Thermal transformations of sonicated pyrophyllite

The differences on the thermal behaviour (DTG–DTA) of three pyrophyllite samples measured before and after sonication have been studied. Sonication treatment produces substantial textural modifications but negligible changes in the structure of the material. These modifications produce important changes in the thermal behaviour of pyrophyllite samples. Thus, it produces a decrease of more than 100 °C in the dehydroxylation temperature as measured by DTG and DTA effects. In addition, the exothermic effect of mullite formation shifts to lower temperature (about 30 °C) in sonicated pyrophyllite. These modification in the thermal behaviour are related to the pronounced decrease in particle size. The dehydroxylation effect of kaolinite that accompanies two of the studied samples, overlaps with that of sonicated pyrophyllite; however, the exothermic effect at 975 °C of kaolinite remain unchanged with the treatment.