Tungsten Diphosphide, WP₂

Tungsten Diphosphide, WP₂ is prepared by heating tungsten hexachloride at 450° to 500° C. in a current of dry hydrogen phosphide. The product is washed with carbon disulphide to remove any free phosphorus present. The phosphide is obtained in black crystals, of density 5.8, insoluble in water, and in the usual organic solvents. It is stable in air, but decomposes on fusion. When heated in hydrogen to 600° C. partial reduction occurs, but at 900° C. phosphorus still remains, probably as the phosphide WP. The halogens react vigorously on heating; it burns brilliantly in oxygen at 450° C. Many metals reduce it to tungsten at high temperatures, e.g. copper, zinc, or iron at 1000° C. Hydrofluoric and hydrochloric acids do not attack it, but a mixture of either of these acids with nitric acid dissolves it readily. When fused with alkali carbonate, a mixture of phosphate and tungstate is obtained.