Why Do Anions Inhibit or Stimulate the Anodic Process of Iron Corrosion in an Acid Solution?

Abstract

It has been reported in the previous studies that anions like Cl^－, Br^－, and I^－ inhibit and those like SCN^－, SH^－, and S₂O₃^2－ stimulate the anodic process of iron corrosion in 1 M HClO₄. These effects of anions on the anodic process were interpreted on the basis of the hard and soft acids and bases principle. The former three anions classified into the soft bases suppress the anodic process by the formation of a stable adsorption bond on bare iron, a soft acid. The latter three anions of the soft and hard bases accelerate the process due to soft acid-soft base and hard acid-hard base interactions.