Stability of Fe-Cr alloy interconnects under CH_4-H_2O atmosphere for SOFCs

摘要

The chemical stability of Fe-Cr alloys (ZMG232 and SUS430) was examined under humidified CH_4 gases at 1073 K to simulate the real anode atmosphere in SOFC operation. Surface microstructure change and oxide scale layer formation were observed on the oxidized Fe-Cr alloy surfaces. The main reaction products were Mn-Cr-(Fe) spinels for both alloys. Secondary ion mass spectrometry (SIMS) was applied to measure the elemental distribution of minor and major elements around the oxide scale/alloy interface. A high concentration of Mn on the oxide scale surface suggested the fast diffusion of Mn in the oxide scale to form the spinels. Annealing in CH_4-H_2O made the oxide scale thicker with duration time on the alloy surface. The parabolic growth rates (k_p) of oxide scale layer were evaluated from the thickness of oxide scales by secondary ion mass spectrometry (SIMS) depth profiles, which were calculated to the following: k_p = 6.25 x 10~(-6)μm~2/s for SUS430 and k_p = 4.42 x 10~(-6)μm~2/s for ZMG232. The electrical conductivity of oxidized alloys showed the semi-conductor temperature dependence for both alloys. The electrical conductivity of oxidized ZMG232 alloy was higher than that of oxidized SUS430.