Synthesis and Characterization of Sol-Gel-Derived Chemical Mullite

Mullite (3Al(2)O(3)center dot 2SiO(2)) precursor gel was synthesized using aluminum nitrate nonahydrate and liquid sodium silicate as starting materials based on the sol-gel route. The gel was characterized by means of chemical analysis, surface area and bulk density measurements. Fourier transformation infrared spectroscopic (FTIR) and differential thermal analysis (DTA) were performed to study the course of mullitization. The gel was calcined at 800 degrees C and compacted at 100 MPa pressure. The compacted masses were sintered at different elevated temperatures and subjected to SEM and XRD analysis for microstructure and phase development studies. FTIR studies confirmed the diphasic nature of the gel during its formation. Primary mullitization started at around 980 degrees C with an average activation energy of similar to 772 kJ/mol. Crystallization of mullite with a lower amount of Si02 was completed after sintering at 1600 degrees C.