Electrochemical behavior of aluminum bronze in sulfate-chloride media

The electrochemical behavior, especially the corrosion and passivation, of a Cu-Al bronze was investigated. Conventional electrochemical techniques including open-circuit potential, anodic polarization, cyclic voltammetry and electrochemical impedance spectroscopy were used. It was found that the addition of chloride ion up to 0.15 M in 0.5 M Na2SO4 solution decreases the corrosion rate due to the formation of CuCl, whereas at higher concentration of the chloride ion, the corrosion rate increases due to the formation of the soluble CuCl2- The activation energy was found to be 10 kJ mol(-1). This value indicates that the corrosion process is under diffusion control. The impedance measurements showed that the passive film can be represented by a duplex layer, a relatively thick porous outer film on top of a thin compact layer. An equivalent circuit was used to explain and analyze the impedance data. The model includes another R-C combination and Warburg impedance in addition to the simple Randles cell to account for the spontaneously formed passive film and the diffusion phenomena.