Protective coating on stainless steel interconnect for SOFCs: oxidation kinetics and electrical properties

An effective, dense and well adherent coating was produced on 430SS that has the result of significantly reducing the oxidation rate of this alloy at elevated temperatures. The coating is essentially a Mn-Co-O spinel, applied in powder form, and compacted to improve its green density. A simplified model is presented that allows an assessment of the effects of the contact and scale geometries. For 850degreesC, an area specific resistance (ASR) can be predicted of approximately 0.5 Omega cm(2), after 50,000 It in air, taking into account a factor of 10 penalty for unfavorable contact geometries. The effect of the densified Mn-Co spinel coating is to reduce significantly Cr2O3 sub-scale formation, lower the thermal expansion mismatch, and increase the electronic conductivity of the scale. The findings point to several potential remedies for achieving coatings on 430SS that allow for metal interconnects with a service life of 50,000 It or more. When additionally taking the possibly unfavorable effects of electrodes contact geometries into account, such service life is unlikely to be possible above operating temperatures of about 700degreesC, unless highly specialized alloys are used, with potential processing and cost penalties. (C) 2004 Elsevier B.V. All rights reserved.