TG study of the chlorination of WO3 by COCl2 and CCl4

Abstract

The chlorination kinetics of tungsten trioxide was studied by thermogravimetry, using COCl2 and gaseous CCl4 as chlorinating agents. Thermochemical calculations were made on the main chlorination reactions and also on some assumed side reactions. On the basis of the kinetic results CCl4 proved to be more reactive than COCl2. For both gases apparent activation energies of about 100 kJ.mol−1 and reaction orders of 0.5 were obtained in the temperature ranges where the reaction was controlled by chemical processes. During the chlorination by COCl2 the conversionvs. time data could be described by the contracting sphere model. When chlorinating by CCl4 a continuous decrease of the linear reaction rate was observed. Thus, for describing the isothermal TG curves a kinetic model, based on the retarding effect of non-removable surface side products, was assumed. With this model a fairly good correspondence of the measured and calculated kinetic curves was obtained.