Chromium volatility of coated and uncoated steel interconnects for SOFCs

Collins, C.; Lucas, J.; Buchanan, T.L.; Kopczyk, M.; Kayani, A.; Gannon, Paul; Deibert, Max C.; Smith, Richard J.; Choi, Deuk-Soo; Gorokhovsky, V.

doi:10.1016/j.surfcoat.2006.08.053

Cited by 80 publications

(45 citation statements)

References 9 publications

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“…The amount of chromium volatilization, and thus the associated cell poisoning, can be minimized by applying a ceramic coating to the alloy surface. One promising coating material system is the spinel (Mn,Co) 3 O 4 [1-4], which has been shown to reduce chromium volatilization [5,6].Although chromium can form a spinel phase with other transition metals, chromium has not been observed in the coating during use in a SOFC [7,8]. However, with time, interaction of the coating with the chromia scale or with other SOFC components can lead to changes in the coating composition, which can affect properties and thus performance.…”

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confidence: 99%

Effect of SOFC Interconnect-Coating Interactions on Coating Properties and Performance

Fergus¹

2012

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The high operating temperature of solid oxide fuel cells (SOFCs) provides good fuel flexibility which expands potential applications, but also creates materials challenges. One such challenge is the interconnect material, which was the focus of this project. In particular, the objective of the project was to understand the interaction between the interconnect alloy and ceramic coatings which are needed to minimize chromium volatilization and the associated chromium poisoning of the SOFC cathode.This project focused on coatings based on manganese cobalt oxide spinel phases (Mn,Co) 3 O 4 , which have been shown to be effective as coatings for ferritic stainless steel alloys. Analysis of diffusion couples was used to develop a model to describe the interaction between (Mn,Co) 3 O 4 and Cr 2 O 3 in which a two-layer reaction zone is formed. Both layers form the spinel structure, but the concentration gradients at the interface appear like a two-phase boundary suggesting that a miscibility gap is present in the spinel solid solution. A high-chromium spinel layer forms in contact with Cr 2 O 3 and grows by diffusion of manganese and cobalt from the coating material to the Cr 2 O 3 . The effect of coating composition, including the addition of dopants, was evaluated and indicated that the reaction rate could be decreased with additions of iron, titanium, nickel and copper.Diffusion couples using stainless steel alloys (which form a chromia scale) had some similarities and some differences as compared to those with Cr 2 O 3 . The most notable difference was that the highchromium spinel layer did not form in the diffusion couples with stainless steel alloys. This difference can be explained using the reaction model developed in this project. In particular, the chromia scale grows at the expense of the alloy, the high-chromia layer grows at the expense of chromia scale and the high-chromia layer is consumed by diffusion of chromium into the coating material. If the last process (dissolution of high-chromium spinel phase) is faster than the second process (formation of highchromium spinel phase), the high-chromium layer may be consumed. The other important result of this mechanism is that it could result in a constant scale thickness if the scale forms at the same rate as it is consumed. This helps to explain the unexpected observation that the area specific resistance (ASR) of a SOFC with a (Mn,Co) 3 O 4 -coated ferritic stainless steel cathode becomes constant after long exposures.The project also evaluated the possibility of reducing the chromium content in a stainless steel alloy using experimental alloys. The conclusion of this evaluation is that at least 17-18% chromium is needed for good oxidation resistance is needed even if the alloy is coated with a spinel coating.Additional details on these findings are provided in a later section of this report and in the publications listed below. Submitted in Near FutureGOALI project with NexTech Materials on SOFC coating materials, National Science Foundation, ~$300,000, 10...

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confidence: 99%

Effect of SOFC Interconnect-Coating Interactions on Coating Properties and Performance

Fergus¹

2012

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“…Redistribution subject to ECS terms of use (see 66.108.234. 21 Downloaded on 2019-03-28 to IP Figure 10. Sequence of steps illustrating the formation of Cr 2 O 3 on aluminosilicate fibers.…”

Section: Resultsmentioning

confidence: 99%

XPS Characterization of Aluminosilicate Fibers Post Interaction with Chromium Oxyhydroxide at 100–230°C

Tatar¹,

Gannon²,

Swain³

et al. 2018

J. Electrochem. Soc.

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Chromium containing materials, e.g. stainless steels, are commonly used in high temperature (>500 • C) applications such as solid oxide fuel cell (SOFC) stacks, combustion exhaust systems, and in various chemical process equipment. At these temperatures and in oxidizing atmospheres, chromium oxide (chromia) surface layers form and grow, effectively protecting the underlying alloy. Also known to form under these conditions, however, are volatile chromium species such as CrO 2 (OH) 2 and CrO 3 . Formation of these volatile species may have detrimental effects not only on the source material, but also on surrounding materials in the system which may interact with these species. To better understand how volatile chromium species interact with materials, volatile chromium species were generated from ferritic stainless steel (FSS) T409 at 700 • C and directed into aluminosilicate fibers at 100-230 • C for 150 hours. Post exposure fibers were noted to possess yellow, brown, and/or green stained regions which were isolated and characterized using X-ray photoelectron spectroscopy (XPS). Examination of Cr 2p 3/2 peaks revealed varied Cr(VI) content and Cr(III) multiplet-split components for different discolored regions. Possible explanations for differences in chromium content by discoloration color are discussed. The volatilization of chromium species from chromium containing materials is a well-documented phenomenon which holds consequences for SOFCs, human health, and the environment. Using chromia as an example for a source, in the presence of oxygen and absence of water vapor, the dominant volatilization pathway proceeds according to Reaction 1.If, however, water vapor is present in addition to oxygen, then the dominant volatilization pathway proceeds according to Reaction 2. 1-7The generation of these gas/vapor species is well understood, but the same cannot be said of how they interact with (e.g. condense onto) other materials. This is of great importance for human health and the environment considering that chromium species may take toxic forms (hexavalent) or non-toxic forms (trivalent). This relative dearth of understanding also holds negative implications for SOFCs, and so many investigative efforts have been undertaken to understand how CrO 2 (OH) 2 interacts with ceramic components in SOFCs. Electrochemical reduction of CrO 2 (OH) 2 has often been observed to occur at the triple phase boundary (TPB), where cathode, electrolyte, and gas phase meet. [8][9][10] This electrochemical reaction is not limited to the TPB, however, and can occur away from the TPB given: the formation of a continuous chromia layer for hole transport, a mixed conducting electrolyte, or a mixed conducting cathode. 8 While there is evidence for preferential electrochemical reduction of CrO 2 (OH) 2 , 11,12 open circuit chemical reactions have also been observed with cathodes containing Mn or Sr. 13 It should be noted that Cr transport to lanthanum strontium manganite (LSM) was observed via solid state diffusion, whereas vapor deposition o...

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“…The extensive oxide losses from the surface or oxide spalling has become a serious challenge that leading to serious deterioration of the cell performance [4]. Application of two classes of technology can be used to reduce the growth rate of the oxide scale [5]. The first is to develop new alloys and the other is to conduct surface modifications.…”

Section: Introductionmentioning

confidence: 99%

Effect of Nanocrystalline and Ti Implantation on the Oxidation Behaviour of Fe<sub>80</sub>Cr<sub>20 </sub>Alloy and Commercial Ferritic Steel

Sebayang

Khaerudini

Saryanto

et al. 2011

KEM

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Abstract. The oxidation behaviour of developed Fe 80 Cr 20 alloy and commercial ferritic steel at 1173 -1373 K in air is studied. Effects of crystallite size and titanium implantation on the oxidation behaviour of specimens were analyzed based on oxide morphologies and microstructures. Oxide scales characterisations of specimen after oxidized were identified by X-ray diffraction (XRD). The surface morphology of oxide scales were examined with scanning electronic microscope (SEM) and energy dispersive X-ray analysis (EDX). The rate constant of oxidation were determined using Wagner method. The results show that crystallite size and titanium implantation has remarkably enhanced the oxidation resistance. The oxidation kinetics indicate that the developed Fe 80 Cr 20 as the finer crystallite size both unimplanted and implanted specimens show better performance.

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Chromium volatility of coated and uncoated steel interconnects for SOFCs

Cited by 80 publications

References 9 publications

Effect of SOFC Interconnect-Coating Interactions on Coating Properties and Performance

Effect of SOFC Interconnect-Coating Interactions on Coating Properties and Performance

XPS Characterization of Aluminosilicate Fibers Post Interaction with Chromium Oxyhydroxide at 100–230°C

Effect of Nanocrystalline and Ti Implantation on the Oxidation Behaviour of Fe<sub>80</sub>Cr<sub>20 </sub>Alloy and Commercial Ferritic Steel

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