Characterization of Fe-Cr Alloys in CH4 Fuels for SOFC Interconnects

Abstract

The chemical stability of a ferritic alloy (Fe-Cr alloy) was examined as interconnect under CH 4 -H 2 O gases to simulate the real fuel gas conditions. Oxide scale layers were formed on the alloy surface by reaction with CH 4 -H 2 O gases at 1073 K. The surface morphology varied with the formation of needle-like or plate-like Cr-Mn-(Fe) oxide spinels and Cr 2 O 3 . Secondary ion mass spectrometry (SIMS) was used to measure the distribution of minor and major elements around the oxide scale/alloy interface. High concentration of Mn on the oxide scale surface suggested fast diffusion of Mn in the oxide scale to form spinels. Annealing in CH 4 -H 2 O made the oxide scale thicker with time. Growth of the oxide scale layer thickness followed the parabolic growth relationship with time. The parabolic growth rate constants were in the order of 10 -6 μm 2 s -1 for all experimental conditions. Isotope oxygen ( 18 O 2 ) diffusion coefficients of oxide scale were estimated by the 18 O diffusion profiles at 1073 K, which was in the order of 10 -4 μm 2 s -1 . Therefore, the oxygen diffusion was not the rate determining step for oxide scale formation. The electrical conductivity of oxidized alloy showed no dependence on p(CH4) in the reaction gases.