Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)(-) complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm(-2) in the low frequency region.