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Defects in crystalline materials
 

Defects in crystalline materials

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    Defects in crystalline materials Defects in crystalline materials Presentation Transcript

    • Defects In CrystallineMaterials.
    • For more help contact me Muhammad Umair Bukhari Engr.umair.bukhari@gmail.com www.bzuiam.webs.com 03136050151
    • Defects In Crystalline Materials. Metals, many ceramics and some polymers are crystalline. Real crystals contain various types of imperfections. Many of the important properties of materials are due to the presence of these imperfections.
    • Types Of Defects. Defects are categorized as:1) Point defects.2) Surface defects.3) Volume defects.4) Line defects.
    • Point Defects. All the atoms in a perfect lattice are at specific atomic site. In a pure metal two types of point defects are possible.1) Vacancies.2) Interstitial point defects.
    • Vacancies. Vacant atomic sites in a structure. Due to plastic deformation & high energy particle irradiation.
    • Interstitial Point Defects. “Extra" atoms positioned between atomic sites. Due to plastic deformation & high energy particle irradiation Interstitial atom distortion of planes
    • Extrinsic Point Defects. Introduction of outsider atom. They play an important role in physical & mechanical properties. Impurity atom can take two different sites in crystal. Substitutional or Interstitial.
    • Point Defectsvacancy Interstitial impurity Substitutional impurity
    • In metallic solids defects are not soimportant but in ionic solids presence of avacant site (e.g. in NaCl), changes theelectrical properties.
    • Schottky & Frenkel Defects In order to conserve the overall neutral charge vacancy must be occurred either in pairs of opposite sign forming die- vacancies called Schottky defects. In association of the interstitial of same ion called Frenkel defects.
    • Defects in ionic solids Frenkel defect Cation vacancy + cation interstitial Schottky defect Cation vacancy + anion vacancy
    • Stacking Faults. Stacking fault is a planner defect and formed when regular sequence of stacking is disturbed. Stacking faults are not may observed In planes where the stacking sequence is ABABAB….because there is no alternative site for “A” layer other than resting on a “B” layer of vice versa. In ABCABABC….layers it is visible.
    • A BC
    • Types Of Stacking Faults.1) Intrinsic stacking faults.2) Extrinsic stacking faults.
    • Intrinsic Stacking Faults. Removal of a layer from an arranged sequence layer. E.g. CBACBA…..becomes CBABAC….
    • Extrinsic Stacking Faults. Addition of layer to the arranged sequence layer. E.g. BACBAC….becomes BACABAC…
    • Grain Boundaries. A Grain Boundary is a general planar defect that separates regions of different crystalline orientation (i.e. grains) within a polycrystalline solid. The atoms in the grain boundary will not be in perfect crystalline arrangement
    • Grain Boundaries Cont... Grain boundaries are usually the result of uneven growth when the solid is crystallizing.