材料学基础7.ppt

材料科学基础Fundamental of MaterialsFundamental of MaterialsProf:Tian Min Bo Tel:62795426，62772851 E-mail:Department of Material Science and EngineeringTsinghua University.Beijing 100084Lesson seven2.9 Some Additional Terminology in Crystallographyuu.Single crystal versus polycrystal 1.1.For single crystals there is only one type of structure with For single crystals there is only one type of structure with same orientation.same orientation.Single crystals is characterized by anisotropy.Single crystals is characterized by anisotropy.2.2.Polycrystal consists of a lot of grain,small single crystals,Polycrystal consists of a lot of grain,small single crystals,with same structure but different orientations.These small with same structure but different orientations.These small single crystals are called grains.The boundaries between single crystals are called grains.The boundaries between them are called grain boundaries.them are called grain boundaries.single crystal polycrystalgraingrain boundaryuu.Allotropy Same crystal has different crystallographic Same crystal has different crystallographic structure at different condition.structure at different condition.Examples:Examples:C,C,graphite,diamond,CNT graphite,diamond,CNT BCCBCCBCCBCCFCCFCCGraphiteC60 moleculeCarbon Nanotubesuu.Atomic radiiDefinition:Examples and DiscussionsExerciseThank you!7