PNNL

Abstract

The feasibility of brazing LSCoF ceramic substrates with silver-vanadium pentoxide (Ag-V2O5) alloys for use in solid oxide fuel cell (SOFC) applications was studied. Preliminary testing was also performed on the Ag-V2O5/alumina (Al2O3) system in order to determine the feasibility of brazing LSCoF to FecralloyTM with an Ag-V2O5 alloy since an Al2O3 layer is formed on the Fecralloy surface prior to brazing. Sessile drop tests were performed using liquid Ag with 1 to 20 weight percent (wt%) V2O5 additions at either 1000 or 1100 °C. Similar to previous results for Ag-CuO alloys, additions of V2O5 resulted in a decrease in the apparent contact angle and a transition from non-wetting to wetting behavior for both substrate materials. Mechanical test samples were fabricated by brazing using Ag with 1, 2 and 5 wt% V2O5 additions. For the Ag-V2O5/LSCoF samples, the joint fracture strengths ranged from 10 to 30% of the monolithic LSCoF fracture strength (?joint = 26 ±9 MPa??versus??LSCoF = 151 ±24 MPa). An SEM/EDS microstructural analysis of the brazed cross-sections indicated the formation of a vanadium rich reaction product at the braze/LSCoF interface. It is hypothesized that the reaction product provided improved chemical bonding at the interface that resulted in the modest joint strengths. In the the Ag-V2O5/ Al2O3 system, although the contact angles were less than 90°, all of the brazed Al2O3 samples failed to bond during brazing or fractured during sample preparation. These poor adhesion results indicate potential problems with the FecralloyTM/Ag-V2O5/LSCoF system.