In situ investigation of U(IV)-oxide surface dissolution and remineralization by electrochemical AFM

Surface chemical processes of UO2 are investigated on a nanoscopic scale by electrochemical atomic force microscopy (ECAFM) using a home-developed electrochemical cell. Dissolution reactions of the solid surface and subsequent remineralization are observed at the solid–water interface under different redox conditions and carbonate concentrations. The local dissolution rates vary between different grain faces, grain boundaries and etch pits. A correlation between dissolution rates and the grain orientations relative to the specimen surface can be demonstrated by electron backscatter diffraction (EBSD). Remineralization under oxidizing conditions occurs mainly at grain faces with higher dissolution rates. The remineralized products are particles of 200–900 nm in diameter and exhibit a tabular morphology. Profound knowledge of the UO2 surface chemistry on a nanoscale may help to clarify the related mechanisms explaining the macroscopically observed dissolution rates.