che 333 class 23
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CHE 333 Class 23.
Ceramics
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.
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.
AnXm and AnBmXp Structure
Calcium Flouride CaF2 Barium Titanate Piezoelectric material
Ceramic Structures
Glass Silica Tetrehedra
Tetrahedral Structure SiO44-
Si – O ionic ratio is 0.29 tetra CN
Unit cell of silicates. High Crystobalite 1470 to 1710C
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