Lanthanum and Barium in Glass-Forming Systems

JSGT 1947 V31 T153-T169

Barium and lanthanum oxides decrease the reciprocal relative dispersion (ν-value) comparatively less than other constituents which impart equal increases of refractive index to high index, low dispersion crowns. Quantitative data were obtained when 7·5 mol% of various oxides were introduced into the simple base glass 27·5 BaO, 15 B₂O₃, 7·5 Al₂O₃, 50 SiO₂. The chemical resistance is impaired by increase of the BaO as well as by La₂O₃, Small amounts of Al₂O₃, ZrO₂, ThO₂, and particularly of TiO₂, Nb₂O₅ and Ta₂O₅, increase the chemical resistance of barium and lanthanum glasses more than SiO₂. In a large area of the field BaO–La₂O₃–B₂O₃, formation of glasses having favourable index-dispersion relations was observed, particularly near the narrow zone of lanthanum borates containing little or no barium. Lanthanum borate, modified by barium, may be considered the basis of modern complex non-silica and low silica glasses of high index and low dispersion. Lanthanum oxide was found to form glasses with phosphoric acid and barium oxide. A pure lanthanum metaphosphate glass exists and has a refractive index of 1·60 and a reciprocal relative dispersion of 60. Data obtained in the borosilicate, borate and phosphate system permit the discussion of the application of barium and lanthanum in conjunction with other more or less frequently-used elements in the construction of high index, low dispersion crowns.

Gordon F. Brewster, Norbert J. Kreidl & Tyler G. Pett