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

Abstract

In this paper, the modification and strengthening dual functionality of rare-earth oxide is authenticated by the effect La2O3/BaO on composition-structure-property correlations of new type La2O3-BaO-SiO2 (LBS) glass-ceramics sealing material with high softening point, high coefficient of thermal expansion and excellent high temperature resistivity. As the network modifier, the La2O3 can create more non-bridging oxygen than the BaO, resulting in the increase of Q0 and Q1 units and the decrease of Q2 and Q3 units in the La2O3-BaO-SiO2 glass according to Raman and 29Si Solid-State Nuclear Magnetic Resonance. The strengthening functionality of La2O3 is declared by Static 139La WURST-QCPMG NMR spectra that La3+ ions form La-O bonds with O2- ions in the glass structure and La3+ spectra widens slightly with the increasing of La2O3. Correspondingly, physical properties including Tg, Tc, ρ, and MV of La2O3-BaO-SiO2 glass gradually increase with increasment of effective cation field strength. The main crystal phase of LBS glass-ceramic transforms from Ba2Si3O8 to Ba5Si8O21 and furthur to Ba3Si5O13 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 106 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 La2O3-BaO-SiO2 glass-ceramic will be an excellent candidate for solid oxide fuel cell, solid oxide electrolysis cell, oxygen sensors, and so on.