Preparation And Properties Of Co-Mn Spinel Coating On Ferritic Stainless Steel SUS 430

Due to the limitation of LT-SOFC's working environment,ferritic stainless steel interconnects are troubled by problems such as high temperature oxidation,oxide layer breaking off and cathode Cr poisoning.Researchers often prepare protective coatings on the surface of interconnects to solve these problems.Co-Mn₂O₃,Co-Mn₃O₄ and Y doped Co-Mn₃O₄(YCMO)coatings have been prepared by composite electrodeposition on the surface of ferritic stainless steel SUS 430.The parameter optimization of the coating preparation process,the research of coating performance and the doping optimization of coating are systematically studied.Through the experimental research,the final conclusions include:(1)The process parameters of Co-Mn coating prepared by composite electrodeposition were optimized.When Mn oxide was selected as Mn₂O₃,the optimal process parameters were p H=5,?(Mn)=120g/l,and the maximum Mn content in the coating was 0.5%.The optimum process parameters for taking Mn₃O₄ were p H=5,concentration of Mn oxide particle?(Mn)=160g/l,and the maximum Mn content in the coating was 10.98%.(2)After high temperature oxidation,the coating is converted into composite spinel coating,which is composed mainly of MnCo₂O₄ and Co₃O₄spinel.And a double-layer structure consisting of Cr₂O₃ layer and Co-Mn composite spinel layer is formed on the surface of the substrate.It was found that the Cr₂O₃ layer grows preferentially along the[110]direction.But the first-principles calculation result shows that the diffusion barrier of Cr atom is only 1.03e V,so the outer diffusion of Cr atom cannot be effectively inhibited by the layer of Cr₂O₃.In the process of high temperature oxidation,Cr,Mn and Fe elements in the substrate will diffuse outwardly.The preparation of coating effectively inhibits the further diffusion of Fe and Cr elements.(3)The increase of Mn content in the coating is beneficial to improve the high temperature oxidation resistance of the coating,and the oxidation rate of the coating decreases with the increase of oxidation time.After the same time of high temperature oxidation,the oxidation rate constant of Co-Mn₃O₄ coating is reduced by 56%,compared with Co-Mn₂O₃ coating.(4)The increase of Mn content in the coating can lead to the formation of a certain amount of Co Mn₂O₄ spinel during oxidation and sintering,and with the increase of oxidation time,the spinel will further transform into the phase of MnCo₂O₄ spinel,which will affect the electrical conductivity of the coating.The preparation of the coating can effectively reduce the area specific resistance(ASR)of SUS 430 matrix,the Co-Mn₂O₃ coating can reduce about 52%,and the Co-Mn₃O₄ coating can reduce about 43%.(5)Compared with Co-Mn₂O₃ coating,Co-Mn₃O₄ coating has better comprehensive performance,but its electrical conductivity is a little inadequate.In this paper,the performance of Co-Mn₃O₄ coating was improved by doping Y in the coating.It was found that the doping of Y can improve the adhesion and compactness of Cr oxide layer,and prevent the diffusion of Fe and Mn in the matrix,thus reducing the generation of Co Mn₂O₄,and effectively improving the high temperature conductivity of the coating.The problem of insufficient high temperature conductivity of Co-Mn₃O₄ coating was solved.