What Is Silicon Carbide?

Silicon carbide (SiC) is a hard chemical compound of silicon and carbon. Commonly referred to as carborundum, it occurs naturally as the rare mineral moissanite and has been manufactured as powder or crystal since 1893 for use as an abrasive.

Industrially produced by the Acheson process in which pure silica sand and ground coke are heated together at high temperatures to form yellow to green to bluish-black crystals that sublimate with decomposition at 2700degC and have a density of 3.21g/cm3.

Thermodynamics

Silicon carbide (SiC), is an alloy composed of pure silicon and carbon that is commonly manufactured as an abrasive and in ceramics for use as an abrasive. While naturally found as moissanite gemstone, SiC is increasingly being utilized by electronic devices at high temperatures or voltages such as light emitting diodes and detectors that utilize its properties.

Physical Vapor Transport (PVT) in silicon carbide requires both thermodynamics and chemical kinetics for its understanding, with thermodynamics providing information on reaction feasibility, end products, reaction stability and reaction kinetics highlighting their dynamic nature.

In this study, we study the structural, thermodynamic and dynamic properties of a-SiC liquid phase by performing ab initio molecular dynamics simulations with density functional theory (DFT). Our simulation results indicate that it melts evenly as one phase at all pressures simulated; which corresponds with experimental observations. Calculated melting temperatures closely reflect those measured experimentally; furthermore lines between silicon and carbon do not appear in any diffraction patterns.

Results also demonstrate that a-SiC boasts the lowest sublimation enthalpy among non-oxide engineering ceramics in this database, and has the highest diffraction energy at room temperature compared with any of them. These findings suggest it can be an ideal material choice for applications requiring high thermal conductivity with limited expansion.

Chemical Reactions

Silicon Carbide (SiC) is a hard and tough material with excellent electrical properties. With a higher temperature range than many semiconductors, SiC makes for ideal high-temperature applications such as jet engines and nuclear reactors, as well as grinding wheels and cutting tools due to its superior strength, wear resistance, thermal conductivity and electrical field withstanding capabilities compared to silicon.

Commercially available SiC comes in two forms, alpha and beta. The former boasts a hexagonal crystal structure similar to Wurtzite and is the more commonly encountered polymorph. Zin blende is less frequently encountered but still found at some facilities; due to its lower melting point and toughness it has limited industrial uses; but has found some applications as support material for heterogeneous catalysts.

SiC is notable for having an exceptionally wide bandgap between its valence and conduction bands, commonly referred to as its bandgap. Ceramic materials offer many advantages over other semiconductors, which only conduct electricity when electrons move from their valence band into their conduction band. Furthermore, this property makes ceramic an excellent choice for environments requiring strong yet durable ceramic solutions. At present, two types of silicon carbide are available for industrial use: sintered silicon carbide (SSiC) and reaction bonded silicon carbide (RBSiC). SSiC can be produced by pressing and sintering SiC powder together under heat and pressure while RBSiC requires reacting a mixture of SiC, binder materials and liquid silicon in an electric furnace reducing furnace. Both methods offer distinct advantages; however SSiC offers greater cost effectiveness compared to its RBSiC counterpart. Both types come equipped with advantages; however SSiC offers greater affordability when it comes to production costs compared with its counterpart RBSiC counterpart.

Stability

Silicon Carbide (SiC) is an extremely stable non-oxide ceramic material with exceptional thermal, electrical and mechanical properties. Due to its high temperature strength and Mohs hardness (9 near diamond), low thermal expansion rate and chemical reaction resistance it makes SiC an attractive material choice for high temperature components such as reactors, furnace parts, car brakes/clutches/clutches and bulletproof vests. SiC also functions well as a semiconductor material due to its wide band gap which makes it suitable for nuclear reactors due to radiation damage tolerance making SiC ideal.

Stability in these structures comes from two factors. First is their symmetric structure which prevents formation of fragile crystal grains; and secondly is due to large stabilizing forces within their atomic matrix caused by bonding between silicon atoms and carbon, creating threefold coordination among adjacent atoms for better bonding between layers making dislodgement or destruction more difficult.

SiC’s stability is further strengthened by its wideband-gap semiconductor properties, high strength, excellent thermal shock resistance, and abrasion resistance. Due to these features, SiC makes an ideal material choice for extreme engineering applications such as pump bearings, valves, injectors for abrasive sandblasting injectors and extrusion dies.

Applications

Silicon carbide has many applications. As a hard, durable non-oxide ceramic with desirable properties such as high oxidation resistance, dimensional stability, chemical stability and mechanical strength it has several applications including protective coating for nickel superalloy turbine blades and nozzle vanes as well as use in industrial abrasives, ceramics and hard metal cutting tools.

Pure SiC is typically an electrical insulator but can be made more conductive through doping. Its tough material with excellent wear resistance withstands very high temperatures and pressures while serving as an excellent refractory material with multiple engineering applications such as bricks, machinery components and electronic devices.

Reaction Bonded (RB) Silicon Carbide (SiC) is made by infiltrating molten silicon into porous carbon that has been packed in the desired shape with heat and pressure, yielding a ceramic that provides excellent thermal, chemical and wear resistance and comes in various shapes and sizes for use as mechanical seals, bearings or larger wear parts for mining or pump equipment; or into refractory bricks used as industrial construction material at high temperatures; additionally it’s often the go-to material for gas turbine engine nozzles/blades due its ability to handle heat/pressure conditions.