| In this research, cathode-side contact materials with high sinterability were studied for intermediate-temperature SOFC applications. These highly-sinterable contact materials included the Ag-base alloys/composites and (Mn,Co) 3O4 spinels. Firstly, silver evaporation suppression through alloying addition was studied by investigating the weight change of silver-based alloys with various alloy additions after thermal exposure. Initial testing indicated that some of the alloying elements, specifically Mn, Zn, and Pd were effective in reducing the weight loss of the alloys during thermal exposure. However, long-term tests concluded that the evaporation rates of Mn- and Zn-containing alloys reached comparable levels to pure silver after the first weighing interval. The oxides formed on the surface became very porous with the consumption of the alloying addition and allowed silver to evaporate through these pores. Pd was effective in suppressing silver evaporation over long-term exposure because it filled the silver surface sites and thus blocked silver evaporation. Ceramic-metallic composite Ag-(La0.8Sr0.2)MnO3 (LSM) samples were tested for evaporation suppression and it was found that the LSM addition did not meaningfully suppress evaporation even when the amount of silver present in the sample was low. It was concluded that the LSM was so porous that the silver evaporated from these pores, as indicated by the comparable weight loss of the composites to pure silver.;Secondly, a relatively new spinel, (Mn,Co)3O4, was tested for its sinterability as a SOFC contact material. The glycine nitrate process and the solid state synthesis were utilized to produce (Mn,Co) 3O4-forming contact materials. Among the various powders mixtures investigated, the solid state Mn-Co metallic mixture produced the best sintered spinel. Two application methods, including screen printing and air spray, were studied with regard to their ability to make an acceptable contact layer. The air spray method proved to produce a more dense layer and be able to apply the coating to complex shapes and surfaces. The mixed Mn-Co contact material were applied to a simulated cathode-side cell and tested for their ASR performance and Cr blocking characteristics under isothermal conditions. It was concluded that this contact material possesses excellent ASR performance and Cr blocking capabilities. Furthermore, this material is highly sinterable and requires a sintering temperature of only 850-900°C. |
