Tungsten trioxide nanopowder applying for ceramic microsphere may be obtained by calcining pyrochlore-type tungsten trioxide (WO3•0.5H2O) with high purity. It is worth to note that the WO3•0.5H2O may be a feasible direction for further development of tungsten smelting. Therefore, it is necessary to pay attention to the preparation method of WO3•0.5H2O.
Under hydrothermal conditions, ultrafine pyrochlore-type tungsten trioxide powders may be prepared directly from sodium tungstate solution using pure tungsten trioxide (WO3) as an additive. The results showed that the response rate may reach about 80% by adding WO3 to a 100g/L sodium tungstate solution at 140°C for 24h in a closed pressure vessel. The hydrothermal products were characterized by XRD and SEM. And it was found that the product had a well-crystallized cubic structure and the average size of the particles was less than 1μm. The EDS test showed that the obtained product contained a trace amount of Na element. After washing with hydrochloric acid, the pyrochlore-type tungsten trioxide powder was obtained containing almost no impurity Na. The change of ionic structure of sodium tungstate solution under hydrothermal conditions was determined by IR spectroscopy, and it was preliminarily considered that the growth unit of pyrochlore-type tungsten trioxide was WO42-.
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