Abstract
A potentiodynamic method was used to study the influence of various factors on the formation of films on the copper anode in air-saturated 3%NaCl aqueous solutions. The various factors were as follows: Potential sweeping rate of upward and downward scan, contamination of solutions with copper ions and soft mechanical abrasion of electrode surface. Four potential sweeping rates (1.0, 0.125, 0.04 and 0.01 V/min) were adopted. Polarization curves involving active-passive transitions were different depending on the potential sweeping rates. In a less noble potential region, the transformation from CuCl to Cu2O is relatively slower and the diffinite thickness of surface films were demanded for passivation. These films are reduced to copper at a potential below −0.09 V (S.C.E.). The concentrations of both Cl− ion and OH− ion of the solution near the electrode surface decrease with polarization, and it tends to establish the (Cu/Cu2O+CuCl/Cl−) electrode potential, resulting in the anodic dissolution of Cu2O. The surface films are removed by the soft mechanical abrasion. By the electron diffraction analysis the anode films are found to be composed of Cu2O in all anodic polarizing regions, CuCl in an intermediate potential region and CuCl including Cu in a higher potential region.
