Detailed OMCTS/H2/O2 chemical kinetics mechanism and its application in the fused silica glass synthesis

Abstract

The application of OMCTS/H2/O2 combustion process for the fused silica glass synthesis can prevent the halide emission compared to the conventional SiCl4/H2/O2 system. Detailed chemical kinetics of OMCTS/H2/O2 is critical for the prediction of flame characteristics, vapor nucleation, particle growth and deposition in the synthesis process. In this work, a detailed OMCTS/H2/O2 mechanism consisting of 55 species and 239 elementary reactions is formulated, which accounts for the oxidation, pyrolysis and hydrolysis of OMCTS, the combustion processes of H2/O2 and low hydrocarbon intermediate species. The dominant reaction pathways at representative thermo-chemical conditions for the fused silica glass synthesis are further analyzed through the directed relation graph method and a reduced mechanism of 24 species and 39 reactions is developed. The fused silica glass synthesis processes with OMCTS/H2/O2 and SiCl4/H2/O2 are then simulated respectively with the proposed mechanisms to reveal the differences in the flame, radicals and SiO2 formation characteristics. It is shown that although the two systems yield similar flame characteristics such as temperature and OH distributions, the SiO2 formation characteristics is different. The OMCTS/H2/O2 system has significant larger SiO2 concentration and a wider spread of SiO2 near the silica glass ingot and consequently a higher SiO2 formation rate. It is also shown that one new peak appears in the SiO distribution between the nozzle and SiO2 peak because the OMCTS pyrolysis process is important and it yields a larger amount of SiO. The effects of hydrogen inflow mass flow rate on the flame and SiO2 formation characteristics in the OMCTS/H2/O2 system are also analyzed.