查看更多>>摘要：As a quite unique case a high-temperature modification was previously described for the well-known MoSi2. A detailed reinvestigation, however, proves that even minute amounts of beryllium trigger the formation of a hexagonal CrSi2-type phase rather than the established tetragonal prototype. This ternary MoSi2?xBex is stable at ambient conditions and very likely resembles the high-temperature polymorph of MoSi2. With the help of powder X-ray diffraction, electron backscatter diffraction and energy-dispersive X-ray spectroscopy analyses it was concluded that beryllium replaces silicon atoms in the crystal structure, and that the Be/Si network may contain vacancies.
查看更多>>摘要：The advanced structural design of supercapacitor (SC) electrodes is an effective approach to enhance their performance towards energy conversion and storage. Herein, ultrathin NiCo2S4 nanosheets on Ni foam (NF) with uniform Ni3S2 nanocrystals were synthesised via a simple microwave-assisted sulfidation process. The cooperation of massive ultrathin Ni3S2 nanocrystals and cross-linking NiCo2S4 nanosheets endowed the Ni3S2/NiCo2S4/NF electrodes with a high specific capacitance of 3299 F/g at 13.3 A/g (11.5 F/cm2 at 5 mA/cm2), a remarkable rate capacity of 77% retention at 20 A/g, and cycling performance of 61% retention after 8000 cycles at 50 mA/cm2. This work illustrates that the Ni3S2/NiCo2S4/NF electrodes synthesised via a simple microwave-assisted method are promising anode materials in asymmetric SCs.
查看更多>>摘要：Ni3S2/rGO (reduced graphene oxide) nanoparticles ensemble has been synthesized on the nickel foam as the supercapacitor electrode material by a facile microwave irradiation route. The resultant Ni3S2/rGO electrode exhibits superior capacitive performance, which is severalfold that of the bare Ni3S2. Especially, the Ni3S2/rGO electrode with 20 mg GO precursor (Ni3S2-20) shows highest areal and mass specific capacitances of 1.96 F cm?2 and 1192 F g?1 among all the studied samples, respectively, at the current density of 2 mA cm?2, and the capacitance can be retained to 95.4% after 10,000 cycles at the current density of 10 mA cm?2. A supercapacitor device fabricated by the Ni3S2-20 as both cathode and anode delivers a wide potential window in the range of 0–1.62 V, high areal and mass specific capacitances of 553.2 mF cm?2 and 179.6 F g?1 at the current density of 2 mA cm?2, respectively, together with a high energy density of 67.9 Wh kg?1 at the power density of 535.7 W kg?1. The design of fast and facile synthesis strategy can offer a new insight into developing novel composite electrodes composed of carbon-based materials and pseudocapacitor materials for emerging energy storage applications.
查看更多>>摘要：A new approach based on modified stress and strain with considering micromechanics and dislocation theory, has been extended to find the deformation mechanism during hot deformation of particulate metal matrix composite. The impact of main influential processing parameters, such as temperature, strain, and strain rate in addition to reinforcement characteristics, i.e., particle size, and volume fraction, were successfully taken into account in the calculation of deformation activation energy and stress exponent. Besides, the effect of particle fracture, and diffusion relaxation around particles, were participated in the presented formulation. To evaluate the applicability of the developed formulation, different aluminum matrix particulate composites with different particle sizes and volume fractions were subjected to investigation. Using the modified recovery stress for calculating the activation energy, results in reduction of the stress exponent to a meaningful range. It was shown that deformation mechanisms in metal matrix composite and unreinforced alloy are the same. It was also found that for the low value of stress, i.e., the low strain rate and high temperature, the stress relaxation, and for the high value stress, the particle fracture, disturb the load transfer mechanism and reduce the impact of reinforcement on activation energy.
查看更多>>摘要：In this work, the magnetization isotherms, the magnetic entropy change and the specific heat change in MnFeP0.45As0.55 and MnFeP0.47As0.53 transition metal-pnictides were modeled by the mean-field and the Bean-Rodbell models. The first-order magnetic phase transition (FOMPT) of these compounds was confirmed by examinating of the Bean-Rodbell parameter, η. Our consideration of the Bean-Rodbell model, which is a complement of the mean-field theory, in the emergence of the magneto-volume effects, led to a good agreement between the simulated and the experimental results.
查看更多>>摘要：Sluggish reaction kinetics of lithium-sulfur (Li-S) battery is the key issue affecting cycle capacity and rate performance. Highly conductive and catalytically active sulfur host is still a research hotspot in recent years. Herein, the sulfur host of Co nanoparticles anchored on the Co-Nx active centers grafted nitrogen-doped graphene (Co/Co-Nx@NG) with high catalytic activity and electrical conductivity was prepared via a simple and feasible in situ method. The cobalt-based nanocatalytic center exhibits efficient sulfur conversion efficiency. Moreover, the Co-Nx coordination group is beneficial to inhibit the agglomeration of cobalt nanoparticles to form large particles and further improve the catalytic activity. In addition, the graphene structure formed at low temperature based on the two-dimensional guide of dicyandiamide in combination with the catalytic graphitization of cobalt nanoparticles has excellent electrical conductivity. Owing to the high catalytic activity, appropriate adsorption ability, and excellent electrical conductivity, the Co/Co-Nx@NG applied as sulfur cathode matrix exhibits high capacities of 1300.3 mA h g?1 at 0.1 C and 884.2 mA h g?1 at 2 C, and good cycling stability with a capacity decay of only 0.069% per cycle at 2 C for 705 cycles.
查看更多>>摘要：The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to a range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is a key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the e?ects of substituting Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reduction from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics.
查看更多>>摘要：In this study, X-ray absorption spectroscopy (XAS) experiments for Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy were performed under high magnetic fields up to 12 T using a pulsed magnet. Field–induced reverse transformation from martensite phase to austenite phase caused considerable changes in the magnetic circular dichroism (MCD) signals and the magnetic moments of the Mn, Ni, and Co with ferromagnetic coupling were determined. The spin magnetic moment, Mspin, and orbital magnetic moment, Morb, of Mn atom in the induced austenite ferromagnetic phase, estimated based on the sum-rule analysis, were 3.19 and 0.08 μB, respectively, resulting in an Morb / Mspin ratio of 0.03. In the element-specific magnetization curves obtained at 150 K, metamagnetic behavior associated with the field–induced reverse transformation was clearly observed and the transformation magnetic fields could be detected. There was almost no change in the magnetically averaged XAS spectrum for Mn-L2,3 edges between in the martensite and in the magnetic field-induced austenite phases, however, it was visible for Ni. This implies that Ni 3d-electrons mainly contribute to martensitic transformation.
查看更多>>摘要：In recent years, LiFePO4 is considered to be a promising cathode material for lithium-ion batteries (LIBs) and has attracted increasing attention due to its good thermal stability, safety and environmental friendliness compared with layered cathode materials (such as Li[NixCoyMnz]O2). However, the low electrical conductivity and slow lithium-ion diffusion hampers the use of LFP in applications. Herein, we report a creative and facile method for fabricating nitrogen and phosphorus dual-doped carbon-coated LiFePO4 (LFP@NPC) via the pyrolysis of egg yolk. Egg yolk is a widely available and low-cost raw material and is used in this work as both the carbon precursors and the dopant source. LFP@NPC materials produced by one-step pyrolysis of egg yolk were systematically studied by various characterization techniques. The obtained results show that LFP@NPC has smaller uniform particle sizes, better grain-to-grain electrical contact, and faster diffusion of both electrons and lithium ions. As expected, the LFP coating with 1 mL egg yolk exhibits a high discharge capacity of 150.2 mAh g?1 at 1 C and ultralong cycle performance with only 0.016% capacity fading rate per cycle in 300 cycles at 2 C. Therefore, we suggest that the LFP@NPC composite is a promising cathode material with high performance for LIBs.
查看更多>>摘要：Hot Isostatic Pressing (HIP) is a well-known technique that lately is gaining more interest because of its growing involvement in the Additive and Near-Net Shape manufacturing fields. When HIP is used for near-net-shape manufacturing, the raw gas atomized powders assume the uttermost importance, and special attention should be given to their quality and characteristics. Based on this statement, the powder should be sieved directly after production to select only those that best suit the HIP process. Typically, a broad Particle Size Distribution is indicated for HIP purposes and looks economically advisable because it leads to a higher yield. Despite this, if the PSD is not strictly controlled, particles with high Oxygen content or chemical inhomogeneity could enter the production chain, leading to compacted components with insufficient mechanical properties. In this paper, Nickel-based superalloy Astroloy particles were assessed in depth both at their surface and in the core, dividing them into sub-batches via mechanical sieving. This procedure evidenced which contribution was brought to the final raw material by each sub-batch. Furthermore, physical properties such as flowability and tap density were studied as a function of the PSD. Next, a complete morphological assessment was conducted to understand the possible defects of each sub-batch better. Similarly, every particle group was chemically studied to determine the Oxygen, Carbon, Nitrogen, and Hydrogen content of each sub-batch. Micro and nano indentations combined with EBSD were used to understand how the particle size may affect the mechanical properties of the powders during the Hot Isostatic pressing. Furthermore, EDS and XRD analysis were used to thoroughly understand how Ti segregation starts forming and what effects are likely to develop. Based on these investigations, it was possible to rationally identify the upper and lower boundary for particle PSD without excessively limiting the overall process yield.
NSTL
Elsevier