Diffusion of oxygen in the scales of Fe–Cr alloy interconnects and oxide coating layer for solid oxide fuel cells

Oxygen diffusivity was examined in the oxide scales formed on Fe–Cr alloy surface and Mn–Co spinel coating layer. The stable isotope oxygen (18O2) was adopted to visualize the diffusion profiles of oxygen in the oxide scales and coating layer. A relatively fast diffusivity of 18O was observed (diffusion coefficients were 10− 12 cm2 s− 1 orders of magnitude at 1073 K) in the oxide scale. MnCo2O4 spinel coating was examined on the Fe–Cr alloy surface to clarify the 18O diffusion in the coating oxide layer. Two drops of 18O diffusion profiles were observed in the MnCo2O4 spinel coating layer; first one was at surface region and second was MnCo2O4 spinel coating/alloy interface. Relatively fast 18O diffusion coefficients were observed on the Mn–Co spinel surface (the diffusivities of 18O were 10− 13–10− 12 cm2 s− 1 at 1073 K). A significant fast diffusivity of 18O was observed in the middle of the MnCo2O4 spinel coating. The second drop of 18O concentration can be related to the existence of Cr around the MnCo2O4 spinel coating/alloy interfaces. The growth rate of oxide scale was controlled by the existence of Cr around the oxide scale/alloy or oxide coating/alloy interfaces.