The long-term behaviors of passivation and hydride layer of commercial grade pure titanium in TRU waste disposal environments

Preservation of the passivity under reducing environmental conditions for extended periods of time and the behavior of hydrogen evolution as the results of the preservation of the passivity of several candidate commercial grade pure titanium related to the small amount of palladium addition, such as Ti–Gr.17 for metallic containers to be buried under deep ground for disposing of transuranic (TRU) waste is investigated. The present investigation has revealed the following corrosion paths for the titanium alloys investigated. The passivity of the alloys is preserved as the result of repeated destruction and recovery of the surface films on the alloys. The long-term corrosion rate under the preserved passivity is of the order of 10−6–10−8 my−1 with evolution of hydrogen. The substrate alloys absorb parts of the hydrogen generated to form lath-type hydride phase before forming hydride layers at the final stage.