KINETICS OF COPPER PASSIVATION AND PITTING CORROSION IN NA2SO4 CONTAINING DILUTE NAOH AQUEOUS-SOLUTION

The electrochemical behaviour of Cu in alkaline solutions containing N a2SO4 was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na2SO4 e nhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH-/sulphate concentratio n ratio for the onset of localized corrosion. The competitive interact ion between OH- and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for pas sivity breakdown. Pit growth involves a number of current contribution s which can be distinguished through the analysis of current transient s at constant potential by using nucleation and growth models.