Hydrothermal synthesis products of CaO metakaolin H2O system at 90 °C

Abstract

In order to fully utilize the low-grade kaolin resources, the hydrothermal synthesis products of CaO-Metakaolin-H2O system at 90 °C were studied. Starting from in-depth analysis of the hydration characteristics and mechanism of CaOSiO2- H2O systems and basing on calculation of its Gibbs free energy at different temperature, the stable hydration products at different temperature or n(Ca)/n(Si) are identified. Meanwhile, 363 K (90 °C) has been designated as the hydrothermal temperature. The relationship between the extent of hydration and reaction time of three n(Ca)/n(Si) varieties was studied by the coordination of six curves subsequently. The analysed conclusion showed that their best mimic curves were Jander equation. It was calculation through the equation that their KJ value are 49.06 × 10−4, 42.22 × 10−4 and 27.3 × 10−4 in each variety. According to the result of SEM, X-ray, the major hydration products of hydro-thermal synthesis were porous surface and semi-crystalline C-S-H (B), filament and network shape C-S-H (II), numerous cube and granule shaped C3ASnH6−2n encapsulated within C-S-H gel, a small quantity of C4AH13 and C2ASH8.