| 摘要 |
PURPOSE:To obtain a uniform synthetic silica glass free from both bubbles and striae with high high-temperature viscosity by purity enhancement by hydrogen chloride gas and melting in a vacuum, at each specified temperature, of silica from wet reaction between an alkali silicate and acid to effect vitrification. CONSTITUTION:Silica >=1000Angstrom in mean pore size produced by reaction between an alkali silicate and acid is subjected to purity enhancement at 1000-1400 deg.C using hydrogen chloride gas. Thence the resultant silica is melted in a vacuum at 1700-2100 deg.C to effect vitrification, thus obtaining the objective silica glass. In said purity enhancement process, treatment with hydrogen chloride gas converts impurities such as Na, K and Al into NaCl, KCl and AlCl3, respectively, which are then sublimated at high temperatures and removed out of the system through the pores. The remaining HCl is also easy to be removed compared to Cl2, thereby providing an advantage of causing no foaming in the following melting process. |
