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Unformatted text preview: ENMA 300/ENME 382 Homework 6 Solutions Fall 2011 1a) How can you distinguish between steady state and non-steady state diffusion? In steady-state diffusion the diffusion flux and thus the concentration profile are independent of time. There is no net accumulation or depletion of the diffusing species. In non-steady state diffusion, the concentration profile changes with time. This is usually a result of a finite source of the diffusing species becoming depleted or the lack of removal of reactants in a reaction that occurs as a result of diffusion. b) What is the driving force for steady state diffusion? The most common driving force for steady state diffusion is a concentration gradient. The most general answer to this question is that the driving force is a chemical potential gradient, this includes stress gradients, temperature gradients, and electric field gradients, etc. c) What is the difference between self diffusion and interdiffusion? Interdiffusion involves more than one type of atoms, during which atoms of different types diffuse from high- to low-concentration area, and cause compositional change. In real life interdiffusion can occur when the temperature of materials that are welded or butted together is raised or when a two phase mixture is heated. Self-diffusion occur both in elemental solids or compounds. It is the process whereby like atom exchange positions with each other usually via exchange with vacant positions (vacancies). It normally doesnt lead to compositional change. 2a) When would you expect a vacancy diffusion mechanism?...
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This note was uploaded on 04/03/2012 for the course ENME 382 taught by Professor Christou during the Spring '12 term at Maryland.
- Spring '12