Corrosion of mild steel in static and dynamic solutions of HCl, HCl + HPO and HPO containing Fe(III) salts, including media containing two-component inhibitor IFKhAN-92 + KNCS has been studied. In the discussed media, partial reactions of anodic ionization of iron, cathodic reduction of H and Fe(III) compounds are realized on steel. Iron ionization and proton reduction proceeds with kinetic control, while Fe(III) reduction is characterized by diffusion kinetics. In the solutions under consideration the addition of 4.5 mM IFKhAN-92 + 0.5 mM KNCS inhibits all partial reactions occurring on the metal surface, which is a consequence of its formation of a polynolecular protective layer on the steel. The result of inhibition by the investigated inhibitor in HCl, HCl + HPO and HPO solutions containing Fe(III) salts of all partial reactions realized on the steel surface is its slowing down of its corrosion. The mixture inhibitor strongly retards the corrosion of steel in 2 M HPO and 1 M HCl + 1 M HPO, but provides poor protection of the metal in 2 M HCl. This is due to the different ability of the anions of the aggressive medium to bind Fe(III) cations into complex compounds. Phosphate anions, in comparison with chloride anions, more strongly bind Fe(III) cations into complex compounds, determining for them in such media lower values of D. The protective film of the inhibitor, formed on steel, most effectively slows down the reduction of Fe(III) compounds, present in solution, realized in diffusion mode, with relatively low values of the diffusion coefficient.
Ya.G. Avdeev (Wed,) studied this question.