Photochromic boro-silicate glass
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United States of America Patent
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Sep 22, 1981
Issued Date -
N/A
app pub date -
May 18, 1978
filing date -
Jan 30, 1976
priority date (Note) -
Expired
status (Latency Note)
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Abstract
Fast-response photochromic boro-silicate glasses which have a half-fading time of not more than 145 secs, have silver halide crystals dispersed throughout the glass and are free from barium, comprise, in weight percentages: SiO.sub.2 --31 to 59% B.sub.2 O.sub.3 --18 to 28% Al.sub.2 O.sub.3 --8 to 20% R.sub.2 O--6 to 16% wherein R.sub.2 O represents one or more of Li.sub.2 O, Na.sub.2 O and K.sub.2 O in amounts within the ranges 0 to 3% Li.sub.2 O, 0 to 8% Na.sub.2 O and 0 to 16% K.sub.2 O, and where the content of silver, expressed as Ag.sub.2 O, lies within the range 0.05 to 0.4% by weight, while the content of halide lies within the range 0.13 to 1% by weight of the glass. Further optional constituents are MgO (up to 2.6%) and P.sub.2 O.sub.5 (up to 12%). Refractive index n.sub.D can be corrected to the standard ophthalmic value of 1.523 by additions of ZrO.sub.2, TiO.sub.2 and/or PbO.
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