Sintering behavior of SiO2 aerogel composites reinforced by mullite fibers via in-situ rapid heating TEM observations

The direct in situ TEM imaging method is adopted to investigate the sintering behavior of SiO2 aerogels during the rapid heating process. The structural evolution of SiO2 aerogels and composites at different times during the heat treatment process are further investigated via SEM, FT-IR, BET and XRD. The results indicate that the shrinkage of the SiO2 aerogels and composites primarily occurs during the initial stage of the heating process (within 20 min) with the shrinkage primarily linked to the fusion of small aerogel particles at high temperatures. The aerogel structure then stabilizes with no further shrinkage observed as the heating process continues. The heat treatment process only promotes the space rearrangement and fusion of small aerogel particles with no observed changes to the amorphous structure of the aerogels, and the small-sized particles fusion was the main causes for the structural evolution of SiO2 aerogels and composites under rapid heating condition.