Effect of the Scan Rate on the Kinetic Parameters of Active Dissolution and Passivation of Iron in a Neutral Solution

Abstract

The effect of the potential scan rate (V = 0.2–100 mV/s) of a rotating disk electrode (rotational speed ν = 6000 rpm) on the kinetics of active anodic dissolution and active-passive transition of Armco iron in a deaerated borate buffer (pH 7.40) was studied by cyclic voltammetry. The rates of active dissolution and the formation of a prepassive film were found to be determined, under free-diffusion conditions, by slow electrochemical steps of electron transfer throughout the V range studied; the cyclic voltammogram is a transient, thermodynamically nonequilibrium curve. The anodic current peak linearly grows and its potential is shifted in the positive direction with an increase in logV. The apparent coefficients of electron transfer for active anodic dissolution depend on V in the whole range studied. This can provide explanation to a large scatter of literature data on the active anodic dissolution and active-passive transition of iron in neutral media.