PerspectiveCombustion Chemistry

A radical approach to soot formation

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Science  07 Sep 2018:
Vol. 361, Issue 6406, pp. 978-979
DOI: 10.1126/science.aau5941

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Humans have used the high-temperature synthesis of carbon particles as a source of pigments since prehistoric times (1), and today, “carbon blacks” are used in tires, inks, coatings, plastics, and electrical applications. For most substances, solid particles become gases when heated, but solid soot forms from gaseous molecules at high temperature through a mechanism that is still not understood. The high-temperature synthesis of carbon particles (see the figure) occurs under oxygen-starved conditions where simple hydrocarbons can grow into larger molecules, especially polycyclic aromatic hydrocarbons (PAHs), in the gas phase. These large molecules cluster into carbon nanoparticles, a process often referred to as soot inception. The carbon nanoparticles then grow and aggregate to form larger, fractal-like structures. On page 997 of this issue, Johansson et al. (2) propose a new mechanism based on chain reactions of resonance-stabilized radical (RSR) species to explain this transition from gas-phase molecules to nanoparticles.