EFFECT OF LaCoO 3 COATING ON THE INTERMEDIATE TEMPERATURE OXIDATION BEHAVIOR OF SUS 430 METALLIC INTERCONNECT

Low costly ferritic stainless steels,especially the Cr_2O_3-forming alloys,are promising interconnect materials for solid oxide fuel cells(SOFCs) due to their thermal expansion compatibility with other cell components.However,the oxidation resistance of commercial ferritic stainless steels in the operating temperature range of 600—800℃is not adequate,forming relatively thick,poorly conducting oxide scale on the surface of the stainless steel interconnect and decreasing the cell performance. Surface modification is necessary to improve the oxidation behavior and electrical property. The present study investigates the effect of a LaCoO_3 protective coating by the sol-gel process on the intermediate temperature oxidation behavior of SUS 430 alloy,which is frequently considered as the interconnect material for SOFCs.X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were used to characterize the phase structure,surface morphology and composition of the coating and the oxide scale.The"4-probe"method was employed to determine the area specific resistance(ASR) of the surface oxides.Long-term thermally cyclic oxidation at 750℃in air has shown that the oxidation kinetics obeys the parabolic rule with a rate constant of K=4.18×10~(-15) g~2/(cm~4·s),which is 1—2 orders of magnitude lower than that of the uncoated alloy,the LaCoO_3 protective coating effectively suppresses the formation of Cr_2O_3 and slows down the growth of MnCr_2O_4 spinel.As a result,the oxidation resistance and electrical conductivity of the coated SUS 430 alloy are significantly enhanced,resulting in an ASR at 750℃of only 3.13 mΩ·cm~2 after oxidation at 750℃for 850 h in air and an extrapolated ASR of 21.5 mΩ·cm~2 for 4×10~4 h oxidation.