The Cathodic and Anodic Behavior of Iron in Acetate Buffer Solutions

Abstract

The cathodic and anodic behavior of iron was investigated in different acetic acid/sodium acetate and borate buffer solutions. Passive oxide films were formed in pH 8.4 borate buffer solution and cathodically reduced in pH 7.0 and pH 8.4 borate as well as different acetate buffer solutions. The ratio of the two cathodic reduction arrest charges, i.e., , is related to the composition of the oxide film and tends to the almost independent of passivation potential for films reduced in borate buffer. A different ratio is, however, observed for cathodic reduction of the air‐formed oxide film on electropolished iron. For cathodic reduction in acetate buffer solutions, the ratio is quite different from that observed in borate buffer solution and depends on the concentration of the electrolyte species and the solution pH. Complex, different cathodic reduction profiles are observed in acetate buffer solutions with high electrolyte concentration and/or low pH. The results are discussed in terms of the influence of the various solution parameters on the efficiency and mechanism of oxide reduction. Passive oxide films were also formed in acetate buffer solution and were cathodically reduced in either borate or acetate buffer solution. Both the oxide film growth efficiency and composition were dependent on the nature of the acetate formation solution. In fact, a correlation exists between oxide film composition, as defined by the ratio, and anodic growth efficiency.