The Electrochemical and Corrosion Behavior of Aluminum
PENNSYLVANIA STATE UNIV UNIVERSITY PARK ORDNANCE RESEARCH LAB
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The electrochemical behavior of high-purity aluminum was 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, E sub M, of the electropolished high-purity aluminum decreases as the pH is increased except in the intermediate pH range 4 to 8 where E sub M increases. A local maximum in the corrosion potential curve as a function of pH is thus observed. Potentiostatic polarization data obtained at pH 4.0 suggest that the rate of dissolution of high-purity aluminum is nearly 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. Dissolved oxygen influences the type of corrosion when cathodic potentials are applied. Based on the potentiostatic data, a corrosion diagram believed to be valid for sodium chloride solutions from pH O 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 results appear to be consistent with the Pourbaix Diagram for the aluminum-water reaction and with the dissolution- reprecipitation mechanism for the dissolution of aluminum recently proposed by Vedder and Vermilyea.
- Properties of Metals and Alloys