材料科学基础07相图ppt课件.ppt

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1、相图（phasediagram）物质有熔点：Al2O3,MgO，TiO2，SiO2Al2O3和TiO2混合在一起，多高温度下开始出现液相？Al2O3和TiO2混合在一起，在一定的温度下会发生化学反应吗？不同比例的Al2O3和TiO2混合在一起，反应后的产物组成有什么不同？开始出现液相的温度有什么不同？1相图（phasediagram）2相图（phasediagram）的作用Usedtodetermine反应方向（reactionsdirections）Reactions(automatically自动地)happenstowardtowhatdirection?Whatdrivesarea

2、ctiontohappen?Reactionshappenstowardthedirectionwithwhichtheenergyofthesystems(materials)isminimized3Whydoweneedtostudyphasediagrams?Manufacture（制造）ofmaterials(材料):PredictphasecompositionofrefractoriesCanyougiveanexample?Application/useofrefractories:understandslagcorrosion渣腐蚀bychemicalreactionCan

3、yougiveanexample?ThisquestionmayberaisedwhenyouattendajobintervieworaninterviewforPhDcomprehensiveexamination4PhasediagramsBEAWARE（注意）:Phasediagramsarephaseequilibrium（平衡）diagramsSolidreactionsinrefractoriesseldom（很少）reachcomplete（完全的）equilibriumAl2O3MgOMgAl2O41650C5DefinitionsofPhaseDiagramsBoun

4、darybetweentheLiquidregionandtheCaOss+LiscalledtheLIQUIDUS.TheboundarybetweentheMgOssandMgOss+LiscalledtheSOLIDUSPointatwhichtheLIQUIDUSlinesmeetiscalledtheEUTECTICPOINT液相线:liquidus固相线:solidus最低共熔点:eutecticpoint6DefinitionsofPhaseDiagramsMgOssrepresentsaMgO-richsolidsolutionwithCaOasthesoluteSimil

5、arly,CaOssrepresentsaCaO-richsolidsolutionwithMgOasthesolute固溶体：solidsolution7Whatdoweknowfromthediagram?LowesttemperatureatwhichliquidbeginstoformPrecipitationofMgOssfromCaOsswhentemperaturedecreasesMaximumamountofMgOinCaOssThecompositionoftheeutecticpointMeltingtemperatureComposition:组成Precipita

6、tion:析出8DefinitionsofPhaseDiagramsLiquidphaseispresentatalltemperaturesandcompositionsabovethislineOnlysolidphaseMgOssexistsbelowthislineHomogeneousliquidsolutionMgOsolidsolutionCaOsolidsolutionSinglephaseregionsRegion：区域Homogeneous：均匀的9DefinitionsofPhaseDiagramsCaOssandLiquidco-exist共存MgOssandLiq

7、uidco-existMgssandCaOssco-existTwo-phaseregions10TheEutecticReactionLMgOss+CaOss‘EutecticPoint’isthe‘Invariant’3phasesexistinequilibriumWhyisitcalledtheeutecticpoint?SimplybecauseeutecticmeansEASILYMELTED!Invari