Silicon Carbide Ceramic Properties

Engineering variability

• Saint-Gobain publishes approximately 410 GPa on general Hexoloy SA material/application pages and 430 GPa on several finished-shape datasets; this reference therefore shows 410–430 GPa rather than a false single constant.
• Strength is flaw-statistical and depends on surface finish and test method.
• Thermal conductivity decreases substantially with temperature.
• Different SiC processing routes—sintered, siliconized, nitride-bonded, recrystallized—have different properties.
• Oxidizing/non-oxidizing atmosphere changes usable high-temperature limits.

Selection note

Excellent for seals, semiconductor equipment, heat-transfer parts, furnace fixtures, armor and chemically aggressive wear components.

Where a property is shown as qualitative rather than numeric, that is intentional: the selected source or the material physics does not justify a single comparable scalar.

Where it is specified

Mechanical seal faces and bearings in pumps handling abrasive or poorly lubricating fluids, kiln furniture and burner nozzles, heat exchanger tubes for aggressive chemistry, ballistic armour, abrasive grit and grinding wheels, and diesel particulate filters.

Separately and increasingly, SiC as a wide-bandgap semiconductor for power electronics — electric vehicle traction inverters, solar inverters, rail traction — where it enables higher voltage, higher temperature and higher switching frequency than silicon.

Form matters as much as composition: sintered SiC (SSiC) is fully dense, chemically resistant and used for seals and chemical duty; reaction-bonded SiC (RBSiC) contains free silicon, is cheaper, near-net-shape and dimensionally accurate but limited to about 1350 °C and attacked by alkalis.

Chosen over what

Against alumina: far better thermal conductivity (roughly 120–200 W/m·K against 30), better thermal shock resistance and greater hardness, at higher cost. For a seal face running dry or with poor lubrication, SiC's ability to conduct frictional heat away is decisive.

Against tungsten carbide for seal faces: SiC is lighter, harder, chemically inert and does not rely on a cobalt binder that acids attack. WC is tougher and less prone to chipping.

Against silicon in power devices: roughly three times the bandgap and ten times the breakdown field, allowing thinner drift regions, much lower on-resistance at high voltage, and operation above 200 °C.

How it fails

Brittle fracture and chipping, particularly at edges. Seal faces fail at handling damage and at edge chips rather than by wear.

Oxidation above 1200–1600 °C. A protective silica layer forms in dry oxidising conditions (passive oxidation), but in low-oxygen or wet conditions the silica volatilises — active oxidation — and material is lost rapidly. Water vapour in combustion gas accelerates recession, which is the central problem for SiC in gas turbines.

Alkali attack, especially on reaction-bonded grades, where free silicon is preferentially dissolved.

Thermal shock is far better than alumina but not unlimited; rapid quenching still cracks it.

Fabrication notes

Extremely difficult to machine after firing. Only diamond grinding and lapping are practical, and the cost is high enough that near-net-shape forming is the norm. Reaction bonding is favoured partly because it produces accurate shapes with minimal shrinkage.

Sintering requires boron and carbon additions and temperatures above 2000 °C in inert atmosphere; SiC does not densify easily by itself.

Lapping to optical flatness is standard for seal faces, and flatness of a few helium light bands is what determines whether a seal leaks.

In semiconductor use the challenge is crystal quality: micropipe and basal plane dislocation densities historically limited device yield, and wafer cost remains the main barrier against silicon.