Comparison of corrosion behaviour of zinc in NaCl and in NaOH solutions; Part II: Electrochemical analyses

Research highlights: → Corrosion layer formed on zinc depends on the electrolyte and ambient conditions. → In NaOH, compact corrosion layer is formed and the passivation of zinc occurs. → In NaCl, porous corrosion layer and non-passivation of zinc. - Abstract: Electrochemical impedance spectroscopy (EIS) is a powerful analysis technique which can provide a wealth of information about the corrosion reactions of pure zinc. Although a huge amount of potentially useful data can be generated using the EIS technique, these data need to be carefully interpreted. This is usually done using an 'equivalent circuit' which comprises an assembly of electrical circuit elements allowing to model the physicoelectric characteristics of the electrode/solution interface. Research on corrosion behaviour of pure zinc in 0.6 M NaCl and 0.5 M NaOH solution was carried out using the EIS technique. The relevant equivalent circuits (EC) are developed by fitting EIS data to build up a description of the influence of the corrosion layer formed on the top of pure zinc immersed in 0.6 M NaCl and 0.5 M NaOH solution. Before using EIS analysis, voltammetric studies (open circuit potential and anodic polarization) completed by scanning electron microscope observations were conducted. A difference in corrosion behaviour was relieved between the two corrosive media. In 0.5 M NaOH solution, the passivation of zinc was observed but not in 0.6 M NaCl solution.