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MCE 230_F10_ lec_12 - 2 Linear defects 3 Planner defects 4...

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MCE 230 – Materials Science Fall 2010 Lecture - 12
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Imperfections in Solids
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Imperfections (defects) in solids So far we considered “ideal” case: unit cells and atoms are in perfect order in crystalline solids. In reality: the perfect order of unit cells and atoms does not exist. All materials contain large number of defects (imperfections) The existence of imperfections significantly change the material properties. Imperfections are sometime introduced to change a certain properties ( one way to do this is alloying)
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Defect types Four basic defect types: 1. Point defects (atoms)
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Unformatted text preview: 2. Linear defects 3. Planner defects 4. Volumetric defects Point Defects a) Vacancy (1) b) Self-interstitial (2) c) Interstitial impurities ( 3) d) Substitutional impurities (4& 5) Vacancies  Vacancy: missing atom  All crystals solid contains vacancies, and it is not possible to have a vacancy free material  Equilibrium number of vacancies ( Nv) Where N: total number of atomic sites Qv: energy needed for vacancy formation T: absolute temperature (K) k: Gas (Boltzmann’s) constant ( 1.38x10-23 J/atom-K)  See Example 4.1 Solved Problems  4.2...
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MCE 230_F10_ lec_12 - 2 Linear defects 3 Planner defects 4...

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