Under hydrothermal conditions, the superfine powders of cubic pyrochlore-type of tungsten oxide and hexagonal tungsten bronze were obtained by using Na2WO4·2H2O as the starting material. The products were characterized by XRD, TG, IR, UV and EPMA, respectively. The effects of the pH value, the acid concentration, reaction temperature and time on the structure and particle size of products were investigated in detail. The conditions for the preparation of superfine powders of tungsten oxide were optimized. The pH 2.5～4.5 of the reaction system led to the formation of a pyroehlore phase and pH 0.5～2.0 gave the hexagonal tungsten bronze structure. The photochromism property of the hexagonal tungsten bronze was studied. The results show that pyroehlore and bronze phases are decomposed at 300℃ and 450℃, respectively. With the increasing of temperature, the structure of the two oxides changes. The pyrochlore-type powder changes completely into trielinic Na2W4O13 around 500℃, while the bronze phase into a mixture of Na2W6O19 and trielinie WO3 at 550℃. The powder of the hexagonal tungsten bronze showed better photochromism property。
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