Kinetic Study of Europium Oxide Chlorination (original) (raw)
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Study of the Reaction Stages and Kinetics of the Europium Oxide Carbochlorination
Metallurgical and Materials Transactions B, 2014
The europium oxide (Eu 2 O 3 (s)) chlorination reaction with sucrose carbon was studied by thermogravimetry between room temperature and 1223 K (950°C). The nonisothermal thermogravimetry showed that the reaction consists of three stages, and their stoichiometries were studied. The product of the first stage was europium oxychloride, and it showed independence of the reaction kinetics with the carbon content. Subsequently, in the second stage, the Eu-OCl(s) was carbochlorinated with formation of EuCl 3 (l) and its evaporation is observed in the third stage. The analysis by Fourier transform infrared spectroscopy of gaseous species showed that the reaction at second stage occurs with the formation of CO 2 (g) and CO(g). Both reactants and products were analyzed by X-ray diffraction, scanning electron microscopy and wavelengthdispersive X-ray fluorescence spectroscopy. The influence of carbon content, total flow rate, sample initial mass, chlorine partial pressure, and temperature were evaluated. The second stage kinetics was analyzed, which showed an anomalous behavior caused by generation of chlorine radicals during interaction of Cl 2 (g) and carbon. It was found that the reaction rate at 933 K (660°C) was proportional to a potential function of the chlorine partial pressure whose exponent is 0.56. The conversion curves were analyzed with the Avrami-Erofeev model and it was obtained an activation energy of 154 ± 5 kJ mol-1 .
Journal of Electroanalytical Chemistry, 2006
Electroreduction of EuCl3 in alkali chloride melts (NaCl–KCl, KCl, CsCl) was studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) for Eu(III) and Eu(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods, showing that D decreases with increase of europium oxidation state, while the activation energy for diffusion increases. Decreasing values of D were also obtained when the cation in the second coordination sphere changed from Na to Cs. It was shown that such changes are due to the decreasing counter polarizing effect of cations at increasing cationic radius. The standard rate constants of charge transfer (ks) for Eu(III)/Eu(II) redox couple were calculated on the basis of cyclic voltammetry data. It was found that ks increase from NaCl–KCl to CsCl melt and electron transfer for the redox reaction proceeds over outer-sphere cation. The larger values for ks were determined in CsCl melt, because of caesium larger polarizability. The formal standard potentials EEu(II)/Eu∗, EEu(III)/Eu∗ and formal redox potentials EEu(III)/Eu(II)∗ were determined from open-circuit potentiometry and linear sweep voltammetry data. Some thermodynamic properties relative to the formation of europium di- and trichloride dilute solutions in alkali chloride melts were obtained. The relative partial molar enthalpies of mixing EuCl2 with alkali chloride melts when dilute solutions are formed, have been measured by electrochemical transient techniques. It was shown that the values determined from electrochemical measurements are in fairly good agreement with those data obtained by a calorimetric method.
Journal of Rare Earths, 2007
L-1-Vis spectroscopy was used to directly determine the concentration of Eu(R) during electroreduction of EU (a) in hydrcchloric acid medium. Electroreduction was carried out in a flow type electrolyzer with glassy carbon cathode at the constar t potential of-800 mV vs. Ag/AgCl. The effects of oxygen and concentration of hydrochloric acid on the sytem were i ivestigated. For 0,Ol rnol. L ~ ' hydrochloric acid, calibration curves for Eu(fl) absorption bands at 248 and 320 nrn were constructed. Molar absorption coefficients were estimated to be 2016 and 648 L*mol-'.cm-', respectively. The absorban Y stronglv decreased with decrease in p1-I of the solution, whereas concentration of chloride had only a negligible effect.
Thermochimica Acta, 2012
In this work the kinetics of the chlorination of molybdenum trioxide has been studied by thermogravimetry between 798 and 873 K. The starting temperature for the reaction of MoO 3 with chlorine is determined at about 770 K. The influence of gaseous flow rate, sample mass, temperature, and chlorine partial pressure in the reaction rate is analyzed for two MoO 3 samples having different particle size and morphology. The experimental conditions for chemical control of the reaction rate were established for both types of samples. An average activation energy of 211 kJ mol −1 and a reaction order of 1 with respect to chlorine partial pressure were determined for the chlorination of MoO 3 with gaseous chlorine. A complete rate equation was formulated that describes the reaction evolution of each type of solid.
Some kinetics aspects of chlorine-solids reactions
Revista de Metalurgia, 2010
The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl 2 +N 2 (chlorination), Cl 2 +O 2 (oxychlorination), and Cl 2 +CO (carbochlorination). Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III) oxide was possible only above 500°C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.
ELECTROCHEMICAL STUDY OF EUROPIUM TRICHLORIDE IN MOLTEN EUTECTIC LiCl-KCl
The present work is part of a research project that study the feasibility of the actinide separation from the rest of fission product contained in the nuclear spent fuel by pyrochemical processes with the aim of their transmutation. In order to design these processes it is necessary to determine basic thermodynamic data of the elements, especially actinides, in the molten salt, such as standard redox potential, standard free Gibbs energy of chloride formation, and activity coefficients of solvation. The electrochemical study of europium trichloride in molten eutectic LiCl-KCl has been performed at solid cathodes, vitreous carbon and tungsten, in a temperature range of 698-773K in order to obtain these basic properties. Here are presented some preliminary results obtained in this stud y, which indicate that Eu(III) is reduced to Eu(II) by a single step through a quasi-reversible reaction. The average diffusion coefficient of Eu(III) ions is D ∼ 1.3 10-5 cm 2 ·s-1 at 723 K.
XAFS study of europium chloride at high temperatures
Progress in Nuclear Energy, 2005
Local structural changes in europium dichloride around europium ion at high temperature are evaluated by using X-ray absorption fine structure technique. A distinct phase shift in EXAFS oscillation observed between 700 and 950K arises from Eu2+ to Eu3+ oxidation. Referring to the difference in EXAFS oscillation between oxide and oxychloride of lanthanum, the chemical state of europium on oxidation is identified mainly as Eu2O3.
Kinetic study of the formation of N -chloro compounds using N -chlorosuccinimide
Journal of Physical Organic Chemistry, 2014
Second-order rate constants were determined for the chlorination reaction of 2,2,2-trifluoethylamine and benzylamine with N-chlorosuccinimide at 25°C and an ionic strength of 0.5 M. These reactions were found to be of first order in both reagents. According to the experimental results, a mechanism reaction was proposed in which a chlorine atom is transferred between both nitrogenous compounds. Kinetics studies demonstrate that the hydrolysis process of the chlorinating agent does not interfere in the chlorination process, under the experimental conditions used in the present work. Free-energy relationships were established using the results obtained in the present work and others available in the literature for chlorination reactions with N-chlorosuccinimide, being the pK a range included between 5.7 and 11.22.
In situ analysis for spontaneous reduction of Eu3+ in LiCl pyroprocessing media at 923 K
Journal of Radioanalytical and Nuclear Chemistry, 2010
The spontaneous reduction of Eu 3? to Eu 2? was examined when EuCl 3 was added into a pyroprocessing media of LiCl molten salt at 923 K. The amount of Eu 2? was calculated by measuring the total charge consumed to oxidize Eu 2? ions to Eu 3? ions. The concentration ratio of Eu 2? to Eu 3? was estimated to be about 0.40 in the media. In addition, it is confirmed that the reduction of Eu 3? to Eu 2? is caused by the oxidation power of Clto Cl 2. The coexistence of Eu 3? and Eu 2? in the LiCl molten salt system was examined by UV-Visible and luminescence spectroscopy. The molar absorptivities of Eu 3? and Eu 2? , calculated from UV-Visible absorption spectra, were 423 and 1954 M-1 cm-1 , respectively.
Kinetic study of the chlorination of gallium oxide
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2005
The kinetics of the chlorination of gallium oxide in chlorine atmosphere was studied between 650 °C and 800 °C. The calculations of the Gibbs standard free energy variation with temperature for the reaction Ga2O3(S)+3Cl2 (g)→2GaCl3(g)+1.5O2 (g) show that direct chlorination is favorable above 850 °C. Thermogravimetric experiments were performed under isothermal and nonisothermal conditions. The effect of temperature, gas flow rate, and Cl2 partial pressure were studied. The solids were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The nonisothermal results showed that chlorination of Ga2O3 starts at approximately 650 °C, with a mass loss of 50 pct at 850 °C. The isothermal results between 650 °C and 800 °C indicated that the reaction rate increased with temperature. The correlation of the experimental data with different solid-gas reaction models showed that the results are adequately represented by the model proposed by Shieh and Lee: X=1−{1−b 22[b 21t+e −b 21t−1]}1/(1−γ). From this model, it was found that the rate of reaction for the chlorination of Ga2O3 is of the order 0.68 with respect to Cl2 and the activation energy is 113.23 kJ/mol. On the other hand, the order of the activation rate of the interface surface is 0.111 with respect to Cl2 and its activation energy is 23.81 kJ/mol.