ABSTRACT
This chapter discusses the experimental data as presented below show that spinel formed in both two cases of mullite gels is Al-Si spinel and its composition is analogous to composition of o-mullite which transforms directly to mullite. Therefore, it is concluded that monophasic gels, SH gel, Polymeric gel, Type I gel also transformed to mullite via an intermediate noncrystalline aluminosilicate precursor phase during 980 C exotherm. This may be a case of polymorphic transformation of Al-Si spinel to mullite as shown in the present study. The elaborative investigation showed variations in the intensity of Al-Si spinel phase formed out of precursors synthesized by either of the methods. Besides the crystallization of weakly crystalline phases either t-mullite or spinel or a mixture of t-mullite and spinel phase as mentioned above during 980°C exotherm of the monophasic precursors, a residual quantity of noncrystalline aluminosilicate phase is also remaining in association with those crystalline phases.
