Uranium Disulphide, US₂

Uranium Disulphide, Uranous Sulphide, US₂, is formed when metallic uranium is heated in sulphur vapour at 500° C.; at higher temperatures the uranium burns, yielding the same product. It is also produced when uranous chloride is heated to redness in a current of hydrogen sulphide; or better, by heating the less volatile double chloride, Na₂UCl₆, in carefully dried hydrogen sulphide, or hydrogen laden with sulphur vapour, the disulphide being separated from sodium chloride by rapidly washing the product in cold boiled water; or the sodium uranium chloride may be fused with certain sulphides, preferably stannous sulphide, but those of sodium, aluminium, magnesium, or antimony may be used, in a slow stream of dry hydrogen. If moisture is not rigorously excluded in these operations some uranyl sulphide is formed.

Uranium disulphide obtained from uranous chloride is a greyish- black amorphous powder. As prepared by Colani from the double chloride, it yields black to iron-grey lustrous crystals belonging to the tetragonal system, a:c = 1:0.6152. It may be heated to 1000° C. without decomposition or fusion. It oxidises in air to uranyl sulphide, and deflagrates at higher temperatures. It is decomposed by steam at red heat. It is fairly stable towards cold water, but is rapidly decomposed by dilute acids, nitric acid reacting very violently with formation of uranyl sulphate.

A hydrated uranium disulphide is obtained as a black precipitate when a solution of a uranous salt is treated with an alkali sulphide. It is unstable and oxidises on exposure to air.