Tungsten Disulphide, WS₂

Tungsten Disulphide, WS₂, occurs native in the mineral tungstenite. It may be prepared by heating tungsten hexa-chloride in a current of hydrogen sulphide at 375° to 550° C.; by fusing together pure dry potassium carbonate, flowers of sulphur, and tungsten trioxide; or by strongly heating tungsten trioxide with excess of mercuric sulphide, or with sodium thiosulphate, or (with or without the addition of carbon) in a current of hydrogen sulphide, or of sulphur or carbon disulphide vapour. It is also formed by direct synthesis, by strongly heating metallic tungsten and sulphur.

Tungsten disulphide is a soft, lustrous, dark grey crystalline powder, of density 7.5 at 10° C. When heated in air it yields the trioxide, but if heated out of contact with air it loses sulphur only at high temperatures, the temperature of the electric furnace being necessary to reduce it to the metal. When heated in hydrogen it is completely reduced at 800° to 900° C. It is attacked by fluorine at ordinary temperatures, yielding the fluoride. Chlorine at 400° C. yields tungsten hexachloride. Bromine attacks the sulphide at 700° C. Hydrogen chloride has no action.

The disulphide is insoluble in water and in most acids. Aqua regia has little action; but a mixture of nitric acid and hydrofluoric acid dissolves it readily. It is readily decomposed by molten alkalies.