Uranium hexafluoride (UF6) is highly utilized material feedstock for uranium enrichment processes and reacts readily with atmospheric humidity. The mechanism for this spontaneous hydrolysis reaction is poorly understood. If released into the atmosphere, UF6 reacts with water to form chemically toxic and radioactive reaction products, uranyl fluoride (UO2F2) and HF gas. Historical UO2F2 particulate research performed at Oak Ridge National Laboratory has shown the end state of the chemical reaction to be dependent on the amount of water present in the atmosphere. Here we have used a cryogenic layering technique to study the reaction kinetics of the hydrolysis of the metal hexafluorides MoF6 and UF6. Metal hexafluoride gas and air were sequentially layered on a diamond substrate kept at liquid nitrogen temperature (~-193 °C) and then allowed to warm and react. This was achieved using a custom designed cryogenic cell using a copper cold finger. Reaction progress was monitored via FTIR over several hours while allowing the substrate top warm up to room temperature and substrate temperatures were recorded. Products were characterized via UV/Vis, XRF, SEM and FTIR.

Condensed phase reaction dynamics of the hydrolysis of the metal hexafluorides UF6 and MoF6 by cryogenic layering on a diamond substrate

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