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<p>The thermodynamic behavior associated with the conversion of metastudtite (UO<sub>4</sub>·2H<sub>2</sub>O) to uranium trioxide (UO<sub>3</sub>) was firstly investigated in this study through the application of two isoconversional models, namely the integral Starink and the differential Friedman. Thermogravimetric analysis (TGA) was performed at heating rates of 10, 15, 20, and 30&#xa0;°C ·min<sup>-1</sup> to evaluate the thermal decomposition process. Based on the obtained TGA data, the activation energy (<i>E</i>) corresponding to different conversion coefficients (<i>α</i>) was determined. The activation energy increased from approximately 85 to 150&#xa0;kJ·mol<sup>-1</sup> as <i>α</i> increased from 0.15 to 0.85, indicating that the conversion process became progressively more energy demanding. The peak temperatures (<i>T</i><sub><i>peak</i></sub>), corresponding to the maximum conversion rate, were recorded as 245.71, 254.01, 261.78, and 268.94&#xa0;°C at heating rates of 10, 15, 20, and 30&#xa0;°C·min<sup>-1</sup>, respectively. These activation energy and <i>T</i><sub><i>peak</i></sub> values were subsequently employed to determine the Arrhenius pre-exponential factor (<i>A</i>) and related thermodynamic data. The calculated A values were 3.5 × 10<sup>10</sup>, 5.4 × 10<sup>10</sup>, 7.5 × 10<sup>10</sup>, and 11.5 × 10<sup>10</sup> min<sup>-1</sup> for heating rates of 10, 15, 20, and 30&#xa0;°C·min<sup>-1</sup>, respectively. Furthermore, the thermodynamic data revealed that both enthalpy change (<i>ΔH</i>) and Gibbs free energy change (<i>ΔG</i>) increased with increasing conversion coefficient, ranging from 80 to 120&#xa0;kJ·mol<sup>-1</sup> and 90–125&#xa0;kJ·mol<sup>-1</sup>, respectively, as α increased from 0.15 to 0.85. In contrast, the entropy change (<i>ΔS</i>) decreased within the range of − 15 to − 20&#xa0;J·mol<sup>-1</sup>·K<sup>-1</sup>. The positive values of <i>ΔH</i> and <i>ΔG</i> suggest that the metastudtite-to-UO<sub>3</sub> conversion is non-spontaneous under the investigated conditions, while the negative <i>ΔS</i> values indicate a transition from the relatively disordered structure of metastudtite to the more ordered structure of UO<sub>3</sub>. These thermodynamic studies provided a better understanding of the conversion process of metastudtite to UO<sub>3</sub> nuclear materials, thereby enabling improved control of this process.</p>

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A study on the thermodynamics for conversion of metastudtite-to-uranium trioxide nuclear materials

  • 期刊论文

  • 发表日期：

    2026年6月27日

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  • Nguyen Trong Hung,
  • Wantae Kim,
  • Jin-Young Lee

摘要

The thermodynamic behavior associated with the conversion of metastudtite (UO4·2H2O) to uranium trioxide (UO3) was firstly investigated in this study through the application of two isoconversional models, namely the integral Starink and the differential Friedman. Thermogravimetric analysis (TGA) was performed at heating rates of 10, 15, 20, and 30 °C ·min-1 to evaluate the thermal decomposition process. Based on the obtained TGA data, the activation energy (E) corresponding to different conversion coefficients (α) was determined. The activation energy increased from approximately 85 to 150 kJ·mol-1 as α increased from 0.15 to 0.85, indicating that the conversion process became progressively more energy demanding. The peak temperatures (Tpeak), corresponding to the maximum conversion rate, were recorded as 245.71, 254.01, 261.78, and 268.94 °C at heating rates of 10, 15, 20, and 30 °C·min-1, respectively. These activation energy and Tpeak values were subsequently employed to determine the Arrhenius pre-exponential factor (A) and related thermodynamic data. The calculated A values were 3.5 × 1010, 5.4 × 1010, 7.5 × 1010, and 11.5 × 1010 min-1 for heating rates of 10, 15, 20, and 30 °C·min-1, respectively. Furthermore, the thermodynamic data revealed that both enthalpy change (ΔH) and Gibbs free energy change (ΔG) increased with increasing conversion coefficient, ranging from 80 to 120 kJ·mol-1 and 90–125 kJ·mol-1, respectively, as α increased from 0.15 to 0.85. In contrast, the entropy change (ΔS) decreased within the range of − 15 to − 20 J·mol-1·K-1. The positive values of ΔH and ΔG suggest that the metastudtite-to-UO3 conversion is non-spontaneous under the investigated conditions, while the negative ΔS values indicate a transition from the relatively disordered structure of metastudtite to the more ordered structure of UO3. These thermodynamic studies provided a better understanding of the conversion process of metastudtite to UO3 nuclear materials, thereby enabling improved control of this process.