Effects of rare earth oxides on viscosity, thermal expansion, and structure of alkali-free boro-aluminosilicate glass

Effects of rare earth oxides (Y2O3, La2O3, and Er2O3) on the viscosity, thermal expansion, and structure of alkali-free boro-aluminosilicate glasses were investigated by the rotating crucible viscometer, dilatometry and FT-IR absorption spectra. The results showed that the melting temperature of alkali-free boro-aluminosilicate glasses decreased from 1 697.55 to 1 662.59, 1 674.37 and 1 640.87 °C with the introduction of 1 mol% La2O3, Y2O3 and Er2O3, respectively. However, the glass transition temperature Tg, dilatometric softening temperature Td and coefficient of thermal expansion of alkali-free boro-aluminosilicate glasses increased when adding the rare-earth oxides. At high temperatures, incorporating rare earth oxides into glass resulted in the peak at about 1 085 cm-1 towards lower wavenumber and the absorption band in the region of 850-1 260 cm-1 broader, which indicated that rare earths acted as network modifiers and increased the numbers of non-bridging oxygen in the glass melts. However, the rare earths had an opposite effect and accumulated the glass structure at low temperatures near Tg.