① Black silicon carbide contains about 95% SiC and has higher toughness than green silicon carbide. It is mostly used to process ceramics, refractory materials and non-ferrous metals.
② Green silicon carbide contains more than about 97% SiC and has good self-sharpening properties. It is mostly used to process cemented carbide and optical glass as well as fine grinding of high-speed steel tools.
Characteristics of silicon carbide
Hardness
Silicon carbide has high hardness and is generally hard and brittle. It can be used as a grinding material. Silicon carbide particles used as abrasives break during grinding to form new broken surfaces, which are then ground again. This process is repeated to achieve higher grinding efficiency. Its disadvantage is that it is difficult to process ceramics after sintering. Because it is brittle, it is easily damaged when used as a product.
Heat resistance
Silicon carbide has a high melting point and good heat resistance.
Thermal conductivity
Generally speaking, the thermal conductivity of silicon carbide depends on the content of impurities in the silicon carbide crystal particles. The less impurities, the higher the thermal conductivity.
Rigidity (elastic modulus)
The elastic modulus of silicon carbide ceramics is very high, exceeding 400GPa, second only to boron carbide (B4C), and twice that of stainless steel (about 200GPa).
Conductivity
Silicon carbide powder produced by the Acheson process contains solid solution nitrogen, so it is semiconductive and has a wide range of volume resistivity.
Uses of silicon carbide
Refractory materials
In terms of refractory applications, the majority are used for crude steel production. It is estimated that about 80% of silicon carbide powder used in refractory materials is used for crude steel production. As refractory bricks, Al2O3-SiC-C bricks are used in mixing iron cars in crude steel production, and silicon carbide bricks are used in blast furnace walls. In addition to crude steel production, silicon carbide bricks are also used in incinerators.
Deoxidation and carbon addition materials (ironmaking, casting, etc.)
They are generally used for the purpose of adding carbon, adding silicon, heating, and deoxidation in the ironmaking and casting industries. When used as a silicon source, it competes with ferrosilicon, but when using silicon carbide, it has the following advantages: good physical properties (improved tensile strength and machinability, etc.); less impurities (Al, S, N); in the case of 90% silicon carbide, the silicon content is 63%, and the C content is about 27%, which has a carbon addition effect (the pass rate varies depending on the production method, and theoretically, silicon carbide can supplement 1/3 of the carbon addition material). When used as a carbon source, it competes with carbon addition materials (fixed carbon of more than 90%). The use of silicon carbide can be expected to reduce costs.
Grinding materials (granular abrasives, solid grinding stones)
Silicon carbide is divided into black silicon carbide and green silicon carbide, and is used as a raw material for granular abrasives and solid grinding stones.
Ceramics (machine parts)
In addition to having high heat resistance and corrosion resistance, silicon carbide also has high specific rigidity. As a substitute for metals (stainless steel, etc.), it can also be used in parts of semiconductor production equipment. Taking advantage of its low thermal expansion and high rigidity, it is used as a material for ultra-precision positioning devices. Silicon carbide has good sliding properties and can be used as a sealing material (mechanical seal) in a hot and corrosive environment.
Filter
It can be used as a filter material to remove diesel exhaust particulate matter. Since the captured particulate matter needs to be burned and cleaned regularly, the temperature is very high, so heat resistance is required, so silicon carbide is used.
Filler (exothermic, wear-resistant, etc.)
It uses the characteristics of high thermal conductivity and is used in exothermic materials. Specific uses include adding silicon carbide to metals and resins to make composite materials and adding silicon carbide to improve the wear resistance of paint surfaces.
