Silicon carbide is a hard, chemically bonded material that is one of the hardest materials known to man. Its crystalline form has low thermal expansion, and its particles have high thermal conductivity. These properties make it a viable material for the manufacture of abrasives and other hard ceramics. Besides its use as an abrasive, silicon carbide has been found to have other applications, including use in the production of graphene, a type of material that is thin and transparent, and is highly conductive.
In 1890, Edward Goodrich Acheson began his experiments with making artificial diamonds. He started by heating clay, aluminum silicate, and powdered coke in an iron bowl, and believed that blue crystals formed carborundum. Later, he patented a method of making silicon carbide powder, and the Carborundum Company was formed.
Silicon carbide is formed by the reaction of silicon dioxide with carbon. The ratio of the two compounds is about one to one. During this process, a layer of silicon dioxide forms, and the remaining carbon reacts with the silicon dioxide to produce silicon monoxide. This mixture then sublimes at about 2500 degC, and is broken up into a variety of silicon compounds, which then crystallize into the desired shapes. Some of these compounds are alpha and beta silicon carbide.
Because of its hardness, silicon carbide is used as an abrasive. It is also a good insulator, and is a candidate material for use in fusion reactors. As such, it has been used in nuclear fuel particle coatings, as well as in high-temperature gas-cooled reactors. Additionally, it has been used as an electrical heating element for electric furnaces.
SiC is typically formed by a high-temperature reaction between silicon monoxide gas and carbon. It is soluble in molten alkalis and in molten iron. However, it is insoluble in water. Despite its low density, it has excellent endurance in hot environments, as well as in corrosive environments. Furthermore, it is used in a variety of applications, including high-voltage devices, high-temperature gas-cooled reactors, and light-emitting diodes.
Silicon carbide particles have high resistance to abrasion, and are able to withstand temperatures as high as 1650 degC. Their high thermal conductivity allows them to be used in composites for improved strength. They also retain elastic resistance up to this temperature. Silicon carbide particles can be used as reinforcement in metal matrices. When mixed with boron, it can form a metallic-conductive material.
It is important to remember that while the production of silicon carbide is a relatively low-energy process, it is still an energy intensive endeavor. It requires approximately 11-13 MWh of electric energy to produce a mass of silicon. Ultimately, the amount of silicon produced will depend heavily on the type of carbon used in the process. Currently, methane is not used as a source of carbon in the production of silicon. While it has a high reactivity, it does not contribute to the upper furnace zone, where the carbon monoxide is formed.
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