Investigation of the first stages of the localized corrosion of pure copper combining EIS, FE-SEM and FE-AES

During the first 48 h that pure copper is submerged in a chloride containing solution, an oxide layer is formed that acts as a barrier layer between the aggressive solution and the substrate, offering some protection to the material. This barrier layer itself is subsequently attacked and localized corrosion is observed. The study of the corrosion behavior was based on open circuit potential (OCP) measurements. The evolution of this value was concurrent with the evolution of the state of the oxide layer. Furthermore the surface state was evaluated by taking impedance spectra every 2 h. This method proved to be insufficient to elucidate the surface evolution and additional techniques were employed. The thickness and the composition of the oxide layers as well as the different composition of the corrosion products in and around the zones of localized attack were determined by means of an FE-AES equipped with an ion gun. The scanning electron microscope (SEM) allowed us to visually discriminate between the three stages the surface passes through during the first 48 h. Mathematically the equivalent circuit used in literature fits the impedance data very well. The observations in this work are however in contradiction with the different physical meanings attributed to the circuit elements found in literature. Further research is necessary to reveal the real mechanism of copper corrosion in this sort of systems.