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Supported Homogeneous CatalystsTRANSIT ION METAL COMPLEXES WI TH POLY MERIC LI GANDSBy Zofia M. Michalskaarid David E. WebsterInstitute of Polymers, TheTechnical University, Lodz, Poland

Chemistry Department, University of Hull

Almost all industrial catalysts are heterogeneous, the reaction takingplace on a solid surface. During thepast decade homogeneous catalysts,soluble in the liquidphase reactant, have received a great deal of attention,although they have so far found only limited industrial use, chiefly be-cause o the di$culty of their separation from the reaction products.More recently an intermediate type, made by attaching the active metalcomplex to an insoluble polymer support, has been found to o$er apromising new rangeof catalystsfor the future. I t i s likely that a largeproportion of these will be based on the platinum group metals.

A short review of catalysis by transitionmetal complexes with polymeric ligandscontributed to this journal by Manassen inI971 (I) had just three references. The 36references of this article are an indication ofthe growth of interest during the past twoyears. A wide-ranging review, in French,of catalysis by all types of metal organicpolymers covering the literature up to themiddle of 1971 is the only other availablesurveyof this topic (2).

Catalysts made by chemically bonding atransition metal complex to a polymer lie inbetween those usually classified as hetero-geneous and those classified as homo-geneous. They are, like most polymers,insoluble in a solvent, and in this sense theyare clearly heterogeneous. However, we have,for four reasons, chosen to call the systemshomogeneousJJ. First, because these com-plexes with polymeric ligands are preparedfrom the usual small complexes that areused as homogeneous catalysts. Secondly,they are studied under comparable conditionsto conventional homogeneous catalysts, forexample at temperatures below 100C.

Thirdly, they retain many of the ligandsof thecomparable small transition metal com-plexes and, fourthly, their chemistry can bemost closely compared with homogeneoussystems in that in the region around the metalatom it is tobe expected that the interactionstaking place are very similar to those for acomplex that dissolves in the solution. Butit should be recognised that others prefer toconsider such catalysts as heterogeneous(3, 4). That these systems span both areas ofcatalysisis well recognised (I , 5).Homogeneous versusHeterogeneous Catalysts

The relative merits of homogeneous andheterogeneous catalysts to the industrialchemist are well known and are only outlinedhere. Homogeneous catalysts have better de-fined active sites, usually have all of the metalatoms available as the catalyst, and the stericand electronic environment of the metalatom can be, at least in principle, varied verywidely. The major disadvantage of thehomogeneous catalysts is the need to separateoff the reaction products and recover the

PlatinumMetals Rev., 1974, 18, (2), 65-73 65

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catalyst. This can be both complex andexpensive. Other disadvantages are thatthese catalysts are relatively easily decomposedso temperatures must be well controlled,and that they can be deactivated if poisonousby-products are formed. Also corrosion ofreactors by metal complexes is possible.

The advantages might be retained and thedisadvantages removed if the homogeneouscatalyst is either impregnated on to a solidsupport, or in some way chemically bondedto it.*

Preparation of SupportedTransition Metal ComplexesThe first attempts were made by Bond andhis colleagues in the laboratories of Johnson

Matthey (7), and by llony (8). Bond usedrhodium trichloride in ethylene glycol im-pregnated on to Silocel as a packing for ag.1.c. column, and showedthat pent-I-ene was iso-merised to pent-2-ene /t;l;lystyr&;t..J - 'isomers as it passed through d

Most workers have used complexes inwhich phosphine groups are used to linkthe metal to the solid support. Two types ofpolymer support, polystyrene and silica, havebeen most studied. With polystyrene theform of the polymer can be changed bychanging the amount of cross-linking, afeature that appears to have importantconsequences on the type of catalyst pro-duced. This is the type of support that hasbeen most widely used. The polymersupport based on silica has been developed bychemists at British Petroleum Co. L td., andthe only work known to us so far is thatreported by them (3, IZ), and that carriedout in our laboratory (13).

Polystyrene supports are most easilyprepared by chloromethylation of a poly-styrene cross-linked with divinylbenzene,and subsequent treatment with lithiumdiphenylphosphide(3, 14, 15, 16) (Equation

the column. Rony studiedthe hydroformylation ofpropylene by RhCl(C0)(PPhJ Z n butyl benzyl phthalate on granularsilica gel. This reaction also takes place onthis complex supported on carbon or aluminain the absence of the solvent(9).

The first attempts to bond the catalystchemically to the support used ion-exchangeresins with a variety of Group VI I I metalcomplexes and the reactions studied includedcarbonylation, hydrogenation and hydro-formylation (10). A detailed study of hydro-genation using K,PdCI, on Amberlyst A27resin has been published (I ).*An interestingalternativeapproachtoseparatingcatalysts and products without supporting thecatalyst on a polymer has been reported byParshall (6), who has used a molten salt (thetetralkylammanium salts of SnC1,- and GeC1,-)as the solvent. The organic products may thenbe easily separated by distillation. Using PtClein these molten salts, alkene hydrogenation,isomerisation, hydroformylation and carboakoxy-lation havebeen studied.

PlatinumMetals Rev., 1974, 18, (2)

I ), although the support has been preparedby polymerisingp- di phenyl phosphi nostyrene( I ) . The transition metal complex with thisphosphenatedt polymer ligand is then pre-pared by equilibrationof the polymer with aknown complex in an inert solvent (17).Equilibration times and temperatures varyfrom two to four weeks at room temperature(14), to short periods under reflux.

Transition metal complexes with a silicaligand have been made by two routes (3). Byone route the silica is first treated with (2-di phenyl phosphi noethy1)tr i ethoxysi l ane. Thiscan be prepared by the addition of diphenyl-phosphine to vinyltriethoxysilaneunder ultra-violet irradiation (18) (Equation 2). The

tPhosphenated will be used throughout to meanthat the polymer has organophosphorus groupsattached to it (e.g. in this casePPhl groups).

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Ph,PH +CH, =CH Si(OEI), +Ph2PCH2CH2Si(OEt),PhzPCH,CH2Si-(0),- +3EtOH

phosphenated silica is then equilibrated witha known complex, in a manner analogous tothe polystyrene support above. The otherroute to the silica-supported complex involvesthe initial formation of a complex containingthe (2- di phenyl phosphi noethy1) t r i ethoxy-silane ligand, and condensation of this withthe silica (Equation3).[RhCI(CO),], +Ph,PCH,CH,Si(OEt),+RhC1(CO)(Ph, PCH CH Si (OEt), )2

NaBH,Ph,PCH,CH,Si(OEt),' R~(CO)(Ph,PCH,CHzSi(OEt),)3 complexes, the C-0 stretching vibra-

The Structure of the Catalyst(2 ) Detailed information about the

structure of the complexes with poly-meric ligands is difficult to obtain. In-

deed, it is our belief that advancement ofthis area of chemistry could be seriouslyimpeded by this very difficulty. Elementalanalysis of the complexes gives the amount ofthe elements that are in the particular com-plex, but this information is of only limitedvalue. Detailed information about theenvironment of the metal atom, what other

ligands are present, and how theychange when chemical reactions occur,is generally not known. For supportedcomplexes prepared from carbonyl

A rangeof metal complexes in which thepolymer is either polyvinylalcohol (19, 20) orpolybutadiene (zI), or many other polymers(32), has been patented, although there are noreports of these complexes being used ascatalysts. Also a polymer made by co-polymerisingan alkene containing phosphorusviz. Ph,PCH,CH =CH,, with styrene isclaimed to give a viscous liquid that can beused as a catalyst support (22).

tion in the infra-red spectrum of adisc or mull can sometimes be detected(3,24), and diffuse reflectance electronic

spectra have been reported for bothcobalt(I1) and nickel(I1) compounds (3). In astudy of rhodium and iridium complexesby Collman and his co-workers (24), theligands present in the supported-complexwere deduced by analysing the solutionremaining after a phosphenated 2 per centcross-linked polystyrene was equilibratedwith a known rhodium or iridium complex.If the complex MCl(CO)(PPh,), [M=Rh or

Ir] is used, both

(3)

triphenylpho sphinegroups are displac-CH,CH,OCH,ClGG=& ~ SnCI,ed, and it can thusbe deduced that theproduct is MC1

F W H z a l + (CO)L, [M=Kh orIr, L =phosphenat-

p i a l y B t y r e * C H + T 1 ~ 4H3L 1> Reactive Grey Polymer ed polystyrene](4 ) with two phospho-

(C p=cyclopentadlenyl) rus atoms on thepolystyrene orming

CpTlCl j

/ \c1 CI

Fi g. 1 Product MCE(CO)L,attached to a polystyrene resin has been / \ [ I ,1 hosphenated poly-prepared (23) by the reaction sequence of styrene] o equilibrating aphosphenated 2per cent cross-equation 4 and it has been shown to be a linked polystyrene with MClvery active catalyst (see later). (Co)(Pph,), 24 )

An interesting complex of titanocene C1\ ,COs(M=Rh or Id

M

PlatinumMetals Rev., 1974, 18, (2) 67

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$ ? $ ?Rh-CI Rh-CII Ipoi ystyr eneL-

Fig. 2 Product oreaction of [Rh(cyclo-netndi ene)Cl ] withphnsphenated polysty-rene, as reported byCollrnan (24)

Fi g. 3 Product ofreaction of Fig. 2,using 2 per cent cross-linked polystyrene, asreported by Grubbs (23)Fig. 4 Product oreaction o Fi g. 2,using 20per cent crnss-linked polystyrene. Halfthe rhodium atoms willhe hound as in F ig. 3and half as here

a chelate ring to each metal atom, as in Fig. I .In this, and similar cases, it was not possible

to form a complex by displacementof onlyone triphenylphosphine group, and it issuggested that the polymer chain is sufficientlymobile to bring nonadjacent sites together.Two triphenylphosphine groups per moleculeof complex were also liberated when morehighly cross-linked polystyrenes were studied.There appears to be some doubt about theproduct formed by the reaction of [ Rh(cyclooctadiene)C1] with phosphenated poly-styrene. Collman (24) reports the formationof the complex shown in Fig. 2, formed bysplitting the chloro-bridges. In contrast,Grubbs and his co-workers (23) report thatcyclooctadiene is liberated. If a 2 per centcross-linked polystyrene is used (like Collman(24)),2 moles of cyclooctadiene are liberatedper mole of complex used, to form, pre-sumably, the complex shown in Fig. 3, but ifa 20 per cent cross-linked polystyrene is usedonly 1.4 moles of cyclooctadiene are liberatedper mole of complex used. In this case half ofthe rhodium atoms will be bound as inFig. 3, and half as in Fig. 4. These resultswould indicate, as might be expected, that inthe20per cent cross-linked polystyrene thereis less mobility of the polymer chains than inthe2 per cent cross-linked polymer.

CatalyticReactionsA wide range of hydrocarbon reactionshave been catalysed by these complexeswith polymer ligands, viz. hydrogenation,hydrosilylation, hydroformylation, acetoxy-lation, polymerisation, and oligomerisation.

The published reactions are collectedtogether in the table on pages 70and 71withthe complex used in the preparation of thesupported catalyst, the polymer used, andthe organic molecules studied. The datagiven earlier by Manassen (I) are not in-cluded here, nor is the table totally compre-hensive. For example, some patents tend tobe wide ranging in their claims, and it is notpossible to summarise them all in a smalltable.Hydrogenation is a useful test reaction thathas been widely used in homogeneouscatalysis studies. Tris(tripheny1phosphine)chlororhodium(1) has been much studied(33).With one of the triphenylphosphine ligandsreplaced by phosphenated polystyrene theactivity of the complex as a hydrogenationcatalyst is much more sensitive to the sizeof the alkene substrate. Whereas the ratesof hydrogenation on RhCl(PPh,), of manyalkenes are comparable, on the polymersupported catalyst the rate of hydrogenationof hexene is 6.25 times that of cyclooctene(14). This is attributed to restriction ofmovement of the solution within the cross-linked polymer, indicating that most of thereaction is taking place inside the polymerbead.

These lower rates of hydrogenation re-ported for cyclic alkenes compared withlinear alkenes on a rhodium complex sup-ported on polystyrene (14) are not foundwhen a silica supported complex is used (13).Indeed, using a silica supported catalyst,cyclohexene is the most reactive alkenestudied so far. Silica appears to have distinctadvantages over polystyrene as the catalystsupport, in that the rates of hydrogenationare higher. Using a catalyst formed byequilibrating RhH(CO)(PPh,), with phos-phenated silica, the rate of hydrogenation of


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pent-I-ene is six times that observed whenthe same complex is supported on phos-phenated Amberlite XAD-2. A catalystformed by reacting RhH(CO)(PPh,CH,CH,Si(OEt),), with silica is of comparablereactivity to the equilibrated silica-basedcatalyst. The reason for the higher activityof the silica supported catalysts is possiblythat the rhodium complex molecules are onthe outside of the silica particles, and there-fore are more readily available to the re-actants, than for the polystyrene supportedcatalysts where the rhodium complex may bedeep inside the polymer beads. Thesesupported complexes are still somewhatless reactive than related unsupported com-plexes in homogeneous solution. Grubbset al. (34) report an activity of polystyrene-supported rhodium catalysts of 0.06 timesthat of an equivalent amount of the homo-geneous counterpart, and the difference forthe silica-supported catalysts will clearly berather less.

Interesting differences occur in the patternof the reaction with different complexes. Forexample, if RhC1,.3H,O is equilibratedwithphosphenated silica, the catalyst formed isabout half as active as a hydrogenationcatalyst as that prepared from RhH(C0)(PPh& (13). However, the RhC1,-basedcatalyst is a very active isomerisation catalystand almost all of the terminal alkene used inthe reaction is converted to the internalisomer before it is hydrogenated. Thereasons for these differences have yet to beexplored. The efficacy of polystyrenesupported rhodium complexes decreases asthe following complexes are used for theequilibration with the phosphenated poly-styrene: RhCl,> RhC1,+PPh,>RhC1,+PHPh, >RhCl,+C,H, >RhCI(PPh,), >RhCI(PHPh,), (15). Catalysts using phos-phenated polyvinylchloride as support do notappear to be very active(26).

Catalysts that selectively hydrogenate thepolyunsaturated components of soybean oilwithout producing the saturated fats are ofinterest. Platinum and palladium chlorides

on a cross-linked polystyrene support givesimilar results to their homogeneous ana-logues; the products of hydrogenation ofsoybean methyl ester being the monoene anddiene(27).

Activationof the catalyst by attachment tothe polymer support is the most importantfeature of the work with titanocene(23). Anecessary feature of a homogeneous catalystis the existence of a free coordination siteon the metal atom to which alkene moleculescan attach themselves. Often attempts toproduce a free site results in polymerisationof the complex and the free site is removed,but if the complex is bound to a rigid polymerthere is the possibility that free sites can beproduced. Titanocene is a reactive catalystfor alkene reduction, but it rapidly poly-merises to an inactive compound (35). Thecatalyst produced by reduction of titanocenedichloride attached to polystyrene is sixtimes as active as the analogous catalyst madefrom titanocene dichloride itself.

In addition to hydrogenation, hydro-formylation is the other reaction that has, sofar, been studied in some detail. Duringhydroformylation of a terminal alkene thealdehyde group can add to the end carbon atomgiving a linear aldehyde, or to the internalcarbon atom giving a branched aldehyde (seefootnote to the table for descriptionof hydro-formylation). The amount of each aldehydeis dependent on the catalyst. For examplewhen the catalyst is Rh(acac)(CO), the rationorma1:branched is 1.2:1, and when thecatalyst is Rh(acac)(CO)PPh, the ratio is2.9:1 (3). If Rh(acac)(CO), is equilibratedwith a phosphenated polymer, either poly-styrene, or polyvinylchloride, or silica, thecatalysts obtained give a normal :branchedaldehyde ratio in hydroformylation of 2.0-2.5:1, indicating, as would be expected,that they contain rhodium linked to phos-phorus (3). The above change in aldehyderatio on replacing a CO by a PPh, ligand isilluminated by the report that uses [Rh(CO),Cl], as a hydroformylation catalyst and alsothe complexes prepared by attaching this


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Reactions Catalysed by Polymer-supported Transition M etal ComplexesMetal Complex Polymer Substrate Referenci

pol y-p-diphenylp hosphinostyrene 25RhC P PhJ , phosphenated 2 per cent cross-linkedpolystyrene-divinyl benzene cyclo hexenehex-I -eneA*-cholestene

octadecenecyclooctenecyclododecene

14

RhCI,RhCI, then PPh,RhCI, then PHPh,RhCI, then C,H,RhCI(PPh3),RhCI(PHPh,)

phosphenated 2 per cent cross-linkedpolystyrene-divinyl benzene hept-I-enecrotonaldehyde

vinyl acetatevinyl ethyl ether

15

K,PdCI, Arnberlyst A27 cyclohexenestyrene 11

[RhCI(COD)], phosphenated Amberlite XA D-2 hex-I-ene 3NiCI, then NaBH,Rh(acac)(CO),[RhCI(COD)],RhCI,

phosphenated PVC propylenehex-I-eneoct-I ene26

(EtO),SiCH,CH,PPh, silica hex-I ene 3[IrCI(COD)], phosphenated SiO, hex-I-eneisoprene 42

PtCI,PdCI, 27oybean methyl esterhosphenated polystyrene-divinyl benzenechloromethylated cross-linked

polystyrenetitanocene 23ycloocta-l,3-dienecycloocta-1,5-dienestyrenehex-3-ynehex-I-eneRhH(CO)(PPh,), phosphenated SiO, andphosphenated Amberlite XAD-2 13ent-I enetrans-pent-2-ene2-Me-but-2-ene2-Me-bu t-I enecyclohexenecycloocteneRhCI, >hosphenated SiO, pent-I ene 13


Hydrogenation

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1eferencetal Complex PolymerHydrofarmylation SubstrateRh(acac)(CO), hex-I enehosphenated Amberlite X AD-2phosphenated PVCSiO,phosphenated 20 per cent cross-linkedpolystyrene-divin yIbenzene

3. 28

RhCI, then C,H, hept-I-ene 15- _ _

hex-I-eneross-linked polystyrene-divinylbenzene substitutedwith -P(Ph),, -P(Bu),, -SH,-CH,NMe,, o r -P(OMe),4

15,29

30

Hydrosi ly lat ienRhCI,RhCI, then C,H, phosphenated 20 per cent cross-linkedpolystyrene-divinyl benzene (EtO),SiH andhex-I-ene orvinylethylether oracrylonitrile ortrans-hept-2-encH,PtCI, o r RhCI, cross-linked polystyrene-divinyl benzene substitutedwith -CH,PPh,, -CH,NMe, or-CH,CNpolymethacrylate with ester group-OC,H,PPh, or -O(CH,),PPh, or-O(CH,),NMe, o r -O(CH,),CN

Amberlyst A21ally1 chloride-divinylbenzenecopolymer with -CH,PPh,functional group

hex-I-enehept-I-enewith HSi(OEt),or HSiEt, or HSiCI,Acetoxylation:PdCI, phosphenated silica ethylenepropyleneisobutene

12

PolymerisationNi(COD), phosphenated silica butadiene 12

phosphenated polystyrene 31thyl propiolate -NiCI,Oligonerisat lonNiCI, then NaBH,

~ ~

phosphenated PVC phenylacetylene 3NiCI, 3.1henylacetylenehosphenated polystyreneMe=methyl, Et=ethyl, Bu=butyl, Ph=phenyl, COD-cycloocta-1 ,Ediene, phosphenated -see tex tHydrosilylation:Hydrofo rmylation: -CX:CX-+CO+H, --t -CX(CHO)-CXH-Hydrogenation: -CX=CX-+ H + C X H A X H --CX =CX-+ Si-H +CX(Si =)-CX H-Acetoxylation: -CX=CX-+CH3COOH +CX(0.C0,CH3)-CXH-Polymerisation and n( A X =C X - ) + (cx-q"-Oligomerisation:


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complex to polystyrene by a number ofcoordinating groups (see Table)(4). The ratioof linear and branched aldehydes formedfrom the terminal alkene is independent ofthe ligands on rhodium; however, theamount of isomerisation of terminal tointernal alkene is very dependent on theligands, being more for carbon monoxideand less for triphenylphosphine. Thelower normal-branched ratio for the carbonylcomplexes (3) can be explained in terms ofthese two competing reactions. Onlybranched aldehyde can be formed from theinternal alkene that has been formed byisomerisation, and as more isomerisationoccurs the linear to branched aldehyderatio will fall.Another feature of interest is that thesehydroformylation catalysts with polystyreneligands vary markedly in their efficiency asaldehyde hydrogenation catalysts, dependingon the groups used to attach the rhodium tothe polymer (4). Rhodium-phosphine poly-mer complexes are poor aldehyde hydro-genation catalysts, but rhodium-minepolymer complexes catalyse alcohol formationunder very mild conditions. This is par-ticularly interesting in view of the fact thatthe homogeneous counterparts of theseamine complexes are far less active.

Complexes of cobalt carbonyls with poly-vinylpyridine have been used to catalysehydroformylation(36),but the catalyst in thiscase has been shown to be a solution ofcobalt carbonyl that has dissociated from thepolymer support.

Hydrosilylation is a reaction of someconsiderable interest and potential to theorganosilicon industry. The usual homo-geneous hydrosilylation catalyst is chloro-platinic acid, and its use necessitates thereaction being carried out in inconvenientalcoholic solvents to obtain a homogeneousreaction mixture. One group has reportedthe use of polymer supported catalysts(IS, 29, 30). A whole range of functionallysubstituted alkenes can be hydrosilylated, theextent of the reaction decreasing as electron

withdrawing groups are substituted in thealkene(29). Unsupported chloroplatinic acidis a good hydrosilylation catalyst, andrhodium trichloride shows little activity.However, putting these two compounds on topolymer supports has a marked effect ontheir activity (30). Both complexes on allsupports catalyse the addition of triethoxy-silane to alkenes but differences in catalyticactivity occur with triethylsilane and tri-chlorosilane. The complexes which are goodcatalysts for the addition of triethylsilane areless effective for trichlorosilane and viceversa. For some catalysts, such as therhodium complexes with amino and cyan0groups, there are no comparable solublecatalysts.Conclusions

This review shows that research interestin transition metal complexeson a polymersupport has increased rapidly during the pasttwo years. The technological difficulties inusing homogeneous catalysts have un-doubtedly been the major factor in initiatingthis research. It is to be hoped that theadvantages that homogeneous catalysts some-times have to offer over their heterogeneouscounterparts can be realised by putting thecatalyst on a polymer support. As in allareas of research a number of interesting newfacets of the chemistry these compoundshave already become apparent. As thepotential of these systems has only started tobe explored, work will undoubtedly continueat an increasing rate. It is interesting to notethat most of the compounds studied so farhave been complexes of rhodium. It wouldseem likely that, as with most other typesof catalysts, a large proportion of polymersupported catalysts will be based on theplatinum group metals.

AcknowledgmentsOne of us (Z.M .) would like to thank theChemistry Department atHull University for itshospitality during the past year, and the BritishCouncil for its support.


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ReferencesJ . Manassen, PlatinumMetals Rev., 1971, 15,(4), 142N. Kohler and F. Dawans, Rev. Znst. Fr.Petrole,1972,27, 105K . G. Allurn, R. D. Hancock, S. McKenzieand R. C. Pitkethly, Proc. 5th Znternat. Cong.Catalysis, Palm Beach, 1972W. 0.Haag and D. D. Whitehurst,Zbid.H. Heinemann,Chem Tech., 1971, 286G. W. Parshal1,J. Am. Chem SOC.1972, 94,8716G. J. K. Acres, G. C. Bond, B. J . Cooper andJ. A. Dawson,J. Catalysis, r966, 6, 139P. R. Rony,J . Catalysis, 1969, 14, 142K . K. Robinson, F. E. Paulik, A. Hershmanand J. F.Roth,J. Catalysis, 1969,15,245W. 0.Haag and D. D. Whitehurst, BelgianPatent 721,686, 1969R. L. Lazcano andJ. E. Germain,Bull. SOC.Chim Fr., 1971, 1869B.P. CO.Ltd., U.S. Patent 3,726,809, 1973Z . M. Michalska and D. E. Webster, un-published observationsR. H. Grubbsand L. C. Krol1,J. Am. ChemSOL.,1971, 93, 3062M. Capka, P. Svoboda, M. Cerny and J.Hetflejs, Tetrahedron Lett., ~971, 787B.P. Co. Ltd., British Patent 1,277,737, I972For example see reference 16

18 H. Niebergall,Makromol. Chenz.,1962,52,21819 B.P. Co. Ltd., British Patent 1,291,237, 197220 B.P. CO.Ltd., British Patent 1,295,673, I97221 B.P. Co. Ltd., Canadian Patent 903,950, I97222 B.P. Co. Ltd., British Patent 1,287,566, I97223 R. H. Grubbs, C. Gibbons, L. C. Kroll,W. D. Bonds and C. H. Brubaker, J . Am.24 J . P. Collman, L. S. Hegedus, M . P. Cooke,J . R. Norton, G. Dolcetti and D. N.Marquardt, . Am. Chem SOC.,972, 94, 178925 J . Manassen, Israel J . Chem, 1970, 8, 5 p26 B.P. CO.Ltd., British Patent 1,295,475, I97227 H. S. Bruner and J. C. Bailar, J . A m. Chem28 B.P. Co. Ltd., Dutch Patent 70.06,740, I97029 P. Svoboda, M. Capka, V. Chvalovsky,V. Bazant, J . Hetflejs, H. Jahr andH.Pracejus,Angew. Chem, 1972, 12, 15330 M. Capka, P. Svoboda, M. Kraus andJ . Hetflejs, Chem6Znd., 1972, 65031 B.P. Co. Ltd., British Patent 1,295,674, I97232 B.P. Co. Ltd., British Patent 1,277,736, I97233 For example, seeF. H. Jardine, J. A. Osbornand G. Wilkinson, J . Chem SOC.,A, Znorg.Phys. Theor., 1967, 157434 R. H. Grubbs, L. C. Kroll andE. M. Sweet,J . Macromol. Sci., 1973,A7, I04735 J .E.Bercaw,R.H.Marwick,L. G.Bal1andH.H.Brintzinger, .Am. ChemSOC. ,97z,94, 121936 A. J . Moffat, J . Catalysis, 1970,18, 193

Chm. Soc.9 1973, 951 2373

sot.,1972, 49, 533

Weld Metal TemperatureMeasurementHARPOON TECHNIQUE WITH RHODIUM -PLATI NUM THERMOCOUPLES

The thermal history of weld metal gives agood indication of the behaviour of the weldthereafter. For example, the thermal be-haviour of the weld bead affects the pro-perties of transformable steel. To record thethermal history of a weld bead platinummetal thermocouples may be inserted duringthe welding process but until recently manyof them melted in use and the instrumentsbecame open circuit.C. Pedder of the Welding InstitutesMetallurgical Department at Abington Hall,Cambridge, has now described a simpletechnique in which platinum: 13 per centrhodium-platinum harpoon thermocouplesof 0.5 mm wire arc used. The wires areinsulated in twin bore ceramic insulatorssupported in a close-fitting steel tube so thatthey protrude 3 mm beyond the insulator,which itself protrudes 5 mm beyond the steeltube end. They dip into the pool of weldmetal which completes the circuit by actingas the thermocouple hot junction. Testsshowed similar results to those using con-

PlatinumMetals Rev., 1974, 18, (2)

ventional thermocouples up to I OOO~C.The e.m.f.s differed by less than 0. 01mV(10Cat IOOOC).Manual and semi-automatic methods havebeen used to plunge the thermocoupleaccurately into the weld metal pool. In thelatter case the welder can also operate theharpoon thermocouple, and when used withimplant cracking test equipment the thermo-couple records the thermal cycle and alsoactuates the implant loading mechanism at thepredetermined temperature.Weld thermal cycles and cooling times havebeen measured by the harpoon thermocouplefor the MMA, MIG and submerged arcprocesses. It has also made possible thethermal analysis of weld metal austenitetransformation immediately after deposition,whereas previous dilatometry studies gavetransformation characteristics of reheatedmetal. The thermal analysis process uses a

differential amplifier to convert thermocoupleoutput to a voltage proportional to the coolingrate. F. J . S.

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