Electrical silicon carbide

The covalent carbides These include boron carbide B4C and silicon carbide SiC the latter is made by heating a mixture of silica and coke in an electric furnace to about 2000 K ... 

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

In 1885, Charles Martin Hall invented his aluminum process and Hamilton Young Castner in 1890 developed the mercury-type alkali-chlorine cell, which produced caustic (sodium hydroxide) in its purest form. Edward G. Acheson in 1891, while attempting to make diamonds in an electric furnace, produced silicon carbide, the first synthetic abrasive, second to diamond in hardness. Four years later, Jacobs melted aluminum oxide to make a superior emeiy cloth. Within two decades, these two abrasives had displaced most natural cutting materials, including naturally occurring mixtures of aluminum and iron oxides. 

Many ceramic applications are high value and small volume, so energy expenditure is high. Ferroelectric magnets, electronic substrates, electrooptics, abrasives such as silicon carbide and diamond, are examples. Diamond is found naturally, and made synthetically by the General Electric Company at high pressure and temperature. Synthetic diamonds for abrasives require less energy to make than the value in Table 4 nevertheless, the market is carefully divided between natural and synthetic diamonds. 

The main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

Silicon, like carbon, is relatively inactive at ordinary temperatures. But, when heated, it reacts vigorously with the halogens (fluorine, chlorine, bromine, cmd iodine) to form halides and with certain metals to form silicides. It is unaffected by all acids except hydrofluoric. At red heat, silicon is attacked by water vapor or by oxygen, forming a surface layer of silicon dioxide. When silicon and carbon are combined at electric furnace temperatures of 2,000 to 2,600 °C (3,600 to 4700 °F), they form silicon carbide (Carborundum = SiC), which is an Importeint abrasive. When reacted with hydrogen, silicon forms a series of hydrides, the silanes. Silicon also forms a series of organic silicon compounds called silicones, when reacted with various organic compounds. 

Infrared thermal destruction technology is a thermal processing system that uses electrically powered silicon carbide rods to heat organic wastes to combustible temperatures. Any remaining combustibles are incinerated in an afterburner. One configuration made by ECOVA Corporation consists of four components65 ... 

Acheson (1) A process for making silicon carbide from sand and coke, in an electric furnace, at 2,200 to 2,400°C ... 

Electrical applications silicon carbide in, 22 539 silver in, 22 658 Electrical behavior... 

Radiation in the infrared region of the spectrum is obtained from heated ceramic devices such as the Nemst glower or Globar. The Globar is made of silicon carbide and is heated to approximately 800-1500°C to emit black-body radiation in the infrared region of the spectrum. Coils of nichrome wire also emit infrared radiation when electrically heated. 

Diamond and silicon carbide are nonconductors of electricity and have very high melting points. The melting point of diamond is about 3500°C and that of SiC 2830°C. 

Source of Heat Industrial furnaces are either fuel-fired or electric, and the first decision that a prospective furnace user must make is between these two. Although electric furnaces are uniquely suited to a few appheations in the chemical industry (manufacture of silicon carbide, calcium carbide, and graphite, for example), their principal use is in the metallurgical and metal-treatment industries. In most cases the choice between electric and fuel-fired is economic or custom-dictated, because most tasks that can be done in one can be done equally well in the other. Except for an occasional passing reference, electric furnaces will not be considered further here. The interested reader will find useful reviews of them in Kirk-Othmer Encyclopedia of Chemical Technology (4th ed., vol. 12, articles by Cotchen, Sommer, and Walton, pp. 228-265, Wiley, New York, 1994) and in Marks Standard Handbook for Mechanical Engineers (9th ed., article by Lewis, pp. 7.59-7.68, McGraw-Hill, New York, 1987). 

Polysilanes can be regarded as one-dimensional analogues to elemental silicon, on which nearly all of modern electronics is based. They have enormous potential for technological uses [1-3]. Nonlinear optical and semiconductive properties, such as high hole mobility, photoconductivity, and electrical conductivity, have been investigated in some detail. However, their most important commercial use, at present, is as precursors to silicon carbide ceramics, an application which takes no advantage of their electronic properties. 

Silicon carbide is prepared by heating fine sdica with carbon (coke) and a little salt and sawdust in an electric furnace. 

The electric infrared incineration technology is a mobile thermal processing system that is suitable for soils or sediments contaminated with organic compounds, polychlorinated biphenyls (PCBs), and metals. Liquid organic wastes can be treated after mixing with sand or soil. Electrically powered silicon carbide rods heat organic wastes to combustion temperature while any remaining combustibles are incinerated in an afterburner. 

As previously discussed, silicon dioxide appeared to be a nonideal gate dielectric to be used with silicon carbide in UMOS configuration. Different design solutions used to protect SiO gate dielectric from a high electric field in SiC UMOSFETs resulted in dramatically complicated transistor structure. Because of the problems with SiC UMOSFET, the classical vertical double-diffused MOSEET (VDMOS)... 

Silica is reduced to silicon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous silicon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum halides, silica can be converted to silane in high yields by reaction with hydrogen (15). Silicon itself is not hydrogenated under these conditions. The formation of silicon by reduction of silica with carbon is important in the technical preparation of the element and its alloys and in the preparation of silicon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and silicate. At 800—900°C, silica is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce silica to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

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