Investigation of Chromium Vaporization From Interconnector Steels With Spinel Coatings

The vaporization of Cr-rich volatile species from interconnector materials for high temperature solid oxide fuel cells (SOFCs) is considered to be a major source of degradation that limits the lifetime of planar SOFC systems (Fujita et al., 2004, “Prevention of SOFC Cathode Degradation in Contact With Cr-Containing Alloy,” J. Power Sources, 131(1–2), pp. 261–269; Hilpert, 1996, “Chromium Vapor Species Over Solid Oxide Fuel Cell Interconnect Materials and Their Potential for Degradation Processes,” J. Electrochem. Soc., 143(11), pp. 3642–3647; Kurukowa et al., 2007, “Chromium Vaporization of Bare and of Coated Iron-Chromium Coatings,” Solid State Ionics, 178, pp. 287–296; Quadakkers, Greiner, and Köck, 1994, “Metals and Alloys for High Temperature SOFC Application,” SOFC Forum, Lucern, Switzerland; Quadakkers et al., 1996, “The Chromium Base Metallic Bipolar Plate-Fabrication, Corrosion and Cr Evaporation,” European Oxide Fuel Cell Forum, Oslo, Norway; Yang, 2006, “Evaluation of Ni-Cr-Base Alloys for SOFC Interconnect Applications,” J. Power Sources, 160(2), pp. 1104–1110). For a longer lifetime of these systems, the Cr vaporization of the interconnector material shall be reduced (Collins, Lucas, and Buchanan, 2006, “Chromium Volatility of Coated and Uncoated Steel Interconnects for SOFCs,” Surf. Coat. Technol., 201(7), pp. 4467). The potential of reduction in the Cr vaporization using coatings with spinel layers is the subject of the present work. In this study the influence of processing parameters for Crofer22APU coated with a spinel based on $(Mn,Co,Fe)3O4$ on the Cr vaporization rates was studied at $800°C$ in air using the transpiration method. The measured Cr release of the coated samples was compared with an uncoated Crofer22APU. The aim of this work was to find the optimum conditions to prepare the spinel coating regarding to Cr vaporization. By using such a coating, the Cr vaporization rate was found to be two orders of magnitude lower than uncoated steel. The sintering temperature and pretreatment of the sample showed a high influence on the Cr release.