Oxidation resistance of novel ferritic stainless steels alloyed with titanium for SOFC interconnect applications

Abstract

Chromia (Cr 2O 3) forming ferritic stainless steels are being developed for interconnect application in Solid Oxide Fuel Cells (SOFC). A problem with these alloys is that in the SOFC environment chrome in the surface oxide can evaporate and deposit on the electrochemically active sites within the fuel cell. This poisons and degrades the performance of the fuel cell. The development of steels that can form conductive outer protective oxide layers other than Cr 2O 3 or (CrMn) 3O 4 such as TiO 2 may be attractive for SOFC application. This study was undertaken to assess the oxidation behavior of ferritic stainless steel containing 1 weight percent (wt.%) Ti, in an effort to develop alloys that form protective outer TiO 2 scales. The effect of Cr content (6–22 wt.%) and the application of a Ce-based surface treatment on the oxidation behavior (at 800 °C in air + 3% H 2O) of the alloys was investigated. The alloys themselves failed to form an outer TiO 2 scale even though the large negative Δ G of this compound favors its formation over other species. It was found that in conjunction with the Ce-surface treatment, a continuous outer TiO 2 oxide layer could be formed on the alloys, and in fact the alloy with 12 wt.% Cr behaved in an identical manner as the alloy with 22 wt.% Cr.