THE STRUCTURE OF ACETYLENE FLAMES FOR DIAMOND SYNTHESIS

An acetylene flame was photographed with an SIT camera through optical filters, and the signals were Abel transformed to obtain two-dimensional emission-intensity profiles. It was found that the intensive emissions of CH* and C2* are localized at the feather boundary, while the OH* emission is localized at the intermediate zone. Thc structure of the acetylene flame was made clear: it consists of a carbon-radical-rich feather and an oxygen-radical-rich intermediate zone. The carbon-radical concentrations are approximately in equilibrium near the burner exit while they decrease almost linearly via interdiffusion and reactions with the oxygen-radicals in the intermediate zone. Numerical simulations including detailed gaseous and surface reactions reproduced well previous preliminary calculations showing that CH4 is rapidly produced in the boundary layer near the substrate followed by an increase in CH3. This result satisfactorily explains the measured dependence of growth rate on the substrate temperature and C2H2/O2 ratio.