ABSTRACT
Nature of the noncrystalline mullite precursor phase prior to exhibition of the 980°C exotherm has been studied by various physicochemical methods. At the earlier studies, noncrystalline aluminosilicate precursor phase accumulated during progressive heating of mono phasic gel/precursor transforms to either alumina rich mullite or Al-Si spinel phase at the first exothermic peak temperature. In the case of monophasic gel SHIV or RH gel, the transformation likely proceeds as described earlier and is shortly reproduced as follows. After it's crystallization, an amorphous band is still observed as a residual phase. Moreover, a certain portion of the amorphous band still persists in the temperature range 1100°C–1200°C. So the observation of amorphous band beyond mullite and or Al-Si spinel formation may be due to the presence of newly formed noncrystalline silica rich alumina phase and residual noncrystalline aluminosilicate phase formed during dehydroxylation process of gel at earlier temperature range.
