The Kinetics of the Chlorination of Yttrium Oxide

Abstract

The chlorination kinetics of Y₂O₃ 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 Cl₂ 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 ${\text{R}} = d\alpha /dt = 10^{5}\,{\text{kPa}}^{{ - 1}} {\cdot} \exp {\left( { - \frac{{187\;{\text{kJ}} {\cdot} {\text{mol}}^{{ - 1}} }} {{{\text{R}} {\cdot} T}}} \right)} {\cdot} p{\text{Cl}}_{2} {\cdot} 1.51 {\cdot} {\left( {1 - \alpha } \right)} {\cdot} {\left[ { - \ln {\left( {1 - \alpha } \right)}} \right]}^{{0.34}}$