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Title: Fabrication of (Mn,Co)3O4 Surface Coatings onto Alloy Substrates

Abstract

Ferritic stainless steels are promising candidates for IT-SOFC interconnect applications due to their low cost and resistance to oxidation at SOFC operating temperatures. However, several challenges remain, including long term electrical conductivity and surface stability under interconnect exposure conditions and chromia scale evaporation. One means of extending interconnect lifetime and improving performance is to apply a protective coating, such as (Mn,Co)3O4 spinel, to the cathode side of the interconnect. These coatings have proven effective in reducing scale growth kinetics and Cr volatility. This report describes several procedures developed at PNNL for fabricating (Mn,Co)3O4 spinel coatings onto ferritic stainless steels.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1031994
Report Number(s):
PNNL-16470
AA2530000; TRN: US201202%%115
DOE Contract Number:
AC05-76RL01830
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; 36 MATERIALS SCIENCE; ALLOYS; CATHODES; COATINGS; ELECTRIC CONDUCTIVITY; EVAPORATION; FABRICATION; KINETICS; LIFETIME; OXIDATION; PERFORMANCE; PROTECTIVE COATINGS; SOLID OXIDE FUEL CELLS; SPINELS; STABILITY; STAINLESS STEELS; SUBSTRATES; SURFACE COATING; VOLATILITY; solid oxide fuel cells; interconnects; coatings; spinel

Citation Formats

Yang, Zhenguo, Xia, Guanguang, Li, Xiaohong S., Singh, Prabhakar, and Stevenson, Jeffry W. Fabrication of (Mn,Co)3O4 Surface Coatings onto Alloy Substrates. United States: N. p., 2007. Web. doi:10.2172/1031994.
Yang, Zhenguo, Xia, Guanguang, Li, Xiaohong S., Singh, Prabhakar, & Stevenson, Jeffry W. Fabrication of (Mn,Co)3O4 Surface Coatings onto Alloy Substrates. United States. doi:10.2172/1031994.
Yang, Zhenguo, Xia, Guanguang, Li, Xiaohong S., Singh, Prabhakar, and Stevenson, Jeffry W. Mon . "Fabrication of (Mn,Co)3O4 Surface Coatings onto Alloy Substrates". United States. doi:10.2172/1031994. https://www.osti.gov/servlets/purl/1031994.
@article{osti_1031994,
title = {Fabrication of (Mn,Co)3O4 Surface Coatings onto Alloy Substrates},
author = {Yang, Zhenguo and Xia, Guanguang and Li, Xiaohong S. and Singh, Prabhakar and Stevenson, Jeffry W.},
abstractNote = {Ferritic stainless steels are promising candidates for IT-SOFC interconnect applications due to their low cost and resistance to oxidation at SOFC operating temperatures. However, several challenges remain, including long term electrical conductivity and surface stability under interconnect exposure conditions and chromia scale evaporation. One means of extending interconnect lifetime and improving performance is to apply a protective coating, such as (Mn,Co)3O4 spinel, to the cathode side of the interconnect. These coatings have proven effective in reducing scale growth kinetics and Cr volatility. This report describes several procedures developed at PNNL for fabricating (Mn,Co)3O4 spinel coatings onto ferritic stainless steels.},
doi = {10.2172/1031994},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Apr 30 00:00:00 EDT 2007},
month = {Mon Apr 30 00:00:00 EDT 2007}
}

Technical Report:

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  • A spinel-based surface protection layer has been developed for alloy SOFC current collectors and bi-polar gas separators. The (Mn,Co)3O4 spinel with a nominal composition of Mn1.5Co1.5O4 demonstrates an excellent electrical conductivity and thermal expansion match to ferritic stainless steel interconnects. A slurry-coating technique provides a viable approach for fabricating protective layers of the spinel onto the steel interconnects. Thermally grown protection layers of Mn1.5Co1.5O4 have been found not only to significantly decrease the contact resistance between a LSF cathode and stainless steel interconnect, but also inhibits the sub-scale growth on the stainless steel. The combination of the inhibited sub-scale growth,more » good thermal expansion matching between the spinel and the stainless steel, and the closed-pore structure contribute to the excellent structural and thermomechanical stability of these spinel protection layers, which was verified by a long-term thermal-cycling test. The spinel protection layers can also act effectively to prevent outward diffusion of chromium from the interconnect alloy, preventing subsequent chromium migration into the cathode and contact materials. PNNL is currently engaged in studies intended to optimize the composition, microstructure, and fabrication procedure for the spinel protection layers.« less
  • The paper reports the development of a coating approach that simultaneously achieves the advantages of conductive (Mn,Co)3O4 spinel coatings and of RE-surface treatment on alloys for SOFC interconnect applications,. This approach involves the modification of (Mn,Co)3O4 spinel coatings through addition of a rare earth to the spinel composition. In particular, Ce-modified spinel coatings (Ce0.05Mn1.475Co1.475O4) behaved similarly to unmodified Mn1.5Co1.5O4 spinel coatings by acting as a Cr-outward and O-inward diffusion barrier, thus improving the surface stability and electrical performance of ferritic stainless steel. In addition, the rare earth addition appeared to alter the scale growth beneath the coating, so that alloymore » samples with the Ce-modified spinel coating exhibited a stronger scale/metal interface compared to samples with the unmodified spinel coating. As a result, it is anticipated that, compared to unmodified spinel coatings, the rare earth modified coatings may lead to improved structural stability and electrical performance for ferritic stainless steel-based SOFC interconnects.« less
  • Styrene/acrylate copolymer coatings were electrophoretically deposited on four types of substrates. Processing characteristics were observed including cell voltage vs time for current densities of 0.05 to 4 mA/cm/sup 2/; polymer coating thickness vs cell voltage; and polymer coating thickness vs Coulombic consumption. Properties of the resultant polymer coatings were evaluated including breakdown voltage vs thickness; capacitance and dielectric constant; composition (from Fourier transform infrared spectroscopy); and morphology (from Scanning Electron Microscopy). Little polymeric coating deposition occurs if the current density is low. Defective coating growth occurs at high current density. The relationship between polymer thickness and cell voltage depends onmore » the type of substrate coated and the current density used. After the initial stages of deposition, coating formation proceeds at a rate of 0.2 ..mu..m/ mA cm/sup -2/ s. Anodization occurs during electrophoretic deposition onto the aluminum alloy and the anodized aluminum alloy substrates; more anodization occurs at lower current densities and at the beginning of electrolysis. The dielectric constants and the intrinsic breakdown strength exhibited by the coatings depend on the coating thickness and on substrate type. The release of water from the coatings during the curing cycle allows coatings exhibiting breakdown a strength as high as 1000 V/..mu..m to form at cell voltages of 4 to 14 V per ..mu..m polymer coating thickness.« less