材料物理课后习题答案 25页

'MP2-homework-withanswer1.Trueorfalsequestions.a)Metallicandionicbondingsarecoulombicinnature.Tb)Themeltingpointsofmetalsaregenerallyhighduetothestrongmetallicforcebetweennucleusandelectrons.Tc)Ionicmaterialsareelectricalconductiveatroomtemperature.F2.Plsschematicallydraweachofthefollowingsiteinacrystala)Cubicsite,b)octahedralsite,c)tetrahedralsite,d)rhombohedralsite3.Inthefollowingfigure,twoplanesAandBareshownwiththeirintercepts.PleasedeterminetheMillerindicesofplaneAandplaneB.ForplaneA:x=1,y=1/2,z=1/3takingthereciprocalsoftheintercepts.xaxis1/1=1yaxisl/(1/2)=2zaxis1/(1/3)=3 result:(123)ForplaneBInterceptsare:x=1,y=2/3,z=2/3Takingreciprocals:xaxis1/1=1yaxis1/(2/3)=3/2zaxisl/(2/3)=3/2commonmultiplier=21×2=23/2×2=33/2×2=3result:(233)4.Pleasewritethefullnameoffcc,bccandhcpFcc:Facecenteredcubic,Bcc:bodyconteredcubic,Hcp:hexagonalofclosepacked5.Forcrystalofpuremetalwithfcc,bcc,andhcp,respectively,pleasetellthe1)coordinationnumber(CN)and2)numberofatomsperunitcell(Nunit).fcc:CN=12,andNunit=4bcc:CN=8,andNunit=2hcp:CN=12,andNunit=26.Pleaseenumeratealltheatomicbondingmodes,andstatematerialpropertieswitheachofthebondingmode,respectively.Metallicbond,ionicbond,covalentbond,andmolecularbondMaterialswithmetallicbonding:1)Highconductive 2)Highreflection3)Highmeltingpoint4)Malleable5)DuctileMaterialswithionicbonding:1)NotconductiveatRT2)Brittle3)Relativelyhighmeltingpoint4)ExhibitionicconductivitywhenclosetoorabovethetemperatureofmeltingpointMaterialswithcovalentbonding:1)Lowconductivity2)Likelyhardandbrittle3)HighmeltingpointMaterialswithmolecularbonding:1)Discreteenergylevel2)Lowconductivityandcarriermobility3)Narrowbandwidthandwidebandgap.4)Softwithlowmeltingpoints5)Loosestack6)Largelatticevariation7.PleaseclassifyvanderWaalsforcewithbrieflyexplanationTherearethreetypesofvanderWaalsinteractions,namely1)Londonforces,2)Keesomforces,and3)Debyeforces. 1)Londonforcesrefertotheinteractionsbetweentwodipolesthatareinducedinatomsormolecules.2)Debyeforcesrefertotheinteractionbetweentwodipolesofonepermanentandoneinduced.3)Keesomforcesrefertotheinteractionbetweenmoleculesthatarepermanentlypolarized8.CanvanderWaalsforceexistbetweenatoms,giveanexample.Yes,itcan.Betweenthelayersofgraphite,therearevanderWaalsforces.Alsotheinertgasesaremadeofatoms,amongthemarevanderWaalsforces.9.Accordingtoatomstacking,howmanytypesofmaterials?Whatarethey?4singlecrystalline,polycrystalline,amorphous,quasicrystalline10.WhatareFrenkeldefectandSchottkydefect?AFrenkeldefectisformedbyexcitationandmigrationofanatom/ionfromitsnormalsiteinthelattice,whichisleftempty.Theatom/ionbecomesaninterstitial.Eachprocessresultsinavacancy-interstitialpair.ASchottkydefectisavacancyinacrystallatticewheretheionhasbeenremovedfromitssitetothesurfaceofthelattice.Thevacancyisnotcoupledtoanyinterstitial. MP3-homework-solidstatetransfermationpartiallywithanswer1.Whatisphasetransformationandsolidstatephasetransformation?Phasetransformationreferstotheprocessthatmaterialchangesfromtheoldphasetoanewone.Solid-statephasetransformationreferstoachangeinphasethatoccursinthesolidstate.2.Usingthefollowingfigure,determinethedegreesoffreedominaCu-40%Nialloyooattemperatureof(a)above1280C,(b)between1280to1240C,and(c)below1240oC(assumingconstantpressure)SOLUTIONThisisabinarysystem(C=2).ThetwocomponentsareCuandNi.Wewillassumeconstantpressure.Atconstantpressure,f=C–Ph+1 o(a)above1280C,Ph=1,sinceonlyonephase(liquid)ispresent;C=2,sincebothcopperandnickelatomsarepresent.Thus,f=C-Ph+1=2-1+1=2Wemustfixboththetemperatureandthecompositionoftheliquidphasetocompletelydescribethestateofthecopper-nickelalloyintheliquidregion.o(b)between1280to1240C,,Ph=2,sincebothliquidandsolidarepresent;C=2,sincecopperandnickelatomsarepresent.Now,f=C–Ph+1=2-2+1Ifwefixthetemperatureinthetwo-phaseregion,thecompositionsofthetwophasesarealsofixed.Alternately,ifthecompositionofonephaseisfixed,thetemperatureandcompositionofthesecondphaseareautomaticallyfixed.o(c)below1240C,Ph=1,sinceonlyonephase(solid)ispresent;C=2,sincebothcopperandnickelatomsarepresent.Again,f=C–Ph+1=2-1+1=2andwemustfixbothtemperatureandcompositiontocompletelydescribethestateofthesolidoo3.DeterminethecompositionofeachphaseinaCu-40%Nialloyat1300C,1270C,oo1250C,and1200C.(seefollowingfigure) SOLUTIONTheverticallineat40%Nirepresentstheoverallcompositionofthealloy.(1)1300°C:Onlyliquidispresent.Theliquidmustcontain40%Ni,theoverallcompositionofthealloy.(2)1270°C:Twophasesarepresent.Ahorizontallinewithinthefieldisdrawn.Theendpointattheliquidus,whichisincontactwiththeliquidregion,isat37%Ni.Theendpointatthesolidus,whichisincontactwiththesolidregion,isat50%Ni.Therefore,theliquidcontains37%Ni,andthesolidcontains50%Ni.(3)1250°C:Againtwophasesarepresent.Thetielinedrawnatthistemperatureshowsthattheliquidcontains32%Ni,andthesolidcontains45%Ni.(4)1200°C:Onlysolidispresent,sothesolidmustcontain40%Ni.4.Basedonthefollowingfigure,pleasestatethatamongdisc,ballandneedleshapesfornewphaseinphasetransformationprocess,whichshapeforthenewphasepresentsthemaximumstrainenergy? Ball12shape.0Needle0cshape(c/a).752E20Discshapeaa2c.502.252c0a12c/aAsshownintheabovefigure,ballshapewiththelargestvolumepresentsthemaximumstrainenergy.5.Besidesthefreeenergychanges,pleasestatetheothertwofactorsthataccountforthedrivingforceofsolidstatephasetransformation.Thenpleaseexplainwhy:1)incoherentphasetransformation,thecrystalusuallyadoptsdiscorneedlestructure.and2)innon-coherentphasetransformation,ballstructureisgenerallypreferred.Besidesthefreeenergychanges,othertwofactorsaretheinterfaceenergyandstrainenergy.1)Incoherentphasetransformation,interfaceenergyissmall,thestrainenergyisdominatefactor.Inordertoreducestrainenergy,thusthecrystalusuallyadoptsdiscorneedleshape.2)Innon-coherentphasetransformation,theinterfaceenergyislarge,andstrainenergyisnegligible.Inordertoreduceinterfaceenergy,smallsurfaceareaispreferred,thusballstructureisadopted6.Plspickoutthetruestatementsamongthefollowingitems:(a)Newphaseusuallymakesnucleationatdefectpoints.(T)(b)Solidstatephasetransformationiseasiertoidentify.(F)(c)Precipitationisasecondordersolidphasetransformation.(F)(d)Phasediagramreflectsphasesunderthermodynamicequilibriumconditions(T)(e)Insolidstatephasetransformation,thenewphasegenerallygrowsalonghabitplane.(T) (f)Polycrystallinetransformationisafirstorderphasetransformationanditisdiffusional(T)(g)Insecondorderphasetransformation,thereexistvolumeandentropychanges(F)(h)Ineutectoidreaction:1)Withcarboncontent<0.77%(亚共析钢，hypoeutectoidsteel),thereisproeutectoidphaseintheinterface.(T)2)WithC>0.77%(过共析钢,hypereutectoidsteel),thereisproeutectoidFe3Cphaseintheinterface.(T)3)WithC=0.77%(共析钢，eutectoidsteel),theFe3Cisgenerallyconsideredasproeutectoidphase.(T)(i)Eutectoidtransformationisakindofdiffusiontypetransformation.(T)7.Plsbrieflydescribethegeneralstepsinsolidstatephasetransformation.(1)seeds：Mostphasetransformationsbeginwiththeformationofnumeroussmallparticlesofthenewphasethatincreaseinsizeuntilthetransformationiscomplete.(2)Nucleationistheprocesswherebynuclei(seeds)actastemplatesforcrystalgrowth.Nucleationisgenerallyoccurredatinterfacialsites.Homogeneousnucleation-nucleiformuniformlythroughouttheparentphase;requiresconsiderablesupercooling(typically80-300°C).Heterogeneousnucleation-formatstructuralinhomogeneities(containersurfaces,impurities,grainboundaries,dislocations).(3)Growth:referstotheprocessthatcrystalgrowsfromthenucleationsiteandalongthedirectionofthenucleation,leadingtotheformationofanewphase8.Consideringapolycrystallinephasetransformationfromtophase,andtheirfreeenergycurvesareasfollowing: ΔGGGGT0TWhentemperatureisgreaterthanT0,cantheabovephasetransformationoccur?Why?Cannotoccur.Reason:Fromtheabovefigure,itcanbeseenthatwhenT>T0,G0,thusthereactioncannotoccur.9.Pleasededucethefreedomofaeutectoidtransformationforasystemwithtwocomponentsatfixedpressure.Andwhatdoesthisvaluemean?F=C-Ph+1=2-3+1=0Thismeansthatinatwocomponentssystem,eutectoidreactionoccursunderfixedtemperatureandwithfixedcompositionineachphase.10.Pleaseexplaintheformationprocedureofperlitefromaneutectoidsteel.Attheinterfaceof1and2,nucleationofFe3Coccursatcertainphasedirection,i.e.(010)C//(110)Inordertoreducetheworkofnucleation.InthevicinityofFe3C,concentrationofCdecreases,formingthenucleusatcertainorientationtoFe3Cand.Thesekindsofnucleationrepeatedalongtheoutsideof2phase.Inthemeantime,somenon-coherentinterfaceswerealsoproduced.Thegrowthwillhappeninbothoutsidesandtheforwarddirections,accompanyingwiththetransverseandthelongitudinaldiffusions.11.Accordingtothefreeenergydiagramofasystemwithtwocomponents(shownin thefollowing),pleaseschematicallydrawthephasediagramforthissystem(Temperatureversuscomponentconcentration,treatpressureasconstant).Answer:AttemperatureTC,thereisacommontangentforthethreecurves,withtangentpointsofxγ,xα,andxβ,whicharethelowestpointsineachcurve.Eutectoidtransformationsatisfiesthecommontangentrule,thatis:IntheG-Ccurves,atafixedcompositioninthecompositionrangeofxγtoxβ,thecorrespondingcommontangentvalueisthefreeenergyofthesystemconsistingα,β,γphasesanditisnotgreaterthanthatforα,β,γphasesatthesamecompositionwhenthesephasesexistalone.Hence,α,β,γphasesarecoexistinginthecompositionrangeofxγtoxβ.Theeutectoidtransformationoccursatfixedtemperture,thusitisahorizatallineinthephasediagram,thecompositionofphaseα,β,γisxγ,xα,andxβ,respectively. MP4-homework-withanswer-out1.Define“engineeringstress”and“engineeringstrain.”,“truestress”and“truestrain.”Engineeringstressisthenormalizedloadingforcecorrespondingtotheoriginaldimensionofthetestspecimen.Truestressisthenormalizedloadingforcecorrespondingtothefinaldimensionofthetestspecimen.Engineeringstrainandtruestrainrefertodimensionchangesofthespecimenrelativetotheoriginalandthefinalgeometry,respectively,underastress.2.Accordingtothedirectionofforces,pleaseclassifythestress.Tensilestress,compressivestressandshearstress.3.三4.5.Trueorfalsequestions:a)Theyieldstrengthshowstheresistanceofthematerialstopermanentdeformation.Tb)Theplasticdeformationisakindoftemporarydeformation.Fc)Theyieldstressofceramicsisgenerallyhigherthanthatofmetals.Td)Themaximumstrengthinthestress-straincurveistheyieldstrength.Fe)Ductilityindicatesthegeneralabilityofamaterialtobeplasticallydeformed.Tf)Plasticdeformationisgenerallyrealizedbyatomicplaneslipping.Tg)Metalspossesslargedislocationwidth,resultinginsmallyieldstrength,thusmoreductile.Whileceramicspossesssmalldislocationwidth,thuslatticeresistanceislarge,leadingtobrittlefeature.Th)Materialwithmoreslipsystemexhibitsbetterductility.T6.7. 8.Whatisthefundamentalmechanismofplasticdeformation?Thefundamentalmechanismofplasticdeformationisthedistortionandreformationofatomicbonds.Planeslipping9.10.Thealuminumalloywithinitiallengthof2.000in.hasafinallengthafterfailureof2.195in.Calculatetheductilityofthisalloy. MP5-homework-withanswer-conceptsforelectricity-waveparticledurabilityandclassical-quantumstatisticsSectionone:conceptsforelectricity-waveparticledurabilityandclassical-quantumstatistics1.2.3.(a)Calculatethemaximumwavelengthoflightthatisabletoreleasephotoelectronsfromasodiumelectrodeiftheworkfunctionofsodiumis2.3eV.(b)Photonsofwavelength200nmhittheelectrode.Calculatethemaximumkineticenergyofthereleasedphotoelectrons.12(a)Photoelectronemissionsatisfies:hn=f+mv2Theminimumconditionforphotoelectroneffectisv=0,theminimumenergyoftheincidentlightis:hn=f=2.3eVTheminimumenergylightcorrespondstothelongestwavelength:cc-9l==´10(nm)»540(nm)n2.3/h(b)=200,=2.3eV12kineticenergy:mv=hn-f=3.9eV24.5.6.Usingtheconceptofcurrentdensity,electricfield,mobilityandresistivity,basedontheOhm’slaw,deducetherelationshipbetweentheconductivityandmobility.j=sFj=nqvvj/(nq)sm===Fj/snqs=nqm 7.8.9.Trueorfalsequestions1)Ifonlythefreecarrierdensityishigh,materialexhibitshighconductivity.(F)2)Theconductivityofsemiconductorsislowerthanmetal.(T)3)Freeelectronsinmetalpossesswaveparticleduality.(T)4)Maxwell-Boltzmanstatisticsisnotvalidtofreeelectroninmaterials.(T).5)Bose-Einsteinstatisticsbelongstoquantumstatistics,applyingtosystemthatdoesnotobeyPauliexclusiverule.(T) MP6-homework-withanwer1-out1.Trueorfalsequestions.1)EnergydistributionoffreeelectronsinametalobeysFermi-Diracdistribution(T)2)Thenumberofoccupiedcollectiveelectronenergystatesinametalcrystalisequaltothetotalnumberofvalenceelectrons.(T)3)AccordingtothePauliprinciple,eachenergystatecanonlyaccommodatetwoelectronswithoppositespins.(T)4)ThemostenergeticvalenceelectronsinthemetalatT=0KlocateatFermilevel.(T)5)TheFermilevelinametalisrelatedtothedensityoffreeelectroninmetal.Anditisusuallytreatedasconstantatdifferenttemperature.(T)6)Accordingtoquantumfreeelectrontheory,thedistributionoffreeelectronagreeswithMaxwell-Boltzmannstatistics.(F)7)Althoughtherearemanyelectronenergylevelsinmetals,electronsgenerallyoccupytheenergylevelsbelowFermilevel,andonlyelectronsnearFermilevelcanbeexcitedtohigherenergylevelsbythermalactivation.(T)2.3.4.PleaseexplainthemeaningofN(E)~Ecurveinthefollowingfigure.Note:thesolidlineisthedensityofstateunderdifferentenergy,thedashlineistheprofileofaparabola.Atlowenergylevel,thedensityofelectronenergystatesversusenergycansatisfytheparabola(OApart),andthestatedensityincreaseswithenergywithinathree-dimensionBrillouinzone.WhenelectronenergyclosetotheboundaryoftheBrillouinzone,theincreaseofthedensitystateisratherabrupt,notalongtheparabolacurveanymore(ABpart). Thesecornerstatesareratherfewandbecomefilledfairlyquickly.Hencethedensitystatesdecreasesrapidlytozero(BCpart)5.6.7.8.Pleasepointsoutthemainhypothesisofquantumfreeelectrontheory1)Atomsinmetalmateriallosetheirvalenceelectron,leadingtopositiveionsandfreelymovedvalenceelectrons(freeelectron).2)DuetotheColumbicattractionbetweenthepositivecoresandthefreeelectrons,thematerialisneutralandtheelectronscannotbescatteredbytherepulsiveinteractionbetweenthem.3)ThesefreeelectronsobeyPauliexclusionprinciple,theirenergysatisfyFermi-Diracdistribution.9.PleasegivethedifferencesbetweenthehypothesisofclassicalfreeelectrontheoryandthequantumfreeelectrontheoryUnderclassicalfreeelectrontheory,electrondistributionobeysMaxwell-Boltzmannstatisticandthereisnospindescription;whileunderthequantumfreeelectron,Fermi-Diracstatisticsisapplied,andthesefreeelectronobeyPauliexclusiveprinciple.10.11.12.Pleasededuceexpressionofdensityofstatefor2-dimensionalfreeelectronemployingkspace.Ink-space,thesmallestspacefor2Delectrontooccupyis:22p24p()=2LLHence,thestatedensityshouldbeareciprocalexpression:2L24p thetotalnumberofelectronswithenergiesnotgreaterthanEshouldbe:2L2N(E)=2´(pk)24pWithoutconsideringpotentialenergy,theenergyforfreeelectronshouldbe:22212(mv)p(h/)Emv22m2m2m2k222hk2Ek22m42mThus,Bydifferentialtreatment,statedensitycanbeobtained:13.14.Usingfreeelectrontheory,explaintheopaquefeatureofmetal:Theenergystatesofthevalenceelectronsaresocloselyspacedthattheyarepracticallycontinuousandformanenergyband.Valenceelectronsinlow-lyingenergystatesinsidethemetalcaneasilyabsorbphotonsofarbitraryenergiesandbeexcitedtohigheremptyenergylevelsintheenergyband,abovetheupperlimitoffilledenergylevels.Iftheboundvalenceelectronswithhighkineticenergiesareexcitedsufficientlytheymayescapefromthesurfaceofthemetal.Inthiscasetheenergyoftheelectronsisnolongerquantizedasarbitraryvaluesofthekineticenergyareallowedoutsidethemetal.Hencephotonsofallenergiescanbeabsorbed.Consequently,allwavelengthsofvisiblelightbecomeabsorbedandnowavelengthsaretransmitted.Theresultisthatthemetalbecomesopaque. MP9-homework-withanwser-superconductor-out1.Statetheadvantages,andthecurrentandpotentialapplicationsofsuperconductor1)Advantages:zeroresistance,highmagneticfield,sensitivetoveryweakmagneticfield.2)Currentapplication:(a)Medicalmagneticresonanceimagingsystem(b)Acceleratorforexperimentalphysics:fabricationofhighmagneticsuperconductingmagnet.(c)Josephsondevice:superconductingmagneticsensorwithhighresolution.Itcan-5detectveryweakmagneticfieldof1×10Tinhumanbrain.(d)Maglevtrain:3)PotentialApplications(a)Superconductingelectricalgenerator:utilizingofsuperconductingmagneticfieldcoilcansignificantlyreduceenergyloss.(b)Superconductingcable:noheatproduced,nohighvoltageiseverneeded.2.3.Pleasetelltrueorfalseaboutthefollowingstatements:(1)Inasuperconductor,belowTc,thefreeenergyislowerinthestateofsuperconductorthaninthenormalstate.T(2)Inasuperconductor,belowTc,thespecificheatcapacityislowerinthestateofsuperconductorthaninthenormalstate.F(3)SuperconductingquantuminterferencedeviceutilizesthesuperconductorfeatureofJosephsonEffect.T(4)ThezeroresistanceofasuperconductorisduetotheformationofCooperpairbytheassistingoflatticephonon.T (5)Whenasuperconductorinafixedmagneticfield,iscooledtotemperaturebelowTC,itwillexpelthemagneticfield.T4.5.6.Explainthefollowingterms:1)Superconductivity,2)Meissnereffect1)Superconduction:Someconductors,whenitstemperaturereachesalowtemperatureofTc,theresistancedecreasestozero.Andifamagneticfieldisexertedtoit,expelforcesalwaysoccur.Thisphenomenoniscalledsuperconduction2)Meissnereffect:Asuperconductorcooledinaconstantmagneticfieldwillsetupitsowncurrentandexpelthemagneticfieldwhenthecriticaltemperatureisreached.Inotherwords,atsuperconductionstate,themagneticfieldcannotgetintotheinsideofthematerial.ThisphenomenoniscalledMeissnereffect. MP10-homework-withanswer-dielectricandthermoelectricitymaterial1.Trueorfalse,andblank-fillingquestions.1)Innonpolardielectricmaterials,thestatisticcentersofthepositiveandnegativechargesofmoleculesoverlap.(T)2)Comparedtopolardielectricmaterials,thedielectricconstantofanonpolardielectricmaterialislower.(T)3)Thermoelectriceffectisirreversible.(F)4)Foraparallelplatecapacitorinvacuum,thecapacitanceishigherintheoneemployingaluminumastheelectrodesthantheonewithsilveraselectrodes.(F)5)Inadielectricmaterial,applyingaalternativeelectricfield,thephaseofchargingcurrentwillbethesameasthatoftheelectricfield.(F)6)Therefractiveindexrelatestothepolarizationofdielectricmaterialunderopticalfrequencythatonlyresponsestotheelectricpolarization.(T)2.Pleasegivethedefinitionaboutdielectricmaterials.Tellthreebasictypesofpolarization,andgivetheorderbasedontheirresponsetime.Answer:Dielectricmaterialsrefertomaterialswhichexhibitpolarizationunderelectricfieldbutnotlongrangedrift.Polarizationtypes:1)electronic,2)ionic,3)orientationalResponsetime:1)<2)<3)3.4.Whatisadipole?PlspointoutthedirectionadipolemomentAdipoleisapairofoppositechargesseparatedbycertaindistance.Thedirectionofa dipolemomentisfromthenegativechargetothepositivecharge. MP11-andMP12-homework-withanwers1.WhatisthemeaningofthegasconstantR?R=NAk.Oryoucansay:RmeanstheBoltzmannconstantmultipliedbyAvogadro’snumber.2.3.4.5.6.Accordingtothefollowingfigureformetalheatcapacity,pleaseexplainthedifferenttemperaturedependenceineachregion.1)regionI(0-5K):C∝TPhononsarefrozen,electronsarethemaincontributiontoheatcapacity32)regionII:C∝TMainfactorislatticevibration,theheatcapacitysatisfieswithDebyemodel3)AtDebyetemperature,C=3R,4)regionIII(aboveDebyeT),C>3RBothlatticevibrationandelectroncontributetoheatcapacity.7.PleaseexplainDebyetemperature. Debyetemperatureisthedeterminantpointforchoosingeitherclassicalmodelorquantummodel.Thatis:a)BelowDebyetemperature,phononsarefrozen,quantummodelshouldbeapplied.b)AboveDebyetemperature,allphononsareactive,classicalmodelsuchasDulong-Petitlawcanbeused.8.Trueorfalsequestions1)Heatcapacityisindependentofspinarrangement.(F)2)Theheatcapacityofonematerialisdependentoncrystalstructure.(T)3)Thefactorsthatcontributetoheatcapacityincludeatomicvibrationandelectronvibration.(T)4)Comparedtometal,thecapacityofceramicsshowsmoreagreementwithDebyemodelbecausetherearehardlyfreeelectronsthere.(T)9.10.Comparethethermalconductingfactorsofnonconductingsolidswithmetals.Innonconductingsolids,freeelectronsarenegligible,phononvibrationisthedominatefactorforthermalconduction(involvingthermalcapacity,meanfreepathandvelocityofphonon)Inmetals,freeelectronsarethedominatefactorforthermalconduction,especiallyatThigherthanD.AtlowT,bothelectronandphononareresponsibleforthermalconduction.Atextremelylowtemperature,duetothefrozenofphonon,electronthermalconductionisdominate.11.12.13.Trueorfalsequestions1)Incopper,thedominantfactorforthermalconductionisphonon.F2)Formetalswithrelativelylowelectricalconductivityandatrelativelylow temperature,bothelectronandphononarethemaincontributionforthermalconduction.T3)ThethermalconductivityofmaterialsisindependentoftemperatureF4)ThethermalconductionbyphotontakeseffectonlyathightemperatureT5)Inagoodconductor,theratioofthermalandelectricalconductivitiesisproportionaltoabsolutetemperature.T6)Generallyspeaking,athermalconductivityofametalalloyislowerthancorrespondingmetal.T7)Thethermalconductivityofaceramicwithcrystallinestructureisgenerallylowerthanthatinamorphousstate.F8)Comparedtoopaqueamorphousceramic,thesharperincreasingofthermalconductionathightemperatureinatransparencyamorphousceramicisduetophotonthermalconduction.T9)Inanisotropicmaterial,thevolumeexpansioncoefficientisthreetimesthelinearexpansioncoefficient.T10)Generallyspeakingthethermalexpansioncoefficientisreciprocaltomeltingpoint.T'