Influence of the melting conditions of heavy metal oxide glasses containing bismuth oxide on their optical absorption

Abstract

Glasses of the systems Bi 2O 3–SiO 2, Bi 2O 3–PbO–Ga 2O 3, Bi 2O 3–PbO–Ga 2O 3–GeO 2 and Bi 2O 3–GeO 2–Li 2O have been prepared and the interaction of their melts with crucibles of different materials has been analytically determined. Silica and porcelain crucibles were very strongly corroded and the glass composition was noticeably altered. Instead platinum crucibles are not affected if the Bi 2O 3 content is not too high. The color of the glasses changes in all cases from pale yellow to deep brown when the melting temperature reaches approximately 1000 °C. The higher the temperature and the Bi 2O 3 content the darker the brown color, independently of the nature of the employed crucible. The addition of oxidizing ions (Sb 5+, As 5+ or Ce 4+) to the glass batch prevents darkening. Nanoparticles of elementary bismuth Bi 0 are observed by transmission electron microscopy in the glasses melted above 1000 °C. The partial thermoreduction of the Bi 2O 3 during the heating of the glass melt is proposed as the mechanism responsible for the observed darkening.