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

• Ya.G. Avdeev¹, A.V. Panova¹, K.L. Anfilov² and Yu.I. Kuznetsov¹

¹ A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation
² Bauman Moscow State Technical University (Kaluga Branch), Bazhenov str. 2, 248000 Kaluga, Russian Federation

Abstract: The effect of Fe(III) and Fe(II) salts on the corrosion of low-carbon steel 08PS in 1 M HCl+1 M H₃PO₄, 2 M HCl and 2 M H₃PO₄ was studied in the temperature range of t=25–100°C. Mixtures of chemical compounds containing IFKhAN-92, a 1,2,4-triazole derivative, were studied as steel corrosion inhibitors in these environments. The inhibitory effect of the binary formulation IFKhAN-92+KNCS (molar ratio of components 9:1) and the three-component formulation IFKhAN-92+KNCS+hexamethylenetetramine (HMT) (9:1:400) on steel corrosion in these media was considered. The IFKhAN-92+KNCS+HMT formulation was shown to be promising for the protection of low-carbon steel in 1 M HCl+1 M H₃PO₄. It was found that under the experimental conditions, the three-component mixture provides protection for steel in 1 M HCl+1 M H₃PO₄, even if the solution contains Fe(III), Fe(II) salts or their mixtures. The protective effects of the inhibitors studied are weaker under similar conditions in 2 M HCl alone. The stronger inhibition of steel corrosion by the composite inhibitors based on IFKhAN-92 in HCl+H₃PO₄ solutions containing Fe(III) salts in comparison with similar solutions of HCl 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.

Keywords: acid corrosion, hydrochloric acid, phosphoric acid, corrosion inhibitors, triazoles, low carbon steel, iron(III) chloride, iron(III) phosphate, iron(II) chloride, iron(II) phosphate

Int. J. Corros. Scale Inhib., 2024, 13, no. 1, 567-582
doi: 10.17675/2305-6894-2024-13-1-28

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