Features of Corrosion of Low-Carbon Steel in a Flow of Acid Solutions of Various Anionic Composition Containing Iron(III) Salts

The corrosion of low-carbon steel in HCl, HCl + H₃PO₄, and H₃PO₄ solutions containing Fe(III) salts was studied. In the studied systems, steel corrosion occurs as a result of its reaction with an acid solution and Fe(III) salt. In the discussed environments, partial reactions of anodic ionization of iron and cathodic reduction of H⁺ and Fe(III) cations are realized on steel. The first two reactions are characterized by kinetic control, and the last one occurs in diffusion mode. The accelerating effect of Fe(III) cations on steel corrosion in the studied environments is mainly due to the reduction of Fe(III). The binding of Fe(III) cations into complex compounds with anions of the corrosive environment reduces the values of their diffusion coefficients (D_Fe(III)). The value of D_Fe(III) is maximum in HCl solution and minimum in H₃PO₄ solution. The rate of the partial cathodic reaction of Fe(III) reduction is determined by the value of D_Fe(III). As a result, the accelerating effect of Fe(III) on the cathodic reaction and, as a consequence, the general corrosion of steel in a flow of an aggressive environment is the most significant in a solution of HCl and is the least in a solution of H₃PO₄.