Phase Evolution and Formation Mechanism in Acicular Mullite Prepared from Kaolinite via Wet Chemistry Method

Mullite was synthesized by firing precursors prepared from kaolinite via a wet chemistry method at various temperatures. The acicular mullite grains were formed in samples with addition of AlF3 by this process. The phase evolution and morphology of the fired samples were investigated. For the samples without AlF3, the mullitization began to occur at 1300 and almost completed at 1550 , the grains formed were normal-shaped. For the samples with AlF3, acicular mullite was formed, and mullitization began to occur at 1100 and completed at 1250 . The growth of the acicular mullite was associated with a liquid phase. The formed acicular mullite was alumina-rich and had a composition of about 73.4 wt% Al2O3 and 26.6 wt% SiO2 (Al2O3/SiO2=1.65, molar ratio).