High Pressure Oxidation of Metals—Tungsten in Oxygen

Abstract

Tungsten rod and sheet were found to oxidize linearly in oxygen from 600° to 850°C at oxygen pressures ranging from 20 to 500 psia. Oxidation rate increased with increased oxygen pressure at temperatures 750°–850°C. Theoretical considerations indicate that an equilibrium adsorption process occurs prior to the rate‐determining step. The assumption of a linear change of adsorption energy with increase of surface coverage allowed observed oxidation rates to be corrected for pressure effect. The activation energy was 48 kcal. Tungsten sheet volatilization losses were appreciable above 800°C. Only tungsten rod data were free from volatilization losses at 850°C, Photographs are included showing the effect of shearing samples at room temperature prior to oxidation on the final physical appearance of the oxide. Cold shearing produces exfoliated tungsten oxide.