Binary tungsten oxides

Amorphous species form by dehydration which, on further heating, convert into crystalline binary tungsten oxides as well as tungsten bronzes. The conversion from amorphous to crystalline is a slow process. Therefore, if the heating period is short, as in rotary furnaces, the time available for overall crystallization is insufficient. This is why rotary-fumace-derived TBO can be high in amorphous oxide when compared to TBO from pushers. 

From this point of view, therefore, there is no evidence in the literature to suggest that concentrations of point defects are a mode of accommodating major stoicheio-metry changes in either the binary or ternary tungsten or titanium oxides. This would seem likely to hold for other CS phases, with the only exception to the general trend so far reported seeming to be Mo03. ... 

The tungsten-oxygen system is rather complex. Besides the stable stoichiometric binary oxides (WO3, WO2.9, WO2.72, and WO2), and the stoichiomettic tungstates and acids, a variety of nonstoichiometric, fiilly oxidized and reduced compounds exists, according to the scheme in Fig. 4.2. 

Binary and Ternary Compounds with Elements of Groups II, III, and V. 2f-ray electron spectroscopy has been used to probe the electronic structures of tungsten borides, nitrides and also some carbides and oxides. Enthalpies of formation AH°298.i5 the tungsten borides WB and W2B have been determined by fluorine calorimetry and are — 66.5 and — 68.2 kJ mol respectively. The theoretical possibilities of preparing M02B, a-MoB, MO2B5, WjB, a-WB, and W2B5 by chemical vapour deposition is discussed and MoXj (X = B or Be) have been prepared and examined by X-ray methods. ... 

High conversions of cyclopentene were obtained by Nuetzel et al. [59] with hydroperoxides, inorganic peroxides, or aromatic nitroderivatives. To increase the stability of some tungsten-based catalytic systems, Witte et al. [63] employed a-halogenated alcohols such as chloroethanol, 2-chlorocyclohexanol, bro-moethanol, l,3-dichloro-2-isopropanol, o-chlorophe-nol, and 2-iodocyclohexanol. It was observed that methyl and ethyl acetals of formaldehyde, acetaldehyde, chloroform, and benzaldehyde impart good staiblity to the binary systems of tungsten, whereas epoxides such as ethylene oxide and butylene oxide lead at the same time to an increase in activity and stability. 

Figure 10.3 Photographs of the segregated state of binary granular mixtures of particles differing only in density after being shaken repeatedly until a steady segregation state is reached. The lighter particles are made of aluminum oxide (density p 1.31 g/cm ) and the heavier ones are made of (a) zirconium oxide (density p 2.87 g/cm ), (b) titanium alloy (density p 4.45 g/cm ), (c) cobalt-chromium-molybdenum alloy (density p 8.37 g/cm ), and (d) tungsten alloy (density p = 18.0 g/cm ), respectively. (Shi, Q. et al., Phys. Rev. E, 061302/1-4, 2007.)...

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