silicon

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.

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silicon

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. See also silane; silicone.

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(Si) The base material used in chips. Next to oxygen, it is the most abundant element in nature and is found in a natural state in rocks and sand. Its atomic structure and availability make it an ideal semiconductor material. In chip making, it is mined from white quartz rocks and put through a chemical process at high temperatures to purify it. To alter its electrical properties, it is mixed (doped) with other chemicals in a molten state. See silicon germanium and silicone.

A Silicon Moon

This intriguing picture, which looks like it was shot from the moon, symbolizes the fact that chips are made from the same material that is also found in sand. The "moon" is a finished wafer full of memory chips. (Image courtesy of Texas Instruments, Inc.)

Drawing the Silicon Ingot

This picture shows the drawing of a silicon ingot in a fiery furnace containing molten silicon. Special high-speed saws slice the ingots into wafers about the thickness of a dime. They are then ground thinner and polished mirror smooth. (Image courtesy of Texas Instruments, Inc.)

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1.	(electronics)	silicon - The material used as the base (or "substrate") for most integrated circuits.
2.	(jargon)	silicon - Hardware, especially integrated circuits or microprocessor-based computer systems (compare iron). Contrast: software. See also sandbender.