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Vol.52, No.1, 41 ~ 47, 2014
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| Title |
| Formation of Phases and Variation of Area Specific Resistance with Surface Roughness in Oxidized Crofer 22 APU |
| Myoung Youp Song , Daniel R Mumm , Ji Young Song , Soon Do Yoon |
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| Abstract |
| Ferritic stainless steel Crofer 22 APU specimens with various surface roughnesses were prepared by grinding with different grit SiC grinding papers. The samples were then thermally cycled 20 times between 298 K and 1073 K (a total oxygen exposure time of 500 h at 1073 K). Observations of the microstructure, measurements of the area specific resistance (ASR), and analysis of the atomic percentages of elements by energy dispersive X-ray (EDX) spectroscopy were performed. As the grit number of the grinding paper, with which the sample was ground, increased from grit 80 through grit 800, the particle size decreased. The particle sizes of the sample ground with grit 800 and the polished sample were similar. A trench of a Crofer 22 APU sample ground with grit 80 after 120 thermal cycles between 298 K and 1073 K (a total oxygen exposure time of 3000 h at 1073 K), observed by scanning electron microscopy (SEM) after focused ion beam (FIB) milling, exhibited an alloy substrate phase, Cr2O3 layer, and (Cr, Mn)3O4 spinel phase from the inside to the surface of the sample. The Cr2O3 layer was undulated with a thickness of about 3 μm. At the same measuring temperature, the ASR increased as the surface of the sample became rougher. Plots of ln (ASR/ T) versus 1/ T for samples ground with grit 120, grit 240, and grit 800 after 20 thermal cycles exhibited good linearity. |
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| Key Words |
| fuel cells, oxidation, microstructure, X-ray diffraction, thermal cycling |
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