Silicon Carbide Applications and Advantages by Industry
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Material Properties That Drive the Applications
Silicon carbide is a covalent ceramic with a combination of hardness, thermal conductivity and high-temperature stability that few single materials match. Hardness is close to diamond, thermal expansion is low, and the material does not melt but dissociates at high temperature, which is why it can be used in contact with molten metal and in power electronics where heat removal limits performance.
| Property | Typical value for dense silicon carbide |
|---|---|
| Density | 3.21 g/cm3 |
| Mohs hardness | 9-9.5 |
| Knoop hardness | About 2,500 kg/mm2 |
| Elastic modulus | About 410 GPa |
| Flexural strength, sintered grade | 380-450 MPa |
| Coefficient of thermal expansion | About 4.0 x 10-6 per K |
| Thermal conductivity | 110-120 W/(m.K) for sintered material |
| Decomposition temperature | About 2,830 C |
Grades and Purity Classes
Silicon carbide is not one product. Metallurgical grade material produced in an Acheson-type resistance furnace contains 85-90% silicon carbide with iron, aluminium and free carbon as the balance, and it is sold for steelmaking and foundry use. Abrasive and refractory grades are refined to 97-99% silicon carbide. Sintered silicon carbide is a shaped engineering ceramic with controlled grain size and near-zero porosity, and semiconductor grade material is grown as single crystals of a specific polytype, most commonly 4H, with electronic-grade purity.
Abrasives and Machining
Silicon carbide is one of the two dominant abrasive grains, competing with fused alumina where a sharper, harder grain is required. It is used in bonded wheels and stones, in coated belts and papers, in blasting media and in non-slip surface products. Grain is classified by size designation rather than by a physical measurement alone, and the standardised FEPA 42-1 grain size series is the reference used when wheels and coated products are ordered across borders. Chemical analysis of abrasive grade grain, including free silicon, free carbon and total silicon carbide content, is performed against a recognised method such as ISO 9286, and the certificate of analysis normally accompanies each lot.
Refractories and Metallurgical Use
Silicon carbide refractories resist thermal shock, molten metal and slag attack, and they conduct heat, so they appear in blast furnace linings and taphole areas, in aluminium reduction cell side walls, in kiln furniture and in burner nozzles. In steelmaking and foundry practice, silicon carbide is added as a deoxidiser and as a carbon and silicon carrier, and it offers an advantage over separate silicon and carbon additions because both elements are delivered in the same particle. It also dissolves more smoothly than graphite in iron melts, which reduces the risk of carbon flotation.
Semiconductor and Optoelectronic Applications
Single-crystal silicon carbide is a wide bandgap semiconductor. The 4H polytype has a bandgap of about 3.26 eV, a breakdown field in the region of 3 MV/cm and a thermal conductivity near 490 W/(m.K), all substantially better than silicon. Those figures translate into devices that switch at higher voltages and run hotter without derating, which is why silicon carbide Schottky diodes and MOSFETs are used in traction inverters, photovoltaic converters and fast chargers. The same material forms the substrate for light emitting diodes, where its wide bandgap allows blue and ultraviolet emission. Substrate diameters of 150 mm and larger are in volume production, and surface preparation, polishing and epitaxial layer quality are the critical process steps.
Advantages Over Competing Materials
Against fused alumina, silicon carbide is harder and far more thermally conductive, so it removes heat from a cutting zone faster and holds an edge longer in hard, low-ductility workpieces; alumina remains the better choice for steel at high grinding pressure because of its tougher grain structure. Against tungsten carbide it is much lighter and keeps its hardness at higher temperature, which matters for wear parts that must not add rotating mass. Against graphite it is harder, far more wear resistant and chemically inert to a wider range of melts. The limitation is inherent brittleness: silicon carbide has almost no plastic deformation, so designs must avoid point loading and sharp section changes.
Frequently Asked Questions
Q: What is the density of silicon carbide?
A: About 3.21 g/cm3 for fully dense material. Porosity in sintered or reaction-bonded grades lowers the measured value, and the density figure is a useful quality indicator.
Q: At what temperature does silicon carbide fail?
A: It does not melt in the usual sense; it dissociates at approximately 2,830 C. In service the practical limit is set by oxidation and by the bond phase in the product rather than by the temperature alone.
Q: Which grade is used in steelmaking?
A: Metallurgical grade silicon carbide at 85-90% silicon carbide content, supplied as lump or granules, is added as a deoxidiser and as a combined silicon and carbon carrier.
Q: Why is silicon carbide used instead of silicon in power devices?
A: Wide bandgap, high breakdown field and high thermal conductivity allow a much thinner, more lightly doped drift layer, so the device blocks higher voltage with lower conduction loss and can run at higher junction temperature.
Q: Can silicon carbide parts be machined after sintering?
A: Only with diamond tooling and slow, controlled removal rates, and near-net shape forming before sintering is strongly preferred because the finished material is extremely hard and brittle.
