FRACTAL ANALYSIS OF FLAME-SYNTHESIZED NANOSTRUCTURED SILICA AND TITANIA POWDERS USING SMALL-ANGLE X-RAY-SCATTERING

The morphology of flame-generated silica and titania aggregates is cha racterized by small-angle X-ray scattering(SAXS). Nearly all these pow ders display mass-fractal morphologies, which are composed of ramified aggregates of nanoscale primary particles. Primary particle size, agg regate size, fractal dimension, and specific surface area are obtained from this analysis. The mass-fractal dimension varies from 2.5 to 1.6 for flame generated silica and titania aggregates in single and doubl e diffusion flame reactors. However, titania powders made in a single diffusion flame reactor appear as nonaggregates and nonfractals. Silic a powders synthesized with an imposed electric field in a laminar, pre mixed flame reactor are mass fractals with narrowly confined fractal d imensions from 1.5 to 1.9 regardless of aggregate size.