Abstract
Based on the specific structure of tubular solid oxide fuel cell stacks, a good chemical, microstructural and phase stability for the protective coating are required in both the oxidizing and reducing environments. In this work, MnCO2O4 coatings of approximately 150 µm were deposited onto porous Ni50Cr50-Al2O3 substrate by atmospheric plasma spray (APS) process. The coated samples were tested at 800°C with the coating exposed in air environment and the substrate in H2 environment. Reducing and pre-oxidizing treatments were performed prior to the stability test. Then the tested coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results elucidated that the tested coating had a high structural stability on the upper layer, while presented a reducing microstructure on the substrate side. The surface morphology of 100 hours tested coating indicated that the spinel granules still arranged closely with small particle size of ~ 250 nm and no obvious grain enlargement was observed. According to the cross-section, the upper layer kept stable and dense. While at the underneath region, the microstructure presented to be rather porous. However, the resistance presented a decreasing trend with the extension of exposure duration. After exposure for 95 h, the ASR decreased to 18.5 mΩ·cm2 although a substantial Cr diffusion from the substrate was detected.
