1,721,003 research outputs found
Comparative analysis of insulating properties of plasma and thermally grown alumina films on electrospark aluminide coated 9Cr steels
No full textIron aluminides with a protective alumina layer are considered candidate coating for test blanket modules of fusion reactor. In order to study the properties of plasma grown alumina in comparison with thermally grown alumina, oxidation studies on electro spark deposited (ESD) FeAl coating have been conducted. Glow discharge plasma oxidation has been adopted as plasma oxidation technique. Reduced activation 9Cr steel samples were coated with a coating of iron aluminide (FeAl) layer containing 45at% Al. The ESD coated 9Cr steels were oxidized in air and plasma environments at 750°C for 48h. Resultant surfaces were studied using X-ray diffraction, electron probe microanalysis, SEM and electrochemical impedance spectroscopy (EIS) techniques. Although the presence of Al2O3 was found on both thermally oxidized and plasma oxidized samples, the EIS studies clearly revealed improved dielectric properties of plasma grown Al2O3. The plasma grown oxide thin films seems a promising approach to apply alumina coatings with improved dielectric properties onto fusion reactor materials. © 2015 Elsevier B.V
Molten carbonates for advanced and sustainable energy applications: Part II. Review of recent literature
No full textUnprecedented interest for clean and sustainable energy innovation has recently stimulated a return of attention on molten alkali carbonate salts not only for traditional use as electrolyte and high temperature reaction media but also as innovative energetic material for advanced applications in hybrid fuel cell systems and high-temperature CO2 gas separation processes. The main focus of this literature review is on examining novel and emerging molten carbonate applications in energy sectors beyond the well-assessed and mature domain of the Molten Carbonate Fuel Cells. In general, a number of advanced processes and highly functional materials are currently under investigation involving molten carbonates in a key role, suggesting a high potential of these salt systems for the future development of sustainable energy technologies. Current research activities can be grouped into three main energy research areas related to generation/conversion/storage of energy, materials and manufacturing processes, hot gas processing and gasification technologies. As already analyzed in Part I of this work, notable features of molten carbonates include their chemical stability, safety and optimal performance under a wide range of moderate (500–600 °C) and moderate-to-high temperature (600–800 °C) conditions. Thanks to these peculiar aspects, molten carbonate processes can be ideally integrated with solar energy sources for maximum sustainable level of use and with broad development prospects in the storage of solar energy and solar-to-chemical conversion systems. This view is confirmed, for example, by a series of extensive studies that has recently investigated novel solar-to-chemical energy conversion strategies based on a molten carbonate electrolysis process for solar production of fuels and other important chemical products, including iron and cement. In the last part of this work, several directions and opportunities for future research and studies on molten carbonates are suggested. © 2016 Hydrogen Energy Publications LL
Influence of lanthanum carbonate additions on thermal stability of eutectic lithium-sodium carbonate near its melting point
No full textThermal behavior and stability of eutectic 52/48 Li/Na carbonate mixture containing various concentrations of lanthanum carbonate in the range 0.5-2.0 mol% was investigated by a combination of thermal analysis (DSC) and spectroscopic (EGA-FTIR) techniques under CO2 and N2 gas flows. Thermal decomposition of lanthanum carbonate with CO2 gas release was observed in the 470-480 °C range close to the melting point of eutectic alkali carbonate giving raise to formation of lanthanum oxycarbonate species. It was also found that the lanthanum carbonate phase promptly reformed, when the eutectic carbonate melt samples were cooled down to 440-460 °C under CO2 atmosphere. © 2012 Elsevier B.V. All rights reserved
Molten carbonates for advanced and sustainable energy applications: Part I. Revisiting molten carbonate properties from a sustainable viewpoint
No full textIn addition to the traditional fuel cell field, recent research on molten alkali carbonates is increasingly directed towards their use as efficient reaction medium or for the preparation of highly functional materials in advanced, low fossil-carbon and sustainable energy applications. The expansion of renewable energy use, and particularly of solar power, appears to be a major driving force behind the new wave of molten carbonate studies. However, since the relevant molten carbonate literature in the new field of sustainable energy is still relatively small, this work is an attempt to stimulate further and more systematic investigations on molten carbonates by revisiting some of their characteristic properties from a modern and sustainable perspective. In particular, this work is specifically focused on molten carbonate properties that are important for uses as electrolyte or reaction media. Specific properties that have been considered as major indicator of technological sustainability include safe melt chemistry, thermal and moisture stability, high electrical conductivity combined with low metallic corrosiveness, ease to regenerate, tunable acid-base and redox properties, and catalytic activity in gasification and partial oxidation reactions. From this analysis it can be concluded that molten carbonates are very stable systems under a wide range of chemical conditions and mild to moderate temperature ranges, giving the possibility of designing ideal reaction and electrolyte media for advanced chemical/electrochemical processes related to production, storage, conversion and efficient uses of renewable energy, particularly of solar energy, in future low-carbon energy scenarios
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
Thermal stability and oxidizing properties of mixed alkaline earth-alkali molten carbonates: A focus on the lithium-sodium carbonate eutectic system with magnesium additions
No full textA comparative study on thermal behavior and oxygen solubility properties of eutectic 52/48 lithium/sodium carbonate salt containing minor additions of magnesium up to 10 mol% has been made in order to determine whether a general correlation between these two properties can be found or not. Consecutive TG/DSC heating/cooling thermal cycles carried out under alternating CO2 and N2 gas flows allowed to assign thermal events observed in the premelting region to a partial decarbonation process of the magnesium-alkali mixed carbonates. The observed decarbonation process at 460 C is believed to come from initial stage of thermal decomposition of magnesium carbonate resulting in the metastable formation of magnesium oxycarbonate-like phases MgO·2MgCO3, in a similar manner as previously reported for lanthanum. Reversible formation and decomposition of the magnesium carbonate phase has been observed under a CO2 gas atmosphere. The intensity of the decomposition process shows a maximum for a 3 mol% MgO addition that gives also the highest oxygen solubility, suggesting therefore that instability thermal analysis in the premelting region can be considered as providing an effective measure of the basicity/oxidizing properties of alkali carbonate melts with magnesium or, in more general terms, with cations that are strong modifiers of the carbonate melt basicity through formation of soluble oxycarbonate phases. © 2013 Elsevier B.V
The role of foreign cations in enhancing the oxygen solubility properties of alkali molten carbonate systems: Brief survey of existing data and new research results
No full textThis work presents a summary of experimental data on the oxygen solubility-speciation properties of alkali molten carbonates that have been obtained by the authors through the development of a highly sensitive analysis method. The purpose of this summary is to show in particular the effect of foreign cation additions on both oxygen solubility and dissolution mechanisms at 650°C. Our findings may be used to clearly indicate that rare earth and magnesium cations are the most effective in enabling oxygen solubility and basicity/oxidizing melt properties. The second part of this work reports new experimental results concerning the effect of simultaneous additions of La and Mg cations to an eutectic Li/Na carbonate system. A dramatic increase in oxygen solubility and active peroxide oxygen species has been found, thus revealing a strong synergistic effect of rare earth and alkaline earth cations on the molten carbonate oxygen chemistry. The results of this investigation suggest therefore that foreign cation addition is a potentially attractive option to design alkali molten carbonate salts with a high oxidizing power. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
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
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
Temperature-independent sensors based on perovskite-type oxides
No full textThe need of energy security and environment sustainability drives toward the development of energy technology in order to enhance the performance of internal combustion engines. Gas sensors play a key role for controlling the fuel oxygen ratio and monitoring the pollution emissions. The perovskite-type oxides can be synthesized for an extremely wide variety of combinations of chemical elements, allowing to design materials with suitable properties for sensing application. Lanthanum strontium ferrites, such as La 0.7Sr0.3FeO3, are suitable oxygen sensing materials with temperature-independence conductivity, but they have low chemical stability under reducing conditions. The addition of aluminum into the perovskite structure improves the material properties in order to develop suitable oxygen sensing probes for lean burn engine control systems. Perovskite-type oxides with formula (La0.7Sr0.3FeO 3,)(AlxFe1-x)O3 was synthesized by the citrate-nitrate combustion synthesis method. XRD analyses, show that it was synthesized a phase-pure powder belonging to the perovskite structure. Aluminum affects both the unit cell parameters, by shrinking the unit cell, and the powder morphology, by promoting the synthesis of particles with small crystallite size and large specific surface area. The partial substitution of iron with aluminum improves the chemical stability under reducing gas conditions and modulates the oxygen sensitivity by affecting the relative amount of Fe4+ and Fe3+, as confirmed from TPR profiles. In the same time, the addition of aluminum does not affects the temperature-independent properties of lanthanum strontium ferrites. Indeed, the electrical measurements show that (La0.7Sr0.3)(AlxFe1-x)O3 perovskites have temperature-independence conductivity from 900 K. © 2014 AIP Publishing LLC
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