Silicon carbide (SiC) is a nonoxide ceramic used in numerous thermally demanding applications. Harder than diamond and aluminum oxide, SiC is widely utilized as an abrasive material due to its extreme hardness, as well as in refractories for its heat resistance.
Washington Mills offers various varieties and sizes of SiC produced through electric furnace reaction between silica sand and carbon.
Hardness
Silicon carbide (SiC) is a hard chemical compound composed of silicon and carbon that occurs naturally as the mineral moissanite; however, since 1893 mass production as powder and crystal has made this hard substance accessible. Grains of SiC can also be fused together through sintering to produce extremely hard ceramics for use in products like car brakes and clutches; alternatively it can also serve as raw material in producing semiconductor materials.
Washington Mills offers an array of high-quality green and black Silicon carbide samples to test new applications of this versatile material. Green Silicon carbide is commonly used as an abrasive in grinding wheels and cutting tools due to its hardness and thermal properties; additionally, it makes an excellent raw material for the creation of refractories due to its exceptional toughness and resistance against wear.
SiC is widely recognized for its superior hardness and corrosion-resistance. Chemically inert, SiC is used in many refractory products including blast furnace linings, muffles, and kiln furniture as well as for thin filament pyrometry crucibles and other high temperature applications.
WC and SiC possess low neutron cross-sections, making them excellent candidates for use in nuclear reactor construction. Their unique properties also make them popular abrasives or reinforcement materials in composite material compositions.
Flexural strength of concrete can be dramatically increased by adding small percentages of both WC and SiC into its mixture, according to research conducted by its lead author of this article. Their research indicates that increasing percentages of these carbides correlate directly to increased flexural strength.
This encouraging result provides the basis for creating special concrete with enhanced mechanical properties, but further investigation needs to be conducted on higher percentages of both WC and SiC to confirm these results; this can be done through examining X-ray micrographs of calcined and sintered composites, and studying their behavior as neutron shielding materials or electromagnetic radiation barriers within nuclear reactors.
Thermal Conductivity
Silicon carbide boasts high thermal conductivity, enabling it to absorb and transmit large amounts of energy at very high temperatures. Due to this quality, silicon carbide has many applications across many fields of industry – ranging from abrasives and polishing powders to high temperature industrial machinery. Its resistance to corrosion also makes it an attractive material choice.
With its low thermal expansion coefficient and hardness, rigidity, and thermal conductivity properties, carbon fiber makes an excellent material choice for mirrors used on large astronomical telescopes, like Herschel Space Telescope mirrors as well as spacecraft subsystems. Furthermore, carbon fibre is often employed as an abrasive and grinding media material in many grinding operations.
The high thermal conductivity of this compound can be attributed to its close-packed structure of covalently bonded Si and carbon atoms in a hexagonal lattice, enabling atoms to share electrons more freely while reducing chemical reactivity. Furthermore, crystals formed within this close pack possess high surface area as well as melting points that significantly exceed typical material properties.
Sintered silicon carbide forms a dense body with a low thermal expansion coefficient and very high tensile strength, producing shapes ranging from irregular grits to flat sheets or wafers in an assortment of sizes and shapes. Furthermore, silicon carbide powder can also be transformed into an array of abrasives and polishing powders with grain size distributions from very coarse pieces of 1/2″ diameter up to 20-100 nanometer particles for use as polishers and abrasives.
Edward Acheson first synthesized silicon carbide artificially in 1891 while trying to produce synthetic diamonds. While conducting his experimentation he discovered small blue crystals in an electrically heated mixture of clay and powdered coke which he named carborundum; later discovered it contained carbon and silicon compounds similar to corundum. Nobel Prize winner Henri Moissan later discovered natural silicon carbide deposits at Diablo Canyon, Arizona where he noted its hard and brilliant surface qualities similar to diamond.
Modern production methods for silicon carbide used in abrasives and metallurgical industries involve mixing pure silica sand with ground coke in an electric furnace, placing a carbon conductor as an electrode, passing an electrical current through it, causing chemical reactions that yield SiC and carbon monoxide gas; then grinding/sifting off impurities before finally producing a fine powder for use in these fields.
Resistance to Corrosion
Silicon carbide powder offers excellent resistance to corrosion from various acids such as hydrofluoric, nitric and sulfuric acids, as well as strong erosion protection in liquid environments, including molten salt and alkali solutions.
These characteristics make abrasive material an appealing option in several abrasive machining processes. Abrasives such as silicon carbide are commonly employed for making sandpaper and grinding wheels, cutting tools, refractory linings for industrial furnaces with high temperature applications (refractories), wear-resistant parts for mining equipment such as pumps and wear-resistant parts for wear detectors (LEDs and detectors), as well as wear resistant semiconductor components (light emitting diodes (LEDs). Furthermore, silicon carbide can endure various chemical and mechanical stressors without failure; therefore it makes this material suitable for many different tribological applications where chemical and mechanical stresses must be tolerated without breaking.
Corrosion resistance of materials depends both on their structure and on the presence of impurities such as iron, aluminum and calcium impurities. Sintered SiC’s corrosion resistance is dictated by its high content of a-form silicon carbide which is more resistant to corrosion than its commercially available counterpart b-form silicon carbide products.
Additionally, the crystalline nature of a-form silicon carbide helps prevent it from dispersion into solution and therefore limits the number of pores on its surface. This prevents the formation of protective oxide scale and minimizes its susceptibility to chemical attack even in presence of oxygen.
Silicon carbide’s a-form is particularly stable at higher temperatures and has much greater strength compared to its weaker-performing b-form, making it suitable for high temperature tribological applications such as sealing and bearings.
Moissanite jewels were among the earliest recorded uses of silicon carbide a-form, made by mixing together sand and carbon extracted from corundum deposits such as those found in kimberlite. Although some mines still produce this form of silicon carbide today, most silicon carbide manufactured today is synthetically manufactured – natural moissanite can still be found in small amounts in meteorites, corundum-rich igneous rocks or diamond deposits.
Chemical Resistance
Silicon carbide is one of the hardest materials on Earth. Its Mohs hardness scale rating falls between that of alumina (9), and diamond (10). Silicon carbide boasts numerous desirable attributes including chemical inertness, thermal conductivity, low coefficient of expansion and wear resistance which make it suitable for an array of applications and refractory materials; its superior strength at high temperatures also making it an attractive material choice; electronic devices also rely on it due to its ability to withstand thermal shock.
Silicon carbide’s chemical structure consists of tightly packed carbon and silicon atoms covalently bonded together in tetrahedral units by covalent bonds that form polytypes, or linked at their corners to form polytypes, linked by links at corners and stacked to form polar structures, providing inherent corrosion protection in most environments. Silicon carbide has excellent insolubility in water, alcohol and acid environments while remaining resistant to most organic and inorganic salts and acids with the exception of hydrofluoric acid or acid fluorides.
Silicon carbide processing routes yield different external and internal microstructures that result in various properties, including low expansion and good thermal conductivity. Sintering of silicon carbide produces an exceptionally hard ceramic with very low expansion, known as synthetic moissanite. Large single crystals produced via the Lely method may also be cut into gems known as synthetic moissanite gems.
Silicon carbide powder is made by reacting a mixture of carbon and silica in electrical resistance furnaces at temperatures between 1700-2500degC, then crushing and grading into finished sizes such as grains or powders for various uses. Unfortunately, production costs can be costly due to energy requirements for crushing and purification costs for ground powder; attrition; heating of furnaces and attrition of production processes.
Washington Mills offers CARBOREX(r) silicon carbide in various chemistries and particle sizes to address a wide range of applications, such as Abrasive Blasting, Anti-Slip Coated Abrasives Grinding Wheels Cutting Tools Refractories Refractories Wiresawing. Contact our team of experts to explore possibilities for your application!