LARGE-AREA PHOTOCURRENT BEHAVIOR AND LASER SPOT SCANNING OF PASSIVATED STAINLESS-STEELS

The semiconductor properties of passive films on different stainless steels were investigated by photoelectrochemical methods. Photocurrent-potential measurements together with data for the susceptibility of the materials to localized corrosion revealed that above a critical potential value (U(crit)) photocurrents as well as the pit initiation rate decrease with increasing potential. The occurrence of U(crit) could be explained by a Cr(III)/Cr(VI) oxidation in the passive film starting at this potential. By applying a laser spot scanning technique it was possible to resolve local variations in the photocurrent response of the passive films studied. Microscopic investigations revealed that sites which exhibit an enlarged photocurrent coincide with inclusions present in the bulk material of the steels.