The kinetics and mechanism of the high temperature solid state reactions of kaolinite minerals

Abstract

This thesis describes a kinetic study of the solid state reactions of kaolinite minerals at high temperatures. These reactions can be represented by the idealized equations: The formation of mullite and cristobalite from metakaolinite has been studied in the temperature range 1060°C - 1220°C using several different but well characterized starting materials. A method of X-ray analysis for mullite has bean developed for following the reaction. The experimental data, which suggest that the mechanism is independent of the starting materials, have been compared with several theoretical models for nucleation and diffusion processes. The data up to 90% conversion of mullite can be explained satisfactorily by exponential nucleation followed by rapid crystal growth. Rate constants for the reactions of kaolinite, halloysite, and copper halloysite have been determined. The corresponding enthalpies of activation (87-96 K cal. mole.-1), free energies of activation (108-130 K cal. mole.-1) and entropies of activation (-15.3- -28.8 cal. deg.-1 mole.-1) are independent of the starting materials.