Lecture 5 - The Structure of Ceramics Learning Objectives...

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1 The Structure of Ceramics The Structure of Ceramics Learning Objectives Learning Objectives • Identify the differences between ceramics and metals regarding their crystal structures • Describe the structures for sodium chloride, cesium chloride, zinc blende, diamond cubic, fluorite • Given chemical formula and radii of ions, predict likely crystal structure
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2 Ceramics Ceramics • Ceramics are inorganic and nonmetaalic materials. • Most ceramics are formed by metallic and non- metallic elements – Predominantly ionic bonding • Two or more components – Structures more complex than metals • Anion: – Negative ion • Cation – Positive ion Crystalline Ceramics Crystalline Ceramics Most common elements on earth are Si & O SiO 2 (silica) structures are quartz, crystobalite, & tridymite The strong Si-O bond leads to a strong, high melting material (1710ºC) Si 4+ O 2- Adapted from Figs. 12.9-10, Callister 7e. crystobalite
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3 Amorphous Ceramics Amorphous Ceramics Silica gels - amorphous SiO 2 Si 4+ and O 2- not in well-ordered lattice Charge balanced by H + (to form OH - ) at “dangling” bonds very high surface area > 200 m 2 /g SiO 2 is quite stable, therefore unreactive makes good catalyst support Adapted from Fig. 12.11, Callister 7e. Crystal Structures Crystal Structures • Two important characteristics define crystal structure of ceramics: – Magnitude of electrical charge of ions • Crystal structure must be electrically neutral • Chemical Formulas tell you ratio between cations and anions –N aC l , A l 2 O 3 , CaFl 2 – The relative size of anions and cations • Cations have usually smaller radii •W h y ?
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This note was uploaded on 06/24/2009 for the course MEEN 222 taught by Professor Radovic during the Fall '08 term at Texas A&M.

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Lecture 5 - The Structure of Ceramics Learning Objectives...

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