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1、材料科学基础Fundamental ofMaterialsScienceProf:TianMinBoTel:62795426，62772851E-mail:tmb@mail.tsinghua.edu.cnDepartmentofMaterialScienceandEngineeringTsinghuaUniversity.Beijing100084Lessonseven2.9SomeAdditionalTerminologyinCrystallography2.9.1Crystalstructureofsomeelement
2、sAccordingtothecrystalstructure,theelementsoftheperiodictablecanbesortedtothreetypes:TypeⅠ：withtypicalmetallicstructure——FCC，BCC，HCPTypeⅢ：covalentbonding,obey8－Nrule①N＝4Crystalstructureofdiamond②N＝51234CrystalstructureofSbCrystalstructureofSeandTe③N＝62.9.2Allotropy
3、andpolymorphictransformationsSamecrystalhasdifferentcrystallographicstructureatdifferentcondition.Examples:BCCBCCFCC②C,graphite,diamond,CNT①FeGraphiteC60moleculeCarbonNanotubes2.9.3Singlecrystalversuspolycrystal1.Forsinglecrystalsthereisonlyonetypeofstructurewithsa
4、meorientation.Singlecrystalsischaracterizedbyanisotropy.2.Polycrystalconsistsofalotofgrain,smallsinglecrystals,withsamestructurebutdifferentorientations.Thesesmallsinglecrystalsarecalledgrains.Theboundariesbetweenthemarecalledgrainboundaries.GrainboundaryDiscussion
5、Amorphous,singlecrystal,andpolycrystal.Glass.SiO2,Al2O3,B2O3,MgO,CaO,Na2O,K2OExercise1.Comparethecrystalstructure,atomicbondingandpropertiesofgraphitewithdiamond.2.Whypropertiesofelementschangesperiodicallyastheatomicnumberschange?Whatthedifferencesofchangesbetween
6、shortperiodelementsandlongperiodelements?Andwhy?3.Calculatethepercentvolumechangeaszirconiatransformsfromatetragonaltomonoclinicstructure.Thelatticeconstantsforthemonoclinicunitcellsare:a=5.156,b=5.191,andc=5.304Å,respectively.Theangleβforthemonoclinicunitcellis98.
7、9°.Thelatticeconstantsforthetetragonalunitcellarea=5.094andc=5.304Å,respectively.Doesthezirconiaexpandorcontractduringthistransformation?Whatistheimplicationofthistransformationonthemechanicalpropertiesofzirconiaceramics?Thankyou!7
