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CERAMICS

CERAMICS . 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.

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CERAMICS

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  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

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