Electrochemical Behavior of Cu-9% Al-5% Ni-2% Mn Alloy in Chloride Media

Abstract

The electrochemical behavior of Cu-9% Al-5% Ni-2% Mn alloy in different NaCl concentrantions and pHs was studied by means of open-circuit potential (E(OC)), cyclic voltammetry and polarization curves. The E(OC) curves showed a considerable influence of NaCl concentration and solution pH in the steady-state potential values. It was observed by the I/E profiles that the scan rate variation indicated the formation of a porous film of low conductivity which was the responsible by the linear increase of current due to the solution resistance contained in the film pores. In order to investigate the products formed during the potential scan, the potential was held at different values of applied potential of the cyclic voltammogram and analyzed by OM, SEM and EDS. In general, it was noticed the presence of CuCl precipitates in applied potentials equals to 0.20, 0.85 and 0.00 V (vs. Ag/AgCl/KCl((3 mol L-1))) and only Cu in -0.70, -1.00 and -1.35 V. In the latter cases, a Cu layer was observed on the alloy surface due to the cuprous chloride reduction. This film blocked the EDS peaks appearance related to the other metals present in the alloy. The polarization curves for Cu-9% Al-5% Ni-2% Mn showed that E(OC) varied according to the solution pH and NaCl concentration. As the NaCl concentrantion increased the E(OC) became more negative for the three pHs studied. The Tafel coefficients were calculated from the polarization curves and the values were 60 and 120 mV decade(-1), for anodic and cathodic region, respectively.