Question

Please show work for problems 1-4

1. Calculate the activation energy for vacancy formation in aluminum, given that the equilibrium number of vacancies at 500°C (773 K) is 7.57 x10m3. The atomic weight and density (at 500°c) for aluminum are 26.98 g/mol and 2.62 g/cm, respectively 2. What point defects are possible for Al,0, as an impurity in Mgo? How many Al ions must be added to form each of these defects? 3. A sheet of steel 4.5 mm thick has nitrogen atmospheres on both sides at 1200°C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6 x 10 m'/s, and the diffusion flux is found to be 1.2 x 10 kg/m'-s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m. How far into the sheet from this high-pressure side will the concentration be 2 kg/m? Assume a linear concentration profile 4. An FCC iron-carbon alloy initially containing 0.35 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1400 K (1127°C). Under these circumstances the carbon diffuses from the alloy and reacts at the surface with the oxygen in the atmosphere; that is, the carbon concentration at the surface position is maintained essentially at 0 wt% C. (This process of carbon depletion is termed decarburization.) At what position will the carbon concentration be 0.15 wt% after a 10-h treatment? The value of D at 1400 K is 6.9 × 10-11 m 2/s.

Answer 1

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