Kinetic analysis of sinter-crystallization of mullite and cristobalite from kaolinite

A non-isothermal kinetic analysis of high-temperature processes occurring during thermal treatment of kaolinite is performed by the thermodilatometric analysis. The measurements are carried out using the horizontal pushrod dilatometer on compact samples with heating rates from 1 to 10 degrees C min(-1) in dynamic N-2 atmosphere. For the parameterization of thermodynamically stable phases such as mullite and cristobalite, the Kissinger method is used. The obtained value of apparent activation energy for sinter-crystallization of mullite is (726 +/- 9) kJ mol(-1) and the thickening of long mullite needles is determined as a mechanism of this process. The results also show that the apparent activation energy for sinter-crystallization of cristobalite is (565 +/- 38) kJ mol(-1).