What You Don't Know About Abrasives: Natural Abrasive Materials
Because of its stable chemical properties, high thermal conductivity, small thermal expansion coefficient and good wear resistance, Si carbide has many other uses besides abrasives, such as: coating Si carbide powder on turbine impellers or cylinder blocks by a special process. The inner wall can improve its wear resistance and prolong the service life by 1 to 2 times; the advanced refractory material used to make it is resistant to shock, small in size, light in weight, high in strength, and good in energy saving effect. Low-grade Si carbide (containing about 85% SiC) is an excellent deoxidizer, which can speed up steelmaking, facilitate chemical composition control, and improve steel quality. In addition, Si carbide is also widely used to make Si carbide rods for electric heating elements.
Silicon carbide abrasive powder has a very high hardness, with a Mohs hardness of 9.5, second only to the world's hardest diamond (10), with excellent thermal conductivity, is a semiconductor, and can resist oxidation at high temperatures.
Silicon carbide has at least 70 crystalline forms. Alpha-Si carbide is the most common allomorph, formed at high temperatures above 2000°C, and has a hexagonal crystal structure (like wurtzite). Beta-Si carbide, a cubic crystal structure similar to diamond, is formed below 2000°C. Although in the application of heterogeneous catalyst support, it is noticeable because of its higher unit surface area than the α-type, and another kind of Si carbide, μ-Si carbide is the most stable, and has a more pleasant sound when colliding, But until today, these two types have not been used commercially.
Because of its specific gravity of 3.2g/cm3 and high sublimation temperature (about 2700°C), Si carbide is very suitable as a raw material for bearings or high-temperature furnaces. It does not melt at any achievable pressure and has fairly low chemical activity. Due to its high thermal conductivity, high breakdown electric field strength and high maximum current density, many people try to use it to replace silicon in the application of semiconductor high-power components. In addition, it has a strong coupling effect with microwave radiation, and all its high sublimation points make it practical for heating metals.
Pure Si carbide is colorless, and industrially produced brown to black is due to iron-containing impurities. The iridescent luster on the crystal is due to the protective layer of silica produced on its surface.
Pure Si carbide is a colorless and transparent crystal. Industrial Si carbide is pale yellow, green, blue or even black due to the type and content of impurities, and its transparency varies with its purity. The crystal structure of Si carbide is divided into hexagonal or rhombohedral α-SiC and cubic β-SiC (called cubic Si carbide). α-SiC constitutes many different variants due to the different stacking sequences of carbon and silicon atoms in its crystal structure, more than 70 species have been discovered. β-SiC is transformed into α-SiC when the temperature is above 2100°C. The industrial method of Si carbide is to use high-quality quartz sand and petroleum coke to refine it in a resistance furnace. The smelted Si carbide blocks are crushed, washed with acid and alkali, magnetic separation and sieving or water separation to produce products of various particle sizes.
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