FUNDMNT MATERLS SCI
FUNDMNT MATERLS SCI MSE 170
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This 8 page Class Notes was uploaded by Foster Hahn IV on Wednesday September 9, 2015. The Class Notes belongs to MSE 170 at University of Washington taught by Staff in Fall. Since its upload, it has received 13 views. For similar materials see /class/192202/mse-170-university-of-washington in Materials Science Engineering at University of Washington.
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Date Created: 09/09/15
Chapter 12 Structures of Ceramics Outline El Introduction El Crystal structures Ceramic structure AX type crystal structures 39 AmXPtype AmBnXp type El Silicate ceramics El Carbon Ceramic structures El Two or more different elements El More complex than metal structures El Ionic andor covalent bonds El A mix of ionic and covalent bonds electronegativity El Ionic bonds form ions Metals give up electrons metallic ions cations positively charged Non metals gain electrons nonmetallic ions anions negatively charged El Crystals must be electrically neutral eg CaF2 Ceramic structures continue El Factors influence crystal structure Mag iitude of electrical charge of ims I Relative size of ions Nonrinetal gt metal ions RcRalt1 OCatiOnS must be next to anionswrnaxirnize 13 of nearest neighbors that are anions OStable Structure anions and Cations must Contact each other n stable stable oThe z of anions depends on ratio of RcRa Coordination numbers and geometries for various cationanion radius ratios RCRa a mum hum awnW WM MW W quot44quot um i Mum AXtype crystal structure El Rock salt structure gt 0 Sodium chloride NaCl is the most 39 t I common l I A i o RcRa 04140732 i g o 77 7 s o CN6 for both cations and anions g 5 I 0 Unit cell FCC arrangement of anions i i with one cation at center of each of 12 i 5J cube edges 5 L g i 0 Two interpenetrating FCC lattices O Na Cl A unit cell of rock salt AXtype crystal structure continue El Cesium chloride structure 0 CN8 8 anions at cube corners and 1 cation at center of cube simple cubic not BCC El Zinc Blende structure 0 CN4 FCC structure of S with Zn at interior tetrahedral bositions cr I A unit cell of cesium chloride A unit cell of zinc blende The AmXp type crystal structures El RcRa08 CNCa8 CNF4 El Ca atoms at center of cubes with F atoms at cube corners similar to CsCl but only 12 of sites are filled with Ca atoms El Unit cell consists of 8 cubes A unit cell of Can AX2 The AmBnXp type crystal structures El Ba at cubic corner 0 at center 39 o a of 6 faces Ti at body center I El CNO12 CNBa6 and CN 6 El Large A cation and oxygen 0 a o 0 form an FCC lattice El Cubictetragonal at 130 C Curie points El Cubic orthrhombic and 4 2 2 rhombohedral at low T T39 33 o O 7 A unit cell of perovskite crystal structure ABX3 Example Predicting Structure of FeO On the basis of ionic radii what crystal structure would you predict for FeO Cation Ionic radius nm Answer Ai3 0053 row 7 0077 m Fe3 0069 0550 Ca2 0100 based on this ratio Anion aggrircjufe 6NaC 02 0140 CI39 0181 P 0133 Ceramic density p n39ZAC 2AA VCNA 131 where n thc number 0quot l39m mulzi unils within he unit Cell A 7 he sum ofthc atomic weights 0t all cations in the formula unit 3AA the sum ofrhc atomic wcxghlx ol39all unions in the formula unit 4 the unit cell volume V T Avogadro s number 6023 X 10W formula unitsmo Silicate ceramics El Silicates are materials composed primarily of silicon and oxygen soils rocks clays sand and glass 0 Si o 027 K a g Adapted from Figs 12 940 Callisler 79 W crystobalite El Silica silicon oxide SiOZ Three crystal structures quartz cristobalite and tridymite Open structure not closepacked low density Silicate ceramics continue El Silica glasses amorphous a high degree of atomic randomness additives CaO and NaO network modifier modify the silicon and oxide network and low melting T El The silicates 3 soilquot 0 Srquot 00239 O OHquot gt 6 Sodiumsilicate glass S207 5806 Various silicate ion structures Carbon forms El Carbon black amorphous surface area ca 1000 mZg El Diamond tetrahedral carbon Uhard no good slip planes Ubrittle can cut it 0 large diamonds jewelry 0 small diamonds Uoften man made used for cutting tools and polishing diamond films Uhard surface coat tools medical devices etc Carbon forms graphite El layer structure aromatic layers Adapted from Fig 12 17 Calisler 7e 0 weak van der Waal s forces between layers 0 planes slide easily good lubricant Carbon Forms Fullerenes and nanotubes El Fullerenes or carbon nanotubes wrap the graphite sheet by curving into ball or tube Buckminister fullerenes ULike a soccer ball C50 also C70 others
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