Oxidation of uranium mononitride

The oxidation of powdered uranium mononitride begins at 2000C by a slow absorption of oxygen. Weakly crystallized products, U2N3 and UO2, are formed. An intensive incorporation of oxygen occurs at 2500C accompanied by a loss of nitrogen. Simultaneously, the amount of U2N3 diminishes and the α-UO3 phase appears. As the temperature increases, UO2 oxidizes into α-UO3 which has the composition UOsub(3-x)Nsub(y). A gradual conversion of α-UO3 into U3O8 starts at about 4000C. The remaining nitrogen disappears above 7000C and U3O8 is the final oxidation product. The isothermal oxidation of sintered UN is characterized by an exponential-rate law in the beginning stage (lateral oxide growth). The activation energy was found to be 61.0 kcal/mol. Later on, the reaction rate increases and the oxidation continues, until all the material is reacted. (Auth.)