| 摘要 |
PROBLEM TO BE SOLVED: To obtain an inorganic glass having a sufficient mechanical strength and a sufficient impact resistance when preparing a thin eyeglass lens. SOLUTION: This glass can be tempered by ion exchange and has a refractive index between 1.67 and 1.72 and further the following composition expressed in terms of wt.% based on oxides. 33-37 of SiO2, 7.5-13 of B2O3, 44-48 of SiO2+ B2O3, 5-8 of Li2O, >2.5 to 7.5 of Na2O, 0-2 of K2O, <14 of Li2O+Na2O+K2O, 0 to <8 of CaO, 0-6 of Al2O3, 8-13 of Nb2O5, 4-6 of ZrO2, 5-10 of TiO2, 12-19 of La2O3, 2-4 of SrO and 0-0.8 of As2O3 and/or Sb2O3.
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