TRANSFORMATION KINETICS OF DIPHASIC ALUMINOSILICATE GELS

The formation of mullite in diphasic aluminosilicate gels of stoichiometric composition was studied by quantitative X-ray diffraction (QXRD) and electron microscopy (AEM and SEM). The transformation is preceded by an incubation time which is apparently an activated process with an activation energy of 236 plus or minus 15 kcal/(g multiplied by (times) mol) ( approximately equals 987 plus or minus 63 kJ/(g multiplied by (times) mol)). Microscopic observations show that mullitization occurs via nucleation and growth as a mechanism either interface-controlled or controlled by short-range diffusion near the interface. The kinetic time exponent (n), determined by microstructural and QXRD observations, is close to 1. 3. The transformation kinetics involve a nearly constant nucleus density, and time-dependent growth rate for nearly spherical grains. A linear time-temperature-transformation diagram is observed.