Tungsten salts

Wolframit, n. (Min.) wolframite. Wolfram-lampe, /. tungsten lamp, metall, n. metallic tungsten, -ocker, m. tungstic ocher, tungstite. -oxyd, n. tungsten oxide, -salz, n. tungsten salt. 

Chemical routes involving the use of tungsten salts have been reported. W2C was claimed to be formed by the pyrolysis of an organometallic complex containing cyclopentadiene and carbonyl groups.8 The W2C formed was useful for ceramic applications such as wear resistant surfaces and cutting tools. The same phase was also prepared by the reduction of WC14 with sodium triethylborohydride.9 The material was formed as 1-5 nm-sized crystallites as shown by SEM and TEM. 

The tungsten salt resulting from treatment of nonylphenol with tungstic hexachloride has found an application as a catayst for the metathetical copolymerisation of dicyclopentadiene and 5,5,6-trlchloronorbornene (ref. 43). Antimony and lead salts of alkyidithiophosphates are important additives for lubricating greases. In the nonylphenyl series such compounds are considered to have the dimeric structure shown (where M = Pb and Sb) (ref. 44). 

Tungsten carbides were fabricated via polymer-induced carburization of the mixture of a tungsten salt (ammonium metatungstate) and carbon polymer structures (resorcinol-formaldehyde polymer) by Lee and co-workers (33-35). The polymer intermediate, in which the metal salt was trapped, was annealed at 1173 K under Ar and H2 gas. Various phases and morphologies of WC were prepared by control of polymerization conditions. The surface areas of obtained hep W2C and hex WC were 176 and 77 m /g, respectively. However, these high surface areas contained some contribution from the unreacted carbons. 

Surfactant templating chemistry can be extended to many nonsilicate compositions after modifications to the synthesis route. These materials are less structurally stable than the mesoporous silicates, which is attributed to the thinness of the amorphous pore walls ( 1 to 2 nm). Stucky and coworkers [85,86] showed that this problem could be mitigated by preparing the materials with thicker walls. To prepare mesoporous WO3, they dissolved a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer and WCle salt in ethanol, and dried the resulting solution in open air. The tungsten salt reacted with moisture to undergo hydrolysis and condensation reactions. These chemical reactions caused the eventual formation of amorphous WO3 around triblock copolymer micelle-like domains, and after calcination at 400 C, a mesoporous WO3 with thick, nanocrystalline walls ( 5 nm) and surface area of 125 m /g was formed. 

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