About the nature of iron anodic activation in solutions of mineral acids

• Ya.G. Avdeev

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: Some aspects of the effect of hydrogen absorption on the anodic ionization of iron in solutions of mineral acids, both in the absence and in the presence of corrosion inhibitors, are discussed. It is shown that the process of iron anodic ionization in acid media is sensitive to the hydrogen content in the metal. The stronger the hydrogen content in the metal, the lower the rate of its ionization. In many cases, anodic activation of iron can result from the desorption of adsorbed hydrogen which, like an inhibitor, blocks the active centers of the metal ionization from the surface. The anodic activation of iron in inhibited acid solutions can be provoked by removal of adsorbed hydrogen from the metal surface, partial or complete desorption of the inhibitor, and formation of pits. It is noted that in inhibited acid solutions, even at potentials higher than the anodic activation potential, an adsorbed inhibitor can not only be partially retained on iron surface but also be adsorbed on a newly formed metal surface. The development of pitting upon anodic activation of iron results from partial desorption of an inhibitor from the metal surface. Pits form on inhibitor-free areas of the steel surface. The possibility of pitting corrosion of iron in inhibited solutions of mineral acids in the case of a shift of the corrosion potential by inhibitors to the pitting potential is discussed.

Keywords: anodic dissolution of iron, inhibition, activation potential, desorption potential, acid solutions

Int. J. Corros. Scale Inhib., 2020, 9, no. 4, 1375-1380 PDF (221 K)
doi: 10.17675/2305-6894-2020-9-4-10

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