THERMODYNAMICS AND KINETICS PREDICTIONS OF FORMATION OF OXIDE-SULFIDE SCALES ON CHROMIUM AND IRON

摘要

The corrosion of Fe and Cr in SO_2 has been studied at 1073 K - 1273 K only for Cr, but (873 - 1173) K for Fe at 100 K intervals. The corrosion kinetics follow the parabolic rate law to a good approximation for iron. Only small deviations from the parabolic rate law In the Initial stage were observed, whereas the oxidation of chromium proceeded according to the linear rate law under 10~5 Pa of SO_2 at (1073 - 1273) K, but to the parabolic rate law at 1173 K and 1273 K under 3·10~4 Pa of SO_2. The transport phenomena by radiotracer techniques were studied. The scales were composed of sulflde and oxide and grew by outward diffusion of the metals. Inward transport of SO_2 molecules through the discontinuities in the scale was observed. The mechanism of sulflde and oxide formation Is discussed on the basis of the thermodynamics and kinetics predictions.