Inhibition of pitting formation on copper by microadditives of halide ions in alkaline glycinate media

• M.Yu. Sanina¹, S.A. Kaluzhina², N.G. Nafikova² and Yu.V. Berdysheva²

¹ Voronezh State Pedagogical University, 86 Lenina Street, 394043, Voronezh, Russian Federation
² Voronezh State University, 1 Universitetskaya Square, Voronezh, 394018, Russian Federation

Abstract: Using a complex of physicochemical methods: voltammetry, chronoamperometry, scanning electron microscopy, X-ray spectroscopic analysis, it was shown that in alkaline glycinate solution in the presence of microadditives of Br^– or F^– ions, copper is subjected to local depassivation accompanied by an antagonistic effect of activators. This effect is expressed as the suppression of local activation (LA) caused by the addition of amino acids and micro quantities of halide ions. Indeed, the hysteresis loop was not detected on cyclic voltammograms of copper in the solutions studied, which indicates the suppression of pitting formation processes in the presence of microadditives of inorganic anions of the copper electrode where local damages have the form of a few little pits in media with halide ions, in contrast to the alkaline glycinate electrolyte where the surface damages are more significant. It has been found that the process of pitting formation in alkaline glycinate–halide systems occurs by the nucleophilic substitution mechanism of dissociative type. At the same time, the inhibitory effect of inorganic anions is manifested in a wider range of concentrations from 1·10^–6 to 1·10^–3 M as compared with that for chloride ions. The values of the potential of LA (ELA) in the media studied exceed the value of ELA in an alkaline glycinate solution. In NaBr solutions, an increase in its concentration results in improved copper resistance to LA and ennoblement of ELA to 0.360 V for the solution containing 1·10^–3 М NaBr. For alkaline glycinate–fluoride systems in the indicated concentration range of NaF, the above-noted tendency of ELA ennoblement remains, but there is no dependence on the F^– content (ELA~0.360 V). The established suppression of pitting formation in alkaline glycinate media with additions of halide ions may be due to the fact that small concentrations of halide ions (especially Br^–) force water molecules out of the adsorbed amino acid complex on the metal. As a result, the surface complex becomes more hydrophobic and its solubility decreases. This complicates copper activation due to blocking of a fraction of active centers. Comparison of the results with data on the behavior of copper in alkali–glycinate–chloride solutions shows that as the corrosivity of inorganic activators decreases in the Cl^–, Br^–, F^– series, the range of concentrations in which they inhibit LA caused by the organic activator (glycine) expands.

Keywords: copper, alkaline media, organic and inorganic additives, passivity, local activation, inhibition

Int. J. Corros. Scale Inhib., 2019, 8, no. 2, 275-281 PDF (639 K)
doi: 10.17675/2305-6894-2019-8-2-9

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