Lead-free optical flint glass with good processing properties e.g. for pressing

摘要

Optical flint glass, which has a refractive index nd of 1.60-1.70, an Abbe no. vd of 30-40, good chemical resistance and very good devitrification stability, comprises 46-70 wt.% SiO2 and 0-5 wt.% GeO2 such that total of SiO2+GeO2 is 46-70; 0-6 wt.% B2O3; 0-2 wt.% P2O5; 0-4 wt.% Li2O, 5-15 wt.% Na2O, 4-12.5 wt.% wt.% K2O and 0-3 wt.% Cs2O such that total of Li2O+Na2O+K20+Cs2O is 10-25; 0-5 wt.% MgO, 0-6 wt.% CaO, 0-6 wt.% SrO, 0-10 wt.% BaO and 0-5 wt.% ZnO such that total of MgO+CaO+SrO+ZnO is no more than 12; 0-3 wt.% Al2O3, 0-5 wt.% La2O3, 0-5 wt.% Y2O3, 0-5 wt.% Bi2O3 and 0-5 wt.% Gd2O3 such that total of La2O3+Gd2O3+Bi2O3 is 0-5; 20-35 wt.% TiO2; 0-5 wt.% ZrO2; 0 to less than 5 wt.% Nb2O5; 0-5 wt.% Ta2O5; 0-5 wt.% WO3; and opt. the usual amts. of refining agent.