Kinetics of copper passivation and pitting corrosion in Na₂SO₄ containing dilute NaOH aqueous solution

Abstract

The electrochemical behaviour of Cu in alkaline solutions containing Na₂SO₄ was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na₂SO₄ enhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH^-/sulphate concentration ratio for the onset of localized corrosion. The competitive interaction between OH^- and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for passivity breakdown. Pit growth involves a number of current contributions which can be distinguished through the analysis of current transients at constant potential by using nucleation and growth models.