| 摘要 |
1286903 Photochromic glass CORNING GLASS WORKS 18 Feb 1970 [24 Feb 1969] 7695/70 Heading C1M [Also in Division C4] A transparent photochromic glass comprises by weight 30-76% SiO 2 ; 0-26% Al 2 O 3 ; 4-26% B 2 O 3 ; 10-50% Ta 2 O 5 ; one or more alkali metal oxides, the alkali metal content including 2-8% Li 2 O, 3-15% Na 2 O, 6-20% K 2 O, 8-25% Rb 2 O, or 10-30% Cs 2 O; one or more of Cl, Br and I, the halogen content including at least 0À2% Cl, at least 0À1% Br or at least 0À08% I; and silver, in an amount of at least 0À05% where Br or I are present and at least 0À2% when Cl is present; the balance, if any, comprising compatible constituents to a total not exceeding 15%. Optionally present may be CuO (0À01-0À1%); As 2 O 3 (0-0À2%); Mg (0-4%); CaO (0-6%); BaO (0-8%); SrO (0-7%); ZnO (0-8%); and PbO (0- 10%). The glass has a refractive index of above 1À52 and may be used as the core of an optical fibre. The crystal content of the glass is preferably 0À005 to 0À1% by volume, and the crystal size does not exceed 0À1 micron in diameter. The glass may be prepared by melting the batch at 1300-1500‹ C. for 4-8 hours, cooling and shaping the solidified glass, and re-heating to 550-850‹ C. for “-8 hours to cause crystallization and development of photochromicity.
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