Chemical Analysis of the Alkali Metal Tungsten Bronzes.

A method has been developed for the chemical analysis of the three major constituents in alkali metal tungsten bronzes: alkali metal, tungsten, and oxygen. The analyses are based on the reactions of bromine trifluoride and hydrogen with the bronzes. This analytical system has been successfully employed for alkali metal tungstates and tungsten oxides as well as for the bronzes. Bromine trifluoride reacts with tungsten bronzes to produce alkali metal tetrafluorobromate (III), tungsten hexafluoride, bromine, and oxygen. At the temperature of dry ice, oxygen is the only product which is not a solid; it is transferred into a constant volume manometer for measurement. Subsequently, the bromine, tungsten hexafluoride, and excess bromine trifluoride are distilled out of the reactor. This operation isolates the alkali metal tetrafluorobromate(III) which is easily rinsed out of the reactor with dilute sulfuric acid and converted to the alkali metal sulfate for gravimetric determination. Because the tungsten-- fluorine system is quite complex, it is necessary to determine tungsten in quite a different manner. The bronzes react with hydrogen to produce alkali metal oxide, tungsten metal, and water. Tungsten is the only non-volatile product and remains in the reaction boat for direct weighing. Although hydrogen reduction is valid formore » the other alkali metal compounds, it cannot be used with the corresponding lithium compounds because of the low volatility of lithium oxide. Lithium bronzes are dissolved by a basic, oxidizing fusion which converts the bronze to water-soluble tungstate. Tungsten is determined in this case by precipitation with hydrogen peroxide and nitric acid; the precipitate is ignited to and weighed as tungsten trioxide. This analytical system is capable of determining all the constituents of alkali metal tungstates and bronzes and in tungsten oxides with an accuracy better than 0.5 to 0.7 per cent of the relative values. Two interesting items of information were produced by this research. One is that the oxygen-to-tungsten ratios of alkali metal orthotungstates and bronzes are really 4.000 and 3.000 respectively; the corresponding lithium compounds appear to be anomalously oxygen-rich. The other is a determination of the correct conditions for the preparation of tungsten trioxide so that there are no interferences by volatility and changes in stoichiometry. (auth)« less