Tungsten trioxide

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Tungsten trioxide
Sample of Tungsten(VI) Oxide
Names
IUPAC name
Tungsten trioxide
Other names
Tungstic anhydride
Tungsten(VI) oxide
Tungstic oxide
Identifiers
3D model (
JSmol
)
ECHA InfoCard
 100.013.848 Edit this at Wikidata
RTECS number
  • YO7760000
UNII
  • 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
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).
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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(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

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 = 80–90 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.

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.[citation needed]

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

cesium tungstate Cs2WO4, give dense solutions that can be used to separate minerals.[1]
Other applications, actual or potential, include:

References

  1. ^ a b c d e f 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. ^
    ISBN 978-0-306-45053-2
    .
  3. doi:10.1007/BF02877593
  4. ^
    doi:10.1007/s10948-019-05329-9
  5. S2CID 121476634
  6. ^
    ISBN 978-0-07-049439-8
    . Retrieved 2009-06-06.
  7. ^ Merck (2006): "Tungsten trioxide." The Merck Index, volume 14.
  8. doi:10.1088/0957-0233/13/6/314
  9. 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. doi:10.1021/jz100233w
  12. doi:10.1016/j.cattod.2012.09.038
  13. doi:10.3390/ma9040258
  14. doi:10.1016/j.mssp.2015.08.042
  15. PMID 29615620
    .
  16. doi:10.1021/jp1096162
    .
  17. S2CID 49716355
    .
  18. S2CID 201278374
    .

External links
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