Electrochemical Evaluation and Surface Characterization of Josephinite as a Natural Analog for Container Materials

Abstract

AbstractA sample of josephinite, a rock containing predominantly a Ni-Fe metallic phase, was evaluated as a natural metal analog to increase confidence in the assessment of waste package performance for the potential high-level radioactive waste repository at Yucca Mountain, Nevada. The josephinite sample was characterized electrochemically in simulated groundwater environments using cyclic potentiodynamic polarization and potentiostatic tests. The passive surface layers formed potentiostatically were examined by X-ray photoelectron spectroscopy. These results were compared to those obtained with a synthetic Ni3Fe alloy with a chemical composition similar to that of josephinite. Electrochemical studies showed that josephinite exhibited passivity at a slightly higher pH than did the cast Ni3Fe alloy and was found to be slightly more susceptible to pitting corrosion. The passive films formed on the josephinite and the cast Ni3Fe alloy have a duplex structure consisting of an Fe-rich hydroxide outer layer and a Ni-rich oxide inner layer. Results obtained from this study provide an appropriate characterization of the environmental conditions leading to the passivity and localized corrosion of josephinite. Extended persistence of a stable passive film, however, is essential for the long-term stability of the josephinite sample. The relationship between the passive behavior and the formation of alteration layers needs to be established for assessing the survivability of josephinite.