Study On Oxidation Resistance,Electrical Conductivity Of Interconnects For Medium And Low Temperature Solid Oxide Fuel Cell

The ferritic stainless steel materials are widely used in medium and low temperature Solid Oxide Fuel Cell?SOFC?interconnects due to excellent properites,such as thermal expansion matching with the components,low cost,flexible process,good corrosion resistance,and thermochemical stability.However,they also have some drawbacks,obviously insufficient of the mechanical strength,the low electrical conductivity of oxides,Cr vaporation and poisoning,etc.,which all limit interconnects long-term application.In order to improve the properties of ferritic alloys,some Fe-Cr alloys with trace amounts of reactive elements have been developed in recent years,Croffer 22H,ZMG232J3 alloys for example.These ferritic alloys will gradually replace the common Fe-Cr alloys and become the mainstream in medium and low temperature interconnecs.It is necessary to research these materials and related scientific issues.In this paper,the oxidation resistance and electrical conductivity of different ferritic alloys as well as alloy/coating system at medium and high temperature have been investigated to solve this problem.New Fe-Cr alloy ZMG232L as well as traditional SUS430L were cyclically oxidized in air at 800°C to study the change of oxidation weight gain after long-term cyclic oxidation;the evolution of surface morphologies and microstructures after 100h,500h and 1000h were observed to study high-temperature oxidation behavior;the electroconductive properties of two samples were analyzed.And in order to further improve the oxidation resistance of the ferritic alloys,the coating technique was applied to two Fe-Cr alloys,and the corresponding oxidation resistance and electroconductive properties of two samples are also observed after long-term cyclic oxidation.The results of two bare samples show that the ZMG232L ferritic alloy has significantly better oxidation resistance than the SUS430L.After heating at 800°C for 1000h,the oxidation weight gain of ZMG232L was 1.11 mg²·cm^-4 and SUS430L was 9.38 mg²·cm^-4.The formed oxide scale of the former one was mainly MnCr₂O₄ spinel with a small amount of Cr₂O₃ oxide,while the latter was mainly Cr₂O₃ accompanied by a small amount of MnCr₂O₄ spinel.The difference in oxidation behavior also affects the difference in electrical conductivity,Mn-Cr spinel can increase more the activation energy of the sample than Cr₂O₃.The results obtained about surface coating samples indicted that the coating can significantly improve the oxidation resistance and electrical conductivity of Fe-Cr alloys.The oxidation weight gain of ZMG232L and SUS430L alloys with coating was 0.013 mg²·cm^-4 and0.588 mg²·cm^-4 after oxided for 1000h.Compared with the bare samples,the weight gain was much lower.The interface of the two coating samples will react and diffuse and simultaneously contains Mn,Co,and Cr,and a small amount of Cr enrichment between the alloy and the coating.However,XRD analysis show that there was no diffraction peak of Cr₂O₃ on the coating surface,implying that the outward diffusion of Cr was inhibited by the coating.Furthermore,it was found to be superior to the uncoated samples in the electrical conductivity,and the activation energy was related to the interface layer between the coating and the alloys.