ABSTRACT
This chapter discusses the methods and techniques as used and reported by earlier authors for proper mullite identification and characterization and the resulting problems they faced. An additional minor quantity of Al-Si spinel phase duly transformed to mullite type phase during the occurrence of second exotherm at 1250 C. The result concurs with that of Okada and Otsuka as noted in case of transformation of SH gel. In the temperature range between first and second the formation of mullite showed two dimensional grain growth of crystal nucleus. Formation of mullite particularly in precursors SHII takes place rapidly at first exotherm by Path I. Another slow increment of mullite is noticed in SHII beyond 1200 C out of a small amount of spinel phase. The probable change in lattice constant with heating is due mainly to increase in crystallinity of mullite phase by gradual relief of strain present during its incipient formation stage than to changes in chemical composition.
