Lead-free optical dense and extra-dense barium crown glasses have a refractive index n d of between 1.60, and 1.65 an Abbe number # d of between 49 and 60, and have the following composition (in % by weight, based on oxide): SiO 2 38 - 45; B 2 O 3 5 - 10; BaO 29 - 42; ZnO 0 - 10; CaO 0 - 5; where BaO + ZnO + CaO 35 - 50; TiO 2 1 - 5; ZrO 2 0.5 - 3; where (SiO 2 + TiO 2 + ZrO 2 )/(BaO + ZnO + CaO) 0.84 - 1.35; La 2 O 3 0 - 2.5; Al 2 O 3 1 - 3.5; where La 2 O 3 + Al 2 O 3 2.5 - 3.5; Na 2 O 0 - 2; K 2 O 0 - 6 where Na 2 O + K 2 O 0 - 7. The glasses have very good chemical resistance and very high crystallization stability. Fining agents such as Sb 2 O 3 and/or fluoride may be present in amount up to 0.5 wt%.
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机译：无铅光学致密和超重钡冠玻璃的折射率nd在1.60和1.65之间，阿贝数＃d在49和60之间，并且具有以下成分（以重量％计，基于氧化物计）： SiO 2 38-45; B 2 O 3 5-10; BaO 29-42; ZnO 0-10; CaO 0-5;其中BaO + ZnO + CaO 35-50; TiO 2 1-5; ZrO 2 0.5-3;其中（SiO 2 + TiO 2 + ZrO 2）/（BaO + ZnO + CaO）0.84-1.35; La 2 O 3 0-2.5; Al 2 O 3 1-3.5;其中La 2 O 3 + Al 2 O 3 2.5-3.5; Na 2 O 0 -2; K 2 O 0-6，其中Na 2 O + K 2 O 0-7。玻璃具有非常好的耐化学性和很高的结晶稳定性。澄清剂例如Sb 2 O 3和/或氟化物可以以至多0.5重量％的量存在。
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