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Influences

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InfluencesInflue

    Influences

Dec.2008,Volume2,No.12(SerialNo.13)JournalofMaterialsScienceandEngineering,ISS

    N19348959,USA

    ;InfluencesofMoS2contentsonsinteringprocess ;andpropertiesofCuMoS2composites

    ;CHENShu-xian.FENGYiLIShu,XIEYu-juan

    ;(DepartmentofMaterialsScienceandEngineering,Hefeif’,ersi~ofTechnolog%Hefei230009,China)

    ;Abstract:TheCuMoS2compositeswerepreparedbypowder

    ;metallurgyrouteinahydrogenatmosphere,anddetectedusing ;thetechnologiesofXraydiffraction(XRD1andXray

    ;photoelectronspectroscopy(xPs)toanalyzetheformation ;phasesandcompositions.TheinfluencesofMoS,additionon ;mechanicalpropertiesofcompositesandsinteringprocess, ;duringwhichthereactionswereprovedwiththermodynamics ;analysis,wereinvestigated.Itisfoundthat,insinteringprocess ;MoS2onlyreactwithCuintoanintricatecompoundmadeof ;Cu,MoandSelements,withsimultaneousemissionofcopper ;sulfideandelementaryMointwosteps,ratherthanwithH2. ;Sinteredproductsvaryregularlywiththeincreasingamountof ;MoS2addition,andthebendingstrengthofcomposites ;decreasesobviouslywhiletheresistivitypresentsanadverse ;tendency.Theresultofthermodynamicsanalysismatcheswell ;withtheoutcomesofXRDandXPS.

    ;Keywords:Cu-?MoS2composite;powdermetallurgy;X--ray ;diffraction(XRD);Xrayphotoelectronspectroscopy(XPS); ;thermodynamicsanalysis

    ;1.Intr0ductiOn

    ;Electricaltransmissionbetweenrelative

    ;removablecomponentsinaerospaceindustryis

    ;completedthroughbrushrotorsystem,sothe

    ;reliabilityofaerodynamodependsstronglyon

    ;propertiesofbrushest-.Mostoftheaerobrushes ;currentlyinservicearecomposedofcommonmetals ;andgraphitewithadditionofsoftmetalsassolid ;lubricants,suchaslead,tin,eta1.Theleadandtinin ;Acknowledgement:Thepaperwasfinanciallysupposedby ;theNationalNaturaIScienceFoundationofChina(No ;50741003),AnhuiProvincialNaturalScienceFoundation(No ;070414l81)andkeyprojectofScienceandTechnologyof

    ;MinistryofEducationofChinafNo.107066). ;Correspondingauthor:FENGYi(1964),male,professor;

    ;researchfield:metalmatrixcomposite.Emai1:

    ;fyl23@mail.hLah.ca.

    ;brushescanforintinleadsolidsolutionatalower

    ;temperature,whichpenetratesintosurfacelayersof ;commutatorsindynamorunningprocessandinteracts ;withcommutatorCuresultinginaprotectingfilmof ;n-Cu5Sn5solidsolution.Theformationofaspecial ;lubricantfilmwiththisprotectingfilmandgraphite ;powdermakesthebrushesworknormallyunder ;conditionswithoutvaporandair3?.

    ;Yettheproperties

    ;ofabovecitedbrusheshavenolongertomeetthe

    ;requirementsofmetallicself-lubricatematerialsused ;insatellites,spaceships,shuRlesandsoon,withthe ;developmentofaerotechnics.

    packedhexagonal ;MoS2possessesaclose

    ;structure,andthecrystallatticeisclosepackedthin

    ;layerunitsformedbythreeplanelayersofS,Mo,S. ;Thebondingbetweentheatomswithinthelayersofthe ;structureiscovalentandstrong,whilebetweenthe ;layersisconsiderablyweakerwhichiseasytoslipand ;separatecausinglowfriction.Furthermore,Satomsin ;theunitshavegoodmorphotropyandstrongadhesion ;forceonmetals.ThusMoS2isanexcellentsolid ;lubricateandadditivewhichcanadherefirmlyon ;commutatorsurfacesandmakethefrictioncoefficient ;ofmaterialsinupperairessentiallystablef5_6].Though ;cuprousoxidefilmcanhardlyfonninupperairon ;brushsurfacewhereexitinganorderofMoS2addition, ;itiseasytoformsulfidefilmwhichabsorbstightlyon ;rotorsurfaceandprovidedwithgoodlubricateaction. ;Besidesthat,MoS2hasprettygoodradiationresistance. ;Thecrystallatticeofgraphiteisseriouslydeteriorated ;whenthedosageofneutronis3.66~1020NVT,

    ;whereasthatOfMoS,keepsinvariable[-.

    ;7

    ;!uences0fM0contentsonsinteringprocessandpropertiesofCu-MoS2composites

    ;Ithasreportedthatcertainreactionswouldtake ;placebringingaboutsomenewphasesduringsintering ;processesofiron?-basedandcopper-?basedcomposites ;withMoS2addition,buthowthereactionshappened ;andtheformingmechanismofnewphaseshaven’t

    ;beeninvestigatedindetail.Inthispaper,XRDandXPS ;wereemployedtodetecttheformingphasesand ;compositionsofCuMoS2compositespreparedby

    ;powdermetallurgyrouteasafunctionofMoS2content ;andcorrelatedittomechanicalpropertiesof ;composites.

    ;2.Experimentalprocedures

    ;Electrolyticcopperpowderf325mesh,99.7%

    ;pure)andMoS2powder(325mesh,98%pure)were ;selectedforpreparationofCuMoS2composites.

    ;Thecompositespecimens,whosenominal

    ;compositionsarelistedinTable1andhereinafter ;designatedasspecimenA,B,C,D,EandF

    ;respectively,werepreparedbypowdermetallurgy ;route.Thepowderswereweighedinproper ;proportionsandmixedinatrituratorfor12h,priorto

    ;compactedataninitialpressureof300MPaatroom ;temperature.Thegreencompactswerethensinteredat ;900~Cfor1hunderahydrogenatmosphereandcooled ;inthefumacetoroomtemperature.Finally,thebulk ;specimenswith40mmx8mmx5mminsizewere ;machinedoutofsinteredonesafterbeingconsolidated ;againbydiecompactionat500MPa.

    ;Table1Compositionsofspecimens(massfraction,%) ;X-raydiffraction(XRD)andXrayphotoelectron

    ;spectroscopy(XPS)analysiswereperformedona ;RigakuD/MaxRbdiffractometerwithCuKs

    ;:1.54041radiationsourceandaThermo

    ;ESCALAB250XPSspectrometerwithmonochromatic ;AIKGt(v=1486.6eV)radiation,respectively.The ;bendingstrengthofspecimenswasevaluatedusinga ;8

    ;DCS-5000Daojinomnipotenttesterwithcrosshead ;movementspeedof3iYllnminuntilfailure.Andthe

    ;resistivitywasmeasuredbydoublebridgemethod,

    ;accordingtoGB1994.288.

    ;3.Resultsanddiscussion

    ;3.1XRDanalysis

    ;Fig.1showsXRDpattemofspecimenAbefore ;sintering,whileFig.2presentsthatofspecimenAF

    ;aftersintering.NoMoS2butsomenewformation ;phasesareobservedinFig.2,fromcomparisonwith ;Fig.1whichhasobviousMoS2diffractionpeaks.Itis ;foundthat,newphasesineachsinteredspecimenhave

    ;somedifferences,identifiedrespectivelyas: ;Cuo9Mo354;Cu09Mo354,Cu0.

    ;9Mo3S4andCUl93755;

    ;Cul8Mo6S8andCu2S;CUl83Mo3S4andCu7S4; ;Cu1.83Mo3S4andCu31Sl6(Cu0.9Mo354andCu1.8Mo658 ;aren’tthesamesubstanceduetodifferentcrystal

    ;lattice).ThisindicatesthatinsinteringprocessMoS2 ;reactswiththematrixoratmosphereintocompounds ;madeofCu,MoandSelements,followedbycopper ;sulfides.WiththeincreasingamountofMoS2addition, ;thesinteringproductsvaryregularlyasfollows.The ;rationsofMo/SatomsinCu-Mo--Scompoundsremain

    ;steadyat3:4.whereasthecontent0fCuincreases ;continuously;alsothecoppersulfideswhichhave ;lamellarstructureandlubricateeffectsimilartoMoS2 ;changeconstantly.ItwasconsideredinRef[10].That ;CuxMo6S8(wherex=2-4)calledChevreltype

    ;compoundsandCu2SwouldbeproducedifMoS2and ;Cupowderweresinteredinproperproportion,andthe ;contentofCuinCuxMo6S8decreasedasthe

    ;temperaturerose.

    ;1nthecurrentresearch,MoS2wassinteredat ;850.Cand950~Cinahydrogenatmosphere.Asaresult, ;theweightsofMoS2powderbeforeandaftersintering ;maintainalmostthesame(presentedinTable2);.m ;addition,onlyMoS2phasepeaksarefoundinXRD ;patternofsinteredpowderat950~C(showninFig.3,. ;InfluencesofMoS2contentsonsinteringprocessandpropertiesofCuMoSscomposites ;SotheconclusioncanbeobtainedthatMoS2doesn’t

    ;reactwithHzduringsinteringprocess.

    ;0203040506O7080

    ;20/.

    ;Fig.1XRDpatternofspecimenAbeforesintering ;l02030405O607O8O

    ;20/.

    ;o20304050607080

    ;20/.

    ;Fig.2XRDpatternsofsinteredspecimens

    ;2O3O405O607080

    ;20,/.

    ;Fig.3XRDpatternofsinteredMoS2in

    ;H2streamat950?

    ;Table2Theweightlossofpowderinan

    ;H2streamaftersintering

    ;ThusltcanbelnferredthatInsmtermgprocess ;MoS2reactsonlywiththeCumatrixwhichcanbe ;undertakenintwosteps.Firstly,Cuatomsinsertinto ;vacanciesbetweenMoS2layersformingintricate ;compoundsmadeofCu,MoandSelements;secondly, ;CudirectlyreactswithMoS2athighertemperatureinto ;coppersulfideandelementaryMo[11].

    ;Itdepends

    ;stronglyondiffusionofCuintoMoS2toformcopper ;sulfideandelementaryMoaccordingtothefactsthat ;thediffusionofSintoCUmatrixcanbeinprogressat ;considerablylOWtemperatureandtheformationof ;solidsolutionispracticallyimpossiblethoughthe ;diffusionofMointoCUmatrixexits.

    ;AsthephasediagramofCuMosystemshownin

    ;Fig.4,itcanbeseenthatbelow1000?CuandMo

    ;coexistwithcrystalstructureofface.centeredcubic ;(fcc)andbodycenteredcubic(bcc).Molybdenumcan ;onlyexitaselementaryMoratherthanpackingintoCu ;matrixformingsolidsolution.

    ;9

    ;InfluencesofMoS2contentsonsinteringprocessandpropertiesofCu-MoS2composites

    ;

    ;a)

    ;?

    ;E

    ;?

    ;i--

    ;/

    ;///.

    ;,\

    ;/\

    ;/2788

    ;/L.+b..

    ;1356

    ;fcccc

    ;O

    ;Cu

    ;204060801O0

    ;At0mfracOnOfM./%.

    ;Fig.4PhasediagramofCuMosystem

    ;Thereactionscanalsobeinterpretedby

    ;electricnegativetheorywhichindicatesthecapability ;ofatomsabsorbingelectrons.Theelectricnegative

    ;levelofCu(1.75)ishigherthanthatofMo(1.30),so ;thecapabilityofCuatomstoabsorbelectronsinouter ;shellofSatomsisstrongerthanthatofMoleadingto ;thefactthatelectroncloudsofSatomssignificantly ;inclinetoCuatomsformingcoppersulfide.Meanwhile ;suspendedbondingofMoatomsappearinginthe ;hexagonalstructureofMoS2promotesMotoform ;compoundsmadeofCu,MoandSelementsby

    ;incorporatingwithCuandSatoms,alsounitwith ;interfacingMoatomstoformelementaryMo. ;3.2XPSanalysis

    ;ThesinteredspecimenFwasfurthersurface ;analyzedbyaXPSspectrometerwhoseXrayprobe

    ;wassetat500gminsizeandwithapassenergyof20 ;eV.TheelementsasMo,Cu,S,OandCeta1.are ;observed(referencedinFig.5)andspecialattention ;hasbeenpaidtothepeakfittingofMo3ds/2,Mo3d3/2, ;Cu2p,S2pphotopeakstodeterminetheexistingstate ;ofeachelementaftereliminatingtheinterferencesof ;ambientair.

    ;AfterwellfittingofXPSspectraofMo3d

    ;photopeaks,itisdetectedthatMoexitsinvaried ;chemicalstatesduetoitscomplicateenvelopepeaks. ;AsshowninFig.6,wecanseethatthepeaksof ;Mo3d5,2andMo3d3/2occurringintheplaceswherethe ;10

    ;bondingenergyage227.96eVand231.09eV

    ;correspondwellwiththebondingenergyofelementary ;Mo,whilethepeakpositionsofMo3dsr2andMo3d3/2at ;231.64eVand234.65eVascribabletoCU1.

    ;83Mo3S4.

    ;Thefourpeakpositionsagequitedifferentfromthe ;bondingenergyofMoS2whichfullyimplicatesthat ;thereisnoMoS2insinteredspecimenF.

    ;Fig.5XPSwhole-scanningspectraofsinteredspecimenF ;

    ;190

    ;18.o

    ;236234232230ZB226

    ;BirdingenergyB

    ;Fig.6XPSspectraandfittingCUliWeof

    ;Mo3dofsinteredspecimenF

    ;TheXPSspectraofCu2pandS2pageorderly

    ;showninFig.7andFig.8.Thetwopeakpositionsof

    ;Cu2pat932.26eVand952.06eVpresentaspositive1 ;stateCu(Cu3andtheweakerphotopeakoccurring ;betweenthempresentsaspositive2stateCu(C’)

    ;whichcanbeinfcrredascribabletoCU1.

    ;83Mo354and

    .,>?q0?80???II?II0>’}.0 ;_u

    ;InfluencesofMoS2contentsORsinteringprocessandpropertiesofCu-M

    ;oS2com

    ;

    ;posites

    ;Cu31St6respectively.Moreover,thepeaksofS2p ;emergingintheplaceswheret/eV

    ;Fig.8XPSspectraofS2pofsinteredspecimenF ;TheXraydiffractionpeakisprobablyconcealed ;bysubstrateandthephasecanhardlybedetectedifthe ;massfractionofamatterislessthan5%.Bythisreason. ;itmaybeexplainedwhynoelementaryMoisobserved ;inXRDpatternshowninFig.2andwhythereareno ;coppersulfidesinsinteringproductsofspecimenAand ;B.

    ;Inconclusion,theresultofXPSanalysisstates ;thatinsinteringprocessratherthanwithH2MoS2only ;reactswithCuintoanintricatecompoundmadeofCu, ;MoandSelements,incombinationwithcoppersulfide ;andelementaryMo,whichmatcheswellwiththe ;outcomesofXRDanalysis.

    ;3.3Thermodynamicsanalysis

    ;Thermodynamicsanalysisisusedtoprovide ;evidencefornoreactionshappeningbetweenMoS2 ;andH2insinteringprocess.PostulatingthatMoS2 ;reactswithH2asformulation(I):

    ;MoS,+2H,=Mo+2H,S(1)

    ;H,+0.5S,=H,S(2)

    ;Mo+S,=MoS,(3)

    ;Reaction(1)canbeacquiredbyincorporating ;reaction(2)with(3)accordingtothermo-dynamics ;factors~thusthecomputingformulaofformation ;freeenergy(Kalmol)ofreaction(1)canbeexpressed ;asfollows:

    ;AGl@=214.24--0.08084T

    ;Thisisanendothermicreactionandtheminimum ;temperatureforreactionis2650.17K(2377.17?)

    ;whichisfaroutofthescopeofexperimentalsintering ;temperature.Therefore.itiscorroboratedthatMoS2

;doesn’treactwithH2duringsinteringprocess.

    ;ThefirststepofreactionbetweenCuandMoS2 ;caneasilyhappenrightafter500~C,whilethe ;followingstepneedshighertemperature[t0].Takingthe ;sinteringproductCu2Sforexample,using

    ;thermodynamicsanalysistoverifythereactions ;betweenCuandMoS2.

    ;MoS2+4Cu=2Cu2S+Mo

    ;Thermodynamicdataofreactantandformation ;freeenergyofreaction(4)atvariedtemperaturesare ;listedinTable3.Wecanseethattheformationfree ;energyofreaction(4)at1200K(927~C)isl4.91Kal

    ;molillustratingthatthereactioncanstilltakeplaceup ;to927~Cintheory.Infact,theformationfreeenergyof ;MoS2isreducedbytheeffectofatmosphericpressure, ;purityofreactant,highsurfaceenergyofpowdersand ;otherreactionscausingreaction(4)happensinslightly ;lowertemperature.

    ;j对一I1?c.c—三旦.

    ;

    ;InfluencesofMoS2conte

    ;

    ;ntsonsinteringprocessandpropertiesofCuMoS2composites

    ;Table3Thermodynamicdataandfree

    ;energyofreaction(4)

    ;MoS2293.97301.39320.96345.58374.08405.

    ;77

    ;Cu.9.8713.6322.85.33.87.46.

    ;29.59.86

    ;3.4Mechanicalproperties

    ;Table4liststhemechanicalpropertiesof

    ;compositeswithdifferentMoS2massfractions.from ;whichevaluatedthatwithincreasingamountofMoS2 ;additionthebendingstrengthofcompositesdecreases ;byalargemagnitudewhiletheresistivitypresentsan ;adversetendency.ThematrixCuplayingthedominant ;roleonbearingweightdecreasesconstantlybyreacting ;withMoS2thatcutsdowneffectualbearingareaof ;materialleadingtothereductionofbendingstrength. ;Inaddition,thebendingstrengthofcompositesis ;furtherreducedwiththeeffectoffollowingfactors:the ;residualstressstemmingfromthefrictionbetween ;powderanddiewallduringcompactionprocess ;releasescreatingholes;thecubicalexpansionof

    ;supersaturatedhydrogen,whichsolutionizesintoCu ;matrixasinterstitialatomorgathersatdefects(holes, ;crackles,eta1)ofmaterialashydrogenmolecule, ;bringingaboutstronginternalstressthatimpelsthe ;stressconcentrationandemergenceofcracksources ;insidethecomposites.

    ;Table4Bendingstrengthandresistivityofcomposites ;withdifferentMoS2massfractions

    ;Similarlytheresistivityofcompositesincreasesas ;aresultofreductionofmetalphasewhichembarrasses ;theorientedmovementofelectrons.Ontheotherhand, ;accordingtotheruleofMadsen[.

    ;thenumberofholes

    ;12

    ;andhydrogenmoleculesgrowslargerwhichproduces ;defectresistivitythuscausingalargemagnitudeof ;increaseinresistivitywiththeincreasingamountof ;MoS2addition.Inviewofthese,thesinteringproducts ;varyandhavegreateffectsonmechanicalpropertiesof ;compositeswithdifierentMoS2massfractions. ;4.Conclusions

    ;TheCuMoS2compositewaspreparedbypowder

    ;metallurgyrouteandtheinfluencesofMoS2contenton ;sinteringprocessandmechanicalpropertiesof ;compositewereevaluated.Theconclusionscanbe ;drawnasfollows:

    ;(1)Duringsinteringprocessunderahydrogen ;atmosphere,thelubricatingcomponentMoS2only ;reactswithCumatrixintoanintricatecompoundmade ;ofCu,MoandSelements,withsimultaneousemission ;ofcoppersulfideandelementaryMointwosteps, ;ratherthanwithH2.

    ;(2)WiththeincreasingamountofMoS2addition, ;sinteringproductsarerespectivelyidentifiedas ;Cuo9Mo3S4,Cuo.

    ;9Mo384;Cuo9Mo354andCul93755;

    ;Cu1.

    ;8Mo658andCu2S;CUl83Mo354andCu7S4;

    ;Cul83Mo3S4andCH3IS16,amongwhichtherationsof ;Mo/SatomsinCu--Mo--Scompoundsremainsteadyat ;3:4,whereasthecontentofCuincreasescontinuously. ;(3)Theresultsofthermodynamicsanalysis, ;whichdemonstratethatreactionsofMoS2happenwi?

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