title: Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate.
abstract: Two types of ammonium uranyl nitrate (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3, were thermally decomposed and reduced in a TG-DTA unit in nitrogen, air, and hydrogen atmospheres. Various intermediate phases produced by the thermal decomposition and reduction process were investigated by an X-ray diffraction analysis and a TG/DTA analysis. Both (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3decomposed to amorphous UO3regardless of the atmosphere used. The amorphous UO3from (NH4)2UO2(NO3)4·2H2O was crystallized to γ-UO3regardless of the atmosphere used without a change in weight. The amorphous UO3obtained from decomposition of NH4UO2(NO3)3was crystallized to α-UO3under a nitrogen and air atmosphere, and to β-UO3under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3were as follows: under a nitrogen atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4→ NH4UO2(NO3)3→ A-UO3→ γ-UO3→ U3O8, NH4UO2(NO3)3→ A-UO3→ α-UO3→ U3O8; under an air atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4→ NH4UO2(NO3)3→ A-UO3→ γ-UO3→ U3O8, NH4UO2(NO3)3→ A-UO3→ α-UO3→ U3O8; and under a hydrogen atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4→ NH4UO2(NO3)3→ A-UO3→ γ-UO3→ α-U3O8→ UO2, NH4UO2(NO3)3→ A-UO3→ β-UO3→ α-U3O8→ UO2.
authors.affiliation: Department of Fast Reactor Technology Development, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Daejeon, 305-353 Korea.
authors.forename: B H
authors.initials: BH
authors.lastname: Kim
authors.affiliation: Department of Fast Reactor Technology Development, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Daejeon, 305-353 Korea.
authors.forename: Y B
authors.initials: YB
authors.lastname: Lee
authors.affiliation: Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Prelas
authors.affiliation: Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Ghosh
keywords: Ammonium uranyl nitrate; Modified direct denitration; Thermal decomposition