4 - IMPERFECTIONS IN SOLIDS ISSUES TO ADDRESS. What types...

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ISSUES TO ADDRESS. .. • What types of defects arise in solids? • Can the number and type of defects be varied and controlled? • How do defects affect material properties? 1 • Are defects undesirable? CHAPTER 4: IMPERFECTIONS IN SOLIDS
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Real crystals are never perfect, there are always defects Defects have a profound impact on the macroscopic properties of materials The processing determines the defect type and defect concenration: Imperfections in Solids (Defects): Introduction
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• Vacancy atoms • Interstitial atoms • Substitutional atoms • Dislocations • Grain Boundaries Point defects Line defects Area defects TYPES OF IMPERFECTIONS
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3 Vacancies : -vacant atomic sites in a structure. Vacancy distortion of planes Self-Interstitials : -"extra" atoms positioned between atomic sites. self- interstitial distortion of planes POINT DEFECTS
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Schematic representation of different point defects : (1) Vacancy; (2) Self-interstitial; (3) Interstitial impurity; (4,5) Substitutional impurities
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(1.38 x 10 -23 J/atom K) (8.62 x 10 -5 eV/at om K) N D N = exp Q D k T No. of defects No. of potential defect sites. Activation energy Temperature Each lattice site is a potential vacancy site • Equilibrium concentration varies with temperature! EQUIL. CONCENTRATION:
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This note was uploaded on 11/11/2010 for the course METE 227 taught by Professor Ali during the Spring '10 term at Middle East Technical University.

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4 - IMPERFECTIONS IN SOLIDS ISSUES TO ADDRESS. What types...

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