Effects of the scale of precursor mixing on densification behaviors and phase-transformation kinetics of cordierite gels

Effects of the scale of precursor mixing on densification behaviors and phase-transformation kinetics of multicomponent aluminosilicate gels were examined using cordierite gels prepared by two different processing routes: a monophasic (single phase) gel having molecular homogeneity, and a triphasic gel in which constitutive precursor phases are uniformly mixed in a nanometer scale (∼50 nm). In the case of the monophasic cordierite gel, homogeneous molecular-scale mixing of precursors induces a direction formation of μ-cordierite without a preceding crystallization, and the densification stops at the onset of crystallization to μ-cordierite at 960 °C. On the other hand, the densification of triphasic cordierite gel was not affected by the crystallization of intermediate spinel phase at 700 °C. The triphasic gel continues to densify until amorphous silica matrix crystallizes to quartz at 1180 °C. The enhanced densification observed in the triphasic gel was attributed to the retarded crystallization of amorphous silica component caused by the increase in diffusion distances.