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.

2 WO3 + 3 C → 2 W + 3 CO2 (high temperature)

WO3 + 3 H2 → W + 3 H2O (550 - 850 °C)

Tungsten(VI) oxide occurs naturally in form of hydrates, which include minerals: tungstite WO3·H2O, meymacite WO3·2H2O and hydrotungstite (of same composition as meymacite, however sometimes written as H2WO4). These minerals are rare to very rare secondary tungsten minerals.

 

Tungsten trioxide was prepared by calcination of pure ammonium paratungstate in the air. The obtained tungsten trioxide powder was reduced in pure hydrogen gas(purity of 99.99%,dew point of-40℃) to tungsten powder.The resulting tungsten powder was oxidized in the air and then was reduced in the pure hydrogen gas. The samples were characterized by laser particle size distribution instrument and scanning electron microscope.The results show that percentage of the particle size(between 0.1μm and 0.5μm) of submicron tungsten powder obtained by circulatory oxidation-reduction at twice is 94.81% and BET specific surface area is 2.684m2/g.