Formation kinetics and transition mechanism of CaO·SiO2 in low-calcium system during high-temperature sintering

The crystal structure, formation kinetics and micro-morphology of CaO·SiO 2 during high-temperature sintering process were studied in low-calcium system by XRD, FT-IR, Raman and SEM-EDS methods. When the molar ratio of CaCO 3 to SiO 2 is 1.0, β-2CaO·SiO 2 forms firstly during the heating process, and then CaO·SiO 2 is generated by the transformation reaction of pre-formed 2CaO·SiO 2 with SiO 2 . 3CaO·SiO 2 and 3CaO·2SiO 2 do not form either in the heating or sintering process. Rising the sintering temperature and prolonging the holding time promote the phase transition of 2CaO·SiO 2 to CaO·SiO 2 , resulting in the sintered products a small blue shift and broadening in Raman spectra. The content of CS can reach 97.4% when sintered at 1400 °C for 1 h. The formation kinetics of CaO·SiO 2 follows the second-order chemical reaction model, and the corresponding apparent activation energy and pre-exponential factor are 505.82 kJ/mol and 2.16×10 14 s −1 respectively.