Polarization behaviour of some Fe-Cr alloys in acidic chloride solutions

Abstract

Potentiostatic polarization studies were performed in chloride solutions with two Fe-Cr alloys of 5 and 15% Cr contents. The exchange current density of hydrogen evolution was found to decrease with increasing Cr content. The rate of anodic dissolution of the low Cr alloy (5% Cr) strongly depended on pH and showed a Tafel slope of 70 mV decade −1 . That of high Cr content alloy (15% Cr) was independent of pH which is similar to that of pure Cr content. An increase in the chloride ion concentration at a constant pH increased the dissolution rate of 15% Cr alloy and the reaction order with respect to Cl − concentration was found to be 0.5. Passivation of 15% Cr alloy in chloride solution was a function of pH. Thus, below pH 1.5 no true passivation was observed whereas passivation commences when the pH of chloride solution is > 1.5.