What is silicon carbide?

Basics of silicon carbide particles

Silicon carbide is a kind of nonmetallic carbide with covalent bond between silicon and carbon, whose hardness is second only to diamond and boron carbide.  Chemical formula is SiC.  Colorless crystal, bluish-black when oxidized or containing impurities.  Silicon carbide variants with diamond structure are commonly known as emery.  Emery hardness is close to diamond, good thermal stability, 2127℃ by β- silicon carbide into α- silicon carbide, α- silicon carbide is still stable at 2400℃.  Hydrofluoric acid solution and concentrated sulfuric acid stable, concentrated hydrofluoric acid and nitric acid mixed acid or phosphoric acid is not stable.  Differentiated by a molten base in an empty atmosphere.  It is divided into synthetic silicon carbide and natural silicon carbide.  Natural silicon carbide known as carbon silica, mainly occurs in kimberlite and volcanic hornblende, but its amount is very little, no mining value.

Industrial silicon carbide for artificial silicon carbide, SiC content of 95% ~ 99.5%, often contain a small amount of free carbon, as well as Fe2O3, Si and SiO2 impurities.  Silicon carbide can be divided into hexagonal crystal system (α -sic) and cubic crystal system (β -sic) according to the crystallization type, hexagonal crystal system and because of the periodic different crystal arrangement of hexagonal cell crystal type (2H, 4H, 6H......  And rhomboid crystal cell (15R, 21R, 27R......etc.), silicon carbide has more than 100 homogeneous polycrystalline structures.  Industrial silicon carbide is a mixture of α -sic and β -sic, with black and green colors.  Pure silicon carbide is colorless and bright, black, green, blue and yellow when containing impurities.  Hexagonal and cubic crystal system, crystal plate, complex cubic columnar.  With glassy luster, density 3.17 ~ 3.47g/cm3, mohs hardness 9.2, microhardness 30380 ~ 33320MPa;  Melting point: differentiation begins at 2050℃ in atmosphere and 2600℃ in recovery atmosphere;  Elastic modulus is 466, 480MPa;  The tensile strength is 171.5mpa;  The compressive strength is 1029MPa;  Linear expansion coefficient is 5.0×10-6/℃ from 25 ℃ to 1000℃.  Thermal conductivity (20℃) is 59W/(m·K).  It has stable chemical properties and is not corroded even when boiled in HCl, H2SO4 and HF, but begins to differentiate at 230℃ in concentrated H3PO4.

According to different uses: silicon carbide is divided into abrasives, refractory materials, deoxidizer, electrical silicon carbide and so on.  The SiC content of abrasive silicon carbide should be above 98%.  

Refractory materials are divided into silicon carbide  

(1) high-grade refractory material black silicon carbide, its SiC content and abrasive silicon carbide completely the same;  

(2) secondary refractory material black silicon carbide, SiC content is greater than 90%;  

(3) low-grade refractory material black silicon carbide, SiC content is greater than 83%.  Deoxidizer with silicon carbide, SiC content is generally required to be greater than 90%.  But carbon industrial graphitization furnace insulation guess silicon carbide content more than 45% after treatment can also be used as steel deoxidizer.  

Deoxidizer with silicon carbide powder and shaped block two kinds.  Powdered deoxidizer black silicon carbide generally has 4 ~ 0.5mm and 0.5 ~ 0.1mm two particle sizes.  

There are two primary categories of silicon carbide for electrical use:  

(1) Electric heating element with green silicon carbide, its essence and abrasive with green silicon carbide completely the same.  

(2) Lightning arrester with silicon carbide, its electrical function requirements are special, different from abrasives with refractory materials with black silicon carbide.

The application of silicon carbide nanoparticles  

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 it has a wide range of uses in various departments of the national economy.  In China, green silicon carbide is mainly used as abrasive.  Black silicon carbide is used for manufacturing abrasives, mostly used for cutting and grinding materials with low tensile strength, such as glass, ceramics, stone and refractories, etc., and also used for grinding of cast iron parts and non-ferrous metal materials.  The grinding tools made of green silicon carbide are mainly used for grinding hard alloy, titanium alloy, optical glass, and also for honing cylinder liner and fine grinding of HSS tool.  The cubic silicon carbide grinding tool is specially used for ultra-fine grinding of miniature bearings.  The wear resistance of water turbine impeller can be greatly improved by coating silicon carbide powder on it by electroplating.  With mechanical pressure will be cubic SiC200 grinding powder and W28 micro powder pressed into the cylinder wall of the internal combustion engine, can prolong the cylinder life more than one times.