Growth Mechanisms and Electrical Conductivity of Oxide Scales on Ferritic Steels Proposed as Interconnect Materials for SOFC's

Abstract

Abstract The oxidation behaviour of two ferritic steel variants was studied at 800 °C in air and the results were compared with data obtained for two Cr‐based materials. The mechanisms of scale formation were investigated for oxidation times ranging from a few minutes up to 6,000 hours. A number of conventional analysis techniques such as optical metallography, scanning electron microscopy, and X‐ray diffraction were used for scale characterization, in combination with two‐stage oxidation studies using an 18 O‐tracer. It was found that the growth rates of the scales on the two steels were not only governed by the main scale forming alloying elements, Cr and Mn, but to a substantial extent by minor additions of Si and Al. At the test temperature of 800 °C these latter elements affect scale formation, although they are not directly incorporated in the surface scales. Independent of a detailed alloy composition, the conductivities of the scales on the ferritic steels were found to be higher than those of the surface scales formed on the Cr‐based materials studied.