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Tungsten disulfide

Names
IUPAC name Bis(sulfanylidene)tungsten
Systematic IUPAC name Dithioxotungsten
Other names Tungsten(IV) sulfide Tungstenite
Identifiers
CAS Number	12138-09-9
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30521
ChemSpider	74837
ECHA InfoCard	100.032.027
PubChem CID	82938
CompTox Dashboard (EPA)	DTXSID2065256
InChI InChI=1S/2S.WKey: ITRNXVSDJBHYNJ-UHFFFAOYSA-N InChI=1S/2S.WKey: ITRNXVSDJBHYNJ-UHFFFAOYSA-N
SMILES S==S
Properties
Chemical formula	WS2
Molar mass	247.98 g/mol
Appearance	blue-gray powder
Density	7.5 g/cm, solid
Melting point	1250 °C decomp.
Structure
Crystal structure	Molybdenite
Coordination geometry	Trigonal prismatic (W) Pyramidal (S)
Related compounds
Other anions	Tungsten(IV) oxide
Other cations	Molybdenum disulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). N verify (what is  ?) Infobox references

Tungsten(IV) sulfide is the chemical compound with the formula WS₂. It occurs naturally as the rare mineral called tungstenite. This material is a component of certain catalysts used for hydrodesulfurization and hydrodenitrification.

WS₂ adopts a layered structure related to MoS₂, with W atoms situated in trigonal prismatic coordination sphere. Owing to this layered structure, WS₂ forms inorganic nanotubes, which were discovered on example of WS₂ in 1992.

Properties

Bulk WS₂ forms dark gray hexagonal crystals with a layered structure. They are not chemically active and can only be dissolved by a mixture of nitric and hydrofluoric acids. When burned 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 at 1250 °C.

Synthesis

WS₂ is produced by a number of methods:

• Hydrothermal synthesis
• Gas phase reaction of H₂S or H₂S/Ar mixture with tungsten metal
• Reduction of ammonium tetrathiotungstate ((NH₄)₂WS₄) at ~1300 °C in a flow of hydrogen gas
• Direct decomposition of various tetraalkylammonium tetrathiotungstate precursors in inert gas atmosphere.
• Microwave treatment of a solution of tungstic acid, elemental sulfur and monoethanolamine.
• Heating WS₃ in absence of oxygen (otherwise the product is tungsten trioxide).
• Melting a mixture of tungsten trioxide, potassium carbonate and sulfur.

Uses

Nanostructured WS₂ finds application as hydrogen and lithium storage material, as material for solid-state secondary lithium battery cathodes; as a component of batteries and other electrochemical devices; as a dry lubricant; and as catalyst in hydrodesulfurization of crude oil. WS₂ also catalyses production of carbon monoxide

CO₂ + H₂ → CO + H₂O

bringing the reaction yield to the level above 99.9%.

Nanotubes

Tungsten disulfide is the first material which was found to form inorganic nanotubes, in 1992. This ability is related to the layered structure of WS₂, and macroscopic amounts of WS₂ have been produced by the methods mentioned above. Apart from scientific interest, these nanotubes are studied for potential applications. The addition of WS₂ nanotubes to epoxy resin improves adhesion, fracture toughness and strain energy release rate. The wear of the nanotubes-reinforced epoxy is eight times lower than that of pure epoxy. WS₂ nanotubes were embedded into a poly(methyl methacrylate) (PMMA) nanofiber matrix via electrospinning. The nanotubes were well dispersed and aligned along fiber axis. The enhanced stiffness and toughness of PMMA fiber meshes by means of inorganic nanotubes addition may have potential uses as impact-absorbing materials, e.g. for ballistic vests.

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, inorganic nanotube hybrids were made by filling WS₂ nanotubes with molten lead, antimony or bithmuth iodide salt by a capillary wetting process, resulting in PbI₂@WS₂, SbI₃@WS₂ or BiI₃@WS₂ core-shell nanotubes.

References

1. ^ Mary Eagleson (1994). Concise encyclopedia chemistry. Walter de Gruyter. p. 1129. ISBN 978-3-11-011451-5. Retrieved 6 November 2011.
2. ^ Tenne R, Margulis L, Genut M, Hodes G (1992). "Polyhedral and cylindrical structures of tungsten disulphide". Nature. 360 (6403): 444–446. doi:10.1038/360444a0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
3. ^ Panigrahi, Pravas Kumar; Pathak, Amita (2008). "Microwave-assisted synthesis of WS2 nanowires through tetrathiotungstate precursors". Sci. Technol. Adv. Mater. 9 (4): 045008. doi:10.1088/1468-6996/9/4/045008. {{cite journal}}: |format= requires |url= (help)CS1 maint: multiple names: authors list (link)
4. ^ Erik Lassner; Wolf-Dieter Schubert (1999). Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds. Springer. pp. 374–. ISBN 978-0-306-45053-2. Retrieved 6 November 2011.
5. E. Zohar, S. Baruch, M. Shneider, H. Dodiu, S. Kenig, D.H. Wagner, A. Zak, A. Moshkovith, L. Rapoport and R. Tenne (2011). "The Mechanical and Tribological Properties of Epoxy Nanocomposites with WS₂ Nanotubes". Sensors & Transducers Journal. 12 (Special Issue): 53–65.{{cite journal}}: CS1 maint: multiple names: authors list (link)
6. C. S. Reddy, A. Zak and E. Zussman (2011). "WS₂ nanotubes embedded in PMMA nanofibers as energy absorptive material". J. Mater. Chem. 21 (40): 16086–16093. doi:10.1039/C1JM12700D.
7. Physorg.news – Nano-Armor: Protecting the Soldiers of Tomorrow
8. R. Kreizman, A. N. Enyashin, F. L. Deepak, A. Albu-Yaron, R. Popovitz-Biro, G. Seifert and R. Tenne (2010). "Synthesis of Core-Shell Inorganic Nanotubes". Adv. Funct. Mater. 20 (15): 2459–2468. doi:10.1002/adfm.201000490.{{cite journal}}: CS1 maint: multiple names: authors list (link)

• Tungsten compounds
• Sulfides
• Dry lubricants