Lecture04.Slides%20of%20Point%20Cooridnates%20Directions%20Surfaces

Lecture04.Slides%20of%20Point%20Cooridnates%20Directions%20Surfaces

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Amorphous and crystalline Amorphous: Position of atoms is completely random Crystalline: Position of atoms is ordered Crystal: Ordered region where all atoms have same structure and same orientation Polycrystalline Made of lots of different crystals material: Grains: Individual crystals in a polycrystalline material
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Micrograph of grains in alumina Micrograph taken by B.J. Dalgleish
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Close packing of spheres
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Stacking layers of close-packed planes A x xxx x x x x x x xx x B C A - B or A - C etc.
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Hexagonal close-packed (h.c.p) crystals Close-packed hexagonal (c.p.h) A ABABABAB etc. B A
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Unit cell of h.c.p. Unit cell: Minimum basic repeat unit of a crystal c a a
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Face-centered cubic (f.c.c) crystals A ABCABCABC etc. B C
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Unit cell of f.c.c. √2 a
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• APF for a simple cubic structure = 0.52 APF = a 3 4 3 π (0.5 a ) 3 1 atoms unit cell atom volume unit cell volume Atomic Packing Factor (APF) APF = Volume of atoms in unit cell* Volume of unit cell *assume hard spheres Adapted from Fig. 3.23, Callister 7e. close-packed directions a R =0.5 a contains 8 x 1/8 = 1 atom/unit cell
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Face-centered cubic crystal Coordination # = 12 Adapted from Fig. 3.1, Callister 7e. ex: Al, Cu, Au, Pb, Ni, Pt, Ag 4 atoms/unit cell: 6 face x 1/2 + 8 corners x 1/8 • Atoms touch each other along face diagonals.
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Lecture04.Slides%20of%20Point%20Cooridnates%20Directions%20Surfaces

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