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

Kim BH, Lee YB, Prelas MA, Ghosh TK - J Radioanal Nucl Chem (2012)

Bottom Line: 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.The amorphous UO3 obtained from decomposition of NH4UO2(NO3)3 was crystallized to α-UO3 under a nitrogen and air atmosphere, and to β-UO3 under a hydrogen atmosphere without a change in weight.Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 were 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, NH4 UO2(NO3)3 → A-UO3 → β-UO3 → α-U3O8 → UO2.

View Article: PubMed Central - PubMed

Affiliation: Department of Fast Reactor Technology Development, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Daejeon, 305-353 Korea.

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)3 decomposed to amorphous UO3 regardless of the atmosphere used. The amorphous UO3 from (NH4)2UO2(NO3)4·2H2O was crystallized to γ-UO3 regardless of the atmosphere used without a change in weight. The amorphous UO3 obtained from decomposition of NH4UO2(NO3)3 was crystallized to α-UO3 under a nitrogen and air atmosphere, and to β-UO3 under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 were 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, NH4 UO2(NO3)3 → A-UO3 → β-UO3 → α-U3O8 → UO2.

No MeSH data available.


DTA curves for (NH4)2UO2(NO3)4·2H2O in a N2, b Air, and c H2 atmosphere
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Fig1: DTA curves for (NH4)2UO2(NO3)4·2H2O in a N2, b Air, and c H2 atmosphere

Mentions: The DTA results from the thermal decomposition of (NH4)2UO2(NO3)4·2H2O as manufactured under a nitrogen, air, and hydrogen atmosphere are shown in Fig. 1. The reaction under the nitrogen atmosphere started at around 50 °C with a dehydration of the hydrate, which is an endothermic reaction. Endothermic peaks, which seemed to be a phase change of NH4NO3, were due to the presence of extremely small amount of impurities. These peaks appeared around 84, 130, and 155 °C. An endothermic peak as a result of the first thermal decomposition of (NH4)2UO2(NO3)4·2H2O into NH4NO3 appeared within a temperature range of 168 to 240 °C. A second endothermic that was due to the second thermal decomposition of NH4NO3 appeared in the temperature range of 268 to 307 °C. After the second endothermic peak continued, a weak exothermic reaction took place around 400 °C. This reaction continued for a while, and then ended as an endothermic reaction that took place at 579 °C.Fig. 1


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

Kim BH, Lee YB, Prelas MA, Ghosh TK - J Radioanal Nucl Chem (2012)

DTA curves for (NH4)2UO2(NO3)4·2H2O in a N2, b Air, and c H2 atmosphere
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4514459&req=5

Fig1: DTA curves for (NH4)2UO2(NO3)4·2H2O in a N2, b Air, and c H2 atmosphere
Mentions: The DTA results from the thermal decomposition of (NH4)2UO2(NO3)4·2H2O as manufactured under a nitrogen, air, and hydrogen atmosphere are shown in Fig. 1. The reaction under the nitrogen atmosphere started at around 50 °C with a dehydration of the hydrate, which is an endothermic reaction. Endothermic peaks, which seemed to be a phase change of NH4NO3, were due to the presence of extremely small amount of impurities. These peaks appeared around 84, 130, and 155 °C. An endothermic peak as a result of the first thermal decomposition of (NH4)2UO2(NO3)4·2H2O into NH4NO3 appeared within a temperature range of 168 to 240 °C. A second endothermic that was due to the second thermal decomposition of NH4NO3 appeared in the temperature range of 268 to 307 °C. After the second endothermic peak continued, a weak exothermic reaction took place around 400 °C. This reaction continued for a while, and then ended as an endothermic reaction that took place at 579 °C.Fig. 1

Bottom Line: 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.The amorphous UO3 obtained from decomposition of NH4UO2(NO3)3 was crystallized to α-UO3 under a nitrogen and air atmosphere, and to β-UO3 under a hydrogen atmosphere without a change in weight.Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 were 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, NH4 UO2(NO3)3 → A-UO3 → β-UO3 → α-U3O8 → UO2.

View Article: PubMed Central - PubMed

Affiliation: Department of Fast Reactor Technology Development, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Daejeon, 305-353 Korea.

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)3 decomposed to amorphous UO3 regardless of the atmosphere used. The amorphous UO3 from (NH4)2UO2(NO3)4·2H2O was crystallized to γ-UO3 regardless of the atmosphere used without a change in weight. The amorphous UO3 obtained from decomposition of NH4UO2(NO3)3 was crystallized to α-UO3 under a nitrogen and air atmosphere, and to β-UO3 under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 were 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, NH4 UO2(NO3)3 → A-UO3 → β-UO3 → α-U3O8 → UO2.

No MeSH data available.