Some aspects of the mechanism of steel protection in hydrochloric acid solutions by propargyl alcohol

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

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

Abstract: The specific features of iron corrosion in HCl solutions with addition of propargyl alcohol (PA) and products of its conversion in the corrosive system, namely, acrolein and allyl alcohol (AA), were studied by voltammetry. PA has the strongest inhibitory effect on the cathodic and anodic reactions of iron in acid solutions among the unsaturated compounds (UC) studied since PA forms a protective film of an organic polymer on the metal surface. Acrolein and AA slow down the electrode reactions of iron much more weakly. It has been shown that the presence of adsorbed atomic hydrogen on iron surface enhances the inhibitory effect of the UCs studied on the electrode reactions of iron. The UCs studied are cathodically reduced on iron surface under diffusion control. This result is an experimental confirmation of PA and acrolein to AA conversion on iron surface. The corrosion rate of mild steel calculated from the mass loss of metal samples in HCl solution in the presence of the UCs studied decreases in the series: AA>acrolein>PA, which is consistent with the results of electrochemical studies of these compounds on iron. Analysis of experimental data shows that the conversion of PA by isomerization to acrolein or by reduction to AA on the metal surface in the course of inhibition of the corrosion of iron or steels in HCl solutions is an undesirable process. The compounds formed slow down the electrode reactions and the corrosion of metals more poorly than the original inhibitor. We identified the main pathways of UC conversion in the course of steel corrosion inhibition in acid solutions, namely, the formation of a protective polymer film from an UC on steel and UC degradation processes that diminish the content of the reactive compound in the corrosive environment. The degradation of UCs is determined by reactions of their cathodic hydrogenation, polymerization in the bulk of the corrosive medium, and reactions with components of the acid solution.

Keywords: acid corrosion, corrosion inhibitors, propargyl alcohol, acrolein, allyl alcohol, unsaturated organic compounds, acetylenic alcohols, mild steel, hydrochloric acid

Int. J. Corros. Scale Inhib., 2022, 11, no. 2, 577-593
doi: 10.17675/2305-6894-2022-11-2-8

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