A model of diamond growth in low pressure premixed flames

Abstract

Recognizing the potential importance of diamond thin film growth from combustion environments, a computational investigation of diamond synthesis in low pressure premixed flames has been conducted. The model employed solves the two-dimensional continuity, momentum, global energy, and species conservation equations in stagnation point flow geometry, and accounts for gas phase and surface reaction kinetics. The heterogeneous mechanism employed to describe diamond growth assumes that the methyl radical is the primary growth precursor. The gas phase mechanism includes elementary reaction pathways which generate methyl radicals from acetylene and in addition, includes a mechanism for cyclization (the formation of benzene) via acetylene and ethylene precursors. In this way, the pathway towards soot formation, which is believed to be a consequence of the formation of fused polycyclic aromatics, is shown to be a possible explanation for an eventual decrease in diamond growth rates at increasing fuel to oxygen flow ratios. A competition between oxidative pyrolysis of post flame hydrocarbons and cyclization establishes a criterion for optimum growth conditions.