FORMATION OF URANIUM MONONITRIDE BY THE REACTION OF URANIUM-DIOXIDE WITH CARBON IN AMMONIA AND A MIXTURE OF HYDROGEN AND NITROGEN .2. REACTION-RATES

Kinetics of the carbothermic synthesis of UN from UO2 in an NH3 stream and a mixed 75% H2 + 25% N2 stream were studied in the temperature range of 1400-1600°C by X-ray analysis and weight change measurement of the sample. The weight change was divided into two parts; i.e. weight loss due to carbothermic reduction of UO2 and weight loss due to removal of carbon by hydrogen. The former followed the first-order rate equation -1n(1 - α0) = k0t, and the latter the rate equation of phase boundary reaction 1 - (1 - αc)1/3 = kct. The apparent activation energy of the former was in the range of 320-380 kJ/mol. The value of the latter in an NH3 stream was 175-185 kJ/mol, which was smaller than that in a mixed 75% H2 + 25% N2stream (285 kJ/mol). In this method, the rate of the removal of carbon by hydrogen determines that of the formation of high purity UN. © 1979.