Kinetics of the Oxidation of Pure Tungsten from 500° to 1300°C

Kinetic studies were made on the oxidation of tungsten from 500° to 1300°C for time periods up to 6 hr, and for oxygen pressures from 0.1 atm to 0.00132 atm. The rate data were fitted to the parabolic rate law. A number of deviations and transitions were observed. For all of the experiments the initial slopes of the parabolic rate law plots were smaller than the final values found for thick films. A transition in the rate of oxidation was observed for weight gains of 2500–4000 µg/cm 2 at temperatures of 650°–800°C. Photographs of the oxidized surface above 650°C show that oxidation occurs in a preferential manner at the edges. Pressure had a strong effect on the rate of oxidation for the experiments above 950°C. At 1200°C weight loss curves were observed for pressures as high as 0.1 atm. Above 1200°C the oxidation reaction is similar to the combustion of graphite. The rate of oxidation is limited by the volatility of , the diffusion of oxygen to the surface, and the diffusion of away from the surface.