Abstract
Temperature dependencies of the DC conductivity of kaolin and illite are measured from 20°C up to 450°C using “as received” samples and samples after heating to 400°C and 450°C. Release of physically bound water (PBW) from green kaolin shows two maxima, at 55°C and 298°C. Release of the PBW from green illite takes place in 3 steps at 72°C, 186°C, and 298°C. Up to 200°C, the dominant charge carriers are H+ and OH– ions in both materials. At higher temperatures, alkali ions (both Na+ and K+ in kaolin, prevalently K+ in illite) are the dominant charge carriers with the conduction activation energy of 1.19±0.02eV in kaolin and of 1.12±0.02eV in illite. Above 400°C, dehydroxylation runs in illite. Due to this process, the DC conductivity of illite increases; in partly dehydroxylated illite, higher conduction activation energy (1.22eV) indicates that alkali metal ions are moving in a more disordered structure. In kaolin, dehydroxylation starts only above 450°C.
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