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Research Papers

Investigation of Chromium Vaporization From Interconnector Steels With Spinel Coatings

[+] Author and Article Information
R. Trebbels1

Forschungszentrum Jülich, Jülich 52425, Germanyr.trebbels@fz-juelich.de

T. Markus, L. Singheiser

Forschungszentrum Jülich, Jülich 52425, Germany

1

Corresponding author.

J. Fuel Cell Sci. Technol 7(1), 011013 (Nov 10, 2009) (6 pages) doi:10.1115/1.3117607 History: Received September 13, 2007; Revised August 11, 2008; Published November 10, 2009; Online November 10, 2009

Abstract

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, 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, 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, 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.

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Figures

Figure 1

Geometry of the samples used in the transpiration experiments

Figure 2

Schematic of the experimental apparatus for measurements according to the transpiration method

Figure 3

Cr vaporization rates of coated Crofer22APU (MCF) with polished and sand blasted surfaces at 800°C in air with a humidity of 1.90%, in comparison to an uncoated Crofer22APU. The coated samples were preoxidized in air at 1050°C for 10 h.

Figure 4

SEM micrograph (bse mode) of the samples (Crofer22APU+MCF) after 1100 h at 800°C. (a) and (b) show the sand blasted sample, and (c) and (d) show the polished sample in two different resolutions.

Figure 5

Exemplary detection of the sample roughness. (a) shows the polished sample and (b) shows the sand blasted one. Ra is the average roughness of the surface.

Figure 6

Cr vaporization rates of coated Crofer22APU (MCF and LCC10) at 800°C in air with a humidity of 1.90%, in comparison to uncoated Crofer22APU. The coated samples were preoxidized in air at 950°C and 1050°C for 10 h.

Figure 7

SEM micrograph (bse mode) of the samples (Crofer 22APU+MCF+LCC10) after 1100 h at 800°C. (a) and (b) show the preoxidized sample at 950°C, and (c) and (d) the preoxidized sample at 1050°C in two different resolutions.

Figure 8

Cr vaporization rates of coated Crofer22APU (MCF and LCC10) at 800°C in air with a humidity of 1.90% in comparison to uncoated Crofer22APU (MCF). The coated samples were preoxidized in air at 1050°C for 10 h.

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