{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 440453423
| Name = Tungsten trioxide
| ImageFile = TungstenOxideSmall.jpg
| ImageName = Sample of Tungsten(VI) Oxide
| ImageFile1 = Kristallstruktur Wolfram(VI)-oxid.png
| IUPACName = Tungsten trioxide
| OtherNames = Tungstic anhydride<br />Tungsten(VI) oxide<br />Tungstic oxide
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 1314-35-8
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 940E10M08M
| RTECS = YO7760000
| PubChem = 14811
| InChI = 1S/3O.W
| SMILES = O=[W](=O)=O
}}
|Section2={{Chembox Properties
| Formula = WO<sub>3</sub>
| MolarMass = 231.84 g/mol
| Appearance = Canary yellow powder
| Density = 7.16 g/cm<sup>3</sup>
| Solubility = insoluble
| SolubleOther = slightly soluble in [[hydrofluoric acid|HF]]
| MeltingPtC = 1473
| BoilingPtC = 1700
| BoilingPt_notes = approximation
| MagSus = &minus;15.8·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
|Section3={{Chembox Structure
| Coordination = Octahedral (W<sup>VI</sup>)<br />Trigonal planar (O<sup>2– </sup>)
| CrystalStruct = [[Monoclinic]], [[Pearson symbol|mP32]]
| SpaceGroup = P12<sub>1</sub>/n1, No. 14
}}
|Section7={{Chembox Hazards
| ExternalSDS = [http://avogadro.chem.iastate.edu/MSDS/WO3.htm External MSDS]
| HPhrases = 
| PPhrases = 
| GHS_ref  = 
| MainHazards = Irritant
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S = 
| FlashPt = Non-flammable
}}
|Section8={{Chembox Related
| OtherAnions = [[Tungsten trisulfide]]
| OtherCations = [[Chromium trioxide]]<br />[[Molybdenum trioxide]]
| OtherFunction = [[Tungsten(III) oxide]]<br />[[Tungsten(IV) oxide]]
| OtherFunction_label = [[tungsten]] [[oxide]]s
| OtherCompounds = 
}}
}}

'''Tungsten(VI) oxide''', also known as '''tungsten trioxide''' or '''tungstic anhydride''', WO<sub>3</sub>, is a chemical compound containing [[oxygen]] and the transition metal [[tungsten]]. 

Tungsten(VI) oxide occurs naturally in the form of [[hydrate]]s, which include minerals: [[tungstite]] WO<sub>3</sub>·H<sub>2</sub>O, [[meymacite]] WO<sub>3</sub>·2H<sub>2</sub>O and [[hydrotungstite]] (of the same composition as meymacite, however sometimes written as H<sub>2</sub>WO<sub>4</sub>). These minerals are rare to very rare secondary tungsten minerals.

==History==
In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and [[sodium tungstate]].<ref name=lass1999/> He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.<ref name=lass1999/>

==Preparation==
===Industrial===
Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals.<ref name=prad2003/> Tungsten ores are treated with [[alkali]]s to produce WO<sub>3</sub>. Further reaction with [[carbon]] or [[hydrogen]] gas reduces tungsten trioxide to the pure metal.{{Citation needed|reason=Primary reference for these reactions should be provided|date=November 2015}}

:2 WO<sub>3</sub> + 3 C → 2 W + 3 CO<sub>2</sub>  (high temperature)
:WO<sub>3</sub> + 3 H<sub>2</sub> → W + 3 H<sub>2</sub>O  (550 - 850 °C)

===Laboratory===
Tungsten trioxide can be prepared in several different ways. CaWO<sub>4</sub>, or [[scheelite]], is allowed to react with [[HCl]] to produce [[tungstic acid]], which decomposes to WO<sub>3</sub> and water at high temperatures.<ref name=prad2003/>

:CaWO<sub>4</sub> + 2 HCl → CaCl<sub>2</sub> + H<sub>2</sub>WO<sub>4</sub>
:H<sub>2</sub>WO<sub>4</sub> → {{H2O}} + WO<sub>3</sub>

Another common way to synthesize WO<sub>3</sub> is by [[calcination]] of [[ammonium paratungstate]] (APT) under oxidizing conditions:<ref name=lass1999/>

:(NH<sub>4</sub>)<sub>10</sub>[H<sub>2</sub>W<sub>12</sub>O<sub>42</sub>]{{Hydrate|4}} → 12 WO<sub>3</sub> + 10 NH<sub>3</sub> + 10 {{H2O}}

==Structure and properties==
The crystal structure of tungsten trioxide is temperature dependent. It is [[tetragonal]] at temperatures above 740 °C, [[orthorhombic]] from 330 to 740 °C, [[monoclinic]] from 17 to 330 °C, [[triclinic]] from -50 to 17 °C, and monoclinic again at temperatures below -50 °C.<ref name=wrie1989/> The most common structure of WO<sub>3</sub> is monoclinic with [[space group]] P2<sub>1</sub>/n.<ref name=lass1999/>

Possible signs of [[superconductivity]] with critical temperatures T<sub>c</sub> = 80 to 90 K were claimed in sodium-doped and oxygen-deficient WO<sub>3</sub> crystals. If confirmed, these would be the first superconducting materials containing no copper, with T<sub>c</sub> higher than the boiling point of liquid nitrogen at normal pressure. <ref name=reic1999/><ref name=shen2020/>

==Uses==
Tungsten trioxide is a starting material for the synthesis of [[tungstate]]s.  [[Barium tungstate]] {{chem2|BaWO4}} is used as a [[x-ray]] screen [[phosphor]]s. Alkali metal tungstates, such as [lithium tungstate]] {{chem2|Li2WO4}} and [[Cesium tungstate]] {{chem2|Cs2WO4}}, give dense solutions that can be used to separate minerals.<ref name=chri2011/> Other applications, actual or potential, include:

* [[Fireproofing]] fabrics<ref name=merck2006/>
* [[gas sensor|Gas]] and [[humidity sensor]]s.<ref name=willXXXX/><ref name=chri2011/>
* [[Ceramic glaze]]s where it gives a rich yellow color.<ref name=prad2003/>
* [[Electrochromic]] glass, such as in [[smart windows]], whose transparency can be changed by an applied voltage.<ref name=leew2000/><ref name=pate2013/>
* [[Photocatalytic water splitting]].<ref name=aist2010/><ref name=kara2013/><ref name=szek2016/><ref name=baia2016/>
* Subtrate for [[surface-enhanced Raman spectroscopy]] with performance could be comparable or even higher than those of commonly used noble-metal elements.<ref name=oug2018/><ref name=hurst2011/><ref name=liuw2018/><ref name=zhou2019/>

==References==
<references>

<ref name=pate2013>K.J. Patel et al., All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO, J. Nano-Electron. Phys. 5 No 2, 02023 (2013)</ref>

<ref name=reic1999>{{Cite journal|url=https://link.springer.com/article/10.1007/s100510050735|doi = 10.1007/s100510050735|title = Possible nucleation of a 2D superconducting phase on WO single crystals surface doped with Na|year = 1999|last1 = Reich|first1 = S.|last2 = Tsabba|first2 = Y.|journal = The European Physical Journal B|volume = 9|pages = 1–4|s2cid = 121476634}}</ref>

<ref name=shen2020>https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A27208/datastream/PDF2/Shengelaya-2020-Signatures_of_filamentary_superconductivity_up-%28accepted_version%29.pdf {{Bare URL PDF|date=March 2022}}</ref>

<ref name=willXXXX>David E Williams et al, "Modelling the response of a tungsten oxide semiconductor as a gas sensor for the measurement of ozone", Meas. Sci. Technol. 13 923, {{doi|10.1088/0957-0233/13/6/314}}</ref>

<ref name=aist2010>[http://www.aist.go.jp/aist_e/latest_research/2010/20100517/20100517.html Development of a high-performance photocatalyst that is surface-treated with cesium] {{Webarchive|url=https://web.archive.org/web/20100520051241/http://www.aist.go.jp/aist_e/latest_research/2010/20100517/20100517.html |date=2010-05-20 }}</ref>

<ref name=kara2013>{{cite journal | doi=10.1016/j.cattod.2012.09.038 | volume=208 | title=The photocatalytic activity of TiO2/WO3/noble metal (Au or Pt) nanoarchitectures obtained by selective photodeposition | journal=Catalysis Today | pages=19–27| year=2013 | last1=Karácsonyi | first1=É. | last2=Baia | first2=L. | last3=Dombi | first3=A. | last4=Danciu | first4=V. | last5=Mogyorósi | first5=K. | last6=Pop | first6=L.C. | last7=Kovács | first7=G. | last8=Coşoveanu | first8=V. | last9=Vulpoi | first9=A. | last10=Simon | first10=S. | last11=Pap | first11=Zs. }}</ref>

<ref name=szek2016>[http://www.mdpi.com/1996-1944/9/4/258 Székely, I., et al. Synthesis of shape-tailored WO<sub>3</sub> micro-/nanocrystals and the photocatalytic activity of WO<sub>3</sub>/TiO<sub>2</sub> composites (2016) Materials, 9 (4)].</ref>

<ref name=baia2016>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 [https://hungary.pure.elsevier.com/en/publications/preparation-of-tiosub2subwosub3sub-composite-photocatalysts-by-th Baia, L.,  et al. Preparation of TiO<sub>2</sub>/WO<sub>3</sub> composite photocatalysts by the adjustment of the semiconductors' surface charge (2016) Materials Science in Semiconductor Processing, 42, pp. 66-71]</ref>

<ref name=oug2018>{{cite journal|author=G. Ou|title=Tuning Defects in Oxides at Room Temperature by Lithium Reduction |journal=Nature Communications|volume=9|date=2018|doi=10.1038/s41467-018-03765-0|issue=1302|pages=1302 |pmid=29615620 |pmc=5882908 |bibcode=2018NatCo...9.1302O }}</ref>

<ref name=hurst2011>{{cite journal|author=S. Hurst|title=Utilizing Chemical Raman Enhancement: A Route for Metal Oxide Support Based Biodetection |journal=The Journal of Physical Chemistry C |volume=115|pages=620–630|date=2011|doi=10.1021/jp1096162|issue=3}}</ref>

<ref name=liuw2018>{{cite journal|author=W. Liu|title= Improved Surface-Enhanced Raman Spectroscopy Sensitivity on Metallic Tungsten Oxide by the Synergistic Effect of Surface Plasmon Resonance Coupling and Charge Transfer |journal=The Journal of Physical Chemistry Letters|volume=9 |pages=4096–4100|date=2018|doi=10.1021/acs.jpclett.8b01624|issue=14|pmid= 29979872 |s2cid= 49716355 |url=https://www.nature.com/articles/s41467-018-03765-0}}</ref>

<ref name=zhou2019>{{cite journal|author=C. Zhou|title=Electrical tuning of the SERS enhancement by precise defect density control |journal=ACS Applied Materials & Interfaces|volume=11|pages=34091–34099|date=2019|doi=10.1021/acsami.9b10856|issue=37 |pmid=31433618 |s2cid=201278374 |url=http://www.unilim.fr/pages_perso/zeng/a196.pdf }}</ref>

<ref name=prad2003>{{cite book|last =Patnaik|first =Pradyot|year = 2003|title =Handbook of Inorganic Chemical Compounds|publisher = McGraw-Hill|isbn =978-0-07-049439-8|url= https://books.google.com/books?id=Xqj-TTzkvTEC|access-date = 2009-06-06}}</ref>

<ref name=lass1999>{{cite book|author=Lassner, Erik and Wolf-Dieter Schubert|title= Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds|place=New York|publisher=Kluwer Academic|year=1999|isbn=978-0-306-45053-2}}</ref>

<ref name=wrie1989>H. A. Wriedt: ''The O-W (oxygen-tungsten) system.'' In: ''Bulletin of Alloy Phase Diagrams.'' 10, 1989, S. 368, {{doi|10.1007/BF02877593}}.</ref>

<ref name=merck2006>"Tungsten trioxide." ''The Merck Index'' Vol 14, 2006.</ref>

<ref name=chri2011>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.</ref>

<ref name=leew2000>{{cite journal|doi=10.1007/s11664-000-0139-8|title=Effects of surface porosity on tungsten trioxide(WO3) films' electrochromic performance|year=2000|last1=Lee|first1=W. J.|last2=Fang|first2=Y. K.|last3=Ho|first3=Jyh-Jier|last4=Hsieh|first4=W. T.|last5=Ting|first5=S. F.|last6=Huang|first6=Daoyang|last7=Ho|first7=Fang C.|journal=Journal of Electronic Materials|volume=29|issue=2|pages=183–187|bibcode=2000JEMat..29..183L|s2cid=98302697}}</ref>


</references>

==External links==
*[http://www.itia.info International Tungsten Industry Association]
*[http://www.rsc.org/publishing/journals/JM/article.asp?doi=jm9930300833 Preparation of tungsten trioxide electrochromic films]
*[http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/204781 Sigma Aldrich (supplier)]

{{Tungsten compounds}}
{{Oxides}}

{{DEFAULTSORT:Tungsten Trioxide}}
[[Category:Tungsten compounds]]
[[Category:Transition metal oxides]]