EFFECTS OF THE SCALE OF PRECURSOR MIXING ON DENSIFICATION BEHAVIORS AND PHASE-TRANSFORMATION KINETICS OF CORDIERITE GELS

Abstract

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 (similar to 50 nm). In the case of the monophasic cordierite gel, homogeneous molecular-scale mixing of precursors induces a direction formation of mu-cordierite without a preceding crystallization, and the densification stops at the onset of crystallization to mu-cordierite at 960 degrees C. On the other hand, the densification of triphasic cordierite gel was not affected by the crystallization of intermediate spinel phase at 700 degrees C. The triphasic gel continues to densify until amorphous silica matrix crystallizes to quartz at 1180 degrees 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.