Kinetic study of the chlorination of gallium oxide

Abstract

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 Ga 2O3(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 pet 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 - b22[b21t + e -b21t - 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.