Effect of Oxygen Pressure on the Oxidation Rate of Cobalt

Co was oxidized from 800° to 1200°C in 0.013–27.2 atm O2. It oxidized in accordance with the parabolic rate law above 950°C and formed the single oxide, , above 900°C. Pressure increase accelerated the rate of oxidation. However, the oxidation rate eventually ceased to increase with increase of oxygen pressure at temperatures below 1150°C. 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.