Effect of Vacuum Annealing on the Compositions of U-0.79wt%Ti Alloy Surface Exposed in a Salt Fog Environment

The evolution of the compositions in two typical regions on U-0.79wt%Ti alloy surface exposed in a salt fog environment was investigated by x-ray photoelectron spectroscopy (XPS) during vacuum annealing. The results show that pitting corrosion tends to occur around titanium inclusions on the alloy surface in the environment containing chloride ions. The compositions in the two regions were transformed with experimental temperature increasing. The complex oxide compound, α-U₃O₈, was detected by both XPS and Raman spectrum in the blackened region, while UO_2+x/UO₂ were the main oxide compounds in the other region where pitting corrosion did not occur. The different compositions in the two typical regions were slightly changed as temperature ramps up from room condition to 200°C. The α-U₃O₈ in the blackened region started to be reduced to UO₂ while UO_2+x in the other region to be converted into UO₂ at 300°C. An oxycarbide (UO_xC_y) compound was observed due to the reaction between UO₂ and carbon at 400°C. Between 500°C and 700°C, the UO_xC_y formed in the blackened region was partly converted into UO₂, while the UO_xC_y formed in the other region was almost completely converted into UO₂, which was in turn reduced to metallic uranium.