Tungsten Sesquisilicide, W₂Si₃

Tungsten Sesquisilicide, W₂Si₃, is obtained by heating a mixture, containing 10 parts of silicon and 23 parts of tungstic anhydride, in an electric furnace. The product is suspended in dilute hydrochloric acid, and the excess of free tungsten removed by electrolysis; the silicide collects at the bottom of the vessel and is treated successively with aqua regia, ammonia, and hydrofluoric acid, any carbon silicide present being finally removed by means of methylene iodide. It forms lustrous steel-grey plates, of density 10.9. It is fusible at red heat and readily oxidises; in oxygen it burns brilliantly at 500° C. The halogens attack it at comparatively low temperatures. On the other hand, it is very resistant to acids and alkalies in solution; aqua regia has practically no action, but a mixture of nitric and hydrofluoric acids decompose it even at ordinary temperatures, whilst fused alkali hydroxides and carbonates also attack it readily.