silicon carbide


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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 Carbide

 

(SiC), a compound of silicon and carbon; one of the most important carbides used in industry. In pure form, silicon carbide is a colorless crystal with an adamantine luster; the industrial product is green or blue-black. Silicon carbide exists in two main crystal modifications—the hexagonal (α-SiC) and cubic (β-SiC); the hexagonal modification is a “giant molecule,” constructed in accordance with the principle of a unique structurally directed polymerization of simple molecules. The layers of carbon and silicon atoms in α-SiC are arranged in various ways with respect to one another, thus forming many structural types. The transition from β-SiC to α-SiC occurs at 2100°-2300°C (the reverse transition is usually not observed). Silicon carbide is refractory (melts with decomposition at 2830°C) and is extremely hard (microhardness 33,400 meganew-tons per m2, or 3.34 tonsforce per mm2), being second only to diamond and boron carbide, B4C. It is brittle; its density is 3.2 g/cm3. Silicon carbide is stable in various chemical media even at high temperatures.

Silicon carbide is produced in electric furnaces at 2000°-2200°C from a mixture of quartz sand (51-55 percent) and coke (35-40 percent) with admixture of NaCl (1-5 percent) and sawdust (5-10 percent). Owing to its great hardness, chemical stability, and durability, silicon carbide is widely used as an abrasive (in grinding), as well as for cutting hard materials and sharpening tools. It is also used in the production of various parts of chemical and metallurgical equipment that is operated at high temperatures. Alloyed with various admixtures, it is used in semiconductor technology, particularly at high temperatures. An interesting application of silicon carbide in electrotechnology is in the manufacture of heaters for high-temperature electrical resistance furnaces, lightning rods for power transmission lines, and nonlinear resistors for electrical insulating devices.

G. V. SAMSONOV

silicon carbide

[′sil·ə·kən ′kär‚bīd]
(inorganic chemistry)
SiC Water-insoluble, bluish-black crystals, very hard and iridescent; soluble in fused alkalies; sublimes at 2210°C; used as an abrasive and a heat refractory, and in light-emitting diodes to produce green or yellow light.
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