Tetraboron carbide, B4C, is a very hard substance used for grinding purposes, ceramics, and armor plating. Because boron is an efficient absorber of neutrons, B4C is also used as a protective material in nuclear reactors. The reaction that forms B4C from boron(III) oxide, B2O3, is
2 B2O3 + 7 C → B4C + 6 CO (at 2400°C)