Silicon carbide (SiC) is a synthetic material discovered by Acheson (of USA) in 1891. Today it finds extensive applications in refractories, as abrasive materials or as heating elements.

Silicon carbide is made by heating silica sand and petroleum coke packed around carbon electrodes in an electric furnace to above 2200 degree C. The forming process of SiC is complex, including vapour-solid reaction. In this process, a SiC zone develops outside of a graphite zone (formed through decomposition of first formed SiC) around the electrodes. Outside of SiC zone exists fine SiC and then an unreacted zone. The SiC ingot is ground and graded.

There are two types of silicon carbides - black and green. For refractories, black silicon carbide is mostly used. Green silicon carbide is used mainly in manufacturing of abrasive materials or heating elements.

SiC has a layer structure and many polymorphs. The variation in the number of layers in a unit cell provides many different crystal systems.

In general, SiC is divided into alfa-SiC and beta-SiC. Of these alfa-SiC includes hexagonal and rhombic systems, and beta-SiC is a cubic system. Alfa-SiC has many polymorphs, differing from each other in respect to the number of layers in a unit cell. These polymorphs are expressed by a system of nomenclature in which the number of layers in each is used together with the initial letter of the name of the corresponding crystal system.  Industrial silicon carbides include 4H (hexagonal system with four layers in a unit cell), 6H (hexagonal system with six layers in a unit cell), 15R (rhombic system with fifteen layers in a unit cell) and 3C (cubic system, beta form,with three layers in a unit cell). Most of the black silicon carbide is made up of the 4H and 6H forms; green silicon carbide contains predominantly the 6H form. Excluding electric resistance, the properties of black and green silicon carbides do not differ much.

Silicon carbide is harder than corundum, and is resistant to abrasion. Further, it is resistant to corrosion in contact with molten slag. Its coefficient of thermal expansion is relatively low and it has a high thermal conductivity, hence it has excellent resistance to thermal spalling. On the other hand, since it is a carbide, it readily undergoes oxidation at high temperatures. In an oxidising atmosphere, it starts oxidising at around 800⁰C, the rate of oxidation increases increases with rise in temperature. If it comes in contact with steam at a high temperature, oxidation proceeds more rapidly.  The oxidation of SiC is also accelerated in the presence of compounds like Al₂O₃, B₂O₃, CaO, PbO and V₂O₅. One of the best methods by which oxidation can be prevented is to form a film around the SiC grains. In a reducing atmosphere, silicon carbide decomposes at temperature of 2000 degree C or above without melting. 

Being a carbon compound, silicon carbide is chemically neutral. However, a thin film of SiO₂ (formed by oxidation of SiC) forms around the grains of SiC when it is heated. The presence of this film causes it to behave as an acidic refractory.

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