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 461Maité Ochoa et al. / Procedia Materials Science 9 ( 2015 ) 460 -468 were observed in the curves: current densities were lower than in sulfate containing solutions and an anodic peak appeared under certain conditions.

Use of Multielectrode Arrays and Statistical Analysis to Investigate the Pitting Probability of Copper: Part II. The Effect of Sulfate and Bicarbonate

“…Al-Khariafi 33 discussed the competition between the adsorption of halide ions and OH − on the copper surface and reported that halides with a larger ionic radius yields a lower Cu dissolution rate; although, Kong 51 proposed that the ability of halide ions to polarize copper is directly proportional to the size of the ions and a larger peak current density was observed for halides with a larger radius. In our case, E corr decreased with increasing [ − SO 4 2 ], which is in good aggrement with our observation in chloridecontaining solution, 69 but it is not in good agreement with the results of Ochoa et al, 72 whos howed that E corr increased slightly with increasing [ − SO 4 2 ]. The reason for this discrepancy could be that Ochoa et al 72 did not acquire enough data to properly define the trend; however, in this study, 60 data acquired in two runs of 30 simultaneous measurements were averaged.…”

“…In our case, E corr decreased with increasing [ − SO 4 2 ], which is in good aggrement with our observation in chloridecontaining solution, 69 but it is not in good agreement with the results of Ochoa et al, 72 whos howed that E corr increased slightly with increasing [ − SO 4 2 ]. The reason for this discrepancy could be that Ochoa et al 72 did not acquire enough data to properly define the trend; however, in this study, 60 data acquired in two runs of 30 simultaneous measurements were averaged.…”

“…22,57,58 The relationship between E b and log [ − SO 4 2 ] appears to be linear and can be represented by Eq. 1 72,74,75 : With an increase in the concentration of aggressive anions up to a certain level, the adsorption of aggressive anions such as − SO 4 2 became more favourable than OH − adsorption, leading to a shift in E b to a more negative value. As a result, the distribution of E b would be more likely to be below the distribution of E corr , resulting in a higher probability of passive film breakdown.…”

Use of Multielectrode Arrays and Statistical Analysis to Investigate the Pitting Probability of Copper. Part I: The Effect of Chloride

“…The E b values were more negative at higher chloride concentrations, in keeping with the general observations of others. 18,24,28,31,40,[44][45][46][47] Starosvetsky et al 46 observed local copper activation (pitting) in lowchloride solutions, while activation extended rapidly over the whole electrode surface in high-chloride solutions; however, other researchers demonstrated that decreasing the chloride concentration improved the density and decreased the porosity of the passive film, which resulted in a higher E b .…”

Countermeasure for corrosion and hydrogen embrittlement of Ni-Ti superelastic alloy in acidic fluoride solution by adding sodium bicarbonate and hydrogen peroxide

“…For stainless steels, pitting corrosion is inhibited by adding sodium bicarbonate (NaHCO 3 ) or sodium carbonate (Na 2 CO 3 ) to NaCl solutions; in the presence of CO 3 2− ions, the oxide film is considered to be instantaneously repaired [27][28][29]. For copper in NaHCO 3 , the initially formed oxide film is protective [30][31][32]. Similarly, corrosion of Ni-Ti superelastic alloy may be substantially inhibited by NaHCO 3 , but its effects when added to APF solutions on corrosion behaviour are unknown.…”