气体流量对熔石英玻璃的影响

Effects of Gas Flow Rates on Fused Silica Glass

大尺寸熔石英玻璃的折射率均匀性对其光学特性有重要影响,本文对利用SiCl_4水解合成熔石英玻璃的过程开展数值模拟研究,揭示H_2和O_2当量比以及载料气与SiCl_4质量比对温度分布和组分浓度分布的影响,及其对熔石英玻璃折射率均匀性潜在的影响.研究结果表明,在径向方向上,火焰温度分布呈现"高-低-高"的M型分布规律;增大H_2/O_2当量比,会使轴向火焰预热区变短,当量比为1.0时,会产生一个比较长的火焰射流长度及宽的径向高温区,但是羟基浓度变化比较大,导致熔石英玻璃折射率不均匀性增加;采用小的当量比对提高玻璃折射率均匀性有一定的作用,因为在小的当量比下玻璃体沉积面上的温度梯度以及羟基浓度梯度较小,但是同时会降低火焰整体温度以及SiO_2生成量;另外,增加载料气对SiCl_4的质量比会降低玻璃体沉积面的温度变化,有利于改善折射率均匀性,但是与此同时,玻璃体沉积面上羟基浓度梯度增加了,对熔石英玻璃的折射率均匀性会产生不良影响.

The refractive index homogeneity of large-sized fused silica glass has great impact on its optical character- istics. In this paper, a numerical study on synthesis of fused silica glass by SiCl4 hydrolysis deposition is per- formed. The effects of the equivalence ratio of H2 to O2 and the mass ratio of carrier gas to SiCl4 on temperature pro- file and species concentration distributions are investigated, together with their potential impact on the homogeneity of refractive index of large-sized fused silica glass. It is found that the temperature profile in radial direction exhibits a high-low-high M-shape profile, and the increase of equivalence ratio of H2 to O2 results in a shorter axial preheating region. A long flame length and a broad high-temperature region can be obtained when the equivalence ratio is 1.0, but the residue of OH concentration and its gradient increase on the deposition surface of fused silica glass ingot, which will lead to the high inhomogeneity in refractive index. Small equivalence ratio is beneficial to refractive index homogeneity due to its small temperature gradient and OH concentration gradient, but the overall flame temperature and silica production are reduced. Additionally, increasing the mass ratio of cartier gas OR to SICl4 will reduce the temperature gradient and silica production, and concurrently increase the OH concentration gradient. Its effects on the refractive index homogeneity~ need to be considered comprehensively.