Thermoluminescence of kaolinite

Abstract

Natural kaolinite (size < 5 ¿m) shows strong thermoluminescence (TL) which could be linked with water loss (~ 120°C peak) and dehydroxylation changes (~ 300°C peak). After 100 min of dehydration at room temperature, kaolinite displays microcracks, isothermal luminescence emissions and the starting point of a desiccation plateau. These phenomena were tested through 34 X ray diffractograms measuring the area increase of the (001) peak each 3 min. The DTA-TG analyses of natural kaolinite and the FTLR bands at 3696, 3668, 3652 and 3619 wave-number.cm-1 of preheated kaolinite show water loss, dehydrox ylation and above 450°C, metakaolinite formation. TL glow curves after ß irradiation of preheated kaolinite drop from 270 to 345°C, the maximum TL peak of kaolinite is around 300°C. These data fit well with the dehydration-related proton conductivity in kaolinite as follows: below 275°C the activation energy of kaolinite is 7-8 kcal.mol-1, at 300°C the kaolinite produces the largest photon emission, later, between 300-450°C, the activation energy is 18-20 kcal.mol-1.