The application of DTA and TG methods to investigate the non-crystalline hydration products of CaAl_2O_4 and Ca_7ZrAl _6O_(18) compounds

摘要

The hydration products and thermal decomposition mechanism of hydrated CaAl_2O_4 and Ca_7ZrAl_6O_(18) compounds were investigated by X-ray diffraction, SEM/EDS and thermal analysis. The processes of crystal hydrate nucleation and precipitation were preceded by the evolution of the X-ray amorphous phase during the first 24 h of hydration. DTA-TGA-EGA techniques allowed the study of the detailed decomposition and identification of intermediate and stable to be performed. The differential thermal analysis (DTA) curves of hydrated CaAl_2O_4 and Ca_7ZrAl_6O_(18) compounds show five similar endothermic peaks due to crystal water desorption. According to the quantitative TGA-EGA analyses performed on hydrated CaAl_2O_4 and Ca_7ZrAl_6O_(18) compounds, it was found that C _2AH_8, C_3AH_6 and Al(OH)_3 phases are the main hydration products of CaAl_2O_4. Under the same laboratory conditions, the hydration of Ca_7ZrAl _6O_(18) proceeds with the formation of mainly CAH10 and AH_3-gel phases. We provide the original illustrations of the hydrate crystals formation via amorphous phases.