| Due to their high efficiency and cleanliness, solid oxide fuel cells(SOFCs) have been the focus of intensive research for targeted applications as primary power source for distributed residences, as well as auxiliary power unit for vehicles. As one of the critical components in SOFCs, the interconnectors transport the electronic current between the individual cells and separate the anode and cathode gases. The decrease of the operation temperature of SOFCs enables ceramic oxide interconnectors to be replaced by heat-resistant alloys, which decreases the fabrication cost of SOFCs. Iron-based alloys are favored as interconnector materials owing to their moderate thermal expansion, high ductility, good workability and low cost. In this paper, the oxidation and electric conductivity of Fe-Cr heat-resistant alloys were investigated. The results were obtained as follows:1. Two different contents of chromium commercial SUS430 Fe-based alloys were compared. The chromium contents of two alloys were 13wt％and 16 wt％respectively. The oxidation resistance of SUS430-16wt％Cr alloy was better than that of SUS430-13wt％Cr alloy. According to the XRD, thermodynamics and oxidation analysis, the primary product of oxidation was Cr2O3 and the minor form was Mn1+δCr2-δO4-λ. The oxidation temperature characteristic between 750℃and 850℃was tested. The oxidation characteristic was affected obviously by temperature. The weight gain rate between 750℃and 800℃was lower than that between 800℃and 850℃. The activation energy between 750℃and 800℃of SUS430-13wt％Cr alloy was about 320kJ/mol. The area specific resistance (ASR) of oxide scale of SUS430-16wt％Cr was tested, which didn't meet the requirement of interconnector.2. In this paper, series of Fe-21Cr-RE (RE represents rare earth) alloys were designed. The oxidation and electrical conductivity of Fe-21Cr-RE alloys were examined. The oxidation resistances of Fe-21Cr-RE alloys were better than SUS430-16wt％Cr alloy. Cr2O3 scales were formed during oxidation on the surface of all the alloys. The oxidation rates of Fe-21Cr-RE alloys were lower than that of Fe-21Cr binary alloy, while the oxide scales of Fe-21Cr-RE alloys were thinner. The segregation of La, Ce, Gd to the oxide grain boundaries greatly retards the transport of Cr outward, so the transport rate of Cr is lower than that of O2. The transport of O2 inward became dominant in the oxide kinetics. In the series of Fe-21Cr-RE alloys, the oxidation resistances of the Fe-21Cr-Gd alloys were slightly better than that of the other two series of alloys due to the closer affinity to the oxygen. The relative decrease of temperature made the notable improvement of oxidation resistance, which showed the Fe-21Cr-Gd alloys could meet the requirement of oxidation resistance with the decrease of the operation temperature of SOFCs though the ASR was great.3. Idea gave birth to that the oxides with high electrical conductivity were grown in situ. The series of Fe-Cr-Gd-Mn-Co alloys were designed by theory analysis. The oxides grown in situ showed higher electrical conductivity than other alloys that we studied in this paper, but the oxidation is linear. The idea that the oxides with high electrical conductivity were grown in situ wasn't mature. The oxidation of the alloys followed the thermodynamic rule according to the calculation of the standard free energies of the formation of the oxides and the equilibrium oxygen pressure Po2. When the alloy contained Mn, the Mn-Cr oxide rather than Mn-Co oxide was formed preferentially during oxidation. When the alloy didn't contain Mn, the Cr oxide rather than Cr-Co or Co oxide was formed preferentially during oxidation.4. The MnCo2O4 spinel and La0.5Sr0.5CoO3 perovskite oxides were prepared by sol-gel method. The electrical conductivity of MnCo2O4 spinel and La0.5Sr0.5CoO3 perovskite oxides were all better than the doped La0.8Sr0.2CrO3 oxide. At 800℃, the electrical resistance rate of La0.8Sr0.2CrO3 oxide is 0.1Ωcm, and that of MnCo2O4 is 0.017Ωcm and La0.5 Sr0.5 CoO3 only 0.004Ωcm. Amorphous coatings appeared after La0.5Sr0.5CoO3 and MnCo2O4 were magnetic-sputtered on the Fe-21Cr-0.3Gd alloy substrate. The La0.5Sr0.5CoO3 and MnCo2O4 coatings were formed separately after crystallized treatment. The ASR of the sample coated La0.5Sr0.5CoO3 was 6mΩ.cm2 after oxidation for 100h, and that of the sample coated with MnCo2O4 was 100mΩ.cm2 after oxidation for 50h at 800℃. The study of the sample coated with La0.5Sr0.5CoO3 showed the ions transport rapidly during oxidation. The elements Cr and Mn in substrate diffused outward and reacted with La0.5Sr0.5CoO3 coating. Simultaneously, the element Co in the coating diffused inward and part of La and Sr diffused inward.
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