Alumina aerogels were synthesized by low temperature CO2 supercritical drying (SCD) of gels via the Yoldas process. The aerogels have a surface area of ˜425 m2/gr, similar to that obtained under high pressure/temperature SCD. The surface area and the cluster size of the aerogels are strongly influenced by the amount of acid during gelation. Gels and aerogels were studied by small angle x-rays scattering (SAXS), and the data were analyzed using the Fisher–Burford equation. The SAXS results along with TEM observations support the existence of a hierarchical aggregation at the gelation stage, having a mass fractal dimension of Dm = 2.6−2.8. During the SCD the morphology collapses to form a structure with surface fractal dimension Ds = 2.6−2.9.
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