Characterizing the solid hydrolysis product, UF4(H2O)2.5, generated from neat water reactions with UF4 at room temperature

Abstract

Uranium tetrafluoride (UF₄) is an important intermediate in the production of UF₆ and uranium metal. Room temperature hydrolysis of UF₄ was investigated using a combination of Fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR), Raman and infrared spectroscopy, powder X-ray diffraction, and microscopy measurements. UF₄(H₂O)_2.5 was identified as the primary solid hydrolysis product when anhydrous UF₄ was stirred in deionized water. Static NMR and ¹⁹F magic angle spinning NMR measurements revealed that a small amount of uranyl fluoride can also form when anhydrous UF₄ is left in water, although this species comprises less than 5% of the total sample with the remaining parts being UF₄(H₂O)_2.5. Since UF₄ is generally considered to be stable under ambient conditions, these findings mark the first time that a room temperature reaction between UF₄ and water has been detected and analyzed without interference from additional chemical reagents. The Raman characterization of UF₄(H₂O)_2.5 presented herein is the first on record. Since UF₄ is one of the most used intermediates during chemical conversion of uranium ore to uranium metal for nuclear fuel and weapons, the results presented herein are applicable to numerous nuclear science fields where solid state detection of uranium is of value, including nuclear nonproliferation, nuclear forensics, and environmental remediation.