Silicon Carbide

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Silicon Carbide is the only chemical compound of carbon and silicon. It was originally produced by a high temperature electro-chemical reaction of sand and carbon. Silicon carbide is an excellent abrasive and has been produced and made into grinding wheels and other abrasive products for over one hundred years. Today the material has been developed into a high quality technical grade ceramic with very good mechanical properties. It is used in abrasives, refractories, ceramics, and numerous high-performance applications. The material can also be made an electrical conductor and has applications in resistance heating, flame igniters and electronic components. Structural and wear applications are constantly developing.
General Silicon Carbide Information
Silicon carbide is composed of tetrahedra of carbon and silicon atoms with strong bonds in the crystal lattice. This produces a very hard and strong material. Silicon carbide is not attacked by any acids or alkalis or molten salts up to 800°C. In air, SiC forms a protective silicon oxide coating at 1200°C and is able to be used up to 1600°C. The high thermal conductivity coupled with low thermal expansion and high strength give this material exceptional thermal shock resistant qualities. Silicon carbide ceramics with little or no grain boundary impurities maintain their strength to very high temperatures, approaching 1600°C with no strength loss. Chemical purity, resistance to chemical attack at temperature, and strength retention at high temperatures has made this material very popular as wafer tray supports and paddles in semiconductor furnaces. The electrical conduction of the material has lead to its use in resistance heating elements for electric furnaces, and as a key component in thermistors (temperature variable resistors) and in varistors (voltage variable resistors).
Silicon Carbide (SiC) devices belong to the so-called wide band gap semiconductor group. They offer a number of attractive characteristics for high voltage power semiconductors when compared to commonly used silicon (Si). In particular, the much higher breakdown field strength and thermal conductivity of SiC allow creating devices which outperform by far the corresponding Si ones. This way you can reach unattainable efficiency levels in your designs.

The modern method of manufacturing silicon carbide for the abrasives, metallurgical, and refractories industries is basically the same as that developed by Acheson. A mixture of pure silica sand and carbon in the form of finely ground coke is built up around a carbon conductor within a brick electrical resistance-type furnace. Electric current is passed through the conductor, bringing about a chemical reaction in which the carbon in the coke and silicon in the sand combine to form SiC and carbon monoxide gas. A furnace run can last several days, during which temperatures vary from 2,200° to 2,700° C (4,000° to 4,900° F) in the core to about 1,400° C (2,500° F) at the outer edge. The energy consumption exceeds 100,000 kilowatt-hours per run. At the completion of the run, the product consists of a core of green to black SiC crystals loosely knitted together, surrounded by partially or entirely unconverted raw material. The lump aggregate is crushed, ground, and screened into various sizes appropriate to the end use.

For special applications, silicon carbide is produced by a number of advanced processes. Reaction-bonded silicon carbide is produced by mixing SiC powder with powdered carbon and a plasticizer, forming the mixture into the desired shape, burning off the plasticizer, and then infusing the fired object with gaseous or molten silicon, which reacts with the carbon to form additional SiC. Wear-resistant layers of SiC can be formed by chemical vapour deposition, a process in which volatile compounds containing carbon and silicon are reacted at high temperatures in the presence of hydrogen. For advanced electronic applications, large single crystals of SiC can be grown from vapour; the boule can then be sliced into wafers much like silicon for fabrication into solid-state devices. For reinforcing metals or other ceramics, SiC fibres can be formed in a number of ways, including chemical vapour deposition and the firing of silicon-containing polymer fibres.

Silicon Carbide Typical Uses
Suction box covers
Seals, bearings
Ball valve parts
Hot gas flow liners
Heat exchangers
Semiconductor process equipment

Properties of Silicon Carbide

SiC is a ceramic material with an outstanding hardness, only surpassed by diamond, cubic boron nitride and boron carbide. The material is highly wear resistant and chemically inert to all alkalies and acids. It is also highly heat resistant. These properties makes Silicon Carbide an outstanding abrasive and ceramic material to be used under extreme operating conditions.
.Key Silicon Carbide Properties
 Low density
 High strength
 Low thermal expansion
 High thermal conductivity
 High hardness
 High elastic modulus
 Excellent thermal shock resistance
 Superior chemical inertness
 extreme good thermal conductivity (7 x better than stainless steel)
 high thermal shock resistance
 highest wear resistance
 extremely hard
 extreme chemical resistance
 highest Young’s modulus
 very good sliding properties
 small electric resistance
 low density
 Density: 3.21 g/cm3
 Vickers hardness: 29 GPa
 Coefficient of Thermal expansion: 5•10-6/K
 Thermal conductivity: 50 to 100 W/m K
 Typical temperature resistance: 1500°C in air, 2400°C in inert atmosphere
 Specific heat: 750 J/kg K


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