The surface oxide layer of Fe-Cr-Al alloy was modified for use as the metal support of SOFCs. The Fe-Cr-Al alloy was firstly coated with LSCF and pre-heat-treated in a vacuum at 1000 °C for 1 h. In comparison with heat treatment at 700 °C, in which the surface oxide was identified as columnar γ-Al2O3/Sr3Al2O6, durability was greatly improved while maintaining electric conductivity at the same level. High-resolution STEM/TEM analysis revealed that the morphology was a similar columnar structure arranged in the same direction. The primary component was -Al2O3 polycrystal (>80%) and the secondary component was Sr3Al2O6 (∼15%). After the formation of columnar γ-Al2O3/Sr3Al2O6 in the low temperature range (<800 °C), γ-Al2O3 was transformed to a more stable -Al2O3 by increasing the temperature to 1000 °C. Ionic diffusion paths, which cause growth of the oxide during operation, were reduced in the columnar structure. Electronic conduction similarly occurred for both γ-Al2O3/Sr3Al2O6 and -Al2O3/Sr3Al2O6, which was enhanced along the interface between Al2O3 and Sr3Al2O6. Thus, we obtained a stable semiconductive Al2O-based surface oxide layer with a columnar -Al2O3/Sr3Al2O6 structure.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry