Two-dimensional simulation of an oxy-acetylene torch diamond reactor with a detailed gas-phase and surface mechanism

A two-dimensional model is presented for the hydrodynamics and chemistry of an oxy-acetylene torch reactor for chemical vapor deposition of diamond, a nd it is validated against spectroscopy and growth rate data from the liter ature. The model combines the laminar equations for flow, heat, and mass tr ansfer with combustion and deposition chemistries, and includes multicompon ent diffusion and thermodiffusion. A two-step solution approach is used. In the first step, a lumped chemistry model is used to calculate the flame sh ape, temperatures and hydrodynamics. In the second step, a detailed, 27 spe cies / 119 elementary reactions gas phase chemistry model and a 41 species / 67 elementary reactions surface chemistry model are used to calculate rad icals and intermediates concentrations in the gas phase and at the surface, as well as growth rates. Important experimental trends are predicted corre ctly, but there are some discrepancies. The main problem lies in the use of the Miller-Melius hydrocarbon combustion mechanism for rich oxy-acetylene flames. [J. A. Miller and C. F. Melius, Combustion and Flame 91, 21 (1992)] . Despite this problem, some aspects of the diamond growth process are clar ified. It is demonstrated that gas-phase diffusion limitations play a minor role in the diamond growth process, which is determined by surface kinetic s. Except for atomic hydrogen, gas phase diffusion is also of minor importa nce for the transport of species in and behind the flame front. Finally, it is shown that penetration of nitrogen from the ambient air into the flame cannot explain the observed changes at the center of the diamond films as r eported in the literature. (C) 2000 American Institute of Physics. [S0021-8 979(00)06420-3].