| 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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Investigation of Chromium Volatilization from FeCr Interconnects by a Denuder Technique
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:9, s. B1295-B1300
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Tidskriftsartikel (refereegranskat)abstract
- A technique is presented for accurate and time-resolved quantification of chromium volatilization from alloys at high temperature. A denuder tube which is coated with Na2CO3 is placed downstream of the samples. CrO2(OH)(2) that evaporated from the samples is collected on the denuder and converted to the thermally stable Na2CrO4. The chromate is then dissolved in water and determined quantitatively. Three commercially available ferritic 22% Cr steels intended for use as solid oxide fuel cell interconnect materials (Sanergy HT, Crofer 22 APU, and ZMG 232) have been investigated with respect to chromium volatilization and oxidation rate. The effect on chromium volatilization of a submicrometer cobalt coating on the steel surface is reported. Comparisons are made with a conventional thick ceramic coating. The experiments are carried out at 850 degrees C in N-2 - 20% O-2 - 3% H2O atmosphere. The submicrometer Co coatings proved to be very efficient, reducing Cr volatilization by 1 order of magnitude. Microscopic studies show that both uncoated steel and steel coated with a submicrometer cobalt film develop two-layered oxide scales with the bottom part consisting of a Cr-rich corundum-type oxide. The uncoated samples develop a top layer consisting of (Cr, Mn)(3)O-4 oxide, whereas the Co-coated samples exhibit a top layer consisting of Co-rich spinel oxide. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3462987] All rights reserved.
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| 3. |
- Grolig, Jan Gustav, 1986, et al.
(författare)
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Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Oxidation performance and chromium evaporation
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 248, s. 1007-1013
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Tidskriftsartikel (refereegranskat)abstract
- Reactive Element (RE) and RE/cobalt-coated stainless steel AISI 441 was exposed at Solid Oxide Fuel Cell (SOFC) cathode conditions (850 degrees C in air with 3% water content) for up to 500 h. The chromium evaporation was measured by applying the denuder technique. Uncoated material exhibited severe spallation which could be successfully prevented by using cerium or lanthanum coatings. By applying double layer coatings of cerium or lanthanum in combination with cobalt the oxidation rate was decreased and the chromium volatilisation was also about 90% lower than the uncoated material.
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| 4. |
- Grolig, Jan Gustav, 1986, et al.
(författare)
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Copper based conversion coatings on ferritic stainless strip steel as solid oxide fuel cell interconnects: Oxidation performance and chromium evaporation
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2339-2347
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Konferensbidrag (refereegranskat)abstract
- Ferritic stainless steels such as Crofer 22 H or Sanergy HT have been proven to be effective interconnect materials when additionally coated. These coatings, mainly based on cobalt spinels, successfully prevent chromium evaporation and are stable for long exposure times. A new approach is using copper based spinel coatings which are promising concerning price, conductivity and stability. This investigation is dedicated to a selection of copper spinel conversion coatings, their stability and ability to prevent chromium evaporation. Chromium release was monitored in humidified air (at 850 °C) using the denuder technique. The coatings were post analysed utilizing electron microscopy.
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| 5. |
- 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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| 6. |
- Alnegren, Patrik, 1988, et al.
(författare)
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Degradation of Ferritic steel interconnects in SOEC environments
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2261-2270
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Konferensbidrag (refereegranskat)abstract
- This study investigates the corrosion performance of selected ferritic steels in simulated solid oxide electrolysis cell (SOEC) environments for exposure times up 500 h. Ferritic steels have many properties that are desirable for interconnects but suffer from oxidation and chromium evaporation over time. Four different FeCr alloys have been exposed in different concentrations of dry O2 (anode side) and in 34 % H2O -3 % H2-Ar (cathode side) at 850 °C and gravimetrical measurements have been performed to study oxidation rates. Chromium evaporation has been measured and compared for the oxygen containing environments. Chromium evaporation was found to vary largely with oxygen partial pressure, while the oxidation rate of the steels did not vary substantially in the different oxygen partial pressures. Differences in oxidation behavior of the steels were observed between the exposures in dry O2 and in 34 % H2O -3 % H2 -Ar. Both reduced and increased oxidation rates were observed in the cathode side atmosphere compared to the oxygen side atmosphere for different materials.
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| 7. |
- 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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| 8. |
- Falk Windisch, Hannes, 1984, et al.
(författare)
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Influence of chromium evaporation and oxidation on interconnect steels at 650-850°C
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2225-2233
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Konferensbidrag (refereegranskat)abstract
- Chromium evaporation and oxide scale growth are two important degradation mechanisms in SOFCs when chromia-forming alloys are used as the interconnect material. In this paper the influence of temperature on both mechanisms were studied. Isothermal exposures were carried out for 24, 168 and 500h at 650, 750 and 850°C in an air-3%H2O atmosphere. In the second part uncoated and metallic nano-coated samples were exposed for 3000h. This study clearly points out the relevance of Cr-evaporation at reduced temperatures and the importance of high quality coatings not only to protect the cell from cathode poisoning but also to reduce the risk of Cr-depletion within the interconnect steel.
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| 9. |
- 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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| 10. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Multifunctional Nano-Coatings for SOFC Interconnects
- 2011
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607682127 ; 35:1, s. 2503-2508
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Konferensbidrag (refereegranskat)abstract
- Chromium evaporation from metallic interconnects in SOFCs is commonly poisoning the cathode of SOFCs. To reduce chromium evaporation, rather thick coatings have been deposited using various coating techniques. In this study a 22% Cr ferritic steel has been coated with multilayered nano coatings. The best coatings combine a Cr retention layer (800nm Co) with a 10nm layer of Ce that reduces the corrosion rate of the metallic interconnect. Such coatings might be a cost efficient way to meet the required lifetime targets for SOFC interconnects. The Cr evaporation measurements are carried out with a recently developed denuder technique which allows time resolved quantification of volatile chromium species. Downstream of the samples a denuder tube is placed which collects any CrO2(OH)(2) evaporating from the samples.
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| 11. |
- 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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| 12. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Nanocoatings for SOFC interconnects - Mitigating chromium volatilization and improving corrosion properties
- 2011
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783037852354 ; 696, s. 412-416
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Konferensbidrag (refereegranskat)abstract
- Two important degradation mechanisms in Solid Oxide Fuel Cells (SOFC) are directly related to the metallic interconnects. The formation of volatile chromium oxides from metallic interconnects commonly causes fast degradation in cell performance due to poisoning the cathode. Secondly is the ability of the metallic interconnect to form a thin protective oxide one of the most important lifetime limiting factors for SOFC. Chromium volatilization of various uncoated steels is studied as a function of temperature by a recently developed denuder technique which allows time resolved quantification of volatile chromium species. The inhibition of Cr evaporation by Co thin film coatings (800nm) is investigated; it will be shown that these coatings are more effective than much thicker ceramic coatings that are commonly used for this purpose. In order to increase the lifetime of the metallic components in SOFC nano-coatings of reactive elements (RE) have been investigated as well. The application of such coatings can reduce the corrosion rates substantially and thus increase the lifetime of the fuel cell stack. It will be shown that it is possible to combine the positive effects of RE with the beneficial effects of a Co coating and thus to obtain an interconnect material with low Cr evaporation and increased oxidation resistance.
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| 13. |
- Andersson, S., et al.
(författare)
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Sulfur recirculation for increased electricity production in Waste-to-Energy plants
- 2014
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Ingår i: Waste Management. - : Elsevier BV. - 0956-053X .- 1879-2456. ; 34:1, s. 67-78
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur recirculation is a new technology for reducing boiler corrosion and dioxin formation. It was demonstrated in full-scale tests at a Waste to Energy plant in Goteborg (Sweden) during nearly two months of operation. Sulfur was recirculated as sulfuric acid from the flue gas cleaning back to the boiler, thus creating a sulfur loop. The new technology was evaluated by extensive measurement campaigns during operation under normal conditions (reference case) and operation with sulfur recirculation. The chlorine content of both fly ash and boiler ash decreased and the sulfur content increased during the sulfur recirculation tests. The deposit growth and the particle concentration decreased with sulfur recirculation and the dioxin concentration (I-TEQ) of the flue gas was reduced by approximately 25%. Sulfuric acid dew point measurements showed that the sulfuric acid dosage did not lead to elevated SO3 concentrations, which may otherwise induce low temperature corrosion. In the sulfur recirculation corrosion probe exposures, the corrosion rate decreased for all tested materials (16Mo3, Sanicro 28 and Inconel 625) and material temperatures (450 degrees C and 525 degrees C) compared to the reference exposure. The corrosion rates were reduced by 60-90%. Sulfur recirculation prevented the formation of transition metal chlorides at the metal/oxide interface, formation of chromate and reduced the presence of zinc in the corrosion products. Furthermore, measured corrosion rates at 525 degrees C with sulfur recirculation in operation were similar or lower compared to those measured at 450 degrees C material temperature in reference conditions, which corresponds to normal operation at normal steam temperatures. This implies that sulfur recirculation allows for higher steam data and electricity production without increasing corrosion.
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| 14. |
- 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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| 15. |
- Eziashi, J., et al.
(författare)
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Measuring Cr volatility from ferritic stainless steels: Novel and conventional methods compared
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 50:44, s. 43-49
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Konferensbidrag (refereegranskat)abstract
- Reactive evaporation of Cr-species from ferritic stainless steels is a technical challenge for solid oxide fuel cell (SOFC) systems and other devices operating in high-temperature (>600°C) oxidizing environments. One traditional method for quantitatively measuring Cr volatility is by using a transpiration system, in which oxidizing gases are flown by Cr-containing materials and the exhaust is condensed and subsequently analyzed using ICP-MS. While this method is well established and accurate, it also has limited sensitivity and challenges associated with sample collection. Novel methods have recently been developed to more quickly and accurately quantify lower levels of Cr volatility. These include the denuder technique, which employs a water-soluble reactive collection and optical analysis; a cold quartz wool collection method with ICP-MS; and, a cold Si-wafer collection with ionbeam analysis. Each method has advantages and disadvantages in terms of cost, operation, sensitivity and accuracy. In this poster, Cr volatility measurement techniques will be presented and compared in the context of facilitating new and ongoing research efforts.
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| 16. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Anode Side Diffusion Barrier Coating for Solid Oxide Fuel Cells Interconnects
- 2010
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Ingår i: Journal of Fuel Cell Science and Technology. - : ASME International. - 1550-624X .- 1551-6989. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- During the operation of solid oxide fuel cells (SOFCs) the Ni base anode and/or Ni-mesh is in direct contact with the ferritic steel interconnect or the metallic substrate. For assuring long-term stack operation a diffusion barrier layer with high electronic conductivity may be needed to impede interdiffusion between the various components. A pre-oxidation layer on the ferritic steel turned out to be not viable as a barrier layer since a Ni-layer tends to dissociate the oxide scale. Therefore the potential of ceria as a diffusion barrier layer for the anode side of the SOFC was estimated. The barrier properties of a ceria coating between the Ni and the ferritic steel Crofer 22 APU were tested for 1000 h in Ar–4H2–2H2O at 800°C. Conductivity experiments were performed in the same atmosphere at different temperatures. After long-term exposures no indication of interdiffusion between Ni and ferritic steel could be detected, however, sputtered coatings on ferritic steel substrates showed significantly lower conductivities than bulk ceria samples because of void formation between the ceria and the oxide on the steel surface. The latter could be prevented by an intermediate copper layer, which resulted in overall area specific resistance values lower than 20 mΩ cm2 after 100 h exposure at 800°C.
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| 17. |
- Key, C., et al.
(författare)
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Methods to Quantify Reactive Chromium Vaporization from Solid Oxide Fuel Cell Interconnects
- 2014
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 161:9, s. C373-C381
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature (>600 degrees C) reactive vaporization of Cr from chromia and stainless steels in oxidizing environments is an industrially relevant phenomenon that has been and will continue to be studied extensively for decades. Recently, many experimental techniques have been developed to measure Cr vaporization from stainless steel interconnect (IC) components within solid oxide fuel cell (SOFC) systems. Many of these techniques are based on an experimental method known as the transpiration method, which is used to generate Cr vapors and subsequently collect them for quantitative analysis. However, vapor collection and analysis methods differ significantly between investigators within the community, as does the array of alloys (with and without protective surface coatings), temperatures, flow rates, and water vapor pressures used in experimentation. Therefore, the purpose of the present work is to provide an overview of experimental techniques used to quantify reactive Cr vaporization, and to compare data reported in literature on Cr vaporization from Cr2O3 and chromium containing alloys in oxidizing environments.
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