SiO2 soot preform sintering process for the synthesis of large-size and high-purity silica glass

Abstract

The indirect chemical vapor deposition (CVD) method is a promising method to synthesize high-purity silica glass. As a critical procedure of this method, the sintering process is rather complex due to the interactive physical phenomena, and an in-depth understanding is therefore required. In this paper, a comprehensive multiphase porous medium model is developed by introducing the shrinkage mechanism, which agrees well with the experimental results. With this model, the dynamic characteristics during the sintering process, including temperature distribution, volumetric deformation, hydroxyl content evolution, and internal stress development, are well predicted. A parametric sensitivity analysis is conducted then, which shows that the average porosity and hydroxyl concentration are mainly affected by the average particle radius, while the maximum effective stress is sensitive to both Young's modulus and the average particle radius. Finally, the effects of key operating parameters are explored, and it is found that a lower working pressure, an appropriate sintering temperature such as 1450 °C, or a proper initial porosity such as 80.0%, is more desirable for a sintered product with high optical performance. This study can deepen the understanding of the SiO2 soot preform sintering process, and provide a good basis for further optimization.