Tungsten Disilicide, WSi₂

Tungsten Disilicide, WSi₂, is obtained by heating together copper silicide and amorphous tungsten in an electric furnace. The product is washed and treated successively with nitric acid, sodium hydroxide, warm hydrofluoric acid, and water. It may also be obtained by the aluminothermic process, by ignition of a mixture containing 45 grams tungstic anhydride, 180 grams silica, 250 grams sulphur, and 200 grams aluminium, the product being purified by successive treatment with hydrochloric acid, sodium hydroxide, and hydrofluoric acid. Tungsten disilicide yields lustrous, light grey prisms, probably dimorphous, of density 9.4 at 0° C. The crystals are non-magnetic and are more stable than the silicide W₂Si₃. Fluorine only attacks the disilicide when slightly heated; chlorine reacts at 450° C., yielding silicon tetrachloride and tungsten hexachloride. It may be heated in air to 900° C. without change. It is slowly oxidised when heated in a current of oxygen. It is decomposed by a mixture of nitric and hydrofluoric acids, or by fused alkalies.