Tantalum Disulphide, TaS₂

Tantalum Disulphide, TaS₂, is most conveniently prepared by passing a dry mixture of hydrogen sulphide and carbon disulphide vapour over tantalum pentoxide between 900° and 1300° C. It has also been obtained by the action of carbon disulphide on tantalum pentoxide at a white heat, by the action of hydrogen sulphide on tantalum pentachloride, or by gently heating tantalum in sulphur vapour, but the true composition of the products in these cases is somewhat uncertain. Tantalum disulphide is a black powder with a metallic lustre; when heated above 1200° C. it forms yellowish crystals. It burns in air or oxygen with evolution of sulphur dioxide; the tantalum pentoxide simultaneously produced contains sulphuric anhydride. Hydrogen attacks it only feebly; chlorine does so more readily. It takes up traces of water, which it retains very firmly; at high temperatures the absorbed water reacts to form hydrogen sulphide and tantalum oxides. Concentrated solutions of potassium polysulphides and boiling hydrochloric acid are without action; it is slowly attacked by cold nitric acid, hydrofluoric acid, sulphuric acid, or a mixture of nitric acid and hydrofluoric acid; boiling nitric acid and aqua-regia oxidise it completely to tantalum pentoxide and sulphuric acid.