| 摘要 |
<p>Fast-response alumino-phosphate photochromic glasses having silver halide crystals dispersed throughout the glass comprise, in weight percentages: SiO2 8.5 to 25% Al2O3 13 to 36.5% P2O5 7.5 to 33.5% B2O3 7 to 28% R2O 7 to 20.5% where R2O represents at least one of Na2O, K2O and Li2O, the maximum content of Li2O being 5%; the amount of SiO2 is not less than 16% when the B2O3 content is less than 8%; and the silver content of the glass, expressed as Ag2O, is not less than 0.05% by weight. Such glasses in which Al2O3 is the largest constituent are preferred for ophthalmic purposes, but it is also possible for either B2O3 or P2O5 to be the largest constituent. The glass can also contain 1% to 21% by weight R'O where R'O represents MgO, CaO, SrO or BaO. The refractive index can be corrected by nD = 1.523.</p> |
