Formation of uranium mononitride by the reaction of uranium dioxide with carbon in ammonia and a mixture of hydrogen and nitrogen: II. Reaction rates

Abstract

Kinetics of the carbothermic synthesis of UN from UO 2 in an NH 3 stream and a mixed 75% H 2 + 25% N 2 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 UO 2 and weight loss due to removal of carbon by hydrogen. The former followed the first-order rate equation −1 n(1 − α 0) = k 0 t, and the latter the rate equation of phase boundary reaction 1 − (1 − α c ) 1/3 = k c t. The apparent activation energy of the former was in the range of 320–380 kJ/mol. The value of the latter in an NH 3 stream was 175–185 kJ/mol, which was smaller than that in a mixed 75% H 2 + 25% N 2stream (285 kJ/mol). In this method, the rate of the removal of carbon by hydrogen determines that of the formation of high purity UN.