The passivity behavior of Alloy 22 and Grade 7 titanium has been studied at 95°C in a high pH salt environment characteristic of concentrated Yucca Mountain groundwater. Measurements of corrosion potential (CP) versus time, potentiostatic polarization (PP) and cyclic potentiodynamic
polarization (CPP) behavior were conducted to evaluate the passivity of these alloys. The characterization of passive films was also analyzed by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to obtain the chemical composition and cross-sectional view of the metal, interface, and oxide layers. It was observed that the oxide layer responsible for passivity of Alloy 22 consisted of chromium oxide (Cr203) containing Ni. The surface analysis showed that the passive films formed on Alloy 22 at high anodic potentials (> 0 mV vs. SCE) contained more Mo and W than ones formed at lower anodic potentials (< 0 mV vs. SCE). However, no visual evidence of localized corrosion on Alloy 22 after potentiostatic polarization measurements was observed.
Keywords: open-circuit potential, polarization, Alloy 22, Titanium Grade 7, concentrated groundwater, nuclear waste.