Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate.

Two types of ammonium uranyl nitrate (NH)UO(NO)·2HO and NHUO(NO), 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 (NH)UO(NO)·2HO and NHUO(NO) decomposed to amorphous UO regardless of the atmosphere used. The amorphous UO from (NH)UO(NO)·2HO was crystallized to γ-UO regardless of the atmosphere used without a change in weight. The amorphous UO obtained from decomposition of NHUO(NO) was crystallized to α-UO under a nitrogen and air atmosphere, and to β-UO under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH)UO(NO)·2HO and NHUO(NO) were as follows: under a nitrogen atmosphere: (NH)UO(NO)·2HO → (NH)UO(NO)·HO → (NH)UO(NO) → NHUO(NO) → A-UO → γ-UO → UO, NHUO(NO) → A-UO → α-UO → UO; under an air atmosphere: (NH)UO(NO)·2HO → (NH)UO(NO)·HO → (NH)UO(NO) → NHUO(NO) → A-UO → γ-UO → UO, NHUO(NO) → A-UO → α-UO → UO; and under a hydrogen atmosphere: (NH)UO(NO)·2HO → (NH)UO(NO)·HO → (NH)UO(NO) → NHUO(NO) → A-UO → γ-UO → α-UO → UO, NH UO(NO) → A-UO → β-UO → α-UO → UO. [ABSTRACT FROM AUTHOR]