Anodic polarization behavior and film breakdown potential of pure copper in the simulated geological environment containing carbonate

Kawasaki, Manabu; Taniguchi, Naoki ; Naito, Morimasa 

In order to clarify the influence of environmental factors on the corrosion behavior of copper overpacks in oxidizing environment, potentiodynamic and potentiostatic anodic polarization tests were performed in carbonate aqueous solutions at 80 C. As the results, the passivation was promoted and film breakdown was suppressed in higher carbonate concentrations, in lower chloride ion concentrations, and in higher pH conditions. The sulfate ion tended to promote the film breakdown of copper. The effects of the composition of the test solutions on the anodic polarization curve of copper in bentonite/sand mixture were quite smaller than those in simple aqueous solution. By comparison with previous data for lower temperature condition, it was clarified that passivation of copper was promoted in higher temperature condition, but breakdown potential, Eb was independent of temperature. The Eb, was expressed as a function of the ratio of aggressive ion and inhibiting ion such as [Cl]/[HCO] and [SO]/[HCO], and it was confirmed that the Eb was lowered with increasing the ratio. When the ratio exceeds a certain value, the Eb was no longer able to be determined since the anodic poralization curve becomes active dissolution type. The lower limit of Eb in passive type region was estimated to be about -200mV vs. SCE. The results of potentiostatic tests showed that pitting corrosion or non-uniform corrosion was observed at the potentials over Eb or second current peak potentials in anodic polarization curve.