The modification and strengthening dual functionality of rare-earth oxide in La2O3-BaO-SiO2 glass for high temperature sealing application

In this paper, the modification and strengthening dual functionality of rare-earth oxide is authenticated by the effect La ₂O ₃/BaO on composition-structure-property correlations of new type La ₂O ₃-BaO-SiO ₂ (LBS) glass-ceramics sealing material with high softening point, high coefficient of thermal expansion and excellent high temperature resistivity. As the network modifier, the La ₂O ₃ can create more non-bridging oxygen than the BaO, resulting in the increase of Q ⁰ and Q ¹ units and the decrease of Q ² and Q ³ units in the La ₂O ₃-BaO-SiO ₂ glass according to Raman and ²⁹Si Solid-State Nuclear Magnetic Resonance. The strengthening functionality of La ₂O ₃ is declared by Static ¹³⁹La WURST-QCPMG NMR spectra that La ³⁺ ions form La-O bonds with O ^2- ions in the glass structure and La ³⁺ spectra widens slightly with the increasing of La ₂O ₃ . Correspondingly, physical properties including Tg, Tc, ρ, and M _V of La ₂O ₃-BaO-SiO ₂ glass gradually increase with increasment of effective cation field strength. The main crystal phase of LBS glass-ceramic transforms from Ba ₂Si ₃O ₈ to Ba ₅Si ₈O ₂₁ and furthur to Ba ₃Si ₅O ₁₃ phase with high coefficient of thermal expansion and there is not lanthanum-contained phase precipitation. The coefficients of thermal expansion (CTE) of LBS glass-ceramic increases from 12.48 × 10 ⁻⁶/℃ to 13.18 × 10 ⁻⁶/℃ (30–1000 ℃) and the softening temperature are between 1231.1 ℃ and 1305.1 ℃. The direct-current (DC) resistivity of the LBS glass-ceramics is higher 10 ⁶ Ω·cm at a high temperature of 700 °C, which has good high-temperature electrical insulation. All in all, the high CTE, high Ts and high electrical insulation “Tri-high” properties of rare-earth oxide La ₂O ₃-BaO-SiO ₂ glass-ceramic will be an excellent candidate for solid oxide fuel cell, solid oxide electrolysis cell, oxygen sensors, and so on.