Anodic polarization behavior of pure copper in carbonate solutions

Kawasaki, Manabu*; Taniguchi, Naoki ; Naito, Morimasa 

Copper is one of the candidate materials for overpacks. The redox condition at the early stage of the post closure will be oxidizing. In order to understand the influence of environmental factors on the corrosion behavior of copper in such oxidizing environment, anodic polarization tests were performed in carbonate aqueous solution with varying the concentration of representative chemical species in groundwater. As the results of potentiodynamic and potentiostatic tests, anodic polarization behavior of pure copper was summarized as follows; (1) Carbonate ion and bicarbonate ion promoted the passivation of pure copper, and suppressed the initiation of film breakdown. (2) Chloride ion promoted both the active dissolution and initiation of film breakdown of pure copper. (3) The influence of sulfate ion and pH was small, but the action of sulfate ion to the pure copper was similar to that of chloride ion, and the increase of pH was likely to promote the passivation and suppress the initiation of film breakedown. (4) The film breakedown potential, Eb, was represented as a function of the ratio of aggressive ion and inhibiting ion such as [Cl]/[ HCO], [SO]/[HCO]. When the ratio exceeds a certain value, the anodic poralization curve becomes active dissolution type so that no macroscopic film breakedown can not be occured. The lower limit of Eb in passive type region was estimated to be about -200 mV vs. SCE. (5) As the results of potentio static tests, the corrosion form near the Eb was uniform dissolution over the surface, but pitting corrosion and non-uniform corrosion occurred according to the condition of the test solution. Neither pitting corrosion nor non-uniform corrosion occurred at the potential below Eb in every test cases.