| 摘要 |
PURPOSE:To make it possible to produce preform having improved fluorine amount added, free from residue foam, by heating quartz glass fine particles in an atmosphere comprising SiF4 at >1atm. before a transparent glass making process for the quartz glass fine particles. CONSTITUTION:Porous preform having piled glass fine particles is heat-treated in a SiF4 atmosphere at >1atm. Consequently, a large amount of fluorine can be added to the porous preform, simultaneously bulk density of the porous preform is raised and can be regulated in a fixed range. Successively the preform is further heat-treated in a SiF4 atmosphere at <=1atm. at an elevated temperature and made transparent. |
