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 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}. [ABSTRACT FROM AUTHOR]