Ceramics-Silikáty 57 (4) 342-347 (2013)

HYDROTHERMAL REHYDROXYLATION OF KAOLINITE STUDIED BY THERMAL ANALYSIS

The effect of hydrothermal conditions on process of kaolinite rehydroxylation at 180°C and 230°C and for soaking times from 1 to 200 hour was studied by thermal analysis (DTA, DSC, TG). It is shown that the kaolinite dehydroxylation of rehydroxylated samples shifts to lower temperatures compared to the original kaolinite. Amounts of kaolinite in rehydroxylated samples were calculated from TG curves. The curve of the kaolinite mass gain (Δm) plotted against the time of hydrothermal treatment indicates a two stage process with a different mass gain rate representing short and long-time measurements. Multiple dehydroxylation was studied by repeated calcinations (2 h at 600°C) and hydrothermal treatments (10 h at 230°C). It was proved that values of activation energy (E_a) of multiple dehydroxylations decreased with the increasing number of repeated treatments. Conclusions of the study were applied for the investigation of kaolinite origin in archaeological samples from Roztoky near Prague.

Keywords: Kaolinite, Thermal analysis, Dehydroxylation, Rehydroxylation, Archaeological ceramics