STUDIES ON KINETICS OF LOW-TEMPERATURE CHLORINATION OF ZRO2 BY GASEOUS CARBON-TETRACHLORIDE

Studies on the kinetics of chlorination of ZrO2 powder by carbon tetra chloride vapor in mixture with nitrogen in a low-temperature range of 650 to 825 K at different periods and partial pressures of carbon tetr achloride were carried out. The chlorination results at 650 and 675 K seem to follow a diffusion-controlled reaction model of Jander's type: [1 - (1 - R)(1/3)](2) = k(1)t where R is the fraction of ZrO2 chlorin ated in time t and k(1) is the rate constant. The approximate activati on energy of the process was calculated from k(1) values at the previo usly mentioned two temperatures and found to be 278 kJ/mole. For the c hlorination in the temperature range of 700 to 750 K, the topochemical reaction model 1 - (1 - R)(1/3) = k(2)t was followed. The rate consta nt, k(2), was found to be proportional to the partial pressure of carb on tetrachloride. The activation energy of this reaction was calculate d to be 154 kJ/mole. In the temperature range of 775 to 825 K, the rat e of chlorination was found to be directly proportional to the time of chlorination following Langmuir's Adsorption Isotherm. Because of the very high rate of chlorination and thermodynamic possibility of decom position of CCl4 above 773 K, the rate-controlling step has been sugge sted to be the decomposition of the adsorbed complex formed by ZrO2 wi th carbon and chlorine atoms, obtained from the decomposition of CCl4 vapor. The activation energy of the process was 54 kJ/mole. In view of nearly complete chlorination of ZrO2 by CCl4 in a very short period o f about 15 minutes, at a temperature around 800 K and lesser possibili ty of formation of toxic product gases, the process is recommended for commercial application.