Sol-Gel Synthesis of Mullite Starting from Different Inorganic Precursors

Using silicotetraetilortosilicate (TEOS) mixed with aluminum tri-sec-butoxide (TSBAI) or aluminum cloaures mullite ceramics were created by the sol-gel method. The quantities used of each substance were those that led to obtain stoichiometric mullite (3Al2O3·2SiO2). The experimental methodology used for obtaining mullite consisted in: sol-gel synthesis of precursor materials, isothermal treatment of those materials, and characterization of resulting materials. In order to determine the advance of reactions during mullite formation, isothermal treatments between 300°C and 1600°C were performed, keeping the samples at each temperature during 4 h. From XRD results, it may be said that precursor powders originally amorphous start to crystallize in Al2O3 and SiO2 at 1200°C, and the mullite formation starts at 1200°C, with being completed at 1600°C. The use of TSBAI favors the formation of mullite crystals at lower temperature. From SEM observations a microstructure that presents primary mullite with randomly oriented grains of secondary mullite with acicular shapes and sizes that range between 1.25 and 1.50 μm long may be determined.