A Study of the influence of pH on the corrosion rate of aluminium

Extensive investigations of the aluminium electrolyte interface were undertaken in order to check the pH dependence of the corrosion rate aluminium, i.e. the pH value at which the rate of aluminium corrosion is lowest. Part of this research which deals with measurements of the loss of mass and polarization resistance as functions of pH is presented in this paper. The measurements were performed over a broad range of pH in the presence and absence of ethylenediamine inhibitor. The results are shown as plots of log(1/R_p) and log Δm against the pH. Two straight lines of opposite slope were obtained for each method of investigation and each system investigated. The intercepts obtained by extrapolating the straight lines, which represent minima of 1/R_p and mass loss, indicate the corresponding pH values. The results obtained are discussed in terms of the interaction of water dipoles with the oxide film during the corrosion process. The change in the surface charge of the corroding aluminium as the pH is altered plays an important role in the corrosion process.