Classification Of Black Silicon Carbide

Silicon carbide (SiC) is made of quartz sand, petroleum coke (or coal coke), and sawdust through high-temperature smelting in a resistance furnace. Silicon carbide also exists in rare minerals in nature, moissanite.
Silicon carbide is also called carbon silicon stone. Among contemporary non-oxide high-tech refractory raw materials such as C, N, and B, silicon carbide is the most widely used and economical one. It can be called diamond sand or refractory sand.
Silicon carbide is made of quartz sand, petroleum coke (or coal coke), sawdust (salt is needed when producing green silicon carbide) and other raw materials through high-temperature smelting in a resistance furnace. The silicon carbide produced industrially in my country 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 microhardness of 2840-3320kg/mm2.
Including black silicon carbide and green silicon carbide, among which: green silicon carbide is made of petroleum coke and high-quality silica as the main raw materials, with salt added as an additive, and is smelted at high temperature in a resistance furnace. Its hardness is between corundum and diamond, and its mechanical strength is higher than corundum. There are two different crystals of commonly used silicon carbide abrasives. One is green silicon carbide, which contains more than 97% SiC and is mainly used to grind hard gold-containing tools. The other is black silicon carbide, which has a metallic luster and contains more than 95% SiC. It is stronger than green silicon carbide, but has a lower hardness. It is mainly used to grind cast iron and non-metallic materials.
The molecular formula is SiC, and its hardness is between corundum and diamond. Its mechanical strength is higher than corundum. It can be used as an abrasive and some other industrial materials. Industrial silicon carbide was successfully developed in 1891 and is the earliest artificial abrasive. Although there is a small amount of silicon carbide in meteorites and the earth's crust, no mineral source has been found so far.
Pure silicon carbide is a colorless and transparent crystal. Industrial silicon carbide is light yellow, green, blue or even black depending on the type and content of impurities it contains, and its 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). α-SiC has many different variants due to the different stacking sequences of carbon and silicon atoms in its crystal structure, and more than 70 types have been discovered. β-SiC transforms into α-SiC at above 2100℃.
The industrial method of silicon carbide is to refine it in a resistance furnace with high-quality quartz sand and petroleum coke. The refined silicon carbide blocks are crushed, acid-base washed, magnetically separated and screened or water-selected to produce products of various particle sizes.
There are two commonly used basic varieties of silicon carbide, black silicon carbide and green silicon carbide, both of which belong to α-SiC. ① Black silicon carbide contains about 98.5% SiC, and its toughness is higher than that of green silicon carbide. It is mostly used to process materials with low tensile strength, such as glass, ceramics, stone, refractory materials, cast iron and non-ferrous metals. ② Green silicon carbide contains more than 99% SiC and has good self-sharpening properties. It is mostly used to process cemented carbide, titanium alloy and optical glass, and is also used for honing cylinder liners and fine grinding of high-speed steel tools. In addition, there is cubic silicon carbide, which is a yellow-green crystal made by a special process. The grinding tools used to make it are suitable for superfinishing bearings, and can make the surface roughness from Ra32~0.16 microns to Ra0.04~0.02 microns in one go.