查看更多>>摘要：In this work, Bi3+-doped, Mn4+-doped, and Bi3+/Mn4+ co-doped SrLaGa3O7 (SLGO) phosphors were synthesized by solid-state reactions. Crystal structures, composition and optical properties of these phosphors were studied. Phase purity of SLGO: Bi3+/Mn4+ phosphor was characterized by X-ray diffraction. Elements of SLGO: Bi3+/Mn4+ phosphors were revealed by XPS measurements. Absorptive abilities of the synthesized phosphors were characterized by UV-vis absorption measurements. The UV-vis absorption and excitation spectra showed that the phosphors can be excited by ultraviolet and near ultraviolet light. Upon the excitation at 365 nm, SLGO: Bi3+ and SLGO: Mn4+ phosphors showed cyan and deep red emission, respectively. Energy transfer from Bi3+ to Mn4+ occurred in SLGO: Bi3+/Mn4+ phosphors. The Bi3+-> Mn4+ energy transfer process was revealed by luminescence spectra and fluorescence decay curves. The emission of SLGO: Bi3+/Mn4+ phosphors could be tuned by changing excitation wavelength and Bi3+/Mn4+ doping concentrations. Under the excitation at 365 nm, warm white light was generated by SLGO: 0.005Bi(3+)/0.002Mn(4+) phosphor, which has the CIE coordinates of (0.3697, 0.2864) and the correlated color temperature of 3295 K. Under the excitation at 360 nm, SLGO: 0.005Bi(3+)/0.0015Mn(4+) phosphor showed warm white light with the CIE coordinates of (0.3447, 0.2616) and the correlated color temperature of 4309 K. The values of activation energy were 0.2698 eV (465 nm) and 0.4283 eV (714 nm) for SLGO: 0.005Bi(3+), 0.0015Mn(4+) phosphor. The above results implied that SLGO: Bi3+/Mn4+ phosphors have potential applications in warm WLED lighting. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Rechargeable Zn-air batteries attract much attention because of their high theoretical specific capacity and low cost. However, building an integrated air electrode possessing multiple functions such as catalytic action, current collector as well as the carrier is still a challenge. To raise the catalytic efficiency of the air electrode, hierarchical integrated electrodes assembled by porous carbon nanosheets arrays and CoO nanoparticles on carbon cloth are well designed and prepared. The surface morphology and the catalyst phase of the hierarchical electrode are characterized by SEM, XRD and XPS methods respectively. The electrochemical performances of the electrodes are evaluated by three-electrode system and two-electrode Zn-air battery. The results show that, the hierarchical structure provides abundant platform for catalytic reaction and promotes the transfer of reactants/products, indicating excellent rate and cyclic properties of the batteries. (c) 2021 Elsevier B.V. All rights reserved.
Tahir, Nur Nadhihah MohdBaharuddin, Nurul AkidahSamat, Abdullah AbdulOsman, Nafisah...
18页
查看更多>>摘要：Solid oxide fuel cells (SOFCs) are energy conversion technologies known for their excellent efficiency and high energy density. However, the application of SOFCs is restrained by their high operating temperatures (800-1000 degrees C), which result in overall energy system degradation. Reducing the operating temperatures of SOFCs leads to a reduction in power density because of insufficient protonic-ionic conduction. Ionic con-duction at the cathode component is related to polarization and area-specific resistance that varies fol-lowing the selected material. To date, several types of cathode materials have been investigated, namely, pure electronic conductor, mixed protonic-electronic conductor, mixed ionic-electronic conductor (MIEC) and triple protonic-electronic-ionic conductor (THOEC). Amongst these conductors, MIEC and THOEC currently lead in research development and application in conventional and proton-conducting inter-mediate-low-temperature SOFCs, yet further studies need to be carried out to ensure the continuous im-provement of these materials as SOFC cathode. In this review, an explanation on the different types of cathodes will be discussed, with emphasis on MIEC-and THOEC-based cathodes. This review also includes recent progress and challenges encountered for both materials in the SOFC environment. (c) 2021 Elsevier B.V. All rights reserved.
Panindre, A. M.Colijn, H. O.Taylor, C. D.Frankel, G. S....
11页
查看更多>>摘要：The design and corrosion resistance of five single-phase Ni-Fe-Cr-Mo-W-X (X = Mn, Al, and Cu) multi principal element alloys (MPEAs) has been recently reported. In this study, these alloys were heat treated at 800 degrees C for up to 160 h starting from the solutionized single-phase to allow precipitation of secondary phases that provide increased hardness and strength. During heat treatment at 800 degrees C, Sigma-phase rich in Cr, Ru, Mo and W precipitated at the grain boundaries in each alloy. Furthermore, copious in-grain precipitation was observed in the MPEAs containing Mn and Al. After aging, the hardness of the MPEA containing Al showed the most significant increase in hardness, about 90%, due to the precipitation. Multiple phases that were different from those predicted to exist at thermodynamic equilibrium were identified in the microstructure of the aged MPEAs using electron microscopy. During cyclic potentiodynamic polarization experiments in 0.6 M NaCl, all five aged MPEAs were found to be spontaneously passive. Only the MPEAs containing Mn, Cu or Al became susceptible to localized corrosion at higher potentials due to breakdown at the interface between the matrix and precipitate. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In present work, a novel carbon-doped interstitial strengthening nickel-based heavy density matrix alloy reinforced by high tungsten content (Ni-W-Co) was prepared by conventional casting technology using a laboratory vacuum induction melting (VIM) furnace. The effects of carbon addition on as-cast micro-structure and phase constituents were characterized by field-emission scanning electron microscopy (FE -SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). And the tensile properties and microhardness were tested as well. Results demonstrated that the present heavy density alloy has a single-phase FCC structure and exhibits typical dendrite characteristics. The carbon content (0-0.021 wt%) pre-sents little influence on as-cast microstructure and phase constituents, but significantly improves the mechanical properties. Both tensile strength and ductility of the matrix alloy were increased synchronously with the addition of interstitial carbon atoms on account of the interstitial strengthening. The tensile fracture morphology revealed the transition from complete ductile dominated features to a mixed fracture mode consisting of quasi cleavage and ductile fractures. Minor carbon addition can trigger an obvious in-crease for lattice parameters and thus contribute to the strength improvement, and the increase in lattice friction stress enhanced the work-hardening rate and postponed the necking of C-addition alloy compared with C-free alloy. (c) 2021 Published by Elsevier B.V.
查看更多>>摘要：Gold nanoparticle assisted thermally initiated chemical vapor deposition was used to synthesize nanostructured As-S films. The nanostructures were grown on heated Si substrates covered by spherical gold nanoparticles of different (5, 20, 40 and 60 nm) sizes. In contrast to polycrystalline As-S films prepared by ordinary thermal evaporation and chemical vapor deposition of As2S3 glass without the use of gold nanoparticles, the gold nanoparticle assisted synthesis leads to growth of particular type of crystal-like As-S nanostructures. The As-S micro-crystallites with well-defined size and shape were obtained with 43.9 and 56.1 at% As and S atomic content, respectively. The local structure of the As-S microcrystallites was investigated by Raman and/or surface-enhanced Raman spectroscopy. To assist the interpretation of the experimental Raman spectra and to identify the structure of the crystallites, the vibrational spectra of different cage-like nanocluster models were also calculated by using the density functional theory. Results show that at specific deposition conditions a stimulated formation of As4S5 molecules occurs which activates the growth of micro-crystallites on the gold nanoparticle coated Si surface with well distinguished shape. The structure and properties of nanostructured As-S films synthesized with and without the use of gold nanoparticles were investigated and the gold nanoparticle assisted selective growth of a new type of As-S microcrystallite is discussed. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：A series of Ni0.5Zn0.3Co0.2Fe2O4/epoxy magnetodielectric composites were synthesized through solvent-assisted method and demonstrate tunable permeability and permittivity, ultralow losses and high refractive index over a broad frequency region of the VHF and UHF bands. Experimental results reveal that the permeability mu' decreases from similar to 4.2 to similar to 3.5 while the permittivity epsilon' was improved from similar to 5.0 to similar to 6.1 with an increase in epoxy weight fraction from 1 to 20 wt%. These variations are shown to be intimately related to the microstructures in accordance with effective medium theory and magnetic circuit model. Correspondingly, the characteristic impedance of the magnetodielectric composite medium is varied from similar to 0.75 to similar to 0.90 while maintaining a refractive index around 4.5. Typical magnetic loss as tan delta(epsilon) and dielectric loss as tan delta(mu) at 0.5 GHz are as low as in the order of 10(-2) and 10(-3), respectively. These magnetodielectric materials provide excellent radio frequency results that allowing for the realization of the high-performance miniaturized electronic devices, systems, and platforms. (C) 2021 Elsevier B.V. All rights reserved.
Kappagantula, Keerti S.Smith, Jacob A.Kraft, Frank F.Nittala, Aditya K....
9页
查看更多>>摘要：Composites demonstrating enhanced electrical conductivity compared to copper have been highly sought after for their advantages in efficient energy transport behavior. While such conductors have been demonstrated in 1D (nanowires) and 2D (films) samples, achieving similar behavior in 3D has been challenging owing to the limitations of the synthesis techniques used. In this paper, novel macro-scale 3D copper conductors were demonstrated with increased electrical conductivity through the addition of graphene. Hot extrusion was used to manufacture 12 AWG copper-graphene composite wires with varying graphene content and defect density. Graphene defect density was measured using Raman spectroscopy. Results showed that the electrical conductivity of composites with low defect density graphene increased as a function of graphene content. Comparatively composites with high defect density graphene demonstrated lower electrical conductivity. This study provides first-of-its-kind evidence of 3D metal composites whose bulk electrical performance has been enhanced using graphene additive in minute quantities (15 ppm). Further developments in this area are essential to achieve high performance composite conductors that can improve energy transport efficiency and pave way for industrial adoption of such materials in the future. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：From the perspective of mechanical properties and weldability, four Ni-based superalloys with varying Cr/Mo ratio were designed using cluster model, and fabricated by laser additive manufacturing and subsequent solution treatment and aging. The influence of Cr/Mo ratio on microstructure, hardness, and tensile properties of the alloys in both as-deposited and post heat-treated states were investigated. The results show that the microstructure of all as-deposited alloys is featured by gamma dendrites with fewer interdendritic phases. With the decrease of Cr/Mo ratio, the interdendritic phases evolve from lath and eutectic Laves phases to blocky P phases. The P phase can deteriorate the ductility, while the hardness and tensile strength monotonously increase due to enhanced solid solution strengthening. Post heat treatment results in dissolution of TCP phases and uniform precipitation of gamma '' phases, which enhances remarkably the hardness and tensile strength of as-deposited alloys, but slightly decreases the ductility. At nearly the same level of ductility (23.4-25.8%), the post heat-treated Ni56.3Cr15.2Mo3.52Fe18.8Al1.56Nb3.13Ti1.56 alloy with the Cr/Mo ratio of 13:3 shows the highest hardness (470 HV) and tensile strength (1063 MPa) among the studied alloys. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The (Nd1-xCex)(31.5)Fe67.5B1(x = 0, 0.15, 0.2, 0.25, 0.3, 0.5, 0.75 wt%) alloys were prepared by rapid solidifi- cation method. It is found that the coercivity, H-ci, abnormally increased to 1427.33 kA/m at x = 0.2. With the change of Ce content, the valence state of Ce shifted between 4 f(1) (+3) state and 4f (0) (+4) state. In the x = 0.2 ribbon, the Ce3+ has a high proportion, which is beneficial to the magnetic hardening of Ce2Fe14B type permanent magnetic materials. Meanwhile, the higher proportion of large radius Ce3+ and a lower proportion of small radius Ce4+ promoted the discrete change of the lattice parameters. The first principle calculations showed a large variation of lattice parameters with different Ce substitution occupying different positions. As a result, lattice distortions and scattered stress fields are formed inside the alloy. Such fields have high domain wall energy which hinder the movement of the domain walls during the process of reverse magnetization. (C) 2021 Published by Elsevier B.V.
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