Tungsten trioxide

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Tungsten trioxide
Sample of Tungsten(VI) Oxide
Kristallstruktur Wolfram(VI)-oxid.png
Identifiers
CAS number 1314-35-8 YesY
PubChem 14811
RTECS number YO7760000
Jmol-3D images Image 1
Properties
Molecular formula 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
Solubility in water insoluble
Solubility slightly soluble in HF
Structure
Crystal structure Monoclinic, mP32, Space group P121/c1, No 14
Coordination
geometry
Octahedral (WVI)
Trigonal planar (O2– )
Hazards
MSDS External MSDS
EU Index Not listed
Main hazards Irritant
Flash point Non-flammable
Related compounds
Other anions Tungsten trisulfide
Other cations Chromium trioxide
Molybdenum trioxide
Related tungsten oxides Tungsten(III) oxide
Tungsten(IV) oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tungsten(VI) 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.[1] Tungsten ores are treated with alkalis to produce WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

2 WO3 + 3 C → 2 W + 3 CO2 (high temperature)
WO3 + 3 H2 → W + 3 H2O (550 - 850 °C)

Tungsten(VI) oxide occurs naturally in form of hydrates, which include minerals: tungstite WO3·H2O, meymacite WO3·2H2O and hydrotungstite (of same composition as meymacite, however sometimes written as H2WO4). These minerals are rare to very rare secondary tungsten minerals.

History[edit]

Tungsten has a rich history dating back to its discovery during the 18th century. Peter Woulfe was the first to recognize a new element in the naturally occurring mineral wolframite. Tungsten was originally known as wolfram, explaining the choice of "W" for its elemental symbol. Swedish chemist Carl Wilhelm Scheele contributed to its discovery as well with his studies on the mineral scheelite.[1]

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]

Preparation[edit]

Tungsten trioxide can be prepared in several different ways. CaWO4, or scheelite, is allowed to react with HCl to produce tungstic acid, which decomposes to WO3 and water at high temperatures.[1]

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

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

(NH4)10[H2W12O42]•4H2O → 12 WO3 + 10 NH3 + 11 H2O

Structure[edit]

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, and triclinic from -50 to 17 °C. The most common structure of WO3 is monoclinic with space group P21/n.[2]

Uses[edit]

Tungsten trioxide is used for many purposes in everyday life. It is frequently used in industry to manufacture tungstates for x-ray screen phosphors, for fireproofing fabrics[3] and in gas sensors.[4] Due to its rich yellow color, WO3 is also used as a pigment in ceramics and paints.[1]

In recent years, tungsten trioxide has been employed in the production of electrochromic windows, or smart windows. These windows are electrically switchable glass that change light transmission properties with an applied voltage.[5][6] This allows the user to tint their windows, changing the amount of heat or light passing through.

2010- AIST reports a quantum yield of 19% in photocatalytic water splitting with a caesium-enhanced tungsten oxide photocatalyst.[7]

In 2013, highly photocatalytic active titania/tungsten (VI) oxide/noble metal (Au and Pt) composites toward oxalic acid were obtained by the means of selective noble metal photodeposition on the desired oxide's surface (either on TiO2 or on WO3). The composite showed a modest hydrogen production performance.[8]

References[edit]

  1. ^ a b c d Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. ISBN 0-07-049439-8. Retrieved 2009-06-06. 
  2. ^ a b c d Lassner, Erik and Wolf-Dieter Schubert (1999). Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds. New York: Kluwer Academic. ISBN 0-306-45053-4. 
  3. ^ "Tungsten trioxide." The Merck Index Vol 14, 2006.
  4. ^ 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
  5. ^ Lee, W. J. (2000). "Effects of surface porosity on tungsten trioxide(WO3) films’ electrochromic performance". Journal of Electronic Materials 29: 183. doi:10.1007/s11664-000-0139-8. 
  6. ^ 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)
  7. ^ Development of a high-performance photocatalyst that is surface-treated with cesium
  8. ^ http://www.sciencedirect.com/science/article/pii/S092058611200781X

External links[edit]