Anodic behavior of copper in iodide solutions - Comparison with chloride and effect of benzotriazole-type inhibitors

The anodic polarization behavior of copper in 1 M NaI at similar to 24 degrees C was compared with calculations based on thermodynamic equilibria and shown to be consistent with the potential-pH diagram for the Cu-I--H2O system. An active region was predicted and observed where cuprous complexes, CuI2-, are formed. The active region exhibited a Tafel slope of 60 mV, similar to that observed in 1 M NaCl where CuCl2- complexes are present. The active region occurred at less noble potentials in 1 M NaI than in 1 M NaCl and was consistent with an anodic dissolution model based on mass-transport control of the cuprous complexes. Polarization studies were conducted on copper in the presence of two related inhibitors, benzotriazole and tolytriazole. The inhibitors behaved in a similar manner to each other in 1 M NaI and 1 M NaCl and promoted passivation. Inhibitor-induced passivation commenced in the active region on oxide-free surfaces. The shape of the passive polarization curve in 1 M NaI differed from 1 M NaCl, suggesting structural differences between the inhibitor films in the two solutions. Possible differences are discussed in terms of the presence of copper oxides in the film, together with an assessment of the critical step in the initiation of passivation.