions of ammonia oxidation ( 14).

A high content of base metal solutes is not suit- able in the palladium alloys used for catchment gauzes. This is because the oxide film of the base metal solutes covers the surface of the palladium or palladium alloy, damages the characteristic multilayer structure of the palladium and decreases the platinum recovery. For example, the platinum recovery rate of catchment gauzes made of palladium-40 per cent nickel alloy used in the present experiment was only 32 per cent, whereas the platinum recovery rate of the (G-8) gauzes is 73 per cent, for the same length of time and under the same experimental conditions.

It is worth pointing out that the mechanism of recovery does not ignore any partial reduc- tion of PtO, by remnant ammonia (6).

Conclusions When palladium is heated at the rate of 5

Wmin in an oxygen atmosphere, an exothermal oxidation reaction occurs at 260°C and palla- dium oxide is formed, resulting in a detectable weight gain at 348°C. The palladium oxide film becomes thicker with increasing temperature. The palladium oxide decomposes at 750°C, giving palladium and oxygen, which results in a loss of weight due to the release of oxygen. This is a reversible reaction and palladium can be continuously oxidised. Above 877"C, palla- dium metal and its oxide evaporate and the decomposition pressure of the palladium oxide and the vapour pressure of the palladium metal increase rapidly. Therefore, at temperatures

above 8OO0C, a multilayer structure forms on the surface of the palladium and the bright palladium metal surface becomes covered imme- diately by a thin layer of palladium metal vapour and then by palladium oxide vapour.

Two kinds of chemical species of palladium: palladium metal (Pd') and palladium oxide (PdO) exist on the surfaces of the palladium-5 per cent nickel catchment gauzes used in medium pressure ammonia oxidation appara- tus. The thickness of the oxide film is less than 6 nm. The p1atinum:palladium ratios on vari- ous surfaces of the catchment gauzes are inversely proportional to the concentrations of palladium oxide on these surfaces. Clearly, palladium oxide participates in the platinum recovery process.

A mechanism by which platinum is recovered by high palladium content alloy catchment gauzes is thus proposed and shown schemati- cally in Figure 5. The high platinum recovery rate of the palladium or high palladium content alloy catchment gauzes is attributed to the unique multilayer surface structure and the reduction ability of palladium towards platinum oxide (Pto,). Any factor damaging the oxidation char- acteristic and surface structure of palladium will decrease the amount of platinum recovered by the catchment gauzes. Thus, catchment gauzes made of palladium alloys with large concentra- tions of base metal solutes should not be expected to have high rates of platinum recovery.

Acknowledgement

Natural Science Foundation of China. Project (59271027) was supported by the National

References 1 H. Holzmann, Platinum Metals Rev., 1969, 13,

2 A. E. Heywood, Platinum Metals Rev., 1973, 17,

3 A. E. Heywood, Platinum Metals Rev., 1982, 26,

4 R. W. Hatfield, B. S. Beshty, H. C. Lee, R. M. Heck and T. S. Hsing, European Patent 77,121; 1982

5 J. L. G. Fierro, J. M. Palacios and F. Tomas, Platinum Metals Rev., 1990, 34, (2), 62

6 J. L. G. Fierro, J. M. Palacios and F. Tomas, Sud Interface Anal., 1989, 14, 529

(I), 2

(31, 118

(I), 28

Platinum Metals Rev., 1996, 40, (2) 86

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7 Y. Ning, F. Wen, H. Zhao and D. Deng, Rare Merals, 1994, 13, (Z), 143

8 M. P. Slavinskyl, Physico-Chemical Properties of Elements, Metallurgizdat, Moscow, 1952, (in

1 1 F. M. John, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corporation, Physical Electronic Division, U.S.A., 1992

12 J. C. Chaston, Platinum Metals Rev., 1965,9, (4), Russian) ... 126 9 R. Hulteren. P. G. Desai and D. T. Hawkins. in

vaiues Of the ThemOd~amic hP-=’.ti, ofElements”, American Society for Metals, Metals Park, Ohio, 1973

13 Y. Ning, Z. Yang and H. Zhao, Platinum Merals Rev., 1995, 39, (1), 19

10 K. S. Kim, A. F. Gossmann and N. Winograd, 14 Z. Yang, Y. Ning and H. Zhao, 3. Alloys Compd., Anal. Chem., 1974,46, (l), 197 1995,218,51

Iridium Apparatus for XRF Fusions The properties required of containment mate-

rials used for X-ray fluorescence analysis (XRF) applications include good chemical resistance to the borate fluxes commonly used in the prepa- ration of samples, sufficient hot strength to give an acceptable service life, and good wetting resis- tance. It must also be possible to work the mate- rial into the required form. Therefore, platinum, gold-platinum and gold-rhodium-platinum were widely used for this purpose, and the good sur- face finish on sample beads produced in ZGS 5 per cent gold-platinum casting moulds resulted in improved analytical accuracy (Platinum Metals Rev., 1982, 26, (3), 98).

Even these materials can be damaged, how- ever, by the fusion of certain matrices, includ- ing some sulphides and unoxidised base met- als. Now a paper from the Geoservices Centre of the Ministry of Northern Development and Mines, Canada, describes preliminary tests made to find if iridium could be used for the fusion

of specific samples for XRF analysis (A. Martin, in “Summary of Field Work and Other Activities”, 1995, Ontario Geological Survey, Miscellaneous Paper, 164, pp. 233-236).

The samples tested contained unoxidised base metals, sulphides, carbides and arsenides. Although the iridium crucibles contained manufacturing flaws, they did survive the fusion processes. Experiments were also performed to determine if iridium suffered h m the “memory effect”, where elements present in one melt would enter into the containment material and be released into sub- sequent samples. While iridium possesses wetting properties, it showed little or no loss of surface integrity during these metal permeability tests.

Thus, analytical sample beads have been pro- duced in iridium crucibles from materials that would have significantly damaged and conta- minated platinum apparatus. Further tests are to be carried out on new flaw-free iridium cru- cibles and the results are awaited with interest.

Rutheniutd’latinum in Water Elmtrooxidation The oxidation of water is a basic reaction in

photosynthesis, and for artificial photosynthe- sis any improvements to water oxidation sys- tems must be welcome. Various systems can produce oxygen from water using metal oxides, Ru02, Ir02, PtOz, and heterogeneous and homo- geneous systems with metal complexes acting as the molecule-based catalyst. The trinuclear ruthenium complex, [(NH&Ru-O-RU(NH,)~- O-RU(NH~)~]~+ (Ru-red) is one of the most active molecule-based catalysts. However, such cata- lysts have inefficient charge transfer between the electrode and the metal complex.

Researchers &om Ibaraki University, Mito and the Institute of Physical and Chemical Research, Wako, Japan, have now designed a very active catalyst system for electrochemical water oxi- dation (M. Yagi, I. Ogino, A. Miura, Y. Kurimura and M. Kaneko, Chem. Lett. Jpn., 1995, (lo), 863-864). Ru-red was adsorbed onto platinum black (Pt-black) electrodeposited

onto the surface of a basal-plane pyrolytic graphite (BPG) electrode, and electrochemical water oxidation tests were performed. The BPG/Pt-black [Ru-red] displayed an excep- tionally steep rise in anodic current for oxygen evolution above 1.2 V. The current size after one hour at 1.3 V was 7.4 mA/cm2, almost 10 times that for a BPG/Pt-black electrode. Additionally, oxygen began to evolve at 150 mV lower than for BPG/Pt-black, and the maximum oxygen evolution occurred when the ratio of Pt- blackRu-red was 6.0 x 10“:9.3 x lo-’.

The high activity of the system is ascribed to each Ru-red molecule oxidising water in a 4- electron oxidation, as long as the minuclear struc- ture of the ruthenium red complex is maintained. The electrode matrix also strongly affects the activity of the Ru-red. When adsorbed on the Pt-black surface, charge is directly and efficiently injected from the Pt-black to the Ru-red com- plex; accounting for the high catalytic activity.

Platinum Merals Rev., 1996, 40, ( 2 ) 87

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ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Thermally Induced Structural Modification in PtK X-Ray Multilayer Mirrors Fabricated by Electron Beam Evaporation G. s. LODHA, s. PANDITA, A. GUPTA, R v. NANDEDKAR and K. YAMASHITA, Appl. Phys., 1996, A62, (l), 29-32 The thermal stability of Pt/C multilayer mirrors with a bilayer spacing of 50 A, fabricated in an UHV elec- tron beam evaporator, was studied under vacuum annealing using X-ray reflectivity and XRD. At 2 450"C, the bilayer spacing increased monotonically giving a gradual increase in crystallite size and grain texture. At 500"C, multilayer reflection disappeared, the Pt crystallites grew rapidly and Pt in the [220]- plane had a strong texture.

Hydrogen-Induced Lattice Migration in Pd- Pt Alloys H. NOH, J. D. CLEWLEY and T. B. FLANAGAN, Scr. Metall. Mate,:, 1996,34, (4), 665-668 H, solubilities were determined in -100 p thick foils of Pd-Pt alloys under H, pressures of 5 100 MPa at temperatures 5 873 K. Pd-Pt alloys do not segre- gate at higher temperatures when little Hz dissolves; large amounts of H, are needed for segregation. The ternary (Pd + Pt + H) equilibrium causes a phase sep- aration at 673 K. After H, removal at S 673 K and alloy cooling, metastable segregated Pd- and Pt-rich regions remain. Dissolved H, catalyses the return of the segregated alloy to the homogeneous state.

Properties and Interface Diffusion of Pd/Ni Composite Wire Y. NING, H. DAl and F. WEN, f're- Met. (China), 1995,

Mechanical properties, interface diffusion and changes in Pd coating thickness were investigated in Pd/Ni composite wire. The thickness and weight percent- age of the Pd coat were controllable on demand. The strength of the Pd/Ni composite wires, at ambient and high temperatures, is much higher than for pure Pd, and similar to that of Ni. The Ni diffusion rate from the interface to Pd is higher than that of Pd to Ni.

Magnetic Properties of U(Pd,,Fe,),Ge,

K . D . L A I N , ~ Magn.&Magn. M m . , 1996,153, (1-2),

Solid solutions of U(Pd, ,FeJ2Ge2 with a mixture of 3d and 4d transition elements in one lattice site were prepared. Even very small Pd doping in UFezGe2 and Fe doping in UPd,Ge, changed the magnetic state of the compounds dramatically. Coexistence between the antiferromagnetic ordering and Pauli paramag- netism was observed over the range 0.1 5 x I 0.9.

16, (4), 25-30

H. M. DUH, I. S. LYUBUTIN, I. M. JIANG, G. H. HWANG and

86-96

Magnetism of Body-Centered Tetragonal FeRh,,Pd, Alloys. I. Magnetic Properties; 11. Band Structure s. YUASA, H. MIYAJIMA, Y. OTANI and A. SAKUMA; A. SAKUMA, s. WASA, H. MNAJIMA and Y. OTANI, J. Phys. SOC. Jpn., 1995, 64, (12), 4906-4913; 491p4922 Crystalline structures and magnetic properties of the FeRh-,Pd, system were studied and first-principle spin-polarised band calculations were performed for the b.c.t. FeRh.,Pd, alloys with x = 0, 0.5 and 1 as a function of the axial ratio c:a. A new ferromagnetic phase of orthorhombic structure with space group C,,, was found in the b.c.t. alloys with x = 0.525 - 0.61 below room temperature. At a constant c:a value, substituting Pd for Rh raised the Fermi energy level.

Magnetic Structure and Physical Properties of the Heavy Fermion UIr,Si, A. VERNIERE, s. RAYMOND, J. x. BOUCHERLE, P. LEJAY, B. FAK, J. FLOUQUET and J. M. MIGNOT, J. Magn. & Magn. Mazer., 1996, 153, (1-2), 55-62 Studies of the physical properties of a UIr,Si, single crystal, which has CaBe2Gez-type structure and very high residual resistivity values at low temperature, indicated that UIrzSi, is antiferromagnetic with T, = 6 K. A metamagnetic transition at a field of 1.5 T and heavy-fermion characteristics with a linear specific heat coeficient of y- 300 mJ/mol K' were measured. The antiferromagnetic structure of UIr& was deter- mined by neutron diffraction as (+,-,+,-).

Ruthenium and Sulphide Passivation of GaAa s. T. ALJ, s. GHOSH and D. N. BOSE, Appl. Sut$ Sci, 1996, 93, ( l ) , 37-43 The effectiveness of chemical surface treatment of GaAs using (NH,),S,, Na,S and RuC1, was studied. Modification involved the removal of native oxides and the consequent formation ofbonds with Ru or S. Ga atoms were bonded more strongly with Ru or S than As. This reduced the surface recombination veloc- ity and increased the photoluminescence intensity. S and Ru can be used to passivate the GaAs surface.

Subsolidus Phase Equilibria in the RuOz-Bi,03- ZnO and RuO,-AlzO,-ZnO Systems M. HROVAT, s. BERNIK, J. HOLC and D. KOLAR, 3. Mare,:

Phase diagrams of the ternary systems Ru0,-Bi20,- ZnO (I) and RuO2-Al20,-Zn0 (11) were constructed and showed that the RuOz-ZnO system contained no binary compound or liquid phase (eutectic) at < 1400"C, which is the temperature that RuO, decom- poses to metallic Ru and 0,. Tie lines within the phase diagrams are discussed. The microstructure of a sam- ple of nominal composition 5 mol%Zn0/50 mol%Biz0,/45 mol%RuO,, fired at 700°C, is shown.

S C ~ . , Lett., 1996, 15, (4), 336-338

Platinum Metals Rev., 1996, 40, (2), 88-94 88

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Superconducting Properties of CeRul Single Crystal

R. SE'ITAI and Y. ONUKI, J. Phys. Soc. Jpn., 1995, 64, (12), 48494855 Lower and upper superconducting critical fields at 0 K, of 250-400 Oe and 74 kOe, respectively, were measured on single crystals of superconductor CeRu, grown by using a zone melting method. The upper critical field was slightly anisotropic, and was of size 64.8 kOe for the field along the <loo> direction and 65.6 kOe along the <1 10> direction at 1.5 K. A characteristic feature of the superconducting mixed state was also observed.

H. SUGAWARA, H. SATO, T . YAMAZAKI, N. KIMURA,

CHEMICAL COMPOUNDS Ternary Thallium Platinum and Thallium Palladium Chalcogenides TI-. Syntheses, Crystal Structures, and Bonding Relations W. BRONGER and B. BONSMA", z. Anorg. A&. Chem.,

The compounds TI,Pt,S,, T1,Pt,Se6, TI,Pt,Te, and TlzPd,Se, were fabricated by melting the elements or by the reaction of TI carbonate, Pt group metal and chalcogen powders at 400-950°C. X-ray studies on single crystals and powders showed a new type of structure, which is a stacking variant of the known atomic arrangement of the alkaline metal Pt chalco- genides. The short distances in TI-Pt and TI-Pd indi- cate covalent bonds between the main group and the Pt group metal atoms.

Evidence for a Hydrogen Insertion Compound of Novel Palladium Incorporated Vanadyl Hydrogen Phosphates A. DATTA and R. Y. KELKAR, Chem. Commun., 1996, (l), 89-91 Pd was incorporated into the vanadyl H phosphate phase VOHP0,.0.5Hz0 in various ways depending on the medium used for preparation. In aqueous medium the incorporation of 0.6 1 % Pd2' changes the parent structure, so that Pd" ions appear to be located in the interlayer region. The relatively low reduction temperature of the incorporated Pd indicates it is located in the interlayer region. However, in an organic medium Pd is partially reduced to metal and partially introduced into the lattice of the parent compound.

Stable Carbonyl- and Thioearbonylrhodium(1) Complexes Containing +Bonded Phenyl and Vinyl Groups as Ligands R. WIEDEMANN, J. WOLF and H. WERNER, Chem. Ber.,

Rh(1) phenyl and vinyl complexes, trans- [Rh(R)(CO)(PiPr,),] (1, 2) were prepared from the chloro derivative and Grignard reagents. The corre- sponding thiocarbonyl trans-[Rh(CH=CH,)(CS)- ( P Z F ~ ~ ) ~ ] was obtained from nans-[RhCI(CS)(P~rPr,),] and CH,=CHMgBr. The carbonyl complexes (1) and (2) are inert in the presence of CO and do not react by migratory insertion to give acyl Rh derivatives.

1995,621, (12), 2083-2088

1996, 129, (l), 29-31

Synthesis of the First Bimetallic Ruthenium- Iridium Cluster

V. 1. BREGADZE, Izv. Akad. Nauk Rosii, Ser. Khim.,

A new electron-deficient bimetallic cluster, (9'- CaH,,)IrRu(p-H) (PPh3),(q5-C2B,H, ,) was prepared by the reaction of exo-nid0-5,6,1O-[C1(PPh~)~Ru]- 5,6,1O-@-H),-10-H-7,8-C2B& with dimeric or acetyl- acetonate complexes of Ir in the presence of KOH in EtOH at 22OC. Spectroscopic data are presented.

Formation of Ammonium Complexes dy ing Interaction of Ruthenium Compounds with Hydrazine Chloride w. H. KUKUSHKIN, M. v . BAVINA and A. v. ZINCHENKO, Zh. Obshch. Khim., 1995,65, (8), 1233-1235 The interaction of dimethylsulphoxide complexes [Ru(Me,S0),Cl2] (1) and RuCL.2 Me2S0 with N,H,. 2HC1(2) produced ammonium Ru(II1) compounds, [Ru(NH,)~CI] C1, andfac- [Ru(NH,),Cl,], depending on the length of heating. The interaction of RuCl,. nH20 with (2) resulted in the formation of isomeric compounds mer-[Ru(NH,),Cl,]. After a short heat treatment of (1) with (2), the Ru complex [Ru(MezSO),-(N2H,)Cll] was formed.

I. A LOBANOVA, I. T. CHIZHEVSIUI, P. V. PETROVSKII and

1996, ( I ) , 250-251

ELECTROCHEMISTRY Oxygen Reduction on Well-Defined Platinum Nanoparticles inside Recast Ionomer A. GAMEZ, D. RICHARD, P. GALLEZOT, F. GLOAGUEN, R. FAURE and R. DURAND, Electrochim. Acta, 1996, 41, (2)j 307-314 The effect of particle size on the catalytic activity of the 0, reduction reaction at a Pdrecast ionomer inter- face was studied by TEM and H and CO elec- trosorption, using porous graphite electrodes of well- defined geometry carrying well calibrated Pt particles. The catalytic powders were prepared by cationic exchange. For 0 reduction, the loss of catalytic activ- ity with decreased Pt particle size is correlated with the stronger adsorption of oxygenated species under an inert atmosphere. No interparticle distance effects were seen, even for particles of 1.2 nm, 10 nm apart.

Electrocatalytic Activities of Graphite- Supported Platinum Electrodes for Methanol Electrooxidation P. c. BISWAS, Y. NODASAKA and M. ENYO, J. Appl. Electrochem., 1996, 26, (l), 30-35 Electrooxidation of MeOH in 1 M NaOH at 30°C was studied on graphite-supported Pt electrodes pre- pared both in H, and in air at various temperatures. Heating in H1 produced Pt of higher surface area with greater mass activity, than in air at a specific temper- ature.The electrodes had nearly the same specific activ- ity as a smooth Pt electrode for MeOH electrooxida- tion regardless of the preparation conditions. The difference in mass activity is due to different surface areas resulting from different preparations. The first charge transfer process was the rate-determining step.

Platinum Metals Rev., 1996, 40, (2) 89

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Pt-Base Electrodes and Effects on Phase Formations and Electrical Properties of High- Dielectric Thin Films w.-J. LEE, Y.-M. KIM and H.-G. KIM, Thin Solid Films,

Structures and properties of Pb(Zr, Ti)O,, PZT, and (Ba, Sr)Ti03, BST, thin films deposited on Pt/SiO,/Si substrates by MOCVD and r.f. sputtering were stud- ied. Pt films sputter-deposited at 400°C had perfect (1 1 1) preferred orientation and a dense surface. A 130 nm PZT film deposited on Pt at 400°C had dielec- tric constant, E = 1300 and remanent polarisation = 32 pC/cmZ; a 100 nm BST film had E = 575 and leak- age current density at 2 V = 1.8 x 10.’ Ncm’.

Oxygen Evolution and Hypochlorite Production on Ru-Pt Binary Oxides c.-c . HU, C.-H. LEE andr.-c. WEN,^ Appl. Electrochem.,

The effects of varying coating solutions on the OER and the hypochlorite production ability of Ru-Pt oxide electrodes were studied. Maximum apparent activ- ity occurred for coatings of 60 and 20 mol.% Pt for the OER and the C1 evolution reaction, respectively. Freshly prepared electrodes had lower current effi- ciencies for hypochlorite production than those treated by repetitive cyclic voltammetry, but both types were stable in 0.5 M NaCl at 300 mA/cm2 for a 480 h test.

Structural Effects in Electrocatalysis: Electrooxidation of carbon Monoxide on Pt,Sn Single-Crystal Alloy Surfaces

Lett., 1996, 36, (1, 2), 1-8 The electrochemical oxidation of CO and CO:H, mix- tures in HSO, was studied on clean annealed and sputtered cleaned non-annealed (1 10) and (1 11) sur- faces of single crystal Pt2Sn. Annealed (1 11) and sput- tered non-annealed (1 10) surfaces had very different activities. Relative to pure Pt surfaces, a potential shift > 0.5 V was observed for CO oxidation, which implies catalytic activity of four orders of magnitude higher. This high catalytic activity for the Pt,Sn surface is attributed to a unique adsorbed CO state.

Reactivity of 17- and 19-Electron Organometallic Complexes. Formation of Bent Sandwich 19-Electron Radical Cation Complexes of Ruthenium and Osmium

1995,269, (1-2), 75-79

1996,26, (l) , 72-82

H. A. GASTEIGER, N. M. MARKOVIC and P. N. ROSS, catal.

S . V. KUKHARENKO, V. V. STRELETS, L. 1. DENISOVICH, M. G. PETERLElTNER, A. Z. KREIDLIN, A. R. KUDINOV and M. 1. RYBINSKAYA, Izv. Akad. Nauk, Ser. Khim., 1995, (12), 2394-2399 The redox behaviour of sandwich indenyl complexes (q5-C9H,)ML, M = Ru or Os, L = qZ-C,H,, etc., was studied by cyclic voltammetry at a Pt electrode at -85 to 20°C and by controlled potential electrolysis. The complexes underwent reversible one-electron oxida- tion to the corresponding radical cations. A fast inter- action of the 17-electron radical cations with nucle- ophiles yielded bent sandwich 19-electron radical cations [(q’-C,H,)M(L)(Nu)]’, Nu = C1-, MeCN, etc.

Hi h Sensitivity of Electron Transfer Rates wig in Nafion Coatings Saturated with Os(bpy)? to the Extent of Hydration of the Coating M. SHI and F. c . ANSON, 3 Electrochem. SOC., 1995,142, (12), 42054214 Hydration effects on Nafion coatings on glassy C disk electrodes showed that when only one electroactive counterion is present in the coating the electrochemi- cal response is enhanced. Nafion coatings fully satu- rated with Os(bpy),” but containing little H,O had Nafionate salt properties; these are low ionic and elec- tronic conductance and a high affinity for H20, which occurs when some of the Os(bpy),’+ counterions are ejected from the coating allowing H,O to enter. Hydrated and unhydrated coatings are compared.

Electrooxidative Fission of Carbon-Carbon Double Bond in a K20s0,(OH)JHI0, Double Mediatory System H. TANAKA, R. KIKUCHI, M. BABA and s. TONI, Bull. Chem. SOC. Jpn., 1995, 68, (lo), 2989-2992 Electrooxidative C-C double bond fission of olefins occurred in the presence of catalytic amounts of K osmate and periodic acid. Corresponding carbonyl compounds were produced in moderate to good yields, when the turnover number of periodic acid reached - 3. The oxidative fission occurred by dihydroxyla- tion of olefins followed by glycol cleavage. High selec- tivity to ketones showed that the regeneration of peri- odic species can occur in this electrooxidative media.

Surface Characterization of RuO,-SnO, Coated Titanium Electrodes M. ITO, Y. MURAKAMI, n. KAJI, K. YAHIKOZAWA and Y . T A K A S U , ~ Electrochem. SOC., 1996, 143, (l) , 32-36 Studies of the morphology of RuO,-SnO, coatings supported on Ti showed that Ru is segregated in island-like deposits for Ru0,-rich electrodes (1). For SnOz-rich electrodes, where Sn is localised in the macroscopically flat plane of ultrafine particles, Ru was segregated along cracks. The ultrafine particles on the Sn0,-rich electrodes were smaller than those found for (1) and contributed to the large active sur- face area of the electrode. Only particles < 10 nm will give more active electrodes.

PHOTOCONVERSION Effect of n-Si on the Photocatalytic Production of Hydrogen by Pt-Loaded CdS and CdSlZnS Catalyst G. c . DE, A. M. ROY and s. S. BHATTACHARYA, Int. J. Hydrogen Energy, 1996, 21, (l), 19-23 Studies of H, production on illuminated CdS suspen- sions in Na,S/Na2S0, solution showed that the max- imum rate occurred with a photocatalyst of 1.5 wt.% PtlCdSln-Si (6-7 wt.%)/ZnS in a 1.5:l weight ratio. An increased H, rate was achieved by incorporating P-doped n-type Si in CdS. Combining small-bandgap semiconductor particles and larger-bandgap semi- conductor particles increases photocatalytic efficiency.

Platinum Metals Rev., 1996, 40, (2) 90

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Rigid Mdtinuclear Arrays Assembled Around Platinum Centres A. HARRIMAN, M. HISSLER, R. ZIESSEL, A. DE CIAN and J. FISHER, 3 Chem. soc., Dalton Trans., 1995, (24), 40674080 A series of cis- and trans-Pt(1I) acetylide complexes of type [Pt"(PBu",),L] where L = 2,2'-bipyridin-4- ylethynyl or 2,2':6',2"-terpyridin-4'-yl-ethynyl or - butadiynyl, were prepared and their photophysical properties were measured at 293 and 77 K. The periph- eral metal complexes of these Pt" systems have rela- tively long-lived excited mpler states, and could func- tion as effective photosensitisers. Photons collected by the central PP site are quantitatively transferred to the terminal metal complexes. The I"' centre thus acts as a light-harvesting antenna, for near-UV light.

Photoreactions of Metal Complexes with DNA, Especially Those Involving a Primary Photo- Electron Transfer A. KIRSCH-DE MESMAEKER, J . -P . LECOMTE a n d 1. M. KELLY, Topics Current Chem., 1996, 177, 25-76 Photochemical reactions induced by Ru(II), Rh(II1) and Co(II1) polypyridyl complexes, porphyrins and uranyl ions with DNA are reviewed. Electron trans- fer reactions are examined. Evidence for direct oxi- dation of the DNA bases, production of DNA-dam- aging reactive species, direct H abstraction from the DNA ribose and formation of adducts between the metal complex and DNA is provided. The use of metal complexes as photoprobes for studying nucleic acids and photo-therapeutic applications is discussed.

APPARATUS AND TECHMQUE Development of a Micro Glucose Sensor Using an Electrodeposited Platinum Black with Mechanical Stability s. IKEDA, H. WATANABE and I. IGARASHI, Denki Kagaku,

A glucose sensor has been fabricated from a Pt wire, sealed in the capillary of a 23-gauge needle with epoxy resin and electrodeposited with stable Pt black by ultra- sonic irradiation from a solution containing H,PtC1,.6H20. The sensor responds to glucose con- centration of I 5 0 mg/dl within a few minutes and its output current varies with 0, partial pressure. The sen- sor can be implanted via a semipermeable membrane.

In-situ Modification of the NOx Sensitivity of Thin Discontinuous Platinum Films as Gates of Chemical Sensors

I. KLEPERIS, A. LUSIS and I. LUNDSTROM, Thin Solid

A sensor of improved NOx sensitivity, optimum at - 125OC, was obtained by modifymg a thin discontin- uous Pt gate MOSFET with NH, at 150°C for 10 min. NOx exposure increases the threshold voltage but expo- sure to H,, NH,, alcohols and unsaturated hydrocar- bons decreases it. The sensor was stable to NOx for one month without more NH, treatment.

1995, 63, (12), 1138-1140

J. ZUBKANS, A. L. SPETZ, H. SUNDGREN, F. WINQUIST,

Films, 1995,268, (1-2), 140-143

Voltresistometry of Noble Metals and Extension of Measuring Capability of the Contact Electroresistance Method by Using Iridium Reference Electrodes v. A. MARICHEV and L. A. CHARNY, sur& sea:, 1996,347,

The potential dependence of the contact electrore- sistance (CER) of Pt, Ir, Ag and Au was studied in borate buffer solutions of pH 1-14. Ir has the lowest CER by 3-1 4 mQ and can be used as the reference electrode for measuring high CER values of the oxides of metals, such as Ti, Zr and Cr. The CER of oxi- dised metal surfaces was non-ohmic. Thus, a new method is proposed for an in situ evaluation of the specific area of defects in oxide films on metals.

(1/2), 228-236

HETEROGENEOUS CATALYSIS Adsorbate-Assisted NO Decomposition in NO Reduction by C,H6 over Pt/AI,O, Catalysts under Lean-Burn Conditions R. BURCH and T. C. WATLING, Catal. Lett., 1996, 37,

The rates and product selectivities of the C,H,-NO- 0, (1) and NO-H2 reactions over a PdAl,O, cata- lyst, and of the NO decomposition over the reduced catalyst were compared at 240°C. The NO decom- position rate over reduced catalyst was 7 times greater than the NO decomposition rate in reaction (1). The (extrapolated) rate of the NO-H, reaction at 240°C was - 10' times faster than the rate of the NO decom- position. NO decomposition may be assisted by Hads.

Nitric Oxide and Carbon Monoxide Adsorption on Lanthana-Supported Platinum and Rhodium Catalysts H. CORDATOS and R I. GORTE, Appl. Catal. B: Environ.,

CO and NO adsorption studies by TPD on model Wlanthana and Pdlanthana catalysts showed that the lanthana surface can be reduced in CO by form- ing the carbonate which decomposes at > 650 K. The reduced lanthana has similar adsorption and decom- position properties for NO as those seen for Pt and Rh. Adding Pt and Rh promotes the CO reduction of the lanthana surface, possibly by migration of the 0 from the lanthana to the metal surfaces.

Control of the Efficiency of Low-Percentage Pt-Cu/Al,O, Catalysts in the Activation of C- H and C-C Bonds in Light Alkanes D. B. FURMAN and A. P. BARKOVA, Kinet. Katal., 1995,

The effects of preliminary preheating CU(NO,)~/ALO, on Pt metal deposition and on C-H and C-C bond activation by Pt-CdAl,O, catalysts were studied in ethane and propane. Treating Cu(NO,)JAl,O, in H2 at 300-900°C produced catalysts which activate the ethane C-H bond, and form C,H, selectively in 92-85% yield. Preliminary heat treating the support in air gave catalysts which activate the C-C ethane bond, and form CH, selectively in > 60% yield.

(1-2), 51-55

1995, 7, (1-2), 3 3 4 8

36, (6), 878-882

Plutinum Metals Rev., 1996, 40, (2) 91

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Stationary Kinetics of Essential Reactions on Automobile Exhaust Pt-RWAl,O, Catalyst

M. HARKONEN and J. SOHM, Appl. Catal. B: Environ.,

Oxidation and reduction reactions of three-way cat- alysts were studied over Ce0,-promoted Pt-Rh/ALO, at 100400°C. The concentrations of CO, CO,, total hydrocarbons, NO/NOx and 0, at the monolith out- let were measured for different gas feeds. When H,O was present, oxidation reactions were enhanced at low temperatures, while the H,O-gas shift reaction and steam reforming occurred at higher temperatures.

Aromatics Reduction over Supported Platinum Catalysts. 2. Improvement in Sulfur Resistance by Addition of Palladium to Supported Platinum Catalysts T.-B. LIN, c.-A. JAN and J.-R. CHANG, Ind. Eng. Chem. Res., 1995, 34, (12), 42844289 Effects on the S resistance of a supported Pt catalyst on adding Co, Mo, Ni, Re, Ag and Pd, were studied by accelerated ageing reactions on tetralin hydro- genation with 1000 ppm S at 280°C, 380 psig and H,:oil = 2.7. Pd-Pt had the highest S resistance. Pd- Pt had the best catalytic performance for aromatic reduction, hydrodesulphurisation and hydrodenitro- genation of diesel. Pd-Pt bimetallic interactions lower the Pt electron density and inhibit H,S adsorption.

Surface Structure Change of a [Ptr(p- CH,COO),]/SiO, Catalyst Active for the Decomposition of Formic Acid W.-J. CHUN, K. TOMISHIGE, M. -0, Y. IWASAWA and K. ASAKURA, 3 Chem. SOC., Faraday Trans., 1995, 91, (22), 41614170 Studies of catalytic properties of l%-cluster/SiO, (1) prepared from the [Pb(p-CH,COO),] cluster showed that it is highly active for HCOOH decomposition giv- ing 100% selectivity to CO, and H,, compared with the Pt-particldSi0, catalyst, which also gives CO and HzO. Reaction on (1) involved: an induction period; a slow reaction period; a catalytic high-rate reaction period; and deactivation. The surface structure of (1) changed h m tetrarner to dimer during induction, then to monomers which were active for catalysis.

Effects of Barium on NOx Reduction Activities of Palladium Three-Way Catalyst H. SHINJOH, K. YOKOTA, H. DOI, M. SUGIURA and S . MATSUURA, Nippon Kagaku Kaishi, 1995, (lo), 779-788 Three-way automotive Pdly-Al,O, catalyst modified with Ba was studied by NOx reduction using simu- lated exhaust gases, reaction gas chemisorption, H,O gas shift reaction, etc. A big improvement in the NOx reduction activity was seen at 100-500°C on adding Ba, under stoichiometric simulated exhaust gas (1) and under reduction conditions for the simulated exhaust gas (2). Under (1) NO was selectively reduced, rather than 0,. Under (2), suppression of chemisorbed hydrocarbons allowed smooth NOx reduction.

P. MA"ILA, T . SALMI, H. HAARIO, M. LUOMA,

1996,7, (3-4), 179-198

Effect of Ceria Structure on Oxygen Migration for RWCeria Catalysts

and R. J. GORTE, 3. Phys. Chem., 1996, 100, ( 2 ) ,

The adsorption and reaction properties of Rh parti- cles supported on a CeO,(lOO) surface and on poly- crystalline CeO, film annealed at low (970 K) and high (1720 K) temperatures were studied. S i d c a n t growth of the CeO, crystallite size and change in the surface morphology upon high-temperature anneal- ing was found. High-temperature annealed CeO, sin- gle crystals and polycrystalline !ilms are relatively inert, but CO adsorbed on Wsmall CeO, crystallites can be oxidised by CeO,. Thus, loss of 0, storage capac- ity in automotive catalysts may be due to changes in the CeO, morphology and crystallite sue.

Propionitrile Formation from Ethene and Ammonia over RWY-Zeolite N. TAKAHASHI, H. SAKAGAMI, T. w i s n I m , s. AZUMA

Rh-Y zeolite catalyst was found to be very effective for CzHsCN formation from C,H, and NH,. The cat- alyst was more active and selective than other tran- sition metals supported on Y-zeolites. The reaction between C,H, and HCN is proposed as a reaction route for C2HrCN formation.

One-Step Preparation of Highly Dispersed Supported Rhodium Catalysts by Low- Temperature Organometallic Chemical Vapor Deposition P. SERP, R. FEURER, R. MORANCHO and P. KALCK, 3. Cazal., 1995, 157, ( Z ) , 294-300 A new method for preparing supported Rh catalysts using organometallic CVD, and contacting a Rh com- plex vapour with SiO, in a fluidised bed reactor at 50-100 Torr, is described. Adding small amounts of H, allows Rh deposition at low temperature (100°C). Three Rh precursors, [Rh(p-CI)(CO),],, [Rh(q'- C,H,),] and [Rh(acac)(CO),], were used. Small aggre- gates of 1-2 nm with high dispersions of 0.95-0.70 were obtained. Rh(0) was detected on the surface, and &(I) and Rh(I1) centres were found near the interface, covalently bound to the support. The cat- alyst showed greater hydrogenation activity than its counterpart prepared by conventional impregnation.

Ethanol Synthesis from Carbon Dioxide on Ti0,-Supported [Rh,,Se] Catalyst H. KURAKATA, Y. IZUMI and K.-I. AIKA, Chem. Commun.,

An efficient synthesis of EtOH kom COJH, over Ti0,- supported [Rh,,Se] clusters prepared from [Rh,,Se(CO),,]z is reported. Promoter effects of the interstitial Se inside the [RhlO] framework are dis- cussed. [Rh,,Se]miO, converted CO, into EtOH faster, 60 x lo-' molihlg cat., and more selectively, -83%, than other supported Rh clusters or [Rh&e] clusters on other inorganic oxides. This may be due to effects from interstitial Se and the [Rh,,Se]/Ti02 interface.

H. CORDATOS, T. BUNLUESIN, J. STUBENRAUCH, J. M. VOHS

785-789

andT.MATSUDA, c a d . k t L , 1996,36, (3,4), 241-244

1996, (3), 389-390

Platinum Metals Rev., 1996, 40, (2) 92

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Redox and Carbonylation Chemistry of Iridium Species in the Channels of H-ZSM-5 Zeolite

N. I. JAEGER and G. SCHULZ-EKLOFF, 3 Mol. catal. A: Chem., 1996,104, (3), 299-309 Reduction of Ir/H-ZSM-5 by H, yields Iro clusters with a large positive X P S shift and an upward IR shift of linearly bonded CO, which suggest a strong elec- tron deficiency. Ir clusters (< 1 nm) can be rapidly reoxidised by the highly acidic hydroxyls with sub- sequent formation of Ir+(CO)* gem-dicarbonyl even with residual CO. Displacement of NH, ligands which were co-ordinated to unreduced Ir3' cations formed ItZ'(CO),. This species is reduced stepwise to Ir+(CO), and Iro-CO via the H1O-gas shift reaction.

Preparation of Ruthenium-Containing Polycarbonate Films and the Chemistry of Ruthenium in Polycarbonate I.-w. SHIM, w.-s. OH, H.-C. JEONG and w.-K. SEOK, Macromolecules, 1996,29, (4), 1099-1 104 RuC1,.3Hz0 complexes were incorporated into poly- carbonate (PC) using solvent. Interactions with CO, O,, H2 etc., effects of the Ru complexes and thermal properties of PC were studied in films. Catalytic activ- ities were observed in various gas phase reactions under relatively mild conditions, such as NO reduc- tion, HzO-gas shift reaction, etc.

T. V. VOSKOBOJNIKOV, E. S. SHPIRO, H. LANDMESSER,

HOMOGENEOUS CATALYSIS Polyketone Polymers Prepared Using a PalladidAIumoxane Catalyst System Y. KOWE and A. R BARRON, Macromolecuhs, 1996,29, (4), 1110-1118 The Pd-catalysed copolymerisation of CO and eth- ylene to give polyketone polymers was achieved using either (dppp)Pd(OAc), or (dppp)Pd[C(O)'Bu]Cl in the presence of a ten-butyl alumoxane as a co-cata- lyst. The polymers were alternating ethylene/CO and had high molecular weights. No furanisation or cross- linking was found. The crystal structure of these poly- mers was that of the a-phase polyketone. The increased densities of these polyketones is due to a decrease in the interchain packing distances.

Unprecedented Intra- and Intermolecular Palladium-Catalyzed Coupling Reactions with Methylenecyclopropane-Type Tetrasubstituted Alkenes s. BRASE and A. DE MEIJERE, Angew. Chem., Int. Ed. Engl., 1995, 34, (22), 2545-2547 A cascade of reactions consisting of a Heck coupling, cyclopropyl ring-opening and a domino Diels-Alder reaction proceeded in a one-pot synthesis in the pres- ence ofPd(OAc),. The Pd-catalysed coupling of bicy- clopropylidene with vinyl iodide gave dendralene, even in the presence of dienophile, which then reacted with R' = H, COzMe or R, = COzMe to yield bisadducts. Carbopalladation of the tetrasubstituted alkene pro- ceeds faster than the Heck reaction with the dienophile.

A New, Highly Selective, Water-Soluble Rhodium Catalyst for Methyl Acrylate Hydroformylation G. FREMY, Y. CASTANET, R. GRZYBEK, E. MONFLIER, A. MORTREUX, A. M. TRZECIAK and J. J. ZIOLKOWSKI, 3 Orgunomet. Chem., 1995,505, (l), 11-16 Hydroformylation of methylacrylate to a-aldehyde was achieved in a two-phase system in the presence of two new H20-soluble Rh phosphine PNS and PC catalysts, prepared by reacting [Rh(acac)(CO,)] with various H,O-soluble monodentate phosphines, such as Ph,PCH,CH(COOLi)(CH,COOLi) (PC), Ph,PCH,-CH,CONHC(CH3)2CH,S0,Li (PNS), P(CHz).-C,H,SO,Na],, etc. High yields and selec- tivities of a-aldehyde were obtained.

Substrate Selective Catalysis by Rhodium Metallohosts H. K. A. C. COOLEN, J. A. M. MEEUWIS, P. W. N. M. VAN LEEUWEN and R J. M. NOLTE, 3 Am. Chem. soc., 1995, 117, (48), 1190&11913 A new supramolecular catalyst, consisting of a bas- ket-shaped molecule with a catalytically active Rh(1) complex attached, is described. It functions accord- ing to the principles of enzymatic catalysis. The cat- alyst selectively hydrogenates and isomerises allyl-sub- stimted dihydroxyarene substrates bound in its cavity. The rate-limiting component of these catalysts is the metal centre and the process sequence there.

Ligand Effects in the Catalytic Hydrogenation of Carbon Dioxide to Formic Acid Using in situ Catalysts Formed from [{(cod)Rh(p Cl)],] and Monodentate and Bidentate Phosphorus Ligands E. G R A F ~ ~ ~ W . LEITNER, Chem. Ber., 1996, 129, (l),

Highly active catalysts for the hydrogenation of CO, to formic acid in DMSOhIEr, were formed in situ from [ { (cod)Rh(p-Cl)} ,] and various monodentate or bidentate ligands with P as the donor atom. Formic acid concentrations of I 2.3 ? 0.2 molil were obtained in < 6 h at ambient temperature under a total initial pressure of 40 arm by using Rh concentrations of 5 x 10.' molil. With bidentate ligand R2P(CH2),PR2 the chain length n determines the activity of the catalysts.

Ligand-Induced Selectivity in the Rhodium(JI)-Catalyzed Reactions of a-Diazo Carbonyl Compounds A. PADWA, D. J. AUSTIN and S . F. HORNBUCKLE, J. Org.

The reaction of 3-allyl-2,5-diazopentanedione and 3- butenyl-2,5-diazopentanedione with traces of a R h o catalyst in methylene chloride at room temperature gave products with internal trapping of a carbonyl ylide as well as intermolecular cyclopropanation. When the catalyst was changed from Rh,(OAc), to Rhz(cap), to Rh,(tfa), a sigruficant change occurred in the prod- uct distribution. With %@a),, an unexpected regio- chemical crossover occurred in cycloaddition, due to complexation of the metal with the dipole.

91-96

Chem., 1996,61, (l), 63-72

Platinum Metals Rm., 1996,40, ( 2 ) 93

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Homogeneous Hydrogenation of Carbon Dioxide to Methanol Catalyzed by Ruthenium Cluster Anions in the Presence of Halide Anions K.-I. TOMINAGA, Y. SASAKI, T. WATANABE and M. SAITO, Bull. Chem. Soc. Jpn., 1995, 68, (lo), 2837-2842 Detailed catalytic and mechanistic studies showed the first formation of MeOH, together with CH,, by homogeneous hydrogenation of CO, using a system consisting of RU,(CO)~~ and alkaline iodides in N- methylpyrrolidone solution at 240°C. The successive formation of CO, MeOH, and then CHI was indi- cated. An overall reaction mechanism is proposed.

Coupling H, to Electron Transfer with a 17- Electron Heterobimetallic Hydride: A "Redox Switch" Model for the H,-Activating Center of Hydrogenase R T. HEMBRE, J. s. MCQUEEN and v. w. DAY, J. Am. C h .

The preparation of a meta-stable heterobimetallic mixed-valence ion, ~e(II),Ru(III)], formed by one- electron oxidation of Cp*(dppf)RuH (l), where dppf = 1 ,l'-bis(dipheny1phosphino)ferrocene and Cp* = pentamethylcyclopentadienide, is reported. Cyclic voltammetry of (1) showed that there was great sta- bility for one-electron oxidation. Two reversible oxi- dations at +0.073 and +0.54 1 V and a quasireversible oxidation at +0.975 V (vs NHE) appeared and were assigned to Ru(III/II), Ru(IV/III) and Fe(III/II), respectively. Compound (1) is the first homogeneous catalyst to reduce methyl viologen with H2.

Amino Alcohol Effects on the Ruthenium(II)- Catalysed Asymmetric Transfer Hydrogenation of Ketones in Propan-2-01

T. IKARIYA and R. NOYORI, Chem. Commun., 1996, (2),

A Ru(II) complex, generated in situ from [ {RuC12(q6- C6Me,}],], (IS, 25')-2-methylamino-l,2-diphenyl- ethanol and KOH was found to be an efficient catalyst for asymmetric transfer hydrogenation of acetophe- none derivatives in propan-2-01, The catalyst had high reactivity at room temperature. (5')-enriched alcohols in I 92% ee and in > 90% yield are produced.

SOC., 1996, 118, (4), 798-803

J. TAKEHARA, S. HASHIGUCHI, A. FUJII, S.-I. INOUE,

233-234

FUEL CELLS A New Fuel Cell Electrocatalyst Based on Highly Porous Carbonized Polyacrylonitrile Foam with Very Low Platinum Loading S. YE, A. K. VIJH and L. H. D A O , ~ Electrochem. Soc., 1996,

A carbonised polyacrylonitrile (PAN) microcellular material of high porosity with incorporated Pt load- ing of - 13 pg/cmZ was prepared, characterised and used as the electrode material for O2 reduction. It has excellent electrocatalytic activity which is attributed to the highly homogeneous distribution of the small Pt particles in the carbonised PAN foam surface.

143, (l), L7-L9

Improved Pt Alloy Catalysts for Fuel Cells A. FREUND, J. LANG, T. LEHMANN and K. A. STARZ, Caul. Today, 1996, 27, (1-2), 279-283 Electrode catalysts, Pt-Co-Cr/C black, with increased activity and stability for the O2 reduction reaction in phosphoric acid fuel cells were developed by co-pre- cipitation of the corresponding metal nitrates. A tetrag- onal ordered structure was formed at > 873 K. This method will allow preparation of more efficient cat- alysts of small Pt-Co-Cr alloy particle size.

CORROSION PROTECTION Effect of Mo and Pd on Corrosion Resistance of V-Free Titanium Alloys for Medical Implants Y. OKAZAKI, K. KYO, Y. ITO and T. TATEISHI, J. Jpn. Inst. Met., 1995, 59, (lo), 1061-1069 The corrosion resistance of Ti-1 5%Zr-4%Nb-4%Ta- 0.2%Pd-0.2%0-0.05%N and Ti-1 5%Sn-4%Nb- 2%Ta-0.2%Pd-0.2%0 alloys, for medical implants, were compared with pure Ti Grade 2 alloys, Ti-6%Al- 4%V ELI (Extra low interstitial), etc., by anodic polar- isation and immersion testing at 310 K in various pseudo saline solutions. The rate of Ti ion released by Ti alloys in a deaerated 5% HCl solution decreased with increasing Zr, Nb, Ta and Pd contents.

ELECTRICAL AND ELECTRONIC ENGINEERING Improvedp-Channel W G a A s S b HIGFET Using Ti/Pt/Au Ohmic Contacts to Beryllium Implanted GaAsSb K. G. MERKEL, C. L. A. CERNY, V. M. BRIGHT, F. L. SCHUERMEYER, T. P. MONAHAN, R. T. LAREAU, R. KASPI

179-191 and A. K. MI, Solid-state Electron., 1996, 39, (2),

Ti/Pt/Au metallisation produces an extremely low contact resistance on Be implanted GaAsl.,Sb,. The contact is thermally stable at 250°C for - 500 h and can withstand thermal cycling to 450°C. The use of Ti/Pt/Au as the source, drain and gate metallisation produced a single, conventional metallisation for the Ina r,Al,r,As/GaAs, ,,Sbo ,9 p-HIGFET, which is improved with respect to ohmic contact reliability, etc. Using Be implantation with Ti/Pt/Au metallisa- tion directly enhances future device designs.

Bias and Thickness Dependence of the Infra- Red PtSilp-Si Schottky Diode Studied by Internal Photoemission v. w. L. CHIN, J. w. v. STOREY and M. A. GREEN, Solid- State Electron., 1996, 39, (2), 277-280 IR PtSilpSi diodes with different metal thicknesses were studied at - 80 K by internal photoemission as a fbction of reverse bias. The zero-bias barrier height of PtSilpSi was found to increase only marginally with metal thickness. The main lowering of the Schottky barrier height is at low to moderate electric fields. The carrier mean free path in Si decreased with an increase in the semiconductor acceptor density.

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NEW PATENTS METALS AND ALLOYS High Quality Platinum Alloy HOTAKA KlKlNZOKU KOGEI K.K.

Japanese Appl. 7f 289,3 24 High quality Pt alloy contains 99.0 wt.% Pt and 0.1-1 .O wt.% In. The alloy has good castability, work- ability and strength, even with the high purity that it provides. It is used for decorative applications.

ELECTROCHEMISTRY Stable Graphite Cathodes BAYER A.G. European Appl. 683,247A A graphite cathode, especially for use in HC1 elec- trolysis, is produced by filling the pores before use with a solution of Ir or Rh salts, or their mixtures, with salts of Pt, Pd, 0 s and/or Ru in 2 4 C mono- or polyhydric alcohols. The impregnated surface of the graphite is heated under open gas flames at 200-450"C. This process produces stable, corrosion- and abrasion-resistant electrodes with low over-voltage.

Oxidation in Bipolar Filter Press Cell EILENBURGER ELEKTROLYSE & UMWELTTECHNIK

German Appl. 4,419,683 A bipolar filter press cell for anodic oxidation with- out corrodible or costly composite anodes has smooth Pt anodes on impregnated insulated graphite sub- strate, useful for (re)generating peroxo-disulphate solutions and decomposing pollutants. The anodes are made 6.om strips, tapes or foils of smooth Pt with a thickness of 20-50 pn placed on vertical contact strips of impregnated graphite, which are separated by insulating plates consisting of flexible and heat- resistant plastics.

ELECTRODEPOSITION AND SURFACE COATINGS Barrel Plating Method W. CANNING LTD. British Appl. 2,290,553A A Cr plating method comprises placing the material to be plated in a bath containing trivalent Cr and an anode. The anode comprises a substrate coated with an Ir oxide catalyst. The formation of hexavalent Cr at the anode is suppressed and sludge formation is avoided. The method is especially used for plating components with complex morphologies.

Silver-Palladium Alloy Plating Bath SUMITOMO METAL IND. LTD.

Japanese Appl. 71233,496 A Ag-Pd allof plating bath has the composition 3.C-30.0 gA Pd ions, 2.C-16.0 fl Ag ions, 300.CMOO.O gil alkaline metal bromide, 10.C-50.0 fl alkaline metal nitrite and balance H20. It is used for forming Ag-Pd alloy coatings and gives a smooth surface.

Palladium Plating Solution KOJIMA KAGAKU YAKUHIN K.K.

Japanese Appl. 71278,870 Palladium plating solution contains 1.0110.0 g/l sol- uble Pd, 0.1-20.0 g/l pyridine sulphonic acid, or its salt andlor pyridine carboxylic acid or its salt, and 1 .O-20.0 ppm fluorine-containing surfactant. It pro- vides Pd deposits of stable high purity, good solder wettability, heat resistance and bondability.

Aqueous Palladium Plating Bath w. C. HERAEuSG.m.b.H. German Appl. 4,425,110 An aqueous plating bath for Pd electrodeposition con- tains 5-50 41 Pd as Pd(NH,),CI,, 10-1 50 811 ami- dosulphonic acid and/or NH4 sulphamate, 0.01-2 g/l of a pyridine derivative and NH4Br, such that the molar ratio br0mide:chloride = 3: 1. The pH of the bath is adjusted to 6.5-10, with NH,OH. The bath give adherent, fissure-free Pd layers which are sol- derable and have good bondability to bonding wires.

APPARATUS AND TECHNIQUE Thixotropic Fluorosilicone Gel Composition

European Appl. 676,450A A thixotropic fluorosilicone gel composition com- prising an organopolysiloxane containing an alkenyl group, of specific viscosity, organohydrogenpolysil- oxane, a Pt catalyst and finely powdered S O z was made hydrophobic by treatment with a silazane, chlorosilane, etc. The gel is used in the production of protective materials for semiconductor pressure sen- sors, such as air quality sensors in automotive fuel injection systems, vapour sensors in gasoline tanks, and H,O and gas pressure sensors in hot H 2 0 sup- ply systems. The gel formed has good solvent resistance and low shrinkage.

Production of Single Crystal Oxide Film

Apparatus for the production of single crystal oxide film by liquid phase epitaxy has an insulating Al,O, core tube containing a Pt or Pt alloy cylinder open at both ends and holding a k or Pt alloy crucible coax- ially within it. A high frequency heater is external to the core tube. The apparatus produces magnetic gar- net for use in magnetostatic wave devices and Li niobate for optical devices, etc.

Electrochemical Oxygen Sensor

A sensor is claimed for determining the 0, concen- tration in gas mixtures which are not at equilibrium, such as motor vehicle exhaust gas. It comprises a solid 0 ion conducting electrolyte with a measuring elec- trode exposed to the gas mixture which contains Pt and a material that inhibits the catalytic effect of the electrode, so it is at the potential of the free O2 present.

SHINETSU CHEM. CO. LTD.

MURATA MFG. CO. LTD. European Appl. 676,492A

ROBERT BOSCH G.m.b.H. world Appl. 95125,276A

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Oxygen Concentration Detection Element UNIslA JECS cow. Japanese Appl. 71248,308 An 0, concentration detecting element consists of a ZrO, tube with an inner and an outer electrode, and a Pt layer, vapour deposited on the outer surface of the tube so that it covers the outer electrode. A metal catalyst of Pt, Pd, Rh and Ag, and a sintering agent are adhered to the Pt layer. The element gives prolonged use without increasing the internal resistance due to sintering of the Pt layer, and without deterioration of the catalytic action. It works at low temperature.

HETEROGENEOUS CATALYSIS Exhaust Emission Control Device for I.C.E.

An exhaust emission control device for I.C.E. has a flow-in section containing Pd and a flow-out section containing Pt and Rh upstream of a three-way cata- lyst containing Pt, Rh and Ce. The device prevents the deterioration of Pt and Pd while increasing the efficiency of the exhaust emission control.

Catalyst for Chlorine Dioxide Synthesis DEGUSSA A.G. European Appl. 673,878A A catalyst for low level ClO, production over an extended period of time, where the catalyst has a slow rate of deactivation, consists of a catalyst support mod- ified by a Group IA carbonate salt or a Group IIA car- bonate salt or a Mg salt convertible to MgO. The out- side edge of the support is impregnated with Pd or Pd and another Pt group metal or Pd and a Group IB metal. Also claimed is a two component package comprising the catalyst and a C10, precursor. C10, is a disinfectant or sterilising agent.

Ammonia Decomposition Catalyst MlTSuBISHI JUKoGYo K.K. European Appl. 686,423A An NH, decomposition catalyst comprises a crys- talline silicate carrier and Ir as the active metal. A composite NH, decomposition catalyst comprises: a first catalyst of a carrier selected from y-Al,O,, ZrO,, TiO,, TiO,.ZrO,, etc., and Ir, and a second catalyst comprising an element selected from Ti, V, W and Mo. A layered NH, decomposition catalyst comprises: a first catalyst with a crystalline silicate carrier and an active metal of Pt, Pd, Rh or Ru; and a second cata- lyst comprising an element selected from Ti, V, W and Mo; the second catalyst covers the first catalyst.

Vapour Phase Hydrogenation Process

TOYOTA JIDOSHA K.K. British Appl. 2,290,488A

INST. FRANCAlS DU PETROLE European Appl. 686,615A

A process for the selective vapour phase hydrogena- tion of 2-3C acetylenic hydrocarbons to the corre-

Ether- Carboxylic Acid Production HENKEL K.G.A.A. World Appl. 95128,375A The production of ether-carboxylic acids or their salts (1) comprises the oxidation of ether-alcohols (2) by pure 0, at 50-130°C in the presence of alkali metal hydroxide and PdIC catalyst. The concentration of (2) is kept constant at 0.1-15 wt.% during the reac- tion, and the salt obtained may be converted into acid. The reactor is prefilled with catalyst and H,O only and evacuated to 0.01-0.1 bar at room temperature before the reaction, and to 0.01-0.6 bar partial 0, pressure during the reaction. No off-gas is formed and the catalyst can be repeatedly used.

Tertiary Amine Preparation LONZA A.G. WorM Appl. 95130,666A A tertiary diamine is prepared by reacting a dinitrile with H, at 1OC-250"C under high pressure in the pres- ence of a supported Pd catalyst. Compound 1,5-bis- (3-methyl piperidino)-2-methyl pentane is claimed as a suitable catalyst for the production of polyurethanes, polyureas or polyurethane-ureas as elastomers or foams. The process produces good yields of amine compounds without large amounts of by-products.

Catalytic Combustion of Methane JOHNSON M A n H E Y P.L.C. world Appl. 95131,675A Partly combusted CH, and 0, are combusted at 450-1 500°C by passing over a catalyst of either stan- nic oxide and optionally Pt, Pd, Rh andlor Ru, with a Sn:Pt metal atomic ratio > 12:1, or a catalytically active component on a stannic oxide support. Combustion occurs in two stages: the first at 3O0-80O0C, preferably over a Pd, Pt andlor Rh con- taining catalyst, and the second at 80@1500"C. The catalysts are highly efficient at relatively low com- bustion temperatures and limit the release of unburnt CH, and formation of NOx, etc.

Reduction of Lean-Burn Exhaust Gases ALLIED SIGNAL ENVIRON. CATAL.

World Appl. 95132,790A A catalyst for removing CO, hydrocarbons and NOx from I.C.E. exhaust, containing 0, in excess of stoi- chiomeny, comprises Pt alloyed with Co, Ni, Cu, Rh, Pd, Ag andlor Au on an inert support. The catalyst is prepared in a solvent from Pt compounds and a sol- uble compound of the metals, in the presence of a reducing agent which gives a colloidal suspension of Pt-metal alloy, followed by absorption onto a support, drying, calcining and recovery. The catalyst functions within a predetermined range of engine operating tem- peratures and under highly oxidising conditions.

Preparation of Aromatic Amino Derivatives ClBA GEIGY A.G. World Apjd. 95132,941A

sponding ethylenic compounds uses a catalyst con- taining Pd, at least one Group IB metal and Al,O,. The weight ratio Group IB meta1:Pd is 0.05-0.4 and at least 80% Pd and at least 80% of Group IB metal is present in a defined volume on the catalyst periph- ery. The process converts acetylene or propyne to ethylene or propylene, respectively.

Aromatic amino derivatives, for herbicide intermedi- ates, substituted by at least one group having unsat- urated C-C bonds, are produced by hydrogenating aromatic nitro derivatives in the presence of Pt cata- lysts modified with Pb, Hg, Bi, Ge, Cd, As, Sb, Ag or Au. Also claimed is a metal modified catalytic com- position of Pt, containing a Fe, Mn or Ru promoter.

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Dehydrogenation of Hydrocarbon Feedstock AMOCO cow. US. Patent 5,453,558 The dehydrogenation of a hydrocarbon feedstock and olefin production involves contacting the feedstock with a catalyst of Pt and Zn on a support of L-zeo- lite molecular sieve and an alkali metal. The preferred catalyst contains 0.1-2 wt.% Pt, 0.2-5 wt.% Zn, 4 M O wt.% L-zeolite molecular sieve and 0.5-8 wt.% K. This low cost process is used to produce oxygenates for fuel blending and chemical industry feedstocks.

Catalytic Hydroconversion EXXON RES. & ENG. CO. US. Patent 5,457,253 A catalytic hydroconversion process including hydro- isomerisation involves contacting the feed stream with a catalyst comprising Group IVB oxide, a Pt group metal(s), optionally mixed with Re andor Sn, and an amorphous SO,-Al,O, support containing 2 50 wt.% SiO, with a rare earth oxide dispersion. The cata- lyst has enhanced cyclohexene hydrogenation, activ- ity and aromatic selectivity, especially during 7C reforming. It is used for wax isomerisation.

Catalysts for Dehydrocyclisation of Paraffins UOP US. Patent 5,461,016 A catalyst comprises a Pt group metal component, a non-acidic Lzeolite, an inorganic oxide binder and a Ni component with a higher concentration on the binder than on the zeolite. The catalyst has high activ- ity, selectivity, and improved stability. It provides a S-tolerant reforming process. The catalyst is used for the dehydrocyclisation of paraffis to aromatics, especially for high-octane gasoline components.

Selective Hydrogenolysis of Halofluorocarbons

U S . Patent 5,463,152 The hydrogenolysis of a saturated acyclic starting material, C,H&F,, where X = C1 or Br; n, b = 1 4 ; a = 0-3; and c = 1-9; comprises reacting the start- ing material with H2 at - 300°C in the presence of a catalyst containing Pd supported on Crz03 and a HX acid, X = CI, Br, F, etc. The process allows very selec- tive conversion of C1-containing compounds to cor- responding H-containing compounds, and converts halofluorocarbons and hydrohalofluorocarbons to compounds with a lower C1 or Br content. These are used as refligerant gases for replacing CFCs.

Upgrading Naphtha to Isoparaffins UOP US. P a n t 5,463,155 The selective upgrading of a naphtha feedstock to a product with increased isoparaffin content involves contacting the feedstock with a non-acidic ring cleav-

E.I. DU PONT DE NEMOURS & CO.

Hydrogenation of Maleic Acid STANDARD OIL CO. OHIO US. Patent 5,473,086 The hydrogenation of maleic acid to 1,4-butanediol (BDO) and tetrahydrofuran, comprises contacting the precursor with a Hz containing gas and a C sup- ported catalyst containing Pd, Ag and Re, prepared by impregnation. BDO is produced as the major prod- uct with a yield of > 80-90 mole%, and is useful as a solvent, a humectant and a cross-linking agent, etc.

Selective Hydrogenation Process

The selective hydrogenation of ( P l 0 ) C diolefins to monoolefins by H, uses a catalyst of Pd or Pd oxide, Ag or Ago, alkali metal fluoride, such as K fluoride, and preferably an Al,O, support. The catalyst includes 0.05-0.6wt.%Pd,0.1-5wt.%Agand0.2-5wt.% alkali metal. The weight ratio of Ag:Pd is 2:l-1O:l. The catalyst comprises particles of size 1-1 0 nrn and surface area 1-200 m’/g. The feed contains butenes and 0.01-10 wt.% 1,3-butadiene. The reaction tem- perature is 35-100°C and pressure 50-1000 psig.

High Yield Phenol Preparation UBE IND. LTD. Japanese Appl. 71188,082 The preparation of phenol in high yield comprises dehydrogenating cyclohexanone in the presence of a catalyst consisting of Pd, MgO and alkali metal flu- oride. The Pd content is 0.05-10 wt.% to Mg oxide, the latter having a BET specific surface area of 5-170 m’/g and 2 99.9% purity. Phenol is used as an inter- mediate of synthetic resins, surface active agents and so on. The catalyst can be recycled by baking in air.

Car Exhaust Purification Apparatus SUZUKI K.K. Japanese Appl. 7/194,941 Car exhaust purification equipment consists of a cat- alyst of Pd or Pd and Rh on the upflow side giving good durability and another catalyst containing three kinds of catalyst metals on the downflow side. The three-way catalyst on the downflow side removes NOx, CO and hydrocarbons with a high efficiency.

Preparation of Carbonates UBE IND. LTD. Japanese Appl. 7/196,581 Carbonates are prepared in high yield from alco- hols, CO and 0, in alcohol in the presence of Pd and a co-catalyst, such as Cu halide, other Cu salt and alkali metal halide. Only a small amount of Pd catalyst is needed for efficient production, and the Pd can be easily recovered from the reaction solution. Carbonates, especially dimethyl carbonate, are used as solvents and carbonylation agents. They also raise the combustion efficiency on addition to gasoline.

PHILLIPS PETROLEUM CO. U s . Patent 5,475,173

- - Exhaust Gas Purification Catalyst N S S A N MOTORCO. LTD.

ing catalyst, such as a Pt group metal and an A1203 support, etc., followed by isomerising the paraffin intermediate with a Pt metal catalyst, and recover- Japanese Appl. 71213,905 ing the isoparaffin-rich product. Cliavage conditions are 10Cb5OO0C, pressure 100 Pa-10 MPa and LHSV 0.1-3Oh. The process selectively upgrades naphtha withimprovedyield. The catalysts are especially effec- tive for ring cleavage, which, when combined with p a r f f i isomerisation, improves octane values.

An exhaust gas purification catalyst for removing NOx in 0,-rich atmospheres, is a multicomponent com- posite oxide of formula: Pd.MaFeAhO., where a = 0.01-5 wt.% and c =0.1-7 a.r. (atomic ratio), d = 30-200 a.r., when b = 10 a.r. and e = a.r. of 0-atom. The catalyst depresses the total NOx emission.

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Catalyst for Purifying Exhaust Gas BABCOCK-HITACHI K.K Japanese Appl. 712 13,9 14 An exhaust gas purification catalyst has a metal sub- strate coated by a Pt component layer and a deni- triding catalyser layer. NOx and CO are removed effi- ciently and elution of unreacted NH, can be reduced by using a small amount of the catalyst.

Pharmaceutical Diaminouracil Intermediates

Diaminouracils are produced by the hydrogenation of nitrosoaminouracils in the presence of a Pt group metal catalyst. Diaminouracils are important synthetic drug intermediates. The process produces diamino- uracils simply in high yield, high purity and low cost, compared with the conventional process.

Protection of Ammonium Sulphate Deposition

Exhaust gas containing NH,, following denitdication of the combustion gas from co-generation systems by a reducing agent, is contacted with a catalyst con- taining Pt, Rh or Pd supported on a heat resistant oxide, such as A120,, for oxidation. sulphate depo- sition is protected by removing NH, by this method. The energy recovery temperature is reduced.

Preparation of Phenol Compounds JCC COW. Japanese Appl. 71238,042 Phenol compounds are prepared by reacting aromatic compounds with O2 and CO, in the presence of a sup- ported catalyst comprised of a Pd compound andlor a Rh compound and a V compound. The phenol com- pounds are bisphenol, akylphenol and especially phe- nol. They are useful as intermediates for synthetic resins or chemical industrial products. Phenol compounds are obtained in a high yield by direct oxidation of aromatic compounds.

Exhaust Gas Purifying Catalyst TOKYO GAS CO. LTD. Japanese Appk. 7/241,466-68 An exhaust gas purification catalyst for high temper- ature use consists of crystalline Ti containing SiO, combined oxides and carries Pt group metals. The catalyst is prepared by crystallisation of co-existing amorphous SiOz and titanate in an autoclave. CO is removed from the exhaust gas of a rarefied combus- tion gas engine by a catalyst of PtIAl,O, with 1.2-2.5 g/l of Pt on a honeycomb carrier, by Pt-Pd/Al,O, or by Pt-Rh/Al,O,. The catalyst can remove extremely small quantities of CO and is stable for long periods.

Preparation of Dicyclohexyl Ether COSMO OIL CO. LTD. Japanese Appl. 71242,580 Dicyclohexyl ether (1) is prepared by catalytic reduc- tion of diphenyl ether in the presence of a catalyst con- taining 0.01-10 wt. % of Pt, Pd, Rh, Ru andlor Ni, preferably supported on C, SiOz and Al,O,. The reac- tion is carried out at 80-300°C and at 5-100 kg/cm’ H, pressure. Compound (1) is useful as a non-aro- matic solvent having high solubility with various organic compounds. It is obtained in yields of 72-95% and with a conversion ratio of 88-100%.

NIPPON KAYAKU K.K. Japanese ApPl. 71224,047

TOKYO GAS CO. LTD. Japanese A@/. 71227,521

Reduction of Nitrogen Oxides TOYOTA CHUO KENKYUSHO K.K.

Japanese Appl. 7/246,3 18 NOx-containing exhaust gas with excess 02, but free of reducing agent, is reduced by H, in the presence of 0.1% Pt/Si0,-A120, catalyst, where Si02:A120, = 10-20. This method can reduce NOx from diesel engine exhaust efficiently at quite low temperature.

Hydroconversion of Hydrocracking Residues INST. FRANCAIS DU PETROLE French Appl. 2,7 18,060 A hydroconversion catalyst contains 0.0510% Pt group metal with dispersion 20-100% and coefficient ofdis- tribution > 0.1, on a Si0,-Al,O, support with 5570% SiOz, of surface area, BET, 100-500 m’lg and mean pore diameter 1-12 nm. The catalyst contains no zeo- lites or halogens. It is very active and selective, and hydroisomerises residues from hydrocracking to give high value products: kerosenes, and gas and base oils.

N,N-3,3-Dimethyl Butylated Aspartame C. NOFRE French Appl. 2,719,590 N-(N-(3,3-dimethyl buty1)-L-a-asparty1)-L-phenyl alanine 1 -methyl ester (1) is prepared by treating aspar- tame with 3,3-dimethyl butyraldehyde at ambient temperature under H, at 1 bar, in the presence of a Pt- or Pd-based catalyst, such as Pt/C or PdlC. (1) is a sweetening agent with 50 times the sweetening power of aspartame itself. The process gives good yields of pure product in this simple I-stage process.

HOMOGENEOUS CATALYSIS Heterosubstituted Acetal Compounds BAYERA.G. European Appl. 675,129A Heterosubstituted acetal compounds (1) are prepared in high yields by reacting vinyl compounds with alkyl nitriles in the presence of a Pd catalyst, such as Pd chloride, in alcohols andlor ethers at 40-80°C. The acetals are starting materials for medicaments, plant protectants, dyes and P-containing polymers, etc.

Removal of Ally1 or Allyloxycarbonyl Groups PFIZER INC. European Appl. 676,236A A process to remove ally1 or allyloxycarbonyl groups from compounds (1) protected by them comprises contacting (1) with a sulphinic acid compound in the presence of a Pd catalyst in an inert solvent. The depm- tection is achieved effectively and highly chemise- lectively. The removal process occurs in the presence of the p-lactam group found in natural, biosynthetic, semisynthetic and synthetic antibiotic compounds.

Palladium Catalysts for Carbonylation HOECHST A.G. European Appl. 680,966A Novel Pd compounds containing sulphonated 2,2’- bis(diphenylphosphinomethy1)-1 , 1’-bi-naphthalene compounds (1) as ligands are prepared by reacting Pd @)organic salts or complexes with (1). They are used as catalysts for carbonylation of arylmethyl-halides (to arylacetic acid derivatives), of olefins (to carboxylic acids by hydrocarboxylation) and of alkynes, etc.

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Preparation of 9-Amino-Carnpthothecin FUEL CELLS Pl-IARMAClA S.P.A. Wrld Appl. 95132,207A The preparation of 9-amino-camptothecin (l), an antitumour agent, comprises reducing a halogeno 9-nitro camptothecin in a single step, or involves removing the halogen group and then reducing the NO, group using Pd acetate or Pd halide catalyst, and NH, formate. (1) is an inhibitor of topoisomerase and therefore an antitumour agent, suitable for treating leukaemia, colon and rectal turnours. Administration is oral, parenteral or intravenous. Dosage is 0.1-60 mg/kg. The process eliminates or reduces the formation of undesired by-products.

Allylic Oxidation of Steroid 5-ene MERCK& CO. INC. World Appl. 95/32,2 15A The oxidation of A-5 steroidal alkene to correspond- ing A-5-7-keto compounds comprises treatment in solvent with a hydroperoxide in the presence of a Ru based catalyst, such as RuW,,O,oSiNar, RuCl,, RuCl,(PPh,),, etc. The process is used to prepare 5 a-reductase inhibitors, useful in the treatment of hyper- androgenic disorders. It is more environmentally acceptable and the products do not require chromatographic purification.

Production of Alkadienol MITSUBISHI CHEM. COW. Japanese Appl. 711 79,378 The production of ally1 alcohols comprises reacting H,O and a diallyl ether in the presence of a Pd cata- lyst. Alkadienol(1) is produced by reacting a conju- gated alkadiene and H 2 0 in the presence of a catalyst of a Pd compound and phosphines or phosphites, and CO,, and converting the dialkadienyl ether to (1) by reacting with HzO in the presence of a Pd compound. (1) are useful as intermediates for n-octanol and its esters. The yield of (1) is increased and the loss of the Pd compound is prevented since high boiling prod- ucts are converted to easily separable low boiling ones.

Platinum Hydrosilylation Catalysts N O N E POULENC CHIM. French Appk. 2,7 17,48 1-82 Pt complexes (l), useful as (thermo)photoactivatable hydrosilylation catalysts for crossliking systems, con- tain polyorganosiloxanes and compounds with aliphatic unsaturated andor reactive functions. (1) can crosslink systems containing polyorganosiloxanes with at least one reactive Si-H function. They give storage-stable photoactivatable Si compositions for rapid curing upon UV exposure.

Operation of a Platinum Catalyst Fuel Cell BRITISH GAS P.L.C. British Appl. 2,290,409A A fuel cell with a Pt catalyst operates using H, andor alcohol fuel supplied to the anode and 0, to the cath- ode and works at < 250°C. Two external circuits oper- ate alternately, one takes current flow from the cell flowing from cathode to anode, the second supplies current to the fuel cell in a reverse direction. The poi- soned anode catalyst is thus intermittently rejuvenated and de-toxified by applied DC potential.

Stacked Type Fuel Battery FUJI ELECTRIC co. LTD. Japanese Appl. 7/230,8 14 A fuel battery consists of a multilayered body com- posed of multiple unit cells. Each unit cell is equipped with fuel and air electrodes. A liquid drop sensor in the reaction gas passage detects any droplets formed from steam at an early stage and aids their removal. The sensor is composed of a Pt thin line covered with an insulating material.

Conductive Junction Agent MITSUBISHI JUKOGYO K.K. Japanese Appl. 71235,312 The conductive junction agent for a solid-state elec- trolytic fuel battery is claimed. It is used for joining composition members to electrodes in the fuel battery. Pt powder is mixed with and included in the 02-side electrode. Peeling due to heat expansion is prevented.

Anode Electrocatalyst for Fuel Cell STONEHART ASSOC. INC. Japanese Appl. 71246,336 A Pt anode electrocatalyst is dispersed in a SnCl,-con- taining solution which is converted to an alkali atmos- phere to form Sn(OH),, heated to 80-100°C to form Sn oxide and thermally treated at 300-1000°C in a H,-containing reduction atmosphere. The electro- catalyst contains 1-60 at.% Sn and Pt, Pd and Ru, preferably 9 9 4 0 at.% Pt, or contains 8 4 8 at.% Sn and 52-98 at.% Pt as Pt,Sn phase.

Reforming Catalyst for Fuel Cell FUJI ELECTRIC co. LTD. Japanese Appl. 7125 1,070 A spherical AlzO, support is immersed in Zr salt solu- tion, thermally treated to form a ZrOz layer of thick- ness 115-1/10 times as large as the support diameter and coated with Ru metal catalyst. It is placed in a reac- tor tube and contacted with source gas containing hvdrocarbon and H,O vaDour and heated to Droduce

Catalyst for Hydrogenation ,,f Aldehydes MlTSUBISHI CHEM. COW. German Appl. 1195110,629

H, for a fuel cell. This catalyst is durable aga& heat.

The production of saturated alcohols comprises react- CHEMICAL TECHNOLOGY Electrode for a Hydrogen Storage Cell MOToRoLA MC. US. Patent 5,451,474 An electrode for a H, storage cell, of high power den- sity and capacity, comprises powder particles of a H, storage alloy of ABr or AB, type material. The alloy is coated with a Pd or Pd alloy passivation material which prevents surface oxide formation and is H,-per- meable. Formation of the electrode and cell is claimed.

ing the corresponding aldehydes with Hz in the gas phase. The hydrogenation catalyst consists of the reduced products of a catalyst precursor of Cu(a)- Cr(b)-Zn(c)-Mn(d)-Ba(e)-X(f), where X = Groups VIII or IVA transition metal; a-f = proportions of components converted into the corresponding oxides, a = 20-50 wt.%; b, c = 0-50 wt.%; d, e = 0.1-5.0 wt.%; and f = 0.01-3.0 wt.%. Alcohols are produced in good yield and high selectivity.

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GLASS TECHNOLOGY Coating with Improved Corrosion Resistance JOHNSON MATTHEY P.L.C. European Appl. 679,733A A stable coating for high temperature and corrosive environment use comprises a refractory metal sub- strate, Ni, Fe or their alloys, on which are deposited: an interlayer of ceramics and/or one or more metals or alloys of CrOz, Al,O,, MgO,, SiO, or a mixture of Cr, Hf or their alloys; an optional preliminary coat- ing of ceramics; and a substantially non-porous final coating of one or more Pt group metals or alloys. The coating has improved corrosion resistance and can be used for glass industry equipment, such as crucibles, stirrers, crown spinners and thermocouple sheaths.

ELECTRICAL A N D ELECTRONIC ENGINEERING Solderable Integrated Circuit Lead Frames NAT. SEMICONDUCTOR cow. US. Patent 5,454,929 Lead frames with external and internal leads are pro- duced by spot-plating the external leads with Sn fol- lowed by flood-plating the whole frame with Pd. The lead frame is plated with a diffusion barrier material before Sn plating with an alloy containing one or more of Sb, As, Bi, Cd, Ga, Au, In, Ir, Pb, Pt, Rh, Ru, Ag, Th and Zn. The process enhances the bonding and the solderability to a circuit board.

Electrical Wire Ball Bonding Method TEXAS INSTR. INC. US. Parent 5,455,195 The bond pad wire-bonding method involves form- ing a Pd layer 1-2.5 pn thick on an Al bond pad with a ball bond wire of Au or Cu electrically connecting to the Pd layer. Au and Cu form intermetallics with the Al. The Pd layer does not produce intermetallics during heating. The wire-bond interface has no stress. Au-Pd and Cu-Pd solid solutions formed are stable.

A Thin Film Wiring Layer Formation INT. BUSINESS MACHINES COW.

U S . Patent 5,462,897 A thin film wiring layer is applied onto a layered non- conducting and polymer dielectric substrate by selec- tive metallisation using electroless plating to deposit a seed layer of a salt of at least one of Pt, Pd, Au, Ag, Cu or Ni. At least one additional metallisation layer is plated on the seed layer to form the final struc- ture. The non-conductive layer is blanket-applied to obtain no electronic or ionic leakage. Increased adhe- sion between the metal and organic layer is achieved.

Preset Resistor Composition SUMITOMO METAL MINING CO.

Japanese Appl. 71249,507 The resistor is made up of a material in which RuO, and glass powders constitute - 10-40 parts and - 10-50 parts by weight, respectively, of the whole com- position. The RuOz acts as the electrically conductive component. The glass powder softens at 400-650°C. The resistor has reduced slide noise, lower wear and good performance characteristics.

Colloidal Palladium Solution ATOTECH. DEUT. G.m.b.H. German Appl. 4,412,463 Colloidal Pd solutions for pre-metallising treatment contain reducing agents and protective colloids to sta- bilise the solution and also Rh, Ir or Pt group met- als or their compounds, preferably compounds of Rh(III), Ir(II1) or Pt(II). Also claimed is a process for metal-coating electrically non-conductive surfaces and printed boards made by this process. The col- loidal Pd is used for metallising various substrates, especially the holes in printed circuit boards, etc.

MEDICAL USES Radiopaque Marker for Stent ADVANCED CARDIOVASCULAR SYSTEM

European Appl. 679,372A A radiopaque marker comprises a band of radiopaque material plated onto at least a part of the total outer circumference of an expandable cylindrical stent with Pt, Au or Ag. Also claimed are a medical device for implantation in a blood vessel or artery. The marker may be precisely located on a stent and shows the location of the stent under fluoroscopy.

New Antitumour Platinum (11) Complexes TORAY IND. INC. World Appl. 95128,408A New Pt (11) complexes contain R, = 1-3C hydro- carbyl; R,, R, = H or 1-3C hydrocarbyl; or Rz + R3 = -(CHJ4- or -(CH2)7-; Y, Z = NH, or a monoden- tate amine with 1-7C hydrocarbyl or Y + Z = a biden- tate diamine with a 2-1OC hydrocarbyl; X = inorganic acid anion or organic carboxylic acid anion. The Pt complexes have superior antitumour activity and are efficacious against cisplatin-resistant cancers.

Dental Alloys JENEIUCE'ENTRON INC. US. Patent 5,462,437 Dental alloys, for coating with composite or porce- lain compositions for dental restorations, comprise (bywt.%): 1-60% Au, 23.4-24.9% Ag, 41.6% ther- mal expansion adjuster (Pt andlor Pd), 0.25-34%

Thick Film Resistor ComDosition strengfhener and oxide former (Sn and/or In), I 3% grainrefiner (Ir, Ru, Re, Co and/or Rh) and 50.25% deoxidiser (Ca, B, Si, Al, Li andor P). The alloys are yellow with a melting range 870-1230°C. They are compatible with a variety of porcelain compositions,

E. I. DU PONT DE NEMOURS & CO. US. patent 5,474,711

A thick film resistor composition having a small ther-

oxide, RuO,, a first glass comprising PbO, etc., and mal coefficient Of expansion comprises Pb pyochlore and may be produced as a full crown, bridge, etc.

a second glass comprising SOz, etc. The composition minimises fluctuations and variations in the resistance and TCR, especially during the firing step.

The New Patents abstracts have been prepared from material published by Dement Information Limited.

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