It is promising for metal especially ferritic stainless steel(FSS)to be used as interconnector when the solid oxide fuel cell(SOFC)is operated at temperature lower than 800°C.However,there are many challenges for FSS such as anti-oxidant,poisoning to cathode and high area specific resistance(ASR)when using as SOFC interconnector.The effect of Cr content(12-30 mass%)in Fe-Cr alloys on thermal expansion coefficient(TEC),oxidation resistance,microstructure of oxidation scale and ASR was investigated by thermo-gravimetry,scanning electron microscopy,energy dispersive spectroscopy and four-probe DC technique.The TEC of Fe-Cr alloys is(11-13)×10^(-6) K^(-1),which excellently matches with other SOFC components.Alloys have excellent oxidation resistance when Cr content exceeds 22mass% because of the formation of chromium on the surface of alloy.The oxidation rate constants kdand ksdecrease rapidly with increasing the Cr content and then increase slowly when the Cr content is higher than 22mass%.The kinetic results indicate that Cr evaporation must be considered at high temperature for Fe-Cr alloys.After the alloys were oxidized in air at 800°C for500 h,log(ASR/T)(Tis the absolute temperature)presents linear relationship with 1/T and the conduct activation energy is 0.6-0.8eV(Cr16-30).Optimal Cr content is 22-26mass%considering the oxidation resistance and ASR.
Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I(D)/I(G) of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.
