Effect of sulfide in a 0.2 M NaCl solution on copper and pre-oxidized copper in oxic conditions

• Pre-oxidized Cu corrodes in a NaCl solution, Cu 2 O becomes non-protective. • Cu 2 S forms on the surface in the chloride solutions with added sulfide. • Higher sulfide concentration—greater thickness and different Cu 2 S morphology. • EIS shows similar film properties in chloride solutions with added sulfides. This study investigated copper and pre-oxidized copper immersed in 0.2 M NaCl solutions containing different concentrations of sulfide ions. In order to investigate the corrosion processes, the corrosion potential and electrochemical impedance at room temperature and at an elevated temperature were measured for 24 h during and after exposure to the chloride solution with different sulfide concentrations in aerated conditions. The surfaces of the pre-oxidized copper were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), a focused ion beam scanning electron microscopy (FIB-SEM), and Raman spectroscopy. It was shown that the concentration of sulfide ions in the chloride environments, in addition to the temperature itself, greatly affect the film formation in oxic conditions. The thickness of the films observed corresponds well to those calculated using cathodic stripping voltammetry. The mechanism of corroding copper in chloride/sulfide system was proposed.