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1、相律PhaseRulesPhasediagramsareextremelyusefulforsystemswithmultiplecomponen亳Sandservetodescribephysicalandchemicalequilibriaoverarangeofdifferentcompositions,aswellaspointswheresubstancesaremutuallymiscible,orevenwhenasystemhastobebroughttoaspecificsetofconditionsforequilbriumtoexist(e.g.,pressure,tem
2、peratureandcomposition)Phasediagramsareveryimportantinthedevelopmentof日“alloys毛“ceramicmaterials日“Steels日“Semiconductors里“plastics里“Superconductors日“Cosmetics毛“petroleuinproducts2parations里“foodproducts里“glasSesAllphasediagramsaredevelopedaroundonerelationship,thephaserule,whichwasderivedbyJ.W.Gibbs
3、-itcanbeappliedtoawidevarietyofsystemsPhasediagrams:pictorialwayofunderstandingthepropertiesofasystem相律PhaseRules-SignifiesaformofmatterthatisuniformthroughoutnotonlyinchemicalComEoSmonbutalsoinEhSica_stateNumberofphasesisdenotedby:尸=1forgas,gaseousmixture,crystal,twomiscibleliquids,ice尸=2forslurryo
4、ficeandwater,immisciblemetalalloysSometimesnoteasytodecidehowmanyphasesthereare-forexample,asolutionofsolidAinsolidB-homogeneousonmolecularscale-Aatoms2resurroundedbyBatoms,representativeofcompositiononthewholelexampis3)口Adispersion(exampleb)isuniformmacroscopicallybutnotonthemicroscopicmolecularlev
5、el-forexamples,regionsofAareembeddedwithingamatrixofB,stiluniformcomposition-veryimportantinmaterialssynthesis,especiallyproductionofsteels,tailoringmaterialsmechanicalandelectricalproperties相律PhaseRulesConstituent:Achemicalspeciesthatispresentinasystem、Forexample,amixtureofwaterandethanolhas2consit
6、uenttsComponent:Achemicallyindependentcomponentofthesystem、Thenumberofcomponentsinasystem,C,istheminimumnumberofindependentspeciesneededtodefinethecompositionofallofthephasespresentinthesystem里Whennoieactiontskesplace,Consituents=Components日Whenareactioncanoccur,thenumberofcomponentsistheminimumnumb
7、erofspecieswhichspecifiesthecompositionofalofthephases相律PhaseRules-Cacost)“Caots)+“Cozlg)Phase1Phase2GasPhase,NumberofPhases,尸=3。NumberofConstituents=3NumberofComponents,C=2*CaCOucanbeexpressedintermsof2componentsintwodifferentphasesfromthestoichiometryofthereaction-Considerthethermaldecompositionof
8、ammoniumchloride:NHCl(s)二NHs(g),权HCLH9)“NumberofPhases.尸=NumberofConstituents=3NumberofComponents,C=仁*NHandHClarefixedinstoichoimetricproportionsbythereaction,andcompositionsofbothphasescanbespecifiedbyNHJCl注意:独立浓度关系只限于同一相中相律PhaseRules注意:独立浓度关系只限于同一相中-Considerthethermaldecompositionofammoniumchlorid
9、e:NHCL(s)“NH(g)“。HCL(g)N.B.,ifadditionalHClorNH,wereaddedtothesystem,decompositionoftheNHCIwouldnotgivethecorrectgasphasecompositions,andeitherHClorNHawould-HO()“XO。(g)+H(g)(atroomtemp)*NumberofPhases,P=2,NumberofConstituents=3NumberofComponents,C=3*Atroomtemperature,O。(g)andH。(g)donotreacttoformwat
10、er,sotheyarenotinequilibrium:regardedasindependentconstituents相律PhaseRulesThevariance,FisthenumberofintensivevariablesinasystemthatcanbechangedindependentlywithoutdisturbingthenumberofphasesinequilibriumJW.Gibbs,rsgardedasAinericasfrsttheoreiicalscientistandthefatherofchemicalthermodynamics,wrotetha
11、tthenumberofcomponents,C,andthenumberofphasesatequilibrium,Pforasystemofanycomposition:相图PhaseDiagramPhaseTransition:Spontaneousconversionofonephaseintoanother,occurringatacharacteristictemperatureforagivenpressureConsiderwateratp=1atm:lceisstablephasewhenT0hieshiaudwaerwhenT0hieshiaudwaerwhen70心言东志
12、团2写关口TransitionTemperature,Tos:stetleTemperaturewhenchemicalpotentialsare万五equaliforexample,hics=hiauavateat丁=0TemperatureT相图PhaseDiagramPhaseDiagram:ShowsregionsofpressureandtemperaturewherephasesarethermodynamicallystableVapourPressurecnicalPressureofagasiponinequilibriumwiththeliquidphaseSoidSubl
13、imationVapourPressurePressureofgasinequilbriumwithsolidphase“peressurepPontMapourPhaseBoundaries匹sVapour户separateregionsand1)showpandTwhere1twophasesexistinequilibriumnTenponhmTTriplePoint“CriticalTemperatureVapourpressuresincreasewithhigher7astheEBoltzmanndistributionpopulatesthehigherenergystatesw
14、ithincreasingtemperature单组分系统的相图OneComponentSystems纶分国图Phase7Phasee“2hase8一一F=0,threephasesjnequilibriumPressure,pTemperature,丁单组分系统的相Considerpurewater:PressureplatmTemperateTOneComponentSystemisaIngasphase,cooledatconstantp,F=25“Liquidappearsatthephasetransition(theboilingtemperature),andF=1、Wehavespecifiedconstantp(singledegreeoffreedom),soequilibrium7isnotunderourcontrolc“LoweringTtakesliouidtosinglephaseliquidredion户=27canbevariedatwild“Liquid-solidphasetransitionatThwithF=7,andatconstantp,Tisnotunderourcontrol6LoweringTfurtherresultsinsinglesolidphasewithF=2,wherepand7canbevaried
