Ba/Sn induced high temperature phase and microstructure evolution of silica aerogel via co-precursor sol-gel method

The confined high-temperature reaction and/or phase changes occurred in the nanopores of SiO2 aerogel modified by various oxides is intriguing but receiving less attention. Here we report the distinctive phase conversion from amorphous SiO2 to cristobalite at high temperature in SiO2 aerogel induced by Ba/Sn oxides. We prepare Ba-Sn-SiO2 hybrid aerogel via a co-precursor sol-gel method, and the effects of SiO2 content (40-100%), sintering temperature (100-1000 degrees C) on the crystallinity and microstructure are examined. Results show that the introduction of Ba/Sn and the sintering temperature exert significant influences on the crystallinity, microstructure and pore structure of the hybrid system. In special, the cristobalite SiO2 is formed at higher Ba-Sn content (>33.3%) and higher sintering temperature (>800 degrees C), corresponding with the sharply decrease of the pore volume and surface area. The formation mechanism of cristobalite is explored, and a BaSnSi3O9-induced SiO2 epitaxial nucleation lattice matching mechanism is proposed. The work may induce the interests on the high-temperature synthesis of aerogel-based hybrid materials possessing particular physical/chemical functions, thus paving the way to advanced structural or functional materials/devices.