W bronzes

The author and Sokolova (193) investigated the catalysis of alcohols on tungsten bronzes, which possess a defective structure. An X-ray structural analysis was also made in this research. In spite of the defective structure, the catalytic activity of W-bronzes proved to be rather low, contrary to the electronic theory of catalysis. According to the latter, however, the catalytic activity decreases as bronzes are being reduced or lithium added, the detectivity decreasing too. From the BET data and the X-ray patterns it follows that the surface of bronzes is practically unaltered on reduction. On the other hand, the low activity... 

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... 

The above Sn nitrate ( ) deserves mention because it was thought to be a fire and expin hazard in industrial accidents. For example, at the Spandau plant in Ger, several fires erupted in areas where wet NC came in constant contact with soldered bronze joints. In order to prevent further incidents, all soldered joints were examined and were found to be corroded with a coating contg Sn and nitrate ions. It was also found that the corroded material exploded when removal with a chisel was attempted Ellern (Ref 2) mentions that in the presence of w, cupric nitrate and Sn foil, on prolonged and intimate contact, will produce flaming and sparking... 

Upon reduction, WO3 forms mixed-valence (WjWj W ) tungsten bronzes, H WOj, which have different colors depending on the degree of reduction, x [see Eq. (33.1)]. Due to parasitic reaction, such as hydrogen evolution, and decreased... 

Consider now NajW03 or LiTi204. One might expect to find W(V)-W(VI) and Ti(III)-Ti(lV) MMCT. However, in these compounds all metal ions are equivalent and the d electrons available are spread out in a conduction band. The bronzes NajW03 are metallic. They become superconducting at 6K, whereas LiTi204 becomes superconducting at even 13 K [59]. Here we meet the central problem of mixed-valence compounds [60] which we will postpone till Sect. 5. 

Conroy and Perlow [235] have measured the Debye-Waller factor for W in the sodium tungsten bronze Nao.gWOs. They derived a value of/= 0.18 0.01 which corresponds to a zero-point vibrational amplitude of R = 0.044 A. This amplitude is small as compared to that of beryllium atoms in metallic beryllium (0.098 A) or to that of carbon atoms in diamond (0.064 A). The authors conclude that atoms substituting tungsten in bronze may well be expected to have a high recoilless fraction. 

Smith, A. W. (1978), Stable carbon and oxygen isotope ratios of malachite from the patina of ancient bronze objects, Archaeometry 20, 123-133. 

Zimmerman, D. W., M. P. Yuhas, and P. Meyers (1974), Thermoluminescence authenticity measurements on core material from the bronze horse of the New York Metropolitan Museum of Art, Archaeometry 16, 19-30. 

J. Gabel, W. Vonau, P. Shuk, and U. Guth, New reference electrodes based on tungsten-substituted molybdenum bronzes. Solid State Ionics 169, 75-80 (2004). 

Hosetter, E., Beck, C. W., and Stewart, D. R. (1994). A bronze stitula from tomb 128, Valle Trebba chemical evidence of resinated wine at Spina. Studi Etruschi Bretschneider LIX 211-225. 

Oxygenated Bronzes , P. Hagenmuller, Progr. Solid State Chem., 1971, 5, 71. The Photochemistry of Transition-metal Co-ordination Compounds , W. L. 

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