陶瓷材料的性能特性

• Properties:
-optical -whiteware -bricks for -sandpaper -composites engine high T -composite -bricks -cutting -structural -rotors (furnaces) -polishing reinforce -valves -containers/ -bearings Adapted from Fig. 13.1 and discussion in household Section 13.2-6, Callister 7e. -sensors
--crystallize at melting temp, Tm --have abrupt change in spec. vol. at Tm
• Glasses:
Adapted from Fig. 13.5, Callister, 6e.
--do not crystallize --spec. vol. varies smoothly with T --Glass transition temp, Tg
from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.
Ceramic Their Properties and Material Behavior
Engr 2110 Dr. R. Lindeke
Taxonomy of Ceramics
Glasses Clay Refractories products Abrasives Cements Advanced ceramics
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• Large vs small ionic bond character: CaF2: large SiC: small
Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
• The same ideas apply to all “ceramics” • Principles of Ceramic Architecture:
– – – – Size relationships Cation to Anion Electrical Neutrality of the overall structure Crystallographic Arrangements Stoichiometry Must Match
E.g. Soda lime glass = 70wt% SiO2 + 30% [Na2O (soda) and CaO(lime)
Table 13.1
GLASS PROPERTIES
• Specific volume (1/r) vs Temperature (T): • Crystalline materials:
• better temperature stability & less brittle than sodium glass
GLASSES – transparent and easily shaped
Noncrystalline Silicates + oxides (CaO, Na2O, K2O, Al2O3)
Ceramic Crystal Structures
Oxide structures
– oxygen anions much larger than metal cations – close packed oxygen in a lattice (usually FCC) – cations in the holes of the oxygen lattice
Silica Glass
• A “Dense form” of amorphous silica
– Charge imbalance corrected with “counter cations” such as Na+ – Borosilicate glass is the pyrex glass used in labs
• Fabrication
-- some glasses can be easily formed -- other ceramics can not be formed or cast.
• Bonding:
Ceramic Bonding
-- Mostly ionic, some covalent. -- % ionic character increases with difference in electronegativity (remember!?!).
• Viscosity:
--relates shear stress & velocity gradient: --has units of (Pa-s)
dv t dy
9
GLASS VISCOSITY VS T AND IMPURITIES
• Viscosity decreases with T increase • Impurities lower Tdeform
-- Tm for glass is moderate, but large for other ceramics. -- Small toughness, ductility; large moduli & creep resist.
• Applications:
-- High T, wear resistant, novel uses from charge neutrality.