Microscopic Characterization of Uranium Nitrides Synthesized by Oxidative Ammonolysis of Uranium Tetrafluoride

The oxidative ammonolysis route was used to synthesize three uranium nitrides, UN 2, U 2 N 3, and UN, using UF 4 as the starting material. Powder XRD analysis showed the UN 2 and U 2 N 3 products to contain less than 1.0 wt % uranium oxides. UO 2 level was identified to be 5.0 (0) wt % in the UN product as it is made, but this level increases upon exposure to air. The morphology of these nitrides was studied with SEM, while the microstructures of UN 2 and U 2 N 3 were investigated by TEM techniques for the first time. An explicit microstructural characterization of UN is also presented. These characterizations showed that UN has a long-range order in its structure and bulk of the UO 2 impurities present on the UN microparticle surface, likely originating from minute oxygen impurities in the inert atmosphere cover gas and/or diffusion through the quartz reactor tube at high temperatures. Surface area measurements demonstrated a 10-fold increase in surface area during the ammonolysis step, from 0.03 to 0.26 m 2 /g, and minimal change during the denitriding step.