Tungsten Blue Oxide Research Articles

On the reduction of NS-doped tungsten blue oxide—Part I: Literature review

This paper reviews literature on the K, Al, Si-doping of tungsten blue oxides and the subsequent hydrogen reduction to tungsten metal powder. Some unique properties of the blue oxide with respect to the reactions during doping are discussed. Different aspects of the reduction process such as the formation of intermediate tungsten oxides and β-W, the reactions of dopant-containing compounds and their effects on the reduction kinetics are summarized. A conclusion on the theories concerning the dopant incorporation during reduction is followed by a review of the technological relationships between the reduction parameters and the tungsten powder properties (e.g. grain size and dopant incorporation), as knowledge of these is essential for efficient process control. A further paper on ‘the reduction of NS-doped tungsten blue oxide’ will follow in this journal, based on the authors' own experimental experiences.

On the reduction of NS-doped tungsten blue oxide—Part II: Mechanistic considerations

Part I of this paper gave a review of the literature. A detailed description of experimental observations on the influence of the NS-dopants (K, Al, Si) on the hydrogen reduction of tungsten blue oxide is given in Part II. Alterations in the suboxide sequence as compared to undoped oxides, intermediate formation of β-W, and W separation from dopant–T-O compounds (bronzes, tungstates) during the transition WO 2→W were observed. Incorporation of the dopants, as necessary for the development of non-sag properties in the final wire, occurs via CVT overgrowth of dopant phases in the WO 2→3W step. Particle size of those phases increases with increasing reduction temperature.

Hydrogen reduction of ammonium paratungstate into tungsten blue oxide—Part I: Literature review

To define the characteristic properties of tungsten blue oxide, TBO, published information on the reduction of APT in the temperature range of approximately 300–600°C was reviewed. The ammonia content, the oxygen index, i.e. the degree of reduction, the specific surface area and the Fisher average particle size were found to be typical TBO characteristics.

On the reduction of N.S.-doped tungsten blue oxide—Part III: Technological considerations

Part I of this paper gave a review of the literature, Part II presented a mechanism for the doping element incorporation during reduction and Part III now discusses technological relationships between the reduction parameters and the N.S.-W powder properties. Under isothermal reduction conditions, dopant incorporation is affected predominantly by the reduction temperature (decreasing with increasing temperature), while grain size is influenced by both temperature and boatload. During temperature profile reduction (industrial practice) all parameters influencing the relationship between actual reduction temperature and reduction stage (WO X) affect both grain size and dopant incorporation. Besides the absolute amount of incorporated dopants, the sizes and compositions of the incorporated dopant phases are affected as well, an important factor with respect to the further processing to high-quality non-sag wire.

Hydrogen reduction of ammonium paratungstate into tungsten blue oxide—Part II: Experimental

To determine the feasibility of the direct processing route, the variability of the TBO properties resulting from changes in operating parameters was studied. The operating parameters were: reduction time, reduction temperature, hydrogen gas flow rate and the amount of powder. The factors all influence the ammonia content, the oxygen index and the specific surface area of TBO. The Fisher average particle size, however, cannot be altered sufficiently by changing one of these operating parameters.

PHOTOEMISSION STUDIES ON THE BLUE TUNGSTEN OXIDES

A series of studies were conducted for surface valency in blue tungsten oxides by using pho-toemission technique. Rusults show that, the blue tungsten oxide contains not only one kind of valency, but conbination of two valences, namely the conbination of W+5 and W+6, and also the process of argon ion eching and high temperature treatment all induce the loss of oxygen in W-chemical reduction process, which causes W transfer from high valence to low valence. Meanwhile, the density of state near Fermi level increases with the change from high valence to low valence.

Structures and chemistry of tungsten powder from doped and undoped tungsten blue oxide

Blue tungsten oxide, both without dopant and doped with aluminium, silicon and potassium was reduced to tungsten by heating at 750 and 900° C in flowing hydrogen. The morphology, chemistry, and crystal structure were determined by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and Auger electron spectroscopy. Undoped oxide reduced at a lower rate than did the doped oxide. The potassium, silicon and aluminium appeared to be distributed non-uniformly on the surface of the doped oxide particles. Nucleation of tungsten crystals began earlier in the doped oxides leading to a bimodal distribution of crystal sizes in the doped material. There were pockets of potassium inside the tungsten crystals from the doped blue oxide. This suggests that the tungsten crystals nucleated earlier and at regions of high potassium concentration on the surface of the doped blue oxide. Tungsten was then transported from the surrounding oxide to the nucleus to grow the crystals trapping the potassium inside the crystal. Nucleation of the tungsten crystals occurred more homogeneously on the surface of the oxide that was low in potassium and, of course, on the undoped oxide particles, leading to the smaller size of the tungsten crystals from the undoped oxide.

Lung Clearance of Inhaled Insoluble and Soluble Particles

Lung Clearance of Inhaled Insoluble and Soluble Particles

THERMAL DESORPTION SPECTRA OF PROPENE AND OXYGEN ADSORBED ON BLUE TUNGSTEN OXIDE

The thermal desorption spectra of propene and oxygen adsorbed on blue tungsten oxide WO2.90 have been measured by means of flash heating the sample in ultra high vacuum. It has been discovered that at room temperature only one adsorption state of propene on blue tungsten oxide surface exists, which corresponds to a desorption peak at the temperature around 100℃ appeared in the thermal desorption spectra. The desor- ption parameters determined by the experiment are: n=l (first order desorption) and the activation energy of desorption Ed=10.1 kcal/mol. The probability of forming stable adsorption state of propene on blue tungsten oxide decreases as the sample temperature increases. At room temperature, the blue tungsten oxide doesn't interact with oxygen significantly. But after raising the temperature to above 300℃, WO2.90 is oxidized into WO3 accompanying with a strong adsorption of oxygen. This implies that the blue tungsten oxide could be used as a promising oxygen getter in the vacuum valves.

The controlled reduction of copper tungstate in H2O/H2 mixtures

The controlled reductions of copper tungstate, copper tungstate plus blue tungsten oxide and CuO plus WO3 have been studied at temperatures of 500, 600 and 700δC using H2/H2O mixtures in a glass thermobalance. The copper-tungsten oxide composite powder products have been characterized by X-ray diffraction analysis and scanning electron microscopy. The morphologies of the copper-tungsten oxide products have been related to the morphologies of copper-tungsten powders obtained by dry hydrogen reduction. It is shown that widely varying copper-tungsten oxide morphologies may be obtained as precursors for metal powder production by control of the H2/H2O ratio in the reducing gas mixture.

Effect of reduction parameters on the particle size of tungsten monocarbide obtained from the blue tungsten oxide

A study was made, using the methods of particle size analysis and metallographic examination, of the effects of temperature and bed thickness in the reduction of the blue tungsten oxide upon some properties of tungsten and tungsten monocarbide powders and sintered 6 wt.% Co hard alloys produced from the monocarbide powders. Quantitative results were obtained showing the relationship between these reduction parameters on the one hand and the particle size of the resultant powders and the physicomechanical properties of hard alloys on the other. It was established that the particle size grows with rise in reduction temperature and with increase in the thickness of the blue oxide bed.