Photothermal deflection spectroscopy investigations of uranium dioxide oxidation

Photothermal deflection spectroscopy (PDS) has been applied to the study of uranium oxide electrochemistry. PDS measures the optical absorption of the sample surface and concentration gradients formed in the electrolyte. Both these measurements are performed in situ under dynamic conditions. The combination of these two measurements provides information that can be used to infer the mechanism of the UO₂ surface chemistry. These studies of the uranium dissolution mechanism are performed in pH 10.5 sodium sulfate electrolytes at 22°C. The electrolytes are free from oxygen and complexing species. Our results suggest that dissolution of UO₂ can occur at oxidizing potentials as low as −300 mV/SCE. The optical absorption and concentration gradient results provide evidence for a surface recrystallization reaction that occurs at an oxidation potential of + 300 mV. The results show that the surface layer formed by the recrystallization reaction dissolves slowly by a non-electrochemical reaction.