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| Refractoriness (℃): | 1770< Refractoriness< 2000 |
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Silicon carbide, with the chemical symbol SiC, is a solid industrial mineral crystalline. It is used as a semiconductor and a ceramic, commonly referred to as carborundum. SiC exists naturally in an extremely rare mineral called moissanite. Pure silicon carbides appear as colourless and transparent crystals. When impurities are added such as nitrogen or aluminium, silicon carbide crystals appear green or blue depending on the level of impurity. Silicon carbide is mostly used for its hardness and strength, though its combined ceramic and semiconductor properties make SiC excellent in the manufacturing of fast, high-voltage, and high-temperature devices.
Robust crystal structure
Silicon carbide is composed of light elements, silicon (Si) and carbon (C). Its basic building block is a crystal of four carbon atoms forming a tetrahedron, covalently bonded to a single silicon atom at the centre. SiC also exhibits polymorphism as it exists in different phases and crystalline structures [2][3].
High hardness
Silicon carbide has a Mohs hardness rating of 9, making it the hardest available material next to boron carbide (9.5) and diamond (10). It is this apparent property that makes SiC an excellent material choice for mechanical seals, bearings, and cutting tools.
High-temperature resistance
Silicon carbide's resistance to high temperature and thermal shock is the property that allows SiC to be used in the manufacturing of fire bricks and other refractory materials. The decomposition of silicon carbide starts at 2000°C [2].
Conductivity
If SiC is purified, its behaviour manifests that of an electrical insulator. However, by governing impurities, silicon carbides can exhibit the electrical properties of a semiconductor. For example, introducing varying amounts of aluminium by doping will yield a p-type semiconductor. Typically, an industrial-grade SiC has a purity of about 98 to 99.5%. Common impurities are aluminium, iron, oxygen, and free carbon [2].
Chemical stability
Silicon carbide is a stable and chemically inert substance with high corrosion resistance even when exposed or boiled in acids (hydrochloric, sulphuric, or hydrofluoric acid) or bases (concentrated sodium hydroxides). It is found to react in chlorine, but only at a temperature of 900°C and above. Silicon carbide will start an oxidation reaction in the air when the temperature is at approximately 850°C to form SiO2 [2].
With the excellent combination of properties that silicon carbide has, it is found to be a promising material option for high-temperature and wear-resistant applications [3].
Abrasive material
Silicon carbide powders are utilised for abrasive machining processes such as grinding, sandblasting, and water-jet cutting. SiC can be laminated in paper, cloth, or wood to produce frictional grip. It can also be used for shaping, honing, and polishing other materials.
High-temperature gas sensor
Silicon carbide is used as a sensing device in chemical production, and in turbine or engine testing industries to detect flammable and combustible gases in harsh, high-temperature, and corrosive environments [3].
Electronics
Silicon carbides are used as semiconductors in many circuit elements due to their high voltage resistance. SiC's voltage resistance is ten times higher than that of ordinary silicon and even performs better than gallium nitride in systems that exceed 1000V. As such, SiC proves valuable in the development of electric vehicles, solar power inverters, and sensor systems
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