Some aspects of the mechanism of steel protection in mineral acid solutions by unsaturated aldehydes

• Ya.G. Avdeev and T.E. Andreeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: The effect of α,β-unsaturated aldehydes (cinnamaldehyde (CA), citral, and crotonaldehyde) on the corrosion of low carbon steel in hydrochloric and sulfuric acid solutions was studied by analyzing data on the mass loss of metal samples during their exposure to the corrosive media and the results of voltammetric studies on steel. Among the α,β-unsaturated aldehydes examined, CA is the most efficient corrosion inhibitor of steel in 2 M HCl. The temperature maximum of the corrosion inhibition coefficient for CA in this medium lies no lower than 80°C, which formally makes it possible to classify CA as a high-temperature inhibitor. It was shown that the presence of an α,β-unsaturated C=C bond in the structure of aldehydes largely determines the higher protective effects of the latter in inhibiting steel corrosion compared to structurally similar compounds that do not contain this moiety. Significant inhibition of steel corrosion by CA in hydrochloric acid solutions results from the strong inhibition of the electrode reactions on steel over a wide temperature range. The ability of CA to markedly slow down the electrode reactions of steel in hydrochloric acid is associated with the formation of polymeric organic layers on the metal surface, which effectively isolate the surface from contacting the corrosive medium. The low efficiency of α,β-unsaturated aldehydes in the inhibition of steel corrosion in H₂SO₄ solutions is due to their participation in the electrode reactions of the metal as depolarizers and complexing agents.

Keywords: acid corrosion, hydrochloric acid, sulfuric acid, corrosion inhibitors, mechanism of inhibitor action, aldehydes, α,β-unsaturated aldehydes, cinnamaldehyde

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 2362-2378
doi: 10.17675/2305-6894-2025-14-4-34

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