Inhibitory protection of low-carbon steel in a mixed solution of sulfuric and phosphoric acids containing Fe(II) and Fe(III) salts

The effect of Fe(III) and Fe(II) salts on the corrosion of 08PS low-carbon steel in 1 M H2SO4 + 1 M H3PO4, 2 M H2SO4, and 2 M H3PO4 solutions was examined in a wide temperature range, t = 25-100°C.Formulations of compounds containing a 1,2,4-triazole derivative, IFKhAN-92, used as steel corrosion inhibitors in these environments were studied.The binary mixture of IFKhAN-92+KNCS (molar ratio of components 9:1) and a three-component mixture IFKhAN-92+KNCS+urotropine (9:1:400) were explored.Under the experimental conditions, two-and three-component corrosion inhibitors provide efficient protection of steel in 1 M H2SO4+1 M H3PO4 solution even if it contains a high concentration of Fe(III) and Fe(II) salts or mixtures thereof.The most significant protective effect is provided by the three-component inhibitor mixture.Under similar experimental conditions, the protective effects of the inhibitors in individual 2 M H 3 PO 4 and especially in 2 M H 2 SO 4 solutions are lower.The stronger inhibition of steel corrosion by the composite inhibitors based on IFKhAN-92 in H 2 SO 4 +H 3 PO 4 solutions containing Fe(III) salts, in comparison with similar solutions of H 2 SO 4 alone, is largely due to the binding of Fe(III) cations by phosphate anions into complexes, which significantly reduces their chemical activity, and hence, the corrosion rate of steel.