Photoelectrochemical analysis on the passive film formed on Fe–20Cr in pH 8.5 buffer solution

Abstract

The electronic properties of passive film formed on Fe–20Cr stainless steel in pH 8.5 buffer solution were examined by the photocurrent measurements of the film. The passive film on Fe–20Cr exhibited an n-type semiconductor, which was confirmed by anodic photocurrent. The photocurrent spectrum for the passive films formed on Fe–20Cr was almost same in shape to that for the passive film on Fe except for the large difference in photocurrent intensity, which demonstrated that the passive film on Fe–20Cr is composed of Cr-substituted γ-Fe 2O 3 involving the d-d and p-d electron transitions. However, the large difference in photocurrent intensity for passive film between Fe and Fe–20Cr was due presumably to the fact that Cr 3+ ions in passive film act as effective recombination sites of electron-hole pairs. The abrupt increase in the photocurrent intensity for the passive film formed on Fe–20Cr at a transpassive potential is due presumably to the decrease in the recombination site resulting from the reduction of Cr 3+ content accompanying the oxidation of Cr 3+ to Cr 6+ in transpassive region.