The kinetics and mechanism of thermal decomposition of SrCO3 polymorphs

Abstract The α → β transformation between orthorhombic ( α ) and hexagonal ( β ) polymorphs of strontium carbonate has significant effect on the behavior of SrCO 3 during thermal treatment. The kinetics, mechanism and thermodynamics of activated complex in the process of thermal decomposition were investigated by non-isothermal thermogravimetric analysis (TGA) using mechanism-free (Kissinger equation) as well as kinetic function fitting methods. Both techniques as well as the calculation of theoretical activation energy (third law method) show that the transformation of α -SrCO 3 to β -SrCO 3 reduces the activation energy and changes the mechanism of the process. While thermal decomposition of rhombohedral SrCO 3 is limited by the rate of process to the reaction interface ( R 3 : g ( α )=1−(1– α ) 1/3 ), the process limited by the rate of chemical reaction of 1/3 order ( F 1/3 : 1−(1– α ) 2/3 ) was determined for the hexagonal polymorph. The samples before and after thermal treatment were investigated by infrared spectroscopy, scanning electron microscopy and X-ray diffraction analysis.