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  • 1 AGH University of Science and Technology al. Mickiewicza 30 Department of Solid State Chemistry, Faculty of Materials Science and Ceramics 30-059 Krakow Poland
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Abstract  

Kinetics of oxidation of Fe-Cr steel containing 25 wt.-percent Cr was studied as a function of temperature (1023–1173 K) for up to 480 h in flowing air, which corresponds to SOFC cathode environment operating conditions. The oxidation process was found to be a parabolic, suggesting that the diffusion of ionic defects in the scale is the slowest, rate determining step and it occurs predominantly by short-circuit diffusion paths. Comparison of the determined activation energy of oxidation of the studied steel with literature data indicates that at 1098–1173 K the chromia scale grows by the outward solid-state diffusion of chromium interstitials, whereas at 1023–1098 K — through a significant contribution of counter-current oxygen/chromium diffusion along Cr2O3 grain boundaries. The oxide scales were composed mainly of Cr2O3 with a continuous thin Mn1.5Cr1.5O4 spinel layer on top of the chromia scale. The oxidation test results on Fe-25Cr steel demonstrate the applicability of the commercial type DIN 50049 stainless steel as interconnect for SOFC.