Pure silicon carbide is a colorless and transparent crystal. Industrial silicon carbide is colorless, light yellow, light green, dark green or light blue, dark blue or even black. The abrasive industry divides silicon carbide into two categories: black silicon carbide and green silicon carbide according to color, among which colorless to dark green are classified as green silicon carbide; light blue to black are classified as black silicon carbide. The reason for the polychromaticity of silicon carbide is related to the presence of various impurities. Industrial silicon carbide generally contains about 2% of various impurities, mainly silicon dioxide, silicon, iron, aluminum, calcium, magnesium, carbon, etc. When more carbon is melted in the crystal, the crystal is black. Green silicon carbide is brittle, black silicon carbide is tougher, and the grinding ability of the former is slightly higher than that of the latter. According to the particle size, the products are divided into different grades. According to my country's abrasive professional rules, black silicon carbide has 17 grades; green silicon carbide has 21 particle size grades. Abrasives of No. 80 and above are called abrasive grains, and abrasives of No. 100 to 280 are called grinding powder.
According to different uses: silicon carbide is divided into abrasives, refractory materials, deoxidizers, and electrical silicon carbide. The SiC content of silicon carbide for abrasives should be above 98%. Silicon carbide for refractory materials is further divided into (1) black silicon carbide for advanced refractory materials, whose SiC content is exactly the same as that for abrasive materials; (2) black silicon carbide for secondary refractory materials, whose SiC content is greater than 90%; (3) low-grade Secondary refractory material black silicon carbide, the SiC content is greater than 83%. Silicon carbide is used as the deoxidizer, and the SiC content is generally required to be greater than 90%. However, carbon industrial graphitization furnace insulation with a silicon carbide content greater than 45% can also be used as a steelmaking deoxidizer. Silicon carbide for deoxidizers is available in powder form and in shaped blocks. Powdered deoxidizer black silicon carbide generally has two particle sizes of 4-0.5mm and 0.5-0.1mm. There are two main categories of silicon carbide for electrical use: (1) green silicon carbide for electric heating elements, which is completely the same as green silicon carbide for abrasives. (2) Silicon carbide for arresters has special electrical performance requirements, which is different from black silicon carbide for refractory materials for abrasives.