Non-Isothermal Dehydration Kinetics of Diphasic Mullite Precursor Gel

Aluminosilicate gel precursor having mullite composition was synthesized from inorganic salts of aluminum and silicon by employing the sol-gel method. Chemical analysis, surface area and bulk density measurements were performed to characterize the dried gel. The course of the mullitization was examined by FT-IR analysis which confirmed the diphasic nature of the gel. SEM and XRD analysis were performed to study microstructure and phase development. ThermoGravimetric (TG) analysis of the dried gel was performed at multiple heating rates and from the results obtained; kinetics of thermal dehydration was studied by applying Friedman differential and Kissinger-Akahira-Sunose integral isoconversional procedures. It was observed that the total dehydration process of the gel was accomplished by two different stages and both the stages followed second-order rate kinetics. The first stage was assigned to the dehydration of silicon hydroxide gel whereas the second stage was associated with aluminum hydroxide gel dehydration.