Formation of mullite phase in diphasic gels consisting of TEOS and boehmite with and without dehydroxylation

Abstract Mullite (3Al 2 O 3 2SiO 2 ) samples have been prepared from mixture of TEOS and boehmite, with and without dehydroxylation at 400 °C. The precursor samples during the process of phase formation were characterized with respect to TGA, DTA, TMA, and X-ray diffraction at various temperatures. The result shows that by using a partially dehydroxylated boehmite, an enhanced transitional alumina phase is found at a lower temperature (~1000 °C) along with traces of α-Al 2 O 3 . With an increase in soaking time, the intensity of α-alumina is often found to increase. The formation of mullite takes place at 1225 °C and the α-Al 2 O 3 formed at a lower temperature remains unaffected even at 1500 °C. On the other hand, in the samples prepared from boehmite and TEOS, the transitional alumina phase is observed only at 1225 °C and it transforms to phase pure orthorhombic mullite at 1250 °C. Thus while the partially dehydroxylated boehmite appears to be more reactive to transform to transitional alumina phase at lower temperature, the mullite formation temperature does not occur below 1225 °C. The results of investigation are presented and discussed.