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Abstract  

The kinetics of oxidation of U(IV) in nitric acid solution by nitrous acid and air oxygen have been studied. The effects of concentrations of U(IV), nitric acid, hydrogen ion and nitrous acid in aqueous solution or oxygen in gas on the oxidation rate have been examined. The oxidation rate increases with increasing temperature and the activation energies are 47 kJ mol–1 for nitrous acid and 91 kJ mol–1 for oxygen. The mechanisms for both oxidation reactions are discussed.

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Abstract  

The kinetics of stripping of thorium(IV) and uranium(IV) from tributylphosphate (TBP)-kerosene with dilute nitic acid solution has been studied using the Lewis cell technique. The effects of concentrations of Th(IV), U(IV), nitric acid, TBP, temperature and stirring speed on the stripping rate have been examined. The result show that the stripping rates of Th(IV) and U(IV) are all controlled by diffusion process.

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Abstract  

A study on the synergistic extraction of uranium(VI) from nitric acid media with double-chelating agent systems 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP) plus thenoyltrifluoroacetone (TTA), and 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 plus 1-phenyl-3-methyl-4-trifluoroacetyl-pyrazolone-5 (PMTFP) is described. Some synergistic effects have been observed. The experimental results suggest that the composition of synergistic complex species is UO2PMBP·TTA and UO2PMBP·PMTFP, respectively. The equilibrium constants for these synergistic extractions are calculated by three methods and the mechanism and the regularity of extraction are discussed as well.

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Abstract  

The kinetics of solvent extraction of U (IV), Th (IV) and U (VI) from nitric acid solution with tributyl phosphate (TBP) in kerosene and cyclohexane have been studied using the single drop technique. The effects of concentrations of U (IV), Th (IV), U (VI), nitric acid, nitrate, TBP and temperature on the extraction rates of U (IV), Th (IV) and U (VI) have been examined. The mechanisms for the three extraction processes are discussed.

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Abstract  

The solvent extraction of U(VI) by p-tert-butylcalix[n]-arene acetate (HnL) (n=4, 6, 8) has been studied. The effects of acidity in aqueous phase and concentration of extractant in organic phase on the distribution ratio were examined. It has been found that the distribution ratio is proportional to [H+]−2 and [HnL](O) and the extracted complex species is UO2Hn−2L. The equilibrium constants of the extraction reactions have been determined. The reaction mechanism is discussed.

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Abstract  

The kinetics of solvent extraction of U(VI) with di(2-ethylhexyl) phosphoric acid (HDEHP) using a microporous hydrophobic hollow fiber membrane extractor has been investigated. The effects of U(VI) and hydrogen ion concentrations in aqueous phase, HDEHP concentration in organic phase, flow velocities of aqueous and organic phase and temperature on extraction rate of U(VI) were examined. The experimental results suggest that the extraction rate of U(VI) is controlled by diffusion.

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Journal of Thermal Analysis and Calorimetry
Authors: Liang Xue, Feng-Qi Zhao, Xiao-Ling Xing, Zhi-Ming Zhou, Kai Wang, Hong-Xu Gao, Jian-Hua Yi, and Rong-Zu Hu

Abstract

The thermal decomposition behavior of 3,4,5-triamino-1,2,4-triazole dinitramide was measured using a C-500 type Calvet microcalorimeter at four different temperatures under atmospheric pressure. The apparent activation energy and pre-exponential factor of the exothermic decomposition reaction are 165.57 kJ mol−1 and 1018.04s−1, respectively. The critical temperature of thermal explosion is 431.71 K. The entropy of activation (ΔS ), enthalpy of activation (ΔH ), and free energy of activation (ΔG ) are 97.19 J mol−1K−1, 161.90 kJ mol−1, and 118.98 kJ mol−1, respectively. The self-accelerating decomposition temperature (T SADT) is 422.28 K. The specific heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide was determined with a micro-DSC method and a theoretical calculation method. Specific heat capacity (J g−1K−1) equation is C p = 0.252 + 3.131 × 10−3 T (283.1 K < T < 353.2 K). The molar heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide is 264.52 J mol−1 K−1 at 298.15 K. The adiabatic time-to-explosion of 3,4,5-triamino-1,2,4-triazole dinitramide is calculated to be a certain value between 123.36 and 128.56 s.

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Journal of Thermal Analysis and Calorimetry
Authors: Liang Xue, Feng-Qi Zhao, Xiao-Ling Xing, Zhi-Ming Zhou, Kai Wang, Hong-Xu Gao, Jian-Hua Yi, Si-Yu Xu, and Rong-Zu Hu

Abstract

The thermal decomposition behaviors of 1,2,3-triazole nitrate were studied using a Calvet Microcalorimeter at four different heating rates. Its apparent activation energy and pre-exponential factor of exothermic decomposition reaction are 133.77 kJ mol−1 and 1014.58 s−1, respectively. The critical temperature of thermal explosion is 374.97 K. The entropy of activation (ΔS ), the enthalpy of activation (ΔH ), and the free energy of activation (ΔG ) of the decomposition reaction are 23.88 J mol−1 K−1, 130.62 kJ mol−1, and 121.55 kJ mol−1, respectively. The self-accelerating decomposition temperature (T SADT) is 368.65 K. The specific heat capacity was determined by a Micro-DSC method and a theoretical calculation method. Specific heat capacity equation is (283.1 K < T < 353.2 K). The adiabatic time-to-explosion is calculated to be a certain value between 98.82 and 100.00 s. The critical temperature of hot-spot initiation is 637.14 K, and the characteristic drop height of impact sensitivity (H 50) is 9.16 cm.

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