The ultrafine pyrochlore-type tungsten trioxide powders were hydrothermally synthesized from sodium tungstate solution by adding pure WO3 powders to the reaction system. The results show that the precipitation rate of tungsten species in solution can reach 80%. XRD analyses results indicate that the precipitates are powders with cubic crystal structure. EDS analyses results reveal that a small amount of impurity of sodium is present in the precipitates and it can be completely removed by washing in the diluted hydrochloric acid. SEM micrographs show that the average diameter of the precipitates is less than 1.0 urn. Based upon IR technique, a new reaction mechanism is proposed that WO42- may be the growth unit of pyrochlore-type tungsten trioxide during the hydrothermal precipitation process of sodium tungstate solution.%在水热条件下利用纯WO3作为添加剂能够直接从钨酸钠溶液中制备出超细焦绿石型三氧化钨(WO3·0.5H2O)粉体.结果表明:往100 g/L的钨酸钠溶液中添加WO3,在密闭压力容器内,在140℃下反应24 h,反应率能达到80％左右.采用XRD和SEM等测试手段对水热产物进行表征,产物为结晶良好的立方体结构,颗粒的平均尺寸小于1μ m.EDS检测表明:所得产品含微量的Na元素,经盐酸洗涤后可得到几乎不含杂质Na的WO3·0.5H2O粉体.利用IR光谱测定水热条件下钨酸钠溶液的离子结构变化,初步认为制备WO3·0.5H2O的生长基元为WO42-.
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