Sintering mechanism and ceramic phases of an illitic–chloritic raw clay

Sintering process and ceramic phases of a non-calcareous illitic–chloritic clay were investigated in the range 850–1075 °C by means of X-ray diffraction (XRD), thermal analysis, scanning electron microscopy and energy dispersive X-ray spectrometry as well as by measuring some firing characteristics. It is found that the sintering mechanism is mainly governed by viscous flow and the activation energy turns around 100 kJ/mol.Moreover, it is evidenced that firing characteristics are principally controlled by the glassy phase formation. On the other hand, it is observed that magnesium is the most active element in the neoformation process, and Mg-spinels, olivine and enstatite were the main neocrystallized phases. The formation of the latter magnesian phases was discussed on the basis of the MgO–SiO2–Al2O3 phase diagram. It derived that a part of free silica is involved in the precipitation of Mg-phases.