Thermodynamic Study on the Formation of Nitrogen-rich Uranium Sesquinitride by the Reaction of Uranium with Ammonia

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A thermodynamic analysis was made to confirm how high nitrogen and hydrogen activities can be obtained by supressing the dissociation of NH_3 below its equilibrium dissociation degree. To examine the theoretical analysis, the reaction experiments U+NH_3 (stream) and U+N_2 (stream) were performed in the temperature range from 400 to 900ﾟC. The results show that the use of a stream of NH_3 leads to the formation of nitrogen-rich uranium sesquinitrides, which cannot be obtained by the reactions of uranium with N_2 under normal pressures, suggesting that a stream of NH_3 possesses higher nitrogen activity compared with N_2 at 1 stm. When uranium carbides (UC or UC_2) are reacted with N_2, U_2N_3 and free carbon are formed. To obtain pure U_2N_3 containing no free carbons, H_2 gas is usually passed over the mixture of U_2N_3 and free carbon held at a temperature greater than 1200ﾟC , so that the fromed CH_4 by the reaction of C with H_2 is swept away. When NH_3 is flowed rapidly enough through a high temperature region, so that the dissociation of NH_3 is suppressed to a great extent, high hydrogen activity will be reached. To confirm the possibility of flowing NH_3 as a high potential hydrding agent, the reactions of UC with a stream of NH_3 were carried out at 600, 700, 800, and 900ﾟC. The reaction at 900ﾟC shows that the free carbon can be removed from the solid phase as CH_4, suggesting that a stream of NH_3 possesses a high hydrogen activity compared with H_2 at 1 atm.