Effects of precursors on silica particle generation in CVD synthesis for fused silica glass

Abstract

High purity fused silica glass can be synthesized by CVD process in which silica particles are generated by precursors reacted in H2/O2 flame and deposited on the substrate. Selection of precursors has significant influence on silica particle generation, and further affects particle transport and deposited glass quality. This paper aims to reveal the underlying mechanisms that make silica particles generation different when using the precursors of SiCl4 and OMCTS. Comparative investigations were conducted using the computational fluid dynamics method. When using OMCTS as the precursor, the main reactions of precursor in the H2/O2 flame are exothermic. The rapid heat release from the precursor near the burner exit can promote SiO2 generation from endothermic reactions at the center of the jet close to the inlet. When using SiCl4 as the precursor, the main reactions of SiCl4 in the H2/O2 flame are endothermic. In this case, the precursor will diffuse further to high temperature H2/O2 flame to make SiO2 generation reactions happen. Thus the generated SiO2 will be away from the burner exit. The production efficiency of SiO2 by OMCTS is almost 3 times of that by SiCl4. To achieve a stable and high deposition rate, an oxygen-enriched atmosphere is preferable for both precursors. More fuel is needed for the fused silica glass process using SiCl4 than OMCTS as the precursor.