Journal of Thermal Analysis and Calorimetry, Vol. 77 (2004) 207–216 OXIDATION KINETICS STUDY OF THE IRON-BASED STEEL FOR SOLID OXIDE FUEL CELL APPLICATION T. Brylewski * , J. D¹bek and K. Przybylski Department of Solid State Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Krakow, Poland Abstract Kinetics of oxidation of Fe-Cr steel containing 25 wt.-percent Cr was studied as a function of tem- perature (1023–1173 K) for up to 480 h in flowing air, which corresponds to SOFC cathode environ- ment 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 predomi- nantly 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 signifi- cant contribution of counter-current oxygen/chromium diffusion along Cr 2 O 3 grain boundaries. The oxide scales were composed mainly of Cr 2 O 3 with a continuous thin Mn 1.5 Cr 1.5 O 4 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. Keywords: chromia scale, Fe-Cr steel, kinetics, microstructure, oxidation, SOFC interconnect Introduction The high-temperature oxidation of high-Cr iron-based steel has been recently studied extensively. This interest arises from the possibility of the application of this steel to the metallic-type of interconnect in Solid Oxide Fuel Cell (SOFC) operating at 1073 K [1–7]. The interconnect is one of the critical components of the planar-type high-temperature SOFC, which separates the cathode and the anode gases and pro- vides the electrical connection between the single cells in the stack [7]. The key issue of the chromia-forming Fe-Cr steel application is its good corrosion resistance, its thermal expansion coefficient which is close to that of solid electrolytes of stabilized zirconia and the ability to work efficiently in air and in H 2 -H 2 O gas mixture due to the high oxidation resistance of the thermally grown chromia scale [1–8]. The examined ferritic stainless steel exhibits high temperature resistance owing to the presence of alloying additions such as Cr, Mn, Si, which improve the scale ad- hesion. Furthermore, the electrical resistivity across the oxide scale development 1388–6150/2004/ $ 20.00 © 2004 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: brylew@uci.agh.edu.pl