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| Ceramics(Greek keramos, "potter's clay") |
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originally the art of making pottery, now a general term for the science of manufacturing articles prepared from pliable, earthy materials that are made rigid by high-temperature treatment. Ceramic materials are nonmetallic, inorganic compounds, primarily oxides, but also carbides, nitrides, borides, and silicides. Iron oxide particles are the active component in a variety of magnetic recording media, such as recording tape and the computer diskette. Ceramics includes the manufacture of earthenware, porcelain, bricks, and some kinds of tile and stoneware. Ceramic products are used not only for artistic objects and tableware, but also for such utilitarian items as sewer pipe and building walls. Ceramic insulators with a wide range of electrical properties have increasingly replaced conventional manufacturing materials. The electrical properties of a recently discovered family of copper-oxide-based ceramics allow them to become superconductive at temperatures much higher than those at which metals display this phenomenon. In space technology, ceramic materials and cermets (strong, highly heat-resistant alloys, typically made by mixing, pressing, and then baking an oxide or carbide with a powdered metal) are used to make nose cones, the heat-shield tiles on the space shuttle, and many other components. |
| Clay |
earth or soil that is plastic and tenacious when moist and that becomes permanently hard when baked or fired. Of widespread importance in industry, clays consist of a group of hydrous alumino-silicate minerals formed by the weathering of feldspathic rocks, such as granite. Individual mineral grains are microscopic in size and shaped like flakes. This makes their aggregate surface area much greater than their thickness and allows them to take up large amounts of water by adhesion, giving them plasticity and causing some varieties to swell. Common clay is a mixture of kaolin, or china clay (hydrated clay), and the fine powder of some feldspathic mineral that is anhydrous (without water) and not decomposed. Clays vary in plasticity, all being more or less malleable and capable of being molded into any form when moistened with water. The plastic clays are used for making pottery of all kinds, bricks and tiles, tobacco pipes, firebricks, and other products. The commoner varieties of clay and clay rocks are china clay, or kaolin; pipe clay, similar to kaolin, but containing a larger percentage of silica; potter's clay, not as pure as pipe clay; sculptor's clay, or modeling clay, a fine potter's clay, sometimes mixed with fine sand; brick clay, an admixture of clay and sand with some ferruginous (iron-containing) matter; fire clay, containing little or no lime, alkaline earth, or iron (which act as fluxes), and hence infusible or highly refractory; shale; loam; and marl. |
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