LEAD-FREE OPTICAL LIGHTWEIGHT FLINT OR EXTREMELY LIGHTWEIGHT FLINT GLASS

摘要

PROBLEM TO BE SOLVED: To obtain flint glass having excellent chemical resistance by constituting the flint glass so as to have a composition comprising SiO₂, B₂O₃, K₂O, La₂O₃, Al₂O₃, ΣLa₂O₃+ZrO₂, TiO₂ and F^- in a specific weight ratio based on oxide and having a prescribed ratio of (Al₂O₃+La₂O₃)/(TiO₂+ZrO₂) and as necessary contain a clarifier and have a prescribed refractive index and Abbe's number. ;SOLUTION: As necessary, a clarifier is added to glass raw material prepared so as to become a prescribed composition and the glass raw material is melted at 1250-1300°C and clarified, cast and cooled to provide lead-free optical lightweight flint or extremely lightweight flint glass having a composition comprising 48-55wt.% SiO₂, 7-9wt.% B₂O₃, 18-20wt.% K₂O, 7-9wt.% Al₂O₃, 0.1-2wt.% La₂O₃, 0-1wt.% ZrO₂, 0.5-2wt.% ΣLa₂O₃+ZrO₂, 5.5-12wt.% TiO₂, 1.5-6wt.% F^- and 0.1-0.5wt.% Sb₂O₃+Cl^- based on oxide and having 0.73-1.15 (Al₂O₃+La₂ O₃)/(TiO₂+ZrO₂). The glass has 1.52-1,57 refractive index (n_d) and 43-52 Abbe's number (ν_d).;COPYRIGHT: (C)1998,JPO