ME362_F10-L8-9_Diffusion

ME362_F10-L8-9_Diffu - Lecture 8-9 Diffusion 1 DIFFUSION IN SOLIDS Questions to answer How does diffusion occur Why is it an important part of

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1 Diffusion Lecture 8-9
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2 Questions to answer. .. How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases? How does diffusion depend on structure and temperature? DIFFUSION IN SOLIDS
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3 Interdiffusion : In an alloy, atoms tend to migrate from regions of large concentration. Initially After some time 100% Concentration Profiles 0 Adapted from Figs. 5.1 and 5.2, Callister 6e . DIFFUSION: THE PHENOMENA (1)
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4 Self - diffusion : In an elemental solid, atoms also migrate. Label some atoms After some time A B C D DIFFUSION: THE PHENOMENA (2)
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5 Substitutional Diffusion: applies to substitutional impurities atoms exchange with vacancies (vacancy mechanism) rate depends on: -- number of vacancies -- activation energy to exchange. DIFFUSION MECHANISMS
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6 • Simulation of interdiffusion across an interface: Rate of substitutional diffusion depends on: -- vacancy concentration -- frequency of jumping. (Courtesy P.M. Anderson) DIFFUSION SIMULATION
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7 • Applies to interstitial impurities => smaller atoms can diffuse between atoms. More rapid than substitutional diffusion. INTERSTITIAL SIMULATION Adapted from Fig. 5.3 (b), Callister 7e .
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8 Case Hardening : -- Diffuse carbon atoms into the host iron atoms at the surface (in a gas mixture containing CH 4 and/or CO) carburization -- Example of interstitial diffusion is a case hardened gear. • Result: The "Case" is -- hard to deform: C atoms "lock" planes from shearing . -- hard to crack: C atoms put the surface in compression . PROCESSING USING DIFFUSION Adapted from chapter-opening photograph, Chapter 5, Callister 7e. (Courtesy of Surface Division, Midland-Ross.)
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Doping silicon with phosphorus for n -type semiconductors: • Process: 3. Result: Doped semiconductor regions. silicon Processing Using Diffusion magnified image of a computer chip 0.5mm light regions: Si atoms light regions: Al atoms 2. Heat it. 1. Deposit
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This note was uploaded on 10/03/2010 for the course ME 362 taught by Professor O during the Spring '10 term at Binghamton University.

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ME362_F10-L8-9_Diffu - Lecture 8-9 Diffusion 1 DIFFUSION IN SOLIDS Questions to answer How does diffusion occur Why is it an important part of

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