| 摘要 |
PURPOSE:To remove remaining water and hydroxyl group without lowering evenness, by heat-treating fluoride glass at a temperature not to crystallize the glass while bringing a liquid or gaseous fluoride into contact with the surface of the fluoride glass. CONSTITUTION:A fluoride glass rod 4 (e.g. ZrF4-BaF2-LaF3-based glass rod) is rotatably laid in a reaction tube 1 equipped with an inlet 2 and an outlet 3 for a fluoride. Then the reaction tube 1 is inserted into a heating furnace 8, a gaseous or liquid fluoride (e.g. chlorine trifluoride or nitrogen trifluoride) is sent from the inlet 2 for a fluoride and the fluoride glass rod 4 is heat-treated at a temperature not to crystallize the glass while rotating the glass rod. Consequently, adsorbed water and hydroxyl group remaining in the glass rod 4 are chemically reacted with the fluoride and removed so that fluoride glass having improved optical characteristics such as transmission characteristics can be obtained. |
