Metals tungsten

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

Ferro tungsten Tungsten metal powder Tungsten carbide powder Tungsten e scrap Other tungsten materials Total... 

Syntheses from Dry Metals and Salts. Only metaUic nickel and iron react direcdy with CO at moderate pressure and temperatures to form metal carbonyls. A report has claimed the synthesis of Co2(CO)g in 99% yield from cobalt metal and CO at high temperatures and pressures (91,92). The CO has to be absolutely free of oxygen and carbon dioxide or the yield is drastically reduced. Two patents report the formation of carbonyls from molybdenum and tungsten metal (93,94). Ruthenium and osmium do not react with CO even under drastic conditions (95,96). 

Tungsten bronzes can be prepared by a variety of reductive techniques but probably the most general method consists of heating the normal tungstate with tungsten metal. They are extremely inert chemically, being resistant both to alkalis and to acids, even when hot and concentrated. Their colours depend in the proportion of M and W present. In the case of sodium... 

Wender and Hershkowitz [237] used the sensitivity of the recoil-free fraction in tungsten Mossbauer spectroscopy to deduce the effect of irradiation of tungsten compounds by Coulomb excitation of the resonance levels (2 states of I82,i84,i8 y with 6 MeV a-particles. While no effect of irradiation on the/-factors could be observed for tungsten metal in agreement with [233], a decrease of/was measured for WC, W2B, W2B5, and WO3 after irradiation. 

Tungsten forms several oxides, and the reactions pertinent to the reduction of tungsten oxide to tungsten metal are expressed by the following equations ... 

Tungsten metal can be obtained by exposing tungsten oxides to dry hydrogen in a flow system maintained above about 500 °C. An increase in the temperature shifts the reaction towards metal formation. For the first two stages of reduction, corresponding to the forma-... 

Tungstic oxide —- Hydrogen reduction — Tungsten metal powder Figure 5.39 Processing of tungsten resources. 

The dark spot on the inside of a burned-out light bulb is tungsten metal that has sublimed (vaporized from the solid) as a consequence of the heating of the tungsten filament to produce white light. 

Tungsten metal may be prepared by reducing W03 with H2 gas. How many grams of tungsten may be prepared from 0.0500 mol of W03 with excess hydrogen ... 

Some of these reactions are employed in the metallurgy of oxide ores, for example, in the commercial production of tungsten metal. WO3 in Eq. 5.4 is reduced to the free metal by hydrogen. 

The SCR catalyst designed for FCCU regenerator flue gas service is a homogenous monolith, typically made from 1 mm thick material. Some catalysts are extruded clays that receive a wash coat of titanium dioxide before impregnation of the vanadium and tungsten metals. Another type involves painted plates of expanded metal... 

Tungsten is recovered mostly from mineral scheebte and wolframite. The recovery process depends on the mineral, the cost, and the end use i.e., the commercial products to be made. Typical industrial processes have been developed to convert tungsten ores to tungsten metal and alloy products, tungsten steel, non-ferrous alloys, cast and cemented tungsten carbides, and tungsten compounds. A few processes are mentioned briefly below. 

The APT may directly be reduced with hydrogen to produce tungsten powder. The powder may be pressed, sintered and fabricated to produce tungsten metal and alloy products.The tungsten powder may be heated with carbon to form tungsen carbides which may be converted to cast carbides or certain grades of cemented carbides. Or the tungsten powder may be alloyed with specific metals to form various non-ferrous alloys. 

Tungsten metal is not affected by aqueous alkalies at room temperature. In molten state, caustic soda and caustic potash slowly oxidize tungsten in the presence of air. Oxidiation is more rapid in the presence of an oxidizing agent such as potassium nitrate, potassium chlorate, or lead dioxide. A similar reaction occurs with fused sodium or potassium carbonate. Tungsten dissolves... 

---