Particle aggregation in alumina aerogels

Alumina aerogels were synthesized by low temperature CO2 supercritical drying (SCD) of gels via the Yoldas process. The aerogels have a surface area of similar to 425 m(2)/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 D-m = 2.6-2.8. During the SCD the morphology collapses to form a structure with surface fractal dimension D-s = 2.6-2.9.