Formation and optimization of deposition surface shape during fused silica glass synthesis by chemical vapor deposition

Abstract

This paper investigates the effects of deposition surface shape on temperature distribution of fused silica glass by SiCl4 chemical vapor deposition and performs the optimization of deposition surface shape to obtain the glass with a small temperature gradient. The computational model is first developed to describe the complicated physical and chemical phenomenon in the system. Numerical simulations are then performed to evaluate the effects of SiCl4 injection position on flame characteristics and SiO2 deposition rate. It is found that the SiO2 deposition rates with the unimodal, uniform, and bimodal distributions are obtained when SiCl4 is injected from the central, secondary layer and fourth layer nozzles, respectively. The deposition surface shape is mainly determined by the gas temperature gradient and particle number density near the deposition surface. Thereafter, the temperature distributions in synthetic silica glass are presented for the cases with convex, flat, and concave deposition surface shapes. Large temperature gradients exist at the side of glass if the convex and concave surfaces are formed, although a high temperature uniformity is obtained in the center of glass for the convex deposition surface. The optimal surface shape that has a very small temperature gradient in glass is obtained by the optimization of deposition surface depth.