耐折高导电性银浆的制备

研究了银片粒径对折叠前后银浆电导率的影响。采用不同粒径的片状银制备了具有良好导电性能的低温固化耐折导电银浆料,将银浆网印在聚酰亚胺基板上,在140 ℃下烧结形成网印电路。用微欧姆计检测了印刷电路的电阻率,对印刷银电路折叠前后的电阻变化进行了检测,并用扫描电镜对其表面形貌进行了研究,分析了导电机理。结果表明,小片Ag作为未连接薄片之间的桥梁,在折叠后填补了空白,形成导电网络,提高了折叠后的银浆导电性能。     

Shrinkage features,microstructure evolution and properties of Gd2O3-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd₂O₃ and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd₂O₃ is proved to have a lower lattice parameter (10.7516 Å) using XRD refinement. Pressureless sintering behavior of Gd₂O₃-MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 °C while that of the undoped one shrinks sharply at 1250 °C due to Gd₂O₃ phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd₂O₃ creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %‐85.6 % at 3–5 µm, which show good consistency with the calculated values. The refractive index of Zr- Gd₂O₃ varies from 1.87 at 3 µm to 1.80 at 5 µm, which is smaller than those of monoclinic Gd₂O₃.     

Mn/Cu nanoclusters-grafted N-doped carbon nanotubes: Robust oxygen electrode catalysts for Zn-air batteries

Developing efficient nonprecious electrocatalysts that can drive the oxygen electrode reactions in zinc-air batteries (ZABs) is important but remains challenging. In this work, novel materials comprising Mn/Cu nanoclusters-grafted N-doped carbon nanotubes are synthesized by preparing and then pyrolyzing Mn/Cu polyphthalocyanine-encapsulated carbon nanotubes (CNTs), followed by treating the products with acidic solution. The materials are named CNTs@(Mn,Cu)PPc-T, where T denotes the pyrolysis temperature in °C, and they are demonstrated to serve as efficient oxygen electrode catalysts for zinc-air batteries (ZABs). Among them, the one synthesized at 900 °C, CNTs@(Mn,Cu)PPc-900, requires more positive onset and half-wave potentials for reduction of oxygen and a low overpotential for the evolution of oxygen. A rechargeable ZAB assembled with CNTs@(Mn,Cu)PPc-900 electrocatalyst delivers a high power density (158.5 mW cm⁻²) and displays an excellent stability in 200 cycles of charge/discharge (in over 33 h). Such performance is even superior to that of a ZAB containing the benchmark Pt/C + RuO₂ catalyst as an air cathode under identical testing condition.     

Single crystal structure determination and infrared fluorescence of the system (K3Sr1−xNdx) (Nd1−xSr1+x) Nb10O30

The μ-pulling down technique has permitted to grow single crystal fibers, of the gross chemical formula K₃Sr₂NdNb₁₀O₃₀, having a sufficient optical quality to carry out spectroscopic studies. The crystal structure has been determined and refined to reliability factors: (i) R₁ = 0.0384 (wR₂ = 0.0665) at room temperature; (ii) R₁ = 0.0334 (wR₂ = 0.0638) at 120 K. Difference in the cationic distribution over the 15- and 12-fold sites was noticed. IR fluorescence spectra investigated under different laser excitation wavelength at 300 K and 77 K show strong emissions at 0.9 and 1.06 μm. Low temperature fluorescence behavior is compatible with Nd³⁺ ions located in both Sr²⁺ and K⁺ sites with 15- and 12-fold coordination, respectively.     

Separation of CNF agglomerates from a ceramic suspension by spray drying technique

Aqueous silicon nitride based composite suspensions with the addition of 3.1 wt% of carbon nano-fibers (CNFs) were dried using two different drying techniques: spray drying and freeze drying. The paper deals with optimisation of parameters of the spray drying processwith the aim of maximising the yield and improve the quality of the granulate. Freeze drying was selected as a reference drying method, because no powder separation can occur in the course of the process. Prepared suspensions were spray dried at 4 different temperatures: 80, 110, 140 and 180 °C. After each run, two types of granules were obtained: from the separation flask and from the product vessel. Thermo-gravimetric analysis together with SEM examination show that spray drying results in separation of CNFs agglomerates. The granules from separation flask are always enriched by CNFs agglomerates whilst the granules from product vessel have reduced content of CNFs agglomerates. Sintering of spray-dried granules from the product vessel resulted in the composite with uniform microstructure, low amount of CNFs agglomerates and high relative density.     

Effect of site occupation on thermal and mechanical properties of ternary alloyed Mo5Si3

The fundamental thermophysical properties of Mo₅Si₃ have been investigated. The pronounced mismatch in the coefficient of thermal expansion (CTE) between the c- and a-directions of monolithic Mo₅Si₃ was reduced significantly by alloying additions. 25 at.% Cr reduced the CTE-mismatch to 1.45 in Mo₃Cr₂Si₃, while 25 at.% Ti resulted in a mismatch of 1.32. Rietveld refinement of neutron powder diffraction data of the studied compounds reveals that Cr, having a smaller radius than Mo, has preference for the 4b chain sites of the D8_m unit cell of Mo₅Si₃. In contrast, Ti atoms, being larger than Mo, occupy almost entirely the 16k sites in the unit cell interior. Compression tests of cast Mo₅Si₃ at 1573 K indicate that 25% Ti or Nb additions both result in brittle fracture, whereas Mo₅Si₃ containing 25% Cr deforms plastically. 25% Cr additions decreases the yield strength to approximately half of that of monolithic Mo₅Si₃ at 1573 K.     

Superior hydrogen storage properties of MgH2–10 wt.% TiC composite

The hydrogen storage performance of MgH₂–10 wt.% TiC composite was investigated. The additive TiC nanoparticle led to a pronounced improvement in the de/hydrogenation kinetics of MgH₂. The composite could dehydrogenate 6.3 wt.% at 573 K while the milled MgH₂ only released 4.9 wt.% of hydrogen at the same condition. The improvement came from that the activation energy of dehydrogenation was decreased from 191.27 kJ mol⁻¹ to 144.62 kJ mol⁻¹ with the TiC additive. The MgH₂–10 wt.% TiC composite also absorbed 6.01 wt.% (or 5.1 wt.%) of hydrogen under 1 MPa H₂ at 573 K (or 473 K) in 3000 s. Even at 1 MPa H₂ and 373 K, it could absorb 4.1 wt.% of hydrogen, but milled MgH₂ could not absorb hydrogen at this condition. Additionally, the composite had good cycling stability, and its hydrogen capacity only decreased 3.3% of the first run after 10 de/hydrogenation cycles. The improved hydrogen storage properties were explained to the TiC particles embedded in the MgH₂, which provided the pathways for the hydrogen diffusion into the MgH₂–10 wt.% TiC composite.     

One-pot synthesis of non-noble metal WS2/g-C3N4 photocatalysts with enhanced photocatalytic hydrogen production

As an increasing number of photocatalysis are developed, non-noble metal photocatalysts that can be synthesized from earth-abundant and low-cost materials have received a great deal of attention. In this study, non-noble metal WS₂/g-C₃N₄ photocatalysts were prepared by a facile one-pot synthesis. Varying masses of tungsten disulfide (WS₂) were successfully loaded onto g-C₃N₄ and characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These results indicated that the WS₂ was successfully synthesized and immobilized closely on the surface of g-C₃N₄ to form a sheet-like nanostructure. The H₂ generation results showed that the optimal photocatalyst was 0.3-WCN because it had the highest photocatalytic H₂ production of 154 μmol h⁻¹g⁻¹, which is 34 times higher than bare g-C₃N₄ and even higher than 0.3 wt% platinum-loaded g-C₃N₄. Additionally, the possible mechanism of the photocatalyst was studied by photoluminescence (PL), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoelectrochemical tests, which showed that the WS₂ played a key role in improving the efficiency of separation and migration of the photogenerated carriers in g-C₃N₄.     

Design of Permanent Magnet Systems Using Finite Element Analysis

Rare earth permanent magnets have a wide range of magnetic properties to meet the requirements of an extensive variety of applications. Sintered Sm₂Co₁₇-type magnets have the best thermal stability with high magnetic performance at temperatures up to 550 °C. Sintered NdFeB magnets have the highest maximum energy product, (BH)_max, but are limited to applications with relatively low operating temperatures. Bonded magnets offer some design flexibility at the expense of magnetic properties. In view of these complexities, it is very important to understand the critical factors when designing the magnetic circuit. Using design examples based on finite element analysis (FEA), we will discuss magnetic materials selection, magnetic circuit design principles and design trade-offs for various applications.