A Closer Look at the Passivity and Transpassive Dissolution of Chromium Using Atomic Spectroelectrochemistry

The dissolution and growth kinetics of the passive film upon chromium (Cr) in 0.1 M NaCl was studied using atomic spectroelectrochemistry. The dissolution rate was independent of applied potential in the passive region, and increased exponentially with increasing potential in the transpassive region. The growth kinetics of the passive film upon Cr in the passive state was consistent with the assumptions of the point defect model. The charge balance analysis established an intermediate potential region whereby the growth rate of Cr₂O₃ layer was higher than the dissolution rate in the transpassive state. The interdependence of oxidation and dissolution rate of Cr in non-steady state was revealed and its significance to the passivity of Cr-containing alloys was discussed.