材料热力学与动力学-1

Chapter1:ThermodynamicsandPhaseDiagrams1-1Chapter1.ThermodynamicsandPhaseDiagramsProf.Dr.X.B.ZhaoDepartmentofMaterialsScienceandEngineeringZhejiangUniversityChapter1:ThermodynamicsandPhaseDiagrams1-2HomogeneousSystemwiththesamephysicalandchemicalpropertiesHeterogeneousSystembeingmadeofseveralphases1.0.1ThermodynamicsSystemsChapter1:ThermodynamicsandPhaseDiagrams1-3OpenSystemcanexchangemass,heatandworkwithitssurroundingsClosedSystemnomassexchange,heatandworkexchangepossibleIsolatedSystemnomass,noheat,noworkexchangeChapter1:ThermodynamicsandPhaseDiagrams1-4A.Energy,HeatandWorkTheenergyofanisolatedsystemisconstantTheworkdoneonathermallyisolatedsystemisindependentofthetypeofworkandtheroute1.0.2TheFirstLawofThermodynamicsChapter1:ThermodynamicsandPhaseDiagrams1-5isolatedsystemW=0,E=const.closedsystemDE=Q+WQ0,systemreceivesheatQ0,systemlosesheatforaninfinitesimalchangeofstateinaclosedsystemdE=dQ+dWW0,workisdoneonthesystemW0,workisdonebythesystemW=E2-E1=DEstate1to2:Chapter1:ThermodynamicsandPhaseDiagrams1-6ThetotalenergyEofasystemismadeupofitskineticenergyEkinetic,itspotentialenergyEpotentialanditsinternalenergyUEkinetic+Epotential+U=const.B.InternalEnergyE=Ekinetic+Epotential+ULawofConservationofEnergyforanisolatedsystemChapter1:ThermodynamicsandPhaseDiagrams1-7Atconstantmacroscopicvelocitiesandconstantpositioncoordinates,thefollowingsapplytointernalchangesofstate:DU=WadiabaticprocessDU=0isolatedsystemDU=Q+WclosedsystemdU=dQ-PdVChapter1:ThermodynamicsandPhaseDiagrams1-8C.EnthalpyandHeatCapacityH=U+PV(definition)dH=dU+VdPDH=Q(atconstantP)VVTUCPPTUCChapter1:ThermodynamicsandPhaseDiagrams1-9EverythermodynamicsystempossessesanextensivepropertycalledentropyS.Thechangeinentropyofasystemisdeterminatedbybringthesystemfromanarbitraryinitialstatetoadefinedfinalstate,wherebythesystempassesthroughaseriesofequilibriumstates.AteachstepthequantityofheatdQisaddedtothesystem.DivisionofdQbythetemperatureT,andsummationofthequotientsdQ/Toverallsteps,yieldsthechangeinentropyofthesystemforthechangeofstate.EntropyDdSTQSTT10d1.0.3TheSecondLawofThermodynamicsChapter1:ThermodynamicsandPhaseDiagrams1-10S=klnWBolztmann’sEquationk=1.38065810-23J/K:Bolztmann’ConstantW:numberofpossiblearrangementsofatomsEntropyisastatefunction.Forareversiblecyclicprocess:0DTQSdChapter1:ThermodynamicsandPhaseDiagrams1-112partsofDS(innerandexternal)DSinner:frominnerprocessesDSexner:duetoheatexchangeDSinnerQDSexterreversibleprocess:DSi=0,DS=DSeirreversibleprocess:DSi0,DSDSeadiabaticprocess:DSe=0,DS=DSiirr.adiabaticprocess:DS0rev.adiabaticprocess:DS=0Chapter1:ThermodynamicsandPhaseDiagrams1-12TheSecondLawofThermodynamicsTheentropyofaclosedsystemcannotdecrease.Clausius:Heatcannotflowautomaticallyfromcoldsidetohotside.perpetualmachinestypeIPlanck:Suchaprocessisimpossibleifitsonlyresultweretoexchangeheattowork.typeIIChapter1:ThermodynamicsandPhaseDiagrams1-13Mr.TompkinsinPaperbackG.GamowCambridgeUniversityPress,1965Heatcannotflowautomaticallyfromcoldsidetohotside!!!Chapter1:ThermodynamicsandPhaseDiagrams1-14Phase:aportionofthesystemwhosepropertiesandcompositionarehomogeneous,andisphysicallydistinctfromeachother.Agivensystemcanexistasamixtureofoneormorephases,whichcanchangeintoanewphaseormixtureofphases.Why?theinitialstateofthesystemisunstablerelativetothefinalstate1.1EquilibriuminaClosedSystemChapter1:ThermodynamicsandPhaseDiagrams1-15Howissystemstabilitymeasured?byitsGibbsfreeenergy(atconst.TandP)G=H-TS(1.1)H:ameasureoftheheatcontentofthesystem(H=U+PV)S:ameasureoftherandomnessofthesystemlowT:TSsmall,solidsaremoststable(strongestatomicbinding,lowH)highT:TSdominates,liquidsorgasesarestable(atomsmorefree,highS)Chapter1:ThermodynamicsandPhaseDiagrams1-16Stable,MetastableandUnstableGdG=0BACdG=0dG=0anarbitrarystateparameterBACStable:graphite,singlecrystalsiliconMetastable:diamond,amorphousUnstable:super-coolingliquid(nucleation)BACChapter1:ThermodynamicsandPhaseDiagrams1-17PossibilityandRealizability:ThermodynamicsandKineticsGBACG1G2EnergyHumpDG=G2–G10:onlypossibleforthetransformationfromBtoAAmorphousAlloy(short-lived),Diamond(long-lived)Temperature:kinetickey(vibrationfrequencyandamplitude)Chapter1:ThermodynamicsandPhaseDiagrams1-18ThermodynamicFunctionsStateFunctionsdefinedonlybythestateofthesystem,independentontheroutetothestateIntensivePropertiesindependenttosystemsize(T,P)ExtensivePropertiesdirectlyproportionaltothequantityofmaterialsinthesystem521631180relationsbetweenthermodynamicfunctionsextensivepropertiesusuallyexpressedinunitspermole1molematerial:6.0231023atoms(ormolecules)numberofmoles=mass/molecularweightChapter1:ThermodynamicsandPhaseDiagrams1-191.2.1EffectofTemperatureSpecificHeat:quantityofheat(injoules)requiredtoraisethetemperatureofthesubstancebyonedegreeKelvinPPTHC2cTbTaCPCP0T(K)Forapureelementat298K,H=0TPdTCH298H298KSlope=CP0T(K)1.2SingleComponentSystemsChapter1:ThermodynamicsandPhaseDiagrams1-20EntropyS0T(K)TPdTTCS0PPTSTCS0T(K)T0whatwillhappenatT0?The3rdlawofthermodynamics:S=0at0Kfor