Study of the formation of α-U2N3+x using unstable ammonia - reaction sequence and control of nitrogen activity

The formation of α-U2N3+x by the reactions between U and NH3 or a gas mixture of NH3 and H2 was examined at 300 °C. It was found that there were two routes for the reaction process. One route was the direct formation of α-U2N3+x by the reaction of U and NH3; the other included the formation of UH3. Although the UH3 formed in this way was finally converted to α-U2N3+x, the reaction rate was very slow compared with the rates of nitride and hydride formation. It was presumed that the conversion of UH3 to α-U2N3+x was the rate-determining step in the series of reactions. It was also confirmed that the nitrogen content of α-U2N3+x varied when the composition of the reactant gas mixture was changed. This result implies that the nitrogen activity of the unstable gas mixture is dependent on the composition.