GLASS

摘要

1436562 Spectacle glass CARL-ZEISSSTIFTUNG [trading as JENAER GLASWERK SCHOTT & GEN] 19 Oct 1973 [2 Dec 1972] 48933/73 Heading C1M A spectacle glass comprises at least 90 mol per cent of Component (A) and at most 10 mol per cent of Component (B), and optionally a content of Component (C), Component (A) consisting of SiO 2 + B 2 O 3 + alkali metal oxide(s) + TiO 2 and optionally GeO 2 and/or CaO and/or ZnO and/or MgO, Component (B) consisting of ZrO 2 and optionally SrO and/or BaO and/or Al 2 O 3 and/or La 2 O 3 and/or Y 2 O 3 and/or Nb 2 O 5 and/or Ta 2 O 5 and Component (C) consisting of As 2 O 3 or-other refining agent and/or BeO and/or CdO for stabilization against crystallization, the balance, if any, consisting of one or more compatible constituents, and having the following properties: (i) n d value which is not less than 1À7; (ii) a specific gravity which is not less than 3À0; and (iii) an expansion coefficient valueα.107/20-300‹ C. which is not greater than 100. Advantageously the glass has the following composition expressed in per cent by weight: Component (A) 40-45 SiO 2 , 2-6 B 2 O 3 (SiO 2 + B 2 O 3 = 42-49), 0-4 Li 2 O, 6-16 Na 2 O, 0-10 K 2 O (total alkali metal oxide = 12-17), 24-26 TiO 2 , 0-6 CaO, 0-7 ZnO and 0-4 MgO; Component (B) 2-7 ZrO 2 , 0-10 SrO, 0-10 BaO, 0-2 Al 2 O 3 , 0-5 La 2 O 3 , 0-5 Nb 2 O 5 and 0-3 Ta 2 O 5 ; and Component (C) 0-2 As 2 O 3 or other refining agent, 0-5 BeO and 0-5 CdO.