SOLUTION SOL-GEL SYNTHESIS AND PHASE EVOLUTION STUDIES OF CORDIERITE XEROGELS, AEROGELS AND THIN-FILMS

A sol-gel process employing silicon alkoxide, chelated aluminum sec-butoxide, and magnesium acetate as starting precursors, was used to synthesize cordierite xerogels, aerogels and thin films. The xerogels were prepared using normal drying conditions, while supercritical drying conditions were employed to synthesize the aerogels. Thin films were grown by spin coating polymerized sols on (100) silicon substrates. The aerogel and xerogel powders as well as thin films were studied for phase evolution and phase stability using X-ray diffraction. All three forms indicated the formation of the mu-cordierite phase at 900-degrees-C. In addition, the aerogels and thin films showed evolution of other phases. The initiation of the mu --> alpha cordierite transformation was observed in the temperature range 1000-1100-degrees-C for both the xerogels and thin films, while mu-cordierite obtained from the aerogels showed a much higher stability and transformed to alpha-cordierite only at 1200-degrees-C.