HW4 DiffusionI

HW4 DiffusionI - HW4 Diffusion I 1. The following figure...

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HW4 Diffusion I 1. The following figure shows the self-diffusion coefficient as a function of reciprocal temperature for two hypothetical metals, A and B. a) Which metal has a larger activation energy for diffusion? metal A or metal B. Prove your assertion using an equation. b) Calculate the activation energy for self-diffusion for metal B, using values from the graph. Be sure that you interpolate numbers properly on the logarithmic scale. 2. The self-diffusion coefficient of Cu is at 500°C. D o is and the activation energy for diffusion is 2.19 eV per atom. A) Calculate the Cu diffusion coefficients at 700°C, 300°C, and 20°C. B) Approximately how long will it take an atom of copper to diffuse through the thickness of a penny (say it is 1 mm) at room temperature? How long will it take at 700°C? C) What is the atomic level mechanism for self-diffusion of copper? Explain. 3. A 4 mm thick piece of Pd metal is being considered to use as a semi permeable membrane for hydrogen gas purification. The concentration of hydrogen gas on the high pressure side will be 1.85 kg H m
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HW4 DiffusionI - HW4 Diffusion I 1. The following figure...

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