Electrochemical Behavior of High Purity Aluminum in Chloride Containing Solutions

Abstract

Abstract The electrochemical behavior of high purity aluminum has been studied to clarify the corrosion behavior of the metal when exposed to oxygen free and oxygen saturated saline solutions of varying pH. The mixed or corrosion potential, EM, of the electropolished high purity aluminum decreases as the pH is increased except in the intermediate pH range (4 to 8) where EM increases. A local maximum in the corrosion potential curve as a function of pH is thus observed. The potentiostatic polarization data and controlled potential weight loss data obtained at pH 4.0 suggest that the rate of dissolution of high purity aluminum is independent of electrode potential over a fairly wide range, relatively insensitive to the presence of dissolved oxygen in the electrolyte, and highly sensitive to changes in pH. Based on the potentiostatic data, a corrosion diagram believed to be approximately valid from pH 0 to pH 14 has been constructed. The corrosion diagram is consistent with the observed relation between EM and pH, and also yields estimates of the rate of dissolution of aluminum as a function of pH. The rate of dissolution of high purity aluminum increases slightly between pH 0 and 4, decreases between pH 4 and 8, and increases from pH 8 to 14. The minimum at pH 8 may be the point at which the rate of formation of aluminum hydroxide on the electrode surface equals the rate of formation of the aluminate ion.