Formation of columnar U3O8 grains on the oxidation of UO2 pellets in air at 900°C

Abstract UO 2 is oxidized to U 3 O 8 in air at 900°C via two intermediate oxide phases; UO 2 + x and U 4 O 9 . U 3 O 8 grains are formed in random orientation near the specimen surface, but only the grains having their c -axes parallel to the specimen surface grow inward preferentially enough to be developed into columnar grains. Such preferred orientation can reduce minimize the transformation-induced strain.