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Unformatted text preview: IE 320 - Spring 2003 Homework Ch. 6 Introduction to Materials Science
6.1 Briefly explain the difference between self diffusion and interdiffusion. 6.6 . The purification of hydrogen gas by diffusion through a palladium sheet was discussed in Section 6.3. Compute the number of kilograms of hydrogen that pass per hour through a 5-mm thick sheet of palladium having an area of 0.20 m2 at 500C. Assume a diffusion coefficient of 1.0x10-8 m2/s, that the concentrations at the high- and low-pressure sides of the plate are 2.4 and 0.6 kg of hydrogen per cubic meter of palladium, and that steady state conditions have been attained. 6.12 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 (1127C). 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 6.9x10-11 m2/s.
2 1 IE 320 - Spring 2003 Introduction to Materials Science
6.21 The diffusion coefficients for iron in nickel are given at two temperatures: T(K) D(m2/s) 1273 9.4x10-16 1473 2.4x10-14 (a) Determine the values of D0 and the activation energy Qd . (b) What is the magnitude of D at 1100C (1373 K)? 6.23 Below is shown a plot of the logarithm (to the base 10) of the diffusion coefficient versus reciprocal of the absolute temperature, for the diffusion of iron in chromium. Determine values for the activation energy and preexponential. 3 2 ...
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