Electrochemical Measurement of the Depth-profile of Cr Depletion Layer near the Surface of SUS 304 Oxidized in Air at 1, 273K

Abstract

The author previously proposed the speedy and easy electrochemical measurement of the depth-profile of Cr near the surface of Fe-Cr alloy, and so in this work, the validity of this measurement was evaluated by comparing the depth-profile of Cr measured by this method with that calculated from evapolation model. SUS 304 specimens were oxidized in air at 1, 273K, and after removing only oxide film by careful polishing, polarized at 1.40V (SCE) (transpassive region) in 10% H₃PO₄ (323K, air open) in order to measure the I_{t, p} (10^-3A·cm^-2)-Q(C·cm^-2) curves. From these curves, the experimental depth-profiles of Cr were obtained by converting I_{t, p} into Cr concentration and Q into depth. Comparing experimental and theoretical depth-profiles of Cr, the best fit values of the lattice interdiffusion coefficient, D, in the SUS 304 and the interface transfer coefficient, α, of Cr were estimated by a least squares method of computer simulation. The estimated values of D and α were in good agreement with those obtained in previous work.