ceramics (sərămˈĭks) [key], materials made of nonmetallic minerals that have been permanently hardened by firing at a high temperature, or objects made of such materials. Most ceramics resist heat and chemicals and are poor conductors of heat and electricity. Traditional ceramics are made of clay and other natural occurring materials, while modern high-tech ceramics use silicon carbide, alumina, and other specially purified or synthetic raw materials. Ceramic materials are used in all forms of pottery, from crude earthenware to the finest porcelain, and in industrial and engineering products. Ceramic products include cookware and dinnerware; art objects, such as figurines; building materials, such as brick; abrasives, such as alumina, and specialized cutting tools; electrical equipment, such as insulators in spark plugs; refractories, such as firebrick and the heat shield on the space shuttle; and artificial bones and medical devices. The oldest known fired ceramics date from the Paleolithic period some 27,000 years ago.
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