Tungsten(VI) oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

Tungsten trioxide powder has been prepared from ammonium paratungstate via hydrothermal method using orthogonal and mono-level design of experiments. The effects of preparation process on particle size, specific surface area, crystal form and crystalline morphology of the tungsten trioxide was investigated by TEM and XRD etc. It was found that the optimum conditions of the preparation are hydrothermal crystallization for 8 h at 180°C, followed by vacuum drying at 45°C and calcination at 500°C for 2 h. The blank reference experiment shows that hydrothermal crystallization treatment favors the formation of hexagonal tungsten trioxide, and the tungsten trioxide powder sample prepared by this method has a high degree of crystallinity.