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 temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO-BiO1.5-GaO1.5 glasses. The range of compositions investigated was xPbO.(100 - (x + y))BiO1.5.yGaO1.5 for x between 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 consistent with the weight, size, charge, and bond strength of the cations. The Ga3+ ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi3+ and Pb2+ ions behave as network-modifying cations. It is suggested that a small fraction of the lead ions are present as Pb4+. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.