Effects of Coverage with an Ultrathin Polymer Coating and Healing Treatment on Passive Film Breakdown of Iron in Solutions of Various Anions

Abstract

An ultrathin two-dimensional polymer coating was prepared on a passivated iron electrode and then the passive film was healed by immersion treatment in 0.1 M NaNO₃. The time required for passive film breakdown, t_bd was measured by monitoring the open-circuit potential in 0.1 M solutions of four anions. The protective efficiencies of the passivated, polymer-coated and healed electrodes were extremely high, around 99.9% before t_bd and hence, complete protection against corrosion of iron was accomplished, unless the passive film was broken down. On the other hand, the t_bd values of the passivated Fe electrode, t_bd⁰ have been determined in 0.1 M solutions of 14 different anions. In the present investigation, the t_bd values of the passivated electrode covered with the polymer coating, t_bd¹ and those of the passivated, polymer-coated and healed electrode, t_bd² are estimated from t_bd⁰. These values are discussed using classifications of anions based on the hard and soft acids and bases principle. Further, the effect of anion concentration on the t_bd² value is discussed.