查看更多>>摘要：Graphene has been demonstrated as an effective reinforcement for metal matrix composites, due to its excellent mechanical properties, robust chemical inertness, thermal stability, and self-lubricating. Nevertheless, the limiting factor for its further use in metal matrix composites, is to realize the homogeneous dispersion of graphene for taking advantage of its exceptional and fascinating properties, because of the poor wettability and density contrast between metal matrix and graphene. Herein, we design a gel-assisted route to synthesize high-quality graphene nanoplatelets modified monodispersed copper particles, followed by hot pressing to fabricate graphene reinforced copper matrix composites bulk. This simple route with high efficiency and low cost, offers a new solution for the mass-production of graphene reinforced copper matrix composites and other graphene-based composites on an industrial scale. Significantly enhanced tensile strength of 253 MPa, and yield strength of 145 MPa, accompanied by the low friction coefficient and improved wear resistance, can be simultaneously achieved in the composites. For the real electrical contact performance test, the service life of electrical contacts made of graphene reinforced copper matrix composites, is 10 times longer as that of the commercial pure copper electrical contacts and almost comparable to CuAg20 contacts, demonstrating its superior ability to solve the electrical contact issues in electrical engineering systems.
查看更多>>摘要：To understand the effects of microstructure of powders on resultant thermal and mechanical properties of Al-CNT composite, spherical and flake Al-CNT powders are fabricated by chemical vapor deposition and ball milling. Results showed that the spherical composite powder and its extruded sample feature with coarse grains and integrated CNTs, which imparts excellent thermal conductivity, the maximum of 246.6 W m?1 K?1 (400 ℃) are obtained. However, CNTs are found agglomerating in the grain boundaries of the Al matrix, leading to poor interfacial bonding and deteriorated mechanical properties. Compared to the spherical powders, the ball-milled flake Al-CNT powders have much finer grain structures, as well as more uniformly distributed CNTs which bond better with the Al matrix. After extrusion, their ultimate strengths are significantly improved and CTEs are further reduced, the maximum ultimate strengths of 186.2 MPa and minimum CTEs of 25 × 10?6 K?1 (400 ℃) are achieved. Nevertheless, the CNTs tend to be broken in the ball milling which unfortunately damages the thermal conductivity.
查看更多>>摘要：Mixed sesquioxide crystals (R2O3, R = Lu, Y or Sc, where R is occupied by two different elements) have drawn an increasing attention due to their outstanding physical and chemical properties. In this work, we have grown Ho3+,Yb3+ co-doped mixed sesquioxide LuYO3 and LuScO3 single crystal fibers (SCFs) in centimeter-length by laser heated pedestal growth (LHPG) method for optical temperature sensing. Both mixed sesquioxide SCFs yield strong green emission (5F4,5S2→5I8) and weak red emission (5F5→5I8) under the excitation of 980 nm laser. Their upconversion (UC) levels are not thermally coupled levels (NTCL). Importantly, these mixed sesquioxide SCFs show a good temperature sensitivity in the temperature range of 298–748 K. Using UC fluorescence intensity ratio (FIR) method, the calculated maximum values of absolute sensitivity of Ho,Yb:LuYO3 and Ho,Yb:LuScO3 are 0.1603 (at 303 K) and 0.0886 K?1 (at 300 K), respectively. These features indicate that our grown mixed sesquioxides show a great potential for high-sensitivity temperature sensing applications. Furthermore, the presented mixed sesquioxide SCFs are excellent candidates for the high-integrated temperature sensor.
查看更多>>摘要：Carbides of IV and V group transitional metals with B1 structure have large homogeneity regions due to high amounts of vacancies in the carbon sublattice. Ordering of the vacancies leads to formation of new phases with different compositions and crystal structures. In this work, we performed a theoretical search for the ordered phases in hafnium carbide using evolutionary algorithm USPEX for crystal structure prediction. Four thermodynamically stable compounds with stoichiometries Hf3C2, Hf4C3, Hf7C6 and Hf9C8 as well as near-to-equilibrium variants Hf9C7, Hf5C4, and Hf6C5 have been found in the composition range HfC0.67-HfC1.0. All the stable and meta-stable phases are formed by vacancy ordering in the carbon sublattice of B1 structure. We also described possible ordered structures for hypothetical compositions Hf10C7, Hf7C5, Hf8C7 and Hf10C9. This allowed us to investigate the effect of vacancy concentration on the structural and mechanical properties. The calculations have demonstrated the ordered vacancies with a concentration of less than approximately 11% do not deteriorate the mechanical properties of hafnium carbide. The hardness of ordered phases with vacancy concentrations less than 16.7% is higher as compared to the defect-free HfC.
查看更多>>摘要：It is of immense importance to design and explore efficient electrocatalysts based on low-cost noble-metal free nanostructures toward hydrogen evolution reaction (HER), which remains an immense challenge. Herein, we designed a novel tri-metal phosphides based on Mo-Fe-Ni phosphides nanowires (Mo-Fe-Ni-P NWs) that directly grown on CC through a facile and simple hydrothermal process followed by a phosphorization step in the presence of NaH2PO2 as the P source. Outstandingly, benefiting from the unparalleled hierarchical NWs structure with large surface areas, open channels for effective releasing of gas products, and also special electronic structure engineering with rapid mass/electron transport, the resulting advanced binder-free Mo-Fe-Ni-P NWs@CC renders supreme HER performance in the KOH (alkaline) electrolyte. At an overpotential as low as 75 mV, it renders a current density of 10 mA cm?2. More importantly, it can achieve remarkable operational stability that is very desirable for practical application. Our design exhibits a rational strategy for the fabrication of advanced binder-free ternary metal phosphide NWs as a noble-metal free HER electrocatalyst toward high efficient with low cost H2 production.
查看更多>>摘要：In this study, a series of NaYF4:Yb3+, Tm3+@NaYF4:Yb3+, Er3+ core@shell nanocrystals with different sensitizer contents in the shell were synthesized by a facile solvothermal method to investigate the impact of sensitizer Yb3+ on the upconversion luminescence. Transmission electron microscopy (TEM) results show that all prepared nanocrystals are well-crystallized with a hexagonal phase and have a desirable size distribution. The particle size increases after shell coating as shown in TEM images; however, it changes a little for samples with different sensitizer contents in the shell. Therefore, the effect of different particle sizes on luminescence properties, which is caused by different Yb3+ contents, could be minimized. Subsequently, it was assumed that the luminescent center content (Er3+) is same in all samples and does not influence the emission spectrum differences. Therefore, we investigated the underlying upconversion luminescence mechanism by determining the sample's fluorescence spectrum and assuming that the energy transfer mechanism occurred in all the samples. The results show that the green upconversion luminescence decay was faster than its red counterpart when the Yb3+ content was increased and samples were excited using a 980 nm pulse laser. The transient spectra measured at different times after the excitation pulse reveal the intensity ratio associated with the green to red upconversion luminescence. It was concluded that the back energy transfer (BET) process from Er3+ to Yb3+ led to a conversion of the green emissions into the red emissions, which was beneficial to the red upconversion and the electron relaxation from 4I11/2 to 4I13/2. Therefore, the red to green upconversion luminescence ratio increases significantly in samples highly doped with Yb3+.
查看更多>>摘要：Although lithium-sulfur (Li-S) batteries have high theoretical specific capacity, their development is limited by low reaction kinetics during solid-liquid conversion of polysulfides and severe dissolution of polysulfides leading in loss of active materials and the corrosion of Li metal. In this paper, a novel electrode material which synthesized by yttrium oxide (Y2O3) nanorods modified Ketjen black@sulfur (Y2O3/KB@S) composites is introduced and evaluated in Li-S batteries. Y2O3 nanorods have good adsorption-catalytic synergistic effect on polysulfides, which can curb the shuttle effect and enhance the redox kinetics of polysulfides. The initial specific discharge capacity of Y2O3/KB@S electrode shows 828 mAh g?1 at 0.5 C current density, and the capacity maintains at 388 mAh g?1 after 500 cycles with the areal sulfur loading of 3.1 mg cm?2. Furthermore, Y2O3/KB@S cathode delivered 5.09 mAh discharge capacity and retained 4.21 mAh after 100 cycles at 0.2 C current density when the areal sulfur loading increasing to 5.0 mg cm?2. Therefore, Y2O3 nanorods modified Li-S battery cathode material has good application potential in its industrialization process.
查看更多>>摘要：SiOx is regarded as a promising anode material for the next-generation lithium-ion batteries (LIBs) because of its high theoretical capacity. In order to relieve the volume variation and enhance the electronic and ionic conductivity, a SiOx@TiO2@N-doped carbon (NC) composite is prepared using biopolymer chitin as carbon precursor. The TiO2 coating layer shields the SiOx in the alkaline chitin solution, enabling the homogeneous and stable dispersion of the SiOx during the synthesis process. After emulsion, freeze-drying, and carbonization, the SiOx@TiO2@NC composite is obtained. The dual-confinement of TiO2 and NC effectively buffers the volume variation of SiOx and enhances the electronic/ionic conductivity. The enhanced structural integrity and conductivity guarantee the superior rate capability and the stable long-term cyclability of the SiOx@TiO2@NC composite. After 650 cycles at 0.5 and 1 A g?1, SiOx@TiO2@NC maintains reversible capacities of 633 and 540 mA h g?1, showing capacity retentions of 92.3% and 96.9%, respectively. After 100 cycles at 0.5 C, the assembled SiOx@TiO2@NC//LiFePO4 full cells can retain a discharge capacity of 121 mA h g?1, maintaining 90% of the third capacity. This work provides a chance for the industrial application of biopolymer chitin in LIBs, and may alleviate the pressure of environmental protection.
查看更多>>摘要：Electrode materials with high theoretical capacity and high conductivity are critical for high performance rechargeable batteries. Herein, a leaf-like cobalt silicate nanosheet/carbon nanotube (Co-Silicate/CNT) hybrid film is synthesized through a hydrothermal strategy. The Co-Silicate nanosheets provide large accessible surface area and abundant low-coordinated surface atoms with high reactivity. Meanwhile, the Co-Silicate nanosheets are strongly coupled with internally connected CNTs, which afford fast electron transfer and high mechanical stability. Moreover, the open pores can effectively reduce the ion migration distance and alleviate volume changes during charging and discharging cycle. When used as a binder-free anode for LIBs, the Co-Silicate CNT hybrid film exhibits a high initial charge capacity of 846.8 mA h g?1, a good rate performance (1451.3 mAh g?1 when reset to 0.1 A g?1 after additional 80 cycles) and excellent cycle performance (331.72 mAh g?1 after 1000 cycles at 10 A g?1). As anode materials for sodium storage, it also shows a good rate performance and cycle performance (246.3 mAh g?1 after 500 cycles at 1 A g?1). Reaction mechanism analysis reveals that the good performance results from the optimized 3D “branch-leaf” structure and combined effect of capacitance and insertion mechanism. These results indicate that the Co-Silicate/CNT hybrid film has great potential in practical applications as LIB/SIB electrodes.
查看更多>>摘要：The strategy of the strength-ductility balance of aluminum matrix composites (AMCs) reinforced with nano- and micro-SiC particles via deformation-driven metallurgy was designed. The grain refinement of SiCnp/AMCs was promoted with the nano-SiC particles intragranularly-dispersed, and the stability of the ultra-fine-grains was improved due to the Zener pinning mechanism. The ultimate tensile strength of the SiCnp/AMCs was increased significantly, reaching 435 MPa and kept the ductility at 9%. A typical multimodal grain microstructure of SiCμp/AMCs was obtained with micro-sized grains and ultrafine grains as the localized grain refinement was promoted by the particle stimulated nucleation mechanism and was intensified by the broken micro-SiC particles. The ductility of the SiCμp/AMCs was kept well, reaching 18%, and kept the ultimate tensile strength at 200 MPa. Therefore, the microstructure of SiC/AMCs could be designed to balance the strength and ductility via optimizing the SiC particles according to the needs of practical applications: matrix strength could be increased by selecting a certain amount of nano-SiC particles; while an excellent ductility could be obtained by adding the appropriate amount of micro-SiC particles.
NSTL
Elsevier