The Dissolution Mechanism of Aluminium in Methanol and in Methanol/Water Solutions

Abstract

The present work has used Electrochemical Impedance Spectroscopy (EIS) and polarisation techniques to study the kinetics of dissolution of aluminium in methanol and in mixed methanol/water solutions. In anhydrous methanol, the impedance spectrum is characterized at Ecorr by a single, capacitive-type relaxation, which has been interpreted as arising from the formation of a layer of insoluble aluminium methoxide on the electrode surface. The application of computer simulation techniques has enabled a quantitative model of the dissolution reaction to be developed, in which it is proposed that the metal dissolves through a series of adsorbed intermediates of the type Al(OCH3)n, with the chemical dissolution of the surface layer being rate determining. When water is present in the solution, a more stable oxide layer was formed and the rate of dissolution of the metal was decreased. The experimental impedance data gathered in the present study has been subjected to a verification procedure using Kramers-Krönig Transforms. The KKT were evaluated numerically, using the discrete version of the transforms, and the average deviation of the, transformed from the experimental data was determined. The validity or otherwise of a given series of experiments was determined on the basis of the value of the average error of transformation of the experimental data set.