EGN3365-12

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  1 ãStructures of ceramic materials: How do they differ from those of metals? ãPoint defects:How are they different from those in metals?ãImpurities:How are they accommodated in the lattice and howdo they affect properties? ãMechanical Properties:What special provisions/tests are made for ceramicmaterials? Chapter 12: Structures & Properties of Ceramics  2 ãBonding: -- Mostly ionic, some covalent. -- % ionic character increases with difference in electronegativity. Adapted from Fig. 2.7, Callister 7e. ãLarge vs small ionic bond character: Ceramic Bonding SiC: smallCaF 2 : large  3 Ionic Crystals CationRadius (nm)Anion Radius (nm)0.1000.1330.0720.140.1020.1820.0530.1400.0400.140 Note: larger anion radiusMost ionic crystals can be considered as close-packed structure of anions with cationsin the interstitial sites.Cations: metallic ions, positively chargedAnions: nonmetallic ions, negatively charged  4 Ceramic Crystal Structures Oxide structures  –oxygen anions much larger than metal cations –close packed oxygen in a lattice (usually FCC) –cationsin the holes of the oxygen lattice
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