Corrosion of High Purity Copper in Solutions Containing NaCl, Na2SO4 and NaHCO3 at Different Temperatures☆

Abstract Oxygen free copper is one of the candidate materials for the design of high level radioactive waste containers, due to its excellent resistance to generalized and localized corrosion in aqueous electrolytes; particularly in reducing environments as the ones expected in the repository site. The aim of this work is to contribute to determine the material durability from the corrosion point of view. To this purpose the anodic behavior of copper was studied in solutions with different electrolytes of interest for being present in groundwaters that might be in contact with the containers. The research program began with the study of corrosion susceptibility in chloride solutions, one of the main aggressive species to corrosion, and continued with the study of the behavior of copper in solutions with sulfate and bicarbonate, which are also present in the groundwaters that might be in contact with the repository. The corrosion potential was monitored and anodic polarization curves were performed varying the temperature and the concentration of ions in deaerated solutions of chloride, sulfate and bicarbonate. The study was complemented with microscopic observations of the corrosive attack and compositional determinations using Energy Dispersive Microanalysis (EDS). Preliminary results showed the aggressiveness of chloride ions: the corrosion potential decreased with the ion concentration and with temperature. The current density increased both with temperature and with chloride concentration. A breakdown potential was observed under certain conditions. Corrosion products showed a composition of 30 wt% Cl and 70 wt% Cu. In sulfate containing solutions, the corrosion potential decreased with temperature but increased slightly with the ion concentration, whereas the current density increased with temperature and it was not significantly affected by the concentration. A breakdown potential was identified, which decreased with temperature and increased with sulfate concentration. In bicarbonate containing solutions, the corrosion potential decreased clearly with temperature and slightly with concentration. Different characteristics were observed in the curves: current densities were lower than in sulfate containing solutions and an anodic peak appeared under certain conditions.