Two-step acid-base catalyzed silica xerogels with different amounts of additives, including TiO2 powder, silica xerogel powders and short glass fibers, were prepared through a sol-gel route and ambient pressure drying. The fractal dimensions of these additive silica xerogels were investigated by the means of small-angle X-ray scattering (SAXS). Specific surface area and the average chord length were calculated by the Debye method. The changes of the porous structure were compared between the pure silica xerogels and the impure ones. The results show that additive silica xerogels do not possess a surface fractal character. The mass fractal range of silica xerogels decreases and colloid particle size increases with an increase of additives. The adding of excessive silica xerogel powders results in agglomeration of particles which goes beyond the metrical limit of SAXS. The mass fractal dimension and fractal range decrease with the addition of additional short fibers. The shrinkage was restrained in the course of drying by adding short fibers.

Keywords: Silica xerogels; Additives; Fractal dimensions; SAXS.