Grit blasting sand, also known as silicon carbide (SiC), is produced through high-temperature smelting in resistance furnaces using raw materials such as quartz sand, pet coke (or coal coke), and sawdust (salt is added during the production of green silicon carbide). Silicon carbide also exists as a rare mineral in nature, known as moissanite. It is also referred to as carborundum. In contemporary high-tech refractory materials that are non-oxide, such as carbon, nitrogen, and boron, silicon carbide is widely used and economical, often called grit blasting sand or refractory sand. Currently, silicon carbide produced in China's industrial sector is divided into black silicon carbide and green silicon carbide, both of which are hexagonal crystals with a specific gravity of 3.20~3.25 and a micro-hardness of 2840~3320 kg/mm².
Silicon carbide, known for its stable chemical properties, high thermal conductivity, low thermal expansion coefficient, and excellent wear resistance, has many applications beyond its use as an abrasive. For instance, applying silicon carbide powder to the inner wall of a turbine blade or cylinder using special processes can enhance wear resistance and double its service life. Additionally, high-grade refractory materials made from silicon carbide offer excellent heat resistance, compact size, low weight, and high strength, resulting in superior energy-saving effects. Low-grade silicon carbide (containing about 85% SiC) serves as a good deoxidizing agent, accelerating steelmaking processes and facilitating control over chemical composition, thereby improving steel quality. Moreover, silicon carbide is extensively used in the production of electrical heating elements, such as silicon carbide rods.
Silicon carbide boasts a high hardness, with a Mohs hardness of 9.5, ranking second only to the world's hardest diamond (10 on the Mohs scale). It also exhibits excellent thermal conductivity, acts as a semiconductor, and can resist oxidation at high temperatures.
Silicon carbide has at least 70 crystalline forms. α-Silicon carbide is a common polymorph, formed at temperatures above 2000 °C and possesses a hexagonal crystal structure similar to fibrous zincite. β-Silicon carbide, with a cubic crystal structure similar to diamond, is formed at temperatures below 2000 °C, as shown in the attached image on the page. Although α-Silicon carbide is notable for its higher specific surface area in applications as a heterogeneous catalyst support, and μ-Silicon carbide is stable with a pleasant sound upon impact, neither of these forms has commercial applications to date.
Due to its density of 3.2g/cm³ and high sublimation temperature (approximately 2700 °C), silicon carbide is highly suitable as a material for bearings or components in high-temperature furnaces. It will not melt under any achievable pressure and has a relatively low chemical activity. Its high thermal conductivity and high breakdown electric field strength make it a popular alternative to silicon in semiconductor high-power devices. Additionally, its strong coupling with microwave radiation, along with its high sublimation point, allows for practical applications in heating metals.
Pure silicon carbide is colorless, while the brown to black hues in industrial production are due to impurities containing iron. The rainbow-like luster on the crystals is caused by the silicon dioxide protective layer formed on its surface.
