MSE306Chap8Annealing

MSE306Chap8Annealing - Chapter 8 Annealing The whole idea...

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Chapter 8: Annealing The whole idea is… We can first bring materials to states of metastability Free energy, G, is higher than the equilibrium There is a driving force, ΔG, to proceed towards equilibrium There must be an energy barrier for doing so Thermal vibrations can provide the energy to overcome the barrier (activation energy) We call this a thermally activated process Recall vacancy diffusion from last lecture…
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In order for atom to jump into a vacancy site, it needs to posses enough energy (thermal energy) to to break the bonds and squeeze through its neighbors. The energy necessary for motion, Q d , is called the activation energy for vacancy motion. Diffusion – Thermally Activated Process (I) Schematic representation of the diffusion of an atom from its original position into a vacant lattice site. Activation energy Q d has to be supplied to the atom so that it could break inter-atomic bonds and to move into the new position. Atom Vacancy E m Distance Energy
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Interdiffusion occurs in response to a concentration gradient (more rigorously, to a gradient in chemical potential) What is diffusion? Interdiffusion and Self-diffusion Before After (Heat)
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There will often be some driving force, ΔG, which directs diffusion. Obviously atoms/vacancies will do some random jumping around (back-and-forth). But if there is a
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