Passivation of copper in alkaline chloride solutions

Using polarization and impedance studies, the breakdown of passive films on copper in buffered alkaline sodium chloride was found to be caused by a loss of pH control at the metal surface. The loss of pH control was still observed when there was sufficient buffer species present to neutralize the total protons generated from the aqueous corrosion of copper. This indicates that the loss of pH control is a localized phenomenon. At the onset of passive film breakdown film defects were detected with the use of impedance modeling. The production of protons that accompany the local corrosion of copper to form HCuCV ions at these defect sites consumes all the conjugate base buffer species at the defects. The ensuing drop in local pH has a detrimental effect on the remaining oxide layer. The local acidic condition causes the precipitation of CuCl and hence prevents re-passivation. Impedance modeling was successful in determining the thickness of the passive film in-situ. The passive film thickness was determined to be in the range of 7.0A to 108.8A, which is in line with published values from ex-situ XPS studies. The impedance modeling was also successful in identifying film defects at the onset of passive film breakdown.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat