Boron carbide (chemical formula B4C) is an extremely hard ceramic material used in tank armor, bulletproof vests, and numerous industrial applications. With a hardness of 9.3 on the mohs scale, it is the fifth hardest material known behind boron nitride, diamond, ultrahard fullerite, and aggregated diamond nanorods.
Discovered in the 19th century as a by-product of reactions involving metal borides, however, its chemical formula was unknown. It was not until the 1930s that the formula was determined to be B4C. Boron carbide is now produced industrially by the carbo-thermal reduction of B2O3 (boron oxide) in an electric arc furnace.
Its ability to absorb neutrons without forming long lived radionuclides makes the material attractive as an absorbent for neutron radiation arising in nuclear power plants. Nuclear applications of boron carbide include shielding, control rod and shut down pellets. Within control rods, boron carbide is often powdered, to increase its surface area.