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Papers by Juan Pablo Gaviria
Thermochimica Acta, 2010
The reaction of chlorination of a mixture composed by Y 2 O 3 and sucrose carbon was studied by t... more 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.
Thermochimica Acta, 2011
The chlorination kinetics of the Y 2 O 3-sucrose carbon system was studied by thermogravimetry. T... more The chlorination kinetics of the Y 2 O 3-sucrose carbon system was studied by thermogravimetry. This work is a continuation of a previous one in which the reaction stages and the stoichiometry of each reaction have been determined. The influence of carbon content, total flow rate, sample initial mass and chlorine partial pressure was evaluated. The effect of carbon content on the reactive mixture was studied between 6.7 and 70% (carbon mass/total mass). The results showed that the reaction rate of each stage is strongly increased as the carbon content increases and the range of occurrence of the stages depends on the amount of carbon in the solid reactive mixture. The formation reaction of YOCl (STAGE I) is chemically controlled for temperatures lower than 700 • C with average effective activation energies of 165 ± 6 and 152 ± 7 kJ/mol for 8.7 and 16.7%C, respectively. The formation of the YOCl follows a nucleation and growth mechanism, with a combination of continuous nucleation and site saturation, and anisotropic growth controlled by diffusion. The kinetics of STAGE I can be expressed by the following global rate equation that includes the variables analyzed: dd t = k 0 B exp − Ea R g T pCl 2 {n(1 −˛)[− ln(1 −˛)]} (n−1)/n where k 0 B = 1.9 × 10 4 , n = 1.20 for 8.7%C, and k 0 B = 8.4 × 10 3 , n = 1.14 for 16.7%C. STAGES II and III correspond to the YOCl carbochlorination to form YCl 3 , being these stages kinetically different. It was not possible to obtain kinetic parameters for these stages. The reaction rate of STAGE II is affected by diffusion of Cl 2 through the gas film surrounding the sample and mass changes in STAGE III have two opposite components: formation and evaporation of liquid YCl 3 .
Metallurgical and Materials Transactions B, 2009
The chlorination kinetics of Y 2 O 3 with chlorine to produce YOCl was studied by thermogravimetr... more 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
Thermochimica Acta, 2010
The reaction of chlorination of a mixture composed by Y 2 O 3 and sucrose carbon was studied by t... more 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.
Thermochimica Acta, 2011
The chlorination kinetics of the Y 2 O 3-sucrose carbon system was studied by thermogravimetry. T... more The chlorination kinetics of the Y 2 O 3-sucrose carbon system was studied by thermogravimetry. This work is a continuation of a previous one in which the reaction stages and the stoichiometry of each reaction have been determined. The influence of carbon content, total flow rate, sample initial mass and chlorine partial pressure was evaluated. The effect of carbon content on the reactive mixture was studied between 6.7 and 70% (carbon mass/total mass). The results showed that the reaction rate of each stage is strongly increased as the carbon content increases and the range of occurrence of the stages depends on the amount of carbon in the solid reactive mixture. The formation reaction of YOCl (STAGE I) is chemically controlled for temperatures lower than 700 • C with average effective activation energies of 165 ± 6 and 152 ± 7 kJ/mol for 8.7 and 16.7%C, respectively. The formation of the YOCl follows a nucleation and growth mechanism, with a combination of continuous nucleation and site saturation, and anisotropic growth controlled by diffusion. The kinetics of STAGE I can be expressed by the following global rate equation that includes the variables analyzed: dd t = k 0 B exp − Ea R g T pCl 2 {n(1 −˛)[− ln(1 −˛)]} (n−1)/n where k 0 B = 1.9 × 10 4 , n = 1.20 for 8.7%C, and k 0 B = 8.4 × 10 3 , n = 1.14 for 16.7%C. STAGES II and III correspond to the YOCl carbochlorination to form YCl 3 , being these stages kinetically different. It was not possible to obtain kinetic parameters for these stages. The reaction rate of STAGE II is affected by diffusion of Cl 2 through the gas film surrounding the sample and mass changes in STAGE III have two opposite components: formation and evaporation of liquid YCl 3 .
Metallurgical and Materials Transactions B, 2009
The chlorination kinetics of Y 2 O 3 with chlorine to produce YOCl was studied by thermogravimetr... more 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