最新crystalmeltphasediagrams晶体熔体相图课件PPT.ppt

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1、crystalmeltphasediagrams晶体熔体相图TheGibbsPhaseRuleThephaseruleallowsonetodeterminethenumberofdegreesoffreedom(F)orvarianceofachemicalsystem.Thisisusefulforinterpretingphasediagrams.F=2+C-FWhereFisthenumberofdegreesoffreedom,CisthenumberofchemicalcomponentsandFisthenumberofp

2、hasesinthesystem.ThenumbertwoisspecifiedbecausethisformulationassumesthatbothTandPcanbevaried.PhaseRuleSignificanceforPhaseDiagramsFortwodimensionalphasediagrams:Stabilityfields:Areas(T-P,T-X,P-Xspace)whereaphaseorphaseassemblage(morethanonephase)isstable.Equilibriumboun

3、darylines:Thesedefinethelimitsofstabilityfields.Theserepresentvaluesofintensiveparameterswherephasesinadjacentfieldscoexist.Triplepoints:Pointswhereequilibriumboundarylinesmeet.Allphasesintheadjacentstabilityfieldsmustcoexist.Di-AnBinaryEutecticPhaseDiagramBinaryPhaseDia

4、gramDefinitionsEutecticpoint:LowestTpointontheliquidusatwhichauniquemeltoffixedcompositionisinequilibriumwithtwoormorephases.Isopleth:lineofconstantchemicalcomposition.Isotherm:lineofconstanttemperatureTieline:portionofisothermthatconnectstwostablecoexistingphases,inthis

5、caseL(representingthesilicateliquid)andS(purecrystallineanorthitefeldspar)TheLeverRuleFollowsdirectlyfromtheLawofConservationofMass.Allowsonetocalculateeitheralgebraicallyorgraphicallythemodalabundanceofeachphaseateverytemperature.MASSOFLIQUIDMASSOFSOLIDBULKCOMPOSITIONCo

6、olingHistoryinaBinaryEutecticSystemIntersectionwithliquidus:F=>1(TorX)Eutecticpoint:F=>0InitialState:F=1+C-F=1+2-1=2(T&X)subsoliduscoolingF=>1dQ/dtisconstantF=1F=2F=2F=3Di-AnBinaryEutecticFreeEnergyRelationsMgO-SiO2IncongruentBinaryMeltingRelationsPeritecticpoint:binarys

7、ystemwith3phases,oneofwhichisliquid,areinareactionrelation.AtR,thereactionpoint:Mg2SiO4+SiO2(inmelt)=2MgSiO3+latentheatEnstatitemeltingyieldsliquidricherinsilica.Equilibriumvs.FractionalCrystallizationEquilibriumCrystallization:crystalscontinuouslyreactandre-equilibratew

8、iththemeltatP-T-Xconditionschange.Melt-xtalreactionsarereversibleFractionalCrystallization:Crystalsarei