Inhibition of the corrosion process of alloy AA5083 (Al-Mg) in seawater by cerium cations. An EIS study

Abstract

The principal corrosion process of the alloy AA5083 in aerated NaCl solutions mainly affects the zones occupied by Al(Mn,Fe,Cr) cathodic precipitates, over which the oxygen reduction reaction takes place. Thus, the design of an effective protection system could be based on the use of cathodic inhibitors. In previous papers, the inhibition efficiency of various lanthanide chlorides, particularly CeCl3, has been proved. These compounds act as cathodic inhibitors, blocking these cathodic sites by means of the precipitation of a lanthanide oxide or hydroxide film. In this paper, EIS has been used to detect the blocking effect of the cathodic sites. This fact is reflected in the electrical response of the system through the minimisation of the values of those elements of the electrical loop that are related to the response of the cathodic intermetallics. In addition, the dielectric properties of the anodic film have been evaluated by measuring the value of the associated capacitance. From these values, it can be concluded that the thickness of the film produced over the matrix when the inhibitor is added is much lower than that produced in the bare solution. This finding is in good agreement with the results obtained with other techniques and may be related to the minimisation of the anodic reaction as a consequence of the decrease in the intensity of the cathodic process by the action of CeCl3. © WILEY-VCH Verlag GmbH,2001.