Progress in Natural Science: Materials International最新文献

Achieving subwavelength optical focusing is of great importance in nanophotonics. However, achieving focusing with both a small focal spot size and a large focal length remains elusive so far. Here, a large focal length planar focusing device is presented, utilizing highly oriented Dyakonov polaritons in hyperbolic metamaterial with periodic silver rings as the excitation source. Experimental results show that by controlling the size of the excitation sources, the focal length can reach 6λ₀ (where λ₀ is the illumination wavelength), and the focal spot size can be reduced to λ₀/10. This method provides new prospects for planar polariton optical applications.

A variety of nanoparticles (NPs) (e.g., SiO₂, TiO₂, CeO₂, Co₃O₄, etc.) and their functionalized counterparts have been intensively investigated for improving the electrochemical and mechanical durability of polymer-based proton-exchange membranes (PEMs) for use in low- and intermediate-temperature fuel cells. This study is to conduct a comprehensive review on the roles of functionalized NPs in the performance enhancement of PEMs including proton conductivity, gas crossover resistance, electrochemical and mechanical durability, etc. A brief historical review of PEM fuel cell (PEMFC) technology is made. Typical types of NPs and their functionalization techniques are retrospected and their roles in the performance improvement of PEMs are compared in detail. Consequently, the opportunities and challenges to develop high-performance functionalized NPs for use in PEMs and PEMFCs are prospected and justified.

Cobalt selenide (CoSe₂) emerges as a highly promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity and cost-effectiveness. Despite these merits, its practical utilization faces challenges stemming from substantial volume fluctuations and limited electronic conductivity. To tackle these issues, a plum-branch-like structure of CoSe₂@N-doped carbon that embedded in one-dimensional N-doped carbon fibers (CoSe₂@NC/CFs), is successfully synthesized through an in-situ confinement method. Well-defined CoSe₂@NC nanoparticles, featuring diameters between 20∼30 ​nm, are uniformly dispersed on both the inner and outer surfaces of the carbon fibers. The distinctive architecture of CoSe₂@NC/CFs ensures an increased number of active sites, elevated electronic conductivity, alleviated volume expansion, and accelerated reaction kinetics. Consequently, the CoSe₂@NC/CFs exhibits remarkable cycling performance and exceptional rate capability. Operating at a current density of 1000 ​mA ​g⁻¹, the CoSe₂@NC/CFs anode sustains a capacity of 664 ​mA ​h ​g⁻¹ with no obvious capacity decay over 500 cycles. Even at a high current density of 5000 ​mA ​g⁻¹, it maintains a capacity of 445 ​mA ​h g⁻¹ with a mere 0.02 ​% capacity decay per cycle. This study introduces a novel approach to anode material design, showcasing significant advancements in lithium-ion battery technology.

Different alloys can be flexibly combined to meet the performance needs of different parts of the compressor disc by welding process. However, achieving a good combination of dissimilar alloys with different mechanical properties has always been a research difficulty. In this work, a Ti600/Ti₂AlNb joint was fabricated through electron beam welding and an isothermal forging was used to optimized its microstructure and mechanical performance. The isothermal forging process increases the ultimate tensile strength (UST) and yield strength (YS) of the Ti600/Ti₂AlNb joint by ∼18 ​%, while ∼2.5 times the ductility. It is indicated that before forging, the Ti600/Ti₂AlNb joint exhibits a much lower strength than that of Ti600 matrix, whereas the opposite is true after isothermal forging. The isothermal forging broken the coarse columnar grains of Ti600/Ti₂AlNb joint and render to an equiaxed B2 structure in which the acicular α₂ and O phase are precipitated, resulting a synchronous enhancement of strength and ductility. This work may pave an effective routine for improving the comprehensive mechanical properties of dissimilar metal welding joint.

It is of significance that the wettability between the molten alloy and the Al₂O₃ affects the inclusion removal, nozzle clogging and refractory erosion. In the present work, the wettability between the Al₂O₃ substrate and Fe–P–Ti alloys with different Ti content was investigated by using the sessile droplets method. The interfacial characteristics were investigated by scanning electron microscope (SEM). The contact angles between the sintered Al₂O₃ substrate and Fe–P–Ti alloys with 0, 0.05, 0.10 and 0.15 ​wt% Ti are 100.1°, 97.3°, 94.5° and 90.5°, respectively. The oxidation of [Al] and [Ti] in the molten alloys leads to the formation of the oxides on the droplets. With the increase of Ti content in the Fe–P–Ti alloys, the formed oxides change from Al₂O₃ to Ti-containing oxides. The reaction between [Ti] and Al₂O₃ substrate in the interface results in the formation of Ti-containing oxides. The quantity of the interfacial oxides increases with the increase of Ti content in the alloys. As a result, the synergetic effect of the formation of the interfacial products and the oxides on the surface of droplets leads to the decrease of the contact angles between the Al₂O₃ substrate and Fe–P–Ti alloys due to the increase of Ti content.

Though the current research on vanadium-based glass electrodes has made great progress, the conductivity theory of V-based glasses has not been obviously improved and crystals cannot be positioned precisely. The changes in the valence state of V³⁺, V⁴⁺ and V⁵⁺ are regulated by the strong reducing agent Fe₂P to realize valence bond transformation of the amorphous electrode, explore the redox process of multi-electron reactions and further optimize the conductivity of electrode materials. VPFe2 and VPFe3 precipitate VO₂ crystals and VPFe4 precipitates VO₂ and V₆O₁₁ crystals. Electron back-scattered diffraction was used to accurately identify the distribution and specific positions of both types of crystals. V₆O₁₁ crystals exhibit a strong texture according to pole figure and inverse pole figure. XPS reveals that Fe₂P and V₂O₅, undergo a redox reaction during the high-temperature melting process, where V⁵⁺ is reduced to V⁴⁺ and V³⁺ and V⁴⁺ renders a positive influence on conductivity. The addition of Fe₂P increases the content of V⁴⁺ in the glass and VPFe3 glass contains the highest content of V⁴⁺, leading to the highest electronic conductivity. V₂O₅ transforms into VO₂ crystals and VO₂ transforms into V₆O₁₁ with the increase of Fe₂P content. The type of nanocrystal precipitation in glass affects electronic conductivity.

A tri-layered (B-G-B) dielectric films were simply prepared by alternatively spin-coating boron nitride/polymethylmethacrylate (BN/PMMA, B) and graphene nanosheets (GNS/PMMA, G) compound solutions. The structure, morphology, thermal conductivity, and particularly the dielectric and relaxation behaviors were systematically studied. Results showed that a good exfoliation and dispersion of BN and GNS can be simply achieved through intensive mechanical compounding with PMMA in the internal mixer. The dielectric constant and breakdown strength of the obtained 1-3-1 (B-G-B) sandwich composite film reached 4.3 (@1 ​kHz) and 458.6 ​kV/mm, being 119 ​% and 113 ​% higher than that of pure PMMA, respectively. Furthermore, the overall thermal conductivity of sandwich 1-3-1 composite increased by 112 ​% due to the addition of thermally conductive BN and GNS. The sandwich design strategy provided an effective way of achieving good permittivity, high insulation, and improved thermal conductivity simultaneously, showing potential applications in the miniaturization and integration of electronic devices.

The emergence and development of layered materials have shown great promise for many applications, especially in recent years, the effective modulation of the physicochemical properties of layered materials by intercalation chemistry has led to great potential in material design. In this paper, we review the reaction mechanisms of different guest species (metal atoms/ions, organic molecules/ions, inorganic molecules and inorganic ions) intercalated into the host layered materials as well as the recent progress. It is also reviewed that layered intercalated materials with controllable structure and tunable physicochemical properties can be prepared through the occurrence of interactions between different subjects and guests. The specific applications of intercalation chemistry in the field of electrocatalysis, such as the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction and other electrocatalytic reactions, are then discussed, with emphasis on the mechanism of the improved catalytic activity and stability of the layered materials after guest intercalation.

This article investigates the evolution and control of inclusions in the smelting process of titanium containing ultra-low carbon steel. Through industrial experiments, the influence of oxygen content before aluminum addition on inclusions in ultra-low carbon IF steel was explored, and the evolution process of inclusions was studied. The microstructure of different types of inclusions was observed using three-dimensional analysis techniques. Research has found that the oxygen content before aluminum addition has no significant effect on the final oxygen content. However, under low aluminum and low oxygen conditions, the size of inclusions formed is small and difficult to float and remove. Even if the cycle time is extended, the AF index of inclusions remains at a high level. Through three-dimensional morphology analysis of inclusions, it was found that alumina formed under high aluminum and high oxygen conditions is very dense, while inclusions are relatively loose under low aluminum and low oxygen conditions. In addition, through the analysis of aluminum oxygen supersaturation before the formation of aluminum oxide inclusions, it was found that due to the low oxygen content, the nucleation rate of aluminum oxide in the early stage of inclusion formation is relatively low, and the inclusions grow along the trajectory of oxygen, ultimately forming polycrystalline aluminum oxide inclusions. This article also observed for the first time the initial three-dimensional morphology of Al Ti inclusions, providing a theoretical basis for further optimizing smelting processes and controlling inclusions.

Magnesium-based hydrogen storage materials represent a hydrogen storage technology with broad application prospects. As the global energy crisis and environmental pollution issues become increasingly severe, hydrogen, as a clean and efficient energy source, has garnered growing attention. Magnesium-based hydrogen storage, serving as a crucial means for storing and transporting hydrogen, is gaining prominence due to its abundant resources, low cost, low density, and high hydrogen storage density. However, challenges in terms of absorption/desorption rates, temperature, activation energy, and enthalpy during hydrogen application impede its development. To address these challenges, this paper systematically reviews current research on magnesium-based hydrogen storage materials, encompasses their types, characteristics, and hydrogen absorption mechanisms. Furthermore, it delves into the impacts of nanoscale dimensions, alloying, doping, and catalysis on the performance of magnesium-based materials. The aim is to provide valuable insights for research in related fields.