Electrochemical behaviour of copper-nickel alloys in stagnant Na_2CO_3 solutions

摘要

The electrochemical behaviour of two copper-nickel alloys in solutions containing the carbonate ion has been investigated by cyclic voltammetric, potentiodynamic, and current/time transient techniques. Among the variables studied were alloy composition, stepwise increasing potential, scan rate, carbonate ion concentration and temperature. The composition of the compounds formed on the alloy surface during the anodic polarisation was characterised using X-ray diffraction analysis. The dissolution behaviour of the alloy' consists of two potential regions separated by the critical potential E_(crit). The first potential region involves the selective dissolution of the more active constituent, nickel, and the appearance of one anodic peak A_1 as a result of the formation of Ni(OH)_2 on the alloy surface. The second potential region relates to the simultaneous dissolution of copper and nickel. This region was characterised by the appearance of four anodic peaks A_2, A_3, A_4, and A_5, which are related to the formation of Cu_2O, {CuO and Co(OH)_2}, CuCO_3-Cu(OH)_2 composite, and NiOOH, respectively. Potentiostatic current/time transients showed that the formation of Ni(OH)_2, Cu_2O, CuO, Cu(OH)_2, CuCO_3-CO(OH)_2 and NiOOH layers involves a nucleation and growth mechanism under diffusion control.