The Effect of Metallic Co-Coating Thickness on Ferritic Stainless Steels Intended for Use as Interconnect Material in Intermediate Temperature Solid Oxide Fuel Cells (original) (raw)
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Journal of Power Sources, 2008
As part of an effort to develop cost-effective ferritic stainless steel-based interconnects for solid oxide fuel cell (SOFC) stacks, both bare AISI441 and AISI441 coated with (Mn,Co) 3 O 4 protection layers were studied in terms of its metallurgical characteristics, oxidation behavior, and electrical performance. The addition of minor alloying elements, in particular Nb, led to formation of Laves phases both inside grains and along grain boundaries. In particular, the Laves phase which precipitated out along grain boundaries during exposure at intermediate SOFC operating temperatures was found to be rich in both Nb and Si. The capture of Si in the Laves phase minimized the Si activity in the alloy matrix and prevented formation of an insulating silica layer at the scale/metal interface, resulting in a reduction in area-specific electrical resistance (ASR). However, the relatively high oxidation rate of the steel, which leads to increasing ASR over time, and the need to prevent volatilization of chromium from the steel necessitates the application of a conductive protection layer on the steel. In particular, the application of a Mn 1.5 Co 1.5 O 4 spinel protection layer substantially improved the electrical performance of the 441 by reducing the oxidation rate.
Metal Interconnect Development for Solid Oxide Fuel Cells
2004
Intermediate temperature (750 – 800°C) operation of solid oxide fuel cells allows the use of metallic interconnects. Ferritic stainless steels have attracted considerable attention because of their close thermal expansion match with that of zirconia electrolyte. Continued growth of resistive oxide and evaporation-condensation of chromium that could poison the cathode are the primary challenges in metal interconnect development. These challenges must be addressed in order to achieve the desired long term stability of fuel cells. In the present work, ferritic stainless steel was evaluated for high temperature oxidation properties. Controlled pre-oxidation was found to provide an adherent and conductive oxide scale. Low interfacial resistance of 10 – 20 milliohm-cm 2 was measured in air at 850°C.
High Temperature Oxidation Of Cr-Steel Interconnects In Solid Oxide Fuel Cells
2017
Solid Oxide Fuel Cell (SOFC) is a promising solution for the energy resources leakage. Ferritic stainless steel becomes a suitable candidate for the SOFCs interconnects due to the recent advancements. Different steel alloys were designed to satisfy the needed characteristics in SOFCs interconnect as conductivity, thermal expansion and corrosion resistance. Refractory elements were used as alloying elements to satisfy the needed properties. The oxidation behaviour of the developed alloys was studied where the samples were heated for long time period at the maximum operating temperature to simulate the real working conditions. The formed scale and oxidized surface were investigated by SEM. Microstructure examination was carried out for some selected steel grades. The effect of alloying elements on the behaviour of the proposed interconnects material and the performance during the working conditions of the cells are explored and discussed. Refractory metals alloying of chromium steel s...
Ferritic stainless steel has become a promising material for metallic interconnects for solid oxide fuel cells (SOFCs) operating in an intermediate temperature range (650-800 • C). Ferritic stainless steels containing reactive elements (REs) such as Crofer22APU and ZMG232 have been developed for SOFC interconnects. Nevertheless, the effectiveness of REs on the growth kinetics of the chromia-rich scale that forms on the ferritic stainless steels is not yet well understood. The current study focuses on the investigation of the effect of REs such as Y, Ce and La on the oxidation behaviour and scale properties of Fe-22Cr-0.5Mn stainless steel. The results show that Y is the most effective reactive element for reducing the scale growth kinetics and area-specific resistance of the chromia scale which forms on this stainless steel. The growth kinetics of the chromia-rich scale can be effectively reduced by the dominant segregation of Y at the interface between the oxide scale and alloy substrate, and by the formation of a thin SiO 2 and MnO layer underneath the Cr 2 O 3 -rich oxide.
Metals
Two commercial ferritic stainless steels (FSSs), referred to as Steel A and Steel B, designed for specific high-temperature applications, were tested in static air for 2000 h at 750 °C to evaluate their potential as base materials for interconnects (ICs) in Intermediate Temperature Solid Oxide Fuel Cell stacks (IT-SOFCs). Their oxidation behavior was studied through weight gain and Area Specific Resistance (ASR) measurements. Additionally, the oxide scales developed on their surfaces were characterized by X-ray Diffraction (XRD), Micro-Raman Spectroscopy (μ-RS), Scanning Electron Microscopy, and Energy Dispersive X-ray Fluorescence Spectroscopy (SEM-EDS). The evolution of oxide composition, structure, and electrical conductivity in response to aging was determined. Comparing the results with those on AISI 441 FSS, steels A and B showed a comparable weight gain but higher ASR values that are required by the application. According to the authors, Steel A and B compositions need an adj...
Journal of Power Sources, 2007
Adhesion of thermal oxide scales grown at 800 • C on ferritic stainless steels F18TNb (AISI 441) and F18MT (AISI 444) proposed as interconnectors in solid oxide fuel cells (SOFCs) was investigated. The effect of oxidising atmosphere -synthetic air or 2% H 2 O in H 2 as the representative cathode and anode atmosphere respectively -was considered. Using a room temperature tensile test sitting in the SEM chamber, thermally grown oxide scales were forced to spall and their adhesion energy was derived. Adhesion energy, considered as the elastic energy per unit area stored in oxide was determined at the strain of first spallation or at the strain where the derivative of spallation versus strain was maximum. Adhesion energies were shown to lie in the range 10-100 J cm −2 . Adhesion values exhibited decreasing values with increasing oxide thickness, with higher values for oxidation in 2% H 2 O/H 2 compared to oxidation in synthetic air. The adhesion energy of scales on F18MT was lower than that on F18TNb due to the presence of Mo-containing intermetallic compounds at the metal/scale interface.
Metallic materials in solid oxide fuel cells
Materials Research, 2004
Fe-Cr alloys with variations in chromium content and additions of different elements were studied for potential application in intermediate temperature Solid Oxide Fuel Cell (SOFC). Recently, a new type of FeCrMn(Ti/La) based ferritic steels has been developed to be used as construction material for SOFC interconnects. In the present paper, the long term oxidation resistance of this class of steels in both air and simulated anode gas will be discussed and compared with the behaviour of a number of commercial available ferritic steels. Besides, in-situ studies were carried out to characterize the high temperature conductivity of the oxide scales formed under these conditions. Main emphasis will be put on the growth and adherence of the oxide scales formed during exposure, their contact resistance at service temperature as well as their interaction with various perovskite type contact materials. Additionally, parameters and protection methods in respect to the volatilization of chromia based oxide scales will be illustrated.
Deposition of Conductive Oxide Coatings on Steel Interconnects of Solid Oxide Fuel Cell
A method of Mn-CoO coatings deposi-tion on chromium-based alloy has been described. This method is based on ion-beam-assisted coating deposition by magnetron sputtering of metallic targets. The effect of the coating deposition conditions and yttrium additions on the microstructure and the elemental composition of the coatings and the interface after isothermal oxidation in air at 800 °C has been considered. The results of measuring of the steel oxidation rate and the area specific resistance of the coating in contact with an Sr-doped lanthanum manganite (LSM) cathode have been given. Long-term (8800 hours in a continuous operating regime) tests of a prototype solid oxide fuel cell module, which was outfitted with coated and un-coated interconnects, showed that the protective coating reduces the power loss from an increase in the contact resistance between an LSM cathode and an interconnect by 10%, extending the lifetime for ~4500 hours.
High temperature corrosion of metallic interconnects in solid oxide fuel cells
Revista De Metalurgia, 2006
Research and development has made it possible to use metallic interconnects in solid oxide fuel cells (SOFC) instead of ceramic materials. The use of metallic interconnects was formerly hindered by the high operating temperature, which made the interconnect degrade too much and too fast to be an efficient alternative. When the operating temperature was lowered, the use of metallic interconnects proved to be favourable since they are easier and cheaper to produce than ceramic interconnects. However, metallic interconnects continue to be degraded despite the lowered temperature, and their corrosion products contribute to electrical degradation in the fuel cell. Coatings of nickel, chromium, aluminium, zinc, manganese, yttrium or lanthanum between the interconnect and the electrodes reduce this degradation during operation.