CERAMICS

1. CERAMICS

2. Properties of Ceramic • They are distiguished by its bonding which is ionic or covalent bonding • High elastic modulus and hardness • High melting point • Low thermal expansion • Good chemical resistance • Brittle • Thermal insulators • Electrical insulators • Nonmagnetic

3. Ceramic Structures : Crystal Structure • Factors that affect crystal structure of ceramics : - the magnitude of the electrical charge on each of the component ions and the relative sizes of the cations and anions - the sizes or ionic radii of the cations and anions rC/rA

4. Ceramic Structures • Crystal structures Atomic bonding: ionic bonding Positive charges (metal) cation Negative charges (non metal) anion anion kation

5. AX-Type Crystal Structures A: cation X: anion • Rock Salt Structure ~e.g: NaCl, MgO, MnS, LiF ~The coordination number for both cations&anions: 6 ~Structure: FCC

6. 2. Cesium Chloride Structure ~The coordination number: 8 ~e.g: CsCl • Zinc Blende Structure ~The coordination number: 4 ~atomic bonding: covalent bonding ~e.g: ZnS, ZnTe, SiC

7. AmXp-Type Crrystal Structure • When charges of cations and anions are not the same; where m and/or p ≠ 1 • AX2 e.g: CaF2, UO2, PuO2

8. AmBnXp-Type Crystal Structures • It is possible for ceramic compounds to have more than one type of cation • A & B: cation X: anion • Structure: perovskite • e.g: BaTiO3 (Barium titanat) cation: Ba2+, Ti4+ anion: O2-

9. Classification of Ceramics • Glasses : 1. Glasses 2. Glass-ceramics • Clay Products : 1. Structural clay products 2. Whitewares • Refractories : 1. Fireclay 2. Silica 3. Basic 4. Special • Abrasives • Cements • Advanced ceramics

10. Glasses (1) • Glasses They are noncrystalline silicates containing other oxides

11. Glasses (2) 2. Glass-ceramics • Formed glass ceramics : We use a process that called crystallization which is the most inorganic glasses can be made to transform from a noncrystalline state to one that is crystalline by the proper high temperature heat treatment • Properties : relatively high mechanical strength, low coefficients of thermal expansion, relatively high temperature capabilities, good dielectric properties, good biological compability • Applications : ovenware, tableware, oven windows, and rangetops, and etc

12. Clay Products 1. Structural clay products • Applications : building bricks, tiles, and sewer pipes 2. Whitewares Whitewares become white after the high temperature firing • Applications : porcelain, pottery, tableware, china and plumbing fixtures (sanitary ware)

13. Refractories (1) • Fireclay refractories • The primary ingredients : high purity fireclays, alumina, and silica mixtures usually containing between 25 and 45 wt% alumina. • Applications : in furnace construction, to cofine hot atmospheres and to thermally insulates structural members from excessive temperatures. 2. Silica refractories • Contains over 95% of SiO 2 and not more than 3% CaO both by weight • Well known for their high temperature load bearing capacitiy • Applications : arched roof of steel and glass making furnaces

14. Refractories (2) 3. Basic refractories • Have a high propotions of basic content like CaO and MgO. Also contain chromium and iron compounds • Applications : use in some steel making open hearth furnaces 4. Special refractories • Some of these are relatively high purity oxide materials • Applications : For example SiC are used for electrical resistance heating elements

15. Abrasives • The most common examples of abrasives are diamond, silicon carbide, tungsten carbide, corundum, and silica sand • The prime requisite of this material is hardness • Applications : bonded in grinding wheels, as coated abrasives, as loose grains, etc

16. Cements • Cement used in construction is characterized as hydraulic and non-hydraulic • The characteristic feature in this material is when mixed with water, form a paste • Cementitious bond develops at room temperature • Applications : mortar and concrete

17. Advanced Ceramics (1) • MEMS (Microelectromechanical Systems) • Miniature “smart” system consisting of a multitude of mechanical devices that are integrared with a large numbers of electrical elements on a substrate of silicon • Applications : accelerometer, microsystem for DNA, chemical detectors, etc

18. Advanved Ceramics (2) 2. Optical Fibers • Is made of extremely high purity silica 3. Ceramic Ball Bearings • Consists of balls and races that are in contact with and rub against one another when in use

19. Fabrication and Processing Of Ceramics (1) • Fabrication and Processing Of Glasses and Glass-ceramics • Glasses are formed at elevated temperature, hence, we have to consider the temperature viscosity • Glass forming techniques : pressing, blowing, drawing and fiber forming • After fabrication, glasses may be annealed and/or tempered to improve mechanical characteristics

20. Fabrication and Processing Of Ceramics (2) 2. Fabrication and Processing of Clay Products • Commonly, there are two forming techniques, hydroplastic forming and slip casting • After forming, the body must be dried and then fired at elevated temperature 3. Powder Pressing • Used to fabricate both clay and non clay compositions • Three basic powder pressing : uniaxial, isostatic, and hydro pressing 4. Tape Casting • Pouring the slip onto a flat surface • A doctor blade spreads the slip into a thin tape of uniform thickness • Tape thickness normally range between 0.1 and 2 mm • Usually used in the production of ceramic substrates