ENGR 240 - 8.31.2007

ENGR 240 - 8.31.2007 - ENGR 240 August 31, 2007 FCC face...

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ENGR 240 – August 31, 2007 FCC – face centered cubic Lattice parameter (edge length) – a – important in identifying metals in a cubic structure o Can be found using Pythagorean theorem a 2 + a 2 = x 2 x = 4R => a =2Rsqrt(2) R is the atomic radius o Coordination number – number of nearest neighbor atoms FCC coordination number = 12 o Atomic packing factor – (APF) – how efficiently the atoms are packed APF = Volume of atoms in unit cell/total volume of unit cell FCC => APF = .74 (74% is being occupied and is the most efficient packing with spheres of the same size) o Higher coordination number corresponds to a higher APF Body Centered Cubic o Iron, tungsten,, chromium all have this structure o Contains two full atoms (8 atoms on corners, 1 atom in center) Atoms/unit cell 2 o Lattice parameter a = 4R/sqrt(3) o Coordination number 8 o APF 0.68 Hexagonal Close Packed o Cobalt, titanium, and zinc are examples o Atoms on all 6 corners, 3 full atoms in the center, and atoms on top and

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This note was uploaded on 04/07/2008 for the course ENGR 240 taught by Professor Gross during the Fall '07 term at Bucknell.

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ENGR 240 - 8.31.2007 - ENGR 240 August 31, 2007 FCC face...

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