Tungsten oxide reduced

Other ions which are reduced in the reductor to a definite lower oxidation state are those of titanium to Ti3+, chromium to Cr2+, molybdenum to Mo3+, niobium to Nb3+, and vanadium to V2 +. Uranium is reduced to a mixture of U3 + and U4+, but by bubbling a stream of air through the solution in the filter flask for a few minutes, the dirty dark-green colour changes to the bright apple-green colour characteristic of pure uranium(I V) salts. Tungsten is reduced, but not to any definite lower oxidation state. 

Fig. 6.1b) in which twelve inner ligands bridge the edges of the Me octahedron, and six outer ligands occupy apical positions, predominate. These units are found in reduced zirconium, niobium, tantalum, and rare-earth halides, and niobium, tantalum, molybdenum and tungsten oxides [la, 6, 10]. 

The final aspect of tungsten oxide reduction chemistry that needs to be considered is the kinetics of the reactions. Under most circumstances, the reduction of tungsten oxides is a transport limited process limited by the rate of transport of the water vapor product out of the material. Under such conditions, no shortcuts in the reduction path may be taken, with the WO3 oxide being reduced according to the following path ... 

EIGURE 8.3. High temperature reduction of tungsten oxide. H2O partial pressure is indicative of the rate of reduction. The four reduction steps are distinctly separated, indicating that the material passes through each equilibrium composition as it is reduced. Erom Lessner and Schubert. 

A small number of compounds of Mo(III), W(III), and U(III) are known, and they are very easily oxidized to higher valence states. Tri-valent molybdenum and tungsten are reducing agents comparable with... 

Electrochromic materials are of three basic types [i]. In a given -> electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states, an example being l,l -di-methyl-4,4 -bipyridylium ( methyl viologen ), which, on reduction, switches from the colorless di-cation to the blue radical cation. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. An example here is l,l -di-heptyl-4,4 -bipyridylium ( heptyl viologen ). In type III materials, such as -> tungsten oxide, - Prussian blue, and electroactive conjugated polymers, both... 

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