Simulation of CO2 laser pyrolysis during preparation of SiC nanopowders

Abstract

Ultrafine SiC powders of highly controlled properties are produced in a CO2 laser flame with acetylene/ethylene and silane as gas phase precursors. In the present work, the basic theoretical concepts of the vibrational excitation of the reactant polyatomic molecules by IR-radiation of CO2 laser-induced pyrolysis are presented. A key parameter for multi-photon excitation and dissociation processes is the mean number of photons absorbed per molecule. A detailed analysis of the average number of absorbed photons during infrared multi-photon absorption process is given. In polyatomic molecules the density of vibrational states grows rapidly with the energy due to the permutations and combinations of vibrational modes increases rapidly with the available energy. An important parameter for a quantitative description of the vibrational quasi-continuum that is the density of vibrational states is calculated. The transitions between the different vibrational states are described in detail in terms of simple kinetic or rate equations.