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Artykuły w czasopismach na temat "High entropy oxide"
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Bridges, Craig A., Bishnu Prasad Thapaliya, Albina Borisevich, Juntian Fan i Sheng Dai. "(Invited) High Entropy Multication Oxide Battery Materials". ECS Meeting Abstracts MA2022-02, nr 1 (9.10.2022): 29. http://dx.doi.org/10.1149/ma2022-02129mtgabs.
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High entropy oxides (HEOs), in which multication occupation of a single crystallographic site plays an important role in the properties, have become relevant in energy storage [1,2], catalysis [3.4], and many more areas. In a subset of these compounds the entropy, rather than enthalpy, plays a dominant role in stabilizing a single-phase structure at high temperatures. In other cases, the multication occupation merely contributes to stability and properties, but the entropy remains dominant in the stability. The field originated with high entropy metal alloys (HEAs)[5], and then expanded to oxides, borides, sulfides, and more. In the case of HEOs, the first example is the rock salt (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O, which has generated a great deal of interest in this class of materials.[6,7] It has been shown that HEOs are of interest for high ionic conductivity and electrochemical energy storage. We have examined the electrochemical performance of new high entropy elecrolytes and found an effect of composition on the cycling performance. Samples were prepared through sol-gel routes and high energy milling of starting binary oxides. We have investigated the synthesis using high temperature in-situ X-ray diffraction on a Panalytical diffractometer equipped with an XRK900 stage. STEM/EDS studies on ex-situ samples will be presented that show elemental distribution, with Raman and EIS measurements providing information on ionic diffusion. The results of this study will be highly impactful for the growing community of researchers investigating the design and synthesis of the new class of materials, the high entropy oxides. [1] Q. Wang, et. al., Multi-anionic and -cationic compounds: new high entropy materials for advanced Li-ion batteries, Energy Environ. Sci., 2019, 12, 2433; [2] D. Berardan, et. al., Room temperature lithium superionic conductivity in high entropy oxides, J. Mater. Chem. A, 2016, 4, 9536.; [3] H. Chen, et al., Mechanochemical Synthesis of High Entropy Oxide Materials under Ambient Conditions: Dispersion of Catalysts via Entropy Maximization, ACS Materials Lett. 2019, 1, 1, 83–88; [4] H. Chen, et. al., Entropy-stabilized metal oxide solid solutions as CO oxidation catalysts with high-temperature stability, J. Mater. Chem. A 2018, 6, 11129-11133; [5] Y. Lu, et. al., Sci. Rep. 4, 6200 (2014); Y. F. Ye, et. al., Mater. Today 19 (6), 349 (2016); Zhang, Y., et. al., Nature Commun. 6, 8736 (2015); [6] C. M. Rost, et. al., Nature Commun. 6, 8485 (2015); [7] B. Jiang, et. al., Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides. Journal of the American Chemical Society 2021, 143, (11), 4193-4204
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Meisenheimer, P. B., i J. T. Heron. "Oxides and the high entropy regime: A new mix for engineering physical properties". MRS Advances 5, nr 64 (2020): 3419–36. http://dx.doi.org/10.1557/adv.2020.295.
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AbstractHistorically, the enthalpy is the criterion for oxide materials discovery and design. In this regime, highly controlled thin film epitaxy can be leveraged to manifest bulk and interfacial phases that are non-existent in bulk equilibrium phase diagrams. With the recent discovery of entropy-stabilized oxides, entropy and disorder engineering has been realized as an orthogonal approach. This has led to the nucleation and rapid growth of research on high-entropy oxides – multicomponent oxides where the configurational entropy is large but its contribution to its stabilization need not be significant or is currently unknown. From current research, it is clear that entropy enhances the chemical solubility of species and can realize new stereochemical configurations which has led to the rapid discovery of new phases and compositions. The research has expanded beyond studies to understand the role of entropy in stabilization and realization of new crystal structures to now include physical properties and the roles of local and global disorder. Here, key observations made regarding the dielectric and magnetic properties are reviewed. These materials have recently been observed to display concerted symmetry breaking, metal-insulator transitions, and magnetism, paving the way for engineering of these and potentially other functional phenomena. Excitingly, the disorder in these oxides allows for new interplay between spin, orbital, charge, and lattice degrees of freedom to design the physical behavior. We also provide a perspective on the state of the field and prospects for entropic oxide materials in applications considering their unique characteristics.
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Oh, Seeun, Dongyeon Kim i Kang Taek Lee. "High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells". ECS Transactions 111, nr 6 (19.05.2023): 1743–49. http://dx.doi.org/10.1149/11106.1743ecst.
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Reversible protonic ceramic electrochemical cells (R-PCECs) have become the cornerstone of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.
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Li, Haoyang, Yue Zhou, Zhihao Liang, Honglong Ning, Xiao Fu, Zhuohui Xu, Tian Qiu, Wei Xu, Rihui Yao i Junbiao Peng. "High-Entropy Oxides: Advanced Research on Electrical Properties". Coatings 11, nr 6 (24.05.2021): 628. http://dx.doi.org/10.3390/coatings11060628.
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The concept of “high entropy” was first proposed while exploring the unknown center of the metal alloy phase diagram, and then expanded to oxides. The colossal dielectric constant found on the bulk high-entropy oxides (HEOs) reveals the potential application of the high-entropy oxides in the dielectric aspects. Despite the fact that known HEO thin films have not been reported in the field of dielectric properties so far, with the high-entropy effects and theoretical guidance of high entropy, it is predictable that they will be discovered. Currently, researchers are verifying that appropriately increasing the oxygen content in the oxide, raising the temperature and raising the pressure during preparation have an obvious influence on thin films’ resistivity, which may be the guidance on obtaining an HEO film large dielectric constant. Finally, it could composite a metal–insulator–metal capacitor, and contribute to sensors and energy storage devices’ development; alternatively, it could be put into application in emerging thin-film transistor technologies, such as those based on amorphous metal oxide semiconductors, semiconducting carbon nanotubes, and organic semiconductors.
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Sharma, Yogesh, Min-Cheol Lee, Krishna Chaitanya Pitike, Karuna K. Mishra, Qiang Zheng, Xiang Gao, Brianna L. Musico i in. "High Entropy Oxide Relaxor Ferroelectrics". ACS Applied Materials & Interfaces 14, nr 9 (28.02.2022): 11962–70. http://dx.doi.org/10.1021/acsami.2c00340.
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Kajitani, Tsuyoshi, Yuzuru Miyazaki, Kei Hayashi, Kunio Yubuta, X. Y. Huang i W. Koshibae. "Thermoelectric Energy Conversion and Ceramic Thermoelectrics". Materials Science Forum 671 (styczeń 2011): 1–20. http://dx.doi.org/10.4028/www.scientific.net/msf.671.1.
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Oxide thermoelectrics are relatively new materials that are workable at temperatures in the range of 400K≤T≤1200K. There are several types of thermoelectric oxide, namely, cobalt oxides (p-type semi-conductors), manganese oxides (n-type) and zinc oxides (n-type semi-conductors) for high temperature energy harvesting. The Seebeck coefficient of 3d metal oxide thermoelectrics is relatively high due to either high density of states at Fermi surfaces or spin entropy flow associated with the carrier flow. The spin entropy part dominates the Seebeck coefficient of 3d-metal oxides at temperatures above 300K. Introduction of impurity particles or quantum-well structures to enhance thermionic emission and energy filtering effects for the oxide semiconductors may lead to a significant improvement of thermoelectric performance.
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Tanveer, Rubayet, i Veerle M. Keppens. "Resonant ultrasound spectroscopy studies of high-entropy fluorites". Journal of the Acoustical Society of America 152, nr 4 (październik 2022): A131. http://dx.doi.org/10.1121/10.0015786.
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High entropy oxides (HEOs), also referred to as multicomponent oxides or compositionally complex oxides (CCOs), have attracted attention due to the tunability of multiple cations on a single site. Since the introduction of HEOs stabilized in the rocksalt phase, the high entropy oxide concept has been expanded to various structures, offering a path for the discovery of innovative compounds with unique structure-property relations. Here, we present a study of high entropy fluorites, which have gained recognition for their low thermal conductivity and possible applications as thermal barrier coatings. We have successfully synthesized single phase samples using multiple cations on a single site, in equimolar and non-equimolar ratios. Resonant ultrasound spectroscopy was used to evaluate the elastic moduli as a function of temperature. The results obtained on these multi-component pyrochlores are compared to those of their single-component counterparts.
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Wang, Junfeng, Qiaobai He, Guanqi Liu, Qi Zhang, Guotan Liu, Zhihao Huang, Xiaoshuo Zhu i Yudong Fu. "High-Temperature Oxidation Behavior of AlTiNiCuCox High-Entropy Alloys". Materials 14, nr 18 (15.09.2021): 5319. http://dx.doi.org/10.3390/ma14185319.
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In this study, the high-temperature oxidation behavior of a series of AlTiNiCuCox high-entropy alloys (HEAs) was explored. The AlTiNiCuCox (x = 0.5, 0.75, 1.0, 1.25, 1.5) series HEAs were prepared using a vacuum induction melting furnace, in which three kinds of AlTiNiCuCox (x = 0.5, 1.0, 1.5) alloys with different Co contents were oxidized at 800 °C for 100 h, and their oxidation kinetic curves were determined. The microstructure, morphology, structure, and phase composition of the oxide film surface and cross-sectional layers of AlTiNiCuCox series HEAs were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influence of Co content on the high-temperature oxidation resistance of the HEAs was discussed, and the oxidation mechanism was summarized. The results indicate that, at 800 °C, the AlTiNiCuCox (x = 0.5, 1.0, 1.5) series HEAs had dense oxide films and certain high-temperature oxidation resistance. With increasing Co content, the high-temperature oxidation resistance of the alloys also increased. With increasing time at high temperature, there was a significant increase in the contents of oxide species and Ti on the oxide film surface. In the process of high-temperature oxidation of AlTiNiCuCox series HEAs, the interfacial reaction, in which metal elements and oxygen in the alloy form ions through direct contact reaction, initially dominated, then the diffusion process gradually became the dominant oxidation factor as ions diffused and were transported in the oxide film.
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Hashishin, Takeshi, Haruka Taniguchi, Fei Li i Hiroya Abe. "Useful High-Entropy Source on Spinel Oxides for Gas Detection". Sensors 22, nr 11 (1.06.2022): 4233. http://dx.doi.org/10.3390/s22114233.
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This study aimed to identify a useful high-entropy source for gas detection by spinel oxides that are composed of five cations in nearly equal molar amounts and free of impurities. The sensor responses of the spinel oxides [1# (CoCrFeMnNi)3O4, 2# (CoCrFeMnZn)3O4, 3# (CoCrFeNiZn)3O4, 4# (CoCrMnNiZn)3O4, 5# (CoFeMnNiZn)3O4, and 6# (CrFeMnNiZn)3O4] were evaluated for the test gases (7 ppm NO2, 5000 ppm H2, 3 ppm NH3, and 3 ppm H2S). In response to NO2, 1# and 2# showed p-type behavior while 3–6# showed n-type semiconductor behavior. There are three p-type and one n-type AO structural compositions in AB2O4[AO·B2O3] type spinel, and 1# showed a stable AO composition because cation migration from site B to site A is unlikely. Therefore, it was assumed that 1# exhibited p-type behavior. The p-type behavior of 2# was influenced by Cr oxide ions that were present at the B site and the stable p-type behavior of zinc oxide at the A site. The spinel oxides 3# to 6# exhibited n-type behavior with the other cationic oxides rather than the dominant p-type behavior exhibited by the Zn oxide ions that are stable at the A site. In contrast, the sensor response to the reducing gases H2, NH3, and H2S showed p-type semiconductor behavior, with a particularly selective response to H2S. The sensor responses of the five-element spinel oxides in this study tended to be higher than that of the two-element Ni ferrites and three-element Ni-Zn ferrites reported previously. Additionally, the susceptibility to sulfurization was evaluated using the thermodynamic equilibrium theory for the AO and B2O3 compositions. The oxides of Cr, Fe, and Mn ions in the B2O3 composition did not respond to H2S because they were not sulfurized. The increase in the sensor response due to sulfurization was attributed to the decrease in the depletion layer owing to electron sensitization, as the top surface of the p-type semiconductors, ZnO and NiO, transformed to n-type semiconductors, ZnS and NiS, respectively. High-entropy oxides prepared using the hydrothermal method with an equimolar combination of five cations from six elements (Cr, Mn, Fe, Co, Ni, and Zn) can be used as a guideline for the design of high-sensitivity spinel-type composite oxide gas sensors.
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Ke, Lingsheng, Long Meng, Sheng Fang, Chun Lin, Mingtian Tan i Tao Qi. "High-Temperature Oxidation Behaviors of AlCrTiSi0.2 High-Entropy Alloy Doped with Rare Earth La and Y". Crystals 13, nr 8 (27.07.2023): 1169. http://dx.doi.org/10.3390/cryst13081169.
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High-entropy alloys (HEAs) were prepared with strong antioxidant metals Al, Cr, Ti, and Si as matrix elements, and the effects of rare earth (RE) lanthanum (La) and yttrium (Y) doping on their microstructures and high-temperature oxidation resistance were explored in this study. The AlCrTiSi0.2RE0.02 HEAs were prepared by using vacuum arc melting and were oxidized mass gain at 1000 °C. After oxidation for 53 h, AlCrTiSi0.2 HEA had a mass increase of 1.195 mg/cm2, and it had the best oxidation resistance of three HEAs (AlCrTiSi0.2, AlCrTiSi0.2La0.02, and AlCrTiSi0.2Y0.02). The surface oxide layers of three HEAs mainly consisted of Al and Ti oxides; the layered oxide film of AlCrTiSi0.2 alloy was mainly composed of dense Al2O3, and the acicular oxide films of AlCrTiSi0.2La0.02 and AlCrTiSi0.2Y0.02 alloys were primarily composed of loose Ti oxide. Doping La and Y decreased the oxidation resistance of AlCrTiSi0.2. In the early stage of oxidation of rare earth HEAs, the surface oxide layer was loose because La and Y reacted with the matrix metal, which slowed down the diffusion of element Al or accelerated the diffusion of element Ti. In the late stage of oxidation, La and Y interacted with O and entered the matrix metal to form rare earth oxides.
Rozprawy doktorskie na temat "High entropy oxide"
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Sarkar, Abhishek Verfasser], Horst [Akademischer Betreuer] [Hahn i Jürgen [Akademischer Betreuer] Janek. "High Entropy Oxides: Structure and Properties / Abhishek Sarkar ; Horst Hahn, Jürgen Janek". Darmstadt : Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1222674432/34.
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Sarkar, Abhishek [Verfasser], Horst [Akademischer Betreuer] Hahn i Jürgen [Akademischer Betreuer] Janek. "High Entropy Oxides: Structure and Properties / Abhishek Sarkar ; Horst Hahn, Jürgen Janek". Darmstadt : Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1222674432/34.
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CHIANG, CHIA-LIANG, i 江家樑. "Optical Properties of RF-Sputtered High-Entropy Alloy CrNiTiSiZr Oxide Thin Films". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/43m7sb.
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碩士輔仁大學
物理學系碩士班
106
In this study, the high-entropy alloy CrNiTiSiZr filmsare coated by using an RF sputtering system. The optical properties and compositions of high-entropy alloy CrNiTiSiZr films are observed under different deposition pressures. It is expected that high-entropy alloy CrNiTiSiZr films could be used on the optical system in the future. The samples were illustrated by ellipsometry, spectrometer, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The optical properties of the films were analyzed for their refractive index, absorption, and binding energy. The results show that the high-entropy alloy CrNiTiSiZr film deposited at the argon flow rate of 30 sccm has the maximum variation in refractive index and extinction coefficient as increasing the visible wavelength. The oxygen composition in the high-entropy alloy CrNiTiSiZr becomes less as decreasing the argon flow rate. The optical energy gap is directly proportional to the oxygen content. However, the XRD peaks didn’t change apparently as increasing the argon flow rate. When the film deposited at the argon flow rate 20 sccm, it contains the minimum oxygen composition of (26.36 at.%) and the minimum energy gap of (3.97 eV).The transmittance is also affected by the oxygen content, refractive index and extinction coefficient of the films. Such as, the film deposited at argon flow of 30 sccm has the lowest transmittance.The absorption is the largest at argon flow of 30 sccm.
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Aliyu, Ahmed. "Microstructure and Electrochemical Properties of Electrodeposited High Entropy Alloys Coatings". Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5540.
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High entropy alloys (HEA) are composed of five or more alloying elements in a nearly equi-atomic ratio. HEAs exhibit high oxidation and corrosion resistance behaviour. In this work, HEA coatings were electrodeposited over mild steel substrate from an aqueous electrolyte bath. Microstructure-corrosion property correlation for as-deposited pristine HEA and HEA-graphene oxide (GO) composite coatings was examined. Four different HEA coating systems were investigated: CrNiCoFeCu, CrNiCoFeMn, AlNiCoFeCu, and AlCrNiCoFeCu HEA coatings. Corrosion behaviour and passive film constitution of CrNiCoFeCu and CrNiCoFeMn coatings were compared, and it was observed that the formation of relatively stable protective Cr, Co, and Mn oxide corrosion products on the surface of the CrNiCoFeMn coating enhanced the corrosion resistance of this coating. In contrast, the formation of Fe, Cr, and Cu oxide corrosion products on the surface of CrNiCoFeCu coating were de-stabilized by the inter-dendritic segregation of the Cu-rich phase leading to the lower corrosion resistance of the CrNiCoFeCu coating. In the case of AlNiCoFeCu and AlCrNiCoFeCu coating, the effect of Cr on the evolution of oxide phase in Al-containing HEA coatings was compared. The formation of a denser and more stable protective oxide layer on the surface of AlCrNiCoFeCu HEA coating resulted in better corrosion resistance performance compared to the AlNiCoFeCu HEA coating, which had a lesser stable and defective protective oxide layer. It was observed that Cr facilitates the formation of other metallic oxides in the passive film, which enhanced its ability to reduce ionic diffusion and improve the corrosion resistance of the Cr containing AlCrNiCoFeCu HEA coating. In the case of CrNiCoFeCu HEA-GO composite coatings, with GO addition, the corrosion current density and corrosion rate reduced. while, the polarization resistance increased, indicating an enhancement in the corrosion resistance property of the CrNiCoFeCu HEA-GO coatings with increase in the GO content. The microstructural characterization of the coatings showed that GO addition into the CrNiCoFeCu matrix resulted in two distinct microstructural changes; one was increase in the Cr-rich phase, and the other was the formation of Cu-rich and Cr-rich layer over the coating surface which can facilitate the formation of the protective oxide film that can hinder the penetration of the electroactive media. These factors, along with the impermeability imparted by GO resulted in enhancement in the corrosion resistance of the CrNiCoFeCu HEA-GO coatings. In the case of CrNiCoFeMn HEA-GO composite coating, morphology of the coating showed that the relative smoothness and compactness of the coatings increased with GO additions. A significant improvement in the corrosion resistance in terms of reduction in the corrosion current density and corrosion rate and increased corrosion potential and polarization resistance was recorded for the GO containing CrNiCoFeMn HEA coatings, which implied enhancement in the corrosion resistance performance of the coatings. Microstructural characterization of CrNiCoFeMn HEA coatings revealed that the GO addition resulted in distinct microstructural changes; with GO addition, the microstructure transformed from a nearly homogenous microstructure to a microstructure containing FeCoNi rich regions embedded in an Mn-Cr rich matrix. The formation of a strongly oxidizing matrix capable of forming relatively stable protective oxide layers and impermeability imparted by the GO were accounted for the observed enhancement in the corrosion resistance of the CrNiCoFeMn HEA-GO composite coatings as compared to the pristine CrNiCoFeMn HEA coating. In the case of AlNiCoFeCu HEA-GO composite coatings, the as-deposited AlNiCoFeCu HEA coating exhibited a granular morphology, which became finer and relatively more compact with increasing in the GO amount. Structural characterization revealed a mixture of BCC and FCC phases, with a fraction of the FCC phase increasing with GO. The coatings' electrochemical properties showed that AlNiCoFeCu HEA-GO composite coatings' corrosion rate progressively decreased with increase in the GO content. Microstructural characterization revealed a highly Al-rich matrix phase and Co, Ni, Cu, and Fe containing dendritic phase in the coating microstructure for the pristine coating. With the addition of GO, the coating microstructure progressively became more compositionally homogeneous. Al distribution between the matrix and dendritic phases became more uniform. Microstructural homogenization reduced the extent of galvanic coupling between phases and uniform distribution of Al, which can form stable and protective alumina phase along with the impermeability properties of GO enhanced the corrosion resistance performance of the AlNiCoFeCu HEA-GO composite coatings when compared to pristine AlNiCoFeCu HEA coating. In the case of AlCrNiCoFeCu HEA-GO composite coatings, the corrosion resistance of the AlCrNiCoFeCu HEA-GO composite coatings was higher than the AlCrNiCoFeCu HEA coating without GO. Corrosion resistance gradually increased with increase in the GO content in the coating. Detailed microstructural characterization revealed that GO addition facilitated microstructural and compositional homogeneity, eliminating localized corrosive attack due to elemental segregation induced galvanic coupling, thereby increasing the corrosion resistance for the AlCrNiCoFeCu HEA-GO composite coatings.
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Patel, Ranjan Kumar. "Electronic behavior of epitaxial thin films of doped rare-earth nickelates". Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6129.
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Rare-earth nickelates (RENiO3), a family of transition metal oxides, exhibit a complex phase diagram involving electronic, magnetic, and structural phase transitions. While LaNiO3 remains paramagnetic, metallic down to very low temperature, RENiO3 members with RE=Nd, Pr exhibit simultaneous metal-insulator transition (MIT), paramagnetic to antiferromagnetic transition, structural phase transition and a bond disproportionation (BD) transition as a function of temperature. The other members of the series such as EuNiO3, SmNiO3, etc. first undergo simultaneous MIT, BD, and structural phase transition and further becomes antiferromagnetic upon lowering the temperature. Understanding the origin of the MIT in this family remains a challenging problem and has attracted a lot of attention in recent times. The MIT temperature can be tuned by a variety of parameters such as chemical doping, pressure, epitaxial strain, light, etc. In this thesis, we have grown epitaxial thin films of doped rare-earth nickelates and investigated their electronic and magnetic behavior using several experimental techniques, including synchrotron-based measurements.
In the first part, we have investigated Ca2+ (divalent) and Ce4+ (tetravalent) doped NdNiO3 thin films. Doping with divalent ions at the Nd sites introduces holes, whereas doping with tetravalent ions introduces electrons, resulting in a change in the formal valence of Ni. Both electron and hole doping suppress the insulating phases with asymmetric suppression rates for the metal-insulator phase transition. We have shown that the effective charge transfer energy changes with carrier doping and the formation of the BD phase is not favored above a critical doping, suppressing the insulating phase. Our research clearly shows that the appearance of BD mode is critical for the appearance of MIT in RENiO3 family.
In the second part, we have investigated rare-earth nickelate in high entropy oxide (HEO) form. HEOs are defined as a class of materials containing equimolar or nearly equimolar portions of five or more elements stabilizing in a single phase. HEOs have been explored in recent years to achieve tunable properties in unexplored parts of the complex phase diagram. However, epitaxial stabilization of such multi-element systems is challenging, and it is unknown how epitaxial strain will affect the electronic and magnetic behavior of HEO. We have been able to grow (LaPrNdSmEu)0.2NiO3 [(LPNSE)NO] thin films on different substrates having different epitaxial strains. We have shown that, in spite of having multi-element and strong disorder at the RE site, the average tolerance factor determines the electronic and magnetic properties. We further studied the strain effect on MIT of those HEO thin films. We have observed that (LPNSE)NO film grown under tensile strain (substrates: NdGaO3 and SrTiO3) exhibits a metal-insulator transition. We have found that this transition can be completely suppressed by compressive strain exerted by SrLaAlO4 substrate. Surprisingly, HEO film, grown on SrPrGaO4 substrate, where the strain is almost negligible, does not exhibit any MIT. We have further demonstrated that the octahedral rotation pattern of the substrate governs the octahedral rotation and Ni-O-Ni bond angle of the epitaxial thin films, which in turn controls the MIT.
In the third part, we have explored (LPNSE)NO thin films as electrocatalysts. Oxygen evolution reaction (OER) is a key process in several alternative energy generation platforms such as solar and electric driven water splitting, fuel cells, rechargeable metal-air batteries, etc. We have investigated the thickness dependent OER of (LPNSE)NO thin films and found that the increase of film thickness results in higher OER activity. X-ray absorption spectroscopy measurements find an increase in Ni d-O p covalency and a decrease in charge transfer energy with the increase in film thickness. These facilitate higher charge transfer between Ni and surface adsorbates, resulting in higher OER activity.
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Sarkar, Abhishek. "High Entropy Oxides: Structure and Properties". Phd thesis, 2020. https://tuprints.ulb.tu-darmstadt.de/14345/1/Doctoral_thesis_Abhishek_Sarkar.pdf.
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Since the origin of humankind numerous approaches have been employed to develop new materials. Of these approaches, changing the composition of a given system, typically referred as alloying for metallic and doping for non-metallic systems, is undoubtedly the most common way of designing new materials. Conventionally, alloying or doping implies introduction of relatively small amounts of secondary elements to a base system. The base system typically consists of one major component, e.g., Fe for steels, while in yttria-stabilized zirconia, ZrO2 is considered as the base system. The concept of high entropy materials (HEMs) can be considered as an extreme adaption of alloying or doping, where five or more elements all in (nearly) equal proportions are incorporated into a system. Hence, there is no base element (“baseless”) as such in HEMs. Their unexpected tendency to form single phase solid solutions despite the high chemical complexity makes HEMs unique. Essentially, the combination of several elements in near equiatomic proportion enhances the configurational entropy of HEMs. It is believed, in some cases proven, that this enhanced configurational entropy drives the formation of a single phase solid solution. Due to these distinctive features, the high entropy based design concept is often considered as an original approach, and not a mere extension to alloying or doping.
The subject of studies in this doctoral thesis is high entropy oxides (HEOs). HEOs are phase-pure solid solutions arising from the inclusion of five or more elements into the cationic sub-lattice(s) of oxide materials. Building upon the initial reports on HEOs, the first one published in 2015, the main objective of this work is to investigate the unexplored regions of oxide compositions and structures offered by the high entropy based design approach.
The initial task was the identification and optimization of a suitable synthesis technique for fabrication of HEOs with rocksalt and fluorite structures. In this regard, several techniques, each possessing certain advantages and disadvantages, were explored. Out of these considered ones, aerosol based nebulized spray pyrolysis (NSP) was found to be the most versatile technique for preparation of HEOs on a laboratory scale and was used as the primary synthesis tool in this thesis. The exploration of new HEO systems with different compositions and crystallographic structures was the next challenge. Perovskite type HEOs (P-HEOs) were developed, in which up to 10 different cations in equiatomic proportion can be homogeneously incorporated into a single-phase orthorhombic structure. Besides the synthesis aspect, emphasis was placed on comprehensive understanding of the underlying phase stability mechanisms in different crystal types of HEOs, such as rocksalt, fluorite and perovskite. It was observed that the governing principles were rather distinct for different types of HEOs. In some cases, such as in rocksalt-HEOs (R-HEOs), an entropy-driven phase transformation is dominant, whereas in the other HEOs, aspects like tolerance factors, oxidation state of the cations and related internal charge compensations play determining roles.
Apart from these structural investigations, a major part of this doctoral work is dedicated to explore the functional properties of HEOs. Oxides, in general, show rich structure-composition-property relationships. Hence, the properties of HEOs were explored based on their crystal structure and composition characteristics. Three different classes of properties were investigated: electrochemical, optical and magnetic. Transition metal (TM) based R-HEO was probed as electrode material for secondary Li-ion batteries (LIBs). Highly reversible lithium storage capacities (above 600 mAh/g for more than 900 cycles) were observed. A major part of the capacity is drawn from electrochemical reactions below 1 V (vs Li+/Li), which warrants its possible use as an anode in LIBs. Importantly, a unique electrochemical reaction mechanism, possibly stemming from an entropy effect, was discovered. Rare earth (RE) based fluorite-HEOs (F-HEOs), on the other hand, showed interesting optical properties like narrow band gap of ∼2 eV, which could be reversibly tuned (from 2 – 3.2 eV) by conducting heat treatments under different atmospheres. Element specific techniques, like X-ray absorption spectroscopy (XAS) and energy electron loss spectroscopy (EELS), allowed to disentangle the individual effects of the constituent cations in complex F-HEOs and identify the relevant features in the electronic band structure underpinning the observed reversible changes in the optical behavior. The reason behind the change in band gap is closely associated with the presence of redox active multivalent cations, like Pr3+,4+, which result in the formation of intermediate unoccupied energy states. Finally, P-HEOs comprising of multiple RE cations on the A-site and/or multiple TM cations on the B-site exhibited an interesting interplay between the magnetic exchange interactions and the high degree of chemical disorder in the systems. Additional ferromagnetic interactions in otherwise predominant antiferromagnetic environment leading to exchange anisotropy were observed in phase-pure P-HEOs, wherein the former could be attributed to either small ferromagnetic clusters or spin canting.
In brief, this doctoral work highlights the versatility of the high entropy based design concept in oxides by demonstrating the structure-property relationships in three different crystal structure types of HEOs. As the research on HEOs is still in its early state, a plethora of fundamental aspects of HEOs are yet to be explored to assess their full potential for practical applications.
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張毓倫. "Study on High-Entropy Oxides Synthesized by Nitrate-Solution Method". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/95510250685674090556.
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Yeh, Kuan-Cheng, i 葉冠成. "On the conductivity of high-entropy oxides prepared by nitrate solution method". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/54976830998525260702.
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任德育. "Study on conductivity of high-entropy oxides prepared by solid-state reaction method". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/62206179086891984028.
Pełny tekst źródłaCzęści książek na temat "High entropy oxide"
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Musicó, Brianna L., Cordell J. Delzer, John R. Salasin, Michael R. Koehler i Claudia J. Rawn. "Experimental Characterization of High-Entropy Oxides with In Situ High-Temperature X-Ray Diffraction Techniques". W High-Entropy Materials: Theory, Experiments, and Applications, 413–34. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-77641-1_9.
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Yang, Yu, Tongxiang Ma, Mengjun Hu, Pengjie Liu, Liangying Wen, Liwen Hu i Meilong Hu. "Preparation of CoCrFeNi High-Entropy Alloy via Electro-Deoxidation of Metal Oxides". W TMS 2020 149th Annual Meeting & Exhibition Supplemental Proceedings, 1593–601. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-36296-6_147.
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Kumari, Priyanka, Amit K. Gupta, Shashi Kant Mohapatra i Rohit R. Shahi. "Nanocrystalline High Entropy Alloys and Oxides as Emerging Materials for Functional Applications". W Nanomaterials, 145–76. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-7963-7_6.
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Mebratie Bogale, Gedefaw, i Dagne Atnafu Shiferaw. "Iron-Based Superconductors". W High Entropy Materials - Microstructures and Properties [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.109045.
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Superconductivity is the phenomenon of vanishing an electrical resistivity of materials below a certain low temperature and superconductors are the materials that show this property. Critical temperature is the temperature below which superconducting state occurs. Based on temperature superconductors can be grouped into high-temperature superconductors and low-temperature superconductors. Based on the mechanism, they can be grouped into conventional and unconventional superconductors. Based on magnetism superconducting materials can also be separated into two groups: type-I and type-II superconductors. In this chapter, we will discuss superconductivity, the Meissner effect, type-I and type-II superconductors, convectional and unconvectional superconductors, heavy fermions, cuprates, iron-based superconductors, and high entropy alloy superconductors. High-entropy alloys (heas) are defined as alloys containing at least five elements with concentrations between 5 and 35 atom%. The atoms randomly distribute on simple crystallographic lattices, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures. The superconducting behavior of heas is distinct from copper oxide superconductors, iron-based superconductors, conventional alloy superconductors, and amorphous superconductors, suggesting that they can be considered as a new class of superconducting materials.
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Sarkar, Abhishek, Horst Hahn i Robert Kruk. "High Entropy Oxides". W Reference Module in Materials Science and Materials Engineering. Elsevier, 2023. http://dx.doi.org/10.1016/b978-0-12-819728-8.00096-6.
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Pu, Yuguang, Saifang Huang i Peng Cao. "High-entropy oxides for energy storage and catalysis". W Advanced Ceramics for Energy Storage, Thermoelectrics and Photonics, 209–36. Elsevier, 2023. http://dx.doi.org/10.1016/b978-0-323-90761-3.00015-2.
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Saadat Arif, Huseynova, Panakhova Nushaba Farkhad, Orujova Pusta Ali, Hajiyeva Nurangiz Nizami, Hajiyeva Adila Sabir, Mukhtarova Sevinj Nabi i Agayeva Gulnaz Telman. "Endothelial Dysfunction and Intestinal Barrier Injury in Preterm Infants with Perinatal Asphyxia". W Maternal and Child Health [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.110352.
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Perinatal asphyxia is one of the most frequent causes of perinatal morbidity, accounting for approximately 23% of neonatal deaths worldwide. Fetuses that suffer from hypoxia-ischemia are at high risk of developing multiorgan dysfunction, including the gut. Hypoxie-induced gut injury may result in adverse clinical outcomes, such as feeding intolerance and necrotizing enterocolitis. Increased permeability and subsequently an enhanced entry of bacteria and endotoxins into the systemic circulation can contribute to endotoxin aggression and further trigger numerous diseases. The aim of study is to investigate the effect of perinatal asphyxia on the integrity of the intestinal barrier and the state of antiendotoxin immunity. The study included preterm neonates exposed to perinatal asphyxia, who were comparable with non-asphyxiated infants. The concentrations of intestinal mucosa barrier injury markers (intestinal fatty acid binding protein, liver fatty acid protein, lipopolysaccharide binding protein), neurospecific proteins (neurospesific enolase, NR-2 antibodies), and also endothelial dysfunction markers (endothelin-1, nitric oxide) were determined in serum of included neonates on day of 1 and 7. The high risk of intestinal mucosal injury in newborn exposed to perinatal asphyxia decreases the level of antiendotoxic immunity and should be considered as an unfavorable factor for sepsis.
Streszczenia konferencji na temat "High entropy oxide"
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GUMEN, O. "High-Temperature Oxidation of High-Entropy FeNiCoCrAl Alloys". W Quality Production Improvement and System Safety. Materials Research Forum LLC, 2023. http://dx.doi.org/10.21741/9781644902691-4.
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Abstract. Phase composition and mechanical properties and the formation of oxide layers on Fe40-xNiCoCrAlx (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000°C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = 7.75 e/a). Thin continuous oxide scales containing Cr2O3 and NiCr2O spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al2O3 in the scale on the Fe30Ni25Co15Cr20Al10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe35Ni25Co15Cr20Al5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe30Ni25Co15Cr20Al10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. The hardness (HIT) and elastic modulus (E) of the cast Fe35Ni25Co15Cr20Al5 alloy are equal to 2 and 147 GPa, respectively, and decrease to 1.8 and 106 GPa after a series of long-term annealing operations. The Fe30Ni25Co15Cr20Al10 alloy shows the opposite dependence: HIT increases from 2.5 in the initial state to 3.1 GPa after annealing and E decreases from 152 to 134 GPa. This indicates that the Fe30Ni25Co15Cr20Al10 alloy is promising as a high-temperature oxidation-resistant and creep-resistant material. Introduction
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Kenyi, A., R. Bhaskaran Nair i A. McDonald. "Towards Highly Durable High Entropy Alloy (HEA) Coatings Using Flame Spraying". W ITSC2022. DVS Media GmbH, 2022. http://dx.doi.org/10.31399/asm.cp.itsc2022p0827.
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Abstract High entropy alloys (HEAs) constitute a new class of advanced metallic alloys that exhibit exceptional properties due to their unique microstructural characteristics. HEAs contain multiple (five or more) elements in equimolar or nearly equimolar fractions compared to traditional alloy counterparts. Due to their potential benefits, HEAs can be fabricated with thermal spray manufacturing technologies to provide protective coatings for extreme environments. In this study, the AlCoCrFeMoW and AlCoCrFeMoV coatings were successfully developed using flame spraying. The effect of W and V on the HEA coatings were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and micro-hardness testing. Furthermore, performance of the coating under abrasive loading was investigated as per ASTM Standard G65. Microstructural studies showed different oxides with solid-solution phases for all the HEA coatings. Hardness results were higher for the AlCoCrFeMoV coatings followed by AlCoCrFeMoW and AlCoCrFeMo coatings. Lower wear rates were achieved for the AlCoCrFeMoV coatings compared to AlCoCrFeMoW and AlCoCrFeMo coatings. The evolution of multiple oxide phases and underlying microstructural features improved the resistance to abrasive damage for the AlCoCrFeMoV coatings compared to other HEA coatings. These results suggest that the flame-sprayed HEA coatings can be potential candidates for different tribological interfaces while concurrently opening new avenues for HEA coating utilization.
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Bhattacharya, R., O. N. Senkov, A. K. Rai, X. Ma i P. Ruggiero. "High Entropy Alloy Coatings for Application as Bond Coating for Thermal Barrier Coating Systems". W ITSC 2016, redaktorzy A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen i C. A. Widener. DVS Media GmbH, 2016. http://dx.doi.org/10.31399/asm.cp.itsc2016p0279.
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Abstract High-entropy alloys (HEAs) are well suited for use in high-temperature environments due to their combination of strength, ductility, thermal stability, and corrosion and wear resistance. In this study, NiCoCrAlSi-based HEA coatings are deposited by HVOF and air plasma spraying (APS) and their phases, microstructure, and composition are evaluated by means of XRD, SEM, and EDS analysis. The results show that BCC/B2 phases are the main constituent in HVOF coatings that were diffusion heat treated. APS coatings of the same composition, on the other hand, exhibited a two-phase structure consisting of L12 and BCC/B2 phases. The HEA coatings produced by HVOF were tested for oxidation resistance and their morphology and oxide scales were examined with the aim of developing a high-quality bond coat for thermal barrier coating (TBC) systems.
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Shahbazi, H., H. Vakilifard, R. B. Nair, A. C. Liberati, C. Moreau i R. S. Lima. "High Entropy Alloy (HEA) Bond Coats for Thermal Barrier Coatings (TBCs)—A Review". W ITSC 2023. ASM International, 2023. http://dx.doi.org/10.31399/asm.cp.itsc2023p0659.
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Abstract Due to the aggressive operation conditions of turbine hot sections, protective coatings are required to provide oxidation and hot corrosion resistance for superalloy components. Thermal barrier coatings (TBCs) are comprised of a ceramic top coat and a metallic bond coat (BC) and are typically used as thermal protection systems against these aggressive environments. Conventional BC materials are MCrAlX, with M being metals or alloys (e.g., Ni, Co or NiCo) and X being reactive elements such as Y, Hf, Ta, Si. Due to their strength, thermal stability, and oxidation resistance, high-entropy alloys (HEAs) have presented promise for use as BC materials in hightemperature applications. Owing to its cocktail effect, optimally chosen HEAs could help to enhance the hot corrosion resistance of BCs by forming a more continuous, dense, and uniform thermally grown oxide (TGO). Furthermore, HEAs could help to control the diffusion between the bonding layer and substrate in elevated temperature environments. This paper will discuss the thermodynamic, mechanical, and microstructural behaviour of HEAs. Furthermore, the selection and usage of HEAs as BCs will be explored and compared to conventional BCs in TBC systems.
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Ružičić, Branka, Dragana Grujić, Blanka Škipina, Mladen Stančić, Đorđe Vujčić i Miroslav Dragić. "Enhancement of macro-uniformity of copper(I) oxide printed linen fabrics by addition of Pinus sylvestris L. plant extract". W 11th International Symposium on Graphic Engineering and Design. University of Novi Sad, Faculty of technical sciences, Department of graphic engineering and design, 2022. http://dx.doi.org/10.24867/grid-2022-p83.
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High surface texture of textile materials is rougher than other printing substrates which can cause excessive macro non-uniformity. Adding metal oxides into the ink to enhance material properties usually add to surface roughness and increase print mottle. In this paper copper(I)oxide particles and different amounts of Pinus sylvestris L. plant extract were added to modified alginate paste (CHT-NV) prior to printing. The aim of this paper is to inspect the influence of added metal oxide and plant extract on the print quality of linen based material via surface macro non-uniformity GLCM determination method. In the pattern recognition phase, the co-occurrence matrix is applied to calculate the texture characteristics, such as contrast, correlation, energy, entropy and homogeneity. The research results indicated that the metal oxide particles have had a negative influence on macro uniformity of printed linen. Increasing of the concentration of extract leads to a dilution of the printing paste, and thus to a greater penetration of copper ions between the threads of the fabric, as well as into the yarn itself.
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Pal, S., R. Bhaskaran Nair i A. McDonald. "Influence of Microstructure on Hardness and Electric Resistivity of Flame-Sprayed High Entropy Alloy Coatings". W ITSC2022. DVS Media GmbH, 2022. http://dx.doi.org/10.31399/asm.cp.itsc2022p0534.
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Abstract High entropy alloys (HEAs) are classified as a new class of advanced metallic materials that have received significant attention in recent years due to their stable microstructures and promising properties. In this study, three mechanically alloyed equiatomic HEA coatings – AlCoCrFeMo, AlCoCrFeMoW, and AlCoCrFeMoV – were fabricated on stainless steel substrates using flame spray manufacturing technique. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Vicker’s microhardness were utilized to characterize the fabricated HEA coatings. Furthermore, Joule heating experiments using a modified version of a two-probe test was used to measure the electrical resistivity of the HEA coatings. To prevent short-circuiting of the metallic coatings, a thin layer of alumina was deposited as a dielectric material prior to the deposition of HEA coatings. The microstructure of the HEA coatings showed the presence of multiple oxide regions along with solid-solution phases. The porosity levels were approximately 2 to 3% for all the HEA coatings. The HEA coatings had a thickness of approximately 130 to 140 μm, whereas the alumina layer was 120 to 160 μm thick. The electrical resistivity values were higher for all the HEA coatings compared to flame-sprayed Ni-20Cr and NiCrAlY coatings and AlCoCrFeNi HEA thin film, which may be attributed to the characteristics of HEAs, such as severe lattice distortion and solute segregations. The combined interaction of high hardness and increased electrical resistivity suggests that the flame-sprayed HEA coatings can be used as multifunctional wear-resistant materials for energy generation applications.
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Nishida, Kousuke, Toshimi Takagi i Shinichi Kinoshita. "Analysis of Electrochemical Performance and Exergy Loss in Solid Oxide Fuel Cell". W ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38094.
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A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, the local processes in the electrodes and electrolyte of unit SOFC are analyzed taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.
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Haynes, Comas L., i William J. Wepfer. "Using Component Effectiveness for a More Comprehensive Analysis of High Temperature Fuel Cells". W ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0842.
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Abstract High temperature fuel cells will enable power systems to have unprecedented levels of operation. Second Law studies are an effective means of analyzing these promising cells. The “non Carnot-limited” label applied to fuel cells must first be understood in its proper perspective, however. Electric and voltage efficiencies are often used for fuel cell evaluation, but a component effectiveness was developed for better insight into cell performance. The performance indices were compared via a simulation of Westinghouse Electric’s tubular solid oxide fuel cells. Component effectiveness profiles showed a realistic, decreasing approach to reversible operation. In contrast, electric and voltage efficiencies showed a uniform increase in performance. These latter efficiencies only account for electrochemical losses. High temperature fuel cell operation involves significant heat transfer, however, and thus thermal irreversibilities. Component effectiveness accounts for all forms of entropy generation, and it will be used in subsequent design analyses of high temperature fuel cells.
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Haseli, Yousef, Ibrahim Dincer i Greg F. Naterer. "Thermodynamic Performance of a Gas Turbine Plant Combined With a Solid Oxide Fuel Cell". W ASME 2008 2nd International Conference on Energy Sustainability collocated with the Heat Transfer, Fluids Engineering, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/es2008-54336.
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This paper undertakes a thermodynamic analysis of a high-temperature solid oxide fuel cell, combined with a conventional recuperative gas turbine. In the analysis the balance equations for mass, energy and exergy for the system as a whole and its components are written, and both energy and exergy efficiencies are studied for comparison purposes. These results are also verified with data available in the literature for typical operating conditions, the predictive model of the system is validated. The energy efficiency of the integrated cycle is obtained to be as high as 60.55% at the optimum compression ratio. These model findings indicate the influence of different parameters on the performance of the cycle and irreversibilities therein, with respect to the exergy destruction rate and/or entropy generation rate. The results show that a higher ambient temperature would lead to lower energy and exergy efficiencies, and lower net specific power. Furthermore, the results indicate that increasing the turbine inlet temperature results in decreasing both the energy and exergy efficiencies of the cycle, whereas it improves the total specific power output. However, an increase in either the turbine inlet temperature or compression ratio leads to a higher rate of irreversibility within the plant. It is shown that the combustor and SOFC contribute predominantly to the total irreversibility of the system; about 60 percent of which takes place in these components at a typical operating condition, with 31.4% for the combustor and 27.9% for the SOFC.
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Rajab, Husam, Da Yin i Hongbin Ma. "Effects of Al2O3-Water Nanofluid and Angular Orientation on Entropy Generation and Convective Heat Transfer of an Elliptical Micro-Pin-Fin Heat Sink". W ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-40335.
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This paper presents an investigation of the effect of nanofluid on the heat transfer performance in an elliptical micro-pin-fin heat sink including the influence of entropy generation and pin orientation. The orientation angle of pins is decreased with the number of pins in the array with a 90 degree angle for the first pin and a 0 degree angle for the last pin. To study the flow and heat transfer behaviors in a micro-pin-fin heat sink, steady Navier-Stokes and energy equations were discretized using a finite volume approach and were solved iteratively. Deionized (DI) water was used as a base coolant fluid while aluminum oxide (Al2O3) nanoparticles were used in the present study with mean diameters of 41.6 nm. The results showed that (1) changing the angular orientation of pins can cause significant enhancement in heat transfer, (2) a significant enhancement of heat transfer can be attained in the system due to the suspension of Al2O3 nanoparticles in the base fluid in comparison with pure water, (3) enhancement of heat transfer is intensified with increasing volume fraction of nanoparticles and Reynolds and Prandtl numbers, (4) increasing volume fraction of nanoparticles, which is responsible for higher heat transfer performance, leads to a higher pressure drop, (5) using nanofluids as coolant can cause lower heat transfer entropy generation due to their high thermal properties, and (6) with increasing volume fraction and Reynolds and Prandtl numbers, overall entropy generation rate decreases.