Known for its hardness, silicon carbide is an excellent material for applications in automotive brakes and clutches as well as bulletproof vests. It retains its strength at up to 1400degC and exhibits the highest corrosion resistance among all advanced ceramics.
SiC is a highly stable and chemically inert compound that crystallizes into close packed structures covalently bonded to each other. Each atom in the crystal is surrounded by four carbon atoms and two silicon atoms. The atomic structures form tetrahedra, and these are stacked to form polar structures called polytypes.
Each tetrahedral unit is covalently bonded to each other by hydrogen bonds between the carbon and silicon atoms in the unit. The tetrahedra are then linked together to form a diamond-like lattice with the atomic radii arranged in a similar fashion to that of diamond (Figure 1).
The lattices of different SiC polytypes have distinct electronic band-gaps. The higher the band-gap, the wider the range of frequencies that the electronic device can operate. These properties are ideal for use in high-voltage and high-temperature applications such as semiconductors.
Silicon carbide is a popular abrasive in the art industry and in manufacturing, where it is used for a variety of abrasive machining processes such as honing, grinding, water-jet cutting, and sandblasting. It is also used in lining work for uniformity of abrasion resistance and dimensional stability, as well as in semiconducting substrates for light-emitting diodes.
Its hardness makes it a valuable abrasive in the metalworking industry, where it is used as an additive in steel and as a structural ceramic in refractory and other industrial furnaces. It is also an important component of abrasive and steel additive mixtures and refractory materials for wear-resistant parts in pumps and rocket engines.
Unlike many other abrasives, silicon carbide is resistant to oxidation and corrosion. It has excellent electrical resistance and a low thermal expansion coefficient, so it is suited to use in refractory linings and heating elements for industrial furnaces. It is also used in wear-resistant parts for pumps and rocket engines as well as in semiconducting substrates to make light-emitting diodes.
In the abrasives industry, it is primarily produced by the Acheson process. This method involves heating a mixture of pure silica sand and carbon in the form of finely ground coke in an electrical resistance-type furnace, which enables the carbon to be replaced by silicon during the combustion. This process has been refined to produce a highly consistent, crystalline product.
The modern process of producing abrasives using SiC was developed by Pennsylvanian Edward Acheson in 1891 and is still in use today for production of small crystals for abrasive, steel, and refractory applications. The abrasives are then processed into powders and compacted by means of cold isostatic pressing, a powder compaction technique which involves applying pressure from multiple directions through a liquid medium surrounding the compacted part.
The abrasive is then sintered into its final shape in a temperature-controlled, nitrogen-fueled furnace. The resulting sintered material is extremely hard, strong, and has a high thermal conductivity. It is then machined to precise tolerances using a wide range of precision diamond grinding or lapping techniques. The resulting silicon carbide parts are then carefully inspected to ensure that they have no defects and are free of manufacturing imperfections.
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