Mechanism And Process Parameter Optimization Of Cu And Y Doped Co-Mn Spinel Coating Prepared By Composite Electrodeposition-thermal Conversion On Ferritic Stainless Steel Surfac

With the transition of the working temperature of solid oxide fuel cell（SOFC）to medium low temperature（600℃-800℃）,ferritic stainless steel（FSS）has become one of the ideal materials for SOFC interconnector.It has a broad application prospect and attracted much attention.Because SOFC needs to work in high-temperature environment,severe oxidation and corrosion,as well as volatilization of Cr of the interconnector substrate will occur,resulting in the decrease of the cathode activity and the efficiency of battery.According to the above challenges,a composite electrodeposition-thermal conversion method to prepare Cu and Y doped Co-Mn spinel coatings on SUS430 ferritic stainless steel surface has been proposed to enhance the antioxidant ability of the connector,slow down the generation of Cr compounds on the substrate surface and improve the conductivity.Thus,to provide an effective method for the preparation of high-quality and low-cost protective coatings on the surface of FSS interconnectors and to promote the opalization and application of SOFC.Under the support of the project of National Natural Science Foundation of China,a kind of Cu and Y doped Co-Mn（MCO-Cu-Y）composite precursor coating was prepared on the surface of SUS430 using a composite electrodeposition method.It was then converted into a dense spinel structure through a reasonable heat treatment process.The properties of the coating were tested and analyzed using scanning electron microscopy（SEM）,energy dispersive spectrometer（EDS）,diffraction of x-rays（XRD）,oxidation weight gain rate and area specific resistance（ASR）measurements.The main research contents and conclusions are as follows:（1）The composite electrodeposition method preparing MCO-Cu-Y precursor coating was studied.Optimized process parameters and material ratio has been obtained through multiple factor orthogonal experiments:the stirring rate was 600 rpm,p H value was 5,current density was 45 m A/cm²,electrodeposition time was 15 minutes,Mn₃O₄addition was 160 g/L,Cu O addition was 20 g/L and Y₂O₃addition was 10 g/L.The influence mechanisms of process parameters and materials on the coating has also been clarified.（2）The thermal conversion process and element interface diffusion behavior of the composite precursor coating towards spinel structure were analyzed.The influences of heating rate,heating temperature,holding time on the morphology and stability of the spinel structure were clarified.After heated at a constant rate of 1℃/min to 800℃and holding for 60 minutes,a completely converted Cr resistant spinel coating with flat surface has been obtained.Delamination and cracking phenomenon have not been found on the spinel coating.The surface grains have been refined by doping of Y,and the interfacial adhesion has been enhanced.（3）The high-temperature oxidation resistance and conductivity of MCO-Cu-Y spinel coating were measured and analyzed.After 500 hours of oxidation at 800℃,the coating thickness was about 24μm.The oxidation rate constant was 1.90×10^-14g²cm^-4·s^-1,the ASR was 17.58 m?·cm²,and the oxidation resistance and conductivity of the sample was significantly better than the bare substrates.By doping of Cu,the density has been improved,the ASR and the oxidation speed of the substrate has been decreased and the cohesion between the coating and the substrate has also been obviously improved.