Morphological Description of Flame-Generated Materials

Abstract

The soot formed in a coannular ethene diffusion flame was extracted by a thermophoretic sampling technique for examination by transmission electron microscopy. A detailed analysis of the particle statistics of the samples is presented. Primary particle diameters range from 10 to 40 nm and their spatial variation within the flame affords quantitative information on the specific soot surface growth and oxidation rates. The moment ratio of the aggregate volume-equivalent diameters (D₆₃D₃₀,) is found to be close to the values predicted for the self-preserving size distribution in either the continuum or free molecular limit. The fractal dimensions (1 62 and 1.74) for Iwo samples examined are in the range reported in other combustion related experiments as well as in computational simulations of particle growth when cluster-cluster aggregation is an important growth mechanism The primary particle diameters that have been reported by various investigators in a wide variety of flame environments are reviewed. It is concluded that, while aggregate size may vary over many orders of magnitude, the values of both fractal dimensions and primary sizes of flame-gcneraled carbonaceous soot and silica fume are narrowly confined.