Application of sol–gel technique to synthesis of copper–cobalt spinel on the ferritic stainless steel used for solid oxide fuel cell interconnects

• Cu–Co spinel layer was deposited on AISI 430 by sol–gel dip-coating process.
• CuCo2O4 coating greatly improves the oxidation resistance of AISI 430 alloy.
• CuCo2O4 layer has an acceptable conductivity and long-term stability during oxidation.
• Applied coating acted as an effective barrier to Cr outward diffusion.

The conductive CuCo2O4 spinel coating is applied on the surface of the AISI 430 ferritic stainless steel by the dip-coating sol–gel process and it is evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. The results show that the CuCO2O4 coating forms a double-layer scale consisting of a Cr, Fe-rich subscale and Cu–Co spinel top layer after 500 h in air at 800 °C. This scale is protective, acts as an effective barrier against Cr migration into the outer oxide layer and alleviates the cathode Cr-poisoning. The oxidation resistance is significantly enhanced by the protective coating with a parabolic rate constant of 5.8 × 10−13 gr2 cm−4 s−1, meanwhile the electrical conductivity is considerably improved due to inhibited growth of resistive Cr2O3 oxide scale. The area specific resistance at temperatures between 550 and 800 °C is in the range of 11.5 and 22.2 mΩ cm2.