Photochromic alumino-phosphate glasses

摘要

Fast-response photochromic boron-free aluminophosphate glasses which have silver halide crystals dispersed throughout the glass comprise, in weight percentages: }SiO2 10 to 17% }Al2O3 20 to 29% }P2O5 30 to 40% }R2O 8.5 to 17% }R'O 4 to 18% } WHERE R2O represents Na2O and/or K2O; R'O represents CaO and/or BaO, the CaO content being at least 4% if BaO is absent and being from 0 to 7% if BaO is present, while the BaO content is from 0 to 18%; the total of SiO2 + Al2O3 + P2O5 amounting to not less than 69% by weight of the glass. Preferably the total of SiO2 + P2O5 + Al2O3 is not less than 72% by weight of the glass. The silver content of the glass, expressed as Ag2O, is preferably not less than 0.05%. Refractive index nD can be corrected to the standard ophthalmic value of 1.523 by additions of TiO2, ZrO2 and/or PbO.