SMALL-ANGLE SYNCHROTRON X-RAY SCATTERING TO INVESTIGATE THE PRIMARY PARTICLES OF SOOT GROWING AS SUBPARTICLES CLUSTERS IN A DIFFUSION FLAME

Flame generated soot nanoparticles, sized 10-50 nm and called primary particles, are widely recognized in the literature (Samson et al, 1987; Megaridis and Dobbins, 1990; Sorensen and Feke, 1996; di Stasio, 2001; Sorensen, 2001) to undergo agglomeration process in flame and to form at longer residence times chain-like or fractal type aggregated structures. Some recent experimental evidences (di Stasio, 2001; Hessler, et al, 2001) has put in some doubt the standard combustion scheme, which retained the combustion as the developing of the separate phases of nucleation, surface growth and agglomeration. In particular, evidence has been reported both from ex-situ TEM and in-situ X-ray scattering measurements, that the primary particles of the soot fractals agglomerates are, in turn, formed through a coagulation process of smaller nanoparticles (size below 8 nm) called sub-primary particles. The laser experiments at visible wavelengths are not adapted to allow the coming into existence of so fine structures. The aim of this communication is to demonstrate the feasibility of a synchrotron X-ray scattering technique to probe in-situ the early stage of growth of primary particles born in a diffusion flame.