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Title: Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects

Abstract

The principal objective of this work was to develop oxidation protective coatings for metallic interconnect based on a defect chemistry approach. It was reasoned that the effectiveness of a coating is dictated by oxygen permeation kinetics; the slower the permeation kinetics, the better the protection. All protective coating materials investigated to date are either perovskites or spinels containing metals exhibiting multiple valence states (Co, Fe, Mn, Cr, etc.). As a result, all of these oxides exhibit a reasonable level of electronic conductivity; typically at least about {approx}0.05 S/cm at 800 C. For a 5 micron coating, this equates to a maximum {approx}0.025 {Omega}cm{sup 2} area specific resistance due to the coating. This suggests that the coating should be based on oxygen ion conductivity (the lower the better) and not on electronic conductivity. Measurements of ionic conductivity of prospective coating materials were conducted using Hebb-Wagner method. It was demonstrated that special precautions need to be taken to measure oxygen ion conductivity in these materials with very low oxygen vacancy concentration. A model for oxidation under a protective coating is presented. Defect chemistry based approach was developed such that by suitably doping, oxygen vacancy concentration was suppressed, thus suppressing oxygen ion transportmore » and increasing effectiveness of the coating. For the cathode side, the best coating material identified was LaMnO{sub 3} with Ti dopant on the Mn site (LTM). It was observed that LTM is more than 20 times as effective as Mn-containing spinels. On the anode side, LaCrO3 doped with Nb on the Cr site (LNC) was the material identified. Extensive oxidation kinetics studies were conducted on metallic alloy foils with coating {approx}1 micron in thickness. From these studies, it was projected that a 5 micron coating would be sufficient to ensure 40,000 h life.« less

Authors:
Publication Date:
Research Org.:
University Of Utah
Sponsoring Org.:
USDOE
OSTI Identifier:
920189
DOE Contract Number:
FC26-04NT42220
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CHEMISTRY; COATINGS; DEFECTS; IONIC CONDUCTIVITY; KINETICS; OXIDATION; OXYGEN; OXYGEN IONS; PROTECTIVE COATINGS

Citation Formats

Anil V. Virkar. Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects. United States: N. p., 2006. Web. doi:10.2172/920189.
Anil V. Virkar. Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects. United States. doi:10.2172/920189.
Anil V. Virkar. Sun . "Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects". United States. doi:10.2172/920189. https://www.osti.gov/servlets/purl/920189.
@article{osti_920189,
title = {Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects},
author = {Anil V. Virkar},
abstractNote = {The principal objective of this work was to develop oxidation protective coatings for metallic interconnect based on a defect chemistry approach. It was reasoned that the effectiveness of a coating is dictated by oxygen permeation kinetics; the slower the permeation kinetics, the better the protection. All protective coating materials investigated to date are either perovskites or spinels containing metals exhibiting multiple valence states (Co, Fe, Mn, Cr, etc.). As a result, all of these oxides exhibit a reasonable level of electronic conductivity; typically at least about {approx}0.05 S/cm at 800 C. For a 5 micron coating, this equates to a maximum {approx}0.025 {Omega}cm{sup 2} area specific resistance due to the coating. This suggests that the coating should be based on oxygen ion conductivity (the lower the better) and not on electronic conductivity. Measurements of ionic conductivity of prospective coating materials were conducted using Hebb-Wagner method. It was demonstrated that special precautions need to be taken to measure oxygen ion conductivity in these materials with very low oxygen vacancy concentration. A model for oxidation under a protective coating is presented. Defect chemistry based approach was developed such that by suitably doping, oxygen vacancy concentration was suppressed, thus suppressing oxygen ion transport and increasing effectiveness of the coating. For the cathode side, the best coating material identified was LaMnO{sub 3} with Ti dopant on the Mn site (LTM). It was observed that LTM is more than 20 times as effective as Mn-containing spinels. On the anode side, LaCrO3 doped with Nb on the Cr site (LNC) was the material identified. Extensive oxidation kinetics studies were conducted on metallic alloy foils with coating {approx}1 micron in thickness. From these studies, it was projected that a 5 micron coating would be sufficient to ensure 40,000 h life.},
doi = {10.2172/920189},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 2006},
month = {Sun Dec 31 00:00:00 EST 2006}
}

Technical Report:

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  • This report describes significant results from an on-going, collaborative effort to enable the use of inexpensive metallic alloys as interconnects in planar solid oxide fuel cells (SOFCs) through the use of advanced coating technologies. Arcomac Surface Engineering, LLC, under the leadership of Dr. Vladimir Gorokhovsky, is investigating filtered-arc and filtered-arc plasma-assisted hybrid coating deposition technologies to promote oxidation resistance, eliminate Cr volatility, and stabilize the electrical conductivity of both standard and specialty steel alloys of interest for SOFC metallic interconnect (IC) applications. Arcomac has successfully developed technologies and processes to deposit coatings with excellent adhesion, which have demonstrated a substantialmore » increase in high temperature oxidation resistance, stabilization of low Area Specific Resistance values and significantly decrease Cr volatility. An extensive matrix of deposition processes, coating compositions and architectures was evaluated. Technical performance of coated and uncoated sample coupons during exposures to SOFC interconnect-relevant conditions is discussed, and promising future directions are considered. Cost analyses have been prepared based on assessment of plasma processing parameters, which demonstrate the feasibility of the proposed surface engineering process for SOFC metallic IC applications.« less
  • The magnetron sputtering technique can be used to deposit thick amorphous metallic films of MoRuB on steel. The films exhibit a smooth surface, a zone T microstructure, and good adhesion. The thick MoRuB films on steel exhibited corrosion characteristics equal to the film material on glass. A vapor quenched FeCrPC composition was developed which is better than the best liquid quenched counterpart in terms of corrosion resistance. The corrosion rate of the optimum FeCrPC material was measured to be less than 0.002 mils per year in 1.0N H/sub 2/SO/sub 4/ at room temperature. The process parameters used to deposit FeCrPCmore » on steel require further development to achieve the features of the MoRuB thick films. The atomic absorption spectroscopy method can be used to determine extremely low corrosion rates in a timely manner. Preliminary hot vapor corrosion tests indicate that the corrosion is lower than full immersion tests at room temperature.« less
  • Amorphous metallic coatings of (Mo/sub 0.6/Ru/sub 0.4/)/sub 82/B/sub 18/, Fe/sub 70/Cr/sub 10/P/sub 13/C/sub 7/, and Fe/sub 70/Mo/sub 7/Cr/sub 7/P/sub 13/C/sub 7/ can be deposited utilizing magnetron sputtering technology. Coatings of (Mo/sub 0.6/Ru/sub 0.4/)/sub 82/B/sub 18/ on glass and mica substrates have been shown to exhibit corrosion resistance better than chemically identical liquid quenched samples. Through systematic correlations among position conditions and film characteristics, it has been demonstrated that (Mo/sub 0.6/Ru/sub 0.4/)/sub 82/B/sub 18/ films can be effectively deposited on 1066 steel. The film thickness of (Mo/sub 0.6/Ru/sub 0.4/)/sub 82/B/sub 18/ was required to be several micrometers in order to providemore » corrosion protection to the polished steel substrates, i.e., to cover asperities on the surface and to fill any pinholes in the film. Unpolished steel requires a greater thickness to provide corrosion protection. The (Mo/sub 0.6/Ru/sub 0.4/)/sub 82/B/sub 18/ depositions on steel require that the substrates be biased to achieve good adhesion and a smooth zone T microstructure. There were some indications that substrate heating (275/sup 0/C) may also be beneficial. Fe-based amorphous films crystallize at 420/sup 0/C. The corrosion resistance of these coatings is lower that that of the corresponding liquid-quenched alloys, presumably due to the phosphorus deficiency found in the composition of these coatings.« less
  • Objective is to use sputter-deposited amorphous metallic coatings on alloys in heat recovery systems in power plants. It was found that chromium could be used as a substitute for ruthenium in MoRuB. The new alloy, MoCrB, has corrosion current two orders of magnitude lower than MoRuB. The effort to develop the parameters for depositing FeCrPC on steel was frustrated by a persistent pinhole problem. Two titanium-based alloys were developed which are equal to or better than the optimized FeCrPC alloy in terms of corrosion resistance. The potentiodynamic polarization characteristics of MoCrB and TiCrBC were measured over a range in temperaturemore » from 25 to 100/sup 0/C. The corrosion current increased with temperature as predicted by theory. The corrosion characteristics of MoCrB and TiCrPC were also tested in 1.0N HC1. Cost analysis of the magnetron sputtering coating process indicates that the process cost is in the range of $2.50 to $3.00 per square foot steel.« less
  • Electrically conductive metal-oxide (ceramic) coatings produced by reactive ion plating are being investigated at USA-CERL for potential application in cathodic-protection systems. Ceramic materials are advantageous because of their low dissolution rates (typically less than 1 g/A/yr in 3.5% NaCl solution) and ease of fabrication. Among the ceramic anode materials currently under investigation are two systems: (1) a mixture of titanium oxide and ruthenium oxide and (2) a mixture of titanium oxides doped with niobium, each ion plated on niobium substrates. The mixed-oxide coatings were fabricated by a reactive-ion-plating process involving oxygen and dual electron-beam evaporation sources. An enhanced plasma wasmore » used to increase reactivity. X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were used for characterization of the microstructure, crystallography, and elemental composition of the coating.« less