查看更多>>摘要：Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were fabricated using an electroless plating method, and the effects of the GNP content on the thermal conductivity (TC), coefficient of thermal expansion (CTE), and mechanical properties of the composites were studied. The TC, CTE, and strength of the composites were measured in the in-plane and through-plane directions and compared. Increasing the GNP content in the GNP/Cu composite was effective in reducing the CTE and increasing the compressive yield strength of the composite. The compressive yield strength was higher in the through plane direction, but the maximum compressive strength was higher in the in-plane direction. In the case of compressive deformation in the in-plane direction, a single shear fracture with one fracture direction occurred. The compressive deformation in the through-plane direction of the composite with high GNP content (15% and 20%) exhibited a duplex shear fracture with two fracture directions. The significant findings of the present study are that it is possible to fabricate GNP/Cu composites with uniformly dispersed GNPs and low porosity by electroless plating. In addition, the failure mechanism of GNP/Cu composites was revealed for the first time. (c) 2021 Elsevier B.V. All rights reserved.
Reis, M. S.Pimentel, B.Andrade, V. M.de Paula, V. G....
8页
查看更多>>摘要：The competition between the stability of the cubic and hexagonal full Heusler alloys and the implications concerning their magnetic properties were systematically studied through the detailed structural and magnetic characterization of the Fe2Mn(Si1-xGex) system. This system was specifically chosen as the parent compositions are cubic (x = 0) and hexagonal (x = 1). It is found that the formation of hexagonal phases occurs for the x >= 0.6 samples, whereas its phase fraction monotonically increases with x until the pure hexagonal Fe2MnGe is formed. The change in structure results in high sensitiveness of both the saturation of magnetization (MS) and Curie temperature (TC) with x values, related to a strong magnetocrystalline anisotropy of the hexagonal phase. Both cubic and hexagonal magnetic features were qualitatively reproduced by Density Functional Theory (DFT) calculations. This work provides an experimental and theoretical foundation for further design of Heusler systems with controlled structures and magnetic properties. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, the influence of the stoichiometry of LaxFeOy films on their activity for H-2 production by photoelectrochemical (PEC) water splitting was investigated. Thin LaxFeOy films were deposited on elec-trodes by magnetron co-sputtering and their composition was controlled by adjusting the power applied on metallic iron and lanthanum targets. The highest photoactivity was observed for La0.43FeOy films. The crystallization of these films and their photocatalytic activity were further improved by oxidation in an external furnace at 650 degrees C for 2 h. Transmission electron microscopy (TEM) analyses confirm the formation of LaFeO3 crystallites in the film and show a thin continuous polycrystalline Fe2O3 layer at the surface. The presence of Fe2O3 at the upper surface originates from an exsolution mechanism typically observed for non-stoichiometric perovskites. The improvement of the photocatalytic properties by adjusting the stoichio-metry, the oxidation temperature and the film thickness was confirmed by H-2 production measurements performed by mass spectrometry. We observe a large increase in H-2 production rate (103%) by comparison with a stoichiometric LaFeO3 thin film. The improvement in catalytic performances for these non-stoi-chiometric films composed of earth abundant, low-cost and non-toxic elements, make them of high interest materials for photoelectrodes in PEC water splitting systems. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Graphene nanoflakes (GNFs) surface metallization is a potential method to simultaneously achieve homogeneous GNFs dispersion and suitable interfacial bonding in metal matrix composites (MMCs). In this study, the effect of nickel coating microstructure of GNFs on strengthening titanium matrix composites (TMCs) was investigated. To this end, nickel-coated graphene nanoflakes (Ni-GNFs) with two different states were produced via electroless plating. The Ni-GNFs/Ti bulk composites were consolidated by com-bining short-time ball milling, spark plasma sintering (SPS) and hot rolling (HR). Results showed that the reinforcements were well dispersed in the Ni-GNFs/Ti composites coupled with remarkably strength im-provement, which resulted from the precipitation of NiTi2 intermetallic compound and strong interfacial bonding. The partially Ni-coated GNFs have a better strengthening effect than fully Ni-coated GNFs in TMCs, which was closely associated with the formation of a special interfacial microstructure. As a result, the composite with partially Ni-coated GNFs exhibited the highest tensile strength of 821 MPa, as well as excellent ductility (similar to 18.3%). This finding may provide new strategies for the preparation of high-perfor-mance TMCs through interfacial microstructure design. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, AlxCrFeNi (x = 0, 0.5, 1.0) high-entropy alloys (HEAs) were designed by introducing a high atomic radius element Al. And for x = 1.0 quaternary HEAs with equal molar ratios were studied at various aging temperatures. The microstructural evolution and its effect on mechanical properties were discussed. The results suggested that the addition of Al promoted the transition from face centered cubic (FCC) to body centered cubic (BCC) phase, in which the spherical Al-rich and Ni-rich BCC nanoparticles were dispersed in BCC. Addition of Al optimized the brittle ternary CrFeNi HEA's shortcomings, which have high plasticity and poor strength. Besides, the results showed that the transformation of BCC to B2 phase was promoted via increasing aging temperatures. The B2 phase in the mesh structure and short rod structure was Al-rich and Ni-rich. When Al content increased to 0.5 and 1.0, the compressive yield strength increased to 1338.07 MPa and 1079.03 MPa, respectively. While the elongation remained at 15 similar to 20%. The Vickers hardness enhanced from 147.31 HV (x = 0) to 247.76 HV (x = 1.0). When the aging temperature reached 600 degrees C, the compressive ultimate strength and Vickers hardness increased by 165.84 MPa and 218.04 HV compared with as-cast HEAs, respectively. The series of HEAs were evaluated for the correlation between microstructure and mechanical properties. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Rational construction of interface engineering is a highly effective strategy for modifying the surface properties and enhancing the intrinsic activity of a catalyst. Herein, the three-dimensional (3D) hierarchical Ni3Se2@FeOOH heterostructure nanoforests with rich heterointerfaces were integrated into nickel foam (Ni3Se2@FeOOH/NF) for electrochemical overall water splitting. Coupling FeOOH with Ni3Se2 can favor the formation of oxygen-containing intermediate (*OOH) and facilitate the dissociation of H2O and adsorption of hydrogen (*H), thus dramatically boosting the electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) simultaneously. Furthermore, the self-supported electrode with Ni3Se2@FeOOH heterostructure nanoforests in-situ grown on NF can reduce the indirect contact resistance between the electrocatalyst and substrate, provide abundant electroactive sites, and promote the release of the generated bubbles from electrode timely. Consequently, the Ni3Se2@FeOOH/NF displays outstanding electrocatalytic activity with low overpotentials of 224 mV and 87 mV at 10 mA cm(-2) for OER and HER, respectively. When used as a bifunctional electrocatalyst in a 1 M KOH electrolyzer, the Ni3Se2@FeOOH/NF exhibits a low cell voltage of 1.54 V to drive 10 mA cm(-2) and retains long-term durability over 20 h. This work demonstrates the significance of the heterostructure for improving the catalytic performance of non noble composite electrocatalysts. (C) 2021 Elsevier B.V. All rights reserved.
Belo, J. H.Mudryk, Y.Pereira, A. M.Oliveira, G. N. P....
10页
查看更多>>摘要：Chemical substitution is one of the most efficient tools to tune and optimize magnetic and magnetocaloric properties of the giant magnetocaloric materials. In particular, Indium substitutions could be useful both for tuning properties of these interesting intermetallic materials and to unveil their local-scale behavior across the magnetostructural transition via hyperfine techniques. Hence, in order to investigate the effect of Indium additions on the crystal structure, micro-structure, magnetic and magnetocaloric properties, a series of In-containing samples derived from the base Gd5Si1.2Ge2.8 stoichiometry were prepared. The major findings are that while In is insoluble in the 5: 4 phase, it will instead promote the emergence of the impurity 5: 3 phase and segregates into this phase. Hence, In leads to major crystallographic changes, which enhance atomic disorder and disrupt the Si to Ge ratio in the 5: 4 phase. Subsequently, a higher 5: 4 unit cell volume and a lower magnetic ordering temperature are found in the In-substituted samples. Finally, the magnetocaloric properties of the In-substituted samples reveal a detrimental effect on the maximum magnetic entropy change. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li3Gd3Te2O12 system was investigated for lighting and ratiometric temperature sensing applications. The double substitution at the dodecahedral site was confirmed via Rietveld refinement and Raman spectra analysis. Considering the full advantage of distinct and characteristic cyan and orange emissions of Bi3+ and Pr3+, the emission tunability towards white region was achieved by the proposed co-doping combination. The as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor exhibited characteristic and enhanced emission of Pr3+ under the excitation of 297 nm. The activation energy of 0.29 eV was obtained for the co-doped matrix, exhibiting better thermal stability. Further, the temperature sensing properties were evaluated based on the temperature dependent photoluminescence emission and decay curves in the range 100-300 K. Notably, the as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor showed a maximum relative sensitivity of 0.672% K-1, as based on decay curve method, indicating that the phosphor can act as a potential candidate for optical temperature sensing in the physiological range. These findings demonstrate the efficiency of new co-doping combination Bi3+-Pr3+ for designing multifunctional phosphors. (C) 2021 Elsevier B.V. All rights reserved.
Gupta, Santosh K.Modak, BrindabanGarcia, Mitzy A. P.Modak, Pampa...
9页
查看更多>>摘要：This work manifested the crucial role played by defect and dopant ion local structure in maneuvering light emission characteristics of optical materials. We have harnessed the full gamut of visible light emission from green to yellow to orange-red endowed by oxygen vacancies (OVs) in undoped Lu2Sn2O7 (LSO) pyrochlore and Sm3+/Dy3+ doping in LSO pyrochlore. The energy required to create a OVs at 48f position is lowered with respect to V-O8b, hence V-O48f defects are expected to present at a larger fraction and are responsible for green emission in the LSO. Though Dy3+ ion is distributed at both Lu3+ and Sn4+ site, the contribution of asymmetric Dy@Sn ion is more than that of symmetric Dy@Lu in PL process of Lu2Sn2O7:Dy3+ leading to intense yellow light compared to blue light and is consistent with the DFT calculations. On the other hand, Sm3+ substitution at the Sn lattice site is thermodynamically more favorable in Lu2Sn2O7:Sm3+ (LSOS) by 1.38 eV with respect to Lu lattice site. Based on time-resolved photoluminescence spectroscopy, it is postulated that Sm@Sn with far-off OVs leads to magnetic dipole (MDT) and the one with nearby OVs leads to electric dipole transition (EDT) in LSOS. This concept of defect induced emission and role of defect and dopant local structure can be applicable to various luminescent phosphors which provides a unique approach for tuning other properties of optically multifunctional crystals that are highly sensitive to defect and dopants local site engineering. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The development of recyclable photocatalysts with enhanced photo-induced charge separation and efficient visible light utilization is imperative for antibiotic pollutants removal in aqueous environment. Herein, a Z scheme Fe3O4/BiOCl/BiOI heterojunction photocatalyst was constructed using a facile solvothermal method on the basis of BiOCl/BiOI composites. A series of characterization methods were employed to analyze the microstructure, morphology, optical property and chemical composition of as-prepared ternary Fe3O4/ BiOCl/BiOI composite. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) analysis revealed that Fe3O4 nanoparticles were well loaded on the surface of BiOCl/BiOI microspheres. The main active species of Fe3O4/BiOCl/BiOI during photocatalysis were confirmed by radical trapping experiments, which indicated the formation of Z-scheme heterojunction. Compared to pure BiOCl and BiOI, Fe3O4/BiOCl/BiOI nanocomposite exhibited significantly improved photocatalytic performance toward tetracycline (TC) degradation (89%, 80 min). Furthermore, the photocatalytic activity of Fe3O4/BiOCl/ BiOI remained at a high level after five cycles, which suggested that the ternary composite possessed good stability and reusability. Such superior photocatalytic activity of Fe3O4/BiOCl/BiOI was mainly attributed to the suitable band structure and construction of Z-scheme heterojunction, resulting in the enhanced light utilization and migration rate of charge carriers. In addition, Obviously, the ternary composite revealed a potential prospect in the practical application of photocatalytic degradation due to its good magnetic recovery performance and minimal environmental impact. (C) 2021 Elsevier B.V. All rights reserved.
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