| 摘要 |
This invention is directed to photochromic glasses which darken to a brown coloration upon exposure to actinic radiation, which glasses have a refractive index of about 1.6, and Abbe number between 42-47, a density less than 2.82 g/cm3, and are preferably essentially free of TiO2. The glass compositions consist generally, in weight percent, of: SiO2 43-52 K2O 2-9 Nb2O5 0-5 B2O3 12.5-18 MgO 0-5 Ag 0.100-0.175 Al2O3 0-3 CaO 0-5 Cl 0.140-0.350 ZrO2 6-14 SrO 0-9 Br 0.093-0.195 LiO2 1.5-3.5 BaO 0-9 CuO 0.008-0.030 Na2O 0-3
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