Differential thermal analysis of mullite formation from Algerian kaolin

In the present work, the kinetics of mullite (3Al2O3.2SiO2) formation from Algerian kaolin was investigated using differential thermal analysis (DTA). The raw kaolin was wet ball milled for 5 h followed by attrition milling for 1 h. Differential thermal and thermogravimetric (DTA/TG) experiments were carried out on samples between room temperature and 1350°C at heating rates of 5, 10, 20 and 40°C min−1. The temperature of mullite crystallisation was found to be ∼1005°C. The activation energies measured from isothermal and non-isothermal treatments were around 1290 and 1260 kJ mol−1 respectively. The growth morphology parameters n (Avrami parameter which indicates the crystallisation mode) and m (a numerical factor which depends on the dimensionality of crystal growth) were found to be almost equal to 1˙5. Analysis of the results showed that bulk nucleation was dominant in mullite crystallisation followed by three-dimensional growth of mullite crystals with polyhedron-like morphology controlled by diffusion from a constant number of nuclei.