MCE 230_ F10_lec_6 - MCE 230 Materials Science Fall 2010...

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MCE 230 – Materials Science Fall 2010 Lecture - 6
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Crystalline Structure
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Hexagonal Close Packed (HCP)
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a/c ratio = 1/1.633 A total of 6 “whole” atoms are assigned to the HCP unit cell Coordination Number: 12 APF = 0.74 Hexagonal Close Packed (HCP)
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Allotropy Some metals and non metals have more than one crystal structure depending on the surrounding environment (temperature and pressure), and so properties change Examples: Carbon ( graphite at room temperature, with very high pressure it is diamond ) Iron (BCC at room temperature, and FCC at high temperature)
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Theoretical Density n: no. of atoms assigned to the unit cell A: Atomic weight (g/mol) V c : Volume of the unit cell (cm 3 ) N A : Avogadro’s number (6.023x10 23 atoms/mol) A c N V A n
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Theoretical Density: Copper Cu has FCC structure: A = 63.5 g/mol Atomic radius, R = 0.128 nm V c = a 3 A c N V A n R 2 2 a th = 8.89 g/cm 3 (compare to literature value of 8.94 g/cm 3 ) n =4
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MCE 230_ F10_lec_6 - MCE 230 Materials Science Fall 2010...

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