Ceramics are dened as the art and science of making and using solid articles with inorganic nonmetallic materials as their essential component (Kingery et al., 1976). Ceramics are refractory, polycrystalline compounds, usually inorganic, including silicates, metallic oxides, carbides and various refractory hydrides, suldes, and selenides. Oxides such as Al2O3, MgO, SiO2, and ZrO2 contain metallic and nonmetallic elements and ionic salts such as NaCl, CsCl, and ZnS (Park and Lakes, 1992). Exceptions to the former include covalently bonded ceramics such as diamond and carbonaceous structures such as graphite and pyrolized carbons (Park and Lakes, 1992).