The effects of antimony oxide on the structure of alkaline-earth alumino borosilicate glasses

Antimony oxide is added to alkaline-earth alumino borosilicate glasses primarily as a fining agent. Recently, it was observed that the surface of commercial fusion-drawn Sb2O3-fined calcium alumino borosilicate glass shows a significant segregation of Sb2O3 to the surface. Thus, the motivation for the work reported here was to explore the structure of the Sb-oxide enriched surface layer, and more generally, to understand the effects of Sb oxide on the structure of alkaline-earth alumino borosificate glasses. To mimic the enriched amounts of Sb2O3 found on the surface of the Sb2O3 fined commercial glasses, a series of glasses were produced in which the silicon dioxide to antimony oxide ratio was varied, while the relative concentration of other components was held constant. Si-29, Al-27, and B-11 NMR spectra were obtained to probe the effect of increased amounts of Sb2O3 on the structure of the model glasses. The results show that Sb2O3 enters the aluminoborosilicate network, and thereby increases the connectivity of the structure. Relative to the Sb-oxide enriched surface layer on commercial fusion drawn glass, these findings suggest a higher T, lower expansion, and more chemically durable surface for such antimony-oxide fined glasses. (C) 2004 Elsevier B.V. All rights reserved.