ch4 - Chapter IV Chapter Imperfections in Solids Type of...

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Chapter IV Chapter IV Imperfections in Solids Imperfections in Solids
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Type of Imperfections Type of Imperfections • Vacancy atoms • Interstitial atoms • Substitutional atoms • Dislocations Grain Boundaries • Twin Boundaries Point defects Line defects Area defects Perfect crystals do not exist! Defect exists in crystals, which is lattice irregularity having one or more dimensions on the order of an atomic size.
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Point Defects in Solids Point Defects in Solids Vacancies : -vacant atomic sites in a structure. Self-Interstitials : -"extra" atoms positioned between atomic sites. Vacancy distortion of planes self- interstitial distortion of planes
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Point Defects in Solids Point Defects in Solids impurities
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Equilibrium Concentration of Point Defects Equilibrium Concentration of Point Defects Boltzmann's constant (1.38 x 10 -23 J/atom K) (8.62 x10 -5 eV/atom K) N D N = exp Q D k T No. of defects No. of potential defect sites . Formation energy Temperature Each lattice site is a potential vacancy site
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Equilibrium Concentration of Point Defects Equilibrium Concentration of Point Defects Find the equilibrium number of vacancies in 1m 3 of Cu at 1000C Given: Answer: 8.62 x 10 - 5 eV/atom-K 0.9 eV/atom 1273K N D N = exp Q D k T For 1m 3 N = N A A Cu ρ x x 1m 3 = 8.0 x 10 28 sites = 2.7 x 10 - 4 A Cu = 63.5g/mol ρ = 8.4 g /cm 3 Q V = 0.9 eV/atom N A = 6.02 x 10 23 atoms/mole N D = 2.7 x 10 - 4 x 8.0 x 10 28 sites = 2.2 x 10 25 vacancies
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ch4 - Chapter IV Chapter Imperfections in Solids Type of...

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