Crystalline Solids (고체의 결정구조) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University

OCW 5. Single Crystal, Polycrystalline, Amorphous 11. FCC structure https://www.youtube.com/watch?v=KaJfI3IjcA0&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=5 Families of directions/planes https://www.youtube.com/watch?v=5f4C6e-9rgg&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=6 Crystallographic Points https://www.youtube.com/watch?v=dP3LjWtoeMU&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=7 Crystallographic Directions https://www.youtube.com/watch?v=fYK45OdnZH0&index=9&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm Atomic densities and Packing Factors https://www.youtube.com/watch?v=RGCqLEU2IIM&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=10 11. FCC structure https://www.youtube.com/watch?v=pHt7--8I4bQ&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=11 Ionic crystal structures https://www.youtube.com/watch?v=A3cPHn_OgVQ&list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm&index=12

KOCW 결정질 고체의 구조1 http://www.kocw.net/home/cview.do?lid=e3b3aa8d5f4fe457 결정질 고체의 구조2 http://www.kocw.net/home/cview.do?lid=73a944a210fcc2ff 결정질 고체의 구조 3 http://www.kocw.net/home/cview.do?lid=ac01572fd22d54c9

Cristal Structure Atoms (assume hard spheres) are packed BCC, FCC, HCP structures Atomic Packing Factor, APF (충진율) = Volume of atoms in unit cell / Volume of unit cell Theoretical density (밀도) = Mass of atoms in unit cell / Volume of unit cell Crystallographic planes(결정방향) are expressed by Miller indices. ex) (1 0 0)

Body Centered Cubic, BCC (체심입방) Atoms touch each other along cube diagonal corners. Fe, Cr, W a √3a R 2 atoms / unit cell  

Face Centered Cubic, FCC (면심입방) Atoms touch each other along face diagonals. Al, Cu, Pb, Ni, Au, Pt, Ag 4 atoms / unit cell AFP = 0.74

Hexagonal Close-Packed, HCP (육방조밀) Hexagon-Triangle-H-T… Stacking Sequence Mg, Ti, Zn, Cd Hexagon Triangle 6 atoms/unit cell AFP = 0.74

Crystallographic Planes (결정방향) Miller Indices: Reciprocals of the (three) axial intercepts for a plane. Intercept(교차)Reciprocal(역수)  Integer(정수) values z x y (110) (200) (211) Intensity (relative) Diffraction angle 2q X-ray diffraction pattern (X선회절) for polycrystalline a-iron (BCC)

Single crystal, Polycrystalline, Amophous Amorphous (비정질) Single crystal diamond Cast iron grain Glass

Single crystals (단결정) Material properties generally vary with single crystal orientation. they are anisotropic(이방성). (111) Single crystal silicon wafer & anisotropic etching

fig_03_18 Polycrystalline (다결정) Most engineering materials are polycrystalline. Each grain(결정립) is a single crystal. If grains are randomly oriented, overall component properties are isotropic(등방성, not directional). Grain sizes typically range from 1 nm to 2 cm liquid crystals grow polycrystalline grains Polycrystalline grains of metal

Amorphous (비정질) Amorphous = Noncrystalline Atoms have no periodic packing Transparent ex) Glass Si Oxygen noncrystalline SiO2

Summary Metallic crystal: FCC, BCC, HCP Single crystal: Anisotropic (properties vary with crystal orientation) Poly crystalline: Isotropic (properties are non directional  randomly oriented grains) Amorphous: Isotropic (random)