1,720,979 research outputs found
Composite Cu-LaFeO3 conversion coatings on a 18Cr ferritic stainless steel for IT-SOFC interconnects: Effect of long-term air exposure at 700◦C on Cr diffusion barrier and electrical properties
No full textIn our previous study copper oxide additions were used to accelerate the formation of perovskite LaFeO3 conversion coatings on stainless steels from molten carbonate baths. Incorporation of copper particles into the growing coating was an additional effect resulting in the formation of a composite Cu-LaFeO3 structure. In continuation to our previous study, the aim of this work is to report the effect of copper additions on long-term stability and performance of perovskite conversion coatings under IT-SOFC interconnect conditions. To this end, a Cu-LaFeO3 coated K41 18Cr ferritic stainless steel was examined in air at 700◦C up to 1000 h. In order to simulate properly the situation of a real IT-SOFC cell, Area Specific Resistance (ASR) and Cr-barrier properties of the coated steel were evaluated simultaneously with a special coating characterization setup. Studies were conducted by comparison with single-phase LaFeO3 coatings obtained in a molten carbonate bath similar to that used for the formation of the composite Cu-LaFeO3 coatings but without the addition of copper oxide. Copper addition did not change the general morphology of the perovskite coating, which remains a multi-layer coating, being composed of an outer LaFeO3 crystalline layer, a middle Fe-rich oxide and two inner Fe-Cr rich oxide layers. However, copper was beneficial in promoting a thinner and more stable coating structure along with finer perovskite grain size. These structural improvements were further confirmed by the results obtained with electrical measurements that showed a better ASR behavior of the Cu-LaFeO3 coatings. On the other hand, no relevant copper effects could be detected on the coating oxidation stability and on the Cr-barrier properties of the perovskite conversion coatings. Both LaFeO3 and Cu-LaFeO3 coatings showed similarly high coating stability and excellent Cr-barrier capability in experiments conducted at 700◦C up to 1000 h. In definitive, dual-phase Cu-LaFeO3 seem more promising systems for IT-SOFC interconnects than single-phase LaFeO3 conversion coatings, although further improvements in ASR electrical properties are needed. © The Author(s) 2018
Preparation and Electrical Properties of Sr-Doped LaFeO3 Thin-Film Conversion Coatings for Solid Oxide Cell Steel Interconnect Applications
Full text linkA study was conducted to explore the effects of Sr doping on the electrical properties of perovskite LaFeO3 thin-film protective conversion coatings grown onto a K41 ferritic stainless steel, a typical interconnect material for intermediate temperature solid oxide cell (SOC) applications. The Sr-doped coatings were prepared in La2 O3-and SrO-containing molten carbonate baths with minor added amounts of nitrate salt for accelerated coating formation. For comparison purposes, undoped coatings were obtained using the same carbonate bath, with the only difference being that SrO was replaced by inert MgO. SEM/EDX and XRD analyses were used for coating characterization and confirmed the effective incorporation of Sr but not of Mg into the LaFeO3 layer. Although both the Sr-doped and undoped coatings consisted of a LaFeO3 layer grown above an inner Fe-Cr spinel, the coating thickness of the Sr-doped coating was distinctly higher, approximately 2 μm, which is twice that of the undoped coating. Electrical measurements in terms of Area-Specific Resistance (ASR) were conducted at 700◦ C in air and showed that Sr-doping significantly improved the electrical conductivity of the coated K41 steel. Due to the Sr-doping, the ASR values of the coated steel dropped from 60 to 37 mΩ cm2 after 300 h of exposure, in spite of the higher Sr-doped coating thickness. The study concludes that Sr-doped thin-film perovskite coatings appear to be a promising solution for improved SOCs steel interconnect stability at intermediate temperatures
Sr-doped LaFeO3 thin coatings for protection of ferritic stainless steel interconnects in solid oxide cells: A study on Cr-barrier and electrical properties
No full textA high-temperature conversion process in molten carbonate baths was applied to produce thin Sr-doped LaFeO3 perovskite coatings on the surface of a K41 steel for interconnect applications in Solid Oxide Cells. Two conversion coatings with identical structure and phase composition, but slightly different thickness were produced in nitrate-accelerated baths containing the nitrate additive at two concentration levels. The as-prepared coatings consisted of a dual-layered perovskite-spinel structure with a top sub-micrometric Sr-doped LaFeO3 layer grown onto a micron-range thick inner Fe-Cr spinel oxide layer. Both coatings showed high protection against oxidation and chromia scale formation at 700°C. Further, excellent Area Specific Resistance (ASR) behavior was found for both coatings at 700°C, although an optimal balance of ASR and Cr-diffusion barrier properties was achieved with the coating produced in the lower nitrate content bath (N-02 coating). The causes for the enhanced barrier properties of the N-02 coating were ascribed not to a different coating thickness, but rather to the evolution of the pristine dual-layer into a more impervious three-layer structure during oxidation aging at 700°C. The evolved structure was formed by decomposition of the pristine sub-coating Fe-Cr spinel into two new spinel sublayers: an outer ferrite and an inner chromite layer, whereas the top thin-film perovskite layer remained essentially unaltered. Partial change in the Fe oxidation state and other possible causes involved in the observed decomposition of the pristine Fe-Cr spinel layer during the thermal aging are analyzed and discussed. Measurements of ASR activation energy indicated that the contact resistance behavior of the thin perovskite coatings was dominated by the internal spinel layer conductivity
Effect of additive particle size on the CuO-accelerated formation of LaFeO3 perovskite conversion coatings in molten carbonate baths
No full textAn original iron conversion coating process has been recently developed to enhance the functional properties of ferritic stainless steels for use as Solid Oxide Fuel Cell interconnects. The conversion process produces a dense LaFeO3 perovskite layer grown above a spinel oxide underlayer by an immersion treatment in specially-formulated molten carbonate baths at around 600 °C. Galvanic coupling with a coarse CuO powder added to the bath has been earlier proved to be an effective approach to significantly reduce conversion times and coating thicknesses onto a 18Cr Type K41 ferritic stainless steel substrate. Further investigations on the CuO acceleration effects on the K41 steel are reported in the present work focusing on the effect of CuO particle size on the conversion times and coating structure. Studies carried out with different concentrations and particle sizes of the CuO additive have indicated that conversion coating kinetics is strongly affected by the CuO particle size highlighting thus the fact that CuO did not fully dissolve in the carbonate bath and that galvanic coupling effects took place prevalently with CuO particles dispersed in the molten bath. Dramatic reduction in conversion times could be obtained through CuO nanoparticle additions to the bath. The shortest conversion time of <3 h was achieved by adding 6 mol% nano CuO, at 610 °C. As consequence, perovskite coatings with thicknesses well below 10 μm could be produced due to minimal substrate corrosion and spinel underlayer growth during the short conversion processes in the nano CuO-containing salt baths. This structural refinement could play an important role for improving dimensional stability and functional properties of perovskite coatings in SOFC interconnect applications
Corrosion of inconel alloys for application as inert anodes in low-temperature molten carbonate electrolysis processes
No full textIn this work, five different Inconel alloys were investigated as stable CO2/O2 evolving anodes for possible use in molten carbonate CO2 and H2O electrolysis or CO2/H2O co-electrolysis processes. Experiments were conducted in the molten ternary Li2CO3–Na2CO3–K2CO3 carbonate eutectic at 500 °C, under a CO2 gas atmosphere. Cyclic voltammetry and galvanostatic polarization using DC and pulsed modes of current application were used to evaluate the influence of chemical composition on the Inconel corrosion behavior and anode stability. Results indicated that Ti and Al alloying elements are critical factors in promoting Inconel alloy passivation in molten carbonates, thus allowing high anode stability to be achieved during multiple voltammetric cycles with electrodes made of Inconel 617, 718 and X-750 alloys. It was also found that the mode of current application dramatically affects the galvanostatic polarization results. Although rapid anode degradation was invariably observed in all the Inconel electrodes subjected to DC polarization, electrodes of Inconel 617 and Inconel X-750 alloys were totally immune to anode degradation under pulsed polarization conditions, thus confirming the anode stabilizing effect of (Ti + Al) alloying. The Inconel 617 showed also an excellent gas evolution electrocatalytic activity probably because of its high Co content. Active oxygen formation during anodic gas evolution was a hypothesized mechanism to explain the galvanostatic results. Drastic drop of active oxygen concentration and in particular of the corrosive superoxide ion is supposed to occur on the anode surface during the pulse off-time periods, thus improving Inconel anode stability
Composite Cu-LaFeO3 conversion coatings on a 18Cr ferritic stainless steel for IT-SOFC interconnects: An investigation on structure and formation mechanism
No full textIn this work, a novel iron chemical conversion coating process has been applied to deposit a composite Cu-LaFeO3 perovskite coating layer on a commercial 18Cr ferritic stainless steel for application as Intermediate-Temperature Solid Oxide Fuel Cell (IT-SOFC) interconnect. The conversion process is carried out at 600◦C under a CO2 gas atmosphere in a binary eutectic lithium-sodium molten carbonate bath containing lanthanum, magnesium and copper additions in form of their respective oxides. Multi-layer coatings are obtained, with a surface composite layer formed by a dense perovskite polycrystalline thick film with metallic copper particles encased in the perovskite grains grown on a Fe-rich spinel sublayer. Copper oxide additions significantly promote the formation of the LaFeO3 perovskite layer, and the experimental results suggest that galvanic coupling phenomena between the alloy elements and copper take place during the coating formation process. Chemical stability and Cr diffusion barrier properties of the composite coating have been evaluated in air exposure experiments at 700◦C for 200 h. The perovskite phase shows high stability after the high temperature exposure, with no detectable sign of Cr diffusion in the layer. Details on functional properties of these composite conversion coatings for IT-SOFC applications will be reported in a subsequent study. © The Author(s) 2017. Published by ECS. All rights reserved
Catalytic performance of Ni/CaO-Ca12Al14O33catalyst in the green synthesis gas production via CO2reforming of CH4
No full textDry Reforming of Methane over 15wt.% Ni/CaO-Ca12Al14O33 catalyst was performed in a microreactor in the temperature range 600-800°C under atmospheric pressure, at WHSV of 120 Lg-1h-1 and by time on stream of 12 h for producing synthesis gas. The novel catalyst was prepared by Ni wet impregnation of a mixed calcium-aluminum-oxide (CAO) ceramic support. Similarly, a Ni/γ-Al2O3 reference catalyst was prepared. Characterizations were conducted by TGA-FTIR, XRD, SEM-EDS, N2 physisorption, H2-TPR, CO2-TPD, and CO2-TPRn techniques. After calcination(500°C)/reduction(700°C) steps in situ formed CaO promoter was highly dispersed on Ca12Al14O33 carrier, which induced strong basicity. A good anchorage of NiO on CAO support was evidenced by reduction peaks at 490°C and 650°C on the H2-TPR profile. The reduced mesoporous catalyst presented high SBET, large pores volume, and unimodal pore size distribution. High reactants conversions, good H2 and CO selectivity, and H2/CO molar ratio close to unity at 800°C were achieved. Although the catalytic activity of Ni/γ-Al2O3 reference catalyst was slightly better than that of Ni/CaO-Ca12Al14O33 catalyst the stability was worse owing to the excessive carbon build-ups, whereas the novel catalyst displayed a very low carbon deposit on spent catalyst at 600 and 700°C, and negligible coke deposit at 800°C. It was established that the basicity of CaO-Ca12Al14O33 support can play a key role in preventing coke deposition during DRM. The Ni CaO-Ca12Al14O33 can serve as sorbent for CO2 capture and simultaneously for its catalytic conversion in a valuable fuel
A Smart Large-Scale Synthesis of Na1.0Li0.2Ni0.25Mn0.75O2 as Cathode for Na-Ion Batteries
No full textSodium-ion batteries (NIBs) represent one of the alternatives to lithium-ion batteries (LIBs), especially for large-scale energy storage. The interest in these batteries arises due to the intrinsic characteristics of sodium: it is cheap, abundant and, above all, environmentally friendly. Among the possible Na-based materials that could be used as cathode in NIBs, it was decided to investigate the performance of Na1.0Li0.2Ni0.25Mn0.75O2 (NLNMO) spinel. NLNMO is a P2-type layered oxide and has attracted great attention as a cathode for NIBs. Despite its presenting some critical issues, especially regarding stability at high working voltage, it proved to be the most promising candidate among the materials belonging to this family. The activity carried out in the work envisaged the production of 1 kg of NLNMO suitable to be used as a cathode material in NIBs. The fundamental requirement was to obtain a high-quality material, at least equal to that synthesized on a laboratory scale. The most critical steps of the synthesis were studied for the possible scale-up step, namely the mixing of the reagents and the heating step. The laboratory scale synthesis was studied in terms of feasibility and scalability and the most critical points for a large-scale transition were analysed. In particular, the quantity of water to be added in the dissolution phase and the operating conditions of the heat treatment were optimized. To validate the performance of the NLNMO obtained on large-scale, it was used to prepare electrodes that were tested in battery. The electrochemical performances of these electrodes were then compared with those exhibited by the material prepared by laboratory-scale
Easy and Scalable Syntheses of Li1.2Ni0.2Mn0.6O2
Full text linkSolid-state and sol-gel syntheses were selected as easy and scalable methods to prepare a lithium-rich cathode material for lithium-ion batteries. Among the extended family of layered oxides, Li1.2Ni0.2Mn0.6O2 was chosen for its low nickel content and the absence of cobalt. Both synthesis methods involved two heating steps at different temperatures, 600 and 900 °C. The first step is needed to decompose the metal acetates, which were selected as precursors, and the second step is needed to crystallise the material. To obtain a material with well-defined defects, the rate of heating and cooling was carefully controlled. The materials were characterised by X-ray diffraction, SEM coupled with EDS analysis, and thermal analysis and were finally tested as cathodes in a lithium semi cell. The solid-state synthesis allowed us to obtain better structural characteristics with respect to the sol-gel one in terms of a well-formed hexagonal layer structure and a reduced Li+/Ni2+ disorder. On the other hand, the sol-gel method produced a material with a higher specific capacity. The performance of this latter material was then evaluated as a function of the discharge current, highlighting its good rate capabilities
Composite Cu-LaFeO3 coating on high Cr ferritic stainless steels for IT-SOFC interconnects
No full textA molten carbonate dip-coating passivation method has been applied in this work to produce novel copper-LaFeO3 perovskite composite conversion coatings on a commercial 18Cr ferritic stainless steel. The passivation treatment promotes the formation of a multi-layer conversion coating consisting of a dense perovskite layer grown onto a spinel oxide sublayer and characterized by the presence of copper metal particles embedded in the perovskite grains. A relation between copper addition to the molten salt bath and optimal conversion conditions is observed, with higher copper concentration resulting in accelerated passivation kinetics. When exposed to short-term oxidation experiments in air at 700°C, the perovskite layer exhibits remarkable stability, while copper gets oxidized and diffuses in the spinel sublayer. The coating is found also to act as efficient barrier to the outward diffusion of chromium, being the chromium largely confined to the steel-coating interface. © 2017 The Electrochemical Society
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