Measurements of hydrogen content and visible specific absorption of soot to follow the structural transformation of carbon network

The relation between the optical properties, namely the mass absorption coefficient, and the H/C ratio of soot was studied as tool for following the structural transformation of solid carbon (soot) formed in premixed sooting ethylene flames. The aliphatic and aromatic hydrogen and the mass absorption coefficient of soot were quantified by FT-IR and UV-Visible spectroscopic analysis, respectively. The steep increase of the absorption coefficient and maximum soot formation rate was observed in correspondence of the aliphatic hydrogen loss. The higher reactivity of aliphatic hydrogen in forming radical active sites on soot particle surface was suggested to be responsible for the increase of soot concentration. The loss of aliphatic hydrogen and the corresponding steep increase of absorption coefficient testified the occurrence of thermal annealing and internal structural transformations in turn causing the termination of soot formation and growth.