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

Oxide scale formations on Fe{single bond}Cr alloy interconnects were investigated in anode gas (mixtures of CH₄ and H₂O) atmospheres for solid oxide fuel cells. The silicon concentration in Fe{single bond}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{single bond}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 Fe{single bond}Cr alloy. Oxide scale growth rate constants decreased by lowering the Si concentration in Fe{single bond}Cr 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 Fe{single bond}Cr alloy, which affects the growth rates of oxide scale. The electrical conductivity of oxidized Fe{single bond}Cr alloy shows almost same level regardless the Si concentration (in the orders of 10 S cm^-2 at 1073 K).