Raw silicon carbide (commonly referred to as black SiC) is an extraordinarily hard synthetic crystalline material used in grinding wheels, sandpaper and cutting tools since the late 19th century. Thanks to its rigidity, low thermal expansion rate and resistance to chemical attack it’s also widely employed as a refractory material in industrial furnaces as well as wear resistant parts like pump seals thread guides and acid spray nozzles.
Chemical composition
Silicon carbide is a synthetic material with unparalleled hardness – second only to diamond and some synthetic materials -, high wear resistance, chemical inertness, electrical conductivity at elevated temperatures and shock-resistance properties. Silicon carbide can also be doped with nitrogen, phosphorus and beryllium for n-type semiconductor formation while doping with boron, aluminum gallium and tin can form p-type semiconductors.
Produced by heating silica sand with carbon (typically petroleum coke) at high temperatures in an open “Acheson” furnace, silica gel is produced. As a result, green and black-colored crystal grains form depending on the purity of raw materials used for its creation.
These grains are ground and screened into various sizes that meet their intended applications, with low porosity for improved physical properties of the material.
Black and green silicon carbides, both belonging to the a-SiC group, are the two most widely utilized basic varieties of silicon carbide. Black silicon carbide is typically used for processing materials with low tensile strength such as glass, ceramics, stone, refractory material and cast iron while green silicon carbide is often employed in cutting or grinding abrasive materials such as stone. Both varieties boast high toughness while black silicon carbide has higher hardness compared with its counterpart.
Physical properties
Silicon carbide, an extremely hard and synthetically produced crystalline compound of silicon and carbon, is used in many different industries such as abrasives, refractories and wear-resistant components in mechanical applications. As an electrical semiconductor material it can also be doped with nitrogen, phosphorus and beryllium dopants to form either an n-type semiconductor or aluminum, boron and gallium dopings to form a p-type semiconductor.
Raw material used for SiC production consists of a mixture of coal (usually petroleum coke) and silica sand that is chemically reacted at high temperatures in an electric resistance furnace, to form crude silicon carbide. Once formed, this rough silicon carbide must then be crushed and milled to achieve desired grain sizes before reacting with different amounts of boron for more complex forms of boron carbides such as B3N6.
Reactivity can be controlled through factors like reactant concentration, temperature, feeding time and furnace holding time; the result being products with variable properties depending on polycrystalline type, formation method and purity levels.
Silicon carbide boasts excellent physical properties; its brittleness is low, which lends it great strength at high temperatures. Furthermore, it is chemically inert and boasts excellent erosion and wear resistance as well as high thermal conductivity and low expansion coefficient making it an excellent material choice for refractory linings.
Mechanical properties
Silicon Carbide is one of the hardest materials on earth, boasting a Mohs hardness rating of 9. It’s extremely durable and corrosion-resistant, as well as being thermal shock resistant, maintaining strength under high temperatures, making it perfect for industrial applications. These properties make silicon carbide suitable for use in many different ways.
Production of black or green silicon carbide involves heating a mixture of pure silica sand and carbon in the form of ground coke in an electrical resistance-type furnace, where an electric current passing through its conductor causes chemical reactions which produce silicon dioxide gas and carbon monoxide, creating black or green silicon carbide that can later be processed further to meet specific mechanical requirements for specific uses.
In general, RBSC prepared with careful grading is dense with no pores. The fracture surface of RBSC exhibits smooth grain faces indicative of intergranular fracture, while specimens with 10 weight percent carbon show more transgranular fracture, which drains energy more rapidly from crack energy consumption and may result in poor mechanical properties.
Low c-Si content RBSC displays excellent mechanical properties. It boasts high tensile and flexural strengths, good toughness and a small elastic modulus; as well as good acid, alkali and compound resistance with exceptional wear resistance properties. Used widely in products such as grinding wheels, water sandpaper discs and brushes as well as cutting tools and wear parts used across metallurgical, mining, refractory and other industries.
Electrical properties
Silicon carbide (SiC) is an inorganic material composed of silicon and carbon with the chemical formula SiC. Produced commercially since the late 19th century for use in abrasives and refractories, silicon carbide has proven its worth as an extremely hard material second only to diamond in terms of hardness. Furthermore, this inert material offers excellent thermal properties and resists corrosion well.
Silicon carbide stands out due to its distinct crystal structure: comprising of tightly bound silicon and carbon atoms arranged into tetrahedral structures in a crucible lattice. Furthermore, this material is insolublious with water, alcohol and acids as well as having a low coefficient of expansion; making it perfect for components intended for harsh chemical environments.
Silicon carbide has many applications beyond its abrasive qualities. Not only is it durable, it has semiconductor properties as well. When doped, silicon carbide exhibits improved electrical conductivity and other characteristics that enhance its electrical conductivity and other features. Silicon carbide boasts wide bandgap semiconductor properties with strong breakdown electric field strength, fast electron drift speed, and small dielectric constant, making it an appealing material for future electronics applications.
Raw silicon carbide comes in both black and green varieties, depending on its source material composition. It is produced by heating a mixture of silica sand and coal in an electrical resistance furnace using an electric current passed through a carbon conductor. After cooling, the material can be ground into powder form, mixed with compounds such as tungsten carbide or boron carbide to make ceramic products such as industrial abrasives or refractory linings, wear-resistant parts for pumps and rocket engines or wear-resistant parts.
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