Novel metal-ceramic joining for planar SOFCs

A novel method of ceramic-to-metal joining, referred to as reactive air brazing, was investigated as a potential method of sealing planar solid oxide fuel cells (SOFCs). In the present study, yttria stabilized zirconia (YSZ) and Fecralloy were selected as subject materials to simulate the cell-to-frame seal in planar SOFC. YSZ plates were joined with Fecralloy foils, using a range of CuO-Ag and CuO-Ag-TiO2 braze compositions. Metallographic analysis revealed that a majority of the CuO in the braze preferentially migrates to the braze/Fecralloy interface, indicating a stronger affinity and interaction between the CuO and the alumina scale that had formed on the Fecralloy than with the YSZ substrate. The addition of TiO2 to the braze had no significant effect on the microstructure or mechanical properties of the YSZ/Fecralloy joints, unlike what had been observed previously in YSZ/YSZ joining. Four-point bend tests indicated that joint strength improves with increasing CuO content up to 8 mol % CuO, the maximum concentration of copper oxide tested, likely due to the concomitant improvement in braze wettability. A maximum bend strength of 101 MPa was achieved using the 8 mol % CuO braze composition, demonstrating the feasibility of this joining technique for sealing planar SOFCs. (c) 2005 The Electrochemical Society. All rights reserved.