Features of aluminum anodic behavior in media with various pH values in the presence of sodium chloride and glycine

• T.A. Minakova and S.A. Kaluzhina

Voronezh State University, Universitetskaya pl. 1, 394006 Voronezh, Russian Federation

Abstract: The anodic behavior of aluminum in aqueous solutions with various concentrations of NaCl and glycine (pH=4.8–8.5) was studied. It has been shown that the metal is in a passive state in the presence of glycine zwitter-ions (pH=4.8–5.8), but local destruction of the metal surface occurs in the presence of Cl^– and Gly^– ions. A possible reason for the observed effect of glycine zwitter-ions may lie in the strong intermolecular hydrogen bonds that are formed between the amino and carboxy groups and prevail over the interaction of these groups with the oxidized aluminum surface. The corrosive action of Cl^– and Gly^– ions against aluminum that causes its local activation at all the studied concentrations (from 1.3‧10^–4 M to 1.7‧10^–1 M) of NaCl (pH=4.8–5.8) and glycine (pH=8.5) has been proved. The type of corrosion products differ essentially depending on the рН, concentration and thermal conditions. The experimental results that we obtained are interpreted within the framework of modern competitive adsorption, complexing and nucleophilic substitution theories. They have been confirmed by independent physical and chemical methods (electrochemical and scanning electron microscopy combined with X-ray spectral microanalysis). In the presence of chloride ions, the pit formation process is a nucleophilic substitution reaction of associative type, whereas in the presence of glycine anions, it is of dissociative type.

Keywords: aluminum, sodium chloride, pH, glycine, local activation

Int. J. Corros. Scale Inhib., 2020, 9, no. 4, 1419-1428 PDF (568 K)
doi: 10.17675/2305-6894-2020-9-4-14

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