Silicon carbide is a non-metallic carbide formed by the covalent bond of silicon and carbon, and its hardness is second only to diamond and boron carbide. The chemical formula is SiC. Colorless crystals that appear bluish-black when oxidized or containing impurities. Silicon carbide variants with diamond structure are often called silicon carbide, silicon carbide hardness close to diamond, good thermal stability. At 2127℃, silicon carbide is converted from β-silicon carbide to α-silicon carbide, and α-silicon carbide remains stable at 2400℃. Hydrofluoric acid aqueous solution and concentrated sulfuric acid are stable, and hydrofluoric acid and nitric acid mixed acid or phosphoric acid are unstable. Difference of molten alkali in empty atmosphere. It is divided into synthetic silicon carbide and natural silicon carbide. Natural silicon carbide, known as carbonite, is mainly found in kimberlite and volcanic hornblende, but its amount is very small and has no excavation value.

Pre-discovery history

Silicon carbide is a kind of carbide that was occasionally discovered by the American engineer E.G.Acheson in 1891 while electromelting diamonds. At that time, it was mistaken for a compound of corundum and named emery. In 1893, Acheson developed an industrial method for manufacturing silicon carbide, a resistance furnace with carbon data as the core, and a patent method for generating silicon carbide by energized heating a mixture of SiO2 and carbon (US Patent No. 492,767).
Classification and grading
According to color, use and structure, silicon carbide can be divided into different categories.
Pure silicon carbide is a colorless crystal. Industrial silicon carbide is colorless, light yellow, light green, dark green or light blue, dark blue and even black. Abrasive industry according to the color of silicon carbide is divided into black silicon carbide and green silicon carbide two categories, which colorless until dark green are classified into green silicon carbide; Light blue to black is classified as black silicon carbide. The reason for the multicolor of silicon carbide is related to the existence of various impurities. Industrial silicon carbide generally contains about 2% of various impurities, mainly silica, silicon, iron, aluminum, calcium, magnesium, carbon and so on. When there is more carbon in the crystal, the crystal is black. Green silicon carbide is more brittle, black silicon carbide is tougher, the former grinding ability is slightly higher than the latter. According to the size of the grain, the product is divided into different grades. China's abrasive professional rules, black silicon carbide has 17 grades; Green silicon carbide is available in 21 particle size grades. Abrasives No. 80 and above are called abrasive particles, and abrasives No. 100 to 280 are called grinding powders.
According to different uses: silicon carbide is divided into abrasive, refractory materials, deoxidizer, electrical silicon carbide and so on. The SiC content of abrasive silicon carbide should be above 98%. Fire-resistant silicon carbide is divided into (1) high-grade fire-resistant black silicon carbide, the SiC content is completely the same as abrasive silicon carbide; (2) secondary refractory black silicon carbide, SiC content is greater than 90%; (3) Low grade refractory black silicon carbide, SiC content is greater than 83%. Silicon carbide for deoxidizer, SiC content is generally required to be greater than 90%. However, the heat preservation of carbon industrial graphitization furnace guessing that the silicon carbide content is greater than 45% after treatment can also be used as steelmaking deoxidizer. The silicon carbide used for deoxidizing agent has two kinds of powder and formed block. Powdered deoxidizer black silicon carbide generally has two particle sizes of 4 ~ 0.5mm and 0.5 ~ 0.1mm. There are two primary categories of silicon carbide for electrical purposes: (1) Green silicon carbide for electric heating elements, which is essentially the same as green silicon carbide for abrasives. (2) lightning arrester with silicon carbide, its electrical function requirements are special, different from abrasive refractory materials with black silicon carbide.
The use of silicon carbide
Silicon carbide products have high temperature resistance, wear resistance, heat shock resistance, chemical corrosion resistance, radiation resistance and outstanding electrical conductivity, thermal conductivity and other special functions, so in the national economy has a wide range of uses. In China, green silicon carbide is mainly used as abrasive. Black silicon carbide is used to manufacture abrasives, which are mostly used to cut and grind materials with low tensile strength, such as glass, ceramics, stone and refractory, etc., and are also used for the grinding of cast iron parts and non-ferrous metal materials. Abrasive tools made of green silicon carbide are mostly used for the grinding of cemented carbide, titanium alloy, optical glass, and also for the honing of cylinder liner and the fine grinding of high-speed steel tools. Cubic silicon carbide grinding tools are specially used for ultra-fine grinding of micro bearings. The wear resistance of the turbine impeller can be greatly improved by applying the silicon carbide powder on the impeller by electroplating. The cubic SiC200 grinding powder and W28 micro-powder are pressed into the cylinder wall of the internal combustion engine by mechanical pressure, which can extend the life of the cylinder body more than twice.
In the electrical industry, silicon carbide can be used as a arrester valve body, silicon carbon electric heating elements, far infrared generator and so on. In the electronics industry, such as in the industrial silicon carbide furnace or in the industrial furnace with special methods to cultivate a large piece of intact silicon carbide single crystal, can be used as a light emitting diode (such as crystal lamp, digital tube lamp) substrate; High purity silicon carbide crystal is a high quality material for manufacturing radiation resistant high temperature semiconductor. Silicon carbide is one of the few semiconductor materials with a large bandgap (2.86eV) and two conductive types, P and n.
In the aerospace industry, gas filters and combustion chamber nozzles made of silicon carbide have been used in rocket technology. Now completed industrial production of silicon carbide fiber, is a new type of high strength, high modulus data, with excellent heat resistance and oxidation resistance, and metal, resin has outstanding compatibility. The use temperature can reach 1200℃, and the strength persistence rate can reach more than 80% at high temperature. It can be used to make heat shielding materials, high temperature conveyor belts, filter high temperature gas or molten metal filter cloth, and can also be combined with carbon fiber or glass fiber to strengthen metal and ceramic reinforcement materials.
Low grade silicon carbide can be used as steel deoxidizer and cast iron additive.
In the carbon industry, silicon carbide is mainly used to produce iron blast furnace bricks, such as graphite silicon carbide, silicon nitride combined with silicon carbide bricks.
In the production of graphite electrodes, silicon carbide is also used as a coating refractory sinter for oxidation resistant coating electrodes to add the ability of the coating to withstand rapid temperature changes.
In the manufacture of special carbon materials - biochar, propane and trichloromethyl silane are often used as gas materials, and after high temperature pyrolysis reaction, silicon-containing pyrolytic carbon coating is formed on the graphite matrix to add hardness, strength and wear resistance of the product. The silicon carbide in the coating exists in the form of β-SiC with a grain size of about 1μm. The biochar products produced by this method, such as artificial heart valves containing silicon pyrolytic carbon, have good biocompatibility.
Silicon carbide is mainly reflected in which major areas?
For use in the semiconductor field
Because of its microscopic tracing and crystal structure, silicon carbide one-dimensional nano data has more unique excellent functions and more extensive use prospects, and it is generally believed that it is expected to become an important component of the third generation of wide-band gap semiconductor data.
The third generation of semiconductor information is wide band gap semiconductor information, also known as high temperature semiconductor information, mainly including silicon carbide, gallium nitride, aluminum nitride, zinc oxide, diamond and so on. This kind of data has the characteristics of wide band gap (band gap width greater than 2.2ev), high thermal conductivity, high breakdown electric field, high radiation resistance, high electron saturation rate, etc., suitable for high temperature, high frequency, radiation resistance and high power device manufacturing. The third generation of semiconductor data with its excellent characteristics, the future use of the prospect is very broad.
Use in the photovoltaic category
Photovoltaic inverter is very important for photovoltaic power generation effect, not only with direct communication replacement function, but also with the function of maximizing the function of solar cells and system failure maintenance function. Summed up, there are active operation and shutdown function, maximum power tracking control function, anti-independent operation function (grid-connected system), active voltage adjustment function (grid-connected system), DC detection function (grid-connected system), DC ground detection function (grid-connected system).
The use of new skills and new devices by domestic inverter manufacturers is still too little, and the inverter with silicon carbide as a power device is used in large quantities, and the internal resistance of silicon carbide is very small, the power can be made very high, the switching frequency can reach 10K, and the LC filter and bus capacitor can also be saved. Silicon carbide data may be broken on the use of photovoltaic inverters.
Reaction conditions of gaseous chemical treatment
1, water vapor.CO2 is only active at the dissociation temperature of Sio2 1755-1800℃
2, C12 heating surface is corroded at 600℃
3, boiling HC1.HF boiling does not work
4, boiling H2SO4.HNO3 cooking does not work
5, KC103.KN03 fusion does not work
6, Na203 weld
7, the air is heated between 1000℃-1350℃ slightly oxidized
8. The air heats the surface between 1350℃ and 1500℃ to form a Sio2 layer of fusion insulation
9, the air is heated between 1500℃ and 1600℃ because the oxidation of the insulation layer Sio2 is stopped
10. The air is heated and oxidized rapidly above 1750 ° C Salvage NaoH900℃ corrosion isolation
Silicon carbide can be used as grinding materials, fire-resistant materials, resistance heating elements and deoxidizers. In the refractory industry, silicon carbide is used to produce a variety of silicon carbide bricks, and can also be used as an additive or antioxidant.
The use of silicon carbide in the aviation field
Silicon carbide is manufactured into silicon carbide fiber, silicon carbide fiber is mainly used as high temperature data and enhancement data, high temperature data including heat shielding data, high temperature conveyor belt, filter high temperature gas or molten metal filter cloth. When used as reinforcement materials, it is often used with carbon fiber or glass fiber, mainly reinforced metals (such as aluminum) and ceramics, such as brake pads, engine blades, landing gear boxes and fuselage structural information, etc., can also be used as sporting goods, and its short fiber can be used as high temperature furnace materials.
There is already a lot of supply of coarse silicon carbide, but the use of nanoscale silicon carbide powder with a very high skill content cannot constitute economies of scale in a short time. The development of silicon carbide chips in China is still in the initial stage, the use of silicon carbide chips in the country is less, and the development of silicon carbide data industry lacks the support of downstream enterprises. Close cooperation on personnel training and skill development; Strengthen the communication between enterprises, especially actively participate in international communication activities to improve the level of enterprise development; Attach importance to the construction of enterprise brand, and strive to build the fist products of enterprises.