THERMAL INVESTIGATION OF TUNGSTEN-OXIDE BRONZES

Compounds corresponding to the general formula A(x)MO(n) are designated as oxide bronzes where A is the bronze forming element, M is the central metal ion which determines the value of stoichiometric factor n. The other stoichiometric factor is x < 1 generally. Tungsten oxide bronzes (A(x)WO3) are the best known representatives of this group of compounds. In general, oxide bronzes are extremely stable compounds (except hydrogen tungsten oxide bronzes which decompose rapidly under dry conditions), and on heating two types of decomposition occur. These are as follows: Na0,55WO3 half arrow right over half arrow left 0,55 Na + WO3 Na0,55WO half arrow right over half arrow left 0,275 Na2O + 0,725 WO3 + + 0,275 WO2 (2) After Dickens et al. Eq. 1 is termed as decomposition while Eq. 2 as disproportionation. These processes are not only of theoretical but also of practical importance, e.g. in the production of tungsten metal for light sources (non-sag tungsten). Thermal decomposition of several sodium and potassium oxide bronzes, and that of doped ammonium tungsten oxide bronze was studied applying a micro quartz furnace attached to an atomic absorption spectrophotometer. Our results contributed to a better understanding of chemical questions of the initial steps of non-sag tungsten production as well as to that of the development of complex non-sag characteristics.