Stability of Fe-Cr alloys in SOFC fuel atmosphere

The chemical stability of Fe-Cr alloys (ZMG232 and SUS430) was examined in fuel atmosphere of SOFC, especially in H₂-H₂O atmosphere. Oxide scales were formed on the alloy surface with a thickness of 3-5 μm at 1073 K for 1000 h by the diffusion of cations through the scale. The microstructures and elemental distribution of oxide scale/alloy interfaces were analyzed by the depth and surface analysis techniques: Mn-Cr-(Fe) spinel, Cr₂O₃, and internal Si oxides were identified from surface to inner oxides. An anomalous thick oxide scale formation was found on SUS430 surface in H₂-H₂O atmospheres. A thick oxide scale was composed of Fe, Cr, and Mn oxides. A relatively high concentration of Fe was observed at top surface of oxide scale. The distribution of Si was found inside the oxide scale, suggesting an increase of oxygen potential and fast diffusion of Si inside the oxides. The formation of anomalous thick oxide scale can affect the stability of Fe-Cr alloy interconnects by changing the cell connections at scale/alloy/cell interfaces.