Tungsten oxide also called tungsten trioxide, including yellow tungsten oxide (YTO, WO3), blue tungsten oxide (BTO, WO2.9), violet tungsten oxide (VTO, WO2.72or W18O49) and brown tungsten oxide(tungsten dioxide, WO2).
Tungsten oxide 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 WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.Tungsten oxide is obtained from the minerals scheelite, wolframite, ferberite. It is insoluble in H2O and acids, but soluble in hot alkalis.
Tungsten and Oxygen
The tungsten-oxygen system is rather complex. Besides the stable stoichiometric binary oxides (WO3, WO2.9, WO2.72, and WO2); and the stoichiometric tungstates and acids, a variety of nonstoichiometric, fully oxidized and reduced compounds exists.
In the fully oxidized state (W6+) the octahedral coordination dominates (WO6). The tungsten atoms are situated in the center of octahedrons and are surrounded by six oxygen atoms arranged at the comers. A-s long as all tungsten ions are hexavalent, these octahedrons are only comer-sharing. However, as the oxygen-to-tungsten ratio decreases, which occurs on reduction (transition to lower oxides), the octahedral become more and more intricately joined in combinations of corner-, edge-, and face-sharing.
By the loss of each oxygen atom from the oxide lattice two electrons are added to the conduction band. Reduced compounds are therefore either semiconducting or conducting.
Besides the tungsten-oxygen octahedral, W04 tetrahedra can also be found in fully oxidized compounds (tungstates), as well as WO7 pentagonal bipyramids in reduced compounds.
Several hundreds or even thousands of ternary and quaternary tungsten oxides are known today. They are only partly described in the literature and can be found in the relevant compilations. They are, however, the top of an iceberg of a much larger number of compounds which might form, in principle, with a large number of elements and/or element combinations. In this sense, the crystal chemistry of tungsten oxides can be regarded as one of the most complex and richest fields in the structural chemistry of the elements.
Used in the manufacture of tungsten and tungstates, in alloys, in fire-proofing fabrics and as a ceramic pigment.
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