查看更多>>摘要：In this study, the feasibility and high-temperature stability of Ni-Sn bonded joints fabricated by transient liquid phase sintering (TLPS) were investigated for high-temperature power electronics applications. A 30Ni-70Sn (wt%) TLPS paste was fabricated with micro-sized pure Ni and Sn powders, and chip bonding was performed on a direct bonded copper (DBC) substrate. During TLPS bonding, Sn particles melted and reacted with Ni particles, which resulting in the formation of stable Ni-Sn TLPS intermetallic joints. During aging treatments at 150 and 200 °C, the formed Ni3Sn4 phases were transformed into the Ni3Sn2. With increasing aging treatments, the reactions between Ni3Sn4 intermetallics and remaining Ni particles increased, which resulted in the formation of the Ni-rich Ni-Sn intermetallics. Even after 1000 h at an aging temperature of 200 °C, there is no significant difference in the stable and dense microstructure of Ni-Sn TLPS joints. In addition, their mechanical strengths did not vary significantly even after long-term treatment for 1000 h at 150 and 200 °C. This means that the Ni-Sn TLPS joints have a good long-term microstructural stability and mechanical reliability at high temperatures up to 200 °C. Therefore, we conclude that the Ni-Sn paste is a promising candidate as a die-attach material for high-temperature electronic assemblies.
查看更多>>摘要：The influences of Al and Mn on microstructure, magnetic and mechanical properties of Fe40Co40Ni10M10 (M = Al and Mn) medium entropy alloys (MEAs) have been systematically investigated. It is found that the Fe40Co40Ni10Al10 has body-centered cubic (BCC) structure and Fe40Co40Ni10Mn10 has a mixture of face-centered cubic (FCC) and BCC structures in as-cast state, while the former one changes to FCC + BCC dual-phase structure after heat treatment at 1073 K for 1 h. Fe40Co40Ni10Al10 displays higher saturated magnetization (Bs) as compared to Fe40Co40Ni10Mn10 in as-cast state, while heat treatment significantly enhances Bs of Fe40Co40Ni10Mn10. Besides, it is intriguing that Fe40Co40Ni10Mn10 shows higher yield strength and plasticity compared to Fe40Co40Ni10Al10, while heat treatment could enhance comprehensive mechanical properties of this series of MEAs. In addition, the Bs of heat-treated Fe40Co40Ni10Mn10 is 187.9 emu/g, which is among the highest in the reported ferromagnetic HEAs/MEAs. The correlation among the composition, phase evolution, magnetic properties, and mechanical properties in these MEAs is discussed in detail. This work provides a novel route for developing high-performance ferromagnetic HEAs/MEAs.
查看更多>>摘要：Layered double hydroxide (LDH) is considered as a potential electrode material for supercapacitors (SCs) due to its excellent theoretical capacitance. However, the conductivity of LDH is not particularly ideal. The reasonable design of new electrode materials with core-shell structure is an effective strategy to improve the electrochemical performance. Herein, we prepared NiCo2S4@NiV-LDH/NF composite material with a core-shell nanostructure through a simple hydrothermal method. In addition, NiCo2S4@NiV-LDH/NF-1, NiCo2S4@NiV-LDH/NF-2, NiCo2S4@NiV-LDH/NF-3 were synthesized by adjusting the sulfur concentration. Benefited from the synergistic reaction of each component, the optimized NiCo2S4@NiV-LDH/NF-2 composite material has excellent electrochemical performance. The specific capacity is 1778.8 C g?1 (3557.6 F g?1) at 1 A g?1. In addition, a typical hybrid supercapacitor device was assembled with NiCo2S4@NiV-LDH/NF-2 composite material as the positive electrode and biochar (BC) as the negative electrode. Notably, under the condition of a power density of 749.98 W kg?1, the energy density of the NiCo2S4@NiV-LDH/NF-2//BC device is 120.81 Wh kg?1. In addition, NiCo2S4@NiV-LDH/GCE also showed excellent performance in the detection of tryptophan due to its superior catalytic performance. The low detection limit of NiCo2S4@NiV-LDH/GCE sensor is 0.46 μM, the wide linear range is 0.5–153 μM, and the highest sensitivity.
查看更多>>摘要：The development of functional engineering materials based on non-ferrous metals has progressed in recent years, and the incorporation of rare earth metals is a key strategy aimed at modifying the structural components of alloys to enhance their mechanical properties. The work presented herein investigates the effect of lanthanum addition on the microstructure and type of phases formed during crystallization. The effects of alloying elements on the solidification derivative curve and the monotectoid solid-state transformation of ZnAl10Cu1 alloys are also discussed. The overall impact of lanthanum addition was determined based on studies of the microstructure morphology, phase composition, and changes in the derivation curves of the studied alloys. Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed for structural analysis, and thermal-derivative analysis (TDA) was used to investigate the phenomena occurring during solidification in hypereutectic zinc alloys with various chemical compositions The results of this study indicate that the addition of La modifies the derivation curve during solidification by changing the morphology of the α phase and decreasing the monotectoid transformation temperature (α→α’). The presence of the Zn5La phase in the a′ + η eutectics was also confirmed.
查看更多>>摘要：The poor activation property is the biggest obstacle to the application of TiFe alloy, which can be improved through forming secondary phases in the alloy. In this paper, a new family of the as-cast Ti1.1-xFe0.7Ni0.1Zr0.1Mn0.1Prx (x = 0–0.08) alloys were designed and prepared, and their microstructure and phase composition were examined to determine the effects of alloying with rare earth Pr on the activation property, formation enthalpy of the hydrides, hydriding/dehydriding capacity and kinetics. The results showed that the Pr0 alloy contained the primary phase of TiFe and the residual phase of Ti2Fe. The addition of Pr led to the increase of TiFe phase, the generation of Pr segregative phase, the volume expansion of TiFe lattice cell and the refinement of TiFe grain. Affected by the above factors, the hydrogen storage performances of the Pr-containing alloys were enhanced significantly. The incubation period was 10,000, 200, 0 and 0 s for the Ti1.1-xFe0.7Ni0.1Zr0.1Mn0.1Prx (x = 0–0.08) alloys at 423 K, respectively. The absolute value of the formation enthalpy of the alloys increased with the growth of Pr content, and the hydriding capacity at 1000 s and the hydriding kinetics reached the maximum for the Pr0.02 alloy.
查看更多>>摘要：A new MOF-derived CoCeOx nanosphere/g-C3N4 nanosheet composite material with a high specific surface area, compact interface, abundant active sites, and promotion of electron transfer and separation was successfully prepared. The prepared 10% CoCeOx/g-C3N4 composite material generated hydrogen with an efficiency of 1050 μmol g?1 h?1 under visible light irradiation, and 97% of carbamazepine was degraded in 1 h at a degradation rate of 0.05 min?1 with the help of PDS. Based on DFT calculations and mass spectrometry analysis, the degradation products and degradation pathways of carbamazepine were also proposed. According to tests of the photocatalytic properties, SO4-?, h +,?OH, and ?O2- were produced by the composite itself; these species play an important role in the degradation. The photocatalytic mechanism was also proposed. The prepared CoCeOx/g-C3N4 composite material provides a simple and effective strategy for energy utilization and wastewater treatment.
查看更多>>摘要：Sintered neodymium iron boron (NdFeB) is a widely applied permanent magnet, whose dynamic mechanical properties restrict the further development of its application. In order to provide a theoretical basis for the application of NdFeB in the shock field, the dynamic mechanical behavior of sintered NdFeB was studied experimentally and theoretically in this paper. First, the Split Hopkinson Pressure Bar (SHPB) experiments under different strain rates were carried out. The dynamic process was captured by a high-speed camera, and the strain data measured by oscilloscope was processed with the three-wave method. Combined with the electron microscope analysis of the recovered samples, the dynamic failure process and characteristics of NdFeB under high-speed impact were explored, which provided an experimental basis for the following theoretical research. Given the theoretical deficiency of the dynamic mechanical properties of sintered NdFeB and the assumption of microcracks with uniform distribution and no friction, a theoretical model of damage evolution process of brittle materials was established based on the dynamic crack growth criterion. Combining the damage evolution model with Zhu-Wang-Tang (ZWT) constitutive model, the damage constitutive model of sintered NdFeB was established, whose validity was verified by the comparison with the experimental data.
查看更多>>摘要：La1-xAxMnO3 (A = alkaline-earth or alkali metal) perovskites with large temperature coefficient of resistivity (TCR) offer immense opportunity for the application in high-performance infrared bolometer. However, numerous studies have revealed that the manganite films with large TCR values are not easily obtained by various fabrication technologies. Herein, a facile sol-gel spin-coating technique was used to prepare La1-xCaxMnO3 (LCMO, 0.280 ≤ x ≤ 0.375) films. All the samples were highly oriented along the out-of-plane direction of La0.3Sr0.7Al0.65Ta0.35O3 (001) substrates. With the rise in Ca doping amount, the resistivity of the films first decreased, and then, increased. This change can be attributed to the competition between the carrier concentration and lattice distortion. The LCMO films displayed large TCR and low-field magnetoresistance (MR) values, which exceeded those of previously reported thin films. The maximum TCR and low-field MR values were observed at x = 0.330, reaching 30.13% K?1 (266.43 K) and 68.6% (270.08 K), respectively. The La0.67Ca0.33MnO3 film with large TCR and MR values presents potential for the applications in high-sensitivity infrared bolometers and magnetic sensors.
查看更多>>摘要：The role of Mn existence types on microstructure and mechanical properties of extruded Mg-2.0Zn-1.5Mn magnesium alloy is investigated. Four different Mn existence types in Mg-2.0Zn-1.5Mn magnesium alloy are obtained by different heat treatment. The four types include: (1) solid solution Mn atoms, (2) nanoscale α-Mn phase, (3) solid solution atoms + micron scale α-Mn phase, (4) micron scale α-Mn phase + nanoscale α-Mn phase, respectively. The result shows pre-existed nanoscale α-Mn particles present good pinning effect for refining grains. The micron scale α-Mn phase activates the particle stimulated nucleation (PSN) mechanism. The combination of micron scale α-Mn phase + nanoscale α-Mn phase state presents the best grain refining effect with an average grain size of 1.3 μm. The mechanical properties are significantly enhanced, the tensile yield strength, tensile strength and fracture elongation are 267 MPa, 305 MPa, 28.6%, respectively. Based on the results, four basic rules for preparing fine grained Mn-containing Mg alloys are proposed and an ideal pre-extrusion state of Mn-containing alloy is obtained: namely, direct extrusion in the as-cast-aging state. Besides has great potential for grain refinement, this state also can be regulated by the coordination of PSN effect and pinning effect in Mn-containing Mg alloy.
查看更多>>摘要：Silicon (Si) is considered to be one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). However, the practical application of Si anode is still high cost and hindered by huge volume change. It is significant to produce high-performance Si anode of LIBs inexpensively. Herein, we report the Si/N-doped carbon (Si/NC) composite anode materials constructed by recycling Si waste from the photovoltaic industry as raw materials after simple purification and polydopamine (PDA)-derived carbon coating. The Si micro/nano-plates coated with the NC can facilitate electron transfer and inhibit the volume expansion of Si to stabilize the structure of composites. The resulting Si/NC electrode exhibits a high discharge capacity of 1139 mAh g?1 at 1 A g?1 over 200 cycles. Moreover, the full-cell (LiFePO4//Si/NC) presents excellent cycling performance (108 mAh g?1 at 0.5 A g?1 over 200 cycles). This work not only offers a reasonable solution for the acquirement of Si anode from the photovoltaic industry but also provides a new strategy for the preparation of anodes for the next generation of LIBs, which may bring great economic benefits.
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Elsevier