The influence of the catalyst composition on the structure of silica aerogels

摘要

The structure of aerogels can be controlled by the conditions of their preparation and especially by the choice of catalyst. The structure of seven silica aerogels synthesized at different concentration of catalyst (NH_4OH) and NH_4F) was investigated by small-angle X-ray scattering (SAXS) method. From SAXS results it can be concluded that fluoride anions promote the formation of more ramified, self-similar, polymeric structure with mass fractal dimension D_mapproxapprox2.5, whereas hydroxyl anions give somewhat less ramified structure (D_mapproxapprox2.15) with narrower range of fractality.