Thermal decomposition kinetics of Fe-rich tourmaline

Abstract

The thermal behaviour of different types of tourmaline with varying Fe content has been reported in the literature, which makes comparison of analytical results difficult. The objective of this study was to throw light on the thermal behaviour and to carry out kinetics analysis for Fe-rich tourmaline (schorl). X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) were applied to characterize the thermal behaviour. The Friedman, Flynn-Wall-Ozawa, modified Coats-Redfern and Kissinger integral approaches were carried out to determine the decomposition mechanism. The deprotonation reaction occurred at similar to 700 degrees C with the formation of oxy-tourmaline. Subsequently, oxy-tourmaline decomposition resulted in the formation of hematite, mullite and aluminium boron oxide at similar to 890 degrees C. Good linearity was observed using the Friedman, Flynn-Wall-Ozawa, modified Coats-Redfern and Kissinger integral approaches. The activation energy determined here was in the range 350-530 kJ mol(-1), which offered a simplified approach in understanding the thermal decomposition properties of Fe-rich tourmaline.