Carborundum Explained: Structure, Formula & Properties

Carbides are inorganic or organic chemical compounds that include carbon in an anionic form. The various elements that form carbides are; calcium, boron, silicon, and aluminium. Let us discuss the carborundum meaning, Silicon carbide (SiC), also referred to as carborundum, is a silicon-carbon semiconductor. 

Moissanite, an exceptionally rare mineral, is found in nature. Since 1893, synthetic SiC powder has been mass-produced as an abrasive. Sintering can bind silicon carbide grains together to form very hard ceramics, which are commonly used in applications requiring high endurance, such as car brakes, car clutches, and bulletproof vest ceramic plates. About 1907, silicon carbide was first used in electronic applications such as light-emitting diodes (LEDs) and detectors in early radios. 

SiC is a semiconductor material that is used in semiconductor electronics devices that work at high temperatures, high voltages, or both. The Lely method can be used to grow large single crystals of silicon carbide, which can then be cut into synthetic moissanite gems.

Carborundum Structure

(Image will be uploaded soon)

There are about 250 different crystalline types of silicon carbide. Silicon carbide in a glassy amorphous shape is formed by pyrolysis of preceramic polymers in an inert atmosphere. Polytypes are a wide family of related crystalline structures that define SiC polymorphism. They are two-dimensional variants of the same chemical compound that vary in the third dimension. As a result, they can be thought of as layers stacked in a specific order.

The most popular polymorph is alpha silicon carbide (SiC), which is produced at temperatures above 1700 °C and has a hexagonal crystal structure. At temperatures below 1700 °C, the beta modification (SiC) with a zinc blende crystal structure (similar to diamond) is formed. The beta form has had few commercial applications until recently, but due to its higher surface area than the alpha form, it is now gaining popularity as a support for heterogeneous catalysts.

Carborundum Formula

Carborundum formula (Silicon carbide chemical formula) is SiC. Its molar mass is 40.10 g/mol and its molecular formula is CSi. It's a simple compound with a triple bond connecting the carbon atom to the silicon atom, leaving all atoms with a positive and negative charge. However, rather than being ionic, the bonding between them is primarily covalent. Solid silicon carbide comes in a variety of crystalline shapes, the most common of which is the hexagonal crystal structure.

Properties of Carborundum

• SiC is colourless in its purest form. Iron impurities give the industrial product a brown to black hue. 

• The crystals' rainbow-like lustre is caused by the thin-film intrusion of a silicon dioxide passivation layer that forms on the surface.

• Silicon carbide is useful for bearings and furnace parts because of its high sublimation temperature (approximately 2700 °C). At any known temperature, silicon carbide does not melt.

• Chemically, it is also very inert. 

• Its high thermal conductivity, high electric field breakdown resistance, and high maximum current density make it more promising than silicon for high-powered devices, and there is currently a lot of interest in its use as a semiconductor material in electronics. 

• SiC also has a very low coefficient of thermal expansion and no phase transitions that trigger thermal expansion discontinuities.

Silicon Carbide as a Semiconductor Material

Silicon carbide is a semiconductor that can be doped with nitrogen or phosphorus to make it n-type and beryllium, boron, aluminium, or gallium to make it p-type. Strong doping with boron, aluminium, or nitrogen has been used to achieve metallic conductivity.

At the same temperature of 1.5 K, superconductivity was observed in 3C-SiC:Al, 3C-SiC:B, and 6H-SiC:B. However, there is a significant difference in magnetic field activity between aluminium and boron doping: SiC:Al, like Si:B, is a type-II compound. SiC:B, on the other hand, is a type-I compound. It was discovered that Si sites are more critical for superconductivity in SiC than carbon sites. In SiC, boron replaces carbon, while Al replaces Si sites. As a result, Al and B "see" different worlds, which may explain why SiC has different properties.

Occurrence of Carborundum in Nature

Moissanite is only present in trace amounts in some forms of meteorites, as well as corundum deposits and kimberlite. Almost all-silicon carbide sold in the world is synthetic, like moissanite jewellery. Dr. Ferdinand Henri Moissan discovered natural moissanite as a small portion of the Canyon Diablo meteorite in Arizona in 1893, and the substance was named after him in 1905. Moissan's discovery of naturally occurring SiC was initially questioned due to the possibility that his sample had been tainted by silicon carbide saw blades that were already on the market at the time.

Silicon carbide is extremely popular in space, despite its rarity on Earth. It's a common type of stardust found in the vicinity of carbon-rich stars, and examples have been discovered in pristine conditions in primitive (unaltered) meteorites. The beta-polymorph of silicon carbide is almost exclusively present in space and in meteorites. The isotopic ratios of carbon and silicon in SiC grains found in the Murchison meteorite, a carbonaceous chondrite meteorite, showed anomalous isotopic ratios, suggesting that these grains originated beyond the solar system.

Production of Carborundum

Moissanite is a rare mineral, and most silicon carbide is synthetic. Silicon carbide is used as an abrasive, a semiconductor, and a gem-quality diamond simulant. Combining silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F), is the easiest way to make silicon carbide. By heating in the excess carbon from the organic material, fine SiO₂ particles in plant material (e.g. rice husks) can be converted to SiC. By heating with graphite at 1,500 °C (2,730 °F), silica fume, a byproduct of making silicon metal and ferrosilicon alloys, can be converted to SiC.

The purity of the substance produced in the Acheson furnace varies depending on how far it is from the graphite resistor heat source. The purest crystals are colourless, pale yellow, and green, and they are located nearest to the resistor. At a greater distance from the resistor, the colour changes to blue and black, and the darker crystals are less pure. The electrical conductivity of SiC is affected by impurities such as nitrogen and aluminium.

Uses of Carborundum

Abrasive and Cutting Tools

Silicon carbide, a common abrasive in modern lapidary due to its toughness and low cost, is a popular abrasive in the arts. It is used in abrasive machining processes such as grinding, honing, water-jet cutting, and sandblasting because of its hardness. Sandpapers and skateboard grip tape are made from silicon carbide particles laminated to paper.

In 1982, a composite of aluminium oxide and silicon carbide whiskers was discovered to be extremely solid. It took just three years to transform this lab-created composite into a commercial product. The first commercially available cutting tools made from this alumina and silicon carbide whisker-reinforced composite hit the market in 1985.

In Making Structural Material

Silicon carbide was investigated in many high-temperature gas turbine research programmes in Europe, Japan, and the United States during the 1980s and 1990s. The parts were designed to be used in place of nickel superalloy turbine blades or nozzle vanes. However, none of these ventures resulted in a commercially viable product, owing to its low impact resistance and fracture toughness.

Silicon carbide, like other hard ceramics (such as alumina and boron carbide), is used in composite armour (such as Chobham armour) and in bulletproof vest ceramic plates. Pinnacle Armour used silicon carbide discs in their Dragon Skin armour. The phenomenon of abnormal grain development, or AGG, can help improve the fracture toughness of SiC armour. Similar to whisker reinforcement, the growth of abnormally long silicon carbide grains can help to impart a toughening effect by crack-wake bridging. Silicon nitride has been shown to have similar AGG-toughening effects (Si3N4).

In high-temperature kilns, such as those used for firing ceramics, glass fusing, or glass casting, silicon carbide is used as a support and shelving material. Traditional alumina kiln shelves are significantly heavier and less sturdy than SiC kiln shelves.

In December 2015, it was reported that infusing silicon carbide nanoparticles into molten magnesium could create a new strong and plastic alloy suitable for use in aeronautics, aerospace, automobiles, and microelectronics.

In Making Automobiles Parts

High-performance "ceramic" brake discs are made of silicon-infiltrated carbon-carbon composite, which can withstand extreme temperatures. The silicon in the carbon-carbon composite reacts with the graphite to form carbon-fibre-reinforced silicon carbide (C/SiC). Some road-going sports cars, supercars, and other luxury cars, such as the Porsche Carrera GT, Bugatti Veyron, Chevrolet Corvette ZR1, McLaren P1, Bentley, Ferrari, Lamborghini, and other specific high-performance Audi cars, use these brake discs. Sintered silicon carbide is also used in diesel particulate filters. Friction, emissions, and harmonics are all reduced by using it as an oil additive.

Electronic Elements

SiC's voltage-dependent resistance was discovered early on, and columns of SiC pellets were connected between high-voltage power lines and the earth. The SiC column will conduct when a lightning strike to the line increases the line voltage enough, allowing the strike current to flow harmlessly to the earth rather than to the power line. The SiC columns showed considerable conductivity at standard power-line operating voltages, necessitating their placement in series with a spark gap. As lightning increases the voltage of the power line conductor, the spark gap is ionised and made conductive, essentially connecting the SiC column to the power conductor and the ground. Spark gaps in lightning arresters are unreliable, failing to strike an arc when needed or failing to switch off afterwards, the latter due to material failure or contamination by dust or salt in the latter case. The use of SiC columns in lightning arresters was originally intended to reduce the need for a spark gap. Gapped SiC arresters were sold under the GE and Westinghouse brands, among others, for lightning safety. No-gap varistors that use zinc oxide pellet columns have essentially replaced the gapped SiC arrester.

LEDs

In 1907, silicon carbide was used to discover the phenomenon of electroluminescence, and the first commercial LEDs were made of SiC. In the 1970s, the Soviet Union produced yellow 3C-SiC LEDs, and in the 1980s, the world produced blue 6H-SiC LEDs.

When a different material, gallium nitride, showed 10–100 times brighter emission, LED development was quickly halted. This efficiency disparity is attributable to SiC's unfavourable indirect bandgap, while GaN's direct bandgap favours light emission. SiC, on the other hand, remains a significant LED component because it is a common substrate for growing GaN devices and also serves as a heat spreader in high-power LEDs.

In the Production of Graphene

Silicon carbide can be used to make graphene because of its chemical properties, which encourage graphene to develop epitaxially on the surface of SiC nanostructures. When it comes to manufacturing graphene, silicon is mainly used as a substrate on which the graphene is grown.

However, there are many methods for growing graphene on silicon carbide that can be used. A SiC chip is heated under vaccum with graphite in the confinement controlled sublimation (CCS) growth process. The vacuum is then gradually released in order to regulate the growth of graphene. The graphene layers generated by this method are of the highest quality. However, other methods have been documented to produce the same result.

Another method for producing graphene is to thermally decompose SiC in a vacuum at a high temperature. However, this process produces graphene layers with smaller grains inside the layers. As a result, attempts have been made to increase graphene consistency and yield. Ex-situ graphitization of silicon terminated SiC in an argon atmosphere is one of these techniques. This method has been shown to produce graphene layers with larger domain sizes than those obtained by other methods. This new method of producing higher-quality graphene could be very useful in a variety of technical applications.

When it comes to understanding how and when to use these graphene production methods, the majority of them primarily produce or grow graphene on SiC in a growth-friendly environment. Because of the thermal properties of SiC, it is most commonly used at higher temperatures (such as 1300° C). 

However, such procedures have been performed and studied that could theoretically lead to graphene manufacturing methods that use lower temperatures. This new method of graphene growth has been observed to generate graphene in a temperature setting of about 750 degrees Celsius. This approach combines various techniques such as chemical vapour deposition (CVD) and surface segregation. In terms of the substrate, the technique would include coating a SiC substrate with thin transition metal films. After rapid heat treatment, the carbon atoms at the surface interface of the transition metal film become more abundant, yielding graphene. And it was discovered that this process resulted in graphene layers that were more consistent around the substrate surface.

Jewels of Carborundum

After the mineral name, silicon carbide is called "synthetic moissanite" or simply "moissanite" as a gemstone used in jewellery. Moissanite is similar to diamond in many ways: it is transparent and hard (9–9.5 on the Mohs scale, versus 10 for diamond), and it has a refractive index of 2.65–2.69. (compared to 2.42 for diamond). Moissanite is a little tougher than cubic zirconia. Moissanite, unlike diamond, can be highly birefringent. As a result, moissanite jewels are cut along the crystal's optic axis to reduce birefringent effects. It is lighter than diamond and much more heat resistant. As a result, the stone has a higher lustre, sharper facets, and is more durable. 

Since moissanite is unaffected by temperatures up to 1,800 °C (3,270 °F), loose moissanite stones, like diamonds, can be inserted directly into wax ring moulds for lost wax casting. Moissanite has gained popularity as a diamond replacement, and it is possible that it would be mistaken for diamond because its thermal conductivity is the closest to diamond of any substitute. While several thermal diamond-testing instruments can't tell the difference between moissanite and diamond, the gem is distinguished by its birefringence and a faint green or yellow fluorescence under ultraviolet light. Moissanite also has curved, string-like inclusions, which diamonds do not have.

Did You Know?

• Silicon carbide gets its hardness and strength from tetrahedral silicon and carbon structures kept together by tight covalent bonds in its crystal lattice.

• On the other hand, silicon carbide fibres have been linked to lung fibrosis, lung cancer, and probably mesothelioma. Fibrous silicon carbide can cause cancer in humans.

• Another name of synthetic moissanite is carborundum stone.

Conclusion:

This article contains everything one needs to know about Carborundum. Students can study from this to prepare for exams.