Alloys with thermal expansion matching to electrolyte materials for solid oxide fuel cells

The thermal expansion of the Fe-(30–40) wt.% Ni-(20–30) wt.% Co-(6–10) wt.% Cr alloys matches closely with yttria-stabilized zirconia, often used as electrolyte in solid oxide fuel cells. At the best fit, the difference in the thermal expansion coefficients does not exceed 0.7·10 K in the range from room temperature to ~500°C. Significant mismatch begins above 600°C, but the internal stresses this mismatch might cause in the metallic component of the metal/ceramics junctions remain significantly below the yield strength up to the temperatures exceeding the starting temperature of relaxation processes by ~180–240°C. The above alloys are phase stable so that no phase transformations are expected at the cell operating temperatures. Their resistance to corrosion attacks in cathodic and anodic environments is comparable to ferritic steels containing 25–30% chromium. The transfer of chromium from the alloys containing 34% Ni, 30% Co and 6–14% Cr into the La Sr MnO cathode material occurs after 400–600 h heating at 900°C. Chromium penetrated to a depth of 20 μm at most.