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Research on the properties and uses of silicon carbide

2019-05-10
What is silicon carbide?
Silicon carbide is a non-metallized carbide that is covalently bonded by silicon and carbon. The chemical formula is SiC, also known as silicon carbide. It is made of quartz sand, petroleum coke (or coal char), and wood chips (required when producing green silicon carbide). Raw materials such as salt are added and smelted by electric furnace at high temperature. The obtained silicon carbide block is made into various particle size products by crushing, acid-base washing, magnetic separation, screening or water selection. There are synthetic silicon carbide and natural silicon carbide. In modern C, N, B and other non-oxide high-tech refractory raw materials, silicon carbide is the most widely used and most economical, and can also be called gold steel sand or refractory sand. . Among them, industrial silicon carbide is synthetic silicon carbide, wherein the SiC content is 95% to 99.5%, often containing a small amount of free carbon, and impurities such as Fe2O3, Si and SiO2. At present, China's industrial production of silicon carbide is divided into black silicon carbide and green silicon carbide, both hexagonal crystals, specific gravity of 3.20 ~ 3.25, melting point of 2700 Celsius. The appearance of silicon carbide is yellow to green, to blue to black crystals, depending on its purity.
 
Black silicon carbide and green silicon carbide:
First of all, they are made of quartz sand, petroleum coke and wood chips as raw materials through high-temperature resistance furnace. The green silicon carbide should be made of industrial salt as an additive during smelting. The crystals that have been smelted are of high purity and hardness, and their hardness is between diamond and corundum, and the mechanical strength is higher than that of corundum.
 
Black silicon carbide contains about 98.5% SiC. Its toughness is higher than that of green silicon carbide. It is mainly used to treat low tensile strength materials such as glass, ceramics, stone, refractory materials, cast iron, non-ferrous metals, etc.
Green silicon carbide contains more than 99% SiC, and has good self-sharpness. It is mainly used for processing hard alloys, titanium alloys and optical glass. It is also used for honing cylinder liners and precision grinding high-speed steel cutting tools.
 
Silicon carbide properties:
Silicon carbide has stable chemical properties, high thermal conductivity, small thermal expansion coefficient, good wear resistance and high hardness. Mohs hardness is 9.5, which is second only to the world's hardest diamond. It is a kind of semiconductor and can resist oxidation at high temperature.
There are many kinds of crystalline forms of silicon carbide. Among them, the most common isomorphous substance is α-silicon carbide, which is formed at a high temperature higher than 2000 Celsius and has a hexagonal crystal structure (like wurtzite). Another type of β-silicon carbide, a cubic crystal structure, similar to diamonds, is produced below 2000 Celsius. Pure silicon carbide is colorless, while industrially produced brown to black is due to impurities containing iron. The rainbow-like luster on the crystal is due to the silica protective layer on its surface.

 
Silicon carbide uses:
Silicon carbide is mainly used in ceramics, refractories, abrasives and metallurgical materials. Crude material silicon carbide can be mass-produced, so it can not be called high-tech products, but the application of nano-scale silicon carbide powder with relatively high technical content is not possible for mass production in a short time.
 
1. Silicon carbide can be used as an abrasive, and can be used for various abrasive tools, such as grinding wheels, oilstones, grinding heads, sand tiles, and the like.
 
2. Silicon carbide is also used as a metallurgical deoxidizer and a high temperature resistant material.
 
3. High-purity single crystal silicon carbide is often used as a semiconductor to manufacture silicon carbide fibers.
 
Main use: Silicon carbide can cut 3-12 inches of monocrystalline silicon, polycrystalline silicon, potassium arsenide, quartz crystal and so on. It can also be used as an engineering processing material in the solar photovoltaic industry, the semiconductor industry, and the piezoelectric crystal industry.
 
Silicon carbide is widely used, and new and growing markets are waiting to be developed. New fields represented by wire cutting are leading the upgrading of the silicon carbide industry. With the improvement of the international and Chinese economic situation, the silicon carbide industry will also usher in Certain development opportunities need to be noted that the state's control over the environment will be more stringent.
 
The technology development of silicon carbide is accelerating, and alternative technologies are appearing in large numbers. The solar photovoltaic industry is still in a rapid growth period, and there are many technologies in fierce competition. Currently, crystalline silicon cells occupy a leading position in market share, but other technologies are also rapidly evolving. If the silicon crystal battery is regarded as the first generation battery technology, there will be two or three generations of battery technologies such as inorganic thin film batteries and thin film batteries. Battery technology will develop toward higher power generation efficiency, which is a trend.

Future silicon carbide is mainly used in semiconductors, lightning rods, circuit components, high temperature applications, ultraviolet light detectors, structural materials, astronomy, disc brakes, clutches, diesel particulate filters, filament pyrometers, ceramic films, cutting tools, Heating elements, nuclear fuel, jewelry, steel, protective gear, catalyst carriers and other fields.
 
With the improvement of recycling technology, the recovery liquid, recycled sand and new liquid, and new sand can be mixed and used in a ratio of 1:1, which greatly reduces the production cost of silicon wafers, and more and more cutting manufacturers have been working since 2009. Waste mortar recycling is becoming more and more acceptable, so this will make the silicon carbide industry face serious challenges.