Tungsten(IV) sulfide
Encyclopedia
Tungsten sulfide is the chemical compound
with the formula W
S2
. 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.
and hydrofluoric acid
s. 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.
; and as catalyst in hydrodesulfurization of crude oil. WS2 also catalyses production of carbon monoxide
bringing the reaction yield to the level above 99.9%.
s, 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.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula W
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
S2
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
. It occurs naturally as the rare mineral called tungstenite. This material is a component of certain catalysts used for hydrodesulfurization
Hydrodesulfurization
Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils...
and hydrodenitrification.
WS2 adopts a layered structure related to MoS2
Molybdenum disulfide
Molybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. It is the principal ore from which molybdenum metal is extracted. The natural amorphous form is known as the rarer mineral jordisite. MoS2 is less...
, with W atoms situated in trigonal prismatic coordination sphere
Coordination sphere
In coordination chemistry, the coordination sphere refers to a central atom or ion and an array of molecules or anions, the ligands, around.Molecules that are attached noncovalently to the ligands are called the second 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 nitricNitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
s. When burned in oxygen-containing atmosphere, WS2 converts to tungsten trioxide
Tungsten trioxide
Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3...
. 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 synthesisHydrothermal synthesisHydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mineralogists have studied hydrothermal phase...
- 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 acidTungstic acidTungstic acid refers to hydrated forms of tungsten trioxide, WO3.The simplest form, the monohydrate, is WO3.H2O, the dihydrate WO3.2H2O is also known. The solid state structure of WO3.H2O consists of layers of octahedrally coordinated WO5 units where 4 vertices are shared. the dihydrate has the...
, elemental sulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and monoethanolamine. - Heating WS3 in absence of oxygen (otherwise the product is tungsten trioxide).
- Melting a mixture of tungsten trioxideTungsten trioxideTungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3...
, potassium carbonatePotassium carbonatePotassium carbonate is a white salt, soluble in water , which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide. It is deliquescent, often appearing a damp or wet solid...
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 lubricantDry lubricant
Dry lubricants or solid lubricants are materials which despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid media....
; 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 nanotubeInorganic nanotube
An inorganic nanotube is a cylindrical molecule often composed of metal oxides, and morphologically similar to a carbon nanotube. Inorganic nanotubes have been observed to occur naturally in some mineral deposits....
s, 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
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....
resin improves adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
, fracture toughness
Fracture toughness
In materials science, fracture toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications. The fracture toughness of a material is determined from the...
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.