Brief introduction of silicon carbide products | TRUNNANO
Silicon carbide, also known as moissanite and emery, is an inorganic substance with a chemical formula of SiC. It is smelted by a high-temperature resistance furnace with raw materials such as quartz sand, petroleum coke (or coal coke), wood chips (salt is needed to produce green silicon carbide) Become. Silicon carbide also exists in nature, a rare mineral, moissanite. Among the non-oxide high-tech refractory materials such as C, N, B, silicon carbide is the most widely used and most economical one, and it can be called gold steel grit or refractory grit. The silicon carbide produced in China's industry is divided into black silicon carbide and green silicon carbide, both of which are hexagonal crystals, with a specific gravity of 3.20 to 3.25 and microhardness of 2840 to 3320kg/mm2.
There are two basic types of silicon carbide, black silicon carbide and green silicon carbide, both of which belong to α-SiC. Black silicon carbide contains about 95% SiC, and its toughness is higher than that of green silicon carbide. It is mostly used for processing materials with low tensile strength, such as glass, ceramics, stone, refractory materials, cast iron and non-ferrous metals. Green silicon carbide contains more than 97% SiC and has good self-sharpening properties. It is mostly used for processing cemented carbide, titanium alloy and optical glass, as well as for honing cylinder liners and fine grinding high-speed steel tools. Besides, there is a cubic silicon carbide, which is a yellow-green crystal prepared by a special process. The abrasive tool used for making is suitable for the superfinishing of bearings. The surface roughness can be processed from Ra32～0.16 microns to Ra0.04～ 0.02 microns.
Due to its stable chemical properties, high thermal conductivity, low thermal expansion coefficient, and good wear resistance, silicon carbide has many other uses besides being used as abrasives. For example, silicon carbide powder is applied to a particular process impeller or cylinder of a water turbine. The inner wall can improve its abrasion resistance and prolong its service life by 1 to 2 times; the high-grade refractory made of it has heat shock resistance, small size, lightweight, high strength and good energy-saving effect. Low-grade silicon carbide (containing about 85% SiC) is an excellent deoxidizer, which can speed up steelmaking speed and facilitate the control of chemical composition and improve steel quality. Besides, silicon carbide is also widely used to make silicon carbide rods for electric heating elements. Silicon carbide has a very high hardness, with a Mohs hardness of 9.5, second only to the world's hardest diamond (10). It has excellent thermal conductivity, is a semiconductor, and can resist oxidation at high temperatures.
Silicon carbide has at least 70 crystalline forms. α-Silicon carbide is the most common kind of allomorphs. It is formed at high temperatures above 2000 °C and has a hexagonal crystal structure (like wurtzite). β-Silicon Carbide, cubic crystal structure, similar to diamond, is formed below 2000 °C. The network is shown on the page. Although heterogeneous catalyst support is applied, it is eye-catching because of its higher unit surface area than the α type. Another type of silicon carbide, μ-silicon carbide, is the most stable and has a more pleasant sound when colliding. But until today, these two types have not yet been commercially applied. Because of its 3.2g/cm3 specific gravity and high sublimation temperature (approximately 2700 °C), silicon carbide is very suitable as a raw material for bearings or high-temperature furnaces. It will not melt under any pressure that can be reached and has a relatively 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. Besides, it has a strong coupling effect with microwave radiation, and all its high sublimation points make it practical for heating metals. Pure silicon carbide is colorless, while the industrially produced brown to black is due to impurities containing iron. The rainbow-like luster on the crystal is due to the protective silica layer on the surface. To
Pure silicon carbide is a colorless and transparent crystal. Industrial silicon carbide is light yellow, green, blue, or even black due to impurities' type and content, and its transparency varies with its purity. The silicon carbide crystal structure is divided into hexagonal or rhombohedral α-SiC and cubic β-SiC (called cubic silicon carbide). α-SiC forms many different variants due to the different stacking sequence of carbon and silicon atoms in its crystal structure, and more than 70 kinds have been found. β-SiC transforms into α-SiC above 2100°C. The industrial manufacturing method of silicon carbide uses high-quality quartz sand and petroleum coke to be refined in a resistance furnace. The refined silicon carbide blocks are crushed, acid-base washed, magnetic separation and sieving or water selection to make products of various particle sizes. Due to its low natural content, silicon carbide is mostly artificial. The standard method is to mix quartz sand and coke, use the silica and petroleum coke, add salt and wood chips, put it in an electric furnace, heat it to a high temperature of about 2000°C, and obtain silicon carbide powder after various chemical processes Silicon carbide (SiC) has become an essential abrasive due to its excellent hardness, but its application range exceeds general abrasives. For example, its high-temperature resistance and thermal conductivity make it one of the first-choice kiln furniture materials for tunnel kilns or shuttle kilns. Its electrical conductivity makes it an essential electric heating element. To prepare SiC products, you must first prepare SiC smelt blocks [or: SiC pellets, because they contain C and are super hard, so SiC pellets were once called: emery. But be careful: it is different from natural emery (also known as garnet) in composition. In industrial production, SiC smelting block usually uses quartz, petroleum coke, etc. as raw materials, auxiliary recovery materials, spent materials. After grinding and other processes, they are blended into a charge with a reasonable ratio and a suitable particle size to adjust the charge's gas permeability; an appropriate amount needs to be added. When preparing green silicon carbide, add the proper amount of salt) to prepare it at high temperatures. The thermal equipment for preparing the SiC smelting block at high temperature is a special silicon carbide electric furnace. Its structure consists of the furnace bottom, the end wall with electrodes on the inner surface, the removable sidewall, and the furnace core body (full name: the electric heating element in the center of the electric furnace Graphite powder or petroleum coke is installed in the center of the charge according to a specific shape and size, generally circular or rectangular. Its two ends are connected with electrodes). The firing method used in this electric furnace is commonly known as buried powder firing. It starts heating as soon as it is energized. The furnace core temperature is about 2500°C, or even higher (2600-2700°C). When the charge reaches 1450°C, SiC is synthesized (but SiC is mainly formed at ≥1800°C) and releases co. However, SiC will decompose when ≥2600℃, but the decomposed si will form SiC with C in the charge. Each electric furnace is equipped with a set of transformers. Still, only a single electric furnace is powered during production to adjust the voltage according to the electrical load characteristics to maintain constant power. The high-power electric furnace needs to be heated for about 24 hours. After a power failure, the reaction of generating SiC is over. After a cooling period, the sidewall can be removed, and then the charge is gradually taken out. Silicon carbide products can be divided into many categories and are divided into different categories according to different use environments and generally used on machinery more. For example, when used on mechanical seals, it can be called a silicon carbide seal ring, which can be divided into the static ring, moving ring, flat ring and so on. We can also produce various shapes of silicon carbide products according to customers' special requirements, such as silicon carbide special-shaped parts, silicon carbide plates, silicon carbide rings, etc. Silicon carbide ceramics, one of the silicon carbide products, has the characteristics of high hardness, high corrosion resistance, and high-temperature strength, which makes silicon carbide ceramics widely used. Applied to seal ring: Silicon carbide ceramic has good chemical resistance, high strength, high hardness, good wear resistance, low friction coefficient, and high-temperature resistance, so it is an ideal material for manufacturing sealing rings. When paired with a graphite material, its friction coefficient is smaller than that of alumina ceramics and cemented carbide, so it can be used for high PV values, especially in the working conditions of transporting strong acids alkalis. The SIC-1 silicon carbide atmospheric sintered products produced by our company have the characteristics of high density, high hardness, large production batches, and the ability to make products with complex shapes. They are suitable for high-performance seals, exceptionally high PV values and Resistant to strong acids and alkalis. The SIC-3 silicon carbide ceramic works produced by our company are graphite-containing silicon carbide materials. Since the silicon carbide matrix contains many dispersed fine graphite particles when paired with other materials, its friction coefficient is minimal. It has good self-lubricating properties, which is especially suitable for making air-tight dry-friction seals. It is used in the medium so that the seal's service life and the work's reliability are improved.
The furnace charge after high-temperature calcination is unreacted material (for heat preservation in the furnace), silicon carbide oxycarbide (semi-reactive material, the main components are C and SiO.), the binder layer (for bonding Very tight material layer, the main element is C, SiO2, 40% to 60% SiC and Fe, Al, Ca, Mg carbonate), amorphous material layer (the main component is 70% to 90% SiC, and it is Cubic SiC is β-sic, and the rest are C, SiO2 and carbonates of Fe, Al, Ca, and Mg), second grade SiC layer (the main component is 90%-95% SiC, the coating has formed hexagonal SiC, namely the mouth One SiC, but the crystal is small and fragile, and cannot be used as an abrasive), the first-class SiC layer (SiC content <96%, and it is hexagonal SiC that is a coarse crystal of SiC), furnace core graphite. Among the layers as mentioned above, the unreacted material and a part of the oxycarbide layer material are usually collected as spent material, and the other part of the oxycarbide layer material is collected together with the amorphous material, the second-grade product, and part of the bonded material as recycled material. Charges and some bonds with tight bonding, large lumps and many impurities are discarded. The first-grade product is classified, coarsely crushed, finely crushed, chemically treated, dried and sieved, and magnetically separated into black or green SiC particles of various sizes. To make silicon carbide powder, it must go through a water selection process; to make silicon carbide products, it must go through forming and sintering.
TRUNNANO (Luoyang Trunnano Tech Co., Ltd ) is a professional Silicon carbide manufacturer with over 12 years of experience in chemical product research and development. If you are looking for high-quality Titanium dioxide, please feel free to contact us and send an inquiry.
