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Tungsten disulfide is a compound of tungsten and sulfur, chemical formula WS2, molecular weight 247.97, the state of black-gray powder.Slightly soluble in cold water, soluble in hot water . It is insoluble in hydrochloric acid and alkali (except for concentrated nitric acid and hydrofluoric acid). Soluble in molten alkali, insoluble in alcohol. The density is 7.6g/ ml. It is reductive and can react with strong oxidants such as hot concentrated sulfuric acid, nitric acid and aqua regia. It can be converted into WO3 by heating in air or oxygen. It can be decomposed into tungsten and sulfur when heated to 1250 degrees in vacuum.
Tungsten disulfide (WS2) in bulk has been used for many years as a dry lubricant due to how it exhibits properties of a low coefficient of friction, high chemical stability, and thermal stability. Like MoS2, the band-gap of WS2 change from an indirect band-gap of 1.4eV to a direct band-gap of 2eV when changing from a bulk material to a 2-D material. Due to its band-gap, WS2 is seen as a significantly interesting material for many areas of application.
WS2 possesses a high on/off ratio in field-effect transistors, controllable spin and valley polarisation, strong geometrical confinement of excitons, and tunable photoluminescence. Additionally, WS2 could lead to increased interest in areas such as photodetectors and multi-junction photovoltaics.
Besides, WS2 is used, in conjunction with other materials, as catalyst for hydrotreating of crude oil.
Lamellar tungsten disulfide is used as a dry lubricant for fasteners, bearings, and molds under the brand name Dicronite.