Lec 10 - ENGR ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 ENGR 4250 – Advanced Materials Engineering Lecture 10 Applications & Processing of Ceramics
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he Story of Stuff The Story of Stuff ttp://news bbc co uk/2/hi/business/77854 http://news.bbc.co.uk/2/hi/business/77854 79.stm
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eramics Ceramics
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keramikos - burnt stuff in Greek Desirable properties of ceramics are normally achieved through a high temperature heat eatment process (firing) treatment process (firing).
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nic Character of Ceramics Ionic Character of Ceramics
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nic and Covalent Nature Ionic and Covalent Nature % ionic character = {1-exp[ - (0.25)(X – X ) 2 ]} x 100 %{ p[ () ( A B ) ]} (2.10) X A and X B are electro-negativities for the spective elements respective elements
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Ionic Bonding & Structure 1. Size - Stable structures: --maximize the # of nearest oppositely charged neighbors. Adapted from Fig. 12.1, Callister 7e. - - -- + - - - - + - - - - + unstable Charge Neutrality : stable stable --Net charge in the structure should be zero. CaF 2 : Ca 2+ cation F - anions + --General form: F - A m X p m, p determined by charge neutrality
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Coordination # and Ionic Radii Coordination # increases with r cation r anion Issue: How many anions can you r cation Coord ZnS incblende) arrange around a cation? 2 r anion # < 0.155 linear Adapted from Fig. 12.4, Callister 7e. (zincblende) 0.155 - 0.225 0.225 - 0.414 3 4 triangular T D Adapted from Fig. NaCl (sodium chloride) 0.414 - 0.732 6 O H 12.2, Callister 7e. CsCl (cesium hloride) Adapted from Table 12.2, Callister 7e. 0.732 - 1.0 8 cubic Adapted from Fig. 12.3, Callister 7e. chloride)
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The critical ratio can be determined by simple geometrical analysis A r AP = C A r r AO + = α cos = AO AP 3 30 cos = = = A r O AP 155 . 0 = A C r r 2 + C A r r AO
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etrahedral vs Octahedral Tetrahedral vs Octahedral
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ock Salt Rock Salt
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echanical Properties Mechanical Properties We know that ceramics are more brittle an metals hy? than metals. Why? Consider method of deformation slippage along slip planes in ionic solids this slippage is very difficult too much energy needed to move one anion past another anion
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Silicate Ceramics Most common elements on earth are O & Si Si 4+ O 2- Adapted from Figs. 2 9 0 lli t 7 12.9-10, Callister 7e. crystobalite •S i O 2 (silica) structures are quartz, crystobalite, & tridymite • The strong Si-O bond leads to a strong, high melting material (1710ºC)
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rystalline & Non- rystalline Silica Crystalline & Non Crystalline Silica
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ayered Silicates Layered Silicates • Layered silicates (clay silicates) –S iO 4 tetrahedra connected together to form 2-D plane •( S i 2 O 5 ) 2- Adapted from Fig. 2 13 allister 7e • So need cations to balance charge = 12.13, Callister 7e.
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eatures of Layered Silicates Clay is inexpensive • Adding water to clay Features of Layered Silicates Shear Adding water to clay -- allows material to shear easily along weak van der Waals bonds -- enables extrusion charge neutral
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This note was uploaded on 10/18/2010 for the course ENGR 3360 taught by Professor Ahmadbarari during the Fall '10 term at UOIT.

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Lec 10 - ENGR ENGR 4250 Advanced Materials Engineering...

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