Crystallization behavior and sintering of cordierite synthesized by an aqueous sol-gel route

The purpose of the research was to investigate crystallization behavior and sintering of cordierite synthesized by a low-price aqueous sol gel route starting from silicic acid and magnesium and aluminum salts. Viscous sintering of the gel occurred in the temperature range of 800-850 degrees C, followed by mu-cordierite crystallization at about 900 degrees C, which proves the homogeneity of the gel. Decreasing of mu-cordierite crystallinity in a wide temperature range prior to commencing of alpha-cordierite crystallization at about 1200 degrees C indicates reconstructive type of mu- -> alpha-cordierite transformation. The transformation was fully completed at 1350 degrees C. The value of the Avrami parameter indicates that mu-cordierite crystallization was controlled by surface or interface nucleation, which implies that viscous sintering occurred in the primary gel particles, which leads to shrinkage, and thereafter nucleation occurred on the surface or interface of the particles. The overall activation energy of mu-cordierite crystallization was 382.0 kJ/mol. The sinterability of the powder obtained by calcination at 1300 degrees C, where well-crystallized alpha-cordierite was formed, was better than that of the powder obtained by calcination at 850 degrees C, where the most intensive shrinkage occurred before the onset of crystallization of mu-cordierite. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.