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        Introduction to silicon carbide

        Publisher: Administrator 2019/1/5 9:02:33

        Silicon carbide is also called carborundum or refractory sand. Silicon carbide is made from quartz sand, petroleum coke (or coal coke), wood chips (salt is needed to produce green silicon carbide) and other raw materials in the resistance furnace by high temperature smelting. At present, China's industrial production of silicon carbide is divided into black silicon carbide and green silicon carbide, both hexagonal crystal, specific gravity of 3.20 ~ 3.25, microhardness of 2840 ~ 3320kg/mm2.

        Including black carborundum and green carborundum, in which: black carborundum is quartz sand, petroleum coke and high-quality silica as the main raw materials, through resistance furnace high temperature smelting. Its hardness between corundum and diamond, mechanical strength than corundum, brittle and sharp. Green carborundum is made of petroleum coke and high quality silica as the main raw material, salt as the additive, through resistance furnace high temperature smelting. Its hardness is between corundum and diamond, and its mechanical strength is higher than that of corundum.

        Silicon carbide (SiC) is an important abrasive due to its high hardness, but its application range exceeds that of ordinary abrasive. For example, due to its high temperature resistance and thermal conductivity, it has become one of the preferred materials for tunnel kilns or shuttle kilns, and its electrical conductivity makes it an important electrical heating element. To prepare SiC products, it is necessary to prepare SiC smelting blocks [or SiC particles, which were once called emery due to their C and superhard properties. Garnet) of different ingredients. In industrial production, the SiC smelting block normally with quartz and petroleum coke as raw materials, such as auxiliary recovery, lack of material, after grinding process such as mixing ratio become reasonable and the burden of appropriate size (to adjust the burden permeability need to join the right amount of sawdust, add salt even when preparation of green silicon carbide) high-temperature preparation. Preparation of SiC smelting piece of high temperature thermal technology equipment is a special silicon carbide furnace, its structure of furnace bottom, inside with electrode end wall, removable side wall, furnace body (all referred to as: The electrified heating element in the center of the electric furnace is generally installed in the charging center with graphite powder or petroleum coke in a certain shape and size, generally round or rectangular, and its two ends are connected with electrodes, etc. The firing method used in the electric furnace is commonly known as: Buried powder burning. It is a power for heating, namely furnace core body temperature is about 2500 ℃, even higher (2600 ~ 2700 ℃), furnace charge reaches 1450 ℃ start synthesis SiC (but SiC mainly formed at 1800 ℃ or higher), and release co. However, SiC will decompose when 2600 ℃ or higher, but the decomposition of si and the burden of the generated C SiC. Each group of electric furnace is equipped with a set of transformer, but only when the production of a single electric power supply, so as to adjust the voltage according to electric load characteristic to basically maintain constant power, high power electric furnace to the heating about 24 h, After power failure, the reaction to generate SiC is basically completed. After a period of cooling, the side wall can be removed, and then the furnace charge can be gradually removed.

        In the process of high temperature calcining, the charging materials from the outside to the inside were: unreacted charging materials (playing a role of insulation in the furnace), oxygen sic bumbo (semi-reactive charging materials, mainly composed of C and SiO). , dung layer (is binding tight material layer, the main ingredient is 40% ~ 60% C, SiO2, SiC and Fe, Al, Ca, Mg carbonate) and amorphous layer (main component is 70% ~ 90% SiC, moreover is cubic SiC beta SiC, the rest is C, SiO2 and Fe, A1, Ca, Mg carbonate), second SiC layer (main component is 90% ~ 95% SiC, the layer has generated the six-party SiC or mouth a SiC, but smaller crystals, very fragile, cannot serve as abrasive), first class SiC layer (SiC content < 96%, And it is hexagonal SiC (i.e., one SiC thick crystal), furnace core graphite. In the above layers, the unreacted materials and part of the oxygen carborundum layer materials are usually collected as waste materials, and another part of the oxygen carborundum layer materials are collected together with amorphous materials, second grade products and part of the binder as the return furnace charge, while some of the adhesives with tight bond, high lumpiness and many impurities are discarded. The first grade becomes black or green SiC particles of various sizes after classification, coarse crushing, fine crushing, chemical treatment, drying and screening, magnetic separation. In order to make silicon carbide powder, it has to go through the process of water separation. To make silicon carbide products also go through the process of molding and sintering.

        Silicon carbide has four main application areas, namely: functional ceramics, advanced refractory materials, abrasive and metallurgical raw materials. Silicon carbide raw materials can be supplied in large quantities, so it is not a high-tech product. However, the application of nanometer silicon carbide powder with extremely high technical content is unlikely to form economies of scale in a short time.

        ? as an abrasive, can be used to do grinding tools, such as grinding wheel, whetstone, grinding head, sand tile, etc.

        The paper is used as metallurgical deoxidizer and high temperature resistant material.

        High purity single crystal can be used to manufacture semiconductor and silicon carbide fiber.

        Main applications: 3-12 "single crystal silicon, polycrystalline silicon, potassium arsenide, quartz crystal, etc. Solar photovoltaic industry, semiconductor industry, piezoelectric crystal industry engineering processing materials. Used in semiconductor, lightning rod, circuit element, high temperature application, ultraviolet light detector, structural material, astronomy, disc brake, clutch, diesel particle filter, filament pyrometer, ceramic film, cutting tool, heating element, nuclear fuel, jewelry, steel, protective tools, catalyst carrier and other fields.

        Silicon carbide products can be divided into many categories, according to the different use environment, divided into different categories. Generally speaking, it is often used in machinery. For example, the use of mechanical seals, can be called silicon carbide seal ring, can be divided into static ring, moving ring, flat ring. We can also produce various kinds of silicon carbide products according to the special requirements of customers, such as silicon carbide shaped parts, silicon carbide plates, silicon carbide rings and so on. Silicon carbide ceramics are widely used for their high hardness, high corrosion resistance and high temperature strength. In the application in the sealing ring: silicon carbide ceramics chemical corrosion resistance, high strength, high hardness, good wear resistance, small coefficient of friction, and high temperature, so it is the ideal material for the manufacture of sealing ring. When it is combined with graphite materials, its friction coefficient is smaller than alumina ceramics and cemented carbide, so it can be used for high PV value, especially in the transport of strong acid, strong alkali conditions. The SIC-1 SIC sintered products manufactured by our company are characterized by high density, high hardness, large batch production and complex shape. The SIC-3 SIC ceramic products manufactured by our company are SIC materials containing graphite. Due to the silicon carbide substrate containing large amounts of dispersed small graphite particles, when paired with other materials used, its friction coefficient is very small, has a good self-lubricating performance, especially suitable for making gas seal or seals used in the dry friction condition, which makes the service life of seals and working reliability.

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