Alumino-phosphate photochromic glasses

Abstract

Abstract Photochromic glass compositions which darken on exposure to actinic radiation are made with a phosphate base (at least 17 wt.% P.sub.2 O.sub.5) and silver halide crystals dispersed through the glass, the total silver content being at least 0.05 wt.%. The glasses generally also contain SiO.sub.2 (0 to 40 wt.%) and Al.sub.2 O.sub.3 (9 to 34 wt.%). The preferred ranges, in weight percentage on the oxide basis, are: 17 to 48% P.sub.2 O.sub.5 ; 0 to 40% SiO.sub.2 ; 20 to 34% Al.sub.2 O.sub.3 ; the total of these three major components being between 60% and 86% by weight of the glass and the ratio of P.sub.2 O.sub.5 content to Al.sub.2 O.sub.3 content being not less than 0.7; at least 10% R.sub.2 O where R = K, Na or Li; 0.05 to 1.0% Ag; and 0.2 to 2% X where X = Cl.sup.-, Br.sup.- or any combination of Cl.sup.-, Br.sup.- and I.sup.-. The glasses may also contain between 2 and 20 wt.% of a divalent oxide MO, or 2 to 25 wt.% MO where BaO or PbO is present. The glasses can be used for ophthalmic lenses for sunglasses, for example.

Inventors

• 👤 Stanley Lythgoe

Bibliographic Details