Uranyl fluoride exists both as a hexagonally-coordinated anhydrous crystal (UO2F2) and as a pentagonally-coordinated crystal hydrate ([(UO2F2)(H2O)]7(H2O)4). In-situ Raman spectroscopy with temperature and relative humidity control was used to further characterize the transition between these two phases. Assignment of the phases based on Raman signature is possible because the symmetric uranyl stretching frequency of each phase is distinct. Further hydration of [(UO2F2)(H2O)]7(H2O)4 was also investigated using micro-Raman spectroscopy and scanning electron microscopy with energy-dispersive x-ray spectroscopy to analyze particles equilibrated at different water vapor pressures. Although [(UO2F2)(H2O)]7(H2O)4 is relatively stable at ambient conditions, elevated water vapor pressure induces a loss of fluorine within the crystal structure, producing uranyl hydroxide and peroxide species. The formation of uranyl peroxide species is especially interesting because of the absence of hydrogen peroxide in the system, which has generally been assumed to be necessary for the formation of these species.

Hydration of uranyl fluoride and a novel chemical pathway to uranyl peroxide

255th National Meeting (2018)

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