| 摘要 |
PURPOSE:To prolong the life of a furnace core tube and obtain the titled preform at a low cost, by transparently vitrifying a porous preform, prepared by flame hydrolytic reaction, etc., and consisting essentially of quartz in a transparent vitrifying furnace with the interior thereof, kept at a given temperature and having an atmosphere containing a fluoride. CONSTITUTION:A porous preform 1, e.g. SiO2-GeO2 based preform, formed by flame hydrolytic reaction of thermal oxidation reaction, e.g. VAD, OVD, plasma process, etc., and consisting essentially of quartz is introduced into a transparent vitrifying furnace 2 having a quartz furnace core tube 3, as necessary together with a fluoride gas, e.g. SiF4, etc., and an inert gas, e.g. He, etc., O2, etc., to give a fluoride-containing atmosphere. The preform is then heated to <=1,200 deg.C with a heating furnace 4 and transparently vitrified. |
