Silicon carbide, chemical symbol SiC, is a solid industrial mineral crystal composed of light elements silicon (Si) and carbon (C). Its basic structural unit is a crystal composed of four carbon atoms forming a tetrahedron covalently bonded to a single silicon atom in the center. SiC also exhibits polymorphism as it exists in different phases and crystal structures. Available as both a semiconductor and a ceramic, silicon carbide is primarily used for its hardness and strength, although its combined ceramic and semiconducting properties make SiC excellent at making fast, high-voltage and high-temperature devices.
Silicon carbide features:
1. High hardness
Silicon carbide has a Mohs hardness of 9, making it the hardest material after boron carbide (9.5) and diamond (10). It is this distinct property that makes SiC an excellent material of choice for mechanical seals, bearings and cutting tools.
2. High temperature resistance
The high temperature and thermal shock resistance of silicon carbide makes SiC useful in the manufacture of refractory bricks and other refractory materials. The decomposition of SiC starts at 2000°C.
If SiC is purified, it behaves like an electrical insulator. However, by controlling impurities, silicon carbide can exhibit the electrical properties of a semiconductor. For example, the introduction of varying amounts of aluminum by doping will result in a p-type semiconductor. Typically, industrial grade SiC is about 98% to 99.5% pure. Common impurities are aluminum, iron, oxygen and free carbon.
4. Chemical stability
Silicon carbide is a stable, chemically inert substance that is highly resistant to corrosion even when exposed to or boiled in acids (hydrochloric, sulfuric or hydrofluoric) or alkalis (concentrated sodium hydroxide). It has been found to react in chlorine gas, but only at temperatures of 900°C and above. Silicon carbide will undergo an oxidation reaction at a temperature of about 850°C in the air to form SiO2.
Applications of silicon carbide:
1. Glass and Ceramic industries are the major consumers of feldspar and account for 95% of the total consumption.
2. Porcelain, china and earthenware
3. Preparation of Glazes and Enamel
4. Glass sand batch
5. Used as a bonding agent in the manufacture of bonded abrasives like wheels and discs of garnet, corundum, emery etc.