Particle sizes of fumed silica

Fumed silica is a synthetic amorphous silicon dioxide produced by burning s ilicon tetrachloride in an oxygen-hydrogen flame. Surface areas range from 50 up to 400 m(2)/g. Using particle sizing techniques, fumed silica shows m icro-sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a fluffy solid with bulk densities down to 0.03 g/ cm(3), being invariant over the wide range of surface areas. Attempts to re late the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening efficiency in flu ids, mainly fail and remain ambiguous. The aim of this work was to investig ate the particle sizes and structures of fumed silica aggregates and agglom erates, using different particle dispersion and sizing techniques.