platinum metals review · platinum metals review a quarterly survey of research on the platinum...

E-ISSN 1471–0676

PLATINUM METALS REVIEWA Quarterly Survey of Research on the Platinum Metals and

of Developments in their Application in Industrywww.platinummetalsreview.com

VOL. 49 JANUARY 2005 NO. 1

Contents

The Hardening of Platinum Alloys for Potential Jewellery 2Application

By T. Biggs, S. S. Taylor and E. van der Lingen

Fuel Cells Science and Technology 2004 16Reviewed by Donald S. Cameron

Thermal Conductivities of Platinum Alloys at High 21Temperatures

By Yoshihiro Terada, Kenji Ohkubo and Tetsuo Mohri

Electrochemistry of Proton Conducting Membrane Fuel Cells 27Reviewed by Sarah C. Ball

Ruthenium Indenylidene Complexes 33By Valerian Dragutan, Ileana Dragutan and Francis Verpoort

Platinum Group Minerals in Eastern Brazil 41By Nelson Angeli

Abstracts 54

New Patents 58

Final Analysis: Thermocouples Open Circuit Faults 60By R. Wilkinson

Communications should be addressed to: The Editor, Susan V. Ashton, Platinum Metals Review, [email protected] Johnson Matthey Public Limited Company, Hatton Garden, London EC1N 8EE

Pure platinum (Pt) is generally too soft (HV ~60) to be used for fabricating jewellery, so alloyingadditions are made to increase the hardness.Platinum jewellery alloys usually have platinumcontents of 90 wt.% and higher. The most com-mon alloys are hallmarked as 950 platinum (95wt.%). Unlike carat gold (Au) jewellery alloys,where relatively large additions can be made (toalter the properties of the alloy such as its hardnessor colour): for instance 18 ct gold contains 25 wt.%of alloying additions, the 950 platinum alloy hall-marking, only allows alloying additions of up to 5wt.% (to alter properties, such as increase its hard-ness).

Several platinum jewellery alloys are available,and usage depends on national preference and hall-marking regulations. Typical alloying elementsinclude copper (Cu), palladium (Pd), cobalt (Co),gallium (Ga) and indium (In). Cu is often addedand creates a general-purpose alloy which castswell and is easy to work. Adding Co results in avery good casting alloy, while additions of Ga or Inproduce alloys with good springiness. Other popu-lar alloying additions are iridium (Ir) andruthenium (Ru). Pd can be added to platinum, but

while this alloy has a good surface finish, softnesslimits its use. Examples of hardening platinum byalloying additions are shown in Figure 1 (1, 2).

There has been much work on hardening plat-inum by alloying and this is demonstrated inseveral patents. Citizen Watch Co. holds a patentfor an alloy of 8595 wt.% Pt, 1.56.5 wt.% Si withthe balance being one or more of Pd, Cu, Ir, Rh,Au, Ag, Ni and Co (3). This company also patent-ed a Pt-Fe-Cu-Pd alloy (8590 wt.% Pt, 2.53.5wt.% Fe, 7.512.5 wt.% Cu and 04 wt.% Pd) (4).

A patent on hard Pt alloys for jewellery applica-tion states the hard, high-purity Pt alloy contains10100 ppm Ce with a minimum Pt content of 99wt.% (5). Another patent is concerned with main-taining the high purity of platinum while increasingits hardness by minor additions (0.01 to 1 wt.%) oftitanium or a rare earth metal. No age hardeningwas reported (6).

Hard, but still workable, platinum alloys havebeen reported with good abrasion resistance.These were achieved by modifying a surface layerto induce hardening (7, 8). An intermetallic layer ofplatinum, containing especially aluminium andchromium, developed on the surface. One patent

Platinum Metals Rev., 2005, 49, (1), 215 2

DOI: 10.1595/147106705X24409

The Hardening of Platinum Alloys forPotential Jewellery ApplicationBy T. BiggsFormerly Mintek, now 513 Atkins Place, Burlington, Ontario, L7T 2V2, Canada; E-mail: [email protected]

and S. S. Taylor and E. van der LingenMintek, Private Bag X3015, Randburg, 2125, South Africa

Pure platinum is too soft to be used for jewellery and scratches easily. Alloying platinumincreases its hardness significantly. However, platinum alloys used in jewellery do need tobe easy to work and thus the alloy should be sufficiently soft, but not so soft that their wearresistance is low. A good compromise would be to work with a soft alloy during jewellerymanufacture, then harden the alloy so the final finished properties were improved. In order toidentify platinum alloys suitable for hardening, platinum with different alloying additions wasstudied. Platinum alloys with additions of less than 7 wt.% of Ag, Au, Cu, Co, Cr, Fe, Ga,Ge, In, Mg, Mn, Mo, Ni, Si, Sn, Ta, Ti, V, W or Zr were examined, and the merits of each systemwere assessed for commercial viability. The platinum-titanium system was deemed to showthe most promise.

claims a hard alloy that has a boron-containingsurface layer (9).

However, these surface hardening techniquesadd to manufacturing costs; they produce no visi-ble benefit to the consumer and are technicallyunsuitable for use by small jewellery manufactur-ers. Platinum jewellery alloys need to have goodwear resistance and improved surface finish, and avery high final hardness can often impart theseproperties. Achieving a high hardness is desirable,but if the alloy is too hard it cannot be easilyworked, so hardness and the degree of workabilityhave to be balanced.

Casting is used in mass platinum jewellery pro-duction, but results in pieces having hardnessessimilar to those of the annealed material (50 to 180HV). During fabrication, an alloy will work hardendue to cold working, and intermediate annealing isoften required to soften it for further fabrication.It would thus be very helpful to have an alloy softenough to work but which could then be hardenedafter fabrication or casting. Post-fabrication hard-ening can be achieved by an appropriate heattreatment. Heat treatment can result in: an increase in hardness a decrease in hardness, or

no change in hardness.The parameters of heat treatment time and

temperature need to be controlled, as does thealloy chemistry. Heat treatment is used most oftento anneal and soften the alloy. During deformationan alloy hardens, and subsequent annealing resultsin recovery (rearrangement of dislocations) andrecrystallisation of new grains, producing a softeralloy. The higher the annealing temperature, thefaster this occurs. Most cold-worked platinumalloys begin to stress relieve at 600ºC and theysoften rapidly at 1000ºC, which may be regardedas the general annealing temperature for Pt alloys.

Age Hardening: Prior WorkHeat treatment can result in hardening (age

hardening) if precipitation of another phase, orordering, occurs at that temperature. The likeli-hood of one of these phenomena taking place canoften be inferred from phase diagrams.Unfortunately, information on age hardening islimited due to a lack of research and developmenton platinum systems.

Age-hardenable platinum alloys currently in useby jewellers are from the Pt-Au system. A 95Pt-5Au alloy has an annealed Brinell hardness of 92

Platinum Metals Rev., 2005, 49, (1) 3

Fig. 1 The effects of alloying additions on the annealed hardness of various platinum alloys (1, 2)

ALLOYING ELEMENT ADDED TO PLATINUM, %ALLOYING ADDITION, wt.%

VIC

KE

RS

HA

RD

NE

SS

, AN

NE

ALE

D

and an age-hardened hardness of 155, whereas a90Pt-10Au alloy has an annealed Brinell hardnessof 143 and an age-hardened hardness of 222 (10).The alloy with higher hardness will have betterwear resistance.

Vines and Wise (10) investigated the effects ofalloying additions on the age hardenability of plat-inum systems. They found that platinum alloyswith low calcium additions can be age hardened.Small additions of calcium form insoluble lowmelting or brittle compounds with platinum.

Annealed platinum alloys containing 520% Cudisplayed only slight hardening on ageing at 450 to500ºC for 30 minutes (10).

Pt-10% Ir alloys showed a slight increase in ulti-mate tensile strength after cold work andsubsequent heat treatment. This was attributed toordering, and occurred at around 780ºC after peri-ods of long heat treatment. Pt-Ir alloys with1040% Ir could be mildly hardened by heat treat-ment (550ºC or 800ºC) (10).

Pt-Fe alloys containing 1070% Fe (maximumat 30% Fe) showed age hardening on slow cooling(10).

Finally, marked precipitation hardening wasobserved in the Pt-Ag system for 1535% Ag.Relatively high Ag additions (> 5 wt.%) and longageing times are required for hardening (10).

Recent work has focused on hard platinumalloys for ornamental purposes, with alloys con-taining < 95 wt.% Pt. An aged hardness ofbetween 280 HV and 335 HV has been achievedwith 8590 wt.% Pt, 3.55.5 wt.% Fe and balance≥ 5 wt.% Cu (11). Some alloys have been reportedthat can even be hardened by heat treating.Kretchmer holds patents relating to heat-treatablePt-Ga-Pd alloys for jewellery, for example (12, 13).

Experimental WorkThe ideal outcome would be a platinum alloy

where, at high temperatures, the second elementwould be in solid solution with the platinum, butwhich, at low temperatures, would precipitate out(as a second phase). As hallmarking regulationswere taken into account, only alloys containing atleast 95 wt.% Pt were investigated. Alloying ele-ments identified as having hardening potential,

based on published phase diagram information,were selected for testing (14). If one element in aGroup showed promise, all the elements in thatGroup were considered.

A preliminary study was conducted using 2 and4 wt.% alloying additions. Selected alloys, with 3wt.% alloying additions, were also made. Alloyingelements were selected using criteria such as: cost,hazardous effects and availability, as well as phasediagram information and published data. Forexample, in the Pt-rich end of the platinum-titani-um (Pt-Ti) phase diagram, an ordered TiPt8 phasecan form, which could result in hardening. As zir-conium (Zr) and vanadium (V) are close to Ti inthe Periodic Table and have similar phase relations,they were thought likely to have hardening poten-tial.

As very little phase diagram information wasavailable at the start of this study, the phase dia-grams were only used as a guideline. A furtherstudy was then begun on systems that were identi-fied as having potential. Alloying amounts in theorder of 17 wt.% were added.

Alloy buttons were made by arc melting, on awater-cooled copper hearth, melting three times toensure homogeneity. Heat treatments were con-ducted in a vacuum tube furnace and samples weresubsequently quenched in water. Hardnesses weremeasured on a Vickers hardness tester with a 10 kgload.

Any precipitates that form during casting havethe potential to increase the hardness of the as-castalloy. So in order to start with minimum alloy hard-ness, the arc-melted alloys were given a 1000ºCsolutionising heat treatment for 20 minutes toredissolve any precipitates that had formed duringcasting. A temperature of 1000ºC was selected, asthis is the temperature commonly used to annealplatinum alloys after cold working. Subsequentheat treatments were given to induce hardening.

Ideally, phase diagrams should be used to selectheat treatments but in most cases this informationwas unreliable or absent. As jewellers would use ahardening heat treatment process, temperatures inthe region of 4001000ºC were selected for theheat treatments. Higher temperatures were consid-ered to be impractical, and lower temperatures


were expected to result in only slight changesand/or slow kinetics and thus long times for heattreatment. Times of between 30 minutes and 3hours were considered suitable for heat treat-ments.

Results: Preliminary StudyTable I shows results from 98 wt.% Pt alloys.

The alloys were subjected to an anneal at 1000ºCfor 20 minutes, and successive heat treatments at600ºC for 20 minutes, 800ºC for 10 minutes,800ºC for a further 30 minutes, and finally 800ºCfor 10 minutes. Hardness was measured after eachheat treatment. Additions of 2 wt.% of Ti, Mg, Ge,In or Sn produced potential hardening effects,shown in blue in Table I.

A range of 96 wt.% Pt-4 wt.% X alloys was alsoinvestigated, see Table II. These 4 wt.% as-castalloys were annealed at 1000ºC and then heattreated at 800ºC for 10 minutes, 800ºC for 10 min,

800ºC for 10 min, 800ºC for 30 min and then800ºC for 60 minutes. In contrast to the resultsfrom the 98 wt.% alloys, higher quantities of Gaand Zr improved the hardness by ageing (800ºC),but no significant hardening was observed with 4wt.% Ti and Ge. A slight increase in hardnessoccurred for 2 and 4 wt.% Sn.

Some 97 wt.% Pt alloys were also investigated,see Table III. These 3 wt.% as-cast alloys wereannealed at 1000ºC and then heat treated at800ºC for 10 minutes, 800ºC for 10 min, 800ºC for10 min, 800ºC for 10 min and then 800ºC for 60minutes. This indicated that there is hardeningpotential for additions of 3 wt.% of Sn and Zr.

This preliminary study of 2, 3 and 4 wt.% addi-tions suggested that hardening had resulted fromheat treatments. The preliminary study also sug-gested that alloying additions of Ti, Zr, Sn, Ga,Ge, Mg and In to platinum resulted in increases inhardness after heat treatments at 800°C. These


Table I

Hardness (HV10) of 98Pt-2X Alloys (wt.%): Hardening Potential of X after Ongoing Heat Treatments

Sample HV*after HV after HV after HV after HV after(alloyed HT# at 1000ºC HT at 600ºC HT at 800ºC HT at 800ºC HT at 800ºCcomposition, for 20 min for 20 min for 10 min for 30 min for 10 min~ wt.%) and WQ^ and WQ and WQ and WQ and WQ

98Pt-2Ni 102 100 102 102 10298Pt-2Si 376 339 329 31798Pt-2Ti 177 214 232 231 25198Pt-2V 159 157 148 150 14898Pt-2Cr 113 112 111 104 -98Pt-2Mn 102 102 101 104 -98Pt-2Fe 114 102 100 102 -98Pt-2Co 97 94 95 94 -98Pt-2Mg 140 154 147 139 -98Pt-2Cu 86 88 84 86 -98Pt-2Ga 141 124 118 117 11998Pt-2Ge 265 305 233 230 22298Pt-2Zr 223 207 206 208 20998Pt-2Mo 130 129 125 124 -98Pt-2In 118 133 135 135 13598Pt-2Sn 123 131 138 139 13698Pt-2Ta 125 113 112 114 -98Pt-2W 106 101 99 100 -98Pt-2Ag 97 92 83 80 8098Pt-2Au 86 73 71 71 72

*HV: Vickers hardness #HT: heat treatment ^WQ: water quench

alloy systems were therefore selected for a furtherstudy. Although vanadium did not show a harden-ing effect in the preliminary study, it was includedin a further study.

Results: Further StudyPlatinum alloys in the region of 17 wt.% Ti,

Zr, Sn, Ga, Ge, Mg, In and V were then investi-gated further. As-cast hardness and the hardness

after heat treatment at 1000°C for 30 minutes weremeasured. Hardnesses after heat treatment at800°C for 10 min, then that temperature for 10min, 10 min, 30 min and then 60 min were record-ed (15, 16).

Comments are made in subsequent paragraphsabout the observed hardening in this further study,and pertinent observations are reported. Anyphase diagrams (14) that exist are provided.


Table III

Hardness (HV10) of 97Pt-3X (wt.%): Hardening Potential of X after Ongoing Heat Treatments

Sample HV after HV after HV after HV after HV after HV after(alloyed HT at 1000ºC HT at 800ºC HT at 800ºC HT at 800ºC HT at 800ºC HT at 800ºCcomposition, for 20 min for 10 min for 10 min for 10 min for 10 min for 60 min~ wt.%) and WQ and WQ and WQ and WQ and WQ and WQ

97Pt-3Sn 144 147 140 16397Pt-3Ni 138 130 124 12397Pt-3Zr 286 348 363 355 35897Pt-3Cr 142 13497Pt-3Mn 108 10297Pt-3V 194 168 175 167 169 180

Table II

Hardness (HV10) of 96Pt-4X (wt.%): Hardening Potential of X after Ongoing Heat Treatments

Sample HV after HV after HV after HV after HV after HV after(alloyed HT at 1000ºC HT at 800ºC HT at 800ºC HT at 800ºC HT at 800ºC HT at 800ºCcomposition, for 20 min for 10 min for 10 min for 10 min for 30 min for 60 min~ wt.%) and WQ and WQ and WQ and WQ and WQ and WQ

96Pt-4Ni 138 140 139 141 137 13596Pt-4Ti 297 264 28796Pt-4V 205 195 19596Pt-4Cr 155 142 146 108 143 14296Pt-4Mn 137 130 140 133 118 13096Pt-4Fe 141 131 133 131 127 12496Pt-4Co 135 122 123 141 137 12396Pt-4Cu 119 113 112 112 112 11796Pt-4Ga 232 341 33596Pt-4Ge 406 331 32896Pt-4Zr 365 388 378 393 400 42196Pt-4Mo 185 167 167 165 164 16496Pt-4Sn 170 169 179 172 177 17496Pt-4Ta 165 159 157 154 161 15896Pt-4W 149 144 123 138 138 13896Pt-4Ag 84 73 7196Pt-4Au 100 94 87

Platinum-Gallium (Pt-Ga)The addition of 1 to 6 wt.% Ga to Pt generally

resulted in an increase in hardness, from around80 to 225 HV after heat treatment at 1000ºC. Afterheat treatment at 800ºC hardening was observedin the region 3.8 to 6 wt.% Ga, and was particu-larly noticeable for additions of 4.4, 5.2, 6 and 6.1wt.% Ga. The hardness values attained in this laterstudy differ slightly from earlier values (Table II).This may be due to slight variations in composi-tion. The hardening effect could also be verysensitive to changes in chemical composition.Increases in hardness values of ~ 100 HV, afterheat treatment at 800ºC, were observed for addi-tions of ~ 5 wt.%.

The Pt-Ga phase diagram (Figure 2) shows thatalloys containing less than ~ 2.5 wt.% Ga are a Pt-rich solid solution. At 1000ºC a two-phase regionexists for about 3.5 to 10 wt.% Ga alloys and at800ºC a two-phase diagram exists in the region 3to 10 wt.% Ga. During heat treatments at thesetemperatures a second phase may be precipitatingout for samples containing 3.8 to 6.1 wt.% Ga.

Platinum-Germanium (Pt-Ge)The addition of 1 to 5 wt.% Ge to Pt resulted

in alloys with a range of hardness values, from 175HV to 440 HV after heat treatment at 1000ºC. Insome cases the heat treatment caused an increasein hardness of up to 125 HV above the base value.In these cases, subsequent heat treatments at800ºC resulted in either very slight changes(increases or decreases) or a significant decrease inhardness. The highest observed increase in hard-ening was by around 40 HV, and subsequent heattreatments resulted in a decrease in hardness.

The phase diagram (Figure 3) shows that at lessthan 1 wt.% Ge, a Pt-rich solid solution exists.Above 951ºC, in the region of ~ 3 to 12.9 wt.%Ge, a phase field of [L + (Pt)] exists, with a two-phase region of (Pt) and Pt3Ge below 951ºC in theregion ~ 1 to ~ 9.5 wt.% Ge.

A heat treatment of samples containing morethan 2.6 wt.% Ge at 1000ºC should thus result insome melting. Heat treatment at 800ºC of rapidlyquenched samples could induce changes in hard-ness due to the precipitation of a second phase.


Fig. 2 Pt-Ga phase diagram (14); L is the liquid phase


Fig. 4 Pt-In phase diagram (14)

Fig. 3 Pt-Ge phase diagram (14)

The phase diagram has regions of uncertaintyin the high platinum regions, particularly for theboundary of the Pt-rich solid solution.

Therefore this alloy system is not likely to be agood prospect for a commercial jewellery alloy asit is too sensitive to the specific heat treatmentconditions.

Platinum-Indium (Pt-In)The addition of 1 to 7 wt.% In to Pt resulted in

alloys with a range of hardness values from around110 to 180 HV, but up to around 270 HV afterheat treatment at 1000ºC. No significant changesin hardness were observed after the range of heattreatments at 800ºC. One interesting result was anincrease from ~ 200 to 275 HV in the 6.9 wt. %alloy after heat treatment at 1000ºC, but this needsfurther investigation before it can be confirmed.

The Pt-In phase diagram (Figure 4) shows thata Pt-rich solid solution exists up to 6 wt.% In andfor ~ 6 to ~ 15.9 wt.% In a two-phase region (Pt-rich solid solution and Pt3In) exists. At 800ºC and1000ºC the solid solution boundary is still close to6 wt.% In and, if correct, cannot account for the

observed changes in hardness. A possible explana-tion for the observed hardening may be ordering,but further studies would be needed to verify this.

Platinum-Tin (Pt-Sn)The addition of 1 to 6 wt.% Sn to Pt resulted in

a fairly linear increase in hardness with alloyingaddition, from around 110 HV to 215 HV, afterheat treatment at 1000ºC. Hardening was evidentin alloys containing more than 3 wt.% Sn afterheat treatment at 800ºC. Hardening increases ofbetween 20 HV and 40 HV were noted in alloyswith additions of between 3.4 to 5.5 wt.% Sn.

The Pt-Sn phase diagram (Figure 5) suggeststhat a solid solution exists for alloys in the region0 to 5 wt.% Sn. Thus, 3.4 wt.% Sn should be a Pt-rich solid solution. The 6 wt.% Sn alloy is a Pt-richsolid solution at 1000ºC (on the boundary) and atwo-phase mixture at room temperature. The Pt-Sn phase diagram is uncertain in the region 0 to 17wt.% Sn. In the region 0 to 5 wt.% Sn, no conclu-sions were drawn about the cause of hardening.Ordering may explain the observed hardening, butfurther work would be needed to verify this.


Fig. 5 Pt-Sn phase diagram (14)

Platinum-Magnesium (Pt-Mg)A Pt-Mg phase diagram was not available dur-

ing this study. Adding 1 to 5 wt.% Mg to Pt gavePt-Mg alloys with a range of hardness values from

around 100 to over 170 HV after heat treatment at1000ºC. Heat treatment often resulted in softeningby 15 HV to 25 HV. No increase in hardeninggreater than 20 HV was observed on heat treat-ment at 800ºC, so this system was not studiedfurther.

Platinum-Titanium (Pt-Ti)The addition of 1 to 5 wt.% Ti to Pt resulted in

a fairly linear increase in hardness with alloyingaddition: from around 125 HV to almost 430 HV,after heat treatment at 1000ºC. Slight hardening(around 30 HV) was observed for the 5 wt.% alloy,although the 2 wt.% Ti alloy softened by about 30HV, after heat treatment at 1000ºC. Subsequentheat treatments on this alloy at 800ºC led to a sig-nificant hardening of around 90 HV.

The 2 wt.% Ti alloy had a hardness of around170 to 180 HV after heat treatment at 1000ºC, ahardness of 260 HV after heat treatment at 800ºC,and cold worked and heat-treated hardness valuesof around 400 HV to 430 HV (Figure 6). SEM


100

150

200

250

300

350

400

450

0 1 2 3 4 5 6

Weight% Titanium

Har

dnes

s (H

V10)

As cast HT 1000°C, 20 min, WQ HT 20 min,800°C,WQ

HT 30 min,800°C,WQ HT 60 min,800°C,WQ HT 90min,800°C,WQ

Fig. 6 Hardness values of Pt-Ti after different heat treatments (as cast, followed by heat treatments at 1000ºC andthen at 800ºC for varying times)

Fig. 7 A SEM backscattered image of a sample alloy of98 wt.% Pt-2 wt.% Ti. The bar is 80 µm long


Fig. 8 Pt-Ti phase diagram (14)

Fig. 9 Hardness values of Pt-V after different heat treatments (as cast, followed by heat treatments at 1000ºC andthen at 800ºC for varying times)

95

115

135

155

175

195

215

235

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Weight% Vanadium

Har

dnes

s (H

V10)

As Cast HT 1000°C, 20 min, WQ HT 10 min,800°C,WQ

HT 20 min,800°C,WQ HT 30 min,800°C,WQ HT 60 min,800°C,WQ

HT 120 min,800°C,WQ

examinations of the annealed and heat-treatedmicrostructure showed no evidence of secondphases (Figure 7).

The phase diagram for platinum-titanium hasnot yet been finalised in the regions of high plat-inum (Figure 8). It could be that hardening resultsfrom the formation of Pt11Ti, but in this investiga-tion there were no data to support or dispute this.This system has commercial potential and will beexplored in a future paper in this Journal.

Platinum-Vanadium (Pt-V)The addition of 1 to 6 wt.% V to Pt resulted in

alloys showing a fairly linear increase in hardness,from ~ 100 HV to 193 HV, with alloying additions(Figure 9), after heat treatment at 1000ºC.

After heat treatment at 800ºC, hardening wasnot observed in alloys that contained additions ofless than 2.9 wt.% V. Hardening was observed inalloys with additions of 3 to 5.4 wt.% V. At 3 and3.8 wt.% V a significant increase in hardening of 50HV to 100 HV was observed. A slight hardeningeffect was observed with ongoing heat treatments

at 5.4 wt.%. However, the sensitivity is very highand the hardening range is narrow. In practice, thiswould be very hard to control and hence it wouldnot result in a good commercial alloy. Ordered Pt-V phases have been reported elsewhere (17).

The Pt-V phase diagram is inconclusive below800ºC (Figure 10). It suggests that alloys contain-ing up to ~ 6 wt.% V are Pt-rich solid solutions,which cannot explain the hardening. It may be thatthe boundaries of the Pt3V phase are more Pt-richthan are shown in the phase diagram at lower tem-peratures or that there is another phase present.

Platinum-Zirconium (Pt-Zr)The addition of 1 to 5 wt.% Zr to Pt resulted in

a fairly linear increase in hardness, from around140 HV to 410 HV, with alloying additions, afterheat treatment at 1000ºC.

A significant hardening effect resulting afterheat treatment at 800ºC was observed for 3 and 4wt.% Zr additions, while a slight hardening wasobserved in the region of 4 to 4.7 wt.%. Thereported phase diagram (Figure 11) shows that Zr


Fig. 10 Pt-V phase diagram (14)

was in solid solution throughout the temperatureand composition ranges studied. The phase dia-gram cannot explain the observed hardening. Thehardening effect could be of the order of 75 HV,which is very significant. Again, a possible expla-nation for the observed hardening could be due toordering, but further studies would be needed toverify this.

DiscussionIn this study annealed alloys were heat treated

and investigated. The objective was to discoveralloys that were soft enough to be worked by jew-ellers but which could be hardened subsequentlyto improve wear resistance.

Cold work results in hardening, and is deter-mined by the production route. Heat treatment is


Fig. 11 Pt-Zr phase diagram (14)

Table IV

Hardening Effects of Different Alloying Additions to Platinum

Addition Amount, Approximate increase Approximate initial Is the alloy Comments/problemswt.% in hardening, HV hardness, HV viable?

Ga 5–6 100 175–225 No Hallmarking, volatilityGe 1–5 48–132# 165–351 No Too much fluctuationIn 6.9 68# 205 No Too much fluctuationMg 0.1–5 No Nothing significantSn 5.5 40 215 No HallmarkingTi 2 90 170–180 Yes GoodV 3 50–100 160–180 Yes SensitiveZr 3 70 280–300 No Initial ductility

# On heat treating the as-cast alloy at 1000ºC

another hardening route, which can increase hard-ness if mechanisms such as ordering orprecipitation hardening occur. This is very depen-dent on alloy chemistry and the phase relations inthe system. Binary alloys with additions of Ga, Ge,Sn, Ti, V and Zr showed hardening as a conse-quence of heat treatment. Some of the moreimportant hardening effects are summarised inTable IV and Figure 12. It was difficult to predicthardening behaviour from the phase diagramsbecause the phase diagram information was gener-ally inadequate and incomplete, and more platinumphase diagram work needs to be undertaken.

Factors to be considered must include initialductility a most important factor as a jewelleryalloy must be easily worked. While hardness is nota measure of ductility, it often gives an indicationof this property. From experience, hardness valuesof around 300 HV or more were found to giveformability problems.

The sensitivity of the alloy to compositionalvariation and heat treatment parameters must alsobe considered. If sensitivity to composition is toohigh then the hardening is not reproducible orrepeatable as, realistically, the composition willvary. For heat treatment, a bench jeweller may onlyuse a gas torch (compared to the laser weldingequipment a manufacturer might have (18)) andthis does not allow for accurate temperature con-trol or controlled environments.

The final factor is the hallmarking regulations,and alloying additions of less than 5 wt.% are

preferable to satisfy the requirementsfor popular hallmark 950. The plat-inum-titanium alloy was considered to

be the most viable alloy system and was selected asa candidate for commercialisation.

Properties important for jewellery manufacture:workability, colour, tarnish resistance, wear resis-tance, castability and machinability, were allinvestigated (1923). If alloys are cold workedprior to heat treatment, an even higher finalVickers hardness can be obtained. This wasobserved in the Pt-Ti system, and will be reportedon later in this Journal. The effects of ternary addi-tions on hardening were also studied, and will alsobe reported later.

ConclusionsThis study suggests that the Pt-Ti system is the

most viable one for commercialisation. The 2 wt.%titanium-platinum alloy has as cast and annealedVickers hardness values that are low enough toallow the alloy to be easily formed or worked.Subsequent heat treatment can increase the hard-ness of the alloy by around 90 HV, to give highhardness and improved wear resistance to the fin-ished material. This alloy is considered to havepotential in jewellery fabrication.

References1 Johnson Matthey, An Introduction to Platinum a

manual for jewellers introducing them to platinumjewellery design and manufacturing processes; avail-able on CD-ROM, from [email protected]

2 S. H. Avner, Introduction to Physical Metallurgy,2nd Edn., McGraw-Hill, New York, 1974

3 Y. Yuichiro, Hard platinum alloy for ornamenta-tion, Japanese Patent Appl. 62-130,238; 1987


Fig. 12 The absolute initial and finalhardnesses for a range of platinum alloysmost improved by heat treatment

HA

RD

NE

SS

(HV

10)

ALLOYING ELEMENT ADDED TO PLATINUM

4 Y. Yuichiro and S. Yasusuke, Ornamental hard plat-inum alloy, Japanese Appl. 63-145,730; 1988

5 M. Naohiko, Platinum alloy, British Patent2,279,967; 1995

6 Y. Muragishi, Y. Hagiwara, T. Hamada, Y. Ikematsuand C. Funaki, Precious metal material, U.S. Patent5,518,691; 1996

7 I. R. McGill and K. A. Lucas, Scratch-resistant plat-inum article, U.S. Patent 4,828,933; 1987

8 W. Weber, K. Zimmermann and H-H. Beyer,Surface-hardened objects of platinum and palladi-um and their method of production, U.S. Patent5,518,556; 1996

9 W. Weber, K. Zimmermann and H.-H. Beyer,Objects made of platinum and palladium comprisehard scratch-resistant surface layer contg. boron inthe metal lattice, German Patent 4,313,272; 1994

10 R. F. Vines and E. M. Wise, The Platinum Metalsand their Alloys, The International NickelCompany, Inc., New York, NY, U.S.A., 1941

11 S. Yasusuke and Y. Yuichiro, Ornamental hard plat-inum alloy, Japanese Appl. 61-106,736; 1986

12 S. Kretchmer, Heat treatment of platinum-galliumalloy for jewelry, U.S. Patent 5,846,352; 1998

13 S. Kretchmer, Heat-treatable platinum-gallium-pal-ladium alloy for jewelry, U.S. Patent 6,562,158; 2003

14 Binary Alloy Phase Diagrams, 2nd Edn., eds. T. B.Massalski, H. Okamoto, P. R. Subramanian and L.Kacprzak, Am. Soc. Metals, Ohio, U.S.A., 1990

15 T. Biggs, unpublished results16 T. Biggs and S. S. Taylor, Platinum Alloy, South

African Patent 97/3687; 199717 D. Shryvers and S. Amelinckx, Res. Mechanica, 1987,

22, 10118 J. C. Wright, Platinum Metals Rev., 2002, 46, (2), 6619 T. Biggs, S. S. Taylor, K. L. Rutherford and I.

Hutchings, The wear behaviour of some platinumalloys, 21st Annual Conf. on Precious Metals1997,IPMI, San Francisco, California, U.S.A., June 1997,pp. 331345

20 T. Biggs, S. S. Taylor, D. Freund and B. Fischer, Aninvestigation into the mechanical properties of the98Pt-2 Ti alloy, 25th Annual Conf. on PreciousMetals2001, Session C, 10 June, 2001, IPMI,Tucson, Arizona, U.S.A., proceedings on CD-ROM

21 T. Biggs and N. Nkumbuzi, Tarnish behaviour inplatinum jewellery alloys, Proc. 8th Int. PlatinumSymp., South African Institute of Mining andMetallurgy, Johannesburg, 1998, pp. 3536

22 N. Adams, S. S. Taylor and T. Biggs, The machin-ability of some platinum alloys, Proc. Microsc. Soc.South. Afr., 1999, 29, p. 20

23 S. S. Taylor and T. Biggs, Innovations in platinumjewellery materials, S. Afr. J. Sci., 1999, 95, (11/12),543


Stefanie Taylor works in thePhysical MetallurgyDivision at Mintek, SouthAfrica. Her researchinterests include platinumalloys, particularly jewelleryalloys, and also gold alloysfor jewellery and industrialuse. She has worked withprocesses ranging fromcasting to powdermetallurgy and is currentlylooking at new processesand products for the SouthAfrican jewellery industry.

The AuthorsDr Taryn Biggs is formerlyof Mintek, South Africa,where she was involved innumerous researchprojects in the platinumfield. These ranged frominvestigating anddeveloping jewellery alloysto failure analyses ofplatinum jewellery. Shealso worked on projects todevelop industrial platinumalloys. She currently worksat Dofasco, Canada, as aproject manager in productdevelopment.

Dr Elma van der Lingenheads the Precious MetalsGroup in the PhysicalMetallurgy Division atMintek. She is involved inresearch on preciousmetals (platinum,ruthenium, iridium andgold) for jewellery,catalysis, nanotechnology,corrosion, fuel cellelectrode development andbiomedicine.

Scientific Advances in Fuel Cell Systems (1)was the theme of the second in a series of biannu-al European meetings on fuel cells, that are held inalternate years to the Grove Symposia (2). Theconference reported here was held on the 6th and7th October 2004 at the Hilton Munich ParkHotel, Munich, following the first meeting inAmsterdam in 2002 (3). Organised by Elsevier,these conferences provide a balance between thescientific and the more commercial aspects of thetechnology. Authors from around the world hadsubmitted oral papers and posters for this techni-cally-orientated programme. The meeting attracted320 delegates from 39 countries includingGermany [76], Japan [47], the U.K. [35], Italy [22]and the U.S.A. [13]. These represented universities,research organisations, and fuel cell componentand system manufacturers.

Besides almost 60 oral papers, there were 170high quality poster presentations, and many ofthese will be published in a special edition of theJournal of Power Sources in May 2005. The sympo-sium consisted of eight sessions, on membranescience, fuel processing, materials science, electro-chemistry and catalysis, cell and stack technology,and systems and applications. For this review, onlywork that involves the platinum group metals(pgms) is being reported.

Performance Targets for TransportThe conference began with a Plenary Session

and a keynote talk. In this, Frank Preli of UTCFuel Cells, U.S.A., outlined some of the perfor-mance targets for transport applications, comparedto what is currently achievable with fuel cells.These can be summarised by five interrelated char-acteristics: power density, operability (includingfactors such as cold starting and the range ofacceptable ambient conditions), efficiency, durabil-ity and cost. Small passenger vehicles are likely to

need a power output of around 85 kW, while buseswill need 100200 kW. To compete successfullywith the internal combustion engine, stack powerdensity will need to be over 1.6 kW litre1, while thecomplete system will need to provide more than0.5 kW litre1 to minimise intrusion into the pas-senger space. High overall thermal efficiencyimplies a cell voltage in excess of 0.750 volts, witha decay rate of less than 2 mV per 1000 hours foradequate lifetimes. Performance will need to bemaintained over 17,000 start-stop cycles despiteadverse operating conditions, such as less than60% relative humidity at the air inlet. In addition,stacks will need to have the ability to start upquickly from the frozen state for up to 1000 timeswithout damage.

PEMFCs to Achieve these GoalsProton exchange membrane fuel cells

(PEMFCs) operating at relatively low temperaturesand catalysed by pgm catalysts offer the bestchance of achieving these goals. The cost objectivefor wide-scale applications in transport is set at $35kW1. Currently, the cell stack plates and mem-brane electrode assemblies (MEAs) account for50% of the cost of the whole system, and variousmeans to reduce this proportion are being consid-ered. These include using injection mouldingtechniques for the inter-cell plates. For high stackpower density, the internal resistance of individualcells needs to be reduced, to provide power densi-ties upwards of 0.7 volts per cell at 0.6 A cm2.Water management within the membrane has beenidentified as one of the principal limiting factors tocell performance.

For comparison, the stationary 200 kW PC25phosphoric acid fuel cell system made by UTCcosts $4,300 kW1. Several hundred of these highlydeveloped units have accumulated over 6 millionoperating hours. Laboratory trials indicate that


Fuel Cells Science and Technology 2004SCIENTIFIC ADVANCES IN FUEL CELL SYSTEMS REPORTED IN MUNICH

Reviewed by Donald S. CameronThe Interact Consultancy, 11 Tredegar Road, Reading RG4 8QE, U.K.; E-mail: [email protected]

DOI: 10.1595/147106705X24355

marginally reducing the operating temperature ofthe fuel cell stack has a marked effect in reducingsintering of the platinum catalyst, enabling stacklifetimes to be doubled to over 80,000 hours or 10years. In the past few years the life of PEMFCs hasalso been extended from a few hundreds of hoursto over 10,000 hours and laboratory tests indicatethat these can be extended to over 20,000 hours.

Progress in PEM TechnologyIn a later keynote talk, Charles Stone, of Ballard

Power Systems, Canada, also discussed the techni-cal challenges and progress made in PEMtechnology. The performance and durability ofPEMFCs are already established, and productsbeing evaluated by the public include 30 buses inthe Clean Urban Transport for Europe (CUTE)programme, with 9 more in California, Australiaand China. Hydrogen has evolved as the fuel ofchoice, and a supply infrastructure is being devel-oped in several parts of the world. Power densitiesover 2.2 kW litre1 are achievable for stacks oper-ating at 0.6 volts per cell. However, componentcosts need to be reduced, while technology needsto be developed for the rapid start of frozen cellstacks, for water management and for resistance toimpurities in the reactant gas. In particular, aircathodes that can operate at over 1 A cm2 need tobe developed.

In the longer term, modelling and measure-ment tools should enable more rapid progress inoptimising systems. Membranes with increaseddurability have been developed; these have resis-tance to peroxy radical attack and reduced weightloss with time. Degradation of the anode catalystcarbon support has been greatly reduced, thanksto a programme jointly carried out by Ballard andJohnson Matthey, and new catalysts have demon-strated up to 500-fold greater stability.

For cathode catalysts, graphitised Vulcan car-bon supports provide greatly improved stabilityand durability. Considerable progress has beenmade in reducing the pgm content of PEMFCs.Platinum loadings have been reduced to around1.0 mg cm2 for electrodes made using screenprinting, compared to loadings of 810 mg cm2 Ptthat were common ten years ago. These are pro-

jected to fall further to 0.30.5 mg cm2 using rollcoating techniques, and ultimately to 0.1 mg cm2

with chemical vapour deposition methods.Improved current collector plates and MEAs withnew gas diffusion layers have helped to improvewater management and hence performance.

Stone emphasised the need to carry forwardimprovements to all the interrelated aspects of thetechnology. Several of the subsequent papers high-lighted the efforts being devoted to understandingand developing models of various aspects ofPEMFC operation including water management,low temperature start-up, and the quest forimproved catalyst and membrane materials.

Membrane ScienceDirect oxidation of methanol in fuel cells has

made considerable advances in recent years to thepoint where several are on the verge of being man-ufactured commercially. In a talk entitled 0.5W/cm2 PCM-based methanol-air fuel cell recentprogress at Tel Aviv University, A. Aharon pro-vided details of a novel and inexpensive ($4 m2)nanoporous proton conducting membrane, con-sisting of a non-conducting ceramic powder mixedwith a polymer binder and an acid. This isextremely permeable to water penetration duringcell operation.

One of the problems of direct methanol fuelcells (DMFCs) is the undesirable migration of sol-vated water through the membrane, associatedwith protons, with up to 18 molecules of watertransferred for each molecule of methanol oxi-dised. This has been identified as a major reasonfor cathode flooding and performance loss at highcurrent densities. The high porosity of the TelAviv University membrane enables surplus waterto permeate back through the membrane to theanode compartment. Substituting trifluoro-methane sulfonic (triflic) acid for sulfuric acidyields performances of 0.5 volts at 0.8 A cm2 witha platinum loading of 4 mg cm2. These perfor-mances have been demonstrated on small scalecells which are being increased in size to 50 cm2

bipolar cells, and a 12 W cell is being built whichwill occupy 900 cm3.

Water transfer across the membrane is also


accompanied by loss of methanol into the cathodecompartment by migration. Another approach tothe problem of methanol and water diffusion inDMFCs was presented by L. Pitol-Filho, of theUniversitat Rovira I Virgili, Spain. Compositemembranes were made from mixtures of polysul-fone (PSf) and poly(ethylene glycol) (PEG) andused to study the rates of transfer of reactants.PEG contains OH hydrophilic groups whichcombine with hydrated protons, and experimentaldata confirmed that higher PEG concentrationsassisted proton transport, with a plateau of about50% PEG. At this ratio, the ratio of H+ : methanolwas about 8.8 : 1 compared to 4.0 : 1 for mem-branes containing 20% PEG.

Fuel ProcessingA paper by Q. Li of the Technical University of

Denmark, Integration of high temperaturePEMFC with a methanol reformer emphasisedthe need for high PEMFC stack operating temper-atures to facilitate integrating the reformer into asystem. Newly-developed thermally stable polymermembranes such as acid-doped polybenzimidazolemembranes allow PEMFCs to operate at up to200ºC. Using platinum/ruthenium alloy anode cat-alysts, raising the operating temperature from 80 to200ºC increases the tolerance to carbon monoxidein the fuel gas from 100 ppm to over 30,000 ppm(that is, 3%). The CO impurity content in thehydrogen from a methanol reformer is typicallyless than 1% by volume, and hence reformate canbe directly used to fuel the PEMFC. So far, small(10 cm × 10 cm) fuel cell stacks working at 170ºCcombined with methanol reformers operating at210ºC have demonstrated performances of up to50 A at 750 mV per cell.

Electrochemistry and CatalysisWork by the Energy Research Centre of the

Netherlands ECN, has confirmed that carbondioxide, which is present in reformate fuel in con-centrations of up to 25%, can have a detrimentaleffect on fuel cell performance that goes beyondthe dilution effects associated with an inert gas. Inhis talk Carbon dioxide poisoning on proton-exchange-membrane fuel cell anodes, G. J. M.

Janssen explained that these poisoning effects arisefrom the reverse of the water gas shift reaction:CO2 is reduced by hydrogen to a reduced form(most likely carbon monoxide) which is adsorbedpreferentially on the catalyst. Carbon monoxide isa well-known poison for pure platinum catalysts atlow temperatures, the catalyst becoming inactivefor hydrogen dissociation. From kinetic data, it isevident that some bimetallic catalysts also catalysethe oxidation of the adsorbed species to CO2.Hence catalyst poisoning can be mitigated by usingbimetallic alloy catalysts such as supported Pt/Ru,which has a high CO electrooxidation rate con-stant.

In a talk entitled Novel high performance plat-inum and alloy catalysts for PEMFC & DMFC, Y.Tsou of the E-TEK Division of De Nora NorthAmerica Inc., reviewed the status of their products,including catalysts, gas diffusion electrodes, andmembrane electrode assemblies (MEAs). In adeparture from their traditional platinum sulfiteroute for catalyst preparation, E-TEK have devel-oped new platinum chemistry to provide materialswith a more homogeneous particle size and highersurface area. This enables increased metal loadingson carbon to be achieved while maintaining highmetal surface areas. Using thermal treatments, truebimetallic alloy catalysts such as Pt/Ru can be pro-duced with up to 50% metal loading on carbon.When used in PEMFCs, these exhibit resistance toCO poisoning. Alloy catalysts with a ratio of 80%Pt to 20% Ru have been found to provide opti-mum performance for DMFCs, while othercarbon-supported alloy catalysts such as Pt/Mo,Pt/W and Pt/Sn can be prepared.

In his talk Ultra-low Pt loading anode forDMFC application, A. S. Aricò of CNR-ITAEInstitute, Italy, described work undertaken toreduce the pgm requirements for DMFCs. Apreparation procedure allowing the surface decora-tion of unsupported Ru catalysts by Ptnanoparticles has been developed. These havebeen examined by electrochemical strippingvoltammetry to compare their electrocatalyticactivity to state-of-the-art carbon supported Pt-Ru(1 : 1) alloys and bare unsupported Ru catalysts.Suitable performances have been achieved with


ultra-low Pt loadings on DMFC anodes at temper-atures of 80130ºC. Reducing the anode Ptloading by a factor of twenty produces a loss ofpower density of about 35%. Catalysts containingsmall amounts of Pt nanoparticles on the surfaceof a less expensive metal, such as Ru, may prove auseful route to reducing catalyst costs for DMFCdevices.

However, Aricò emphasised that improve-ments to catalytic activity are dwarfed by theeffects of temperature in increasing the reactionrate. With an anode loading of 0.1 mg cm2 of plat-inum, and 1 molar aqueous methanol solution,raising the operating pressure and the temperatureto 130ºC could increase the current density fromless than 0.6 A cm2 to almost 4.0 A cm2 at 0.4volts per cell.

Stack and Cell Technology In view of the current activity in commercialis-

ing micro fuel cells for electronic and consumerapplications, a paper entitled Miniaturised protonexchange fuel cell in micromachined silicon sur-face by G. DArrigo of CNR-IMM, Italy, was ofparticular interest. In this work, PEMFCs werefabricated using technology developed for ultra-large scale integrated (ULSI) microchips. The fuelcells consist of two symmetrical structures fabri-cated on 2.2 cm × 1.9 cm porous silicon wafers.Miniature rhomboidal microchannels, severalmicrons below the surface, are formed by surfacemicromachining and etching processes. Therhomboidal trenches thus formed are closed upand formed into microchannels by depositing asurface layer of silicon using chemical vapourdeposition. These microchannels distribute fueland oxidant across each electrode. A patternedgold layer is used to define permeable porous sec-tor areas and to collect the current.

Metallic clusters of Pt or Ru catalysts aredeposited inside the porous silicon skeleton byelectrodeposition, while the proton exchangemembrane is deposited on the patterned porousmembrane by a spinning process. The structuresrepresent a novel method of miniature cell con-struction and possibly a new application for theelectronics industry.

Poster ExhibitionThe large number of posters concerned with

pgm catalysts reflects the intense interest in directmethanol and direct ethanol fuel cells, and CO-tol-erant catalysts for PEMFCs. A wide variety ofcatalysts are being investigated, including alloys ofplatinum with ruthenium, rare-earths, seleniumand tin. These are supported on materials rangingfrom titanium mesh to carbon nanotubes, meso-porous carbon and acetylene carbon black.

In their poster Towards shape selectivePEMFC/DMFC catalysts: Dependence of COoxidation on Pt nanoparticle shape, S. Kinge et al.(Max-Planck-Institut für Kohlenforschung,Germany) describe how a seeding method hasbeen developed to produce shape-specificnanocrystallites. This was used to deposit 4 nmtruncated octahedral platinum nanoparticles onVulcan XC72 carbon (20 wt.% Pt). Examinationof these catalysts by cyclic voltammetry in a rotat-ing disc electrode method shows two peakscorresponding to two different sites of CO oxida-tion, with peaks assigned to the 111 (0.72 VNHE) and 100 (0.83 V) crystallographic planesof the platinum particles.

A poster entitled A new direct methanol fuelcell by a membrane electrode assembly zigzagfolded down is self explanatory. This novel designfor a micro DMFC is proposed by M. Shibasaki etal. of Tokyo University of Science. A membrane isfolded into a 3-dimensional zigzag shape with elec-trodes inserted into the folds. Methanol is fedfrom one side of the assembly, and air diffusesinto the cathode side via a porous insulator layer.Overlapping cathode supports provide inter-cellconnectors to enable multiples of cells to be con-nected in series. A cell with an active area of 16cm2 × 2 has demonstrated 3 mW cm2 power den-sity, operating on 2 M methanol and at ambienttemperature.

Poster Prize AwardsOf the 170 posters presented at the conference,

twelve were highly commended and, after a shortpresentation to the final selection panel, four ofthese were chosen to receive a prize. In the LowTemperature Fuel Cell category, W. Y. Lee et al.


(Korea Institute of Energy Research, Korea,(ROK)) received a prize for the poster Effect ofmicro-layers in gas diffusion layer on the perfor-mance of PEMFCs.

In the Systems and Applications category, M.Oszcipok (Fraunhofer Institute for Solar EnergySystems, Germany) was awarded a prize for theposter Statistic analysis of operational influenceson the cold start behaviour of PEM fuel cells.

In the High Temperature Fuel Cells category,K. Sugiura (Osaka Prefectural College ofTechnology, Japan) gained a prize for the posterEvaluation of volatile behaviour and the volatiliza-tion volume of molten salt in DIR-MCFC by usingthe image measurement technique.

Finally, in the Fuel Processing and Storage cat-egory, G. O. Alptekin (TDA Research Inc., U.S.A.)was awarded a prize for the poster Selective sor-bents for natural gas desulfurization.

ConclusionsThe increased attendance at the conference

compared to the one held in 2002, particularly bythe academic community and research studentsindicates a higher level of interest in the technicalaspects of fuel cells. The tremendous variety ofpapers and posters provides ample evidence thatnew ideas and innovative designs continue toadvance fuel cell technology, and are rapidly over-coming the remaining barriers to producingcommercial devices. Perhaps most significantly,development of modelling and other experimentaltechniques will make it possible to study the com-plex interrelated characteristics of cells, stacks andsystems to enable even more rapid strides to bemade in future.

References1 http://www.fuelcelladvances.com/oral.htm2 http://www.grovefuelcell.com/; D. S. Cameron,

Platinum Metals Rev., 2004, 48, (1), 32 (8th); D. S.Cameron, Platinum Metals Rev., 2001, 45, (4), 146(7th); D. S. Cameron, Platinum Metals Rev., 1999, 43,(4), 149 (6th); D. S. Cameron, Platinum Metals Rev.,1997, 41, (4), 171 (5th); G. A. Hards, Platinum MetalsRev., 1995, 39, (4), 160 (4th); D. G. Lovering,Platinum Metals Rev., 1993, 37, (4), 197 (3rd); D. G.Lovering, Platinum Metals Rev., 1991, 35, (4), 209(2nd); D. G. Lovering, Platinum Metals Rev., 1989, 33,(4), 169 (1st)

3 D. S. Cameron, Platinum Metals Rev., 2003, 47, (1), 28

The ReviewerDon Cameron is an Independent Consultant on the technology offuel cells and electrolysers. He is a member of several WorkingGroups of the International Electrotechnical Commission, TechnicalCommittee 105 on fuel cell standards, and is Secretary of theGrove Symposium Steering Committee.



The advantage of using platinum (Pt) in indus-trial applications is due to its unique properties,such as its catalytic activity, high melting point (1),ductility (2, 3) and chemical inertness over a widerange of temperatures (4, 5). Platinum has beenused for biomedical components, specialty chemi-cals, fuel cells and for pollution control catalysts,such as in automobile exhausts, as well as for jew-ellery, thermocouples and the cathodic protectionof ships hulls (3).

One typical application of platinum is in elec-tronics devices, with thick film conductors beingamong the major products (6). Alloying elements,selected from the platinum group metals and noblemetals, are usually employed to help develop high-er strength or to protect a surface againstdeleterious service conditions (3). However, theaddition of an alloying element may degrade theconductivity. Until now, the data available on theconduction properties of platinum alloys havebeen limited (712).

This present investigation will survey the para-

meters of thermal conductivity in various platinumalloys at high temperatures. First, the compositiondependence of thermal conductivity will be inves-tigated and the results will be ordered according tothe Periodic Table; second, the effect of workhardening will be investigated; and third, the tem-perature dependence of thermal conductivity willbe surveyed.

Dependence of ThermalConductivity on Composition

The thermal conductivities at 300 K for Ptalloys as a function of solute concentration, isshown in Figure 1, together with data for pure Pt(1, 13, 14). Vanadium (V) and nickel (Ni) wereselected as solutes. Nickel belongs to the same col-umn as Pt in the Periodic Table (Pt-Ni is anisoelectronic system) while V is positioned hori-zontally far distant from Pt (Pt-V is anon-isoelectronic system). All the alloys used inthis investigation have a face centred cubic (f.c.c.)single phase; whereas in the Pt-V system, the

DOI: 10.1595/147106705X24364

Thermal Conductivities of Platinum Alloysat High TemperaturesOBSERVATIONS COMPLIANT WITH THE WIEDEMANN-FRANZ RELATION

By Yoshihiro TeradaDepartment of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan;

E-mail: [email protected]

and Kenji Ohkubo and Tetsuo MohriDivision of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan

The thermal conductivity of platinum alloys with a f.c.c. single phase was comprehensivelysurveyed by the laser flash method. Thermal conductivity is predominantly determined byalloy composition and temperature and is little affected by work hardening. An addition ofsolute clearly decreases the thermal conductivity of Pt, and the conductivity-compositionrelationship is characterised by a sharp maximum at pure Pt. The Wiedemann-Franz relationshipthat holds for Pt alloys suggests that the electron is the dominant carrier of thermal conduction.An empirical rule is proposed that the thermal conductivity of a Pt alloy decreases significantlyas the position in the Periodic Table of the solute element becomes horizontally more distantfrom Pt (for the B-subgroup). The thermal conductivity of Pt alloys increases with increasingtemperature in the range 300 to 1100 K. The temperature coefficient of thermal conductivitywas found to be inversely correlated with the thermal conductivity.

order-disorder transformation occurs at a stoi-chiometry of 3 :1. The data for Pt3V with a f.c.c.disordered structure and a D022 ordered structureare from earlier work (15). Note that the heat treat-ment at 1573 K for 1 hour was undertaken toachieve the disordered state in Pt3V, while ageingat 1020 K for 168 hours was employed for theordering reaction.

The thermal conductivity of pure Pt found inthe present experiment was 77.8 W m1 K1, whichis slightly higher than values in the literature (1, 13,14). It decreased monotonically with increasingsolute concentration for both alloys. In the com-position ranges used, the conductivity-compositionplots are characterised by a sharp maximum atpure Pt in each case. The composition dependenceis more pronounced in the Pt-V alloy, with theaddition of only two atomic percent V reducingthe thermal conductivity of Pt by one half. Therate of reduction in thermal conductivity becomessmaller at higher V concentrations, typically aboveten atomic percent.

Figure 1 shows that the thermal conductivityincreases on formation of the D022 ordered phase

at composition Pt3V. This increase in conductivityby ordering seems to be a general feature which isalso demonstrated by Pt3Cr with the L12 structure,and in Ni3V(D022), Ni3Mn(L12) and Ni3Fe(L12)(15). Thermal conductivity is usually degraded bythe scattering of carriers in the crystal lattice.Topological and configurational disorder, such asimpurities, vacancies and lattice defects, impedethe flow of heat carriers. Hence, well-orderedintermetallic compounds should have higher con-ductivity than their disordered alloys, assumingthat the carrier concentrations do not change inboth phases (16).

The essential question then to be answered iswhat is responsible for thermal conduction in Ptalloys. The thermal conductivity of metallic mate-rials is generally composed of an electroniccomponent and a phonon component. TheWiedemann-Franz relation is a criterion for identi-fying the carrier of thermal conduction. TheWiedemann-Franz law states that at high tempera-tures the ratio of thermal to electrical conductivity(the reciprocal of the resistivity) for all metals isproportional to absolute temperature. When theelectronic component is the dominant contributorto the total thermal conductivity, λ, theWiedemann-Franz relation should hold (1719), asin Equation (i):

λ = L T σ (i)

where L is the Lorentz number, T is the absolutetemperature and σ is the electrical conductivity. Auniversality constant of λ/σ was found to be equalto 7.5 × 106 Ω K1 at 300 K for pure metals (17).

The Wiedemann-Franz relation was examinedfor the Pt alloys under investigation here. Figure 2shows the electrical conductivity (the inverse ofelectrical resistivity) plotted against the thermalconductivity for Pt-Ni and Pt-V alloys. Thestraight line indicates the Wiedemann-Franz rela-tion given by Equation (i) at 300 K. All the plotsfor the Pt alloys, including pure Pt, fall close to theline. This indicates that Pt alloys satisfy theWiedemann-Franz relation at 300 K, even highlyconcentrated alloys.

The dominant carrier of thermal conduction inPt alloys is, therefore, ascribed to an electron


Fig. 1 Composition dependence of thermal conductivityat 300 K in Pt-Ni and Pt-V alloys. Data for pure Pt arerepresented by the solid square on the axis (1, 13, 14).The recommended values for pure Pt in these datasources are similar. The solid triangle is data for Pt3Vwith the D022 ordered structure (15)

SOLUTE CONCENTRATION, X, at.%

THE

RM

AL

CO

ND

UC

TIV

ITY,

λ, W

m-1

K-1

Pt solid solution

Pt3V(D022)

rather than to a phonon: more specifically, the 6selectrons are considered to be responsible for thethermal conduction.

Dependence on the ConstituentsFigure 1, the dependence of thermal conduc-

tivity on composition in Pt alloys, shows that thereis a drastic decrease in thermal conductivity at lowconcentrations of solute, up to 2 atomic percent,from the value for pure Pt. It is well known that Pthas a wide solid solubility range for most alloyingelements (20). In this section, we focus on thethermal conductivities of various Pt-2 at.% Xalloys to identify the effect of solute, X, on thethermal conductivity of Pt.

Figure 3 summarises the thermal conductivitiesof Pt-2 at.% X alloys at 300 K. Solute X isarranged in Periodic Table order. It can be clearlyobserved that the addition of a solute elementdecreases the thermal conductivity of Pt. Whensolute X belongs to B-subgroup (Cu, Ga, Ge) inthe first long period, the thermal conductivitydecreases monotonically as the horizontal distanceof X from the solvent Pt increases. This trend alsoholds for the solute X in the second long period.It is worth noting that Al and Si, which are locat-ed above Ga and Ge, respectively, also fall on thesame line.

This trend was reported for electricalresistivity and is known as the Norburyrule (21). Norbury studied the change inelectrical resistivity by the addition ofsolutes to Fe, Ni, Cu, Ag, Au and Mgand the molten states of Na and K. An


Fig. 2 Wiedemann-Franz relation for Pt-Ni and Pt-Valloys at 300 K. Alloy compositions are in atomic percent

Fig. 3 The thermal conductivity at 300 K ofPt-2 at.% X alloys as a function of theatomic number of solute X.The solid black square shows the thermalconductivity for pure Pt.Data for Pt-2 at.% Al and Pt-2 at.% Si arethe solid diamond-shaped symbols.As, Pb and Bi are not soluble in Pt (20).There are no data for Tc because the alloyis unstable.There are no data for Zn, Cd, Hg and Tl astheir lower boiling temperatures prevent thealloy ingots being prepared by arc melting

Pt solid solution

Wiedemann-Franz relation

THERMAL CONDUCTIVITY, λ, W m-1 K-1

ELE

CTR

ICA

L C

ON

DU

CTI

VIT

Y, σ

,106

Ω-1

m-1

pure Pt

2Ni

5Ni

2V10Ni

16Ni25Ni

10V

THE

RM

AL

CO

ND

UC

TIV

ITY,

λ, W

m-1

K-1

Pt-2 at.% X

5V

: Pt-Ni alloy: Pt-V alloy

25V

ELEMENT, X

: 1st long period: 2nd long period: 3rd long period

empirical rule was found that the electrical resistiv-ity of binary alloys increases as the position in thePeriodic Table of the solute element becomes hor-izontally distant from that of the host component.The current results imply that the Norbury rulegenerally holds for transport phenomena driven by

electrons. Unlike the case of B-subgroup elements,however, the behaviour is more complicated whenthe solute belongs to the remaining transition ele-ments. For the first long period, the thermalconductivity decreases monotonically as the dis-tance of X from Pt increases. This breaks down atMn. The breakdown occurs at elements distantfrom Pt when solute X belongs to the third longperiod. It is notable that Re most significantlydecreases the thermal conductivity of Pt. Alsonoteworthy is the fact that the thermal conductivi-ties are quite similar to one another for solutesbelonging to the same column, typically demon-strated in the columns IVA, VA and VIII (Fe, Ru,Os). The data in Figure 3 also suggest that the ther-mal conductivity is more dependent on the columnof solute X and is less dependent on the period.

Dependence on Work HardeningIn order to study the sensitivity to fabrication

conditions, thermal conductivity was investigatedas a function of reduction by cold rolling for somePt alloys. Figure 4 shows results for pure Pt and forthree Pt alloys. A slight decrease in thermal con-ductivity was observed in pure Pt, typically atabove 30% of reduction by cold rolling, while afairly constant value is maintained for high con-centrated alloys with lower conductivities. Theresults imply that the thermal conductivity of thesealloys is chiefly determined by the initial composi-tion and hardly by the defect structure developedduring fabrication.

Temperature DependenceThermal conductivities in Pt-Ni alloys as a

function of temperature are shown in Figure 5together with values for pure Pt from data sourcesrepresented by the broken line (13, 14). The ther-mal conductivity of pure Pt, measured in thepresent study, increases monotonically withincreasing temperature and reaches approximately95 W m1 K1 at 1100 K. The monotonic increaseis also confirmed for the reference data, thoughthe magnitude is systematically lower. Adding Nidoes not alter the general trend of monotonicincrease and only results in shifting the entire datato lower values. Furthermore, close observation


Fig. 4 Thermal conductivity of pure Pt and Pt alloys asa function of reduction by cold rolling. The values of thethermal conductivities were measured at 300 K

Fig. 5 Thermal conductivity versus temperature for thePt-Ni alloys. Data for pure Pt recommended in the datasources are shown by the dotted line (13, 14). The valuesfrom the data sources are similar

THE

RM

AL

CO

ND

UC

TIV

ITY,

λ, W

m-1

K-1

REDUCTION BY COLD ROLLING, %

THE

RM

AL

CO

ND

UC

TIV

ITY,

λ, W

m-1

K-1

TEMPERATURE, K

Pt solid solution

Pt solid solution

pure Pt

Pt-2 at.% Ir

Pt-16 at.% Ni

Pt-10 at.% V

pure Pt

Pt-2 at.% Ni

Pt-5 at.% Ni

Pt-10 at.% Ni

Pt-16 at.% Ni

reveals that the temperature coeffi-cient becomes larger with increasingnickel concentration and all the dataseem to converge at higher tempera-tures.

The temperature coefficient, α, inthe temperature range between 300 to 1100 K wasinitially estimated from Equation (ii):

α = (1/λ300 K)(dλ/dT)= (1/λ300 K)(λ1100 K λ300 K)/(1100 300) (ii)

where λ300 K and λ1100 K are the thermal conductivi-ties at the indicated temperatures. In Figure 6, thetemperature coefficients obtained for the Pt alloysare plotted against thermal conductivity at 300 K.

The pure Pt had a thermal conductivity of 77.8W m1 K1 at 300 K with a positive temperaturecoefficient of 2.9 × 104 K1. The thermal conduc-tivity monotonically decreases with increasing Niconcentration, accompanied by the increase in thecoefficient. Such an inverse correlation is moreclearly seen in the semi-log plot, see Figure 6.Interestingly, most Pt-V alloys have the same cor-relation except for Pt-16V alloy. Moreover,various selected elements from the second longperiod shown by open squares also keep the samecorrelation, which implies the correlation mayhave a universal feature. The inverse correlationbetween α and λ300 K may be a general feature formetallic materials, and has been well documented

not only for binary solid solutions but also formulticomponent materials, such as steels andsuperalloys, and for intermetallic compounds (15,22).

ConclusionsThermal conductivity in Pt alloys was compre-

hensively surveyed as a function of soluteconcentration, work hardening and temperature.The results are as follows:[1] The thermal conductivity of Pt alloys is main-ly determined by both alloy composition andtemperature and is hardly influenced by workhardening.[2] Alloying decreases the thermal conductivity ofPt, and the conductivity-composition relationshipis characterised by a sharp maximum at pure Pt.The Wiedemann-Franz relation held for Pt alloysindicates the dominant carriers of thermal conduc-tion are electrons.[3] It is found that thermal conductivity decreas-es monotonically as the position of the soluteelement in the Periodic Table becomes horizontal-ly more distant from that of Pt (but only for


Fig. 6 Correlation at 300 K, between thethermal conductivity and the temperaturecoefficient for Pt-Ni and Pt-V alloys.Each value has an alloy composition.Ten values for Pt-2 at.% X alloys areplotted.Elements X are from the second longperiod

THERMAL CONDUCTIVITY AT 300 K, λ300 K, W m-1 K-1

TEM

PE

RAT

UR

E C

OE

FFIC

IEN

T O

F TH

ER

MA

L C

ON

DU

CTI

VIT

Y, α

, 10-

3K-1

: Pt-Ni alloy: Pt-V alloy: Pt-2 at.%X alloy

Pt solid solution

B-subgroup elements). This is a counterpart of theNorbury rule originally proposed for electricalresistivity.[4] A continuous increase in thermal conductivity

with temperature is observed for Pt alloys in thetemperature range between 300 and 1100 K. Thetemperature coefficient and the thermal conductiv-ity are inversely correlated.


Kenji Ohkubo is a Technician in theDivision of Materials Science andEngineering, Hokkaido University. Hismajor field of interest is thedetermination and characterisation ofthermal properties of metallic materialsby the laser flash method.

Tetsuo Mohri is a Professor in theDivision of Materials Science andEngineering, Hokkaido University. Hismajor field of interest is the first-principles study on phase stability,equilibria and transformation formetallic systems.

Yoshihiro Terada is an Associate Professorin the Department of Metallurgy and CeramicScience, Tokyo Institute of Technology. Hismain activities are in the thermal andmechanical properties of metallic materialsfor high temperature applications.

The Authors

References1 Tables of Physical and Chemical Constants, 16th

Edn., eds. G. W. C. Kaye and T. H. Laby, Longman,Essex, 1995

2 E. Gruneisen, Ann. Phys., 1908, 25, 8253 Metals Handbook, 10th Edn., eds. S. R.

Lampman, T. B. Zorc, S. D. Henry, J. L. Daquilaand A. W. Ronke, Vol. 2, ASM International,Materials Park, OH, U.S.A., 1990, p. 707

4 E. M. Wise and J. T. Eash, Trans. AIME, 1938, 128,282

5 Metals Handbook, 9th Edn., eds. J. R. Davis, J. D.Destefani and G. M. Crankovic, Vol. 13, ASMInternational, Metals Park, OH, U.S.A., 1987, p. 793

6 N. M. Davey and R. J. Seymour, Platinum Metals Rev.,1985, 29, (1), 2

7 W. A. Nemilow, Z. Anorg. Allg. Chem., 1934, 218, 338 O. A. Novikova and A. A. Rudnitskii, J. Inorg. Chem.

(USSR), 1957, 2, 18409 R. G. Stewart and R. P. Huebener, Phys. Rev., 1970,

B1, 332310 W. M. Star, E. de Vroede and C. van Baarle, Physica,

1972, 59, 12811 E. K. Azarbar and G. Williams, Phys. Rev., 1976, B14,

330112 J. R. Kuhn, C. L. Foiles and J. Bass, Phys. Lett., 1977,

63A, 401

13 Y. S. Touloukian, R. W. Powell, C. Y. Ho and P. G.Klemens, Thermal Conductivity, Metallic Elementsand Alloys, Plenum, New York, 1970, p. 262

14 C. Y. Ho, R. W. Powell and P. E. Liley, Thermalconductivity of the elements: a comprehensivereview, J. Phys. Chem. Ref. Data, 1974, 3, 511

15 Y. Terada, K. Ohkubo, T. Mohri and T. Suzuki,Mater. Sci. Eng. A, 1997, 239-240, 907

16 G. K. White, Intermetallic Compounds, Principles,Vol. 1, eds. J. H. Westbrook and R. L. Fleischer, JohnWiley & Sons, Chichester, 1994, p. 1017

17 C. Kittel, Introduction to Solid State Physics, JohnWiley & Sons, New York, 1953

18 J. M. Ziman, Principles of the Theory of Solids,Cambridge University Press, London, 1964

19 F. J. Blatt, Physics of Electronic Conduction inSolids, McGraw-Hill, New York, 1968

20 Binary Alloy Phase Diagrams, 2nd Edn., ed. T. B.Massalski, ASM International, Materials Park, OH,U.S.A., 1990

21 A. L. Norbury, Trans. Faraday Soc., 1921, 16, 57022 Y. Terada, T. Mohri and T. Suzuki, Proc. 3rd Pacific

Rim Int. Conf. on Advanced Materials andProcessing (PRICM-3, Honolulu, Hawaii, 1216July, 1998, eds. M. A. Imam, R. DeNale, S. Hanada,Z. Zhong and D. N. Lee, TMS, Warrendale, PA,U.S.A., 1998, p. 2431


The 2004 Joint International Meeting combin-ing the 206th Meeting of The ElectrochemicalSociety with the 2004 Fall Meeting of TheElectrochemical Society of Japan, was held inHonolulu, Hawaii, from 3rd to 8th October 2004.The programme consisted of over 1000 differentlectures and 500 posters and was attended by aworldwide audience of around 2000 delegates. Themeeting included the Fourth InternationalSymposium on Proton Conducting MembraneFuel Cells, which is the main subject of this review.

Improvements to the materials (cathodes, elec-trolyte and anodes) used in the polymer electrolytemembrane fuel cell (PEMFC) are required beforethey can be successful commercially, and newwork on these, and new catalysts and membranesfor the direct methanol fuel cell (DMFC) aredescribed. Further, there is a need for better under-standing of membrane electrode assembly (MEA)deterioration mechanisms.

The BackgroundCathode Materials

A significant performance loss in the PEMFC isassociated with the oxygen reduction reaction(ORR) at the cathode. While the best cathode cat-alysts are currently Pt-based, the drive to reducemetal loadings and costs and improve activitymeans that new materials, such as Pt alloys andmetal carbides, are constantly being sought. The

conference featured many talks on the activity ofnew ORR catalysts and the use of combinatorialchemistry methods to speed up the search forimproved ORR catalyst formulations.

Investigations into the durability of the plat-inum group metal catalyst materials themselvesand the effects of long-term cycling and highpotentials/temperatures (especially for cathodematerials) showed that there is a loss of metal sur-face area and corrosion of the carbon support.These explain the loss in MEA performance overtime and define the properties required for futurematerials.

Electrolyte MaterialsIn this area there is a need for solid polymer

electrolyte membrane materials that are cheaperand more conductive than the current perfluoro-sulfonic acid (PFSA) materials, and which are alsodurable for up to 10,000 hours. In particular, mem-branes are needed for use at temperatures above100ºC where liquid water is no longer present forproton transport. For DMFCs, new membraneswith reduced methanol permeability are required.

Membrane Electrode Assembly:Deterioration and Diagnostics

In order for PEMFCs to achieve the necessarydurability for commercialisation (up to 10,000hours), significant efforts have been directed

DOI: 10.1595/147106705X25525

Electrochemistry of Proton ConductingMembrane Fuel CellsReviewed by Sarah C. BallJohnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

Work presented at the Fourth International Symposium on Proton Conducting Membrane FuelCells is reviewed here. For these fuel cells to become commercially successful there are anumber of challenges to be met. For instance, the polymer electrolyte membrane fuel cellneeds more active catalysts and cheaper, more durable, membranes. In addition, an improvedunderstanding of the deterioration mechanisms of the membrane electrode assemblies isrequired. New work on all these aspects is described here. Work on direct methanol fuelcells is also reported, focusing on more effective anode catalysts and new proton conductingmembrane materials with reduced permeability to methanol.

towards finding deterioration mechanisms and fail-ure modes. Several studies on the effects ofperoxide radicals, factors controlling their rate andplace of formation in PEMFCs, and evidence oftheir attack on the membrane in PEMFCs werepresented.

New Oxygen Reduction Reaction:Materials and Nanomaterials

New ORR materials for the PEMFC cathodebased on PtX alloys (X = Ni, Co, Fe) weredescribed by N. Wakabayashi and colleagues(University of Yamanashi, Japan) [Abs# W1-1856]. Their Pt alloys showed a higher onsetoxidation potential for the ORR reaction, ratio-nalised by the presence of a Pt skin overlaying thePt alloy. V. Stamenkovic and colleagues(University of California at Berkeley, U.S.A.)[Abs# AD3-2308] also observed the formation ofa Pt skin after annealing sputtered alloy surfaces ofPtX (X = Ti, Fe, Co, Ni). They noted that activityfor the ORR was increased for Pt3Fe and Pt3Cosamples (with a Pt skin) due to reduced numbersof blocking species, such as OH- and otheranions, at the surface.

M. Teliska and D. E. Ramaker (The GeorgeWashington University, U.S.A.) and V. S. Murthiand S. Mukerjee (Northeastern University, U.S.A.)[Abs# W1-1919] used X-ray adsorption spec-troscopy to observe the presence of anions, fromHClO4 and H2SO4 solutions, on the surface of Pt.They examined the anion effects on the absorptionof H2 and O2. PtCo alloys, with and without Ptskins, were also investigated.

J. Zhang and coworkers (Brookhaven NationalLaboratory, U.S.A.) [Abs# W1-1920] deposited Ptmonolayers onto Ru, Ir, Rh, Pd and Au, and byvarying the metal substrates found that the ORRactivity changed, in some cases producing a specif-ic activity several times greater than that for Ptalone.

W. S. Baker, P. J. Bouwman and K. E. Swider-Lyons (Naval Research Laboratory, U.S.A.) and W.Domowski (University of Knoxville, U.S.A.)[Abs# W1-1915] used Pt, Au and Pd depositedonto metal oxides, such as SnOx and TiOx, as ORRPEMFC catalysts, exploiting the strong metal sup-

port interaction (SMSI). These catalysts showedgood resistance to SO2 poisoning and hadenhanced activity.

In general, workers preparing and testing PtXalloys (where X is a base metal such as Co, Fe, V)found problems with base metal corrosion fromthe catalysts in acid media.

A Pt-V2O5 ORR catalyst was produced by Y.Suzuki and colleagues (Yokohama NationalUniversity, Japan) [Abs# W1-1911] by sputteringthin metal oxide layers (Sn, W, V, Cr oxides) ontoa glassy carbon electrode, with Pt particles thendeposited on top. The catalyst had higher specificactivity but lower mass activity than Pt/C. A.Ishihara (Japan Science and Technology Agency(JST), Japan) and K. Lee and colleagues(Yokohama National University, Japan) [Abs#W1-1859] demonstrated that Ta oxynitride(TaON) had some activity for the ORR reaction,but the catalyst was significantly less active than Pt.Poor results were thought to be partly due to diffi-culties with electrode preparation and poor sampleconductivity of the powdered oxides.

Nanoparticle catalysts, described by C. L. Hui,X. Li and I.-M. Hsing (Hong Kong University ofScience and Technology, Hong Kong) [Abs# W1-1861], were prepared using surfactant SB12((dodecyldimethyl 3-sulfopropyl) ammoniumhydroxide) as stabiliser. Preparations at higher pH(> pH 8) gave greater Pt surface area, and highermolar ratios of the surfactant to metal were foundto prevent agglomeration.

The difficult process of depositing Pt onto car-bon nanofibres via colloidal and conventionalroutes was discussed by K. Sasaki and colleagues(Kyushu University, Japan) [Abs# W1-1912]. Ofthe different types of nanofibres studied, the high-est Pt surface areas were achieved from Ptdeposition onto platelet nanofibres, followed byherringbone, with tubular nanofibres allowing onlythe smallest Pt areas.

Metals Loading Targets/IdealPerformance

B. Sompalli and H. Gasteiger (General Motors,U.S.A) [Abs# W1-1867] stated that 0.2 g Pt kW1

at 0.6 V was an ideal PEMFC performance target.


Rotating disc electrode (RDE) measurements inHClO4 of mass and specific activity for catalysts40%Pt/C (Tanaka KK) and 20%Pt/Vulcan (E-TEK) demonstrated the superior performance ofthe Tanaka KK material. Tests on RDE and MEAat 900 mV gave agreement for mass and specificactivity, but differences in the Tafel slopes wereobserved.

In the drive towards lower metal loadings andenhanced activity, F. A. Uribe, T. Rockward and J.A. Valerio (Los Alamos National Laboratory,U.S.A.) and R. R. Adzic (Brookhaven NationalLaboratory, U.S.A.) [Abs# W1-1857] describedthe use of electroless deposition for the produc-tion of monolayer electrodes of Pt on Pdnanoparticles (cathode loadings of 40 and 77 µg Ptcm2) and Pt on Ru nanoparticles (anode loadingsof 18 µg Pt cm2). Anode durability was assessed at50 ppm CO/H2 and 4% air bleed, and a 50 mVdecay was observed over 1000 hours of MEA test-ing. Uribe also showed polar curves for low loadedPtPd cathodes that met a 0.6 g Pt kW1 target.

High Temperature Membranes forPEMFCs

A prototype portable high-temperaturePEMFC set-up, having a MeOH-fuelled steamreformer operating at 280ºC and a polybenzimida-zole-based (PBI) MEA operating at 150ºC, wasdescribed by R. Koripella and coworkers(Motorola, U.S.A.) [Abs# W1-1870]. This systemproduced 0.51 W at steady state. The entire systemwas encased in a thermally insulating ceramic hold-er of size 2'' × 2''× 0.25'' to maintain an outsidetemperature at 45ºC during operation. The systemhas a start-up time of 30 minutes but this isexpected to be reduced by miniaturisation.

A. B. Borcarsly and colleagues (PrincetonUniversity, U.S.A.) [Abs# W1-1976] demonstratedexcellent PEMFC performance using an Aciplex®

perfluorosulfonic acid SiO2 composite membraneat 130ºC. The enhanced performance at low rela-tive humidity was thought to be due to a change inionomer morphology, rather than increased wateruptake. A good performance on 500 ppm CO/H2

at 130ºC for a TiO2-doped membrane demon-strated the benefits of higher temperature

operation for CO tolerance. Using titania, fromdifferent manufacturers, produced different per-formance enhancements when incorporated intothe membrane, and anatase, rather than rutile, wasidentified as contributing most performanceenhancement. This was due to the presence ofunsaturated Ti(IV) on the surface, which allowedinteraction with the sulfonic acid groups in theionomers used.

Catalyst and Membrane StabilityN. Miyake and coworkers (Asahi Kasei

Corporation, Japan) [Abs# W-1880] presented adurability study on the membrane materialAciplex® S1002 at different temperatures, usingdry conditions to accelerate degradation. H2

crossovers from anode to cathode were comparedat different times to quantify membrane integrity.Experiments performed included replacing cath-ode and anode electrodes in turn, with ELAT®

carbon cloth (no Pt), and using N2 instead of air.They concluded that Pt and O2 (air) at the cathodehad the greatest impact on membrane degradationrates; this was thought to be due to combustion ofH2 (from crossover) and accompanying exothermsrather than to peroxide formation. Greater relativehumidity restrains degradation, as H2O dispersesboth the heat and peroxide radicals. Samples didnot fail consistently in the same manner: somefailed by pinholing and others by thinning.

S. Mukerjee, V. S. Murthi, L. Zhang(Northeastern University, U.S.A.) [Abs# W1-1882] described durability measurements onnon-fluorinated ionomers and membranes usingan accelerated fuel cell test. They showed that thecathode was the main point of peroxide attack.

In contrast, M. Murthy and D. Moore (W. L.Gore and Associates, U.S.A.) [Abs# W1-1886]and W. Lui and D. Zuckerbrod (W. L. Gore andAssociates, U.S.A.) [Abs# W1-1894] presenteddata indicating that peroxide was mainly generatedat the fuel cell anode. Murthy described how H2

and O2 (from air bleed) at the anode generate ahigher proportion of peroxide radicals when theMEA anode is poisoned by CO, as Pt sites poi-soned with CO cannot oxidise H2O2 to water.Therefore, the maximum membrane degradation


(in a 500 hour test) was observed for an exampleof 500 ppm CO/H2 + 10% air bleed (300 µV h1),while 500 ppm CO/H2 with no air bleed, or H2 +air bleed with no CO, produced minimal degrada-tion < 10 µV h1 (degradation rates defined interms of non-recoverable losses). W. Lui and D.Zuckerbrod (W. L. Gore and Associates, U.S.A.)[Abs# W1-1894] presented data on peroxide for-mation within the MEA using in situ Pt wireprobes, 2 per MEA, at varying distances from thecathode and anode. A strong correlation wasobserved between decreasing membrane thicknessand increasing H2O2 concentrations. O2 crossoverstrongly correlates with membrane thickness whileH2 crossover does not, so the H2O2 formation wasthought to be due to O2 crossover to the anode.

V. Stanic (Teledyne Energy Systems, U.S.A.)and M. Hoberecht (NASA Glenn Research Center,U.S.A.) [Abs# W1-1891] presented a matrix ofPEMFC experiments with relative humidities of 20and 100% and temperatures of 50 and 60ºC, toinvestigate the mechanism for membrane pinholeformation. Mechanisms for failure were tearingand pinhole formation due to mechanical creepand chemical contamination with metal ions(resulting in blister formation). Membrane crack-ing under dry conditions was also observed.

W. Inaba and coworkers (Doshisha University,Japan) and T. Kinumoto and Z. Ogumi (KyotoUniversity, Japan) [Abs# W1-1885] demonstratedthe effect of impurity ions (Fe2+, Cu2+) on peroxideformation and membrane degradation, and used arotating ring disc electrode (RRDE) to look atORR and H2O2 formation at different Pt loadingsof a 20% Pt/C catalyst. The amount of peroxideformed increased towards anode potentials and forhigher dispersed Pt/C materials with greater Ptsurface area.

By contrast, results from A. S. Agarwal and col-leagues (Case Western Reserve University, U.S.A.)[Abs# W1-1896] implied that the amount of H2O2

produced decreased with increasing Pt area. Theydemonstrated that on agglomerated Pt particles,larger amounts of end-on O2 bonding producedhigh amounts of peroxide, while higher Pt surfacearea enhanced rates of peroxide decomposition.

T. Jarvi (UTC Fuel Cells, U.S.A.) [Abs# W1-

1887] described electrochemical measurements ofcarbon corrosion at 950 mV, for Vulcan XC-72Rcarbon with and without Pt. The results indicatedthat CO2 was produced when Pt was present,implying that Pt facilitates carbon oxidation.

In situ MEA carbon corrosion measurementsfrom R. Makharia and coworkers (General Motors,U.S.A.) [Abs# W1-1888] showed that a 3% loss incarbon could have dramatic effects on PEMFCperformance, due to mass transport problems.Measurements of corrosion rates ex situ showedenhanced corrosion for 50%Pt/Vulcan XC-72Rcompared to Vulcan XC-72R alone. Cycling exper-iments showed a slower fall-off in electrochemicalarea for Pt supported on graphitised Vulcan XC-72R carbon.

H. Colon-Mercado, H. Kim and B. Popov(University of South Carolina, U.S.A.) [Abs# W1-1922] looked at the stability of ORR PtX alloys (X= Ni, Co) using an accelerated durability test,where catalyst layers on gas diffusion layers (ELATfrom E-TEK) were immersed in 0.3 M H2SO4 andheld potentiostatically at 0.8 and 0.9 V for up to250 hours, with periodic electrolyte sampling. TheORR current was observed to fall as leaching of Xprogressed. TEM showed increased metal particlesize on comparing fresh and aged samples, butthere was greater sintering for Pt than for PtCo.

Data from H. Gasteiger, R. Makharia and M.Mathias (General Motors, U.S.A.) [Abs# W1-1927] indicated that Pt alloy cathode catalysts wereable to meet the 2 × Pt activity target, but furtherimprovements would be necessary if these catalystswere to find commercial use in automotive fuelcells. Extrapolated data (based around Pourbaixdiagrams and values from the literature) impliedthat PEMFC operation at 100120ºC would resultin rapid Pt dissolution and loss of area. This indi-cated that new ORR catalysts which retain highactivity, and which are more stable at elevated tem-peratures than the currently availablecarbon-supported Pt catalysts, must be found.

Combinatorial TechniquesCombinatorial techniques are increasingly being

used to identify new PEMFC and DMFC catalystformulations. Combinatorial co-sputtering onto a


glass substrate was used by J. F. Whitacre and S. R.Narayanan (Jet Propulsion Laboratory/CaliforniaInstitute of Technology, U.S.A.) [Abs# W1-1898]to find new DMFC catalysts based aroundPtRuNiZr formulations. Initial results on PtRualone were used to validate the method, and a ratioof 82:18 for Pt :Ru was found to be the optimumcomposition. Tests were carried out withoutannealing the sample, but sputtering gave a well-controlled surface.

High throughput screening was used by Y.-G.Shul and colleagues (Yonsei University, SouthKorea) [Abs# W1-1899] to investigatePtRu/AuTiO2 materials for DMFC and CO-toler-ant PEMFC anode applications.

D. A. Stevens and colleagues (DalhouiseUniversity, Canada) [Abs# W1-1900] described acombinatorial technique in which a mask is usedto deposit an 8×8 catalyst array onto 3M nanos-tructured film. Up to 5 different elements weredeposited by magnetron scattering, building up aseries of submonolayer wedges to generate a truealloy. Samples were transferred onto Nafion®

membrane and tested against a continuous anodein a 64-channel fuel cell set-up. The catalyst dotsare much smaller than the gas diffusion media toavoid mass transport and diffusion issues. ForPtNi, optimum ORR performance occurred withPt0.6Ni0.4.

E. S. Smotkin (NuVant Systems, U.S.A.) [Abs#W1-1901] used a 5×5 array of GDEs (gas diffu-sion electrodes) on Nafion® 117 with a singleanode counter electrode, for combinatorial studiesin a fuel cell set-up. This allowed evaluation of cat-alyst ink preparation/application methods anddifferent GDE types, as well as investigation ofdifferent catalysts.

Electronic impedance spectroscopy (EIS), realtime gas analysis and micro thermocouples wereutilised by Q. Dong and M. M. Mench(Pennsylvania State University, U.S.A.) [Abs# W1-1902]. They sampled MEA performance indifferent regions of the MEA, using a segmentedsingle pass flow field and low humidity conditions.They concluded that a dry cathode responds rapid-ly to changes in voltage and there is a reversalpoint along the flow field/MEA at which the

dominant process changes from electro-osmoticdrag to back diffusion.

Data obtained from a 100-segmented PEMFCcell by Z. Siroma and K. Yasuda (NationalInstitute of Advanced Industrial Science andTechnology (AIST), Japan) and A. Nishikawa, R.Kitayama and S. Koge (Shindaiwa Kogyo Co. Ltd.,Japan) [Abs# W1-1904] produced a map of tem-perature and current variations with time.Unexpectedly, no clear relationship was observedbetween changes in current and temperature. Thiswas explained by assuming there are localisedchanges in water production in the PEMFC as cur-rent and heat vary.

PEMFC Anode MaterialsA. Weickowski and colleagues (University of

Illinois, U.S.A.) [Abs# W1-1858] used 195Pt NMRto study PtRu alloys, including Johnson Matthey(JM) materials. Results indicated that the catalystsurface was enriched in Pt (Pt 65 :Ru 35) for JMmaterials, and that Pt migrated to the surface as aresult of heat treatment.

In a novel approach to enhancing anode COtolerance, W. L. Gellet and J. Leddy (University ofIowa, U.S.A.) and K. Bahram-ahi and S. D.Minteer (Saint Louis University, U.S.A.) [Abs#AD3-2303] added magnetic particles of NdFeBand Sm2Co7 to Pt anode catalysts. This resulted innegative shifts in the CO oxidation feature of upto 600 mV in cyclic voltammetry experiments(when compared to Pt alone) due to the magneticfield enhancing the low potential diffusion-con-trolled CO oxidation. The application of anexternal magnetic field had some benefit, butincluding magnetic particles on a single crystal orcatalyst layer was far more effective at enhancingthe low potential CO oxidation. A Pt anode thatcontained magnetic particles produced PEMFCpolar curves showing significantly better perfor-mance when using a 100 ppm CO reformate.

S. Ball, B. Theobald and D. Thompsett(Johnson Matthey Technology Centre, U.K.)[Abs# W1-1916] demonstrated how PtMo/Canode materials were tolerant to high levels of CO.PEMFC data using 5000 ppm CO reformate at thePtMo/C anode produced enhanced performance


over conventional PtRu anode materials. PtMowas also shown to be active for conversion of per-centage levels of CO2 to ppm of CO, explainingthe origin of the extra CO2 poisoning observedfor PtMo (compared to PtRu materials), when run-ning on real reformate.

Catalysts prepared by deposition of Pt or Pd onto SnO2 nanoparticles absorb little CO, so wereinvestigated as CO-tolerant anodes by Y. Anzai, T.Tageguchi and W. Ueda (Hokkaido University,Japan) and R. Kikuchi and K. Eguchi (KyotoUniversity, Japan) [Abs# W1-1921]. Temperatureprogrammed reduction (TPR) data showed that Snwas present as oxide (unreduced form), and so wassuitable for use in the PEMFC anode. Reduced Snis unstable under acid conditions. Optimum per-formance in an MEA was observed using aPd/C/SnO2 anode at 500 ppm CO/H2.

DMFC Anode MaterialsK. Miyazaki and colleagues (Kyoto University,

Japan) [Abs# Q1-1515] looked at nano gold parti-cles on PtMoOx/C. These were found to havegreater activity for MeOH oxidation below 550mV and reduced CO coverage, compared to con-ventional DMFC catalysts.

DMFC lifetime tests characterising catalystsand membranes, were carried out by X. Cheng andcolleagues (Xiamen University, China) and Q. Fan(Gas Technology Institute, U.S.A.) [Abs# W1-1926]. There is significant degradation after 200hours, and a further degradation at 1000 hours.The catalysts tested were JM 30%PtRu/C and Ptblack and the membrane used was Nafion® 117.End-of-life XRD and high resolution transmissionelectron microscopy (HRTEM) on the catalystsused showed particle agglomeration and growthhad occurred, and there was Ru loss from the PtRuparticles, which may have been converted to Ruoxides.

ConclusionsThe work reported at this conference shows

that commercial use of proton conducting mem-brane fuel cells is not so far away, and that thereare many organisations with dedicated scientistsworking to achieve this. Meetings of The

Electrochemical Society are held every six months,whilst Fuel Cell Symposia are held every year, anddetails of future venues are available on the ECUwebsite at http://www.electrochem.org.

Much of the work presented here was exciting,in particular the new combinatorial methods,which will greatly assist the search for new cathodecatalyst formulations. The new high temperaturemembrane materials will open up possibilities ofgreater efficiency and enhanced reformate toler-ance, and will bring the commercialisation ofPEMFCs closer, especially for automotive applica-tions. At this symposium a greater focus than usualon MEA stability and enhanced diagnostics result-ed in an improved understanding of MEAdegradation processes.

The proceedings for the Fourth InternationalSymposium on Proton Conducting MembraneFuel Cells is currently being compiled by TheElectrochemical Society (http://www.elec-trochem.org) and will contain more informationon the presentations described in this review.


The Reviewer

Sarah Ball is a Research Scientist in the Electrotechnology/CatalystPreparation Group at the Johnson Matthey Technology Centre inthe U.K. She is interested in anode catalysis for reformate-tolerantapplications, and novel cathode materials and alloys for PEMFCs.

Nowadays the synthesis of single-site rutheni-um (Ru) metathesis pre-catalysts (1) is emerging asan appealing challenge for a large number ofresearch groups working in the area oforganometallic chemistry (210). The 16-electronruthenium benzylidene and vinyl carbene com-plexes 1 and 2 (R = Ph or Cy), developed byGrubbs and coworkers (11, 12), turned out to beversatile and reliable metathesis pre-catalystsenjoying a variety of applications in advancedorganic synthesis and polymer chemistry (13, 14).They display a wide spectrum of activity whileexhibiting good tolerance towards air, moistureand many organic functionalities. Despite thisattractive application profile some drawbacks ofthe bisphosphane complexes 1 and 2 have to betaken into account. The drawbacks are:(a) special precautions during their preparationinvolving diazoalkane derivatives and cyclo-propane, (b) limited thermal stability upon heating, and(c) significant sensitivity towards substitution pat-terns in highly substituted olefinic substrates. In the last instance, the complexes allow synthesis

of trisubstituted olefins by ring-closing metathesis(RCM) only with a limited number of olefinic sub-strates and generally fail in the case oftetrasubstituted counterparts.

R is phenyl (Ph) or cyclohexyl (Cy), R´ is methyl(Me) or phenyl (Ph) and Mes is 2,4,6-trimethylphenyl.

With the aim of improving their stability insolution and increasing their metathesis activity,


DOI: 10.1595/147106705X24580

Ruthenium Indenylidene ComplexesMETATHESIS CATALYSTS WITH ENHANCED ACTIVITY

By Valerian Dragutan* and Ileana DragutanInstitute of Organic Chemistry, Romanian Academy, 202B Spl. Independentei, PO Box 15-254, 060023 Bucharest, Romania;

*E-mail: [email protected]

and Francis VerpoortDepartment of Inorganic and Physical Chemistry, Organometallics and Catalysis Division, Ghent University, Krijgslaan 281 (S3),

9000 Ghent, Belgium

This paper describes a class of ruthenium indenylidene complexes which constitute robustand efficient pre-catalysts for olefin metathesis reactions, specifically ring-closing metathesisof substituted linear dienes, acyclic diene metathesis of α,ω-dienes, enyne metathesis andring-opening metathesis polymerisation of cycloolefins. They readily allow reactions notpromoted by many prior ruthenium catalysts, such as the synthesis of tri- and tetrasubstitutedcycloalkenes as well as ring-closing metathesis involving highly substituted dienes. The activityand stability of these pre-catalysts can be finely tuned by adjusting both steric and electroniceffects in the metal coordination sphere through an appropriate selection of ancillary ligands.Due to their accessibility, enhanced activity and good stability, this class of ruthenium complexesgratifyingly extends the scope and utility of the currently used metathesis catalysts.

Ru

PR3

PR3

Cl

Cl

Ph

HRu

Cl

Cl

R'

R'

PR3

PR3

1 2

Ru

PR3

Cl

Cl

Ph

H

NNMes Mes

Ru

PR3

Cl

Cl

Ph

H

NNMes Mes

3 4


new ruthenium complexes were created, in the fol-lowing years, by replacing one or two of thephosphane groups, mainly in the benzylidenecomplex 1, with sterically demanding 1,3-dimesitylim-idazolin-2-ylidene ligands or their fully saturatedanalogues, (as in complexes 3 and 4) (1520).Nonetheless, some applications in RCM reactions,not possible with these ruthenium pre-catalysts,are still restricted to the realm of the more activeand selective, but quite sensitive, Schrock molyb-denum imido alkylidene complex 5 (21, 22).

In addition to the above mentioned inconve-niences, synthesis of complexes 14 requiresrather expensive starting materials and impliescaution during some of the preparation steps.

In order to eliminate these disadvantages, aseries of new ruthenium complexes has recentlybeen designed and prepared by further variationsin the ligand sphere of complex 1. Thus, a novelclass of ruthenium indenylidene pre-catalysts, dis-playing a wide application profile in metathesis

chemistry, has emerged. This type of rutheniumcomplex which is of special interest to organic andpolymer catalysis will be discussed in this paper.

Bisphosphane RutheniumIndenylidene Complexes

The 3-phenyl indenylidene complex 6 was con-veniently obtained from RuCl2(PPh3)4 andcommercially available 3,3-diphenylpropyn-3-ol asthe carbene precursor. Starting from complex 6,the PPh3 ligands have been readily replaced by thebetter donating ligands PCy3, affording the parentindenylidene complex 7 (23, 24) (Equation (i)).

This methodology can also use RuCl2(PPh3)3,(tris(triphenylphosphine) complex) as the rutheni-um source, resulting in the same indenylidenecomplex 6. The rationalisation behind this finding,that the initially formed ruthenium allenylidenecomplex 8 leads by intramolecular rearrangementto the more stable indenylidene complex 6, hasbeen proved unequivocally (25) (Equation (ii)).The above indenylidene ruthenium complexesshowed higher thermal stability than the relatedalkylidene complexes 1 and 2 and performed wellin various ring-closing metathesis reactions.

N-Heterocyclic Carbene (NHC)Indenylidene Ruthenium Complexes

Substitution of phosphane ligands in the ruthe-nium complexes 6 and 7 by imidazolin-2-ylideneligands containing bulky groups in the 1 and 3positions of the five-membered ring allowed the

Me2HC CHMe2N

Mo MeMe

Ph

OO

MeF3C

F3C

CF3CF3Me

5

-2 PPh3

H2O -2 PPh3

2 PCy3HC CCPh2OHRuCl2(PPh3)4] Ru

Ph3P

Cl PPh3

Cl

PhRu

Cy3P

Cl PCy3

Cl

Ph

RuPh3P

Cl PPh3

Cl

PhRuCl2(PPh3)3]

HC CCPh2OH

THF, RefluxRu C C C

Ph

Ph

Cl

Ph3P

PPh3

Cl

76

8 6

(i)

(ii)


synthesis of further 16-electron rutheniumindenylidene complexes of improved activity andstability. Thus, the addition of 1,3-dimesitylimida-zolin-2-ylidene to 3-phenylindenylidene complexes6 and 7, in toluene at room temperature, leads tothe high yield of complexes 9 and 10, respectively(26) (Scheme I).

Most conveniently, complex 10 can be preparedin hot hexane when easier isolation of the product

by simple filtration (vs. evaporation of the solventpreviously), followed by washing with hexane anddrying, becomes possible. A similar procedurestarting from 1,3-bis(2,6-di-isopropylphenyl)imida-zolin-2-ylidene and 3-phenylindenylidene, 6 and 7,yielded imidazolin-2-ylidene ruthenium complexes11 and 12, respectively (Scheme II).

Thermal stability investigations showed com-pounds 10 and 12 incorporating a PCy3 ligand are

NNMes Mes

RuCl

ClPhPR3

PR3Ru

Cl

Cl

PR3

PhNN

MesMes

RuCl

Cl

PR3

PhNN iPr2PhiPr2Ph

RuCl

ClPhPR3

PR3

NNiPr2Ph iPr2Ph

EtOOC COOEtEtOOC COOEt

RuCl

Cl

PCy3

PhNN

MesMes

RT, 25 min, 88 %

RT, 25 min, 94 %

RuCl

Cl

PPh3

PhNNiPr2Ph iPr2Ph

N

Ts

N

Ts

6, R = Ph7, R = Cy

6, R = Ph7, R = Cy

9, R = Ph10, R = Cy

11, R = Ph12, R = Cy

Scheme I

Scheme II

Scheme III

Scheme IV


very stable and do not decompose even after heat-ing at 80°C for several days. RCM studies usingdiethyl diallylmalonate and diallyltosylamide as thesubstrates showed good catalytic activity andselectivity for ruthenium indenylidene complexesof this pre-catalyst family (yield 88% and 94% ofcyclic products, respectively) (Schemes III andIV). Remarkably, these types of complexes evenallow the synthesis of tetrasubstituted cycloalkenesby RCM of the corresponding dienes, a processthat meets severe restrictions or is not possiblewith common diphosphane ruthenium alkylidenecomplexes (Scheme V).

Arene Ruthenium IndenylideneComplexes

Low temperature NMR studies of protonated18-electron ruthenium allenylidene complex 13,undertaken by Dixneuf et al. (27), gave evidence of

the formation of an alkenylcarbyne rutheniumderivative 14 at 40°C which, upon heating at20°C, readily converted to the rutheniumindenylidene complex 15 (Scheme VI).

It has been suggested that the alkenylcarbynederivative 14 arises by protonation at the Cββ atomof the allenylidene ligand in complex 13 while theindenylidene derivative 15 is formed by furtherelectrophilic substitution of the phenyl group withthe rearranged Cαα atom. Complex 15, generated insitu from 13 upon treatment with strong acids(HOTf, HBF4), exhibited high activity in acyclicdiene metathesis (ADMET) of 1,9-decadiene,RCM of diallyltosylamide, enyne metathesis ofallylpropargyltosylamide and the ring-openingmetathesis polymerisation (ROMP) of cyclopen-tene and cyclooctene. For instance, the ADMETreaction of 1,9-decadiene, carried out in CD2Cl2 at0°C, using the precursors HOSO2CF3 and [RuCl(p-

120 min, 66 %

RuCl

Cl

PPh3

PhNN

MesMes

EtOOC COOEtEtOOC COOEt

C6D5CD3 ,80°C

15

1413

1.2 eq HOTf

- 40°C

- HOTf- 20 °C

RuClCy3P

Ph OTf

22

Ru CClCy3P Ph

PhCC

H

(OTf)2OTfC C CPh

PhRuCl

Cy3P

Scheme V

Scheme VI

.

,


cymene)(=C=C=CPh2)(PCy3)][CF3SO3] of the in situgenerated complex 15, gave a 94% yield of poly-meric compound after 12 hours (Scheme VII).

Similarly, in RCM of diallyltosylamide with thesame catalytic system, 99% pyrolidine N-tosy-lamide has been produced after a 10 min reactiontime (Scheme VIII) whereas in enyne metathesis ofallylpropargyltosylamide, only 75% yield of 3-allylpyrolidine N-tosylamide resulted (Scheme IX).

It is important to point out that in the ROMPof cyclooctene using the system [RuCl(p-cymene)(=C=C=CPh2)(PCy3)][CF3SO3]/HOSO2CF3,

in chlorobenzene, an unexpectedly high yield ofpolyoctenamer was obtained, even after a shortreaction time at room temperature (Scheme X). Incontrast, starting from a less reactive monomer likecyclopentene, a maximum yield of 67% could beobtained after 1 hour at 0°C (Scheme XI).

Schiff Base RutheniumIndenylidene Complexes

Starting from the diphosphane indenylidenecomplex 7 and an aromatic salicylaldimine, theSchiff base containing ruthenium indenylidene

Ts N NTs, 0°C, 10min, 99%

RuClCy3P

Ph OTf

CD2Cl2

NTsTs N, 0°C, 1h, 75%

RuClCy3P

Ph OTf

CD2Cl2

PhCl, RT, 5min, 97%n

RuClCy3P

Ph OTf

n6

Scheme VIII

Scheme X

Scheme IX

6

, 0°C, 12h, 94%

RuClCy3P

Ph OTf

6 nn

CD2Cl2

Scheme VII


complex 16 has been obtained in high yield (28)(Scheme XII). Complex 16 was characterised by1H, 13C, 31P-NMR spectroscopies and elementalanalysis, and successfully applied to the synthesisof enol-esters implying nucleophilic addition ofcarboxylic acids to terminal alkynes. Importantly,the results obtained with catalyst 16 are compara-ble with previously reported data for the bestmetathesis ruthenium catalysts (29). Related Schiffbase ligated ruthenium indenylidene complexes 17and 18 have been prepared by this procedure,characterised by 1H, 13C, 31P-NMR spectroscopyand elemental analysis, and tested for their activityin ROMP of cycloolefins and atom transfer radicalpolymerisation (ATRP) of vinyl monomers(3032) (Scheme XIII).

It should be emphasised that the bidentateSchiff base ligands incorporated in this type ofcomplex exert, due to their dangling propensity,a pronounced effect on both their activity and sta-bility (32).

ConclusionsRuthenium indenylidene complexes bearing

different ancillary ligands in the metal coordina-tion sphere emerge as quite efficient and versatilemetathesis pre-catalysts. They proved to be ratherrobust and are stable even upon heating. Thesefeatures are very promising for various metatheticapplications. As a special bonus they allow reac-tions not promoted by many previous Ru catalysts,in particular the convenient synthesis of tri- and

n3

OTfRuClCy3P

Ph

nPhCl, 0°C, 1h, 67%

2.

1. TlOEt, THF/RT

O

ClPCy3

NPh

Ru

R''

R'''R''

R'

RuPhPCy3

PCy3ClClOH

NR''

R'' R'''

R'

2.

1. TlOEt, THF/RT

O

ClPCy3

NPh

Ru

Me

MeBr

RuPhPCy3

PCy3ClCl

OH

NMe

Me Br

Scheme XI

Scheme XII

Scheme XIII 17, R' = H, R'' = i-Pr, R''' = H18, R' = NO2, R'' = Me, R''' = Br

16


tetrasubstituted cycloalkenes, as well as RCMinvolving highly substituted dienes. Due to easyaccessibility, enhanced activity, increased stability,and wide area of application they successfully com-

plement conventional ruthenium complexes cur-rently employed in the RCM of linear dienes,ADMET of α,ω-dienes, enyne metathesis andROMP of cycloolefins.

1 (a) V. Dragutan, I. Dragutan and A. T. Balaban,Platinum Metals Rev., 2000, 44, (2), 58; (b) V.Dragutan, I. Dragutan and A. T. Balaban, PlatinumMetals Rev., 2000, 44, (3), 112; (c) V. Dragutan, I.Dragutan and A. T. Balaban, Platinum Metals Rev.,2000, 44, (4), 168; (d) V. Dragutan, I. Dragutan andA. T. Balaban, Platinum Metals Rev., 2001, 45, (4), 155;(e) V. Dragutan and I. Dragutan, Platinum Metals Rev.,2004, 48, (4), 148

2 (a) A. Demonceau, F. Simal, S. Delfosse and A. F.Noels, Ring-Opening Metathesis Polymerizationand Related Chemistry, eds. E. Khosravi and T.Szymanska-Buzar, NATO Science Series, KluwerAcademic Publishers, Dordrecht, 2002, pp. 91-104;(b) A. Demonceau, A. W. Stumpf, E. Saive and A. F.Noels, Macromolecules, 1997, 30, 3127

3 (a) P. Dixneuf and C. Bruneau, Acc. Chem. Res., 1999,32, 311; (b) I. del Rio and G. van Koten, TetrahedronLett., 1999, 40, 1401

4 (a) A. Fürstner, Angew. Chem., Int. Ed., 2000, 39, 3012;(b) A. Fürstner, Top. Organomet. Chem., 1999, 1, 1

5 (a) R. H. Grubbs and S. Chang, Tetrahedron, 1998, 54,4413; (b) Handbook of Metathesis, ed. R. H.Grubbs, Wiley-VCH, Weinheim, 2003

6 (a) A. Hafner, A. Mühlebach and P. A. van derSchaaf, Angew. Chem. Int. Ed., 1997, 36, 2121; (b) J. P.A. Harrity, D. S. La, D. R. Cefalo, M. S. Visser andA. H. Hoveyda, J. Am. Chem. Soc., 1998, 120, 2343;(c) J. S. Kingsbury, J. P. A. Harrity, P. J. Bonetatebusand A. H. Hoveyda, J. Am. Chem. Soc., 1999, 121, 791

7 (a) W. Herrmann and C. Kocher, Angew. Chem., Int.Ed., 1997, 36, 2162; (b) T. Weskamp, F. J. Kohl andW. A. Herrmann, J. Organomet. Chem., 1999, 582, 362

8 J. Huang, H. J. Schanz, E. D. Stevens and S. P.Nolan, Organometallics, 1999, 18, 2370

9 (a) B. De Clercq and F. Verpoort, Tetrahedron Lett.,2001, 42, 8959; (b) B. De Clercq and F. Verpoort,Adv. Synth. Catal., 2002, 344, 639; (c) B. De Clercqand F. Verpoort, J. Mol. Catal. A: Chem., 2002, 180, 67

10 (a) M. Schuster and S. Blechert, Angew. Chem. Int.Ed., 1997, 36, 2036; (b) M. Zaja, S. J. Connon, A. M.Dunne, M. Rivard, N. Buschmann, J. Jiricek and S.Blechert, Tetrahedron, 2003, 59, 6545

11 (a) P. Schwab, R. H. Grubbs and J. W. Ziller, J. Am.Chem. Soc., 1996, 118, 100; (b) B. M. Novak and R. H.Grubbs, J. Am. Chem. Soc., 1988, 110, 7542

12 (a) S. T. Nuygen, L. K. Johnson, R. H. Grubbs andJ. W. Ziller, J. Am. Chem. Soc., 1992, 114, 3974; (b) S.T. Nuygen, R. H. Grubbs and J. W. Ziller, J. Am.Chem. Soc., 1993, 115, 9858; (c) S. T. Nuygen, R. H.Grubbs and J. W. Ziller, J. Am. Chem. Soc., 1995, 117,5503

13 A. K. Chatterjee, J. P. Morgan, M. Scholl and R. H.Grubbs, J. Am. Chem. Soc., 2000, 122, 3783

14 V. Dragutan and R. Streck, CatalyticPolymerization of Cycloolefins, Elsevier,Amsterdam, 2000

15 (a) J. Huang, E. D. Stevens, S. P. Nolan and J. L.Pedersen, J. Am. Chem. Soc., 1999, 121, 2674; (b) J.Huang, H.-J. Schanz, E. D. Stevens and S. P. Nolan,Organometallics, 1999, 18, 5375

16 (a) L. Ackermann, A. Fürstner, T. Weskamp, F. J.Kohl and W. A. Herrmann, Tetrahedron Lett., 1999,40, 4787; (b) T. Weskamp, F. J. Kohl, W. Hieringer,D. Gleich and W. A. Herrmann, Angew. Chem. Int.Ed., 1999, 38, 2416

17 (a) M. Scholl, T. M. Trnka, J. P. Morgan and R. H.Grubbs, Tetrahedron Lett., 1999, 40, 2247; (b) M.Scholl, S. Ding, C. W. Lee and R. H. Grubbs, Org.Lett., 1999, 1, 953

18 U. Frenzel, T. Weskamp, F. J. Kohl, W. C.Schattenmann, O. Nuyken and W. A. Herrmann, J.Organomet. Chem., 1999, 586, 263

19 (a) C. W. Bielawski, O. A. Sherman and R. H.Grubbs, Polymer, 2001, 42, 4939; (b) R. H. Grubbs,Paper presented at the 221st ACS National Meeting,San Diego, CA, 15 April, 2001; (c) M. S. Sanford,M. Ulman and R. H. Grubbs, J. Am. Chem. Soc.,2001, 123, 749

20 A. Fürstner, L. Ackermann, B. Gabor, R. Goddard,C. W. Lehmann, R. Mynott, F. Stelzer and O. R.Thiel, Chem. Eur. J., 2001, 7, 3236

21 R. R. Schrock, J. S. Murzdek, G. C. Bazan, J.Robbins, M. DiMare and M. ORegan, J. Am. Chem.Soc., 1990, 112, 3815

22 (a) R. R. Schrock and A. H. Hoveyda, Angew. Chem.Int. Ed., 2003, 42, 4592; (b) R. R. Schrock, Top.Organomet. Chem., 1998, 1, 1

23 A. Fürstner, A. F. Hill, M. Liebl and J. D. E. T.Wilton-Ely, J. Chem. Soc., Chem. Commun., 1999, 601

24 H.-J. Schanz, L. Jafarpour, E. D. Stevens and S. P.Nolan, Organometallics, 1999, 18, 5187

25 A. Fürstner, O. R. Thiel, L. Ackermann, H.-J.Schanz and S. P. Nolan, J. Org. Chem., 2000, 65, 2204

26 L. Jafarpour, H.-J. Schanz, E. D. Stevens and S. P.Nolan, Organometallics, 1999, 18, 5416

27 R. Castarlenas and P. Dixneuf, Angew. Chem. Int. Ed.,2003, 42, 4524

28 T. Opstal and F. Verpoort, Synlett, 2002, 93529 A. Fürstner, J. Grabowski and C. W. Lehmann, J.

Org. Chem., 1999, 64, 827530 T. Opstal and F. Verpoort, New J. Chem., 2003, 27, 25731 R. Drozdzak, B. Allaert, N. Ledoux, I. Dragutan, V.

Dragutan and F. Verpoort, submitted to Adv. Synth.Catal.

32 T. Opstal and F. Verpoort, Angew. Chem. Int. Ed.,2003, 42, 2876

References

The Authors

Valerian Dragutan is a SeniorResearcher at the Institute ofOrganic Chemistry of theRomanian Academy. Hisresearch interests arehomogeneous catalysis bytransition metals and Lewisacids; olefin metathesis andROMP of cycloolefins;bioactive organometalliccompounds; and mechanismsand stereochemistry ofreactions in organic andpolymer chemistry.

Ileana Dragutan is a SeniorResearcher at the Institute ofOrganic Chemistry of theRomanian Academy. Herinterests are in stericallyhindered amines, synthesesof olefinic monomers viaolefin metathesis, stableorganic free radicals as spinprobes for ESR of organisedsystems and membranebioenergetics. She is alsointerested in transition metalcomplexes with free radicalligands.

Francis Verpoort is a Full Professor at the Department of Inorganic and PhysicalChemistry, Organometallic Chemistry and Catalysis Division, University of Ghent,Belgium. His main research interests concern the structure and mechanisms inorganometallic chemistry, homogeneous and heterogeneous hybrid transitionmetal catalysts, Schiff bases as co-ligands in metal complexes, Kharash additionreactions, enol-ester synthesis, olefin metathesis and ring-opening metathesispolymerisation and atom transfer radical polymerisation.

40Platinum Metals Rev., 2005, 49, (1)


The platinum group metals occur in specificareas of the world: mainly South Africa, Russia,Canada and the U.S.A. Geological occurrences ofplatinum group elements (PGEs) (and sometimesgold (Au)) are usually associated with Ni-Co-Cusulfide deposits formed in layered igneous intru-sions. The platinum group minerals (PGMs) areassociated with the more mafic parts of the layeredmagma deposit, and PGEs are found in chromitecrystals which are a major component of chromi-tite rock. The PGMs occur in the chromititematrix, in chlorite and serpentine minerals, andaround the borders of the chromite crystals (1).The distribution of PGEs in chromitite is consis-tent with crystallisation being caused bymetamorphic events. PGEs also occur in alluvial,placer deposits (2).

Brazilian Occurrences In Brazil there are several regions where PGEs

occur, for instance, in Goiás State in central Brazil.Here, the Niquelândia mafic/ultramafic Complex(the best known complex in Brazil) is thought tohave a PGE content of high potential (3, 4). Themineralisation of the sulfide levels in Niquelândiahas been described as similar to those of theBushveld Complex in South Africa, the StillwaterComplex in the U.S.A., and the Great Dyke inZimbabwe (5). PGM distribution in chromitites iswell documented, especially in the BushveldComplex (for example, (6)), where Pt, Ru, Ir, Pd,

Rh and Os occur together in minerals in variouscombinations. This particular PGM distributioncan also form noble metal alloys (7), and minerali-sation has been linked to crystallisation duringchromite precipitation of hydrothermal origin.

In central Brazil there are massifs (Americanodo Brasil and Barro Alto) that as yet are little stud-ied, and which are thought to contain small PGMconcentrations. Other complexes in the north ofthe country have PGMs, but need exploration (forinstance Carajás and Luanga). Fortaleza de Minas(south of Minas Gerais) has PGMs with sulfides inthe Ni-Co-Cu ore, and PGMs on the surface asso-ciated with the gossans. The PGEs here are asubproduct. However, the best known PGEdeposits in Brazil are in Minas Gerais State.

The territory of Brazil is almost identical withthe area of the South American Platform, stablefrom the beginning of the Phanerozoic Eon. Basedon the nature of the rocks, the sedimentary coverand on geotectonic evolution, Brazil has beendivided into ten geological structural provinces (8)(Figure 1). The geology of the PGE occurrences inthree Structural Provinces: Mantiqueira, SãoFrancisco and Borborema, is described here.

Mafic/Ultramafic Complexes in East BrazilIn eastern Brazil, the mafic/ultramafic com-

plexes that comprise the Atlantic Belt containallochthonous rocks (formed elsewhere and trans-ported by tectonic processes) and metamorphosed

Platinum Group Minerals in Eastern BrazilGEOLOGY AND OCCURRENCES IN CHROMITITE AND PLACERS

By Nelson AngeliDepartment of Petrology and Metallogeny, University of São Paulo State (UNESP), 24-A Avenue, 1515, Rio Claro (SP),

13506-710, Brazil; E-mail: [email protected]

Brazil does not have working platinum mines, nor even large reserves of the platinum metals,but there is platinum in Brazil. In this paper, four massifs (mafic/ultramafic complexes) ineastern Brazil, in the states of Minas Gerais and Ceará, where platinum is found will bedescribed. Three of these massifs contain concentrations of platinum group minerals or platinumgroup elements, and gold, associated with the chromitite rock found there. In the fourth massif,in Minas Gerais State, the platinum group elements are found in alluvial deposits at theBom Sucesso occurrence. This placer is currently being studied.

DOI: 10.1595/147106705X24391

rocks (changed by pressure, temperature and fluidcirculation). Some rocks have kept their originalstructures and textures, as at Ipanema in MinasGerais (Figure 2). This is an original layeredmafic/ultramafic complex. In the east of MinasGerais State the mafic/ultramafic bodies date from1.0 to 1.1 Ga (billions of years).

The effects of metamorphism increase the Fe3+

at the expense of Al and Fe2+, which are lost tocrystal borders or to matrix minerals, and tend toreduce the PGM content ((9) and references in(10)). This shows the importance of the serpentin-isation process when temperature, pressure, waterand carbon dioxide affect (1): PGE mobilisation, PGE enrichment of the chromitite levels, and PGM formation (11, 12).

During a metamorphic event, chemical and tex-tural/structural changes occur to the chromitegrains (mineral zoning). Chromite crystals usuallyhave a core of aluminous chromite, and a broadmargin of ferriferous chromite (14, 16). The varia-tion in the composition of the chromite grains isrelated to the noble metal content (for example(13), and references in (11)). The textures, size andshapes of chromite crystals are associated with ser-pentinisation and deformation of the ultramafic

rocks. There are Cr-spinel crystals in the chromititethat appear to be the remains of original peridotiteminerals. The Cr-spinel crystals usually have threezones: a dark grey core, a grey intermediate zoneand a light-grey rim. Fractures occur frequently.The crystal core contains high Cr2O3 and Al2O3

contents; the intermediate zone has increasing Fet

(total iron content, with Fe2+ > Fe3+) and decreas-ing Al2O3 and MgO (transition of Cr-spinel toferritchromite); while the outer zone is rich in Fe(mainly Fe3+) and poor in Cr (the magnetite zone).Sperrylite crystals (PtAs2) may be present as inclu-sions in the chromites or disseminated in thesilicatic matrix (16). Many chromite grains containlamellar inclusions of chlorite, oriented parallel to111 planes (15).

Mantiqueira Structural ProvinceIpanema Mafic/Ultramafic Complex

The Mantiqueira Structural Province in MinasGerais State lies along the southern part of theAtlantic coast. In Minas Gerais, two PGE/PGM-bearing mafic/ultramafic belts can be identified.The first belt, outside the cratonic area (a centralstable area during the action of new tectonicprocesses) is in Mantiqueira Structural Province.This belt has Neoproterozoic age (1.1 Ga) (16).


Fig. 1 The structural provinces ofBrazil:1 Rio Branco 2 Tapajós 3 São Francisco 4 Tocantins 5 Mantiqueira 6 Borborema 7 Amazonian 8 Parnaíba 9 Paraná 10 Coastal Province and ContinentalMargin (8)

The black points represent the studiedmafic/ultramafic complexes: a Ipanemab Serro and Alvorada de Minas c Pedra Branca


Glossary

Geological term/mineral Meaning

Mafic/ultramafic Magmatic rock, with high ferrous-magnesium minerals content (mainly olivine and pyroxenes)

Chromitite Levels or lenses with high concentrations of chromite

Intrusions Rock massifs which penetrate into previously consolidated rocks

Chromite A mineral of general formula: (Mg,Fe2+)Cr2O4

Serpentinites Metamorphic rocks composed of mostly serpentine group minerals (antigorite, chrysotile and lizardite) – magnesium-rich silicate minerals

Placer deposit An alluvial zone, where rock fragments and minerals are sometimes exploitable, and (gold, platinum, sand) can accumulate.

Gossans Superficial covers of mafic/ultramafic rocks, formed by sulfide alterations

Serpentinisation Metamorphic/hydrothermal processes in which Mg-rich silicate minerals (e.g. olivine,pyroxenes) are converted into, or are replaced, by serpentine group minerals.

Ferriferous chromite A component of chrome-spinel, rich in Fe; simplified formula: (Mg,Fe2+)Cr2O4

Aluminous chromites A component of chrome-spinel, rich in Al; simplified formula: (Mg,Fe2+)Al2O4Cr2O4

Phanerozoic Eon Geological time after the Proterozoic era (570 Ma (millions of years))

Precambrian age Age between 3.8 Ga (billions of years) to 550 Ma

Chlorite/tremolite schists Metamorphic rocks composed of chlorite and/or tremolite with pronouncedorientation of these minerals

Fig. 2 Geological map of the Ipanema mafic/ultramafic Complex in Minas Gerais State, Brazil (inset). The SantaCruz massif is shown. BH is Belo Horizonte, SP is São Paulo, RJ is Rio de Janeiro and I is Ipanema (from (18))

The second belt, in the cratonic area, isrelated to São Francisco StructuralProvince with Paleo to Mesoproterozoicage (1.5 to 2.0 Ga years ago) (17).

The first belt contains the importantIpanema mafic/ultramafic Complex(Figure 2). This complex is composed offour massifs separated by geologicalfaults. The largest massif is the Santa Cruzmassif.

The country (older) rocks of theIpanema Complex are composed oforthogneisses, paragneisses, migmatites,charnockites and quartzites (from thePaleo-Mesoproterozoic age). In thisregion the youngest rocks are granitoidunity igneous rocks (known as the SantaRita do Mutum Intrusive Suite) dating from theNeoproterozoic age (630 Ma (millions of years)(17)). These rocks cut across the oldest rocksequences (the gneisses, migmatites, charnockitesand quartzites). The granitoid suite is importantbecause of the serpentinisation of rocks of theIpanema Complex.

The second massif in size in the IpanemaComplex is the Santa Maria massif, but this has lit-tle differentiation, and no PGEs have been found.In the past the Santa Cruz and Santa Maria bodieswere mined for nickel.

The Santa Cruz MassifIn the Santa Cruz massif the rocks are layered,

with intense faulting and folding (Figure 3). TheSanta Cruz massif has a differentiated sequencewith layerings of dunites, peridotites, pyroxenites,gabbros and anorthosites. The minerals containingthe PGEs are in an important layer of chromitite,lying between the peridotites and pyroxenites. Thislayer bears PGEs that occur as lenses, due to beingdisrupted by tectonic processes.

In the Santa Cruz massif, the dunites and peri-dotites contain chromite as an accessory mineral;chromite occupies 710% by volume, olivineoccupies > 80% and pyroxene (predominantlyorthopyroxene) ~ 10%. On top of the peridotitesis an important level of chromitite, 1.5 m thick(18). This level comprises chrome-spinel (7590%

by volume), silicates (525% serpentines, chlorite,talc, tremolite-actinolite and anthophyllite), andoxides (210% magnetite, titanium magnetite andilmenite).

In the chromitite the chromite crystals are pri-mary; the crystals are all elongated in the samedirection, parallel to a direction of slide, and their


Fig. 3 Geological section of part of the Santa Cruz massif showingthe main chromitite layer. The elevations are above sea level. Theglossaries explain some of the abbreviations of mineral terms used(10, 17)

Fig. 4 Data from the Ipanema Complex of compositionsof spinel-group minerals from the main chromitite layer,as (Cr × 100)/(Cr + Al) and (Mg × 100)/(Mg + Fe2+).Fields for layered intrusions and alpine peridotites(ophiolites). Filled circles are relict chromite cores;empty circles are chromite margins (10)

textures indicate tectonic deformation; they con-tain inclusions of different minerals. The chromitecrystals have narrow rims of ferritchromite. Thisindicates there was a tectonic and metamorphicevent after the intrusion in the differentiatedsequence (and in the basement rocks). However,many of the crystals were preserved (11), and theyindicate that the layered structure is due to variousmagma coolings. This contradicts the earlier ideaof alpine-type peridotite (Figure 4). The unalteredcrystals are found in layered intrusions, see forexample, (20, 21).

The grain sizes of the PGE-containing chrome-spinel crystals (in the chromitite layer) range from1.5 to 4 mm, sometimes reaching 50 mm. Crystalsof chrome-spinel with imperfect faces and withoutfaces are also found, with later-formed silicaticminerals. These crystals indicate that the PGE-bearing mineral was concentrated later anddispersed in the interior and in the matrix (TableI). The more preserved parts (of only small vol-ume) appear to have low PGE content, and thePGEs are concentrated in the core of the chromitecrystals.

Most of the analysed chromite crystals have ahigh TiO2 content (> 0.3%) and a low Al2O3 con-tent associated with enrichment in Cr2O3. Thisshows direct correlation with oxygen fugacity:enrichment in Fe2O3 and loss of MgO (Figure 5)

indicating the action of O2 in the system. Miningthe PGE-bearing chromite in the IpanemaComplex would be uneconomic, as there is little ofit and the noble metal content is low.

In the Ipanema Complex most of the PGEs areassociated with disseminated chromite ore, andmassive and banded ore has been found. A net-like texture can be seen where the chromite lensesmeet and where small quantities of chromite crys-tallise with pyroxenites (orthopyroxenites), at the


Table I

Platinum Group Elements and Gold in Chromitite from the Santa Cruz Massif in Eastern Brazil

Sample Chromite separate Chromite whole-rock SARM7

Metals Average, ESD1* Maximum, Average, ESD2*ppm ppm ppm

Os 45 24.0 57 7.9 5.3 50Ir 23 7.0 41 19.0 7.8 69Ru 136 73.0 203 49.0 21.0 334Rh 19 7.4 27 3.7 1.5 241Pt 98 131.0 521 29.0 52.0 3792Pd 63 88.0 157 13.7 20.0 1440Au 83 87.0 285 6.0 6.6 325

*ESD: element standard deviation; ESD1- separate chromite, based on 13 samples; ESD2- whole-rock chromite, based on 7 samples.Data were obtained first by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and then by electron probemicroanalysis (EPMA) for whole rock, and by induced neutron activation analysis (INAA) for the grains. INAA, for separation of some crystals of chromite, was calibrated against SARM7 (Standard South Africa) for PGE + Au determinations.These crystals were separated by acid treatment and magnetic separation

Fig. 5 Photomicrograph of a backscattered electronimage of chromite from the Santa Cruz massif showingzoning of the poikiloblastic crystal. The crystal core isrich in chromium and magnesium, and the rim has lostchromium and small quantities of magnesium, but has anenrichment of iron. The matrix is composed mainly ofserpentine and chlorite (10)

base of the pyroxenitic/pyroxenite level.Chromitites in the ultramafic sequences showmarked lateral variation over short distances andcross-cutting faults have displaced the lens-shapedbodies by up to 0.2 to 0.5 km.

Some areas with PGE values exceeding 1 ppmhave been found in the rock geochemistry. Themaximum PGE contents recorded are: 209 ppb(156 ppb Pd and 53 ppb Pt). Platinum group min-erals are not found in the Santa Cruz massif, butanalysis of separate chromite grains shows that thechromites contain PGE + Au values (in ppb): Pt98, Pd 63, Os 45, Ir 23, Ru 136, Rh 19 and Au 83(Table I). This is a significant PGE + Au enrich-ment of approximately 4 times over whole rock.The matrix of the chromitite does not containPGEs and Au (or they are in such small quantitiesthat they go undetected).

The PGE-containing samples from Ipanema,when compared with other complexes around theworld (content of PGE + Au, C1 chondrite nor-malised), were most similar to those in the LowerZone of the Bushveld Complex in South Africa.The rocks of the Santa Cruz massif originate in theEarths mantle. They show a relative depletion inIr and an enrichment in Ru, characteristic of strat-iform deposits.

São Francisco Structural ProvinceThe São Francisco Province differs from the

bordering provinces. It is a cratonic (central stable)area in the neighbouring fold belts. The provincehas massifs with chromitites and regions with plac-er deposits.

Serro and the Alvorada de MinasMafic/Ultramafic Complex/MassifsChromitite Deposits

Deposits in the Serro and Alvorada de Minasmassifs have been examined (Figure 6). Chromiumore was mined here in the 1970s. The Serro(Morro do Cruzeiro body) has country rocks ofmetasedimentary sequences associated to bandediron formations enclosed in granite-gneissic ter-ranes (Minas Supergroup) (21). The Serro body isformed of metaperidotites and metapyroxenites(metamorphosed peridotites and pyroxenites),

with serpentine (mainly antigorite), chlorite, talc,actinolite and anthophyllite (23, 24). Inclusions ofsulfides, for instance, pyrite and chalcopyrite,occur in the chromites and in the silicate gangue(minerals associated with the ore), mainly alliedwith regions rich in carbonates (23).

The Serro and Alvorada de Minas bodies con-tain chromitite lenses of perfect, as well asimperfect, crystal shapes. The crystals are fine-grained, from 0.5 to 4 mm. In some places thetexture is disseminated, but the ore is rich inchromite (75 to 90%). The textures and thickness-es are associated with serpentinisation anddeformation of the ultramafic rocks. Cr-spinelcrystals of various shapes and thicknesses arefound here as remnants of the original peridotites(22).

Some crystals have a preserved core and analtered rim, and the zoning is chemically distinct:the core is rich in Cr and Al and the border is moreiron-bearing, showing high values for Cr/(Cr + Al)and Fe2+/(Fe2+ + Mg), respectively (23). Crystals ofsperrylite are also found as inclusions in chromitesand the silicatic matrix.

In addition, the author has found small crystalsof laurite (Ru,Os,Ir)S2, irarsite (Ir,Ru,Rh,Pt)AsS,cooperite (PtS) and more rarely Pt-Pd and Pt-Iralloys (23). One chromitite sample gave anomalousvalues for PGEs: 196 ppb Ru; 96 ppb Pt; and 72ppb Pd.

The Serro Placer DepositsThis region has three known placer deposits, all

with similar geological setting (where the crys-talline basement rocks meet the EspinhaçoSupergroup (in Minas Gerais)). They are: Morro do Pilar (Limeira), Conceição do Mato Dentro (Salvador), and Serro (Bom Sucesso).

The largest and most important PGM concen-trations are alluvial deposits from the BomSucesso stream. This is being worked by casualprospectors, but to little gain. Pt-rich nuggets andPt-Pd alloys occur in the Bom Sucesso stream innorth Serro, 15 km from the city. In the pastPGMs, Au and diamonds were extracted from thisplacer.



Fig. 6 Geological map of the Serro area in Minas Gerais State, showing the Bom Sucesso stream prospect on thesouthern flank of Mount Condado (modified from 25)

Glossary


Country rocks Rocks occurring in the region beside a mineral deposit

Differentiated sequence A layered sequence of rocks (a continuous series of ultramafic-mafic-intermediaterocks). The complete sequence at Santa Cruz is: dunites-peridotites, pyroxenites,gabbros and anorthosites (from bottom to top). It is a common sequence of stratiform complexes present in small quantities in rock.

Accessory minerals Other minerals present in rocks, but not usually described

Ferritchromite Ferriferous chromite (chromite enriched in Fe3+, impoverished in Mg and Al)

Chondrite rock Similar in composition to the Earth’s mantle and to meteorites; used as a standardin rock analyses

Metasedimentary rock Sedimentary rocks subjected to metamorphism (transformation by fluid, pressureand temperature)

The country rocks here are quartzites and meta-conglomerates with thin intercalations of bandediron formations and metabasic rocks (talc-chloriteschists) (Figure 6). In order to find the source ofthe PGMs, correlations were attempted betweenthe alluvial PGMs and the chromitite lenses fromSerro, but without success. Others have looked atthe rocks high above the Bom Sucesso stream(quartzites, conglomerates and weathered rocks),for the source rocks of the placer deposits (25, 26,27), but no PGMs have yet been identified. Onlyone sample of soil from on top of a quartzite unithas yielded Pt (two grains) and Au (three grains).

Pt-Pd alloy nuggets found in the Bom Sucessostream are botryoidal with pronounced zoning,(Figure 7). The zones have a wide range of mor-phologies of varying thickness (< 1100 µm). Thecore region of the nuggets is composed of massiveauriferous Pd-Hg alloy (potarite [Pd,Au,Pt]Hg),and a narrow zone or cavity space of platiniferous

palladium or alloy of composition nearPt50Pd50, and progressively oscillatoryzones of Pd-Pt (~ Pd60Pt40 to Pd70Pt30).Pd occurs in the core of the nuggets

and may have been formed by changes in earlierauriferous potarite (10 to 34 wt.% Pd) (28).

The PGMs and PGE alloys in the nuggets haverounded as well as irregular outlines, and are muchlarger than primary grains. Particle sizes rangefrom 10 to ≤ 500 µm. In general the nuggets com-prise, a core of dendritic auriferous Pd-Hg alloy(potarite) surrounded by a narrow zone of platinif-erous palladium and an alloy of composition nearto Pt50Pd50. The Ir level was low and did not forma solid solution with the other PGEs, so thehypothesis of hydrothermal origin (for the primaryore) is not likely in the drainage basins (27). Thezoning has been accentuated by chemical leachingprocesses, mainly by organic complexes, in thedrainage basins. Potarite (Pd-Hg) was found in theplacer deposits at Morro do Pilar and in the Serro(26).

The nuggets have a range of shapes: kidney(reniform), mamillary, cavernous, stick-shaped,


Fig. 7 The backscattered image of a zonedbotryoidal Pt-Pd nugget found in the placerdeposit in the Bom Sucesso stream. Thebright zone is enriched in Pt relative to Pd.This is a typical arborescent nugget with acore of dendritic auriferous potarite and anarrow rim of Pd-Pt (28)

Glossary


Banded iron formation Banded rock formed by quartz (SiO2), and hematite (Fe2O3). Sometimes hematite is predominant and constitutes ore.

Laterites Ferralitic soils associated to mafic/ultramafic rocks, and other rocks rich in Fe.These soils are poor in Si and rich in Fe hydroxides, and in acidic rocks, where they are rich in Al hydroxides.

Metagabbros Coarse grained igneous rock of basalt composition

botryoidal, dendritic and arborescent, with themost common being an arborescent-dendritic coreof auriferous potarite, with a broad internal zoneof either pure Pt or Pd-Pt and a narrow rim of Pt.The origin of the deposits is unclear, but may beweathered rocks, and the PGE source is consistentwith precipitation from hydrothermal fluids ofmafic rocks, see Table II. The PGE fractionationpattern is similar to that in New Hambler,Wyoming, U.S.A. Pd is observed to be more solu-ble than Pt in alluvial deposits (29), and in laterites

(30). Some placers in Canada and Russia are simi-lar to the Bom Sucesso deposit (26). The bulk Pdcontent of the alluvial Pt-Pd Bom Sucesso nuggetsranges from 11.7 to 29.3% (28).

Potarite was found in nuggets of Pt and Au insoil on top of quartzites cliffs (Condado Mount) inrocks of the Espinhaço Supergroup in upstreamalluvium. The mineralised zones of the quartzitecliffs at Condado Mount are sheared and iron-richsediments, banded iron formations and maficrocks in the quartzites is common.


Table II

Composition of PGMs Found in Serro (Bom Sucesso) Nuggets by Electron Probe Microanalysis (EPMA)

No. Pt, Pd Hg Au Total* Pt, Pd Hg Auwt.% at.%

Platinum

1 100.01 0.13 0.00 0.00 100.53 99.76 0.24 0.00 0.002 99.31 0.24 0.00 0.00 99.71 99.57 0.43 0.00 0.00

Palladium platinum

3 95.36 4.41 0.60 0.08 100.46 91.59 7.77 0.56 0.084 86.07 13.03 0.46 0.16 99.72 77.84 21.61 0.41 0.155 87.60 11.44 0.47 0.26 99.76 80.16 19.19 0.41 0.236 78.07 21.39 0.28 0.06 99.80 66.37 33.34 0.23 0.057 96.64 3.20 0.09 0.07 100.00 94.13 5.72 0.08 0.078 87.86 12.30 0.15 0.02 100.33 79.46 20.40 0.13 0.02

Platiniferous palladium near Pt50Pd50

9 63.71 36.39 0.05 0.00 100.16 48.82 51.13 0.04 0.0010 62.95 36.21 0.49 0.09 99.75 48.46 51.11 0.37 0.0711 62.33 36.97 0.37 0.00 99.66 47.77 51.95 0.28 0.0012 63.60 35.74 0.24 0.00 99.58 49.16 50.66 0.18 0.00

Platiniferous palladium

13 48.50 49.13 1.56 0.11 99.29 34.59 64.25 1.08 0.0814 50.93 47.34 1.32 0.07 99.67 36.62 62.41 0.93 0.0515 54.58 43.16 0.57 0.10 98.40 40.62 58.90 0.41 0.0716 58.04 40.45 0.45 0.08 99.02 43.73 55.88 0.33 0.06

Pd-Hg alloy (auriferous potarite)

17 0.48 40.20 53.93 6.32 100.93 0.36 55.46 39.47 4.7118 0.75 47.48 49.61 2.06 99.91 0.55 63.04 34.94 1.4819 0.28 42.77 48.35 8.05 99.45 0.21 58.65 35.17 5.9620 0.00 37.48 44.44 18.04 99.97 0.00 52.94 33.30 13.7621 0.38 36.73 47.70 15.31 100.12 0.30 52.09 35.88 11.7322 0.32 36.96 50.82 12.15 100.25 0.24 52.31 38.15 9.2923 0.48 43.30 47.42 8.29 99.50 0.36 59.16 34.36 6.1224 1.17 45.09 50.57 3.59 100.41 0.85 60.53 36.01 2.6025 0.33 43.03 44.60 11.61 99.56 0.25 58.83 32.35 8.57

*The total metal content is sometimes > 100% due to the detection limits of the equipment

Borborema Structural ProvinceThis province is in the northeast Brazilian fold

belt, developed during the Upper Proterozoictime. The Pedra Branca mafic/ultramaficComplex, in Ceará State, 310 km from Fortaleza,comprises five bodies, (Figure 8) (dark greencolour); Esbarro is the largest. Prospecting forchromium ore occurred here before 1978.

Pedra Branca Mafic/Ultramafic ComplexThis belongs to the Tróia Median massif, bor-

dered by the youngest fold systems (LowerProterozoic). Pedra Branca Complex is composedof mafic/ultramafic associations: metagabbros,metapyroxenites, pillowed metabasalts, amphibo-lites, quartzites, metasediments (with sulfides andmanganese), marbles and graphitic schists (30).

Esbarro MassifThe Esbarro massif has stratiform characteris-

tics in spite of its small differentiation, and withfew and incomplete layers (31, 32). The Esbarro

massif presents three units and has been interpret-ed as the sequential product of magmaticdifferentiation, starting with dunite-peridotitethrough pyroxenite and hornblende gabbro (32).These units were metamorphosed into chloriteschist, talc-tremolite-actinolite schist, talc-serpen-tine schist, serpentinite and anthophyllite schist.Relict grains of olivine and orthopyroxene areoccasionally observed (32).

Chromitites occur as lenses in the dunite-peri-dotite, and those with most potential are ~ 30 mlong, 1.4 m wide and 1 m thick. The lenses can betraced for 1.2 km along the strike, and average 55to 65% chromite of cumulate texture. They com-prise chromium ore in which PGMs are found.The chromite grains are octahedral and 0.3 to 0.8mm long, but some grains are very irregular:thought to be due to hydrothermal changes duringlow-grade metamorphism. High levels of PGMs,up to 4 ppm, were found in the chromites, and alsodisseminated in the silicatic matrix, where PtAs2

(sperrylite) occurs, forming small inclusions (15 to40 µm) in chromite and thechlorite-rich matrix (Cr chlo-rites), see Figure 9. Thecrystals are almost spherical,and are composite grains.

Kammererite (Cr chlorite)was found in the margins ofthe altered grains, and in thesilicatic matrix. The kam-mererite is associated with apreferred crystallographicorientation of the fer-ritchromite matrix, orientedparallel to 111 planes (15).


Fig. 8 Geological sketch ofTróia region (Ceará) and theEsbarro body, showing thelocation of the study area(modified from (30))

Sperrylite is the most impor-tant mineral found. Locally thecrystals contain, in at.%, up to1.5 Ir, 2 Fe and 3 S, consistentwith substitution of (Ir,Fe)AsSfor PtAs2. A single grain ofhollingworthite (Rh,Pd,Pt,Ru)AsS was identifiedin the matrix and was shown to contain, in at.%,up to 9 Pd, 4 Pt, and 2 Ru, with zoning with a Pt-rich rim consistent with a substitution of PtAs2 for

(Rh,Pd)AsS (16), see Figure 9.Small fragments of braggite of composition

(Pt,Pd,Ni)S were also identified. Most PGMs aredispersed in the silicatic matrix, associated to


Mineralogical Composition of Cited Rocks

Dunite Olivine (≥ 90%) and pyroxenes-orthopyroxene (≤ 10%)

Peridotite A series of rocks composed of olivine (90–40%) and pyroxenes (≤ 60%)(predominantly orthopyroxene), and the more important rock is harzburgite

Pyroxenite Olivine (≤ 40%) and pyroxenes (≥ 60%) (predominantly clinopyroxene)

Gabbros Plagioclase (mainly calcic) + pyroxenes (predominantly clinopyroxene) + olivine (in order of importance, for example, olivine ≤ 10%)

Anorthosites This rock is on top of the layered sequence and is rich in plagioclase (≥ 90%)

Minerals Cited by Abbreviation (19) and General Formula

Olivine (Ol) Mg2SiO4

Orthopyroxene (Opx) (Mg,Fe)SiO3

Clinopyroxene (Cpx) Ca(Mg,Fe)Si2O6

Plagioclase (Pl) Mineral from feldspars series, where the component calcic is more commonin the mafic/ultramafic sequence: Ca(Al2Si2O8)

Metamorphic Minerals Cited by Abbreviation (19) and General Formula

Serpentine (Srp) Mg3(Si2O5)(OH)4

Chlorite (Chl) (Mg,Al,Fe)12[(Si,Al)8O20](OH)16

Talc (Tlc) Mg6(Si8O20)(OH)4

Actinolite (Ac) Ca2(Mg,Fe)5(Si8O22)(OH)2

Tremolite (Tr) Ca2Mg5(Si8O22)(OH)2

Anthophylite (Ath) (Mg,Fe)7(Si8O22)(OH)2

Fig. 9 An electron microprobe imageof a sperrylite crystal associated withkammererites (matrix) near largecrystals of chromites

prominent chlorite cleavage; a few crystals appearas inclusions in the chromite grains. The chon-drite-normalised signature is similar to those of theIpanema Complex.

ConclusionsThe associations and arrangements of rocks

and minerals in the Santa Cruz massif (IpanemaComplex) with chromitite levels on top of meta-peridotites is the first evidence for an intrusiveorigin of the body. The cumulate texture in themetaultramafic parts (metamorphosed peridotites)and the Cr-spinel crystals are typically encounteredin stratiform complexes. The gradation of massiveand disseminated ore, and the variation in thegranulation of the chromites associated to a lowCr/Fe ratio (~ 2.0) support this conclusion.

A large number of chromite crystals with lowMg/Fe2+ values changed during serpentinisation,and this is thought to be related to thePGM/(PGE + Au) content. As these bodies, havePGM inclusions, more examination is required at

the Ipanema Complex, Pedra Branca (Ceará) andAlvorada de Minas (Minas Gerais), and furtherwork is planned.

Alluvial placers are less important because oftheir limited distribution and much smaller vol-umes, but further work will be undertaken. Theorigins of the PGE seem to be associated to maficlenses along the Bom Sucesso stream, where thebulk composition yield (Pt, Pd) >> (Os, Ir, Ru,Rh). Another hypothesis concerns their relation-ship with metasediments (quartzites andconglomerates), due to the constant presence ofAu (in quantities similar to the PGMs) and dia-monds. This hypothesis links these minerals to theEspinhaço Supergroup, but again, more studies arenecessary, and there is always the possibility offinding other deposits.

AcknowledgmentsThe author wishes to thank D. H. Verdugo for helping in the

composition of Figures and Tables. The author is also gratefulto the referee for helpful suggestions, and to E. C. Daitx for hishelp in simplification of the final text.


References1 L. C. Cabri, The platinum-group minerals, in:

Platinum-Group Elements: Mineralogy, Geology,Recovery, ed. L. J. Cabri, Can. Inst. Min. Metall.,Spec. Vol. 23, 1981, pp. 83150, reprinted 1989

2 R. G. Cawthorn, Platinum Metals Rev., 1999, 43, (4),146

3 A. Ferrario and G. Garuti, Platinum-group mineralsin chromite-rich horizons of the NiquelândiaComplex (Central Goiás, Brazil), Proc. Geo-Platinum Symp., Essex, U.K., 1987, pp. 261272

4 C. F. Ferreira Filho, A. J. Naldrett and M. Asif,Distribution of platinum group elements in theNiquelândia layered mafic-ultramafic intrusion,Brazil: implications with respect to exploration, Can.Mineral., 1995, 33, 165

5 E. S. Medeiros and C. F. Ferreira Filho,Caracterização geológica e estratigráfica das miner-alizações de Pt e Pd associadas à zona máficasuperior do complexo máfico-ultramáfico deNiquelândia, GO, Rev. Bras. Geoc., 2001, 31, (1), 29

6 R. P. Schouwstra, E. D. Kinloch and C. A. Lee,Platinum Metals Rev., 2000, 44, (1), 33

7 G. Von Gruenewaldt, L. J. Hulbert and A. J.Naldrett, Contrasting platinum-group element con-centration patterns in cumulates of the Bushveldcomplex, Mineral. Dep., 1989, 24, 219

8 F. F. De Almeida, Y. Hasui, B. B. Brito Neves andR. A. Fuck, Brazilian structural provinces: an intro-duction, Earth Sci. Rev., 1981, 17, 1

9 K. L. Kimball, Effects of hydrothermal alterationon the compositions of chromian spinels, Contr.Miner. Petrol., 1990, 105, 337

10 N. Angeli, M. E. Fleet, Y. Thibault and M. A. F.Candia, Metamorphism and PGE-Au content ofchromitite from the Ipanema mafic/ultramafic com-plex, Minas Gerais, Brazil, Mineral. Petrol., 2001, 71, 173

11 D. J. M. Burkhard, Accessory chromium spinels:their coexistence and alteration in serpentinites,Geochim. Cosmochim. Acta, 1993, 57, 1297

12 K. Yang and P. K. Seccombe, Platinum-group min-erals in the chromitites from the Great SerpentineBelt, NSW, Australia, Mineral. Petrol., 1993, 47, 263

13 M. Beeson and E. D. Jackson, Chemical composi-tions of altered chromites from the Stillwatercomplex, Montana, Am. Mineral., 1969, 54, 1084

14 M. A. F. Candia and J. C. Gaspar, Chromian spinelsin metamorphosed ultramafic rocks from MangabalI and II complexes, Goiás, Brazil, Mineral. Petrol.,1997, 60, 27

15 M. E. Fleet, N. Angeli and Y. Pan, Oriented chloritelamellae in chromite from Pedra Branca mafic-ultra-mafic complex, Ceará, Brasil, Am. Mineral., 1993, 78,68

16 N. Angeli, M. E. Fleet, D. M. Kingston and J. A.Nogueira Neto, Ir-bearing sperrylite and Pd-bearinghollingworthite in chromitites from the PedraBranca Complex, Ceará, Brazil, Brazilian Meetingon PGEs, I, Brasília, 1993, pp. 4446

17 N. Angeli, W. Teixeira, L. Heaman, M. Moore, M.E. Fleet and K. Sato, Geochronology of theIpanema Layered mafic-ultramafic Complex, MinasGerais, Brazil: evidence of extension at the meso-neoproterozoic time boundary, Int. Geol. Rev., 2004,46, 730

18 N. Angeli, Pesquisa dos jazimentos de níquel egeologia da Folha Ipanema, MG, Ph.D. Thesis,University of São Paulo, Brazil, 1988, p. 290

19 R. Kretz, Symbols for rock-forming minerals, Am.Mineral., 1983, 68, 277

20 T. N. Irvine and T. C. Findlay, Alpine-type peridotitewith particular reference to the Bay of Islands IgneousComplex, Publ. Earth Phys. Branch, Dept. Energy,Mines and Resources, Canada, 1972, 32, (3), 97

21 A. J. Naldrett and G. Von Gruenewaldt,Association of platinum-group elements withchromitites in layered intrusion and ophiolite com-plexes, Econ. Geol., 1989, 84, 180

22 L. G. Knauer and J. H. Grossi Sad, Geologia daFolha, Minas Gerais, Projeto Espinhaço,COMIG/UFMG, Belo Horizonte, 1994, pp. 138244

23 N. Angeli and S. R. F. Vlach, Chromite composi-tion, metamorphism, and PGM distribution inchromitites from the Espinhaço ridge, Brazil,Applied Mineralogy: Developments in Science andTechnology, ICAM, Aguas de Lindoia, 2004, 2, 849

24 A. de C. Zapparoli, Os Depósitos de Cromita daBorda Leste da Serra do Espinhaço Meridional,Minas Gerais: Petrologia, Quimismo e ImplicaçõesGenéticas, Diss. Mestrado (M.Sc.), UNESP, RioClaro, 2001, 133 pp.

25 J. P. Cassedane, J. Jedwab and J. N. Alves, Apportdune prospection systématique à létude de loriginede lor et du platine alluviaux de Córrego BomSucesso (Serro - Minas Gerais), An. Acad. Bras.Ciênc., 1996, 68, 569

26 J. P. Cassedane and J. N. Alves, Palladium and plat-inum from Córrego Bom Sucesso, Minas Gerais,Brazil, Mineral. Rec., 1992, 23, 471

27 L. C. Cabri, D. C. Harris and T. W. Weiser,Mineralogy and distribution of platinum-groupminerals (PGM) placer deposits of the world,Explor. Min. Geol., 1996, 5, 73

28 M. E. Fleet, C. M. De Almeida and N. Angeli,Botryoidal platinum, palladium and potarite fromthe Bom Sucesso stream, Minas Gerais, Brazil: com-positional zoning and origin, Can. Mineral., 2002,40, 341

29 F. K. Grange, PGM occurrence in secondarydeposits, with emphasis on methods of recoveryand observations for temperature climate explo-ration, M.Sc. Thesis, University of Wales, Cardiff,U.K., 1996, 126 pp.

30 J. F. W. Bowles, The development of platinum-group minerals in laterites, Econ. Geol., 1986, 81,1278

31 R. R. Pessoa and C. J. Archanjo, Tectônica deempurrões na região de Tróia, CE, XXXIII Congr.Bras. Geol., Rio de Janeiro, 1984, Vol. 4, pp. 1721

32 N. Angeli, Novas considerações sobre o Complexode Pedra Branca, Ceará, UNIFOR, 1979, InternalReport, Fortaleza, 23 pp.


The Author

Nelson Angeli graduated from the University of São Paulo (USP-São Paulo) in1973. In the 1970s he worked in prospecting and exploration of mineral deposits. Since 1981 he has been a Professor at the University of São Paulo State(UNESP–Rio Claro). From 1991 to 1992 he was a Post-Doctoral Fellow at theUniversity of Western Ontario, Canada. Much of his research has been onmagmatic ores and their country rocks and lateritic ore deposits (Ni, Mn, and Al).Since 1992 he has worked with PGM/PGE + Au associated to mafic-ultramaficrocks and chromitites.He is currently a member of the Commission on Ore Mineralogy of the InternationalMineralogical Association.http://petro.rc.unesp.br/docentes/nelson/nelson.html

PROPERTIESDetermination of Diffusion Coefficient ofHydrogen in Metals and Their Elastic Modulus byGeneralised ImpedanceP. ZOLTOWSKI and B. LEGAWIEC, J. Electroanal. Chem., 2004,572, (2), 205210

Transport of H in elastic metals has been analysedin terms of an impedance-like non-linear transferfunction (TF). The equilibrium in a membrane wasperturbed by application of a sinusoidal signal of con-centrations of H, of large amplitude, to a surface. Thefundamental harmonics of periodically reproducibleflux at this surface is considered as the response. TheTF is defined as the ratio of the signal to theresponse. The TF was used in determining the diffu-sion coefficient of H in α-phase Pd-H andPd81Pt19-H, and their bulk elastic moduli.

Gas Loading of Deuterium in Palladium at LowTemperatureF. SCARAMUZZI, J. Alloys Compd., 2004, 385, (12), 1927

An experimental technique that can be used to mea-sure the absorption of H or D gas in a thin Pd sample(1) at low temperature is described. For D, the resultsconsisted of measurements of the equilibrium loadingratio, X, as a function of pressure, on (1) 3.6 µm thickat 150 K. Values of X ≤ 1 were measured at pressuresof < 1 bar. The electrical resistance of (1) was mea-sured as function of temperature and X.

Effect of Hydrogen on the Electrical Resistance ofMelt-Spun Mg90Pd10 Amorphous AlloyS. NAKANO, S. YAMAURA, S. UCHINASHI, H. KIMURA and A.INOUE, Sens. Actuators B: Chem., 2005, 104, (1), 7579

The electrical resistance of the title alloy (1)increased after electrochemical H charging anddecreased after H discharging in 6 N KOH solution.The electrical resistance of (1) immersed in H-dis-solved H2O increased with immersion time and theincrease was dependent on the H concentration in theH2O. (1) may find use as a H sensor in H2O.

CHEMICAL COMPOUNDSA High-Pressure and High-Temperature Synthesisof Platinum CarbideS. ONO, T. KIKEGAWA and Y. OHISHI, Solid State Commun.,2005, 133, (1), 5559

Pt carbide (1) was synthesised using high pressureand high temperature in a laser-heated diamond anvilcell. (1) has a rock-salt type structure, with spacegroup Fm3m and cubic symmetry. (1) remains stableto ≤ 120 GPa. After decompression, the new high-pressure phase was recoverable at ambient pressure.

Cyclometalated Tridentate C-N-N Ligands with anAmine or Amido Donor in Platinum(II) andPalladium(II) Complexes and a Novel PotassiumAlkoxide AggregateD. SONG and R. H. MORRIS, Organometallics, 2004, 23, (19),44064413

2-Phenyl-6-(2-aminoisopropyl)pyridine (papH2) wasused to prepare Pt(papH)Cl (1) and Pd(papH)Cl. Inboth complexes the κ3N,N,C tridentate papH formedtwo five-membered rings with the metal, one ofwhich was created by cyclometallation of the ortho Cof the phenyl group. (1) reacted with KOtBu to give[Pt(pap)]2(KCl)(KOtBu)8 (2). The novel structure of(2) involves two Pt(pap) moieties being attached tothe K9O8Cl core of the K alkoxide aggregate.

Purine-Based Carbenes at Rhodium and IridiumJ. SCHÜTZ and W. A. HERRMANN, J. Organomet. Chem., 2004,689, (19), 29952999

Purine-based carbenes were attached to Rh and Irthrough the in situ deprotonation of the respectiveazolium salts. Trimethyloxonium tetrafluoroboratewas reacted with caffeine to give 1,3,7,9-tetramethylx-anthinium tetrafluoroborate. The salt and7,9-dimethylhypoxanthinium iodide were used as aconsecutive precursor to form Rh (I) and Ir (I) car-benes, [M(L)(LCarbene)2]I and M(L)(LCarbene)(I) (where M= Rh, Ir; LCarbene = 1,3,7,9-tetramethylxanthine-8-yli-dene, 7,9-tetramethylhypoxanthine-8-ylidene; L =η4-1,5-COD, CO).

On the Silicides EuIr2Si2 and Lu5Si3

U. CH. RODEWALD, B. HEYING, D. JOHRENDT and R. PÖTTGEN,Z. Naturforsch., 2004, 59b, (9), 969974

EuIr2Si2 (1) was synthesised from the elements in asealed Ta tube in a H2O-cooled sample chamber of aninduction furnace. Lu5Si3 was obtained by arc-meltingof the elements. The Ir and Si atoms in (1) build up a3D [Ir2Si2] network with IrSi and SiSi interactions.The Eu atoms fill cages within the network.

High-Pressure Synthesis of Metallic PerovskiteRuthenate CaCu3Ga2Ru2O12

S.-H. BYEON, S.-S. LEE, J. B. PARISE, P. M. WOODWARD and N. H.HUR, Chem. Mater., 2004, 16, (19), 36973701

CaCu3Ga2Ru2O12 (1) was synthesised at 12.5 GPaand 1200ºC and recovered to room pressure and tem-perature conditions. In (1) the Ga and Ru cations inthe perovskite-like structure are disordered over theoctahedral sites. Magnetic susceptibility (at 5300 Kin an applied magnetic field of 5 kG) and electricalresistivity (at 10400 K) measurements showed that(1) is a Pauli-paramagnetic conductor. (1) showsmetallic conductivity in a perovskite-type oxide thatcontains the Ru(V) oxidation state.


ABSTRACTSof current literature on the platinum metals and their alloys

DOI: 10.1595/147106705X25651

ELECTROCHEMISTRYElectrochemical Quartz Crystal Nanobalance toDetect Solvent Displacement by pH-InducedConformational Changes of Proteins at PtN. P. COSMAN and S. G. ROSCOE, Anal. Chem., 2004, 76, (19),59455952

The adsorption behaviour of the proteins holo- andapo-α-lactalbumin at a Pt electrode (1) was studied inelectrolyte solutions of pH < 2, 7.4 and 11 at 298 K.Electrochemical quartz crystal nanobalance frequen-cy measurements gave a measure of nanogramchanges on (1) due to solvent displacement by theadsorbed protein. Simultaneous CV charge transfermeasurements gave protein surface concentration.

Solvent Effects on Charge Transport through SolidDeposits of [Os(4,4'-diphenyl-2,2'-dipyridyl)2Cl2]R. J. FORSTER, J. IQBAL, J. HJELM and T. E. KEYES, Analyst, 2004,129, (12), 11861192

Mechanically attached, solid-state films (1) of thetitle complex were formed on Au macro- and micro-electrodes. The voltammetric response of (1)associated with the Os2+/3+ redox reaction is similarof that observed for an ideal reversible, solutionphase redox couple when the contacting electrolytecontains 40% v/v of MeCN. Preferential solvation ofthe redox centres by MeCN allows the incorporationof charge compensating counterions.

PHOTOCONVERSIONTriplet Exciton Diffusion and Delayed InterfacialCharge Separation in a TiO2/PdTPPC Bilayer:Monte Carlo SimulationsJ. E. KROEZE, T. J. SAVENIJE, L. P. CANDEIAS, J. M. WARMANand L. D. A. SIEBBELES, Sol. Energy Mater. Sol. Cells, 2005, 85,(2), 189203

Nanosecond photoexcitation of a bilayer of anataseTiO2 coated with Pd tetrakis(4-carboxyphenyl)por-phyrin (1) causes a delayed after-pulse growth in theconductivity over many µs. The slow diffusion of (1)triplet excitons was followed by electron injectioninto the TiO2 conduction band. Monte Carlo calcula-tions of the exciton diffusion and exciton-excitonannihilation describe the experimentally observedtemporal form and intensity dependence.

Amphiphilic Polypyridyl Ruthenium Complexeswith Substituted 2,2'-Dipyridylamine Ligands forNanocrystalline Dye-Sensitized Solar CellsP. WANG, R. HUMPHRY-BAKER, J. E. MOSER, S. M.ZAKEERUDDIN and M. GRÄTZEL, Chem. Mater., 2004, 16,(17), 32463251

Ru(dcbpy)(L)(NCS)2 dye (dcbpy = 4,4'-dicarboxylicacid-2,2'-bipyridine; L = N,N-di(2-pyridyl)-dodecy-lamine or N,N-di(2-pyridyl)-tetradecylamine) can beused as solar cell sensitisers. Efficiencies of 8.2% atthe 100 mW cm2 irradiance of air mass 1.5 solar lightand ≥ 8.7% at lower light intensities were achieved.

APPARATUS AND TECHNIQUEEthanol Gas Sensing Properties of Nano-Crystalline Cadmium Stannate Thick Films Dopedwith PtY.-L. LIU, Y. XING, H.-F. YANG, Z.-M. LIU, Y. YANG, G.-L. SHENand R.-Q. YU, Anal. Chim. Acta, 2004, 527, (1), 2126

Pt (0.12 at.%) was incorporated into nanocrys-talline CdSnO3 (1) by the impregnation technique.Conductance responses of thick films of (1) weremeasured after exposure to EtOH, CO, CH4, C4H10,gasoline and LPG at different operating tempera-tures. Sensors doped with Pt had good sensitivity andselectivity to EtOH vapour. The optimum sensitivitywas obtained when (1) was doped with 1.5 at.% Pt.

All-Optical Hydrogen-Sensing Materials Based onTailored Palladium Alloy Thin FilmsZ. ZHAO, Y. SEVRYUGINA, M. A. CARPENTER, D. WELCH andH. XIA, Anal. Chem., 2004, 76, (21), 63216326

The phase-dependent H time response characteris-tics of 20 nm thick Pd-Au (Ag) films (1) wereinvestigated via optical reflectance measurements.They displayed a strong dependence on the α, mixedα/β and β Pd-hydride phases formed in (1). Theresponse time peaks in the α → β phase transitionregion were 1625 s at 0.4% H2 for Pd0.94Ag0.06 and 405s at 1% H2 for Pd0.94Au0.06. The addition of Au (up to40%) shifted and then inhibited the α → β phasetransition region. Pd0.6Au0.4 was above the criticalisotherm threshold for undergoing a phase transitionand had response time < 50 s.

HETEROGENEOUS CATALYSISParallel IR Spectroscopic Characterization of COChemisorption on Pt Loaded ZeolitesP. KUBANEK, H.-W. SCHMIDT, B. SPLIETHOFF and F. SCHÜTH,Microporous Mesoporous Mater., 2005, 77, (1), 8996

Parallel characterisation of Pt-containing zeolitesZSM-5 and Y was achieved using FTIR spectroscopyin transmission mode combined with a focal planearray detector. The Pt species in the zeolite wereinvestigated using the chemisorption of CO. The 8-fold degree of parallelisation lowered the total timerequired for data collection.

Conversion of Halon 1211 (CBrClF2) overSupported Pd CatalystsH. YU, E. M. KENNEDY, MD. A. UDDIN, A. A. ADESINA and B.Z. DLUGOGORSKI, Catal. Today, 2004, 97, (23), 205215

The conversion of halon 1211 was investigatedover γ-Al2O3 and 0.5% Pd supported on Al2O3, fluo-rinated Al2O3, AlF3, and Al2O3 pretreated with CH4

and CHClF2, at 443523 K. The Pd was transformedto Pd carbide in the CH4 treated Pd/Al2O3, but not inthe CHClF2 treated Pd/Al2O3 (Al2O3 was partiallyfluorinated). In the absence of H2, the conversion ofhalon 1211 over Al2O3 and Pd/Al2O3 gave a similarproduct profile and the reactions follow a heteroge-neous halogen exchange reaction pathway.



Heck Reaction Catalyzed by Nanosized Palladiumon Chitosan in Ionic LiquidsV. CALÒ, A. NACCI, A. MONOPOLI, A. FORNARO, L. SABBATINI,N. CIOFFI and N. DITARANTO, Organometallics, 2004, 23, (22),51545158

Pd nanoparticles/chitosan (1) was very effective forthe Heck reaction of aryl bromides and activated arylchlorides in tetrabutylammonium bromide with tetra-butylammonium acetate as base. Conversion ofbromobenzene or p-nitrochlorobenzene into cinna-mates took only 15 min. The Pd colloids arestabilised by the solvent. Any PdH is readily neu-tralised by the base. (1) can be recycled.

One-Pot Synthesis of Recyclable PalladiumCatalysts for Hydrogenations and CarbonCarbonCoupling ReactionsN. KIM, M. S. KWON, C. M. PARK and J. PARK, Tetrahedron Lett.,2004, 45, (38), 70577059

Pd nanoparticles (1) were prepared from Pd(PPh3)4

in tetra(ethylene glycol) and Si(OMe)4 (or Ti(OiPr)4).(1) were then encapsulated in SiO2 (or TiO2) matrixby treatment with H2O. SiO2 (or TiO2)/TEG/Pdshowed high catalytic activity in alkene and alkynehydrogenations and in Suzuki-Miyaura, Sonogashira,Heck-Mizoroki and Stille reactions.

Surface Study of Rhodium NanoparticlesSupported on AluminaA. MAROTO-VALIENTE, I. RODRÍGUEZ-RAMOS and A.GUERRERO-RUIZ, Catal. Today, 2004, 9395, 567574

Rh nanoparticles (1 and 3 wt.%)/Al2O3 were stud-ied by H2 and CO adsorption microcalorimetry andby IR spectroscopy of the chemisorbed CO. The n-butane hydrogenolysis reaction test was employed toexamine surface sites. The energetic distribution ofsurface sites depended slightly on the metal loadingand can be modified by the pretreatment conditions.Partially reduced Rh atoms stabilised by Cl ionsremaining from the precursor were found. Theincreased density on Rh (1 1 1) planes on 3 wt.%Rh/Al2O3 treated with H2O enhanced both activityfor the hydrogenolysis and selectivity towards ethane.

HOMOGENEOUS CATALYSISPalladium-Catalyzed Addition of Mono- andDicarbonyl Compounds to Conjugated DienesA. LEITNER, J. LARSEN, C. STEFFENS and J. F. HARTWIG, J. Org.Chem., 2004, 69, (22), 75527557

An intermolecular addition of the α-CH bond ofmonocarbonyl and 1,3-dicarbonyl compounds todienes was achieved in high yields using a catalystgenerated in situ from CpPd(allyl) (1) and 1,3-bis(dicy-clohexylphosphino)propane. The common additionsof cyanoesters, malonitrile and α-sulfonyl esters read-ily took place; unusual additions of ketones, lactones,esters and nitriles were also possible. The first enan-tioselective version of this reaction was achievedusing (1) and a Josiphos ligand with ≤ 81% ee.

General and Efficient Methodology for theSuzuki–Miyaura Reaction in Technical Grade 2-PropanolO. NAVARRO, Y. OONISHI, R. A. KELLY, E. D. STEVENS, O. BRIELand S. P. NOLAN, J. Organomet. Chem., 2004, 689, (23),37223727

Pd N-heterocyclic carbenes or phosphines wereinvestigated in the Suzuki-Miyaura reaction usingtechnical grade 2-propanol (1) as solvent and K t-butoxide as base. The cross-coupling of electron-richaryl chlorides with sterically hindered aryl boronicacids gave di- and tri-ortho-substituted biaryls in shorttimes. (1) did not require pre-drying or purification.

Palladium-Catalyzed Intramolecular αα-Arylationof Aliphatic Ketone, Formyl, and Nitro GroupsH. MURATAKE, M. NATSUME and H. NAKAI, Tetrahedron, 2004,60, (51), 1178311803

PdCl2(Ph3P)2Cs2CO3 was used for the intramolec-ular arylation of substrates bearing a ketone, formylor nitro terminating group to give carbocyclics.Arylation of the ketones gave benzene-annulatedbridged or spirocycloalkanone derivatives, dependingon the type of cyclisation precursors. Arylation informyl compounds occurred in the α-position or atthe carbonyl C depending on the type of cyclisationprecursors and on the solvent. An α-arylated sec-ondary nitro group was partially transformed toketone, whereas a tertiary nitro group was partiallyeliminated to afford a styrene-type olefin.

Successful Development and Scale-up of aPalladium-Catalysed Amination Process in theManufacture of ZM549865G. E. ROBINSON, O. R. CUNNINGHAM, M. DEKHANE, J. C.McMANUS, A. OKEARNEY-McMULLAN, A. M. MIRAJKAR, V.MISHRA, A. K. NORTON, B. VENUGOPALAN and E. G. WILLIAMS,Org. Process Res. Dev., 2004, 8, (6), 925930

Pd-catalysed amination and ester hydrolysis hasbeen used to synthesise a key intermediate in themanufacture of ZM549865 (a 5-HT receptor antago-nist). Pd dibenzylideneacetone was employed for theamination of ethyl 8-bromo-6-fluoro-4-oxo-4H-2-chromenecarboxylate. Amination at 125ºC instead of80ºC and optimising the reaction conditionsincreased the overall yield from 44% to ~ 70% andreduced the reaction time from days to hours.

A Convenient Synthesis of High-LoadedPalladium(II) ROMP PolymersD. C. BRADDOCK, D. CHADWICK and E. LINDNER-LÓPEZ,Tetrahedron Lett., 2004, 45, (49), 90219024

A method for the immobilisation of two O,O'-chelate Pd(II) complexes via ROMP has beenestablished. The monomer bis[1-(5-norbornen-2-yl)butan-1,3-dionato]palladium(II) (1) was readilyprepared from 5-acetoacetyl-2-norbornene andNa2PdCl4. (1) underwent ROMP under mild condi-tions to give a highly-loaded Pd(II)-containingpolymer (Pd, 23 wt.%).

Rhodium(II)-Catalyzed Aziridination of Allyl-Substituted Sulfonamides and CarbamatesA. PADWA, A. C. FLICK, C. A. LEVERETT and T. STENGEL, J. Org.Chem., 2004, 69, (19), 63776386

Unsaturated sulfonamides underwent intramolecu-lar aziridination in the presence of PhI(OAc)2, MgOand Rh2(OAc)4 to give bicyclic aziridines in excellentyield. The resulting azabicyclic sulfonamides with theaddition of p-TsOH in MeOH underwent exclusiveopening of the aziridine ring at the most substitutedposition giving six- and seven-membered ring prod-ucts in high yield.

Iridium-Catalyzed Hydroboration of Alkenes withPinacolboraneY. YAMAMOTO, R. FUJIKAWA, T. UMEMOTO and N. MIYAURA,Tetrahedron, 2004, 60, (47), 1069510700

Ir(I) phosphine complexes (1) are excellent catalystsfor room temperature hydroboration of terminal andinternal alkenes possessing an aliphatic or aromaticsubstituent on the vinylic C with pinacolborane.[Ir(cod)Cl]2/2dppm was the best catalyst system forhydroboration of aliphatic terminal and internalalkenes at room temperature; addition of the B atomto the terminal C of 1-alkenes was achieved with >99% selectivity. For vinylarenes such as styrene,[Ir(cod)Cl]2/2dppe gave the best yields. (1) exhibitedhigher levels of catalyst activity and selectivity thanthe corresponding Rh complexes.

FUEL CELLSPreparation and Characterization of CarbonSupported Pt and PtRu Alloy Catalysts Reducedby Alcohol for Polymer Electrolyte Fuel CellT. KIM, M. TAKAHASHI, M. NAGAI and K. KOBAYASHI,Electrochim. Acta, 2004, 50, (23), 813817

Highly dispersed fine Pt and PtRu alloy particles onC support were prepared by a simple alcohol-reduc-tion method using polyvinylpyrrolidone as astabiliser. Highly uniform nanoparticles wereobtained. The structure and morphology of the cata-lysts could be readily controlled. The catalystsshowed promising activity in O reduction and MeOHoxidation.

Methanol Electro-Oxidation and Direct MethanolFuel Cell Using Pt/Rh and Pt/Ru/Rh AlloyCatalystsJ.-H. CHOI, K.-W. PARK, I.-S. PARK, W.-H. NAM and Y.-E. SUNG,Electrochim. Acta, 2004, 50, (23), 783786

The title catalysts (1) for application in DMFCswere prepared by a borohydride reduction methodcombined with freeze drying. (1) had specific surfaceareas of ~ 6575 m2 g1. XRD patterns establishedthat (1) were well alloyed and the average size of (1)was confirmed by TEM. (1) of composition Pt/Rh(2:1) and Pt/Ru/Rh (5:4:1) had better catalytic activ-ities for MeOH electrooxidation than Pt or Pt/Ru(1:1), respectively.

Performance of Methanol Oxidation Catalysts withVarying Pt:Ru Ratio as a Function of TemperatureA. J. DICKINSON, L. P. L. CARRETTE, J. A. COLLINS, K. A.FRIEDRICH and U. STIMMING, J. Appl. Electrochem., 2004, 34,(10), 975980

At 25ºC, a Pt-rich 3:2 Pt:Ru atomic ratio DMFC-type catalyst was more active for MeOH oxidationthan a 1:1 catalyst. Only the Pt is active towardsMeOH dehydrogenation, as this process requireshigh thermal activation on Ru sites. At 65ºC, the 1:1catalyst gave much higher currents across the entirepolarisation range. At 45ºC, the 3:2 catalyst is betterat lower current values, while the 1:1 catalyst is supe-rior at higher current densities.

MEDICAL USESSynthesis and DNA-Binding Properties ofBinuclear Platinum Complexes with Two trans-[Pt(NH3)2Cl]+ Units Bridged by 4,4'-DipyridylSulfide or SelenideG. ZHAO, X. HU, P. YU and H. LIN, Transition Met. Chem., 2004,29, (6), 607612

trans-[Pt(NH3)2Cl]2(dpsu)(NO3)2 (1) and trans-[Pt(NH3)2Cl]2(dpse)(NO3)2 (dpsu = 4,4'-dipyridylsulfide; dpse = 4,4'-dipyridyl selenide) were preparedfor use as potential antitumour agents. Comparedwith [cis-Pt(NH3)2Cl(4-methylpyridine)]NO3, (1)exhibits an almost two-fold stronger DNA-bindingability. (1) may bind bifunctionally to DNA.

Synthesis, Characterization, and Cytotoxicities ofPalladium(II) and Platinum(II) ComplexesContaining Fluorinated PyridinecarboxaldiminesS. J. SCALES, H. ZHANG, P. A. CHAPMAN, C. P. McRORY, E. J.DERRAH, C. M. VOGELS, M. T. SALEH, A. DECKEN and S. A.WESTCOTT, Polyhedron, 2004, 23, (13), 21692176

The condensation of 2-pyridinecarboxaldehydewith primary amines containing F groups gave thecorresponding pyridinecarboxaldimine ligands (N-N'). Addition of these ligands to [MCl2(coe)]2 (M =Pt, Pd; coe = cis-cyclooctene) gave cis-MCl2(N-N') (1)in moderate to high yields. Cytotoxicities of (1) wereinvestigated against OV2008 (human ovarian carci-noma) and the analogous cisplatin-resistant C13.

The Potential Use of Rhodium N-HeterocyclicCarbene Complexes as Radiopharmaceuticals:The Transfer of a Carbene from Ag(I) toRhCl3·3H2OC. A. QUEZADA, J. C. GARRISON, M. J. PANZNER, C. A. TESSIERand W. J. YOUNGS, Organometallics, 2004, 23, (21), 48464848

The first reported N-heterocyclic carbene transferfrom Ag(I) to RhCl3·3H2O was used to prepare twonew Rh N-heterocyclic carbenes (1). The syntheseswere carried out in DMSO at 100ºC for 1 h. The veryhigh stability of (1) indicates that 105Rh complexes ofbisimidazole ligands with targeting substituents suchas peptides may be used for radiation therapy.


METALS AND ALLOYSIridium-Based SuperalloyNAT. INST. MATER. SCI. Japanese Appl. 2004-197,223

A superalloy (1) with a high melting point, excellentcreep characteristics and sufficient room temperatureductility is obtained by heat treating an Ir-basedsuperalloy containing 1922 at.% W at 14001800ºC.(1) can be used in high temperature and high stressequipment, such as in jet engines, rocket engines, gasturbines for power generation, etc.

APPARATUS AND TECHNIQUEDye Sensitised Solar Cell EPFL European Appl. 1,473,745

A dye sensitised solar cell is a regenerative photo-electrochemical cell comprising a photoanode, wherethe dye is an amphiphilic Ru polypyridyl complex. Astabilising compound comprising a hydrophobic partand an anchoring group, such as decylphosphonicacid, is co-adsorbed with the dye on the metal oxidesemiconductive (MOS) layer of the photoanode.Electrolyte (1) is put between the MOS and a trans-parent or translucent counter electrode. (1) comprisesa redox system of an electrochemically active salt.

Organic Electroluminescent Material and DeviceSONY CORP European Appl. 1,486,552

A heterocycle-containing Ir complex compound (1)with light emissive properties in the green to blueregion contains, for example, an alkyl group, a phenylgroup, an alkyloxy group, etc. An organic electrolu-minescent device contains an organic layer comprisedof several layers, at least one of which includes (1),resulting in higher efficiency and extended lifespan.

Optical CO2 and Combined O2/CO2 Sensors GAS SENSOR SOLUTIONS LTD World Appl. 2004/077,035

An improved CO2 sensor comprises a pH indicator,such as hydroxypyrene trisulfonate, fluorescein, etc.; along-lived reference luminophore of a luminescent Ptgroup metal complex; and a porous sol-gel matrix,such as methyltriethoxysilane. In a COx sensor, theluminophores are RuII complex-doped sol-gel particles.An O2/CO2 sensor is also claimed. The CO2 sensorsare less sensitive to the moisture content of the envi-ronment and to O2 levels during normal working.

Producing Plasma Display PanelsMATSUSHITA ELECTRIC IND. U.S. Patent 6,805,601

A high-luminance and high-image-quality plasmadisplay panel (PDP) with reduced panel yellowing isclaimed. The formation of electrodes in the PDPincludes a base layer formation step where the baselayer (1) contains metal oxides of Ni, Co, Fe, Zn, In,Cu, Ti, etc., on a glass substrate. A precipitation pro-moting step deposits Pd on regions of (1) where ametal layer will be formed in the metal forming step.

Platinum Compounds for Nucleic Acid LabellingSTRATAGENE CALIFORNIA U.S. Patent 6,825,330

Pt-based compounds for labelling biomolecules,such as nucleic acids, are irreversibly attached to thetarget biomolecule via coordination of a Pt(II) metalcentre with N or S atoms. A detectable marker, suchas a fluorophore, a chromophore, a radiolabel, anenzyme or an affinity tag is used. Methods of makingthe Pt-based labelling compounds are given.

HETEROGENEOUS CATALYSISSupported Nanopalladium Catalyst for C-C CouplingCOUNCIL SCI. IND. RES. European Appl. 1,464,394

A reusable ligand-free heterogeneous nano Pd(0)catalyst (1) for C-C coupling reactions of haloarenes,including unreactive chloroarenes, in the presence ofbase, contains 0.13 mol% of Pd with respect to thesubstrate. (1) is prepared by an exchange of PdCl42

followed by reduction on the support. The support isa layered double hydroxide material of alternatingcationic (Mg2+, Mn2+, Fe2+, Co2+and Ni2+) and anionic(nitrate, carbonate and chloride) layers, and S'-NR3X.S' is an unmodified surface support of resin or SiO2,R is an alkyl group and X is Cl, Br, I, etc.

Diesel Engine Exhaust Gas CatalystICT CO LTD European Appl. 1,475,141

A catalyst (1) is claimed which purges a dieselengine exhaust gas of HC, CO, and soluble organicfractions (SOF) and reduces particulate emission. (1)is produced by adding a Pt group metal component ofPt, Pd and/or Rh into a slurry of SiO2-Al2O3, whichinduces chemical adsorption. β-Zeolite is added tothe mixture. A refractory 3D structure is then dippedin this mixed slurry to induce deposition of the cata-lyst component, followed by calcining.

Capturing Ruthenium from Gaseous EffluentCIE. GEN. MATIERES NUCL. World Appl. 2004/071,640

Ru present in a gaseous effluent is captured by usinga solution or an aqueous paste of a glycol alkylenepolymer (1) or glycol alkylene copolymer (2), wherethe alkylene(s) consist of 26 C atoms. The Ru cap-ture cartridge comprises a surface on which (1) or (2)is disposed. This facilitates the capture and chemicalreduction of Ru oxide, RuO4.

Selective Hydrogenation of AcetyleneBASF AG World Appl. 2004/085,353

A Pd-supported catalyst (1) containing 0.052.0wt.% Pd and La, Ti, Nb, K and/or Si metals has highethylene selectivity, even after a low temperaturereduction in the selective hydrogenation of acetyleneto ethylene. The support is impregnated with an aque-ous solution of tetra amine Pd hydroxide, followed bydrying and calcination. A second, and if necessary athird metal, are then impregnated. (1) is then reducedin H2 at 200600ºC for 15 hours.


NEW PATENTSDOI: 10.1595/147106705X25660

Improved Catalyst Charge DesignJOHNSON MATTHEY PLC World Appl. 2004/096,702

A catalyst charge for NH3 oxidation including theAndrussow process comprises a first stage NH3 oxi-dation catalyst, composed of a high surface area Ptgroup metal, capable of oxidising 2099% NH3

throughput to produce a first stage product gas com-prising unreacted NH3, O2 and NOx. A second stageNH3 oxidation catalyst is capable of completing theoxidation of unreacted NH3. Additional stages select-ed to provide absorbents/getters/catchment gauzes(Pd-< 5 wt.% Rh) are also included.

Isomerisation Catalyst to Convert HydrocarbonsUOP U.S. Patent 6,818,589

An isomerisation catalyst (1) for a selective upgradeof a paraffinic feedstock to obtain an isoparaffin-richproduct for blending into gasoline is claimed. It com-prises: a support of tungstated oxide or hydroxide ofa Group IVB metal, such as Zr; at least one lan-thanide element, such as Y, Yb, Ce, Ho, etc.; and0.012 mass%, on an elemental basis, of a Pt groupmetal, preferably Pt. (1) also comprises 0.150 mass%of a refractory inorganic oxide binder, such as Al2O3.

Treatment of Waste Water Containing OrganicsTANAKA KIKINZOKU KOGYO KK Japanese Appl. 2004-195,382

Waste H2O containing organic material of low mol-ecular weight (fatty acids) is treated by decompositionin the presence of a catalyst containing 0.052% Ptgroup metals supported on Al2O3, TiO2 and ZrO2,under pressure in an O2-containing gas (1). The gasphase total pressure at normal temperature is ≤ 3 atm.At 160180°C the O2 partial pressure is 12 atm. Theorganic materials are oxidised, removed and decom-posed. In (1) the molar ratio of O:fatty acid is 1.0:2.0.The Pt group metal is Ru, Rh, Pd, Os, Ir and Pt.

HOMOGENEOUS CATALYSISAsymmetric Hydrogenation of Hexahydroquinolines DSM IP ASSETS BV European Appl. 1,485,357

The asymmetric hydrogenation of 1-(4-methoxy-benzyl)-3,4,5,6,7,8-hexahydroisoquinolinium salts to(S)- (1) or (R)-1-(4-methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinolinium salts, using Ir or Rhcomplex catalysts having a chiral diphosphine ligand,produced superior optical yield. (1) are intermediateproducts in the manufacture of dextromethorphan,an antitussive agent for relief of coughs.

FUEL CELLSAerogel Type Pt-Ru/Carbon Catalyst for DMFCsKOREA INST. SCI. TECHNOL. U.S. Patent 6,809,060

An aerogel type Pt-Ru/C catalyst (1) for a DMFChas a microporous structure and long-term high cat-alytic activity. (1) is made by a sol-gel process. Solventis removed by supercritical drying. (1) contains 570wt.% of Pt and Ru, remainder C. The Pt :Ru atomicratio is from 1:4 to 4:1. The pH of the final solutionis adjusted to form a sol which is aged at 4090ºC.

Solid Polymer Fuel Cell ElectrodeHONDA MOTOR CO LTD Japanese Appl. 2004-186,142

An electrode structure for a solid polymer fuel cell,with excellent generating performance and durabilitycomprises a pair of electrode catalyst layers (1). (1)contains C particles carrying Pt and a polyelectrolytemembrane of sulfonated polyarylene polymer (2)between the layers. (1) has an ion exchange capacityof 1.72.3 meq g1. The insoluble component contentof (2) to N-methylpyrrolidone, after heating for 200h at 120°C is ≤ 70 wt.% of the total amount of (2).

ELECTRICAL AND ELECTRONICENGINEERINGMagnetic Recording Medium and Device TDK CORP European Appl. 1,485,910

A magnetic recording (MR) medium includes a seedlayer of Pt, Pd, Ru, Ag and/or Cu. A MR layer isformed on the seed layer. The MR layer comprises aplurality of laminated layers and a Ag, Au, Ru and Culayer (1). The laminated layers include Co, Ni and Fe,and Pt and Pd and (1) is interposed between. The MRmedium satisfies the expression 0 < Y/X ≤ 1.0,where X is the thickness of the seed layer, and Y isthe sum total of the thickness of (1) in the MR layer.

Magnetic Transducer with Multilayer LeadsHITACHI GLOB. STORAGE TECHNOL.U.S. Patent 6,813,121

A magnetic transducer (head) includes multilayeredelectrically conductive leads from a magnetic sensorwhich include a thin Ta seed layer followed by a thinCr seed layer and by a thicker Rh layer. The dual seedlayer significantly improves the Rh conductivity. TheTa/Cr/Rh leads can be used with hard bias structuresformed on a PtMn layer without having increasedresistance.

Spin Valve Sensor with Ultra-Thin FreelayersIBM CORP U.S. Patent 6,826,021

A spin valve (SV) sensor has a cap layer of Ta anda Cu layer beneath, and a unique freelayer structure.The freelayer structure includes: layers of first Ni-Fe,then Ru, then a Ni-Fe layer, a Co-Fe nanolayer ≤ 30Å and a spacer layer made of Cu adjacent to thenanolayer of Co-Fe. The net freelayer thickness is <50 Å. The thin structure has a high magnetoresistivecoefficient and soft magnetic properties.

Oxygen Diffusion Barrier for Semiconductor DevicesMICRON TECHNOL. INC U.S. Patent 6,830,983

The fabrication of high dielectric MIM (metal-insu-lator-metal) storage cell capacitors is claimed. A Sicontact connects the bottom electrode layer (1) in thecontainer with at least one associated transistordevice. A TiN barrier layer is formed over the Si con-tact. An O barrier layer with Pt stuffed with SiO2 isthen formed over the TiN layer under (1). A (1) isthen formed using Pt over the interior surfaces of acontainer linked with at least one transistor device onSi. A dielectric insulator and a top electrode follow.


This is the third in a series of short articles onlooking after thermocouples (1, 2). The first articleconsidered safeguarding performance while thesecond examined minimising drift. Compared withthe erroneous readings seen when a thermocoupledrifts, open circuit faults are immediately obvious.

An open circuit is usually caused by breakage ofa thermocouple limb, but always check for poorconnections to the compensating or connectingleads. Limb breakage generally occurs close to thehot junction where the wire is weakest and wherethe effects of contamination are greatest.

Contamination usually results in output drift,but may not if isolated in a short length of wire orin wire that is not in a significant temperature gra-dient. This parallels the wire bridge method ofcalibrating a thermocouple, when a gold wire isused to form the junction between the two limbsand fails at 1064.18°C. The gold wire does notaffect the thermocouple output.

Contaminants act to reduce the melting pointof the limb to below the maximum operating tem-perature, or to reduce the wire strength if a tensileload is present. The contaminant must alloy withPt and be present in significant local concentra-tions, generally at the grain boundaries.

If protective sheathing and 99.7% purity alumi-na ceramics are used, and attention is paid toassembly cleanliness, contamination is usually onlya problem where low melting point metal vapours(not oxides) are plentiful; more likely in a vacuumor reducing atmosphere. Contaminants thatreduce the melting point of Pt to < 1000°Cinclude P, As, Si, Sb, and Pb.

Metalclad or mineral-insulated thermocoupledesigns delay the effect of contamination on out-put, but ultimately cannot prevent failure if theconcentration is sufficient to cause the cladding tofail. In applications where the atmosphere is par-tially oxidising, metalclads have been seen with adark outer layer of immobilised oxidised contam-ination.

However, tensile loading is the more general

cause of limb breakage: just 28 g suspended for100 h will break a 0.5 mm Pt wire at 1400°C (at1200°C the load capacity is 45 g). Pt will form abamboo structure, that is, a chain of single grainseach occupying the full diameter of the wire andoften 1 mm long. Tensile breakage is then evidentas single crystal slip, although higher loads willproduce hot tears in either limb. To prevent tensileloading requires a systematic approach to eliminateboth static and cyclical loading.

Static loading is caused when the thermocouplewires support all or part of the weight of theceramic insulators. One-piece twin-bore insulatorscan be clamped at the head end but may fracturein service. Where an outer sheath is used the lowerend of the twin bore should rest on the end cap,with the bead in a ground-out recess 5 to 10 mmback.

Cyclic loading is due to thermal expansions andcontractions of the wires and insulators. The wiresmust be free to move within the insulator boresand must not be kinked. The bores should be wellformed, giving sufficient clearance. The wiresshould extend from the insulator separator to givea 5 mm clearance gap to the bead.

However, even the best kept platinum thermo-couples do not last forever. Within JohnsonMatthey, bare wire thermocouples employed instress rupture testing at 1400°C fail after manyhundreds of hours of use, even though the ther-mocouples are mechanically well supported andbeing used in a clean oxidising environment. Theeventual failure in these cases is due to evaporationof the wire through the formation of volatile Ptand Rh oxides.

R. WILKINSON


FINAL ANALYSIS

Thermocouples Open Circuit Faults

DOI: 10.1595/147106705X25462

References

1 R. Wilkinson, Platinum Metals Rev., 2004, 48, (2), 882 R. Wilkinson, Platinum Metals Rev., 2004, 48, (3), 145

Roger Wilkinson is a Senior Materials Scientist at Johnson MattheyNoble Metals in Royston, U.K. He has worked with platinumthermocouples since 1987 in manufacturing, calibration andcustomer technical support.

platinum metals review · platinum metals review a quarterly survey of research on the platinum...

Documents