Interaction of Oxygen with Polycrystalline Tungsten. II. Corrosive Oxidation

The kinetics of formation of a corrosive oxide layer of apparently unlimited thickness during the interaction of oxygen with a polycrystalline tungsten filament at temperatures between 500 and 1000°K has been investigated by line‐of‐sight flash desorption mass spectrometry. The major desorption product from this multilayer oxide film is WO2, which desorbs over the temperature range 1000–1300°K. The rate of formation of the oxide film was shown to be directly proportional to the oxygen gas phase pressure at pressures ≲ 10−4 torr. A study of the temperature dependence of the oxidation rate revealed that the formation of the WO2‐producing oxide layer proceeds through two distinct steps; these occur subsequent to the first three stages in the interaction of oxygen with W characterized in Paper I. In the final state of oxidation, the rate is shown to be independent of the thickness of the oxide film. The results are in qualitative accord with the theoretical model of Mott. Desorption of the oxide film is a zer...