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

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 gamma-Fe2O3 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 Cr3+ 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 Cr3+ content accompanying the oxidation of Cr3+ to Cr6+ in transpassive region, (C) 2002 Elsevier Science Ltd. All rights reserved.