Inhibitory Protection of Low-Carbon Steel in a Flow of Sulfuric Acid Solution Containing Iron(III) Sulfate

Abstract

Corrosion of low-carbon steel in a flow of H₂SO₄ solutions containing Fe₂(SO₄)₃ was studied, including media with additions of corrosion inhibitors—catamine AB (a mixture of quaternary ammonium salts) and IFKhAN-92 (3-substituted derivative of 1,2,4-triazole). In these media, partial reactions of anodic ionization of iron and cathodic reduction of H⁺ and Fe(III) cations occur on steel. The former two reactions are kinetically controlled, while the latter is diffusion-controlled. The accelerating effect of Fe₂(SO₄)₃ on steel corrosion in an H₂SO₄ solution is primarily due to the reduction of Fe(III). In contrast, in the inhibited acid, the accelerating effect of Fe(III) cations affects all partial reactions of steel. Data on corrosion of low-carbon steel in the flow of the given media, obtained from the mass loss of the metal samples, are in satisfactory agreement with the results of the study of partial electrode reactions. Steel corrosion in a flow of H₂SO₄ solutions, including in the presence of inhibitors, is accelerated by Fe₂(SO₄)₃. In these solutions, steel corrosion is determined by the convective factor, which is characteristic of diffusion-controlled processes. The IFKhAN-92 inhibitor, unlike catamine AB, significantly slows down steel corrosion in the flow of H₂SO₄ solution containing Fe₂(SO₄)₃. The reason for the higher inhibitory effects shown by IFKhAN-92 for steel in these solutions compared to catamine AB is the more significant slowdown of the partial electrode reactions of the metal.