Effect of sulfide pollution on the stability of Cu–Al–5Ni alloy in 3.5% NaCl solution

The stability of Cu–Al–5Ni ternary alloy used in the manufacture of NaCl and Na2SO4 from the Lake Qaroun in Egypt was investigated in 3.5% NaCl in the presence of sulfide ions. The electrochemical reactions of Cu–Al–5Ni electrode in the test solutions were studied using electrochemical impedance spectroscopy measurements. In addition surface examination and morphological studies were applied using scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX). The results of impedance measurements at open circuit potential have shown that the overall impedance of the system decreases with the increase in sulfide ion concentration and increases with immersion time due to continuous growth of the passive film on the alloy surface. The EDAX analysis showed the presence of copper, aluminum and nickel compounds, Cu-oxides, Cu-chlorides and Cu2S on the alloy surface.