Effects of pre-oxidation on the microstructural and electrical properties of La_(0.67)Sr_(0.33)MnO_(3-δ) coated ferritic stainless steels

摘要

La_xSr_(1-x)MnO_3 (LSM) is commonly used as a protective layer on the metallic interconnects of solid oxide fuel cells (SOFCs) to prevent surface oxidation and chromium poisoning. However, the volume shrinkage at elevated temperatures causes the LSM coatings to crack, resulting in chromium diffusion. Therefore, this paper investigates the effects of pre-oxidation on the microstructure and electrical properties of ferritic stainless steels coated with La_(0.67)Sr_(0.33)MnO_3 (LSM). Four ferritic stainless steels were selected for use as interconnect substrates: Crofer22APU, Crofer22H, ss441, and ZMG232L. The candidate materials were pre-oxidised at 850 C for 25 and 50 h, respectively. After the pre-oxidation process, the LSM films with a thickness of 3-4 μm were deposited on the surface of samples by using Pulsed DC magnetron sputtering. After aging the coated specimens at elevated temperatures, the morphologies and crystalline structures were examined using SEM/EDX and XRD, respectively. The results indicated that the pre-oxidised layer, (Mn, Cr)_3O_4, could significantly suppress chromium penetration from the interior to the surface of the specimens. Moreover, the area specific resistance (ASR) values for the 25-h pre-oxidised specimens were 2.24,12.21, 2.30, and 6.77 mΩcm~2 for Crofer22APU, Crofer22H, ss441, and ZMG232L, respectively, at 800 ℃ for 500 h in an air atmosphere.