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

The oxidative ammonolysis route was used to synthesize three uranium nitrides, UN2, U2N3, and UN, using UF4 as the starting material. Powder XRD analysis showed the UN2 and U2N3 products to contain less than 1.0 wt % uranium oxides. UO2 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 UN2 and U2N3 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 UO2 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/g, and minimal change during the denitriding step.