|Molar mass||231.84 g/mol|
|Appearance||Canary yellow powder|
|Melting point||1,473 °C (2,683 °F; 1,746 K)|
|Boiling point||1,700 °C (3,090 °F; 1,970 K) approximation|
|Solubility||slightly soluble in HF|
|Monoclinic, mP32, Space group P12/c1, No 14|
Trigonal planar (O)
|Safety data sheet||External MSDS|
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 or tungstic anhydride, WO, 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. Tungsten ores are treated with alkalis to produce WO. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.
Tungsten(VI) oxide occurs naturally in the form of hydrates, which include minerals: tungstite WO·HO, meymacite WO·2HO and hydrotungstite (of the same composition as meymacite, however sometimes written as HWO). These minerals are rare to very rare secondary tungsten minerals.
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 with his studies on the mineral scheelite.
In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and sodium tungstate. He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.
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 WO is monoclinic with space group P2/n.
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 and in gas sensors. Due to its rich yellow color, WO is also used as a pigment in ceramics and paints.
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. This allows the user to tint their windows, changing the amount of heat or light passing through.
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 TiO or on WO). The composite showed a modest hydrogen production performance.
In 2016, shape controlled tungsten trioxide semiconductors were obtained by the means of hydrothermal synthesis. From these semiconductors composite systems were prepared with commercial TiO. These composite systems showed a higher photocatalysis activity than the commercial TiO (Evonik Aeroxide P25) towards phenol and methyl orange degradation.
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- ^ Development of a high-performance photocatalyst that is surface-treated with cesium Archived 2010-05-20 at the Wayback Machine.
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- ^ Székely, I., et al. Synthesis of shape-tailored WO micro-/nanocrystals and the photocatalytic activity of WO/TiO composites (2016) Materials, 9 (4).
- ^ Baia, L., et al. Preparation of TiO/WO composite photocatalysts by the adjustment of the semiconductors' surface charge (2016) Materials Science in Semiconductor Processing, 42, pp. 66-71
- International Tungsten Industry Association
- Preparation of tungsten trioxide electrochromic films
- Sigma Aldrich (supplier)