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 T _g, dilatometric softening temperature T _d 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 T _g.