Polarization behavior and passivity breakdown of copper alloys in chloride environments

摘要

The potentiodynamic polarization behavior of copper alloys in chloride solutions (1 M NaCl) of different pH's (6.5 and 10) was investigated. Three commercial alloys of nominal composition Cu-30Ni (Cu-Ni), Cu-30Zn (Cu-Zn) and 90Cu-8Al-2Fe (Cu-Al) were considered. Results at pH of 6.5 showed no evidence of passivity with polarization behavior being dominated by the Cu component. At pH of 10, however, some evidence of limited passivity was seen. Passivity was more evident in buffered chloride (pH=10), in particular for Cu-Zn which showed remarkable passive behavior over a wide potential range. A sudden increase in the current density occurred when the anodic potential exceeded a certain critical potential, i.e., film breakdown potential. The results of these experiments are discussed in reference to potential-pH (Pourbaix) diagrams of the alloying elements.