Optical glass with high refractive index, but contg. no thorium - contains lanthanum oxide, boric oxide, zinc oxide, zirconia, tungstic oxide, and alkaline earth metal oxide

摘要

The glass has a low dispersion, and contains by wt. 22-31% B203, 27-44% La203, 5-14% ZnO, 1-9% RO, 11-19% ZnO + RO, 1-9% Zr02, 1-20% W03, 0-4% Si02, 0-4.5% Y203, 0-7% PbO, 0-5% Al203. The pref. glass contains neither PbO nor Al203. The above compsn. produces a refractive index(nd) of 1.75-1.80, and an Abbe number(vd) of 43-48; and the term RO refers to one or more of MgO, CaO, SrO, BaO. In the past, glass with a high nd value was made using thorium oxide; but Th is radioactive and harmful to humans, so the use of Th02 must be avoided. In addn. to contg. no Th, the glass can easily be mass produced, and has excellent resistance to chemicals and to devitrification.