Recitation- 2

# Recitation- 2 - 4.3 This problem calls for the computation...

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November 16, 2009 4.3 This problem calls for the computation of the energy for vacancy formation in silver. Upon examination of Equation (4.1), all parameters besides Q v are given except N , the total number of atomic sites. However, N is related to the density, ( ρ ), Avogadro's number ( N A ), and the atomic weight ( A ) according to Equation (4.2) as N = N A ρ Ag A Ag = 6.023 x 10 23 atoms/mol ( 29 10.49 g/cm 3 ( 29 107.87 g/mol = 5.86 x 10 22 atoms/cm 3 = 5.86 x 10 28 atoms/m 3 Now, taking natural logarithms of both sides of Equation (4.1), and, after some algebraic manipulation Q V = - RT ln N V N = - 8.62 x 10 -5 eV/atom- K ( 29 (1073 K) ln 3.60 x 10 23 m - 3 5.86 x 10 28 m - 3 = 1.11 eV/atom 4.27 (a) The surface energy will be greater than the grain boundary energy since some atoms on one side of the boundary will bond to atoms on the other side--i.e., there will be fewer unsatisfied bonds along a grain boundary. (b) The small angle grain boundary energy is lower than for a high angle one because more atoms bond across the boundary for the small angle, and, thus, there are fewer unsatisfied bonds. 2

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November 16, 2009 5.1 Self-diffusion is atomic migration in pure metals--i.e., when all atoms exchanging positions are of the same type. Interdiffusion is diffusion of atoms of one metal into another metal.
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