Tungsten disulfide

Tungsten disulfide is an inorganic chemical compound composed of tungsten and sulfur with the chemical formula WS2. This compound is part of the group of materials called the transition metal dichalcogenides. It occurs naturally as the rare mineral tungstenite. This material is a component of certain catalysts used for hydrodesulfurization and hydrodenitrification. WS2 adopts a layered structure similar, or isotypic with MoS2, instead with W atoms situated in trigonal prismatic coordination sphere (in place of Mo atoms). Owing to this layered structure, WS2 forms non carbon nanotubes, which were discovered after heating a thin sample of WS2 in 1992.]] Bulk WS2 forms dark gray hexagonal crystals with a layered structure. Like the closely related MoS2, it exhibits properties of a dry lubricant. Although it has long been thought that WS2 is relatively stable in ambient air, recent reports on the ambient air oxidation of monolayer WS2 have found this to not be the case. In the monolayer form, WS2 is converted rather rapidly (over the course of days in ambient light and atmosphere) to tungsten oxide via a photo oxidation reaction involving visible wavelengths of light readily absorbed by monolayer WS2 (< ~660 nm; > ~1.88 eV). In addition to light of suitable wavelength, the reaction likely requires both oxygen and water to proceed, with the water thought to act as a catalyst for oxidation. The products of the reaction likely include various tungsten oxide species and sulfuric acid. The oxidation of other semiconductor transition metal dichalcogenides (S TMDs) such as MoS2, has similarly been observed to occur in ambient light and atmospheric conditions. WS2 is also attacked by a mixture of nitric and hydrofluoric acid. When heated in oxygen containing atmosphere, WS2 converts to tungsten trioxide. When heated in absence of oxygen, WS2 does not melt but decomposes to tungsten and sulfur, but only at 1250 °C. WS2 also undergoes exfoliation by treatment with various reagents such as chlorosulfonic acid

WS2 is produced by a number of methods. Other routes entail thermolysis of tungsten(VI) sulfides (e. g., (R4N)2WS4) or the equivalent (e. g., WS3).

WS2 is used, in conjunction with other materials, as catalyst for hydrotreating of crude oil. as well as having significant use in aerospace and military industries. WS2 can be applied to a metal surface without binders or curing, via high velocity air impingement. The most recent official standard for this process is laid out in the SAE International specification AMS2530A.

Tungsten disulfide is the first material which was found to form non carbon nanotubes, in 1992. The addition of WS2 nanotubes to epoxy resin improved adhesion, fracture toughness and strain energy release rate. The wear of the nanotubes reinforced epoxy is lower than that of pure epoxy. WS2 nanotubes are hollow and can be filled with another material, to preserve or guide it to a desired location, or to generate new properties in the filler material which is confined within a nanometer scale diameter. To this goal, non carbon nanotube hybrids were made by filling WS2 nanotubes with molten lead, antimony or bismuth iodide salt by a capillary wetting process, resulting in PbI2@WS2, SbI3@WS2 or BiI3@WS2 core–shell nanotubes. Such materials exhibit room temperature photoluminescence in the monolayer limit.

Taiwan Semiconductor Manufacturing Company (TSMC) is investigating use of as a channel material in field effect transistors. The approximately 6 layer thick material is created using chemical vapor deposition (CVD).