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What is silicon carbide? The properties and uses of silicon carbide

Published on:2022-01-04 09:13:31Views:3870Smallinlarge

Silicon carbide (SiC) is made of quartz sand, petroleum coke (or coal coke), wood chips as raw materials by high temperature smelting in the resistance furnace. Silicon carbide is also foun...

Silicon carbide (SiC) is made of quartz sand, petroleum coke (or coal coke), wood chips as raw materials by high temperature smelting in the resistance furnace. Silicon carbide is also found in nature as a rare mineral, i.e. Moissanite. Silicon carbide is also known as carbon silicate. Among C, N, B and other non-oxide high-tech refractory materials used in contemporary era, silicon carbide is the most widely used and the most economic one. Also known as emery or refractory sand, silicon carbide is made of quartz sand, petroleum coke (or coal coke), wood chips (Salt to be added to produce green silicon carbide), and other raw materials in the resistance furnace by high temperature smelting. At present, the carbon carbide manufactured in China is classified into black silicon carbide and green silicon carbide, both of which are hexagonal crystal with the specific gravity of 3.20~3.25 and the micro-hardness of 2840~3320kg/mm2.


The silicon carbide includes black silicon carbide and green silicon carbide. Among them, the black silicon carbide is made of quartz sand, petroleum coke, and high quality silica as the main raw materials by high temperature smelting in the resistance furnace. With the hardness falling between corundum and diamond and the mechanical strength higher than corundum, it is crisp and sharp. The green silicon carbide is made of petroleum coke and high quality silica as the main raw materials with the salt at additive by high temperature smelting in the resistance furnace, with the hardness falling between corundum and diamond and the mechanical strength higher than corundum. There are two different crystals as the commonly used silicon carbide grinding material [1], one of which is green silicon carbide containing more than 97% SiC, and mainly used for grinding of hard alloyed tools; another of which is black silicon carbide with metallic luster, containing more than 95% SiC and with the strength higher than green silicon carbide and lower hardness, and mainly used for grinding of cast iron and non-metallic materials.


Properties of silicon carbide

With the molecular formula of SiC, the hardness falling between corundum and diamond, and the mechanical strength higher than corundum, the silicon carbide can be used as grinding material together with certain industrial materials. As the first artificial grinding material, industrial silicon carbide was developed in 1891. There is small amount of silicon carbide in meteorites and the Earth’s crust, but no mineral source available for mining has been found so far.


The pure silicon carbide is a colorless and transparent crystal. Due to different categories and contents of impurities contained, the industrial silicon carbide is light yellow, green, blue and even black, with the transparency varying with its purity. By crystal structure, the silicon carbide crystal is divided into hexagonal or rhombic α-SiC and cubic β-SiC (Known as cubic silicon carbide). Due to the different stacking sequence of carbon and silicon atoms in its crystal structure, there are many different variants of α-SiC, and more than 70 of which have been found. At the temperature of higher than 2100?C, β-SiC is transformed to α-SiC.


By the industrial manufacturing method for silicon carbide, high quality quartz sand and petroleum coke are refined in a resistance furnace. The refined silicon carbide block are subject to crushing, acid and alkali washing, magnetic separation, and screening or water separation and made into the products with various particle sizes. 


Silicon carbide is classified into two common basic categories including the black silicon carbide and the green silicon carbide, both of which are α-SiC. (1) With the content of SiC up to 98.5% and the toughness higher than the green silicon carbide, the black silicon carbide is mainly used for processing of the materials with lower tensile strength, such as glass, ceramics, stone, refractory materials, cast iron, and non-ferrous metals. (2) With the content of SiC higher than 99% and the good self-sharpening, the green silicon carbide is mainly used for processing of hard alloy, titanium alloy and optical glass, and also used for honing of cylinder liner and precision grinding of high speed steel tool. In addition, the cubic silicon carbide is a kind of yellowish green crystal made by a special process. The grinding tools made of the cubic silicon carbide are suitable for super-precision processing of bearings, and the surface roughness can be processed from Ra32 ~ 0.16 micron to Ra0.04 ~ 0.02 micron in one operation. 


Due to stable chemical properties, high thermal conductivity, small coefficient of thermal expansion, and good wear resistance, the silicon carbide may be used for other purposes than the grinding material. For example, the carbon carbide powder may be applied to the inner wall of the turbine impeller or cylinder body by special process, so as to improve its wear resistance and prolong the service life by 1~2 times; the high-grade refractory materials made of the carbon carbide are characterized by thermal shock resistance, small volume, light weight, high strength, and good energy saving effect. The low-grade silicon carbide (containing approximately 85% SiC) is an excellent deoxidizer and used to speed up steel making, control the chemical composition easily, and improve the quality of steel. In addition, the silicon carbide is also widely used in the production of the silicon carbon rod as an electric heating element.


With very high hardness and excellent thermal conductivity, the silicon carbide is a kind of semiconductor resistant to oxidation at high temperature. 


Purposes

(1) As a kind of grinding material, it is used to make grinding tools such as grinding wheel, oilstone, grinding head, grinding segment, etc.


(2) It is used as metallurgical deoxidizer and high temperature resistant material.


The silicon carbide is used in four major fields, including functional ceramics, high-grade refractory material, grinding material, and metallurgical raw material. At present, the raw silicon carbide can be supplied in large quantities, so it cannot be considered as a high-tech product, and the application of nanometer silicon carbide powder with very high technical content cannot form scale economy within a short period of time.


(3) As a kind of high purity mono-crystal, it can be used to manufacture semiconductors and silicon carbide fiber.


Main purposes: It is used for wire-electrode cutting of 3-12” monocrystalline silicon, polycrystalline silicon, potassium arsenide, and quartz crystal, and used as the engineering-based processing materials for solar photovoltaic industry, semiconductor industry, and piezoelectric crystal industry.


Grinding material and tool

It is mainly used for manufacturing of grinding wheel, abrasive paper, abrasive belt, oilstone, grinding head, grinding paste, as well as for grinding and polishing of monocrystalline silicon and polycrystalline silicon in photovoltaic products and piezoelectric crystal in electronic industry.


Chemical industry

It can be used as a deoxidizer for steelmaking and a modifier for cast iron structure, and it can be used as a raw material for manufacturing of silicon tetrachloride, which is the main raw material for the silicone resin industry. As a new kind of compound deoxidizer, the silicon carbide deoxidizer replaces the traditional solid silicon powder and carbon powder; compared with the original process, it has more stable physical and chemical performance and better deoxidization effect, so that it can shorten the time of deoxidization, save the energy, increase the efficiency of steel making, improve the quality of steel, reduce the consumption of raw and auxiliary materials, reduce environmental pollution, and improve working conditions. It is of great value to improve the comprehensive economic benefit of electric furnace.


Wear, fire and corrosion resistant materials

Due to the characteristics such as corrosion resistance, high temperature resistance, high strength, good thermal conductivity, and impact resistance, the silicon carbide can be used for all kinds of smelting furnace lining, high temperature furnace member, silicon carbide plate, lining board, strut member, saggar, and silicon carbide crucible on the one hand


On the other hand, it can be used for high-temperature indirect heating materials in non-ferrous metal smelting industry, such as vertical tank distillation furnace, distillation furnace tray, aluminum electrolytic cell, copper melting furnace lining, arc plate for zinc powder furnace, thermocouple protection tube; used for manufacturing of wear-resistant, corrosion-resistant, high temperature-resistant advanced silicon carbide ceramic materials; and can also be used for manufacturing of rocket nozzle, gas turbine blade, etc. In addition, the silicon carbide is also one of the ideal materials for expressway, space shuttle runway, and solar water heater.


Non-ferrous metals

Due to the characteristics such as high temperature resistance, high strength, good thermal conductivity, and impact resistance, the silicon carbide can be used for high-temperature indirect heating materials in non-ferrous metal smelting industry, such as vertical tank distillation furnace, distillation furnace tray, aluminum electrolytic cell, copper melting furnace lining, arc plate for zinc powder furnace, thermocouple protection tube, etc.



Steel and iron

Due the characteristics of corrosion resistance, thermal impact resistance, wear resistance, and good thermal conductivity, the silicon carbide can be used for large blast furnace lining, so as to improve its service life.


Metallurgy and mineral dressing

With the hardness only second to diamond and higher wear resistance, the silicon carbide is an ideal material for wear-resisting pipeline, impeller, pump chamber, cyclone, and ore bucket lining. Due to the wear resistance as much as 5-20 times of the service life of cast iron and rubber, it is also one of the ideal materials for aviation flight runway.


Building material ceramic grinding wheel industry

Based on its characteristics of high thermal conductivity coefficient, thermal radiation, and thermal strength, it can be used to manufacture the sheet kiln furniture, so as to not only reduce the capacity of kiln furniture, but also improve the kiln capacity and product quality, and shorten the production cycle, so it is an ideal indirect material for ceramic glaze baking and sintering.


Energy saving

Due to the good thermal conductivity and thermal stability, it is used for heat exchanger to reduce the fuel consumption by 20%, save the fuel by 35%, and improve the productivity by 20-30%; in particular, for the internal emission of the discharge and conveying pipeline for the mine concentrator, its wear-resistant degree is as much as 6-7 times the ordinary wear-resistant material.


(2) The particle size and composition of the grinding material shall be governed by the Standard GB/T2477-83. The determination method for the particle size and composition of the grinding material shall be governed by the Standard GB/T2481-83.


Jewelry

Also known as Moissanite or synthetic carbo silicate (Chemical composition SiC), the synthetic silicon carbide has the chromatic dispersion of 0.104 higher than that of diamond (0.044), the refractive index of 2.65-2.69 (2.42 for diamond), the adamantine luster same as that of diamond, and stronger “fire brilliance”, so it is more similar to diamond than any previous imitation. The synthetic silicon carbide is manufactured and produced by C3 Company in North Carolina, USA, which has obtained the patent for production of synthetic silicon carbide in various countries, which is being promoted and applied all over the world. 



Information Source: moliao.biz, www.abrasives.org.cn; not verified, for reference only.

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