Chpt12_Ceramics-Spr2016.pdf - Chapter 12: Structures &...

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Chapter 12 - 1Chapter 12: Structures & Properties ofCeramicsmany concepts have already been covered as part of other chapters..This is provided to you as a complete slide deck on ceramics..ISSUES TO ADDRESS...How do the crystal structures of ceramic materialsdiffer from those for metals?How do point defects in ceramics differ from thosedefects found in metals?How are impurities accommodated in the ceramic lattice?How are the mechanical properties of ceramicsmeasured, and how do they differ from those for metals?In what ways are ceramic phase diagrams different fromphase diagrams for metals?
Chapter 12 - 2Bonding:--Can be ionic and/or covalent in character.--% ionic character increases with difference inelectronegativity of atoms.Adapted from Fig. 2.7,Callister & Rethwisch 8e.(Fig. 2.7 is adapted from Linus Pauling,The Nature of theChemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition.Copyright 1960 byCornell University.)Degree of ionic character may be large or small:Atomic Bonding in CeramicsSiC: smallCaF2: large
Chapter 12 - 3Ceramic Crystal StructuresOxide structuresoxygen anions larger than metal cationsclose packed oxygen in a lattice (usually FCC)cations fit into interstitial sites among oxygen ions
Chapter 12 - 4Factors that Determine Crystal Structure1.Relative sizes of ionsFormation of stable structures:--maximize the # of oppositely charged ion neighbors.Adapted from Fig. 12.1,Callister & Rethwisch 8e.----+unstable----+stable----+stable2.Maintenance ofCharge Neutrality:--Net charge in ceramicshould be zero.--Reflected in chemicalformula:CaF2:Ca2+cationF-F-anions+AmXpm, p values to achieve charge neutrality
Chapter 12 - 5Coordination # increases withCoordination # and Ionic RadiiAdapted from Table 12.2,Callister & Rethwisch 8e.2rcationranionCoord#< 0.1550.155 - 0.2250.225 - 0.4140.414 - 0.7320.732 - 1.03468lineartriangulartetrahedraloctahedralcubicAdapted from Fig. 12.2,Callister & Rethwisch 8e.Adapted from Fig. 12.3,Callister & Rethwisch 8e.Adapted from Fig. 12.4,Callister & Rethwisch 8e.ZnS(zinc blende)NaCl(sodiumchloride)CsCl(cesiumchloride)rcationranionTo form a stable structure, how many anions cansurround around a cation?
Chapter 12 - 6Computation of Minimum Cation-AnionRadius RatioDetermine minimumrcation/ranionfor an octahedral site(C.N. = 6)a=2ranion2ranion2rcation=2 2ranionranionrcation=2ranionrcation=( 21)ranionarr222cationanion=414.012anioncation==rr
Chapter 12 - 7Bond HybridizationBond Hybridizationis possible when there is significantcovalent bonding

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Term
Fall
Professor
Fong
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