1Louisiana 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 Qv=0.9eV/atom. Knowing that at 400 oC the equilibrium concentration of vacancies is 1.46x1022vacancies/m3what is the vacancy concentration at 900 oC? The Boltzmann’s constant is k=8.62x10-5 eV/atom K.
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2Name:_________________________ 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/m3and 0.17 Kg/m3. Knowing that the pre-exponential coefficient D0=6.2x10-7m2/s and the activation energy for diffusion is Qd= 80,000J/mol compute the temperature at which we have a diffusion flux of 5.8x10-10Kg/m2s.