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Tungsten rod and sheet were found to oxidize linearly in oxygen from 600 ~ to 850~ at oxygen pressures ranging from 20 to 500 psia. Oxidation rate increased with increased oxygen pressure at temperatures 750~176Theoretical 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 Mlowed observed oxidation rates to be corrected for pressure effect. The activation energy was 48 kcal. Tungsten sheet volatilization losses were appreciable above 800~ Only tungsten rod data were free from volatilization losses at 850~ 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.

Niobium oxidizes according to the linear rate law from 400~176 (14.7-605 psia O2). The oxidation rate is extremely pressure sensitive above 550~ Theoretical considerations indicate that an equilibrium adsorption process occurs prior to the rate-determining step. It was necessary to include a term in the rate equation for the interaction between the adsorbed molecules to interpret results above 650~ The interaction energy is influenced by the initial orientation of the metal surface. The activation energy for the oxidation process is approximately 9 to 10 kcal (500~176

Co was oxidized from 800 ~ to 1200~ in 0.013-27.2 atm O2. It oxidized in accordance with the parabolic rate law above 950~ and formed the single oxide, CoO, above 900~ Pressure increase accelerated the rate of oxidation. However, the oxidation rate eventually ceased to increase with increase of oxygen pressure at temperatures below 1150~ Theoretical considerations employing a vacancy saturation mechanism correlated the data. Photomicrographs of the oxide layer are included. Activation energy for the diffusion process is 58,000 cal,

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