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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. [ABSTRACT FROM AUTHOR]

Abstract Large-size and high-purity fused silica glass fabricated by chemical vapor deposition (CVD) has been widely applied to many advanced optical systems. The deposition process is critical during fused silica glass synthesis. In this study, SiO 2 deposition at the substrate is modelled and analyzed. First, numerical simulations are performed with the computational fluid dynamics method to predict the flame feature. The gas temperature and velocity agree well with the experimental data. Then, the predicted distributions of gas temperature and concentrations are used as the input parameters to a two-dimensional soot dynamic model. The particle characteristics and particle deposition at the substrate are analyzed. It is found that the particle number density first increases and then decreases in the flame along the axial and radial directions. The predicted mean diameter of the particle is smaller than 50 nm near the substrate surface. The mechanism for SiO 2 deposition is different along the substrate surface. In the central region of substrate, the particle deposition is dominant, while in the exterior region the surface chemical deposition is more important. [ABSTRACT FROM AUTHOR]

With the development of modern optical systems towards large scale, the fused silica glass with a large size is receiving increasing attention. In this paper, multi-burner chemical vapor deposition technique was proposed to synthesize the large-sized fused silica glass, and an integrated computational model was used to describe the fluid flow, combustion and heat transfer in the furnace. The effects of various process parameters on the distributions of temperature and species were investigated. Based on the evaluation of temperature and key species concentrations on deposition surface, the size and quality of the synthesized fused silica glass were indirectly estimated. Results showed that reducing the deposition surface height and increasing the number of burners could improve the temperature and species concentrations on the deposition surface, while an increase in the number of furnace outlets led to their decreases. The use of two burners would lead to the formation of discontinuous glass regions at the current conditions and a circular glass structure was generated when employing three burners and deposition surface height of 0.5 m, based on the proposed temperature criterion. The combined process parameters of four burners, deposition surface height of 0.5 m, H 2 /O 2 equivalence ratio of 1.00 and two furnace outlets are be of advantage to synthesize the large-sized and high-quality fused silica glass at current sizes and structures of the furnace and burner. [ABSTRACT FROM AUTHOR]