Download - CHE 333 Class 23
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CHE 333 Class 23.
Ceramics
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Ceramic StructuresMIXTURES OF ELEMENTSTwo Criteria for ceramic structures
1. Electrical Neutrality using ionic chargecation (positive charge) must equal anion(negative charge) amounts.Eg NaCl Na one positive, Cl one negative
2. Cations (+ve) – usually smaller, contact Anions (-ve) in structure. Determines the coordination number of the structure forceramics. Within certain ranges onlyparticular coordination numbers willaccommodate the different sized ionscontacting each other.
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AX Ionic Structures
NaCl structure CN 6 CsCl structure CN 8 ZnS structure CN 4
All these have a 1 to 1 cation to anion ratio, but different coordination numbers.
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AnXm and AnBmXp Structure
Calcium Flouride CaF2 Barium Titanate Piezoelectric material
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Ceramic Structures
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Glass Silica Tetrehedra
Tetrahedral Structure SiO44-
Si – O ionic ratio is 0.29 tetra CN
Unit cell of silicates. High Crystobalite 1470 to 1710C