XPS and Electrochemical Studies of Chromium Modified Passive Iron Electrodes

The modification of passive iron electrodes by chromate ion has been studied in three different electrochemical experiments: potentiostatic passivation, open-circuit passivation, and cyclic potential treatment. XPS surface composition and composition-depth profiles obtained by argon ion-sputtering of the modified electrodes show different patterns depending on the electrochemical treatment. Two electrokinetic pathways for the reduction of chromate associated with the different chromium concentration profiles in the film are also apparent and have been related to the reductive precipitation of hydrous Cr(III) species, and to the chromium redox centers entrapped in the passive layer. The latter permanent modification of the passive layer is only obtained by repetitive oxidation-reduction cycles of iron in alkaline chromate and has similarities with passive layers on Fe-Cr alloys. © 1988, The Electrochemical Society, Inc. All rights reserved.