Mechanisms of the Formation of Silica Particles from Precursors with Different Volatilities by Flame Spray Pyrolysis

The flame spray pyrolysis (FSP) synthesis of silica particles from two different precursors, tetraethylorthosilicate (TEOS) and silicic acid which have significantly different volatilities, was investigated. The size and morphology of the particles produced using various concentrations of precursors and flame temperatures were examined. Significantly different volatilities of the precursors affected the particle formation mechanism. Two different particle formation mechanisms, vapor phase reaction (VPR) and intradroplet reaction (IDR), are proposed based on the relative time scale for the evaporation of sprayed precursor droplets and for particle formation at the same process conditions. VPR resulted in silica agglomerates with small primary particles of around 10 nm sizes. IDR resulted in isolated and spherical silica particles with the sizes of around 650 nm from silicic acid.