Silicon Carbide

Silicon carbide, often referred to as sand or corundum, can be found naturally in certain meteorites and kimberlite deposits; however, all commercially produced silicon carbide is synthetic.

Silicon carbide comes in over 70 crystal forms, the most frequently seen being a-SiC. Other varieties include beta (b-SiC), which features a zinc blende crystal structure.

Characteristics

Silicon carbide is the third hardest material on earth after diamond and boron nitride. With characteristics including imperviousness to chemical attack and high-temperature stability, silicon carbide has gained increasing attention as an additive material to metals and plastics to increase hardness and wear resistance. Manufactured synthetically through various means, silicon carbide powder is most often seen used for grinding tools, cutting tools or added as additives to increase wear resistance.

Although several variants of silicon carbide exist, beta and alpha are the two primary forms used for industrial purposes. Alpha has a spherical microcrystalline structure while beta’s cubic structure gives it distinctive qualities that make it suitable for applications across a range of industries.

Cubic silicon carbide can be sintered at a higher density than alpha, producing stronger and harder materials with smaller part sizes. Plus, its resistance to deformation makes it an attractive material choice for use in ballistic protection applications.

High thermal shock tolerance combined with chemical invulnerability make borosilicate glass an ideal material for use in aerospace industry and other demanding fields, including medical devices and pharmaceutical applications. Its low coefficient of expansion also makes it highly tolerant to thermal shock, meaning less likelihood of cracking or breaking in extreme environments. Suitable applications in the aerospace sector and other sensitive fields make borosilicate glass suitable for many different uses – both inside and out!

Silicon components must also have the ability to quickly disperse heat. This enables them to operate at higher temperatures and voltages for enhanced functionality and efficiency, providing greater functionality and efficiency overall. Silicon carbide dissipates heat 1490 times faster than silicon; hence its usage in various electronic devices and semiconductor manufacturing processes.

Although silicon carbide is generally safe for humans, experimental animals have shown evidence of lung damage when exposed to this material. This alters the course of inhalation tuberculosis, leading to extensive fibrosis and progressive disease; yet human dentistry utilizes this material in treating cavities and implant placement procedures without any adverse effect on aquatic ecosystems or the environment.

Applications

Silicon carbide powder has long been recognized for its hardness, high strength, chemical stability and temperature resistance; making it suitable for a range of uses in industries including abrasives, refractories, electrical and electronic, ceramics and more. Combinations with other refractory materials to produce cemented carbide or sintered products with complex shapes may be made by casting, dry press, isostatic press or injection molding processes.

Silicon carbide’s unique thermal properties make it an attractive material for encasing nuclear fuel, with low neutron activation levels and no melting or deformation at elevated temperatures. Due to this property, silicon carbide was chosen as reactor cladding material in the Integral Fast Reactor (IFR). Furthermore, silicon carbide may also be utilized as material for nuclear power plant refueling rods or even fusion reactor liners.

Alpha silicon carbide (ASC) is one of the most frequently utilized industrial materials, particularly for applications involving abrasives and refractories. Denser than its a-SiC counterpart, ASC can be sinter-purified to meet customer specifications, and typically comes in either black or green forms depending on its use case.

A-SiC is widely used for abrasive products like grinding wheels, tipped tools, cutting and drilling bits, carbide dies and other forms of abrasive products. This wear resistant material provides good corrosion, oxidation and shock load resistance and can even be sinter-purified to produce products with desired grain size, chemical composition and microstructure characteristics.

Additionally, a-SiC can be sinter-purified to produce sintered products with complex shapes and sizes – including components for use in refractories such as electric heating elements or silicon wavers – as well as wire sawing applications to cut silicon stones or other stones.

A-SiC powder can also be found in carborundum printmaking – a type of collagraph printing technique in which carborundum grit is applied to an aluminium plate and ink is trapped on its granular surface, creating prints that can then be printed onto paper with a rolling-bed press. This was one of the earliest uses for silicon carbide powder; other notable applications for it include high temperature/voltage applications as well as tools made of tungsten carbide which require extreme durability for high temperature applications like high voltage applications or high temperature/voltage applications.

Properties

Silicon carbide is an extremely hard and dense material with exceptional resistance to fracture and wear, being chemically inert and boasting high thermal conductivity; all characteristics which make it suitable for applications requiring high temperature resistance like refractory bricks and furnace components. Furthermore, silicon carbide serves as an abrasive in applications like grinding chilled iron, marble granite and steel as an abrasive.

Silicon Carbide can be found in minute amounts in meteorites, corundum deposits and kimberlites; however, most synthetic silicon carbide production occurs through synthetic preparation by melting silica sand with carbon under high pressure before sintered and reformed into various shapes.

Alpha SiC (a-SiC) is the most prevalent form of silicon carbide. This monocrystalline material features hexagonal crystal structure similar to that of wortzite. Alpha SiC exhibits excellent thermal conductivity, low expansion coefficient and chemical inertness properties as well as being extremely hard and brittle with a Vickers hardness of around 9 on Mohs scale.

Hexoloy SP SiC is an advanced sintered alpha silicon carbide material designed to meet the stringent nuclear reactor applications, featuring low neutron cross section and resistance to radiation damage. Furthermore, its low neutron cross section and resistance to radiation damage make it suitable for producing high performance low friction sintered abrasives and bearings with no frictional wear. Furthermore, Hexoloy SP SiC enhances this performance through the addition of spherical pores into its material which act as fluid reservoirs promoting retention between component surfaces and helping prevent wear-and tear wear-and tear wear-wearing.

Hexoloy SP SiC stands out from conventional sinterable a-SiC with its distinct combination of properties that sets it apart, making it well suited to high speed and extreme conditions of application. Its combination of high tensile strength, low thermal expansion and superior wear resistance gives Hexoloy SP SiC an extremely long lifespan in harsh environments; additionally its low neutron cross section makes it suitable for radiation sensor protection devices.

Manufacturing

Silicon carbide can be produced in various forms, from powders or particulates, fibers and whiskers, monolithic (non-fiber) forms, and monomorphs such as alpha and beta polytypes – each of which have distinct crystal structures and decomposition temperatures. Alpha silicon carbide boasts a hexagonal crystal structure and higher decomposition temperatures than beta polymorph silicon carbides, making it more suitable for manufacturing fibers and sinters or reaction-bonded material used in composite applications. Alpha silicon carbide fibers may be utilized in ceramic or metal-ceramic articles to store nuclear fuel in reactors such as light water reactors (LWR), pressurized water reactors (PWRs), liquid metal fast reactors (LMFRs), or high temperature gas-cooled reactors (HTGRs).

Alpha silicon carbide is typically created through reacting carbon fiber material with silicon-containing gases in a reaction chamber, usually by adding carbon fiber material that prevents direct air reaction with silicon-containing gas molecules. Carrier gas also assists by continuously extracting excess carbon monoxide from the chamber thereby maintaining low concentrations of carbon monoxide concentration within it which in turn prevents secondary reactions between carbon monoxide and silicon-containing gases.

The reaction will continue until substantially all of the carbon in carbon fiber material has been transformed into alpha silicon carbide, with this process accelerated by adding an alpha forming agent such as propane, butane or methane as a hydrocarbon before entering into the reaction chamber.

Fully converted alpha silicon carbide has an approximate density of 3.21 g/cc and less than 2% dimensional expansion; additionally its silicon-carbon bond length exceeds its carbon-carbon bond length. Thermal shock resistance and excellent wear properties make this material suitable for applications under diverse conditions. Hexoloy(r) SP SiC is a sintered, fully converted alpha silicon carbide material designed for superior sliding contact applications such as mechanical seal faces and product lubricated bearings. Hexoloy(r) SA SiC’s spherical pores serve as fluid reservoirs to promote the formation of a continuous fluid film over the surfaces of sliding components, offering superior lubrication and reduced friction under varying operating conditions.