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

The electrochemical behaviour of pure aluminium in an EDTA-containing chlor ide solution was investigated using potentiodynamic and potentiostatic elec trochemical techniques and electrochemical impedance spectroscopy. A pronou nced EDTA-induced anodic dissolution was observed in alkaline solutions, bu t the presence of EDTA in solution had little activating effect on the pass ivation properties at pH values close to 4.0. This was attributed to the re lative stability of the Al(EDTA)(-) complex formed at the different pH valu es. This EDTA-induced activation had no deleterious effect on pitting attac k, in fact, higher breakdown potentials were observed in the presence of ED TA. This was attributed to the buffering action of EDTA, which inhibited th e attainment of a critical pit solution composition. But, in the presence o f molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorptio n of EDTA species during the dissolution process, which in turn, form a lar ge capacitive network, with capacitance values of the order of 3 mF cm(-2) in the low frequency region.