Magnesium Boride

Dark, impure magnesium borides were obtained by heating boron trioxide and magnesium in appropriate proportions, or with the oxide in excess, by heating magnesium in boron trichloride vapour, and by heating magnesium and boron in a current of hydrogen or alone. Hydrochloric and nitric acids liberated impure boron hydride from them.

According to Winkler, Mg₉B₂ was produced when magnesium was heated with boron trioxide in hydrogen, and Mg₂B₅ when magnesium and borax were heated together. Moissan distinguished an unstable boride, decomposed by water, from a stable form that resisted the action of water, hydrochloric acid, and nitric acid. He obtained the latter in crystalline form by heating magnesium with excess of boron trioxide.

According to Ray, only Mg₃B₂ is produced at a red heat and under normal pressure. It is produced by heating magnesium with amorphous boron, or by heating magnesium and boron trioxide in a current of hydrogen. It dissolves in dilute hydrochloric acid and decomposes when heated.