Tungsten trioxide

Tungsten(VI) oxide, also known as tungsten trioxide is a chemical compound of oxygen and the transition metal tungsten, with formula WO3. The compound is also called tungstic anhydride, reflecting its relation to tungstic acid H2WO4. It is a light yellow crystalline solid.[1]

Tungsten trioxide
Names
IUPAC name
Tungsten trioxide
Other names
Tungstic anhydride
Tungsten(VI) oxide
Tungstic oxide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.013.848
RTECS number
  • YO7760000
UNII
CompTox Dashboard (EPA)
  • InChI=1S/3O.W
  • O=[W](=O)=O
Properties
WO3
Molar mass 231.84 g/mol
Appearance Canary yellow powder
Density 7.16 g/cm3
Melting point 1,473 °C (2,683 °F; 1,746 K)
Boiling point 1,700 °C (3,090 °F; 1,970 K) approximation
insoluble
Solubility slightly soluble in HF
−15.8·10−6 cm3/mol
Structure
Monoclinic, mP32
Space group
 P121/n1, No. 14
Octahedral (WVI)
Trigonal planar (O2– )
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Irritant
Flash point Non-flammable
Safety data sheet (SDS) External MSDS
Related compounds
Other anions
 Tungsten trisulfide
Other cations
 Chromium trioxide
Molybdenum trioxide
Tungsten(III) oxide
Tungsten(IV) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Tungsten(VI) oxide occurs naturally in the form of hydrates, which include minerals: tungstite 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 gave the first procedures for preparing tungsten trioxide and sodium tungstate.[2] He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.[2]

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.[3] The most common structure of WO3 is monoclinic with space group P21/n.[2]

The pure compound is an electric insulator, but oxygen-deficient varieties, such as WO2.90 = W20O58, are dark blue to purple in color and conduct electricity. They can be prepared by combining the trioxide and the dioxide WO2 at 1000 °C in vacuum.[4][1]

Possible signs of superconductivity with critical temperatures Tc = 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 Tc higher than the boiling point of liquid nitrogen at normal pressure. [5][4]

Preparation

Industrial

Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals.[6] Tungsten ores can be treated with alkalis to produce soluble tungstates. Alternatively, CaWO4, or scheelite, is allowed to react with HCl to produce tungstic acid, which decomposes to WO3 and water at high temperatures.[6]

CaWO4 + 2 HCl → CaCl2 + H2WO4
H2WO4 → H2O + WO3

Laboratory

Another common way to synthesize WO3 is by calcination of ammonium paratungstate (APT) under oxidizing conditions:[2]

(NH4)10[H2W12O42] · 4 H2O → 12 WO3 + 10 NH3 + 10 H2O

Reactions

Tungsten trioxide can be reduced with carbon or hydrogen 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 tungstates. Barium tungstate BaWO4 is used as a x-ray screen phosphors. Alkali metal tungstates, such as lithium tungstate Li2WO4 and Cesium tungstate Cs2WO4, give dense solutions that can be used to separate minerals.[1] Other applications, actual or potential, include:

  • Fireproofing fabrics[7]
  • Gas and humidity sensors.[8][1]
  • Ceramic glazes where it gives a rich yellow color.[6][1]
  • Electrochromic glass, such as in smart windows, whose transparency can be changed by an applied voltage.[9][10][1]
  • Photocatalytic water splitting.[11][12][13][14]
  • Substrate for surface-enhanced Raman spectroscopy replacing noble metals.[15][16][17][18]

References
  1. 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.
  2. Lassner, Erik and Wolf-Dieter Schubert (1999). Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds. New York: Kluwer Academic. ISBN 978-0-306-45053-2.
  3. H. A. Wriedt (1898): "The O-W (oxygen-tungsten) system". Bulletin of Alloy Phase Diagrams., volume 10, pages 368–384. doi:10.1007/BF02877593
  4. A. Shengelaya, K. Conder, and K. A. Müller (2020): "Signatures of Filamentary Superconductivity up to 94 K in Tungsten Oxide WO2.90". Journal of Superconductivity and Novel Magnetism, volume 33, pages 301–306. doi:10.1007/s10948-019-05329-9
  5. 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. doi:10.1007/s100510050735 S2CID 121476634
  6. Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. ISBN 978-0-07-049439-8. Retrieved 2009-06-06.
  7. Merck (2006): "Tungsten trioxide." The Merck Index, volume 14.
  8. 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. doi:10.1088/0957-0233/13/6/314
  9. Lee, W. J.; Fang, Y. K.; Ho, Jyh-Jier; Hsieh, W. T.; Ting, S. F.; Huang, Daoyang; Ho, Fang C. (2000). "Effects of surface porosity on tungsten trioxide(WO3) films' electrochromic performance". Journal of Electronic Materials. 29 (2): 183–187. Bibcode:2000JEMat..29..183L. doi:10.1007/s11664-000-0139-8. S2CID 98302697.
  10. 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.
  11. 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. doi:10.1021/jz100233w
  12. 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. doi:10.1016/j.cattod.2012.09.038
  13. 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. doi:10.3390/ma9040258
  14. 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. doi:10.1016/j.mssp.2015.08.042
  15. G. Ou (2018). "Tuning Defects in Oxides at Room Temperature by Lithium Reduction". Nature Communications. 9 (1302): 1302. Bibcode:2018NatCo...9.1302O. doi:10.1038/s41467-018-03765-0. PMC 5882908. PMID 29615620.
  16. S. Hurst (2011). "Utilizing Chemical Raman Enhancement: A Route for Metal Oxide Support Based Biodetection". The Journal of Physical Chemistry C. 115 (3): 620–630. doi:10.1021/jp1096162.
  17. W. Liu (2018). "Improved Surface-Enhanced Raman Spectroscopy Sensitivity on Metallic Tungsten Oxide by the Synergistic Effect of Surface Plasmon Resonance Coupling and Charge Transfer". The Journal of Physical Chemistry Letters. 9 (14): 4096–4100. doi:10.1021/acs.jpclett.8b01624. PMID 29979872. S2CID 49716355.
  18. C. Zhou (2019). "Electrical tuning of the SERS enhancement by precise defect density control" (PDF). ACS Applied Materials & Interfaces. 11 (37): 34091–34099. doi:10.1021/acsami.9b10856. PMID 31433618. S2CID 201278374.
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