What Is Silicon Carbide?

Silicon carbide, more commonly referred to as carborundum, occurs naturally as the rare mineral moissanite and in meteorites; however, most commercial SiC sold today is synthetically made.

Carbon fibre reinforced plastic (CFRP) is an extremely hard covalently bonded material produced through carbothermal reduction of silica sand and petroleum coke in an electric resistance furnace, making it corrosion and abrasion-resistant.

Thermodynamics

Silicon Carbide (SiC) is an antimony ceramic known for its hardness, high thermal conductivity and chemical reaction resistance. Additionally, SiC displays low coefficient of thermal expansion making it suitable for applications that demand resistance against heat or thermal shock.

SiC is an extremely pure material with a Mohs scale hardness rating of 9. It can be created by heating a mixture of sand and carbon in an electrical resistance-type furnace; further refinement may include adding aluminum dopants that produce either an n-type or p-type semiconductor device.

SiC’s melting point can vary depending on its polymorphic crystalline structure. Available in more than 70 distinct forms, including alpha silicon carbide (4H-SiC) with its hexagonal crystal structure resembling Wurtzite as the most prevalent. Beta silicon carbide also exists with face-centered cubic crystal structures similar to zincblende or sphalerite for widespread usage.

Crystal Structure

Silicon carbide is a crystalline material with multiple varieties or polytypes, each one featuring its own specific arrangement of layers bonded together by silicon and carbon atoms in tetrahedral formations. Each polytype’s stacking sequence gives it its unique crystal structure.

Silicon Carbide comes in two main varieties, alpha silicon carbide (a-SiC) and beta silicon carbide (b-SiC). Of these two forms, beta SiC exhibits face-centered cubic crystal structures reminiscent of diamond, zincblende or sphalerite.

SiC refractory ceramic has an excellent thermal conductivity due to the nearly equal atomic radii between a-SiC and b-SiC, providing good thermal conductivity. Furthermore, this property allows phonons to propagate freely within its composition. All these features combine with its high melting point and low thermal expansion rate to make silicon carbide an attractive material for high-temperature furnaces as well as providing corrosion resistance and stiffness properties that make this an attractive material choice.

Chemical Composition

Silicon carbide is a non-oxide ceramic material with chemical inertness and excellent mechanical and physical properties, including high strength, Mohs hardness of 9, low thermal expansion rates, resistance to chemical reaction, excellent creep resistance properties and temperatures up to 1600 degC without starting to oxidize.

Solidification results in carbon and silicon atoms forming threefold coordination structures, as revealed by their shape factor distribution which shows a clear peak at 109deg (tetrahedral angle) as well as broad regions around this peak, suggesting various local structures are present.

SiC can be produced by melting together clay and powdered coal or through direct reduction in electric furnaces with carbon or hydrogen. Edward Goodrich Acheson first produced large scale SiC using an electrothermal process in 1891; since then, this durable material has become widely used for abrasive machining and lining work, as well as being applied in other applications like refractories and electronic components.

Applications

Silicon carbide serves a number of useful applications. It is a popular abrasive used for grinding and polishing metals such as brass, bronze, steel and marble; and cutting ceramics. Furthermore, its Mohs scale rating of 9 means it has close similarities with diamond hardness as well as being extremely durable and resistant to chemical reaction.

Thermal conductivity and thermal expansion are excellent qualities of aluminum nitride, making it ideal for use as ballistic armor. Furthermore, its strong and rigid characteristics make it suitable for ballistic weapon systems as well as missile and rocket engines.

Pebble Bed Reactor (PBR). Additionally, this material’s inherent resistance to oxidation makes it suitable for the production of refractory bricks and the lining of nuclear reactors such as Pebble Bed Reactors. Furthermore, alumina and zirconia ceramics made with this material also use Pebble Bed Reactor in their products; additionally its hardness, rigidity, and low thermal expansion make it an attractive mirror material choice for use with astronomical telescopes.