Phase Evolution Sequences of Mullite Precursors Synthesized by Different Methods Based on Components Used and Processing Variables

A monophasic gel was first synthesized by Insley and Ewell and then by Ossaka, who coprecipitated KAl(SO₄₂) and sodium silicate hexaethylenetetraamine. Although synthesized at acidic pH, some monophasic gels in exceptional cases transform to mullite in a different way. Besides, the importance of pH and its role are highlighted as follows: The figures showed the crystallization of components of diphasic gels to cristobalite and corundum. The effect of the precursor's pH on the phase formation characteristics of diphasic gels showed a variation in the development of the mullite phase as follows: A sharp reactivity in G-101 and in the gel marked VI is observed to develop mullite among others. The tailored the phase transformation behavior of diphasic gels by varying the particle size of the silica particles while keeping a fixed source of the boehmite component. The chapter discusses the aqueous sol-gel method, monophasic SH gel method, polymeric gel method, diphasic gelation method, and SD and SP methods.