Comparative study on thermal decomposition of stromatolite and micrite using the technique of TG and DSC

Previous studies on the characteristics of stromatolite and micrite have carried out a lot of work, but there was less research in thermochemical characteristics. Here, X-ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy were used to determine the mineral composition and organic components of stromatolite and micrite. In addition, TG and DTG were used to analyze their thermochemical characteristics and the non-isothermal decomposition of stromatolite and micrite at multi-heating rates of 5, 10, 20 and 30 K min(-1) in nitrogen atmospheres. Moreover, kinetic model function, kinetic parameters of apparent activation energy (E), and pre-exponential factor (A) were calculated by Popescu, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose. The results of XRD showed that the full width at half maximum (FWHM) of 104 crystal plane of calcite was different although the mineral composition of stromatolite and micrite was calcite. The FWHM value of stromatolites was less than that of micrite, which indicated that the crystallinity of stromatolite was higher. Furthermore, the results of TG analysis showed that the final mass loss of stromatolite was less than that of micrite. Moreover, DTG results showed that the maximum temperature point of mass loss of stromatolite was higher than that of micrite. The average value of E of stromatolite calculated by three different methods was about 252.2 kJ mol(-1) but was about 208.2 kJ mol(-1) for micrite. Hence, the thermal analysis results showed that the crystallinity of stromatolite were relatively higher. These results provided an important reference for analyzing the thermochemical characteristics of different Lingbi stones, especially stromatolite as a typical microbialite.