silicon dioxide: see silica.

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.

silicon, nonmetallic chemical element; symbol Si; at. no. 14; at. wt. 28.0855; m.p. 1,410°C;; b.p. 2,355°C;; sp. gr. 2.33 at 25°C;; valence usually +4. Silicon is the element directly below carbon and above germanium in Group 14 of the periodic table. It is more metallic in its properties than carbon; in many ways it resembles germanium. Silicon has two allotropic forms, a brown amorphous form, and a dark crystalline form. The crystalline form has a structure like diamond and the physical properties given above. Silicon forms compounds with metals (silicides) and with nonmetals. With carbon it forms silicon carbide; with oxygen a dioxide, silica; with oxygen and metals, silicates. With hydrogen it forms several hydrides or silanes, the simplest being monosilane, SiH₄, a colorless gas. It also forms compounds with the halogens, sulfur, and nitrogen and forms numerous organo-silicon compounds. Silicon is the second most abundant element of the earth's crust; it makes up about 28% of the crust by weight. Oxygen, most abundant, makes up about 47%. Aluminum, third in abundance, makes up about 8%. Silicon is widely distributed, occurring in silica and silicates, but never uncombined. Silicon is obtained commercially by heating sand and coke in an electric furnace. It is used in the steel industry in an alloy known as ferrosilicon, and also to form other alloys, such as those with aluminum, copper, and manganese; in these alloys it contributes hardness and corrosion resistance. A purified silicon is used in the preparation of silicones. Silicon of very high purity is prepared by thermal decomposition of silanes; it is used in transistors and other semiconductor devices. Silica is widely used in the production of glass. Silicates in the form of clay are used in pottery, brick, tile, and other ceramics. Silicon is found in many plants and animals; it is a major component of the test (cell wall) of diatoms. Silicosis is a lung disease caused by inhaling silica dust. Discovery of the element is usually credited to J. J. Berzelius, who in 1824 prepared fairly pure amorphous silicon.

Silicon Valley, an industrial region, approximately 20 mi (32 km) long, in the Santa Clara Valley between Palo Alto and San Jose, mainly in Santa Clara and San Mateo counties, W central Calif., where many computer manufacturing and design companies are located. Computer-software and other high-technology industries are also there. The name derives from high-purity silicon used in making the semiconductors used in computers.

Atomic Number:	Atomic Number: 14
Atomic Symbol:	Atomic Symbol: Si
	Name of Element: Silicon
Atomic Weight:	Atomic Weight: 28.0855
Electron Configuration:	Electron Configuration: 2 · 8 · 4

or silicon hydride

Any of a series of inorganic compounds of silicon and hydrogen with covalent bonds and the general chemical formula Si_math.nH_{(2math.n + 2)}. Silanes are structural analogs of saturated hydrocarbons (see saturation; alkane) but are much less stable. All burn or explode when exposed to air and react readily with halogens or hydrogen halides to form halogenated silanes and with olefins to form alkylsilanes, products used as water repellents and as starting materials for silicones.

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Nonmetallic to semimetallic chemical element, chemical symbol Si, atomic number 14. Second only to oxygen in abundance in Earth's crust, it never occurs free but is found in almost all rocks and in sand, clay, and soils, combined with oxygen as silica (silicon dioxide, SiO₂) or with oxygen and metals as silicate minerals. It occurs in many plants and some animals. Pure silicon is a hard, dark gray solid with a metallic lustre and the same crystal structure as diamond. It is an extremely important semiconductor; doped (see dopant) with boron, phosphorus, or arsenic, it is used in various electronic circuit and switching devices, including computer chips, transistors, and diodes. Silicon is also used in metallurgy as a reducing (see reduction) agent and in steel, brass, and bronze. Its usual valence in compounds is 4. Silica is used in the form of sand and clay for many purposes; as quartz, it may be heated to form special glasses. Silicates are used in making glass, enamels, and ceramics; sodium silicates (water glass) are used in soaps, wood treatment, cements, and dyeing. Seealso silane; silicone.

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Industrial region, west-central California. Roughly bounded by San Francisco Bay on the north, the Santa Cruz Mountains on the west, and the Diablo Range on the east, it takes its (unofficial) name from the extensive use of silicon in the region's electronics industries. The U.S. government invested heavily in the region's industry following World War II. A second economic surge occurred with the proliferation of personal computers in the 1980s, and a third surge followed the growth of the Internet in the 1990s.

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