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. 2021 Oct 15;14(20):6136.
doi: 10.3390/ma14206136.

Surface Structure Analysis of Initial High-Temperature Oxidation of SS441 Stainless Steel

Tung-Yuan Yung  1 , Hui-Ping Tseng  1 , Wen-Feng Lu  1 , Kun-Chao Tsai  1 , Tien Shen  1 , Hsin-Ming Cheng  2 , Jeng-Shiung Chen  3 , Po-Tuan Chen  4
Affiliations

Surface Structure Analysis of Initial High-Temperature Oxidation of SS441 Stainless Steel

Tung-Yuan Yung et al. Materials (Basel). .

Abstract

Chromia-forming ferritic stainless steel (FSS) is a highly promising interconnect material for application in solid oxide fuel cells. In this study, initial oxidation of chromium oxides was performed at 500-800 °C to understand the evolution of materials at an early stage. The structural variations in oxide scales were analyzed through scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffractometry (XRD), laser confocal microscopy (LSCM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Surface electrochemical properties were investigated through electrochemical impedance spectroscopy to understand how the heat treatment temperature affected surface impedance. Treatment temperatures higher than 700 °C facilitate the diffusion of Cr and Mn, thus allowing ferritic spinels to form on the surface and leading to high electrical conductivity.

Keywords: high temperature; interconnect; oxidation; solid oxide fuel cells; spinel.

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Conflict of interest statement

The authors declare that they have no competing financial interests.

Figures

Figure 1
Figure 1
Surface morphology after treatment at 500, 600, 700, and 800 °C for 10 min (scale bar: 1 μm).
Figure 2
Figure 2
Cross-sectional SEM and TEM images of samples treated at (a) 500, (b) 600, (c) 700, and (d) 800 °C for 10 min (scale bar: 1 μm). The insets in the bottom left are the selected area diffraction patterns, with scale bars of 0.05 nm.
Figure 3
Figure 3
Oxide scale thicknesses as determined from cross-sectional SEM images.
Figure 4
Figure 4
Oxide scale thicknesses as revealed in cross-sectional analysis through transmission electron microscopy.
Figure 5
Figure 5
XPS results for oxide scales of specimens pre-oxidized at 500, 600, 700, and 800 °C. (a) Cr 2p (b) Mn 2p.
Figure 6
Figure 6
Raman spectra at 785 nm revealing vibrational modes for oxide scales. The black, green, blue, light blue, and red indicate the as-received, 500, 600, 700, and 800 °C samples, respectively.
Figure 7
Figure 7
Nyquist (a) and Bode (b) and plots for heat treatments at 500 °C, 600 °C, 700 °C, and 800 °C with blue, red, green and orange, respectively. The dots are EIS data, and the line is the simulated equivalent circuit.
See this image and copyright information in PMC

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