Cyclic voltammetric behaviour of copper–nickel alloys in alkaline media

Abstract

The electrochemical behaviour of two copper nickel alloys; cu-20 wt-%Ni and Cu-80 wt-%Ni, was studied in alkaline solution using the cyclic voltammetric technique. The voltammograms of the alloys were compared with those of the pure copper and pure nickel recorded under the same conditions. The influence of different variables such as switching potential E_s, scan rate, NaOH concentration, solution temperature, and repetitive cycling was also studied. The forward sweep was characterised by the appearance of five anodic peaks: A₁, A₂, A₃, A₄, and A₅, which are related to the formation of Ni(OH)₂, Cu₂O, Cu(OH)₂, CuO, and Ni₂O₃, respectively. The activity of copper dissolution and, hence, the heights of the corresponding anodic peaks decreased as the nickel content in the alloy increased. X-ray diffraction analysis of the surface of the 80% nickel alloy after polarisation in the anodic direction confirmed the existence of only nickel corrosion compounds. Increasing the nickel content in the alloy retards the dissolution of copper via the formation of a very protective nickel hydroxide passive film. The addition of chloride ions, owing to their ease of adsorption, increases dissolution from the alloy. When the ratio of [Cl^-]/[OH^-] ex ceeds 1·5, the chloride ions initiate pitting attack. To examine the alloy surface for pit formation SEM was used.