Ceramics-Silikáty 57, (4) 342 - 347 (2013) |
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HYDROTHERMAL REHYDROXYLATION OF KAOLINITE STUDIED BY THERMAL ANALYSIS
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Kloužková Alexandra 1, Zemenová Petra 1, Kohoutková Martina 2,
Kloužek Jaroslav 3
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1 Department of Glass and Ceramics, Institute of Chemical Technology Prague, Technická 5, 166 28 Prague, Czech Republic,
2 Central Laboratories, Institute of Chemical Technology Prague, Technická 5, Prague, 166 28, Czech Republic
3 Laboratory of Inorganic Materials, Joint Workplace of the Institute of Chemical Technology Prague
and the Institute of Rock Structure and Mechanics ASCR, v.v.i., V Holešovičkách 41, 182 09 Prague 8, Czech Republic
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Keywords: Kaolinite, Thermal analysis, Dehydroxylation, Rehydroxylation, Archaeological ceramics
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The effect of hydrothermal conditions on process of kaolinite rehydroxylation at 180oC and 230oC 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 600oC) and hydrothermal treatments (10 h at 230oC). It was
proved that values of activation energy (Ea) 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. |
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