Induction period for the formation of nanodispersed carbon particles during hydrocarbon pyrolysis behind a reflected shock front

Abstract

Experiments were performed to estimate the time of isothermal transformation of model hydrocarbons (ethylene, benzene, and naphthalene) to solid carbon nanoparticles. An optical procedure combined with a shock tube was used to experimentally study the duration of the initial reaction stages before the occurrence of emission with a continuous visible spectrum. This emission is caused by the new (condensed and not gaseous) phase of carbon atoms formed in hydrocarbon pyrolysis behind a reflected shock front. The measurements are based on recording the time of occurrence of emission at a wavelength λ = 750 nm. The durations of the induction periods are in the range 12–160 µsec and decrease with increasing temperature in the range 1920–2560 K for each hydrocarbon, and also with increasing number of carbon atoms in the hydrocarbon molecule. The apparent activation energies for the formation of nanodispersed carbon particles were estimated from the measured durations of the initial reaction stages: 204 kJ/mole for ethylene, 65 kJ/mole for benzene, and 44 kJ/mole for naphthalene.