Iron subsilicide, Fe₂Si

Diferro silicide or Iron subsilicide, Fe₂Si, is the form in which silicon occurs in cast iron, and may be obtained in several ways: namely, (1) by heating iron in a porcelain dish brasqued with silicon; (2) by heating iron with 10 per cent, of silicon in an electric furnace; and (3) by similarly heating ferric oxide with excess of silicon.

It may also be prepared by heating iron in silicon tetrachloride vapour at 1100° C.: -

SiCl₄ + 4Fe = Fe₂Si + 2FeCl₂,

or by heating iron and copper silicide containing 10 per cent, of silicon.

Diferro silicide, as obtained by these methods, occurs as small prismatic crystals, possessed of metallic lustre, magnetic, and of density 7.00 at 22° C. Hydrogen fluoride attacks it readily, and aqua regia decomposes it, yielding silica and ferric chloride. Hot potassium hydroxide is without action on it. It is decomposed by chlorine with incandescence.