Evaluation of CaO-Al2O3 adhesive bonding properties for β″-Al2O3 solid electrolyte sealing for alkali metal thermal electric converter

The β″-Al2O3 solid electrolyte (BASE) tube is an essential component of the alkali metal thermal electric converter (AMTEC) system for inducing the conduction of Na ions and generating electricity. Maintaining gas-tightness to produce Na vapor pressure deference and providing insulation to prevent the loss of generated current from BASE are important factors for the AMTEC system. The Na-sulfur (NAS) battery has a similar driving system and uses glass adhesives, which are not adequate for operation temperatures higher than 800 °C or in a Na atmosphere. In this study, CaO-Al2O3 was used as the adhesive to resolve such bonding issues. The bonding strength changes were evaluated as the adhesive bonding process temperature varied and also the results showed that CaO-Al2O3 maintained bonding shear strength of 400 MPa for more than 1000 h in a molten Na environment. This study also proposes an experimental technique based on tube-type impedance measurement to assess the bonding between the BASE and the α-Al2O3 insulator and to detect Na leakage. After conducting the experiment for 500 h, CaO-Al2O3 adhesive can offer higher reliability than glass adhesives.