Effect of Fe(II) and Fe(III) cations on corrosion of low-carbon steel in mixture of hidrochloric and phosphoric acids, containing composite inhibitors based on IFKhAN-92

Corrosion of 08PS low-carbon steel has been studied in a wide temperature range t = 25—100 °C in 1 M HCl + 1 M H3PO4, 2 M HCl and 2 M H3PO4 solutions inhibited by a binary mixture IFKhAN-92 + KNCS (molar ratio of components 9:1) and a three-component mixture IFKhAN-92 + KNCS + urotropine (9:1:400) in the presence of high concentrations of Fe(III) and Fe(II) salts, as well as in their joint presence. It is shown that under experimental conditions the three-component inhibitor mixture provide protection of steel in 1 M HCl + 1 M H3PO4 even in the presence of Fe(III), Fe(II) salts or their mixtures. Under similar conditions in individual 2 M HCl the protective effects of inhibitors are lower. A stronger deceleration of steel corrosion by composite inhibitors based on IFKhAN-92 in HCl + H3PO4 solutions containing Fe(III) salts, in comparison with similar solutions of individual HCl, is largely due to the binding of Fe(III) cations by phosphate anions into complexes, which considerably reduces their chemical activity and, as a consequence, the steel corrosion rate.