Time and temperature dependence of carbon particle growth in various shock wave pyrolysis processes

Abstract

The results of various experiments on carbon nanoparticle formation during gas phase pyrolysis behind shock waves in the temperature range 1200 K ⩽ T f ⩽ 3500 K are analysed. In the wavelength range 0.22 μm ⩽ λ ⩽ 1.31 μm, the optical properties of particles and their current sizes, measured by laser-induced incandescence, are compared. For a correct knowledge of the actual temperature during particle formation, spectral emission–absorption measurements in the IR range were performed. It was found that the light extinction due to particle growth in different mixtures and at different temperatures can be described by a global rate law for optical density. The observed decrease in optical density at 633 nm with increasing temperature is not a result of the decrease in particle yield, as was assumed earlier, but is caused by the size dependent refractive index. Furthermore, the final particle size decrease with the temperature rise is most likely the deceleration of the coagulation rate of the primary clusters and correspondingly, the increase of the particle number density.