silicon carbide, chemical compound, SiC, that forms extremely hard, dark, iridescent crystals that are insoluble in water and other common solvents. Widely used as an abrasive, it is marketed under such familiar trade names as Carborundum and Crystolon. It is heat resistant, decomposing when heated to about 2,700°C;; it is used in refractory materials, e.g., rods, tubes, firebrick, and in special parts for nuclear reactors. Very pure silicon carbide is white or colorless; crystals of it are used in semiconductors for high-temperature applications. Silicon carbide fibers, added as reinforcement to plastics or light metals, impart increased strength and stiffness. Silicon carbide is prepared commercially by fusing sand and coke in an electric furnace at temperatures above 2,200°C;; a flux, e.g., sodium chloride, may be added to eliminate impurities. Silicon carbide was discovered (1891) by E. G. Acheson; early studies of it were made by Henri Moissan.

carbide, any one of a group of compounds that contain carbon and one other element that is either a metal, boron, or silicon. Generally, a carbide is prepared by heating a metal, metal oxide, or metal hydride with carbon or a carbon compound. Calcium carbide, CaC₂, can be made by heating calcium oxide and coke in an electric furnace; it reacts with water to yield acetylene and is an important source of the gas. Barium carbide reacts similarly. Aluminum carbide reacts with water to yield methane. Some carbides are unaffected by water, e.g., chromium carbide and silicon carbide. Silicon carbide, almost as hard as diamond, is used as an abrasive. Tungsten carbide, also very hard, is used for cutting edges of machine tools. Iron carbides are present in steel, cast iron, and some other iron alloys.

Inorganic compound, any of a class of chemical compounds in which carbon is combined with a metal or semimetallic element. The nature of the second element (its position in the periodic table) determines the carbide's type of bonding and its properties. Calcium carbide is useful as a source of acetylene. Carbides of tungsten, silicon (see Carborundum), and boron, called refractory carbides, are extremely hard, remain stable when heated, and have a high melting point and chemical resistance. They are used as abrasives and in cutting tools, as furnace linings, and in other high-temperature applications. Iron carbide (cementite) is an important constituent of steel and cast iron.

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