The morphology of macroscopic soot

The morphology of soot collected from a laminar acetylene/air diffusion flame was studied. Collection methods included both thermophoretic and impaction sampling from both the luminous and nonluminous portions of the flow. The soot was viewed with both electron and optical microscopy. Cluster sizes ranged over four orders of magnitude from 50 nm to 400 mu m to include some clusters visible to the naked eye. A new method of micrograph analysis, necessary when the clusters were large, was developed to account for the unresolved primary particles. Over this entire size range, the same fractal morphology was found with a fractal dimension of D=1.8 and, within a rather large uncertainty, the same prefactor k(0)=1.7. Thus, the fractal morphology of soot remains constant from clusters of about 10 primary particles per aggregate to macroscopic clusters of over 10(8) primary particles.