Anodic Activation of Hydrogen Evolution During Corrosion of AI in NaOH Solutions

S. A. Awad and S. S. Mahmoud

Chemistry Department,University College for Girls, Ain Shams University, Heliopolis, Cairo Egypt.

ABSTRACT:

The rates of corrosion of AI in 0.03-0.4 M NaOH were measured at 20 C. as a function of the anodic current density up to 160 μA/cm2, by measuring the volume of hydrogen gas evolved, as well as by determination of the loss in weight. The two techniques gave similar results. In concentrated solutions (0.4 and 0.3 M) lie rate of hydrogen evolution increased with the anodic current density; whereas in dilute solutions (0.05 and 0.03 M) the rate decreased with the current density. In intermediate concentrations (0.2 and 0.1 M) the rate of hydrogen evolution increased to a maximum value, and then decreased with further increase of the current density. The results demonstrated two abnormal phenomena which contradict with the basic concepts of electrode kinetics; namely, the activation of hydrogen evolution, and the inhibition of active metal dissolution, on anodic treatment. The results were taken to indicate that the predominant part of corrosion is due to metal ions of chemical origin. The proposal was made that the surface atoms interact according to: 2AI <=> AI+ + AI- The positive ions undergo self-oxidation to AI3+ ions, which dissolve as aluminate, and the negative ions deliver electrons to solution and become atoms again.

KEYWORDS:

Hydrogen; Aluminate; Corrosion; NaOH

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Copy the following to cite this article: Awad S. A, Mahmoud S. S. Anodic Activation of Hydrogen Evolution During Corrosion of AI in NaOH Solutions. Orient J Chem 1993;9(1).

Copy the following to cite this URL: Awad S. A, Mahmoud S. S. Anodic Activation of Hydrogen Evolution During Corrosion of AI in NaOH Solutions. Orient J Chem 1993;9(1). Available from: http://www.orientjchem.org/?p=38346