Alkali-free glass seals compositions for electrochemical devices

• An alkali-free glass composition to limit the crystallization • Results indicate that the replacing of Al 2 O 3 with ZrO 2 and of Al 2 O 3 with Y 2 O 3 increases the glass resistance to devitrification • Yttrium-based glass exhibits properties in respect with the SOFC’s sealing specifications • Structural ageing has been studied by XRD and NMR up to 960h at 800°C On the composition-based 47.6SiO 2 – 9.5Al 2 O 3 – 14.3CaO – 28.6BaO, the effects of substituting Al 2 O 3 with ZrO 2 and Y 2 O 3 , and CaO with SrO, respectively, led to four new glass matrix compositions. This study demonstrates the influence of these oxides, commonly used in the formulation of glass seals, on the physicochemical properties and structure of the glass network. Densification behaviour was analysed by hot-stage microscopy, while electrical resistivity was measured by impedance spectroscopy. Thermal ageing at the working temperature, up to 960h, was characterised using X-ray diffraction and solid-state NMR. The results show that the substituting Al₂O₃ with ZrO₂ improves resistance to devitrification but reduces the thermal expansion coefficient, whereas substituting CaO with SrO produces to the opposite effect. The incorporation of Y₂O₃ was found to reduce crystallisation. These effects are attributed to modifications of the glass network structure and connectivity.