| Thermal analysis in clay mineralogy |  |
| Katja Emmerich Water Technology and Geotechnology Division, Institute for Technical Chemistry (ITC-WGT), Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, D-76021 Karlsruhe |
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| Rocks and stones played an important role for the development of Thermal Analysis (TA) and vice versa TA contributed to the development of earth sciences. However, TA has been neglected during the last decades in clay mineralogy. The most important monographs and reviews have been published during the 50ies up to the 70ies of the last century (e.g., Mackenzie, 1957, Smykatz-Kloss, 1974). Fortunately TA is now experiencing a renaissance in clay mineralogy. | |
| An new and important use of Simultaneous Thermal Analysis (STA = TG/DSC linked to a mass spectrometer) in clay mineralogy is for the identification of structural features of smectites. Smectites are swellable 2:1 aluminous silicates with turbostratic disorder. Hence, no information of the structure of the layers can be obtained by common X-ray diffraction analysis. Drits et al. (1995) showed that the dehydroxylation behaviour of aluminous dioctahedral 2:1 layer silicates is related to the distribution of metal ions and vacancies over available sites in the octahedral sheet. Therefore, the dehydroxylation temperature can be used to determine the location of octahedral charge. In addition the position and shape of the dehydration peak gives information on the interlayer cations of smectites. | |
| While investigating clays and clay minerals with STA broad or superimposed peaks often occur. Thus, identification of clay minerals in most cases is restricted to peak temperatures which strongly depend on sample pre-treatment, experimental parameters and the equipment used (Niederbudde et al., 2003). The application of STA in clay mineralogy for the identification of clay minerals and their structural features will be illustrated by examples. | |
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