EXPERIMENTAL AND NUMERICAL-STUDIES ON REFRACTORY PARTICLE FORMATION IN FLAMES - APPLICATION TO SILICA GROWTH

Recent interest in high temperature materials have focused attention on the processing requirements, as well as the fundamentals of submicron particle formation and growth. In this study, silica particle growth in flames was studied using in situ light scattering dissymmetry measurements for the measurement of particle size and number density. In addition, temperature profiles for the flames were obtained by using fine-wire thermocouples. The majority of the experiments conducted have used silane as the source of silicon; a limited number of experiments using organosilicon compounds have also been carried out. The results have shown that the silicon source concentration and the temperature are the two dominant variables controlling particle growth and morphology. The type of silicon-containing precursor was found to affect the mechanism of growth and presumably the morphology of the particles produced. Two particle growth models have been applied, which account for the consumption of the gas precursor, nucleation, and subsequent growth by surface condensation and coalescence. Comparison with experiment have shown good agreement. Finally, numerical simulations of the gas phase chemistry of silane have shown the presence of multicomponent nucleation under some conditions, evidence for which has been observed by laser attenuation measurements.