Considerations Based on the HSAB Principle for Inhibition Mechanisms of Cationic Precipitation Inhibitors in Aerated Neutral Solutions

Abstract

In the present paper, cationic precipitation inhibitors effective for Fe corrosion in aerated 0.5 M Na₂SO₄ are discussed based on the hard and soft acids and bases （HSAB） principle. Multivalent metallic cations are readily precipitated by the formation of their hydroxides due to stable hard acid and hard base interaction. They suppress the cathodic process of Fe corrosion, reduction of dissolved oxygen but promote the anodic process of Fe dissolution. High inhibition efficiencies are obtained by the addition of anionic precipitation inhibitors suppressing the anodic process. On the other hand, high concentration of cerium （III） ion, Ce^3＋ inhibits both cathodic and anodic processes by the direct formation of oxide layer with evolution of H₂.