Reaction of Tungsten with Water

This section is closely related to the following one (3.3.) The basic equation for the reactions involved is 

Water reacts with tungsten below the boiling point. In principle, water acts as an oxidizing agent. According to ESCA investigations WO2, WO3, and oxide hydrates are formed [3.3]  

The reaction with distilled water is very slow at low temperature the corrosion rate is 3.8 pgW m h at 38 °C. The reaction is accompanied by the formation of a nonprotective oxide film, which is in equilibrium with 10 mol/l in solution. At 

Reaction with water vapor or humid air (60-95% relative humidity) in the temperature range 20-500 °C results in the formation of a WO3 layer. No lower oxides or hydrates could be found by ESCA. The thickness of the oxide layer increases with increasing humidity. The reaction rate depends on temperature and I20]/[H2] partial pressure ratio and is more rapid than with liquid water. Water molecules are adsorbed at the tungsten surface and dissociate. The oxygen atoms difiuse into the tungsten metal, forming at first a solid solution and then the oxide compound, while, hydrogen escapes as element. 

Depending on temperature and the ratio, all known oxides can be formed. 

---