Effects of silicon concentration in SOFC alloy interconnects on the formation of oxide scales in hydrocarbon fuels

Oxide scale formations on Fe-Cr alloy interconnects were investigated in anode gas (mixtures of CH4 and H2O) atmospheres for solid oxide fuel cells. The silicon concentration in Fe-Cr alloy changed the microstructures of oxide scales, elemental distribution and oxide scale growth rates. Oxide scale is composed of the following phases from surface to inner oxides: Fe-Mn spinel, Cr2O3, oxide scale/alloy interface and internal oxides of Si and Al. With decreasing the Si concentration from 0.4 to 0.01 mass%, formation of thin Si and Mn layer was observed inside the FeCr alloy. Oxide scale growth rate constants decreased by lowering the Si concentration in FeCr alloy from 4.2 × 10−18 to 2.1 × 10−18 m2 s−1 at 1073 K. Diffusivity of Fe and Cr was changed by the concentration of Si in FeCr alloy, which affects the growth rates of oxide scale. The electrical conductivity of oxidized Fe-Cr alloy shows almost same level regardless the Si concentration (in the orders of 10 S cm−2 at 1073 K).