Tailoring Triuranium Octoxide into Multidimensional Uranyl Fluoride Micromaterials

Abstract

Uranium microstructured materials with controlled size and shape are relevant to the nuclear industry and have found applications as targets for medical isotope production, fuels for nuclear reactors, standards for nuclear forensics, and energy sources for space exploration. Until now, most studies at the microscale have focused on uranium microspheres (oxides, nitrides, carbides, and fluorides), while micromaterials of uranium halides, carbides, and pnictides with other morphologies are largely unknown. A promising method to shape the morphology of uranium micromaterials is the replacement of O by F atoms in oxide materials using a solid−gas reaction. Here, with the aim to elaborate unexplored uranium fluoride micromaterials, the fluorination of uranium oxide (U 3 O 8 and UO 2 ) microspheres (ms), microrods (mr), and microplates (mp) in an autoclave at 250 °C with HF (g) (produced from the thermal decomposition of silver bifluoride (SBF)) and with ammonium bifluoride (ABF) was evaluated. We show that the reactions between U 3 O 8 mr and U 3 O 8 mp and SBF provided the most efficient way to elaborate mr and mp UO 2 F 2 micromaterials in a high yield (∼90%). The resulting UO 2 F 2 mr (length: 3−20 μm) and UO 2 F 2 mp (width: 1−7.5 μm) exhibited a well-defined geometry that was identical to that of the U 3 O 8 precursors. Agglomerated (NH 4 ) 3 UO 2 F 5 and UO 2 F 2 ms (2−3.5 μm) were prepared from the reaction of U 3 O 8 ms with ABF. It is noted that the reaction of UO 2 ms with SBF and ABF did not provide any uranium fluoride micromaterials. The successful preparation of uranium fluoride microstructures (ms, mr, and mp) developed here opens the way to novel actinide fluoride micromaterials.