A main problem for the applicability of silica aerogels as thermal ins
ulation materials at temperatures above 600 degrees C is viscous sinte
ring, which may lead to a significant density increase with time. Modi
fication of silica aerogels via integration of alumina yields aerogels
with increased stability against sintering. The onset of sintering of
alumina silica aerogels occurs at about 900 degrees C compared with a
bout 600 degrees C for pure silica aerogels. The sintering process was
investigated as a function of alumina content, density and particle s
ize. Alumina-modified silica aerogels were studied by dilatometry, vis
cosimetry and thermogravimetry during non-isothermal and isothermal he
at treatment.