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Tungsten disulfide, also known as WS 2, is a layered material with a band-gap similar to graphene. It is a low-dimensional transition metal sulfide with applications in optoelectronics, lubrication and energy storage.
WS2 has a hexagonal crystalline structure similar to molybdenum disulfide. It has six tungsten atoms covalently bound to six selenium ligands in a trigonal prismatic coordination sphere. The tungsten-selenium bonds are coiled and have a length of 0.2526 nm. They are surrounded by van der Waals interactions between the layers.
It is a brittle material and has a high density of 7.6 g/cm3. When heated to 1250 °C, it decomposes into tungsten and sulfur.
Tungsten disulfide (WS2) in bulk has long been used as a dry lubricant for a variety of applications including machine tools, motors and transmissions, plastic injection molding and more. Its low coefficient of friction, chemical stability and thermal stability make it a great choice for harsh environments.
Various synthesis methods can be used to produce WS2. Roasting decomposition is one of the most common methods, but direct synthesis using a combination of concentrated sulfuric acid and hydrofluoric acid has been reported.
Other synthesis methods include hydrogen reduction and alkali-reduction reactions. WS2 can be used as a catalytic agent and for reducing gas separation in petroleum processes.
The use of tungsten disulfide in dry lubricants began in the 1960s when NASA engineers needed a dry lubricant that could be used during space missions and other extreme conditions. WS2 has since become an integral part of many products in the aerospace industry and beyond.