COLOR AND SELECTED PROPERTIES OF PBO-BIO1.5-GAO1.5 GLASSES

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HCl, and NaOH; glass transition and crystallization tem peratures; and the absorption edge in the ultraviolet-visible and infr ared were measured for PbO-BiO1.5-GaO1.5 glasses. The range of composi tions investigated was xPbO.(100 - (x + y))BiO1.5.yGaO1.5 for x betwee n 20 and 60 cat % and y of 20, 25, 30, and 35 cat %. The glass-forming tendency increased with increased GaO1.5 and decreased with increased PbO or BiO1.5. The compositional dependence of these properties was c onsistent with the weight, size, charge, and bond strength of the cati ons. The Ga3+ ions in these glasses are believed to act primarily as n etwork-forming cations, whereas the majority of the Bi3+ and Pb2+ ions behave as network-modifying cations. It is suggested that a small fra ction of the lead ions are present as Pb4+. Depending upon melting con ditions, these glasses ranged in color from brown to yellow. Various a ttempts, including containerless melting, were made to obtain colorles s glasses, but no conditions were found which totally eliminated the c olor. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucibl e.