Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing
silicon and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
. A
semiconductor, it occurs in nature as the extremely rare mineral
moissanite, but has been mass-produced as a powder and crystal since 1893 for use as an
abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...
. Grains of silicon carbide can be bonded together by
sintering to form very hard
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...
s that are widely used in applications requiring high endurance, such as car brakes, car clutches and
ceramic plates in
bulletproof vests. Large single crystals of silicon carbide can be grown by the
Lely method
The Lely method, also known as the Lely process or Lely technique, is a crystal growth technology used for producing silicon carbide crystals for the semiconductor industry. The patent for this method was filed in the Netherlands in 1954 and in the ...
and they can be cut into gems known as synthetic moissanite.
Electronic applications of silicon carbide such as
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light ( ...
s (LEDs) and
detectors in early radios were first demonstrated around 1907. SiC is used in semiconductor electronics devices that operate at high temperatures or high voltages, or both.
Natural occurrence
Naturally occurring
moissanite is found in only minute quantities in certain types of
meteorite
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
,
corundum deposits, and
kimberlite. Virtually all the silicon carbide sold in the world, including moissanite jewels, is
synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to:
Science
* Synthetic chemical or compound, produced by the process of chemical synthesis
* Synthetic o ...
.
Natural moissanite was first found in 1893 as a small component of the
Canyon Diablo meteorite in
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...
by Dr.
Ferdinand Henri Moissan, after whom the material was named in 1905. Moissan's discovery of naturally occurring SiC was initially disputed because his sample may have been contaminated by silicon carbide
saw blades that were already on the market at that time.
While rare on Earth, silicon carbide is remarkably common in space. It is a common form of
stardust
Stardust may refer to:
* A type of cosmic dust, composed of particles in space
Entertainment Songs
* “Stardust” (1927 song), by Hoagy Carmichael
* “Stardust” (David Essex song), 1974
* “Stardust” (Lena Meyer-Landrut song), 2012
* ...
found around
carbon-rich stars, and examples of this stardust have been found in pristine condition in primitive (unaltered) meteorites. The silicon carbide found in space and in meteorites is almost exclusively the
beta-polymorph. Analysis of SiC grains found in the
Murchison meteorite, a
carbonaceous chondrite meteorite, has revealed anomalous isotopic ratios of carbon and silicon, indicating that these grains originated outside the solar system.
History
Early experiments
Non-systematic, less-recognized and often unverified syntheses of silicon carbide include:
*
César-Mansuète Despretz César-Mansuète Despretz (4 May 1791, Lessines – 15 March 1863, Paris) was a chemist and physicist. He became a French citizen in 1838. A street got its name after him in Lessines (rue César Despretz).
Biography
In 1818, Despretz started ...
's passing an electric current through a carbon rod embedded in sand (1849)
* Robert Sydney Marsden's dissolution of silica in molten silver in a graphite crucible (1881)
*
Paul Schuetzenberger
Paul may refer to:
* Paul (given name), a given name (includes a list of people with that name)
* Paul (surname), a list of people
People
Christianity
*Paul the Apostle (AD c.5–c.64/65), also known as Saul of Tarsus or Saint Paul, early Chr ...
's heating of a mixture of silicon and silica in a graphite crucible (1881)
* Albert Colson's heating of silicon under a stream of ethylene (1882).
Wide-scale production
Wide-scale production is credited to
Edward Goodrich Acheson in 1890. Acheson was attempting to prepare artificial diamonds when he heated a mixture of clay (aluminium silicate) and powdered
coke (carbon) in an iron bowl. He called the blue crystals that formed ''carborundum'', believing it to be a new compound of carbon and aluminium, similar to
corundum. Moissan also synthesized SiC by several routes, including dissolution of carbon in molten silicon, melting a mixture of calcium carbide and silica, and by reducing silica with carbon in an electric furnace.
Acheson patented the method for making silicon carbide powder on February 28, 1893. Acheson also developed the electric batch
furnace by which SiC is still made today and formed the Carborundum Company to manufacture bulk SiC, initially for use as an abrasive. In 1900 the company settled with the
Electric Smelting and Aluminum Company when a judge's decision gave "priority broadly" to its founders "for reducing ores and other substances by the incandescent method". It is said that Acheson was trying to dissolve carbon in molten
corundum (
alumina) and discovered the presence of hard, blue-black crystals which he believed to be a compound of carbon and corundum: hence carborundum. It may be that he named the material "carborundum" by analogy to corundum, which is another very hard substance (9 on the
Mohs scale).
The first use of SiC was as an abrasive. This was followed by electronic applications. In the beginning of the 20th century, silicon carbide was used as a detector in the first radios. In 1907
Henry Joseph Round produced the first LED by applying a voltage to a SiC crystal and observing yellow, green and orange emission at the cathode. The effect was later rediscovered by
O. V. Losev in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
in 1923.
Production
Because natural moissanite is extremely scarce, most silicon carbide is synthetic. Silicon carbide is used as an abrasive, as well as a
semiconductor and
diamond simulant of gem quality. The simplest process to manufacture silicon carbide is to combine
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is o ...
sand and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
in an
Acheson graphite electric resistance furnace at a high temperature, between and . Fine SiO
2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material. The
silica fume, which is a byproduct of producing silicon metal and ferrosilicon alloys, can also be converted to SiC by heating with graphite at .
The material formed in the Acheson furnace varies in purity, according to its distance from the
graphite resistor
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
heat source
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
. Colorless, pale yellow and green crystals have the highest purity and are found closest to the resistor. The color changes to blue and black at greater distance from the resistor, and these darker crystals are less pure. Nitrogen and aluminium are common impurities, and they affect the electrical conductivity of SiC.
Pure silicon carbide can be made by the
Lely process, in which SiC powder is sublimed into high-temperature species of silicon, carbon, silicon dicarbide (SiC
2), and disilicon carbide (Si
2C) in an
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as a ...
gas ambient at 2500 °C and redeposited into flake-like single crystals, sized up to 2 × 2 cm, at a slightly colder substrate. This process yields high-quality single crystals, mostly of 6H-SiC phase (because of high growth temperature).
A modified Lely process involving
induction heating in graphite
crucibles yields even larger single crystals of 4 inches (10 cm) in diameter, having a section 81 times larger compared to the conventional Lely process.
Cubic SiC is usually grown by the more expensive process of
chemical vapor deposition (CVD) of silane, hydrogen and nitrogen.
Homoepitaxial and heteroepitaxial SiC layers can be grown employing both gas and liquid phase approaches.
To form complex shaped SiC,
preceramic polymers can be used as precursors which form the ceramic product through
pyrolysis at temperatures in the range 1000–1100 °C. Precursor materials to obtain silicon carbide in such a manner include polycarbosilanes,
poly(methylsilyne)
Polysilynes are organosilicon compounds with the formula Sisub>n. Although their name suggests a relationship to alkynes, polysilynes are a class of silicon-based random network polymers primarily composed of tetrahedral silicon centers, each con ...
and polysilazanes. Silicon carbide materials obtained through the pyrolysis of
preceramic polymers are known as
polymer derived ceramics or PDCs. Pyrolysis of
preceramic polymers is most often conducted under an
inert atmosphere at relatively low temperatures. Relative to the CVD process, the pyrolysis method is advantageous because the polymer can be formed into various shapes prior to thermalization into the ceramic.
SiC can also be made into wafers by cutting a single crystal either using a diamond wire saw or by using a laser. SiC is a useful semiconductor used in power electronics.
Structure and properties
Silicon carbide exists in about 250 crystalline forms. Through the inert atmosphere pyrolysis of
preceramic polymers, silicon carbide in a glassy amorphous form is also produced. The polymorphism of SiC is characterized by a large family of similar crystalline structures called polytypes. They are variations of the same chemical compound that are identical in two dimensions and differ in the third. Thus, they can be viewed as layers stacked in a certain sequence.
Alpha silicon carbide (α-SiC) is the most commonly encountered
polymorph
Polymorphism, polymorphic, polymorph, polymorphous, or polymorphy may refer to:
Computing
* Polymorphism (computer science), the ability in programming to present the same programming interface for differing underlying forms
* Ad hoc polymorphi ...
, and is formed at temperatures greater than 1700 °C and has a
hexagonal crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns t ...
(similar to
Wurtzite). The beta modification (β-SiC), with a
zinc blende crystal structure (similar to
diamond), is formed at temperatures below 1700 °C.
Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for
heterogeneous catalysts, owing to its higher surface area compared to the alpha form.
Pure SiC is colorless. The brown to black color of the industrial product results from
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
impurities. The rainbow-like luster of the crystals is due to the
thin-film interference
Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thickness of the film is an ...
of a
passivation layer of
silicon dioxide that forms on the surface.
The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for
bearings and furnace parts. Silicon carbide does not melt at any known temperature. It is also highly inert chemically. There is currently much interest in its use as a
semiconductor material in electronics, where its high thermal conductivity, high
electric field breakdown strength and high maximum
current density make it more promising than silicon for high-powered devices.
SiC also has a very low
coefficient of thermal expansion (4.0 × 10
−6/K) and experiences no
phase transitions that would cause discontinuities in thermal expansion.
Electrical conductivity
Silicon carbide is a
semiconductor, which can be doped n-type by
nitrogen or
phosphorus and p-type by
beryllium,
boron,
aluminium
Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...
, or
gallium.
Metallic conductivity has been achieved by heavy doping with boron, aluminium or nitrogen.
Superconductivity
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
has been detected in 3C-SiC:Al, 3C-SiC:B and 6H-SiC:B at similar temperatures ~1.5 K.
A crucial difference is however observed for the magnetic field behavior between aluminium and boron doping: 3C-SiC:Al is
type-II. In contrast, 3C-SiC:B is
type-I, as is 6H-SiC:B. Thus the superconducting properties seem to depend more on dopant (B vs. Al) than on polytype (3C- vs 6H-). In an attempt to explain this dependence, it was noted that B substitutes at C sites in SiC, but Al substitutes at Si sites. Therefore, Al and B "see" different environments, in both polytypes.
Uses
Abrasive and cutting tools
In the arts, silicon carbide is a popular abrasive in modern
lapidary due to the durability and low cost of the material. In manufacturing, it is used for its hardness in
abrasive machining processes such as
grinding,
honing,
water-jet cutting and
sandblasting. Particles of silicon carbide are laminated to paper to create
sandpapers and the grip tape on
skateboards.
In 1982 an exceptionally strong composite of
aluminium oxide and silicon carbide
whiskers was discovered. Development of this laboratory-produced composite to a commercial product took only three years. In 1985, the first commercial cutting tools made from this alumina and silicon carbide whisker-reinforced composite were introduced into the market.
Structural material
In the 1980s and 1990s, silicon carbide was studied in several research programs for high-temperature gas turbines in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
,
Japan and the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
. The components were intended to replace
nickel superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, g ...
turbine blades or nozzle vanes. However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture
toughness.
Like other hard ceramics (namely alumina and
boron carbide), silicon carbide is used in
composite armor (e.g.
Chobham armor), and in ceramic plates in bulletproof vests.
Dragon Skin
Dragon Skin was a type of ballistic vest first-produced by the now-defunct company, Pinnacle Armor, and was subsequently manufactured by North American Development Group LLC. The vest manufacturer claimed that it could absorb a high number of bull ...
, which was produced by
Pinnacle Armor
Dragon Skin was a type of ballistic vest first-produced by the now-defunct company, Pinnacle Armor, and was subsequently manufactured by North American Development Group LLC. The vest manufacturer claimed that it could absorb a high number of bull ...
, used disks of silicon carbide. Improved fracture toughness in SiC armor can be facilitated through the phenomenon of
abnormal grain growth or AGG. The growth of abnormally long silicon carbide grains may serve to impart a toughening effect through crack-wake bridging, similar to whisker reinforcement. Similar
AGG-toughening effects have been reported in
Silicon nitride (Si
3N
4).
Silicon carbide is used as a support and shelving material in high temperature kilns such as for firing ceramics, glass fusing, or glass casting. SiC kiln shelves are considerably lighter and more durable than traditional alumina shelves.
In December 2015, infusion of silicon carbide nano-particles in molten
magnesium was mentioned as a way to produce a new strong and plastic alloy suitable for use in aeronautics, aerospace, automobile and micro-electronics.
Automobile parts
Silicon-infiltrated
carbon-carbon composite is used for high performance "ceramic"
brake disks, as they are able to withstand extreme temperatures. The silicon reacts with the graphite in the carbon-carbon composite to become carbon-fiber-reinforced silicon carbide (C/SiC). These brake disks are used on some road-going sports cars, supercars, as well as other performance cars including the
Porsche Carrera GT, the
Bugatti Veyron
The Bugatti Veyron EB 16.4 is a mid-engine sports car, designed and developed in Germany by the Volkswagen Group and Bugatti and manufactured in Molsheim, France, by French automobile manufacturer Bugatti. It was named after the racing driver ...
, the
Chevrolet Corvette ZR1, the
McLaren P1,
Bentley,
Ferrari,
Lamborghini
Automobili Lamborghini S.p.A. () is an Italian brand and manufacturer of luxury sports cars and SUVs based in Sant'Agata Bolognese. The company is owned by the Volkswagen Group through its subsidiary Audi.
Ferruccio Lamborghini (1916–1993) ...
and some specific high-performance
Audi cars. Silicon carbide is also used in a
sintered
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
form for
diesel particulate filters. It's also used as an oil additive to reduce friction, emissions, and harmonics.
Foundry crucibles
SiC is used in crucibles for holding melting metal in small and large foundry applications.
Electric systems
The earliest electrical application of SiC was in
lightning arresters in electric power systems. These devices must exhibit high
resistance
Resistance may refer to:
Arts, entertainment, and media Comics
* Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm:
** ''Resistance'' (comics), based on the video game of the same title
** ''T ...
until the
voltage across them reaches a certain threshold V
T at which point their resistance must drop to a lower level and maintain this level until the applied voltage drops below V
T.
It was recognized early on that SiC had such a
voltage-dependent resistance, and so columns of SiC pellets were connected between high-voltage
power lines and the earth. When a
lightning strike to the line raises the line voltage sufficiently, the SiC column will conduct, allowing strike current to pass harmlessly to the earth instead of along the power line. The SiC columns proved to conduct significantly at normal power-line operating voltages and thus had to be placed
in series with a
spark gap. This spark gap is
ionized and rendered conductive when lightning raises the voltage of the power line conductor, thus effectively connecting the SiC column between the power conductor and the earth. Spark gaps used in lightning arresters are unreliable, either failing to strike an arc when needed or failing to turn off afterwards, in the latter case due to material failure or contamination by dust or salt. Usage of SiC columns was originally intended to eliminate the need for the spark gap in lightning arresters. Gapped SiC arresters were used for lightning-protection and sold under the
GE and
Westinghouse brand names, among others. The gapped SiC arrester has been largely displaced by no-gap
varistors that use columns of
zinc oxide
Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceram ...
pellets.
Electronic circuit elements
Silicon carbide was the first commercially important semiconductor material. A
crystal radio "carborundum" (synthetic silicon carbide) detector diode was patented by
Henry Harrison Chase Dunwoody in 1906. It found much early use in shipboard receivers.
Power electronic devices
In 1993 the silicon carbide was considered a
semiconductor in both research and early
mass production
Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and bat ...
providing advantages for fast, high-temperature and/or high-voltage devices. The first devices available were
Schottky diodes, followed by
junction-gate FETs and
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
s for high-power switching.
Bipolar transistors and
thyristors are currently developed.
A major problem for SiC commercialization has been the elimination of defects: edge dislocations, screw dislocations (both hollow and closed core), triangular defects and basal plane dislocations. As a result, devices made of SiC crystals initially displayed poor reverse blocking performance, though researchers have been tentatively finding solutions to improve the breakdown performance.
Apart from crystal quality, problems with the interface of SiC with silicon dioxide have hampered the development of SiC-based power MOSFETs and
insulated-gate bipolar transistors. Although the mechanism is still unclear,
nitriding has dramatically reduced the defects causing the interface problems.
In 2008, the first commercial
JFETs rated at 1200 V were introduced to the market,
followed in 2011 by the first commercial MOSFETs rated at 1200 V. JFETs are now available rated 650 V to 1700 V with resistance as low as 25 mΩ. Beside SiC switches and SiC Schottky diodes (also Schottky barrier diode,
SBD) in the popular TO-247 and
TO-220 packages, companies started even earlier to implement the bare chips into their
power electronic modules.
SiC SBD diodes found wide market spread being used in
PFC circuits and
IGBT power modules.
Conferences such as the
International Conference on Integrated Power Electronics Systems (CIPS) report regularly about the technological progress of SiC power devices.
Major challenges for fully unleashing the capabilities of SiC power devices are:
* Gate drive: SiC devices often require gate drive voltage levels that are different from their silicon counterparts and may be even unsymmetric, for example, +20 V and −5 V.
* Packaging: SiC
chips may have a higher power density than silicon power devices and are able to handle higher temperatures exceeding the silicon limit of 150 °C. New die attach technologies such as
sintering are required to efficiently get the heat out of the devices and ensure a reliable interconnection.
Beginning with
Tesla Model 3 the
inverters in the drive unit use 24 pairs of silicon carbide (SiC)
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
chips rated for 650 volts each. Silicon carbide in this instance gave Tesla a significant advantage over chips made of silicon in terms of size and weight. A number of automobile manufacturers are planning to incorporate silicon carbide into power electronic devices in their products. A significant increase in production of silicon carbide is projected, beginning with a large plant planned by
Wolfspeed
Wolfspeed, Inc. is an American developer and manufacturer of wide bandgap semiconductors, focused on silicon carbide and gallium nitride materials and devices for power and radio frequency applications such as transportation, power supplies, ...
in upstate New York.
LEDs
The phenomenon of
electroluminescence was discovered in 1907 using silicon carbide and the first commercial
LEDs were based on SiC. Yellow LEDs made from 3C-SiC were manufactured in the Soviet Union in the 1970s and
blue LEDs (6H-SiC) worldwide in the 1980s.
Carbide LED production soon stopped when a different material,
gallium nitride, showed 10–100 times brighter emission. This difference in efficiency is due to the unfavorable
indirect bandgap of SiC, whereas GaN has a
direct bandgap which favors light emission. However, SiC is still one of the important LED components: It is a popular substrate for growing GaN devices, and it also serves as a heat spreader in high-power LEDs.
Astronomy
The low thermal expansion coefficient, high hardness, rigidity and thermal conductivity make silicon carbide a desirable
mirror material for
astronomical telescopes. The growth technology (
chemical vapor deposition) has been scaled up to produce disks of polycrystalline silicon carbide up to in diameter, and several telescopes like the
Herschel Space Telescope are already equipped with SiC optics, as well the
Gaia space observatory spacecraft subsystems are mounted on a rigid silicon carbide frame, which provides a stable structure that will not expand or contract due to heat.
Thin filament pyrometry
Silicon carbide fibers are used to measure gas temperatures in an optical technique called thin filament pyrometry. It involves the placement of a thin filament in a hot gas stream. Radiative emissions from the filament can be correlated with filament temperature. Filaments are SiC fibers with a diameter of 15 micrometers, about one fifth that of a human hair. Because the fibers are so thin, they do little to disturb the flame and their temperature remains close to that of the local gas. Temperatures of about 800–2500 K can be measured.
Heating elements
References to silicon carbide heating elements exist from the early 20th century when they were produced by Acheson's Carborundum Co. in the U.S. and EKL in Berlin. Silicon carbide offered increased
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
s compared with metallic heaters. Silicon carbide elements are used today in the melting of glass and non-ferrous metal,
heat treatment of metals,
float glass production, production of ceramics and electronics components, igniters in
pilot lights for gas heaters, etc.
Heat shielding
The outer thermal protection layer of NASA's LOFTID inflatable heat shield incorporates a woven ceramic made from silicon carbide, with fiber of such small diameter that it can be bundled and spun into a yarn.
Nuclear fuel particles and cladding
Silicon carbide is an important material in
TRISO-coated fuel particles, the type of
nuclear fuel
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...
found in
high temperature gas cooled reactors such as the
Pebble Bed Reactor. A layer of silicon carbide gives coated fuel particles structural support and is the main diffusion barrier to the release of fission products.
Silicon carbide
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
has been investigated for use as a replacement for
Zircaloy cladding in
light water reactors. One of the reasons for this investigation is that, Zircaloy experiences hydrogen embrittlement as a consequence of the corrosion reaction with water. This produces a reduction in fracture toughness with increasing volumetric fraction of radial hydrides. This phenomenon increases drastically with increasing temperature to the detriment of the material. Silicon carbide cladding does not experience this same mechanical degradation, but instead retains strength properties with increasing temperature. The composite consists of SiC fibers wrapped around a SiC inner layer and surrounded by an SiC outer layer. Problems have been reported with the ability to join the pieces of the SiC composite.
Jewelry
As a
gemstone used in
jewelry
Jewellery (British English, UK) or jewelry (American English, U.S.) consists of decorative items worn for personal adornment, such as brooches, ring (jewellery), rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be at ...
, silicon carbide is called "synthetic moissanite" or just "moissanite" after the mineral name. Moissanite is similar to
diamond in several important respects: it is transparent and hard (9–9.5 on the
Mohs scale, compared to 10 for diamond), with a
refractive index between 2.65 and 2.69 (compared to 2.42 for diamond). Moissanite is somewhat harder than common
cubic zirconia. Unlike diamond, moissanite can be strongly
birefringent. For this reason, moissanite jewels are cut along the
optic axis of the crystal to minimize birefringent effects. It is lighter (density 3.21 g/cm
3 vs. 3.53 g/cm
3), and much more resistant to heat than diamond. This results in a stone of higher
luster, sharper facets, and good resilience. Loose moissanite stones may be placed directly into wax ring moulds for lost-wax casting, as can diamond, as moissanite remains undamaged by temperatures up to . Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
is closer to diamond than any other substitute. Many thermal diamond-testing devices cannot distinguish moissanite from diamond, but the gem is distinct in its
birefringence and a very slight green or yellow fluorescence under ultraviolet light. Some moissanite stones also have curved, string-like inclusions, which diamonds never have.
Steel production
Silicon carbide, dissolved in a
basic oxygen furnace used for making
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ...
, acts as a
fuel. The additional energy liberated allows the furnace to process more scrap with the same charge of hot metal. It can also be used to raise
tap temperatures and adjust the carbon and silicon content. Silicon carbide is cheaper than a combination of
ferrosilicon and carbon, produces cleaner steel and lower emissions due to low levels of
trace elements, has a low gas content, and does not lower the temperature of steel.
Catalyst support
The natural resistance to oxidation exhibited by silicon carbide, as well as the discovery of new ways to synthesize the cubic β-SiC form, with its larger surface area, has led to significant interest in its use as a heterogeneous
catalyst support. This form has already been employed as a catalyst support for the oxidation of
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s, such as n-
butane, to
maleic anhydride.
Carborundum printmaking
Silicon carbide is used in
carborundum printmaking – a
collagraph printmaking
Printmaking is the process of creating artworks by printing, normally on paper, but also on fabric, wood, metal, and other surfaces. "Traditional printmaking" normally covers only the process of creating prints using a hand processed techniq ...
technique. Carborundum grit is applied in a paste to the surface of an aluminium plate. When the paste is dry, ink is applied and trapped in its granular surface, then wiped from the bare areas of the plate. The ink plate is then printed onto paper in a rolling-bed press used for
intaglio printmaking
Intaglio ( ; ) is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink. It is the direct opposite of a relief print where the parts of the matrix that m ...
. The result is a print of painted marks embossed into the paper.
Carborundum grit is also used in stone Lithography. Its uniform particle size allows it to be used to "Grain" a stone which removes the previous image. In a similar process to sanding, coarser grit Carborundum is applied to the stone and worked with a
Levigator, then gradually finer and finer grit is applied until the stone is clean. This creates a grease sensitive surface.
Graphene production
Silicon carbide can be used in the production of
graphene because of its chemical properties that promote the epitaxial production of graphene on the surface of SiC nanostructures.
When it comes to its production, silicon is used primarily as a substrate to grow the graphene. But there are actually several methods that can be used to grow the graphene on the silicon carbide. The confinement controlled sublimation (CCS) growth method consists of a SiC chip that is heated under vacuum with graphite. Then the vacuum is released very gradually to control the growth of graphene. This method yields the highest quality graphene layers. But other methods have been reported to yield the same product as well.
Another way of growing graphene would be thermally decomposing SiC at a high temperature within a vacuum. But this method turns out to yield graphene layers that contain smaller grains within the layers. So there have been efforts to improve the quality and yield of graphene. One such method is to perform ''ex situ'' graphitization of silicon terminated SiC in an atmosphere consisting of argon. This method has proved to yield layers of graphene with larger domain sizes than the layer that would be attainable via other methods. This new method can be very viable to make higher quality graphene for a multitude of technological applications.
When it comes to understanding how or when to use these methods of graphene production, most of them mainly produce or grow this graphene on the SiC within a growth enabling environment. It is utilized most often at rather higher temperatures (such as 1300 °C) because of SiC thermal properties. However, there have been certain procedures that have been performed and studied that could potentially yield methods that use lower temperatures to help manufacture graphene. More specifically this different approach to graphene growth has been observed to produce graphene within a temperature environment of around 750 °C. This method entails the combination of certain methods like chemical vapor deposition (CVD) and surface segregation. And when it comes to the substrate, the procedure would consist of coating a SiC substrate with thin films of a transition metal. And after the rapid heat treating of this substance, the carbon atoms would then become more abundant at the surface interface of the transition metal film which would then yield graphene. And this process was found to yield graphene layers that were more continuous throughout the substrate surface.
Quantum physics
Silicon carbide can host point defects in the crystal lattice which are known as
color centers
An F center or Farbe center (from the original German ''Farbzentrum'', where ''Farbe'' means ''color'' and ''zentrum'' means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more un ...
. These defects can produce single photons on demand and thus serve as a platform for
single-photon source. Such a device is a fundamental resource for many emerging applications of quantum information science. If one pumps a color center via an external optical source or electrical current, the color center will be brought to the excited state and then relax with the emission of one photon.
One well known point defect in silicon carbide is the divacancy which has a similar electronic structure as the
nitrogen-vacancy center in diamond. In 4H-SiC, the divacancy has four different configurations which correspond to four zero-phonon lines (ZPL). These ZPL values are written using the notation V
Si-V
C and the unit eV: hh(1.095), kk(1.096), kh(1.119), and hk(1.150).
Fishing rod guides
Silicon carbide is used in the manufacturing of fishing guides because of its durability and wear resistance.
Silicon Carbide rings are fit into a guide frame, typically made from stainless steel or titanium which keep the line from touching the rod blank. The rings provide a low friction surface which improves casting distance while providing adequate hardness that prevents abrasion from braided fishing line.
See also
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Reaction bonded silicon carbide Reaction bonded silicon carbide, also known as siliconized silicon carbide or SiSiC, is a type of silicon carbide that is manufactured by a chemical reaction between porous carbon or graphite with molten silicon. Due to the left over traces of silic ...
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Globar
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Carborundum Universal
References
External links
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Inorganic silicon compounds
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