The molecular formula is SiC, its hardness is between corundum and diamond, its mechanical strength is higher than that of corundum, and it can be used as abrasive and some other industrial materials. Industrial silicon carbide was successfully developed in 1891 and was the first artificial abrasive. Although a small amount of silicon carbide exists in vermiculite and crust, no mineral source has been found yet.
Pure silicon carbide is a colorless, transparent crystal. Industrial silicon carbide is light yellow, green, blue or even black due to the type and content of impurities contained in it. The transparency varies with its purity. The crystal structure of silicon carbide is divided into hexagonal or rhombohedral α-SiC and cubic β-SiC (called cubic silicon carbide). Since α-SiC constitutes many different variants due to the different stacking sequences of carbon and silicon atoms in its crystal structure, more than 70 kinds have been found. β-SiC is converted to α-SiC at 2100 ° C or higher.
Silicon carbide, also known as silicon carbide, includes black silicon carbide and green silicon carbide. Among them, black silicon carbide is made of quartz sand, petroleum coke and high-quality silica as the main raw materials, and is smelted by electric furnace at high temperature. Its hardness is between corundum and diamond, the mechanical strength is higher than corundum, and it is brittle and sharp. Green silicon carbide is made of petroleum coke and high-quality silica as the main raw material, adding salt as an additive and smelting by electric furnace at high temperature. Its hardness is between corundum and diamond, and its mechanical strength is higher than that of corundum. So what are the main uses of silicon carbide?
First, abrasives - mainly because silicon carbide has high hardness, chemical stability and certain toughness, so silicon carbide can be used to manufacture bonded abrasives, coated abrasives and free grinding to process glass and ceramics. , stone, cast iron and some non-ferrous metals, hard alloys, titanium alloys, high-speed steel tools and grinding wheels.
2. Refractory materials and corrosion-resistant materials---mainly because silicon carbide has high melting point (decomposition degree), chemical inertness and thermal shock resistance, so silicon carbide can be used in abrasive kiln for grinding and ceramic products. A variety of silicon carbide ceramic products such as slabs, silicon carbide bricks for aluminum cylinders, aluminum electrolytic cell linings, crucibles, and small furnaces.
Third, chemical industry - because silicon carbide can be decomposed in molten steel and react with oxygen and metal oxides in molten steel to form carbon monoxide and silicon-containing slag. Therefore, it can be used as a purifying agent for smelting steel, that is, as a deoxidizer for steel making and a modifier for cast iron. This generally uses low purity silicon carbide to reduce costs. At the same time, it can also be used as a raw material for manufacturing silicon tetrachloride.
Fourth, electricians - used as heating elements, non-linear resistance elements and high semiconductor materials. Heating elements such as silicon carbide rods (for various electric furnaces operating at 1100 to 1500 °C), non-linear resistance elements, and various types of lightning protection valve sheets.