ABSTRACT
The individual finding of a precursor with those of established thermal sequences given by various earlier authors in the conquest of five points as mentioned above are compared. Precursors synthesized bya large section ofmullite researchers show a varying ratio of mullite to Al-Si spinel phase at 980°C. Precursors synthesized using ammonia as precipitating agents generally crystallized Al-Si spinel phase with mullite and thus developed diphasicity as a character of gel. Deviation from normal gelation procedure of SH gels and polymeric gel are also observed in the literature. Accordingly, a lot of variations in their phase transformation are noted among groups of gels and a few of these are mentioned. Precursor character also changes with use of silicon hydroxide of large colloids or aged gels considering silica component as source or with large aluminum hydroxide colloidal particles during gelation either in aqueous method, in monophasic gel method or in SD or SP techniques.
