Properties: Hard, black, lustrous crystals. Hardness is lower than industrial diamond but higher than silicon carbide. Compared to most ceramics, it has lower fragility. Possesses a large thermal neutron capture cross-section. Highly resistant to chemical action. Not attacked by hot hydrofluoric acid or nitric acid. Soluble in molten alkalis, insoluble in water and acids. Relative density(d204)2.508～2.512. Melting point2350℃. Boiling point3500℃。

Boron carbide (boron carbide ), alias Black Diamond, with the molecular formulaB4C, usually a gray-black fine powder. It is one of the three hardest known materials (the other two being diamond and cubic boron nitride), used in tank armor, bulletproof vests, and many industrial applications. Its Mohs hardness is9.3。

Boron carbide can absorb a large number of neutrons without forming any radioactive isotopes, making it an ideal neutron absorber in nuclear power plants. Neutron absorbers are primarily used to control the rate of nuclear fission. In nuclear reactors, boron carbide is mainly made into control rods, but sometimes it is processed into powder form to increase its surface area.