Kinetics and mechanism of formation of 20CaO·13Al 2 O 3 ·3MgO·3SiO 2

Abstract

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.

Keywords

Q phase Kinetics Solid state reaction Diffusion

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