A comparison of two aluminizing methods for corrosion protection in the wet seal of molten carbonate fuel cells
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A comparison of two aluminizing methods for corrosion protection in the wet seal of molten carbonate fuel cells J. Ernesto Indacochea, Ira Bloom,a) and Michael Krumpelt Electrochemical Technology Program, Argonne National Laboratory, Argonne, Illinois 60439
Thomas G. Benjamin M-C Power Corporation, Burr Ridge, Illinois 60521 (Received 10 February 1997; accepted 8 December 1997)
The corrosion behavior of aluminized Type 310S stainless steel (SS) in the wet seal of molten carbonate fuel cells was investigated. Coupons of Type 310S SS were aluminized by two different aluminizing methods: thermal spray and slurry-coating. In both types of samples Fe and Cr diffused readily into the Al layer at 650 ±C. At first this interdiffusion is limited to the interfacial area. With time, Fe and Cr aluminides precipitate in the Al layer. The slurry-coated layer contains a higher concentration of FeAl and Fe3 Al than does the thermal spray layer. Consequently, the slurry-coated layer also displays a greater degree of corrosion than the thermal spray layer.
I. INTRODUCTION
The conventional molten carbonate fuel cell (MCFC) consists of a porous, lithiated NiO cathode, a molten (Li, K)2 CO3 1 LiAlO2 electrolyte matrix, and a porous Ni anode. A portion of the electrolyte extends beyond the electrode area and forms a wet seal against the stainless steel (SS) cell housing. On the fuel side of the MCFC, the wet-seal area is exposed to highand low-oxygen partial pressures simultaneously. Thus, one or more galvanic cells can form, leading to severe corrosion.1–5 In turn, the corrosion leads to deterioration and to decline of cell performance. Although wet-seal corrosion and its prevention have received some attention in the electrochemical literature,5 no systematic study regarding the corrosion mechanism has been reported. The corrosion rate varies in different areas of the wet seal. Donado et al.6 calculated the thermodynamics of possible corrosion cells in the wet-seal area and reported corrosion rates under conditions simulating those found in a fuel cell. They observed much greater corrosion in the anode wet seal than in the cathode wet seal. For Type 316 SS, the corrosion rates in a cell under load were greater by two orders of magnitude than those found at open circuit. They concluded that the corrosion rates for the anode side of the wet seal are prohibitive, both at open circuit and under load. Only aluminum and aluminum-containing alloys have been reported to have sufficient corrosion resistance for use in the wet seal.6,7 Aluminizing the wet-seal surfaces increases their corrosion resistance by increasing the surface aluminum content.8,9 The corrosion resistance a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 7, Jul 1998
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of coated alloys improves with increasing the thickness of the coating; however, the mechanical properties of the coated alloy may then deteriorate.10 Various coating
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