Facile synthesis of nanocrystalline hexagonal tungsten trioxide from metallic tungsten powder and hydrogen peroxide

A hexagonal form of tungsten trioxide (h‐WO 3 , particle size: 15.9‐57.1 nm) was found to be formed by a direct reaction between metallic tungsten powder (W, particle size: 0.45‐0.59 μm) and 15%‐30% hydrogen peroxide (H 2 O 2 ) aq solution. Oxide film on the powder surface having the similar crystal structure as h‐WO 3 was essential for the formation, and the surface oxide film was formed by aging the powder in air at 45°C, a relative humidity of 100% ( P H2O 96 hPa) for 3‐28 days or in ambient atmosphere at room temperature for 12 years. The Rietveld analysis performed in the space group P 6 3 / mcm ( Z  = 6) indicated the crystal structures were the same as those of the reported h‐WO 3 and that the crystallographic characteristic was as follows: a  = 0.74219 nm, c  = 0.77198 nm for h‐WO 3 from the 28‐day aged powder, and a  = 0.74538 nm, c  = 0.77194 nm for h‐WO 3 from the 12‐year aged powder.