| 1. |
- Alnegren, Patrik, 1988, et al.
(författare)
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Inhibiting chromium evaporation and oxide scale growth on SOFC metallic interconnects by nano coatings
- 2014
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Ingår i: 20th World Hydrogen Energy Conference, WHEC 2014. - 9780000000002 ; 1:2014
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Konferensbidrag (refereegranskat)abstract
- High chromium ferritic steel is today the most commonly considered material for SOFC interconnectors due to many desirable properties, such as matching thermal expansion coefficient with other cell components but most importantly better machinability and price compared to ceramic alternatives. Yet there are some obstacles that need to be addressed before long term stability of a ferritic steel interconnector based fuel cell stack can be realized. First of all the electrical conductivity needs to remain high throughout the fuel cell stack operating life time and thus the formed oxide layers need to be electrically conductive and thin. Secondly, volatilization of chromium from the oxide scale of metallic interconnects causes rapid degradation due cathode poisoning. In the current study both oxidation and chromium evaporation of ferritic steel substrates are investigated in controlled atmospheres that simulates the environments of an operating SOFC stack. Samples coated with nanometer scale dual coatings of Co and Ce were tested. The dual coating substantially increased the performance of the ferritic substrates by i) significantly reducing oxidation rate, ii) increasing scale adherence and iii) diminishing chromium evaporation by 90 % via the formation of a Co-Mn-spinel cap layer.
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| 2. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Nano coated interconnects for SOFC (NaCoSOFC)
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2187-2193
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Konferensbidrag (refereegranskat)abstract
- The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material.
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| 3. |
- Sudireddy, B. R., et al.
(författare)
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Development of Robust Metal-Supported SOFCs and Stack Components in EU METSAPP Consortium
- 2017
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 17:4, s. 508-516
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Tidskriftsartikel (refereegranskat)abstract
- The potential of MS-SOFCs was demonstrated through the previous EU METSOFC project, which concluded that the development of oxidation resistant novel metal-supported solid oxide fule cell (MS-SOFC) design and stack is the requirement to advance this technology to the next level. The following EU METSAPP project has been executed with an overall aim of developing advanced metal-supported cells and stacks based on a robust, reliable and up-scalable technology. During the project, oxidation resistant nanostructured anodes based on modified SrTiO3 were developed and integrated into MS-SOFCs to enhance their robustness. In addition, the manufacturing of metal-supported cells with different geometries, scalability of the manufacturing process was demonstrated and more than 200 cells with an area of approximate to 150 cm(2) were produced. The electrochemical performance of different cell generations was evaluated and best performance and stability combination was observed with doped SrTiO3 based anode designs. Furthermore, numerical models to understand the corrosion behavior of the MS-SOFCs were developed and validated. Finally, the cost effective concept of coated metal interconnects was developed, which resulted in 90% reduction in Cr evaporation, three times lower Cr2O3 scale thickness and increased lifetime. The possibility of assembling these cells into two radically different stack designs was demonstrated.
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| 4. |
- Blennow, P., et al.
(författare)
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Investigation of Cu-based infiltration coatings for metal-supported SOFC
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 771-780
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Konferensbidrag (refereegranskat)abstract
- Metal-supported solid oxide fuel cells are candidates for the next generation of SOFCs. However, the cell design with an FeCr/YSZ-based anode backbone suffers from corrosion when the cells are run at high fuel utilization, which limits the long term durability. In this work, new infiltration coatings based on Cu in combination with Ni:Ce0.8Gd0.2O 1.9 (Ni:CGO) have been studied. The candidates for a corrosion resistant coating should limit the formation of Cr2O3 on the surface of FeCr particles. Promising fuel cell performance with an ASR of 0.5 Ωcm2 was obtained at 650 °C with H2 as fuel. However, various analysis techniques showed no improved corrosion resistance with the addition of a Cu coating.
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| 5. |
- Canovic, Sead, 1979, et al.
(författare)
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Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation
- 2013
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 215, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe-22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.
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| 6. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Long term study of Cr evaporation and high temperature corrosion behaviour of Co coated ferritic steel for solid oxide fuel cell interconnects
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 220, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of the uncoated ferritic Fe-22Cr steel Sanergy HT is compared with an 640 nm Co coated version of the same material. The materials have been subject to corrosion and Cr volatilization measurements in air for up to 3000 h at 850 degrees C. Oxidation tests have been carried out both isothermal and discontinuously. The volatilization measurements were carried out using a recently developed denuder technique, which allows to quantify Cr evaporation in a time resolved manner. The oxidation process is studied from very initial phases (>15 s) to long term behaviour (3000 h). The formed oxide scales are analysed by XRD, SEM/EDX as well as TEM/EDX.The results show that both materials form an oxide scale with an inner layer of Cr2O3 and a spinel layer on top. In the case of the uncoated material, the spinel layer is of (Cr,Mn)(3)O-4 type while in the presence of a Co coating a (Co,Mn,Fe)(3)O-4 is formed. The Cr evaporation measurements show that despite the fact that the Co coating is very thin (640 nm) it effectively blocks Cr evaporation for at least 3000 h. This is in line with TEM analysis showing that after 3000 h there is only a low Cr content in the outer oxide scale. This long term stability indicates the suitability of the coated material as solid oxide fuel cell (SOFC) interconnect.
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| 7. |
- Nugehalli Sachitanand, Rakshith, 1984, et al.
(författare)
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Coatings for SOFC interconnects in fuel side environments
- 2015
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 68:1, s. 1575-1580
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Konferensbidrag (refereegranskat)abstract
- This study focuses on examining the effect of PVD coatings on the oxidation performance of interconnects in fuel side environments. The ferritic steels Sanergy HT and AISI 441 were coated with nanoscale thick rare earth oxides of Ce and La. Additionally, Sanergy HT was also coated with Cu, Co and Ce/Co. The samples were exposed at 850°C in Ar-5% H2-3% H2O in a tubular furnace. Chemical analysis on the samples was subsequently performed with SEM/EDX and XRD. It was established that the Ce and La coatings brought about a ≈4x reduction in the oxidation rate while the presence of a metallic phase in the oxide (Cu and Co) negatively affected oxidation performance. Further, the La coating resulted in the formation of a perovskite phase, showing that the intrinsic electronic properties of the oxide can be tailored using coatings.
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| 8. |
- Nugehalli Sachitanand, Rakshith, 1984, et al.
(författare)
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Evaluation of the oxidation and Cr evaporation properties of selected FeCr alloys used as SOFC interconnects
- 2013
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 38:35, s. 15328-15334
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, a number of ferritic interconnect materials for use in solid oxide fuel cells (SOFC) have been developed and are now commercially available. Although similar, there are substantial variations in minor alloying elements. This study compares the oxidation performance of five such interconnect materials: Crofer 22 H, Crofer 22 APU (ThyssenKrupp VDM), Sanergy HT (Sandvik Materials Technology), ZMG232 G10 (Hitachi Metals) and E-Brite (ATI Allegheny Ludlum). 1000 h exposures have been carried out in tubular furnaces at 850 degrees C, with 6 l/min airflow and 3% H2O to simulate the air side atmosphere in an SOFC. In addition to the oxidation tests, time resolved in-situ chromium evaporation measurements have been carried out using a novel denuder technique. It was found that higher Mn concentrations in the alloy lead to lower Cr evaporation. Nonetheless, all steels exhibit substantial Cr volatilization and coatings are needed for most SOFC applications. Furthermore, this study demonstrates that the mass gain data alone can be misleading, and the mass loss due to Cr volatilization needs to be taken into account. Neglecting Cr evaporation results in an underestimation of the oxidation rate by between 15% and 200% for the studied steel grades.
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| 9. |
- Nugehalli Sachitanand, Rakshith, 1984, et al.
(författare)
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The Influence of Cr Evaporation on Long Term Cr Depletion Rates in Ferritic Stainless Steels
- 2015
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 84:3-4, s. 241-257
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that well defined flow rates are an essential parameter in oxidation experiments influenced by scale volatilisation. The 22 % Cr ferritic steel Sanergy HT, intended for use as an SOFC interconnect material, was exposed discontinuously over 3100 h at 850 °C in air + 3 % H2O @ 6000 sml min−1 (27 cm s−1) and stagnant conditions in a tubular reactor. Time resolved isothermal Cr evaporation measurements over 1000 h were also performed in the 6000 sml min−1 case while the stagnant exposure environment was saturated in Cr(VI) species to suppress any evaporation reactions. Mass balances based on oxidation and evaporation data were in good agreement with SEM/EDX bulk Cr concentration measurements. The time to a bulk concentration of 15 wt% Cr increased by ≈2× from ≈3000 to ≈5500 h when evaporation was suppressed. Further, it was established that a suppressed evaporation reaction affected not just the magnitude of Cr depletion in the steel but even its long term depletion rate.
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| 10. |
- Nugehalli Sachitanand, Rakshith, 1984, et al.
(författare)
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The Oxidation of Coated SOFC Interconnects in Fuel Side Environments
- 2016
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 16:1, s. 32-38
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on examining the effect of PVD coatings on the oxidation performance of interconnects in fuel (anode) side environments. A Fe-22Cr ferritic steel was coated with (i) Ce 10nm (ii) La 10nm and (iii) Co 600nm. The samples were exposed at 850 degrees C in Ar-5% H-2-3% H2O in a tubular furnace over 500 h. Additionally, the effect of a pre-oxidation step was investigated by exposure in air prior to the simulated fuel gas environment. Chemical analysis on the samples was subsequently performed with SEM/EDX and XRD. It was established that the Ce and La coatings brought about a factor 2-3 reduction (k(p)values of 2.16x10(-14)+/- 3.6x10(-15)g(2)cm(-4)s(-1) for the La 10nm coated steel compared to 7.72x10(-14)+/- 5.86x10(-15)g(2)cm(-4)s(-1) for the uncoated steel) in the oxidation rate while the Co coating disintegrated into metallic islands in and on the thermally grown oxide after exposure. Additionally, the La coating resulted in the formation of a continuous perovskite layer by reaction with the thermally grown oxide.
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