Multistep kinetics of the thermal dehydration/decomposition of metakaolin-based geopolymer paste

This study investigated the kinetics of the multistep thermal dehydration/decomposition of the metakaolin-based geopolymer paste. The component two reaction steps were characterized by the evolution of water vapor and the simultaneous evolution of water vapor and CO₂, respectively. In a stream of dry N₂, the kinetics of the first and second reaction steps were characterized by the apparent activation energy (E_a) values of 92 and 166 kJ mol⁻¹, respectively. Both reaction steps exhibited a diffusion-controlled rate behavior. In a stream of wet N₂, the mass loss curves systematically shifted to higher temperatures with an increase in the water vapor pressure (p(H₂O)). The first reaction step was significantly influenced by p(H₂O), and the apparent E_a increased to 175 kJ mol⁻¹ at p(H₂O) = 11.4 kPa. The second reaction step was less sensitive to the atmospheric water vapor, as characterized by its E_a of ∼165 kJ mol⁻¹, irrespective of the p(H₂O).