In situ study of aggregation of soot particles in an acetylene flame by small-angle x-ray scattering

The nucleation and growth of soot particles in an acetylene flame were investigated by synchrotron small-angle x-ray scattering. The scattered intensity spanning over a wide scattering vector (q) range, 10−3nm−1⩽q⩽0.5nm−1, was analyzed using the unified scattering function involving up to three structural levels corresponding to primary particles, aggregates, and agglomerates. The primary particles have a compact morphology with a terminal radius of gyration (Rg) of about 27nm and their growth dynamics is consistent with the nucleation and growth process. The evolution of aggregate Rg reveals a diffusion limited growth mechanism resulting in a fractal dimension (df)≈2 and Rg∼250nm. Although the production of soot dramatically increases with the flow rate, the aggregation dynamics, terminal Rg, and df remain nearly the same. The flow rate used in this study extended to the regime of aerogelation of soot but the aggregation dynamics is found to be similar to the nongelling case.