Effect of Halide Anions on Anodic Behaviour and Passivation of Copper in Alkaline Media
The effect of Cl - and Br - on the anodic behaviour and passivation of copper metal in NaOH solution has been investigated by a potentiodynamic technique complemented with XPS analysis. In halide free solutions, the anodic polarization curves involve three anodic peaks correlated to the electroformation of Cu 2 O, CuO and Cu(OH) 2 on the anode surface. The presence of these species in the passive layer has been confirmed by XPS examination. An addition of the halide anions enhances the peak currents of anodic peaks and tends to rupture the passive layer inducing the pitting corrosion. The critical pitting potentials decrease with rising halide concentration while the alkali concentration has an opposite effect. The accelerating effect of Cl - to pitting corrosion is greater than that of Br - . The pitting corrosion was explained by an instantaneous nucleation and growth of anion salt nuclei. Three cathodic peaks on cyclic voltammetric curve were assigned to the electroreduction of pitting corrosion products, Cu(II) and Cu(I) oxides, respectively.