MULLITE FORMATION FROM GELS DERIVED FROM TETRAETHOXYSILANE OR TETRAMETHOXYSILANE WITH ALUMINUM SEC-BUTOXIDE

Two gels corresponding to the oxide composition, 3Al(2)O(3) . 2SiO(2) were prepared using different alkoxide precursors: aluminium sec-butox ide (ASB) mixed with either tetraethoxysilane (TEOS) or tetramethoxysi lane (TMOS). Mullite formation in the gels was compared using X-ray di ffraction after heat treatment for 1 h at a series of temperatures. Th e crystallisation behaviour in the gels was significantly different. A fter 1 h heat treatment mullite was found at 700 degrees C but not at 600 degrees C for the gel derived from TMOS, and was observed at 1000 degrees C but not at 900 degrees C for the gel derived from TEOS. This marked variation between the gels was attributed to the different hyd rolysis and polymerisation rates of the TMOS and TEOS, resulting in a difference in the homogeneity of the two gels on a molecular scale. (C ) 1997 Elsevier Science B.V.