THERMODYNAMICS OF NITROGEN-RICH URANIUM SESQUINITRIDE FORMATION BY REACTION OF URANIUM MONOCARBIDE WITH AMMONIA

According to our thermodynamic analysis, the flowing NH3 possesses hig h nitrogen and hydrogen activities due to its instability with respect to the dissociation equilibrium, NH3 reversible arrow (1/2)N-2 + (3/2 )H-2. As the extent of dissociation of NH3 into N-2 and H-2, alpha, is lower, nitrogen and hydrogen activities exhibited by unstable gaseous mixture of NH3, N-2 and H-2 become higher. The reaction experiments o f UC with a stream of NH3 at 600, 700, 800 and 900 degrees C were perf ormed at two different values of alpha. Some runs employed 1 g UC as t he starting material and the others used 2 g UC. At each of these four temperatures two runs were performed under the same experimental cond itions except for the difference of the amount of used UC. The experim ental results that the extent of dissociation, a, is larger in the cas e of using 2 g UC than in the case of using 1 g UC may suggest that th e extent of NH3 dissociation is greatly influenced by the amount of UC as the starting material. It was found that the gaseous phase consist ing of NH3, N-2 and H-2 with lower alpha yields U2N3 + x with higher N /U ratio at a given temperature. These experimental results are consis tent with our thermodynamic analysis. (C) 1998 Elsevier Science S.A.