Application of coflow premixed flame for generating aggregate silica particles and its limitation

This paper reports the geometrical characteristics and the growth of aggregate silica particles generated in a premixed flame using thermophoretic sampling, a light scattering technique, and aggregate dynamics modeling only for a premixed flat flame condition. The area equivalent size and the morphology of thermophoretically collected silica aggregate particles were analyzed through images taken from a transmission electron microscope. The particle stream in flames was visualized through a planar light scattering technique. Light scattering intensity at 90° using an Ar-ion laser (wavelength, 514 nm) was monitored for various flame conditions. The results of aggregate dynamics modeling under a one-dimensional assumption indicated that the silica particles grew as the height above the burner increased. Aggregate particles produced at various equivalence ratios showed different levels of OH-species. The OH-related species increased as the equivalence ratio decreased, which implies that a high equivalence ratio is recommended to produce pure silica particles. In this study, the purest silica aggregate particles were produced at the equivalence ratio of 11.4, among others. Our study helps to determine which flame condition is best in terms of the quality and/or quantity of silica aggregate particles generated by a coflow burner.