Effects of Plasma-Sprayed La0.7Sr0.3MnO3 Coating on Thermally Grown Oxide Scale and Electrical Conductivity of Fe-Cr Interconnect for SOFCs

Abstract

A perovskite La0.7Sr0.3MnO3 (LSM) coating was deposited by atmospheric plasma spraying in order to improve the oxidation resistance and the area specific resistance (ASR) of ferritic stainless steel (SS430). The plasma-sprayed LSM coating using a small-sized feedstock powder had a low porosity of 1.0 area% and a high electrical conductivity of 148 S/cm at 800°C. The pristine SS430 suffered from a significant oxidation at 800°C in air, and formed a thick thermally grown oxide scale consisting of SiO2, FeCr2O4, Cr2O3 and MnCr2O4. The oxide scale for the SS430 had a relatively low electrical conductivity of ∼3 × 10−3 S/cm, and therefore the ASR for the oxidized SS430 rapidly increased with oxidation time. The protective LSM coating effectively retarded the growth rate of oxide scale beneath the coating by reducing oxygen inward diffusion. Furthermore, a long-term thermal exposure promoted the formation of duplex Cr2O3-(Mn,Cr)3O4 scale whose conductivity was estimated to be ∼10−2 S/cm. The growth rate of the duplex Cr2O3-(Mn,Cr)3O4 scale in the LSM coated SS430 followed a sub-parabolic law which represented a slow growth rate. The corresponding ASR for the LSM coated SS430 was limited to only ∼10 mΩ·cm2 after oxidation at 800°C for 1200 h.