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 Sb₂O ₃ 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 borosilicate glasses. To mimic the enriched amounts of Sb₂O₃ found on the surface of the Sb₂O ₃ 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. ²⁹Si, ²⁷Al, and ¹¹B 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_g, lower expansion, and more chemically durable surface for such antimony-oxide fined glasses.