Thermal evolution and crystallization kinetics of potassium-based geopolymer

In this paper crystallization kinetics of potassium-based geopolymer (Si/Al = 2.5, denoted as KG2.5) upon heating are investigated by differential thermal analysis (DTA) under non-isothermal conditions at various heating rates. From 35 to 700 °C KG2.5 shows a significant weight loss due to both evaporation of free water and condensation of hydroxyl groups. Crystallization of KG2.5 starts at a low temperature of ∼960 °C according to XRD and DTA analysis. KG2.5 also exhibits a low onset temperature of viscous sintering stage and on heating to 950 °C the sintering is completed. In the DTA graphs, the exothermic peaks which are caused by leucite crystallization shift to higher temperatures with increasing heating rate. The activation energy value of crystallization for leucite is found to be 455.9 kJ/mol and the corresponding Avarami constant is 3.89 indicating the three-dimensional crystal growth mechanism.