Silicon Carbide - SiC

Properties of Silicon Carbide

Physical Properties of Silicon Carbide – SiC

Chemical Properties of Silicon Carbide – SiC

• Silicon Carbide possesses interesting electrical properties because of its characteristics of semiconductors, the resistance of various compositions differing by as seven orders of magnitude.

• Resistant to many organic and inorganic acids, salts, and alkalis in a variety of concentrations except to acid fluorides and hydrofluoric acid.

Silicon Carbide Structure – SiC

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Natural Occurrence

Naturally-occurring moissanites are present only in small numbers in specific forms of meteorites and in kimberlite and corundum deposits. Virtually all the silicon carbide sold in the world is plastic, like moissanite jewellery. In 1893, natural moissanite was first found in Arizona as a small component of the Canyon Diablo meteorite by Dr Ferdinand Henri Moissan, after whom the material was named in 1905. The naturally occurring SiC discovered by Moissan was initially disputed due to his sample may have been contaminated by the silicon carbide saw blades that were already available on the market at that period.

While rare on the Earth, silicon carbide is defined remarkably as common in space. It is also a common form of stardust found around the carbon-rich stars, and the examples of this stardust have been found in pristine condition in unaltered (primitive) meteorites. The silicon carbide can also be found in space and meteorites are beta-polymorph, which is almost exclusively. The SiC grain analysis can be found in the Murchison meteorite, which is a carbonaceous chondrite meteorite and has revealed the anomalous isotopic ratios of silicon and carbon, indicating that these grains have originated outside the solar system.

Production

Because the natural moissanite is an extremely scarcest element, most of the silicon carbide is synthetic. Silicon carbide can be used as an abrasive and as a diamond simulant and semiconductor of gem-quality as well. The simplest process to manufacture the silicon carbide is to combine carbon and silica sand in electric resistance of an Acheson graphite furnace at a high temperature, raging from 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F). The fine particles of SiO2 present in plant material (for example, rice husks) can be converted to SiC by heating the compound in the excess carbon from the organic material. The silica fume, a byproduct of producing ferrosilicon alloys and silicon metal, can also be converted to SiC by heating with graphite at a temperature of 1,500 °C (2,730 °F).

The material, which is formed in the Acheson furnace differs in purity, as per its distance from the graphite resistor heat source. Colourless, green, and pale yellow crystals have the highest purity and can be found closest to the resistor. The colour changes to black and blue at a greater distance from the resistor and these darker crystals are less pure. Aluminium and Nitrogen are the common impurities, and they affect the SiC's electrical conductivity.

Uses of Silicon Carbide

Abrasive and Cutting Tools

Silicon carbide is a popular abrasive in the arts in modern lapidary because of the low cost and durability of the material. Also, in the process of manufacturing, it is used for its hardness in the abrasive machining processes including honing, grinding, sandblasting, and water-jet cutting. Silicon carbide particles are laminated to paper to create grip tape on skateboards and sandpapers.

Automobile Parts

The carbon-carbon composite of Silicon-infiltrated is used for high performance "ceramic" brake disks since they can withstand extreme temperatures. Silicon also reacts with the graphite in the composite of carbon-carbon to form carbon-fibre-reinforced silicon carbide (C/SiC). These brake disks can be used on a few supercars, road-going sports cars, and other performance cars as well, including the Bugatti Veyron, Porsche Carrera GT, the McLaren P1, Ferrari, Bentley, Lamborghini, and a few Audi cars, which have a specific high-performance. Silicon carbide can also be used in a sintered form for diesel particulate filters. It is also used as an oil additive to reduce emissions, harmonics, and friction.

Foundry Crucibles

Silicon Carbide is used in crucibles for holding the melting metal in the applications of both small and large foundry.