Calcium Boride, CaB₆

Calcium Boride, CaB₆, may be obtained by heating lime with boron or by reducing calcium borate with aluminium in presence of carbon in the electric furnace, and also by the action of boric acid on calcium carbide. It may be prepared in a purer form by heating calcium with calcium metaborate under pressure and extracting with dilute acetic acid, followed by dilute hydrochloric acid, and finally hot water, when calcium boride is left as a light brown crystalline powder of density 2.11 at 18° C.

Its properties were studied by Moissan. It is hard enough to scratch ruby, and melts at the temperature of the electric arc.

It is attacked by halogens, but not by hydrogen at red heat. It burns when heated to bright redness in air. Below 1000° C. it is not attacked by water, but is slowly decomposed by halogen acids in the gaseous state at red heat. It reduces concentrated sulphuric acid with evolution of sulphur dioxide, and reacts with nitric acid and other oxidising agents.