Section 1B Metallic CrystalStructure

Section 1B Metallic CrystalStructure - Section 1 Metallic...

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MATE 210 Section 1 Metallic Crystalline Structures Gasses – no order Liquids – short range order Solids – long range order the order is determined by the type of bond STRUCTURE PROPERTIES (Smith Chapter 3, skip 3.11)
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MATE 210 Structure of Materials How atoms are arranged: orderly, periodic crystalline random, nonperiodic noncrystalline , amorphous lack of long range order (similar to atom arrangement in liquids) some glasses & polymers
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MATE 210 Crystalline Material atomic arrangement in solid: • periodic and repeating 3D array • long range order metals, many ceramics, certain polymers unit cell Fe (BCC) 1mm = 3.5 x 10 6 unit cells
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MATE 210 unit cell • basic unit or building block of crystal structure • geometry lattice constants: a, b, c interaxial angles: α, β, γ cubic a = b = c α = β = γ = 90° 7 crystal systems (Smith Table 3.1) tetragonal cubic hexagonal rhombohedral orthorhombic triclinic monoclinic
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MATE 210 Crystal Structure: geometry + atom positions spatial arrangement of atoms, ions, or molecules ceramics NaCl CsCl ZnS FCC BCC HCP a b c polymers metals Cu,Al Cr, Fe Ti,Zn 90% of metals
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MATE 210 Crystal structures Cubic Crystal Structures: a = lattice constant or lattice parameter = length of side of unit cell a a a Si - tetrahedral
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MATE 210 # atoms/unit cell = atomic packing factor (APF) = volume atoms/volume cell = 0.74 “ close packed” (Al, Cu, Au, Ni, Pb, Pt, Ag) 1. FCC: face-centered cubic (8 x 1/8) + (6 x ½) = 4 a r 2 4 = r a 2 2 = V cell = a 3 = () 2 2 2 4 r a a = + 3 2 16 r V s / V c V atoms = 4 x (4/3 π r 3 )
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MATE 210 2. BCC: body-centered cubic # atoms/unit cell = atomic packing factor (APF) = ? (Fe, Cr, Mo, Ta, W, V) atoms touch along body diagonal: (8 x 1/8) + 1 = 2 () ( ) 2 2 2 2 4 a a r + = 3 4 r a = V c = 64 r 3 / 3(3) 1/2 a a 2 a a V s / V c
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MATE 210 3. HCP: hexagonal close-packed noncubic symmetry # atoms/unit cell = ? atomic packing factor (APF) = 0.74 close packed (Cd, Mg, Be, Co, Ti, Zn) a c V c = 19.6 r 3 (3) 1/2 a and c axes c/a ~ 1.633 Smith Table 3.4
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MATE 210 Density ρ = mass of atoms/volume of unit cell n = no. atoms/unit cell AW = atomic weight (g/mol) V c = volume of unit cell N A = Avogadro’s no. (6.023 x 10 23 atoms/mole) r = atomic radius a = lattice constant of unit cell A C N V nAW = ρ Example: Cu crystal structure n = A = r = a (FCC) V c volume of unit cell: a 3 = ρ = (actual density = Smith) FCC 4 atoms/unit cell 63.5 g/mol 1.28 Å = 1.28 x 10
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This note was uploaded on 04/02/2008 for the course MATE 210 taught by Professor Niebuhr during the Spring '05 term at Cal Poly.

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Section 1B Metallic CrystalStructure - Section 1 Metallic...

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