Metal-to-ceramic joining for high-temperature Na-Zn batteries

Reliable metal-to-ceramic joining is crucial for the development of high-temperature Na-Zn batteries. This work investigates the joining of Invar42 (Fe-Ni alloy) to alumina using two glass-based composite sealants: a commercial silica-containing glass (SG) and a newly developed silica-free Y2O3-Al2O3-B2O3-BaO composition (YABB), both modified with 25 wt% Al2O3. In situ high-temperature XRD was used to examine the pre-oxidation behaviour of Invar42 at 650-750 degrees C. Pre-oxidation at 700 degrees C produced a uniform oxide layer approximately 5 mu m thick, which was selected as the oxide scale to enhance wetting and adhesion between Invar42 and the glass sealant. Among the tested sealants, SG-25A (SG + 25 wt% Al2O3) showed the best thermo-mechanical compatibility, resulting in crack-free joined samples that remained stable after 150 h at 600 degrees C and during thermal cycling. Mechanical tests yielded an average apparent shear strength of 23 + 7 MPa, with failure occurring predominantly within the oxide scale.