Molybdenum Disilicide, MoSi₂

Molybdenum Disilicide, MoSi₂, may be prepared by heating a mixture of the oxides of molybdenum, silicon, and boron with metallic copper and aluminium in an arc furnace, cryolite being added as a flux and lime as a retarder to prevent the reaction becoming too violent; by heating a mixture of copper silicide, containing 50 per cent, silicon, and amorphous molybdenum in an electric furnace; or by igniting a mixture of molybdic anhydride, powdered aluminium, flowers of sulphur, and fine sand in a Hessian crucible by the Goldschmidt alumino-thermic method. Molybdenum disilicide crystallises in lustrous iron- grey prisms, of density 6.31 at 20.5° C. It remains unchanged when heated in air or in oxygen, and is very resistant to acids, although it readily dissolves in a mixture of nitric and hydrofluoric acids. It reacts with fluorine at ordinary temperatures, with chlorine at about 400° C., and slowly with bromine in presence of hydrogen at a red heat; it also dissolves in fused alkalies, and in mixtures of these with alkali nitrates and chlorates.