The Influence of Corrosion Product Film Formation on the Corrosion of Copper-Nickel Alloys in Aqueous NaCl

The corrosion resistance of copper-nickel alloys in seawater is known to be due to the development of a protective corrosion-product film. This study is an attempt to elucidate the reason for the protective nature of these films. A rotating disk electrode was used to study the corrosion product formation on three copper-nickel alloys in aqueous 3.4% NaCl. The three alloys studied were 70-30 copper-nickel (C71500), 90-10 copper-nickel (C72200), and pure copper. Electrochemical impedance spectroscopy (EIS), palladium sputter-coating of the corrosion product, and removal of the outer corrosion product layers with adhesive tape were used to follow the growth of the inner and outer film layers. It is concluded that in copper-nickel corrosion, oxygen reduction occurs at the bottom of pores in the outer corrosion product layers, and the corrosion rate is determined by the diffusion of oxygen through the pore electrolyte to these sites.