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

Two types of ammonium uranyl nitrate (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O and NH(4)UO(2)(NO(3))(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 (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O and NH(4)UO(2)(NO(3))(3) decomposed to amorphous UO(3) regardless of the atmosphere used. The amorphous UO(3) from (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O was crystallized to γ-UO(3) regardless of the atmosphere used without a change in weight. The amorphous UO(3) obtained from decomposition of NH(4)UO(2)(NO(3))(3) was crystallized to α-UO(3) under a nitrogen and air atmosphere, and to β-UO(3) under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O and NH(4)UO(2)(NO(3))(3) were as follows: under a nitrogen atmosphere: (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O → (NH(4))(2)UO(2)(NO(3))(4)·H(2)O → (NH(4))(2)UO(2)(NO(3))(4) → NH(4)UO(2)(NO(3))(3) → A-UO(3) → γ-UO(3) → U(3)O(8), NH(4)UO(2)(NO(3))(3) → A-UO(3) → α-UO(3) → U(3)O(8); under an air atmosphere: (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O → (NH(4))(2)UO(2)(NO(3))(4)·H(2)O → (NH(4))(2)UO(2)(NO(3))(4) → NH(4)UO(2)(NO(3))(3) → A-UO(3) → γ-UO(3) → U(3)O(8), NH(4)UO(2)(NO(3))(3) → A-UO(3) → α-UO(3) → U(3)O(8); and under a hydrogen atmosphere: (NH(4))(2)UO(2)(NO(3))(4)·2H(2)O → (NH(4))(2)UO(2)(NO(3))(4)·H(2)O → (NH(4))(2)UO(2)(NO(3))(4) → NH(4)UO(2)(NO(3))(3) → A-UO(3) → γ-UO(3) → α-U(3)O(8) → UO(2), NH(4) UO(2)(NO(3))(3) → A-UO(3) → β-UO(3) → α-U(3)O(8) → UO(2).