Synthesis of nanostructured mullite from xerogel and aerogel obtained by the nonhydrolytic sol-gel method

Synthesis and nanostructure evolution of mullite (3Al(2)O(3).2SiO(2)) from xero- and aerogels, obtained by the non-hydrolytic sol-gel process are desc ribed. Mullite crystallization and gel nanostructure evolution after heat t reatment were studied by differential-thermal, x-ray diffraction, infrared and thermomicroscopic analysis as well as by scanning electron microscopy. Crystallization of mullite from both gels starts at 900 degrees C and furth er increase in temperature increases the size of crystallites formed from 3 2 to 100 nm and 12 to 20 nm in the case of xero- and aerogels, respectively . Accelerated sintering of aerogels in the temperature range 900 to 1000 de grees C is a consequence of the viscous flow of the amorphous SiO2 phase. ( C) 1999 Acta Metallurgica Inc.