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Midterm 1b - In a carburization process of a large steel...

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1 Louisiana State University Mechanical Engineering Department ME 2733- Materials of Engineering; Spring 2003 (Section 2) Midterm Exam Part II March 25, 2003 Name:_________________________ Problem 1 . Consider a copper sample with the energy for vacancy formation Q v =0.9eV/atom. Knowing that at 400 o C the equilibrium concentration of vacancies is 1.46x10 22 vacancies/m 3 what is the vacancy concentration at 900 o C? The Boltzmann’s constant is k=8.62x10 -5 eV/atom K.
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2 Name:_________________________ Problem 2 . Consider a 5 mm thick steel plate through which a steady state diffusion of carbon takes place. The concentrations of carbon at the two faces are maintained constant at 0.62 Kg/m 3 and 0.17 Kg/m 3 . Knowing that the pre-exponential coefficient D 0 =6.2x10 -7 m 2 /s and the activation energy for diffusion is Q d = 80,000J/mol compute the temperature at which we have a diffusion flux of 5.8x10 -10 Kg/m 2 s.
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