THE EMANATION THERMAL-ANALYSIS OF KAOLINITE CLAY-MINERALS

Emanation thermal analysis (ETA) is based on the measurement of the ra te of release of radon from solid samples previously labelled with tra ce concentrations of an inert radioactive nuclide (Thorium-228 or Ra-2 24). This method enables pointing out of the different steps that occu r during the heating of kaolinite: pre-dehydroxylation, dehydroxylatio n, evolution of structural disorder in metakaolinite, segregation of a morphous silica and formation of precursors of high-temperature phases , crystallization and sintering of both mullite and cristobalite. The investigations of two kaolinite samples of quite different crystallini ty demonstrates the role of the structural disorder of the mineral in the manifestation of these structural changes. The differences observe d between the behaviour of the two samples are reflected by different diffusivities of radon which can be related to different morphology ch anges taking place in kaolinite during heating. The results obtained d emonstrate the potential of ETA as a complementary method of conventio nal thermoanalysis and XRD methods.