Ceramics are defined as the art and science of making and using solid articles that have as their essential component inorganic nonmetallic materials [Kingery et al., 1976]. Ceramics are refractory, polycrystalline compounds, usually inorganic, including silicates, metallic oxides, carbides and various refractory hydrides, sulfides, and selenides. Oxides such as Al


, MgO, SiO

, and ZrO

contain metallic and nonmetallic elements and ionic salts, such as NaCl, CsCl, and ZnS [Park and Lakes, 1992]. Exceptions to the preceding include covalently bonded ceramics such as diamond and carbonaceous structures such as graphite and pyrolized carbons [Park and Lakes, 1992].