Silicon carbide (SiC) is a hard, stiff ceramic that is highly heat-resistant. SiC is often found in use as wear-resistant parts due to its extreme hardness; used in metallurgical and refractories industries for its resistance against high temperatures; or used as electronic component due to its semi-conducting properties.
Elkem offers both reaction-bonded and sintered SiC products, suitable for a range of industrial applications.
Electrical Resistance Furnace
Silicon Carbide (SiC) is an inorganic solid compound comprised of silicon and carbon. As one of four commonly known forms of carbides (the others being salt like, metallic and diamond-like carbides), SiC finds wide industrial application due to its high melting point, excellent electrical conductivity and semiconductor behavior.
At large-scale production plants worldwide, silica sand is produced primarily for use as an abrasive and in ceramics; it also can serve as steel additive or fuel, and comes packaged either granular material in bulk bags or bulk. Silica sand can also be found used to produce metallurgical catalysts as an electric furnace lining material; additionally it’s often found as part of high temperature heating elements.
SiC is a gray to black crystalline material that can be formed into various forms and sizes. Its physical characteristics include very strong strength, high hardness and low ductility; good thermal conductivity; chemical inertness and the ability to withstand extreme temperatures make SiC an excellent material choice for use in refractory applications such as furniture’s, bricks and muffles – as well as grinding/cutting applications due to its hardness and excellent wear resistance.
Edward Acheson was responsible for producing SiC on a large-scale in 1890 while accidentally producing it while trying to dissolve carbon into molten clay and powdered coke. Noticing that its blue crystals closely resembled corundum, he named them carborundum.
Acheson introduced an electric batch furnace that is still widely used today to produce silica-carbon crude. Raw materials are mixed together and heated up to temperatures reaching as high as 2,500 degC before being refined into various grains and powders for Washington Mills production.
Pure silica is a poor electrical conductor, but can be doped with nitrogen to improve its electrical conductivity and make it suitable for some electronic device manufacturing processes and ceramic production processes. Though natural moissanite does exist, most of the SiC sold commercially today is manufactured.
Silicon carbide (SiC) is an extremely hard ceramic material, that when joined using sintering can form extremely hard products. SiC is highly wear resistant and chemically inert towards all alkalies and acids; furthermore it boasts very high melting points making it perfect for use as furnace bricks, burner nozzles and composite armour. Not unlike many ceramics it can even withstand very high temperatures without melting or decomposing into other substances; unlike most ceramics however SiC stands up well at temperature fluctuations without melting into decomposing forms like other ceramics cannot.
SiC is manufactured using raw materials that must be processed into grains and powders before being compacted into useful products, and this is accomplished using various forms of crushing, milling and classifying equipment. After processing has taken place, these grains or powders are mixed with non-oxide sintering aids commonly known as binders to form a pasty mixture before it is compacted either through extrusion or isostatic pressing using flexible molds that compress evenly in all directions and significantly decrease friction with die walls reducing friction with powder.
The end product from powder processing can be utilized for various uses depending on its exact composition. Finer grain products may be employed as abrasives in modern lapidary, often combined with aluminium oxide or sand to produce coarse-to-fine grit sandpaper; or added into electrical heating elements in the form of aluminosilicate glass and fibres for use as electrical heating elements; coating refractory products, or grinding wheels used in metalworking applications.
Silicon carbide produced worldwide is predominantly utilized as a steel additive. It can be mixed with iron ore to increase ladle temperature, and even used as an electric furnace slag deoxidizer. Silicon carbide is less expensive than ferrosilicon/carbon combinations; its temperature-lowering effects do not differ as significantly; and is widely available worldwide.
Chemical Vapor Deposition
SiC is known for its superior thermal conductivity and melting point compared to any element on Earth, making it an invaluable material for electric heating elements and hard ceramic bulletproof vests. Unfortunately, due to its hard and brittle composition, manufacturing silicon carbide parts is costly; however, precise tolerances can be reached using precision grinding and lapping techniques; once produced components must undergo stringent quality checks.
Silicon carbide is produced in its crude form by mixing silica (SiO2) with carbon (C) in an electric furnace, yielding grit that is size graded and sintered into various particle sizes for various applications. Coarse grit can also be bonded using silicon nitride oxide, nitrides or aluminosilicate glass as part of an additional bonding phase to increase strength of final products which is particularly crucial when used as electric heating elements.
Commercial-scale single crystals of silicon carbide are typically grown using the Lely technique, originally developed by Edward Goodrich Acheson in 1890. Crystal purity varies, with clear, pale yellow, green, blue and black crystals possessing higher purities; darker hues may contain doping agents like nitrogen to improve electrical conductivity or aluminium and iron for reduced conductivity – though for even purer results the more expensive chemical vapor deposition process should be considered.
Cold isostatic pressing is another means to create silicon carbide. Similar to its hot isostatic press counterpart, but conducted at room temperature using flexible molds immersed in liquid medium for compaction, this method enables manufacturers to produce blocks and plates of various shapes.
Moistsanite was named by Ferdinand Henri Moissan after finding it in Arizona’s Canyon Diablo meteorite in 1905, though its production requires several processes – with dissolving silica in liquid silicon being most common, while other methods include using mixtures of calcined carbon and melted calcium carbide as raw materials.
Physical Vapor Deposition
Silicon carbide’s inherent hardness and thermal conductivity enable it to find many industrial uses, from lapping tools to abrasives (in loose form for lapping, mixed with vehicles to make paste or sticks, or combined with binders and formed into sheets, disks or belts). Due to its corrosion-resistance it also forms high temperature furnace parts like muffles, kiln furniture’s, checker bricks, refractory plates and furnace skid rails; while its low thermal expansion coefficient, melting point and chemical inertness make refractory elements useful in industrial furnaces such as linings, crucibles linings linings crucibles burner blocks and burner nozzles.
Due to its poor electrical conductivity, pure silicon carbide must be doped with impurities to achieve semiconductor properties. This can be accomplished by adding dopants such as nitrogen or phosphorus as n-type dopants and gallium, boron, aluminium or beryllium dopants as p-type dopants; in this doped state it boasts higher maximum current density than un-doped silicon.
Physical vapor deposition allows users to produce coatings with distinct chemical, crystallographic, and mechanical properties – making it suitable for a range of applications. It should typically be conducted under high vacuum conditions to minimize gas collisions with sources materials, unintended reactions and trapped gas layers.
Moissanite can be found naturally in small quantities in meteorites, corundum deposits and kimberlites; however, most moissanite sold today is synthetically produced. One method used for synthesizing silicon carbide involves heating silica and coke in an electric furnace and creating carborundum, which is then cut into gemstones known as moissanite jewels.
An effective third and more popular way of synthesizing silicon carbide involves reacting it with hydrogen in a high pressure gas cylinder at temperatures between 1200 and 1800degC, producing carbon monoxide, hydrogen and acetylene as by-products. This method of production produces silicon carbide used for making high temperature refractory bricks such as furnace walls, checker bricks, kiln furniture’s and plates as well as electrodes for electric resistance furnaces.