Molten Salt Synthesis of Uranium Monocarbide Below 1000 °C

We report a versatile molten salt synthesis (MSS) route to uranium monocarbide (UC) that proceeds below 1000 °C and achieves complete conversion within 1 h. The method employs lithium hydride (LiH) as a salt-soluble reductant/oxygen scavenger and lithium chloride (LiCl) as the molten medium, enabling straightforward product isolation by salt dissolution in polar aprotic solvents. The process tolerates diverse uranium feedstocks, including UO₂, UO₃, UCl₄, and UBr₅, yielding phase-pure UC without coformation of higher-order carbides under the conditions studied herein. Powder X-ray diffraction (XRD) confirms the NaCl-type structure of UC, with a-axis contraction correlated to nonstoichiometric UO defects within the UC lattice, consistent with empirical literature data. Scanning electron microscopy (SEM) reveals larger particles (300-500 nm) for oxide-derived UC and finer particles (100-200 nm) for halide-derived UC, consistent with differences in precursor solubility and crystallization kinetics. This low-temperature, rapid, and feedstock-flexible route addresses historical challenges associated with carbothermal synthesis and supports future fabrication of UC-based fuels, including next-generation transuranic (TRU) fuel fabrication.