Kinetics and mechanism of formation of 20CaO·13Al2O3·3MgO·3SiO2

The formation kinetics of 20CaO·13Al2O3·3MgO·3SiO2 (Q phase) have been studied with quantitative X-ray diffraction method under the reaction conditions of temperature range of 1300–1375°C and 6 h temperature holding time. The results indicated that 12CaO·7Al2O3 (C12A7) and CaO·Al 2O3 (CA) existed as intermediate phases and disappeared until the formation of Q phase was nearly completed. The formation temperature of Q phase is ∼1300°C, and its reaction equation is C2AS(C2S) + CA(CA2, C12A7) + f-MgO → Q phase. The solid–solid reaction kinetic model was used to fit the kinetic mechanism. It can be described fairly well by Ginstling–Brounstein equation. The apparent activation energy and preexponential factor for the reaction among CaCO3, Al2O3, MgO and SiO2 were respectively determined as 380 ± 10 kJ mol− 1 and 4·69 × 109 h− 1.