Abstract
The effect of oxygen pressure in the range on the oxidation kinetics of polycrystalline Cr was investigated at temperatures of 300°, 400°, 490°, and 600°C. Results were obtained by comparing reaction rates of samples oxidized at different pressures and also by observing the effect of abrupt changes in pressure during the course of a reaction. The two types of experiment yielded the same result. At 300°C the pressure exponent in the expression: , is small and positive, decreasing in magnitude with increasing film thicknesses. At it was found that, respectively. The positive pressure exponent at low temperature which accompanies thin film formation, is consistent with the Mott‐Cabrera theory of oxidation, as modified to include adsorption equilibria. The negative pressure exponent, which accompanies parabolic kinetics, is described in terms of an adsorption model in which different adsorbed species are responsible for electrostatic field production and for point defect formation within the oxide.
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