Tungsten Compounds

Abstract

Tungsten combines with many other elements to form simple stable compounds. It readily polymerizes but the chemistry of aqueous solutions is very complex. This is exemplified by the large number of polytungstates. The chemical uses of tungsten have increased substantially in more recent years. The hexacarbonyl has potential as a lubricant additive and as a dye and pigment. The halides are useful as a starting materials in the chemical vapor deposition of tungsten. The oxides are important intermediate products in the stepwise reduction in hydrogen to the metal. Tungsten bronzes constitute a series of well‐defined nonstoichiometric compounds. The sodium tungsten bronzes are interesting not only for their intense color range but exhibit both positive and negative coefficient of resistance as the sodium:tungsten ratio changes. Sodium tungsten bronzes help the catalytic oxidation of carbon monoxide and reformer gas in fuel cells. The tungstates are an important class of materials. The metatungstates are important starting materials for production of tungsten catalysts because of the high solubility in water. Ammonium paratungstate is the intermediate material of choice between chemical recovery from ores and the reduction to tungsten metal. The interstitial compounds, particularly with carbon, represent the largest application for tungsten in cemented carbides. Tungsten compounds, especially the oxides, sulphides, and heteropoly complexes, form stable catalysts for a variety of chemical processes in the petroleum industry and in chemical synthesis. Other uses include fireproofing of textiles, as additives in lubricants and antifreeze solutions, in inks and dyes, as phosphors in fluorescent lights, and for improvement of conductivity of tin oxide coatings on aircraft windows. Because soluble tungsten compounds show varying degrees of toxicity, exposures in the workplace are regulated.