Tungsten(VI) oxide, also known as tungsten trioxide is a chemical compound of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

and the transition metal

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...

, with

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

WO₃. The compound is also called tungstic anhydride, reflecting its relation to

tungstic acid Tungstic acid refers to hydrated forms of tungsten trioxide, WO3. Both a monohydrate (WO3·H2O) and hemihydrate (WO3·1/2 H2O) are known. Molecular species akin to sulfuric acid, i.e. (HO)2WO2 are not observed. The solid-state structure of ...

. It is a light yellow crystalline solid. Tungsten(VI) oxide occurs naturally in the form of

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

s, which include minerals:

tungstite Tungstite is a hydrous tungsten oxide mineral with formula: W O3· H2O. It is a secondary mineral formed by the weathering of other tungsten containing minerals. It crystallizes in the orthorhombic system in translucent yellow to yellow green mas ...

WO₃·H₂O, meymacite WO₃·2H₂O and hydrotungstite (of the same composition as meymacite, however sometimes written as H₂WO₄). These minerals are rare to very rare secondary tungsten minerals.

History

In 1841, a chemist named

Robert Oxland Air Vice Marshal Robert Dickinson Oxland, (4 April 1889 – 27 October 1959) was a senior Royal Air Force officer and member of Bomber Command during the Second World War.''Kelly’s Handbook to the Titled, Landed and Official Classes 1958'', P ...

gave the first procedures for preparing tungsten trioxide and

sodium tungstate Sodium tungstate is the inorganic compound with the formula Na2WO4. This white, water-soluble solid is the sodium salt of tungstic acid. It is useful as a source of tungsten for chemical synthesis. It is an intermediate in the conversion of tungs ...

. He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.

Structure and properties

The crystal structure of tungsten trioxide is temperature dependent. It is

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square ...

at temperatures above 740 °C,

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

from 330 to 740 °C,

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

from 17 to 330 °C,

triclinic 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal is ...

from -50 to 17 °C, and monoclinic again at temperatures below -50 °C. The most common structure of WO₃ is monoclinic with

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

P2₁/n. The pure compound is an electric insulator, but oxygen-deficient varieties, such as = , are dark blue to purple in color and conduct electricity. They can be prepared by combining the trioxide and the dioxide at 1000 °C in vacuum. Possible signs of

superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...

with critical temperatures T_c = 80 to 90 K were claimed in sodium-doped and oxygen-deficient WO₃ crystals. If confirmed, these would be the first superconducting materials containing no copper, with T_c higher than the boiling point of liquid nitrogen at normal pressure.

Preparation

Industrial

Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores can be treated with

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

s to produce soluble

tungstate In chemistry, a tungstate is a compound that contains an oxyanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is , "orthotungstate". Many other tungstates belong to a large group of polyatomic ions that are ...

s. Alternatively, CaWO₄, or

scheelite Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist K. Scheele (1742-1786). Well-formed crystals are sought by collectors a ...

, is allowed to react with

HCl HCL may refer to: Science and medicine * Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia * Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development * Hollow-cathode lamp, a spe ...

to produce

, which decomposes to WO₃ and water at high temperatures. :CaWO₄ + 2 HCl → CaCl₂ + H₂WO₄ :H₂WO₄ → + WO₃

Laboratory

Another common way to synthesize WO₃ is by

calcination Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...

ammonium paratungstate Ammonium paratungstate (or APT) is a white crystalline salt with the chemical formula (NH4)10(H2W12O42)·4H2O. It is described as "the most important raw material for all other tungsten products." Production From tungsten ores Tungsten ores, whic ...

(APT) under oxidizing conditions: :(NH₄)₁₀ ₂W₁₂O₄₂→ 12 WO₃ + 10 NH₃ + 10

Reactions

Tungsten trioxide can be reduced with

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

gas yielding the pure metal. :2 WO₃ + 3 C → 2 W + 3 CO₂ (high temperature) :WO₃ + 3 H₂ → W + 3 H₂O (550 - 850 °C)

Uses

Tungsten trioxide is a starting material for the synthesis of

s. Barium tungstate is used as a

x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

screen

phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...

s. Alkali metal tungstates, such as

lithium tungstate Lithium tungstate is the inorganic compound with the formula Li2WO4. It is a white solid that is soluble in water. The compound is one of the several orthotungstates, compounds that feature the tetrahedral WO42− anion. Structure The salt consis ...

and

Cesium tungstate Caesium tungstate or cesium tungstate is an inorganic chemical compound that is notable for forming a very dense liquid in solution. The solution is used in diamond processing, since diamond sinks in it, whereas most other rocks float. Propertie ...

, give dense solutions that can be used to separate minerals. Other applications, actual or potential, include: *

Fireproofing Fireproofing is rendering something (structures, materials, etc.) resistant to fire, or incombustible; or material for use in making anything fire-proof. It is a passive fire protection measure. "Fireproof" or "fireproofing" can be used as a n ...

fabrics *

Gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

and

humidity sensor Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depen ...

s. *

Ceramic glaze Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holding ...

s where it gives a rich yellow color. *

Electrochromic Electrochromism is a phenomenon in which a material displays changes in color or opacity in response to an electrical stimulus. In this way, a smart window made of an electrochromic material can block specific wavelengths of ultraviolet, visib ...

glass, such as in smart windows, whose transparency can be changed by an applied voltage. *

Photocatalytic water splitting Photocatalytic water splitting is an artificial photosynthesis process using photocatalysis for the dissociation of water (H2O) into hydrogen () and oxygen (). Only light energy (photons), water, and a catalyst(s) are needed, since this is what ...

. * Substrate for

surface-enhanced Raman spectroscopy Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by nanostructures such as plasmonic-magnetic silica ...

replacing noble metals.

References

K. J. Patel, M. S. Desai, C. J. Panchal, H. N. Deota, and U. B. Trivedi (2013):
All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO
. ''Journal of Nano-Electronics and Physics'', volume 5, issue 2, article 02023. S. Reich and Y. Tsabba (1999): "Possible nucleation of a 2D superconducting phase on WO single crystals surface doped with Na". ''European Physical Journal B'', volume 9, pages = 1–4. A. Shengelaya, K. Conder, and K. A. Müller (2020): "Signatures of Filamentary Superconductivity up to 94 K in Tungsten Oxide WO_2.90". ''Journal of Superconductivity and Novel Magnetism'', volume 33, pages 301–306. David E Williams, Simon R Aliwell, Keith F. E. Pratt, Daren J. Caruana, Roderic L. Jones, R. Anthony Cox, Graeme M. Hansford. and John Halsall (2002): "Modelling the response of a tungsten oxide semiconductor as a gas sensor for the measurement of ozone". ''Measurement Science and Technology''. volume 13. pages 923–931. Yugo Miseki, Hitoshi Kusama, Hideki Sugihara, and Kazuhiro Sayama (2010): "Cs-Modified WO3 Photocatalyst Showing Efficient Solar Energy Conversion for O2 Production and Fe (III) Ion Reduction under Visible Light". ''Journal of Physical Chemistry Letters'', volume 1, issue 8, pages 1196–1200. É. Karácsonyi, L. Baia, A. Dombi, V. Danciu, K. Mogyorósi, L. C. Pop, G. Kovács, V. Coşoveanu, A. Vulpoi, S. Simon, Zs. Pap (2013): "The photocatalytic activity of TiO2/WO3/noble metal (Au or Pt) nanoarchitectures obtained by selective photodeposition". ''Catalysis Today'', volume 208, pages 19-27. István Székely, Gábor Kovács, Lucian Baia, Virginia Danciu, Zsolt Pap (2016): "Synthesis of Shape-Tailored WO3 Micro-/Nanocrystals and the Photocatalytic Activity of WO3/TiO2 Composites". ''Materials'', volume 9, issue 4, pages 258-271. Lucian Baia, Eszter Orbán, Szilvia Fodor, Boglárka Hampel, Endre Zsolt Kedves, Kata Saszet, István Székely, Éva Karácsonyi, Balázs Réti, Péter Berki, Adriana Vulpoi, Klára Magyari, Alexandra Csavdári, Csaba Bolla, Veronica Coșoveanu, Klára Hernádi, Monica Baia, András Dombi, Virginia Danciu, Gábor Kovácz, Zsolt Pap (2016): "Preparation of TiO2/WO3 composite photocatalysts by the adjustment of the semiconductors' surface charge". ''Materials Science in Semiconductor Processing'', volume 42, part 1, pages 66-71. H. A. Wriedt (1898): "The O-W (oxygen-tungsten) system". ''Bulletin of Alloy Phase Diagrams.'', volume 10, pages 368–384. Merck (2006): "Tungsten trioxide." ''The Merck Index'', volume 14. J. Christian, R.P. Singh Gaur, T. Wolfe and J. R. L. Trasorras (2011):
Tungsten Chemicals and their Applications
'. Brochure by International Tungsten Industry Association.

External links

International Tungsten Industry AssociationPreparation of tungsten trioxide electrochromic filmsSigma Aldrich (supplier)
{{DEFAULTSORT:Tungsten Trioxide Tungsten compounds Transition metal oxides