查看更多>>摘要：? 2022 Elsevier B.V.Lithium polysulfides shuttle effect and their sluggish redox kinetics have seriously affected the development of lithium-sulfur batteries. To solve these issues, we have designed cubic pyrite-structure NiS2 nanospheres modification of Ketjen black@sulfur (NiS2/KB@S) composite as cathode materials for lithium-sulfur batteries. The NiS2 nanospheres have a positive effect on the adsorption and catalysis performance of the lithium polysulfides, which further facilitates the redox kinetics. Consequently, the NiS2/KB@S cathode with 3.1 mg cm?2 sulfur loading attains a discharge capacity of 869 mAh g?1 at 0.5 C and reversible capacity is 461 mAh g?1 after 500 cycles. Even at high sulfur loading of 5.3 mg cm?2, the NiS2/KB@S electrode still delivers a high initial area capacity of 4.82 mAh cm?2 at 0.2 C with capacity retention capacity of 3.74 mAh cm?2 after 120 cycles. The cyclic and rate properties of NiS2/KB@S are greatly improved over that of KB@S. The results suggest that multifunction cubic pyrite-structure NiS2 nanospheres that anchors effectively and catalysis is beneficial to the large-scale application for lithium-sulfur batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Mg(NH2)2-2LiH is one of the most promising hydrogen storage systems to be applied in hydrogen powered vehicles as hydrogen source. However, the synthesis of the main raw material Mg(NH2)2 is high-cost and time-consuming for the present technologies. Herein, we report a low-cost, time-saving and low-carbon method to synthesize Mg(NH2)2 by mechanochemical reaction of metallic Mg with ammonia. After 72 h of mechanochemical reaction, amorphous Mg(NH2)2 is successfully synthesized by milling metallic Mg and ammonia at room temperature. A two-stage reaction is demonstrated to be responsible for the conversion of Mg and ammonia into Mg(NH2)2. In the initial process of ball milling, Mg particles tend to clump and agglomerate because of the ductility of metallic Mg. The first reaction stage between metallic Mg and ammonia occurs at the surfaces and interfaces of bulk Mg to form MgH2 and Mg(NH2)2 powders. With prolonged milling time, the size of bulk Mg decreases with milling time due to the continuous occurrence of the first-stage reaction. The second-stage reaction is confirmed to be the reaction of MgH2, developed in the first reaction stage, with ammonia to produce Mg(NH2)2. The as-synthesized Mg(NH2)2 is used as raw material for synthesizing Mg(NH2)2-2LiH material, showing almost the same hydrogen storage performance as the Mg(NH2)2 synthesized by heating Mg and ammonia. This study provides a new method to synthesize Mg(NH2)2 for hydrogen storage on a large scale.
查看更多>>摘要：? 2022 Elsevier B.V.In the current study differential scanning calorimetry (DSC) and transmission Electron Microscopy (TEM) analyzes were performed in order to investigate the bimodal microstructure feature by taking into account both density and morphology of precipitates, which are transformed from the retrogression and reaging (RRA) along with interrupted aging (T6I4) conditions within the 7050 aluminum alloy. Results showed that RRA treatment is conducive to a higher density of fine precipitates distributed homogeneously in the Al matrix, with precipitates essentially being shear-resistant η’ in view of a smaller density of shearable GP zone and incoherent η precipitates present. Conversely, the T6I4-65 treatment generated a smaller density of less fine shear-resistant precipitates, but with a higher density of shearable GP zone and incoherent η precipitates. Thus, the RRA treatment might promote a beneficial effect on correlation between yield strength and ductility owing to higher balance of combination mechanisms between shearable GP zones and shear-resistant η’ precipitates with movement dislocations as opposed to T6I4-65 treatment within the 7050 aluminum alloy. Both RRA and T6I4-65 treatments culminated in a slight decrease in either potential or pitting corrosion in comparison to the T7451 treatment.
Laia A.S.Rodrigues J.J.Dos Santos M.A.C.Machado R....
10页
查看更多>>摘要：? 2022 Elsevier B.V.In this work, lithium-boron-aluminum (LBA) glasses doped with Eu3+ were produced by the traditional melting method. These precursor glasses (PG) were heat treated at 400 and 450 °C for 6 h to produce glass-ceramics (GC). The X-ray diffraction measurements showed the formation of a crystalline phase. In the LBA GCs, crystal growth is nucleated at the surface and an increase in the emission intensity of the heat-treated glasses compared with the PG was observed. Spectral analysis of the luminescence indicated that Eu3+ occupies low-symmetry site (asymmetry ratio ≈ 4) and without an inversion center. The emission spectra were analyzed using Judd-Ofelt theory and the intensity parameters Ω2, Ω4 and Ω6 were calculated. The values of these parameters were not significantly affected by the heat treatment process. The application of these materials as optical temperature sensors using the valley-peak intensity ratio (VPIR) was investigated using the multi-peak spectral profile of the 5D0 → 7FJ luminescence bands of Eu3+. We estimated the relative sensitivity, the figure-of-merit of the thermometer, to be as high as 0.40 ± 0.02% K?1. Interestingly, some VPIR that were explored presented a constant value for the relative sensitivity across the temperature interval used in our experiment (between 312 and 393 K), which is advantageous for sensor operation over a broad temperature range.
查看更多>>摘要：? 2022 Elsevier B.V.Large volume fractions of stable δ-phase in nickel-based superalloys, such as in Inconel 718 (IN718), are being avoided in the forging industry because of their deleterious effect in causing brittleness. However, it has been found that a proper morphology of this phase when located at the grain boundaries provides a desirable pinning effect to prevent grain growth during hot deformation. To verify this phenomenon, partially recrystallized samples of IN718 were taken from an industrially deformed workpiece. The specimens were subjected to delta-processing (DP718) in order to reach a δ-phase saturation and, subsequently, were also subjected to hot deformation above and below the δ-solvus temperature (960 °C and 1020 °C, respectively) at three different strain rates (0.001 s?1, 0.01 s?1, and 1 s?1). The corresponding microstructural evolution was evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties were analyzed in terms of microhardness (Vickers). It was found that an intergranular needle-like δ-phase provides a pinning effect on grain growth during deformation, especially when placed at the grain boundaries while keeping an orientation relationship [011]γ//[11?2]δ.
查看更多>>摘要：? 2022 Elsevier B.V.The present work reports synthesis, optical, dielectric and electrical properties of M-type BaFe12?xGdxO19 (x = 0, 1, 1.25, 1.5, 1.75 and 2 mol%) ceramics. Auto combustion synthesis technique was applied for the preparation of the ceramics. Structural analysis was done using PXRD patterns which confirms the hexagonal structure of prepared ceramics. The average particle size of the prepared samples was found to be 25.29 nm and the lattices parameters 'a' and 'c' values ranges from 5.8864 ? to 5.9282 ? and 23.2135–23.3981 ? respectively. UV-Visible spectroscopy and Photoluminescence (PL) analysis were used to investigate the optical characteristics of the prepared samples. The PL emission spectra show that the emission peaks were observed at 689 nm due to the optical transition 6GJ to 6PJ emission. The direct band gap (Eg) of BaFe12O19 is 4.07 eV and Eg value decreases from 4.07 eV to 3.92 eV with substitution of Gd3+ ions. The indirect band gap value also decreases with Gd3+ substitution. The electrical properties were investigated through CIS (complex impedance spectroscopy), EMS (electrical modulus spectroscopy), ac-conductivity and dielectric studies. The dielectric behavior of the samples is explained by Maxwell- Wagner's two-layer model. NTCR behavior of the prepared powder samples are confirmed from CIS studies. The ac-conductivity studies follow the universal power law. By the substitution of Gd3+ ions, the dielectric constant value increases up to four times and value of dielectric loss decreases by four times, so the BaFe12?xGdxO19 samples can be used in various microwave devices.
查看更多>>摘要：? 2022 Elsevier B.V.the five CdS/CdTe heterostructure solar cells were synthesized by using multiple fabrication methods. The structural, optical and electrical characteristics were measured to understand the role of AZO, ZTO, and V2O5 layers in the solar cell operation. The performance of the ZTO, AZO (ETL) as a transparent electrode and V2O5 holes transport layer (HTL) was investigated in the CdS/CdTe solar cell. AZO, ZTO and vanadium pentoxide (V2O5) has shown an efficient role to serve as a charge selective layer in the heterostructure solar cell. XRD pattern revealed that all thin-film HSSCs exhibit crystalline nature with their characteristic phases and growth. Top and cross-sectional FESEM images were captured to observe the morphology and the thickness of AZO, ZTO, CdS, CdTe, and V2O5 thin films. It was observed that V2O5 equipped solar cell offers better performance and high efficiency due to their larger open-circuit voltage. The value of current increases 7.50–10.75 mA with the insertion of the V2O5 layer between CdTe and back surface contact. The conductive AZO and ZTO layer shows high transmittance (above 90%), resulting in the maximum amount of light refracts towards the CdTe absorber layer. The combination of TCO (AZO/ZTO) and HTL V2O5 layer in the CdS/CdTe solar cell promote high efficiency and large open-circuit voltage.
查看更多>>摘要：? 2022 Elsevier B.V.In the present study, the valence electron structures (VESs) of Mo(Si1-xAlx)2 solid solution alloys were calculated according to the empirical electron theory (EET) of solids and molecules, and the relationship between VESs and their properties was determined. The results indicated that the hardness of the phases with the C11b crystal structure could be compared using the quantity of covalent electrons (CEs) and bonding energy on the strongest bonds, the strength by the ratio of the quantity of CEs to the total quantity of valence electrons, and the plasticity by the quantity of lattice electrons (LEs). It was found that the dissolution of Al in the MoSi2 phase could reduce the quantity of CEs, bonding energy, percentage of the total quantity of CEs relative to the total quantity of valence electrons and increase the quantity of LEs in Mo(Si1-xAlx)2 alloyed materials. These results indicated that alloying Al with MoSi2 would decrease the hardness value (HV) and strength and increase the plasticity of Mo(Si1-xAlx)2 solid solutions. Based on these results, samples of Mo(Si1-xAlx)2 solid solutions were prepared; when the Al content reached 12 at%, the hardness and bending strength of Mo(Si1-xAlx)2 solid solutions decreased by 24.84% and 14.96%, respectively, and the fracture toughness increased by 119.94% compared to that of the unalloyed MoSi2.
查看更多>>摘要：? 2022 Elsevier B.V.Here, a three-dimensional electrode substrate derived from graphite paper is developed via an electrochemically assisted modification method. The as-obtained sample (denoted as EGP) containing partially exfoliated graphite sheets atop its surface and expanded lateral graphite layers provides a large surface area for loading NiCo-layered double hydroxide (NiCo-LDH). Therefore, combined three-dimensional electrode architecture with high capacitance of NiCo-LDH, the EGP@NiCo-LDH exhibits ultrahigh capacitance (1650 F g?1 at 1 A g?1) coupled with improved rate performance. In addition, an asymmetric supercapacitor based on EGP@NiCo-LDH supplies a high energy density of 44.31 Wh kg?1 at a power density of 799.98 W kg?1 and remarkable cycling stability with 92.8% retention after 5000 cycles.
查看更多>>摘要：? 2022 Elsevier B.V.To increase the red component and improve the color rendering index, the emission redshift of Ce-doped garnet phosphors was extensively studied by a vast amount of researches. But surprisingly, there are still some fuzzy parts in the luminescence mechanism based on the classic configuration coordinate model, which makes some peculiar situations difficult to explain, e.g., the counterintuitive trends of excitation shift in M2+-Si4+ (M2+= Mg2+, Ca2+, Sr2+, Ba2+) doped Ce: YAG. To figure out the origin of contradiction and reveal the concrete luminescence dynamics, a series of Ce-doped garnet ceramic phosphors were fabricated and characterized in this work. Combined with historical data and current research, it is analyzed that the effects of crystal field splitting and structural rigidity on the luminescent properties of Ce3+ share the same changing trend with the distortion of cubic symmetry. When the distortion of cubic symmetry is strengthened, the eg splitting and the electron-phonon coupling will be strengthened simultaneously, which leads to the downward and rightward shift of the 5d1 parabola curve. This effect can well explain the remaining problems in previous researches, and also provides a guideline for future studies on Ce-doped garnet phosphors.
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