Physical Properties of Silicon Carbide
Silicon carbide is one of the hardest industrial materials after diamond and boron carbide, and its strong covalent bonding gives it excellent mechanical and thermal performance. The Mohs hardness is approximately 9.0 to 9.5, the density is 3.1 to 3.3 g per cubic centimeter, the decomposition temperature is above approximately 2700 degrees C, the thermal conductivity is about 120 to 270 W per meter per kelvin depending on crystal type and purity, thermal expansion is low with excellent thermal shock resistance, and the electrical behavior is semiconducting, varying with purity, crystal structure, and temperature.
High Hardness and Wear Resistance
The Mohs hardness of approximately 9.0 to 9.5 makes SiC suitable for grinding wheels, cutting abrasives, wear-resistant components, and ceramic engineering parts, maintaining performance under severe mechanical wear conditions.
High-Temperature Stability
SiC maintains structural stability under extremely high temperatures with a decomposition temperature above 2700 degrees C, excellent thermal shock resistance, and a low thermal expansion coefficient. These properties make it suitable for furnace components, kiln furniture, and high-temperature refractory products. High thermal conductivity improves heat transfer efficiency, temperature uniformity, and thermal management performance.
Chemical Properties and Oxidation Behavior
Silicon carbide has excellent chemical stability, generally resisting hydrochloric acid, sulfuric acid, and many corrosive environments, with good resistance against alkaline environments at normal temperatures. When exposed to oxygen at high temperatures, SiC undergoes two oxidation stages: active oxidation at about 600 to 900 degrees C forms gaseous products, while passive oxidation above about 1000 degrees C forms a protective silicon dioxide layer on the surface that slows further oxidation and improves high-temperature durability.
Metallurgical Reactivity and Type Differences
In steelmaking and foundry applications, SiC acts as a combined silicon and carbon source for silicon addition, carbon adjustment, deoxidation support, and improved metal cleanliness. Green SiC offers higher purity and hardness for precision abrasives and advanced ceramics; black SiC offers toughness and cost effectiveness for metallurgy, refractories, and general abrasives; fine powder improves sintering behavior; and metallurgical SiC serves steelmaking and carburizing. Purity requirements range from 85 to 99 percent for steelmaking, medium to high for refractories, high for abrasives, and ultra-high, typically 99.99 percent or more, for semiconductors.
Frequently Asked Questions
Q: What is the hardness of silicon carbide?
A: Approximately 9.0 to 9.5 Mohs, one of the hardest industrial materials.
Q: Does silicon carbide melt?
A: At atmospheric pressure it does not melt normally; it decomposes above about 2700 degrees C.
Q: What is the thermal conductivity?
A: About 120 to 270 W per meter per kelvin depending on type and purity.
Q: How does SiC resist oxidation?
A: Above about 1000 degrees C a protective SiO2 layer forms and slows further oxidation.
Q: What does SiC do in steelmaking?
A: It provides silicon and carbon for deoxidation, carburization, and molten metal treatment.
Q: What purity is required for semiconductors?
A: Ultra-high-purity electronic grade, generally 99.99 percent or more.
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