材料化学全英文课件第7课课件

材料科学基础 Fundamental of Materials Science,Prof: Tian Min Bo Tel: 62795426 ，62772851 E-mail: Department of Material Science and Engineering Tsinghua University. Beijing 100084,Lesson seven,2.9 Some Additional Terminology in Crystallography,2.9.1 Crystal structure of some elements,According to the crystal structure, the elements of the periodic table can be sorted to three types:,Type ：with typical metallic structureFCC，BCC，HCP Type ：covalent bonding , obey 8N rule, N 4,Crystal structure of diamond, N 5,Crystal structure of Sb,Crystal structure of Se and Te, N 6,2.9.2 Allotropy and polymorphic transformations Same crystal has different crystallographic structure at different condition. Examples:, C , graphite , diamond , CNT, Fe,Graphite,C60 molecule,Carbon Nanotubes,2.9.3 Single crystal versus polycrystal 1. For single crystals there is only one type of structure with same orientation. Single crystals is characterized by anisotropy. 2. Polycrystal consists of a lot of grain, small single crystals, with same structure but different orientations. These small single crystals are called grains. The boundaries between them are called grain boundaries.,Discussion,Amorphous, single crystal, and polycrystal. Glass. SiO2, Al2O3, B2O3, MgO, CaO, Na2O, K2O,Exercise,1. Compare the crystal structure, atomic bonding and properties of graphite with diamond.,2. Why properties of elements changes periodically as the atomic numbers change? What the differences of changes between short period elements and long period elements? And why?,3. Calculate the percent volume change as zirconia transforms from a tetragonal to monoclinic structure. The lattice constants for the monoclinic unit cells are: a=5.156, b=5.191, and c=5.304 , respectively. The angle for the monoclinic unit cell is 98.9. The lattice constants for the tetragonal unit cell are a=5.094 and c=5.304 , respectively . Does the zirconia expand or contract during this transformation? What is