Kinetics of yttrium oxide carbochlorination (original) (raw)
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The Kinetics of the Chlorination of Yttrium Oxide
Metallurgical and Materials Transactions B, 2009
The chlorination kinetics of Y 2 O 3 with chlorine to produce YOCl was studied by thermogravimetry over a temperature range from 575°C to 975°C. The influence of convective mass transfer into the boundary layer surrounding the sample, gaseous diffusion into the sample pores, partial pressure of chlorine, and temperature on the reaction rate were analyzed in order to determine the rate-controlling step. The thermogravimetric and scanning electron microscopy (SEM) results showed that the process follows a model of nucleation and growth, and the process is chemically controlled for temperatures lower than 800°C, with an activation energy (Ea) of 187 ± 3 kJ/mol. In the 850°C to 975°C range the reaction rate was affected by diffusion of Cl 2 through the gas film surrounding the sample, with apparent Ea of 105 ± 11 kJ/mol. A global rate equation that includes these parameters has been developed R ¼ da=dt ¼ 10 5 kPa À1 Á exp À 187 kJÁmol À1 RÁT ÁpCl 2 Á1:51Á 1 À a ð ÞÁÀln 1 À a ð Þ ½ 0:34
Carbochlorination of yttrium oxide
Thermochimica Acta, 2010
The reaction of chlorination of a mixture composed by Y 2 O 3 and sucrose carbon was studied by thermogravimetry over a temperature range of 550-950 • C. The reaction proceeds through several successive stages. The first of them is the formation of solid yttrium oxychloride (YOCl) and subsequently the YOCl is carbochlorinated to produce YCl 3 (solid or liquid, depending on the temperature) in two stages. The stoichiometries of the first stage and the global reaction were estimated by mass balances, taking into account the chlorine adsorbed by the remainder carbon. The results showed that the reactions involved progress with the formation of CO 2 and CO in the temperature range of 600-775 • C. The interaction between sucrose carbon and chlorine was analyzed by thermogravimetry in order to quantify the amount of chlorine which is adsorbed on its surface. It was studied the effect of the temperature and initial mass of carbon. The morphological analysis performed by SEM of partially reacted samples showed that the formation of YOCl proceeds through a mechanism of nucleation and growth. For temperatures above 715 • C the final product of the carbochlorination is liquid YCl 3 , whose evaporation is observed in the thermogravimetry. The evaporation kinetics was analyzed in argon atmosphere and from the thermogravimetric curves was determined a value of 250 kJ/mol for the heat of evaporation of YCl 3. This value is consistent with a partial dimerization of the gaseous chloride.
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.
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 .
A study of chromite carbochlorination kinetics
Metallurgical and Materials Transactions B, 1999
The carbochlorination of a chromite concentrate was studied between 500 °C and 1000 °C using boat experiments. The reaction products were analyzed by SEM, XRD and chemical analysis. The carbochlorination of a chromite concentrate at about 600 °C led to the partial selective elimination of iron thus increasing the Cr/Fe ratio in the treated concentrate. Total carbochlorination of the chromite concentrates and volatilization of the reaction products was achieved at temperatures higher than 800 °C. Kinetics of the chromite carbochlorination was studied between 750 °C and 1050 °C using thermogravimetric analysis. The results were discussed in terms of the effects of gas flow rate, temperature, partial pressure of Cl 2 +CO and Cl 2 /CO ratio on the carbochlorination process. It was observed that the temperature effect changed significantly with the progress of the reaction. The initial stage of the carbochlorination was characterized by apparent activation energy of about 135 and 74 kJ/mol below and above 925 °C, respectively. While a value of about of 195 kJ/mol was found for the remaining of the carbochlorination process. a. Laboratoire Environnement et Minéralurgie, rue du Doyen M.
Kinetic Study of Europium Oxide Chlorination
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2013
The kinetics of europium oxide (Eu 2 O 3) chlorination using gaseous chlorine as a chlorination agent was studied between 523 K and 1223 K (250°C and 950°C). The relative mass change during the chlorination reaction was continuously monitored using a high resolution thermogravimetric system. The starting temperature for the reaction of Eu 2 O 3 (s) with chlorine was determined at about 523 K (250°C) with the formation of solid europium oxychloride (EuOCl). For temperatures above 1123 K (850°C), the EuOCl(s) is chlorinated producing EuCl 3 (l). The influence of gaseous flow rate, sample mass, chlorine partial pressure, and temperature on the reaction rate was analyzed. The results showed that for 673 K (400°C) and temperatures below, the system is under chemical control. Concerning the influence of chlorine partial pressure, it was determined that pressures greater than 50 kPa do not modify the kinetic regime. For the experiment at 673 K (400°C), it was found that the chlorination rate was proportional to a potential function of the partial pressure of chlorine whose exponent is 0.54. The conversion curves were analyzed with the Johnson-Mehl-Avrami description. Intrinsic activation energy of 115 kJ mol À1 was obtained for the temperature range of 573 K to 673 K (300°C to 400°C). Finally, a global rate equation that includes these parameters was developed.
Study of YBa2Cu3O7−x reaction kinetics by Rietveld method
Powder Diffraction, 2001
Using a recent proposed analysis procedure for quantitative phase determination by X-ray powder diffraction, YBa2Cu3O7−x solid state formation reaction kinetics at 900 °C was studied. Although there was the presence of partial amorphous components, it was possible to determine a reaction route for the synthesis of the title compound from X-ray powder diffraction data collected at various stages of the thermal treatment and using the Rietveld method for the quantitative determination of the phase composition
Eclética Química, 2006
The dehydration kinetic of Yb, Lu and Y 4-chlorobenzylidenepyruvate was studied by using thermogravimetry and the kinetics parameters obtained by Flynn and Wall method suggest that the dehydration step follows a first order mechanism. The activation energies calculated were 103.6, 96.6 and 97.2 kJ/mol and the lifetime considering the temperature of 31 and 101 º C for the dehydration of these compounds were 23, 26, 31 minutes and 0.6, 1.3 and 1.4 seconds, respectively. The results have similar values and suggest that the water is attached in the same way.
MethodsX, 2020
A method of synthesis crystalline yttrium citrate dihydrate was proposed as a result of the transformation of the freshly precipitated basic yttrium carbonate phase in a citric acid solution. The synthesis time was determined on the basis of composition analysis, structure and thermogravimetric studies of samples taken during the synthesis. The research methods used have shown that in the initial stage of the synthesis, the processes of citric acid sorption on basic yttrium carbonate and transformation of amorphous yttrium carbonate hydroxide into crystalline yttrium hydroxide occurs. It is only after 72 h of synthesis that the crystalline yttrium citrate dihydrate is formed. • Synthesis crystalline yttrium citrate dehydrate. • The synthesis time 72 h. • Synthesis components: the freshly precipitated basic yttrium carbonate phase in a citric acid solution.