Tungsten oxide particle dispersion

Ti02 nanotubes were used to support M0O3 observing a spontaneous dispersion of molybdenum-oxide on the surface of nanotubes, which was different from that observed on titania particles.Supporting tungsten oxides a preferential orientation of the (002) planes was observed. Vanadium-oxide in the form of nanorods could be prepared using the titania nanotube as structure-directing template under hydrothermal... 

One important class of particulate composites is dispersion-hardened alloys. These composites consist of a hard particle constituent in a softer metal matrix. The particle constituent seldom exceeds 3% by volume, and the particles are very small, below micrometer sizes. The characteristics of the particles largely control the property of the alloy, and a spacing of 0.2-0.3 tim between particles usually helps optimize properties. As particle size increases, less material is required to achieve the desired interparticle spacing. Refractory oxide particles are often used, although intermetallics such as AlFes also find use. Dispersion-hardened composites are formed in several ways, including surface oxidation of ultrafine metal powders, resulting in trapped metal oxide particles within the metal matrix. Metals of commercial interest for dispersion-hardened alloys include aluminum, nickel, and tungsten. 

For the production of lamp-filament wire, aluminum, potassium, and siHcon dopants are added to the blue oxide. Some dopants are trapped in the tungsten particles upon reduction. Excess dopants are then removed by washing the powder in hydroflouric acid. Eor welding electrodes and some other appHcations, thorium nitrate is added to the blue oxide. After reduction, the thorium is present as a finely dispersed thorium oxide. 

The selectivity of alcohol depends on the carbide preparation. A maximum in alcohol is achieved for the sample WC/Ti02 (T3) for which the preparation of the carbide combines reduction and carburization steps at moderate temperatures (respectively, 873 K and 1073 K). In this case, anionic vacancies stabilized by mixed oxides are formed, associated with carbon vacancies in mixed carbides resulting in a better interaction of carbidic and oxidic phases. On silica, ceria and zirconia, the extent of carburization is too high and the interaction of the carbide phase with the oxide support is suppressed giving larger isolated particles of tungsten carbide with low dispersion. 

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