高密度块状钐铁氮磁体制备的研究进展

钐铁氮化合物(Sm₂Fe₁₇N₃)因具有比钕铁硼(Nd₂Fe₁₄B)更高的磁晶各向异性场和居里温度值及更少的稀土含量,成为新型稀土永磁材料研究热点。但是,由于钐铁氮在600℃左右会分解导致永磁性能消失,因此常规的高温烧结工艺并不适用于钐铁氮烧结磁体的制备,现只能将其与高分子材料复合用作塑磁材料,这就导致Sm₂Fe₁₇N₃的磁学性能无法得到充分发挥。因此,开发低温成型工艺制备全金属高密度块状磁体是获取高性能钐铁氮磁体的关键。经过30多年的努力,科研人员已开发出多种制备钐铁氮磁体的低温快速成型工艺,并获得最大磁能积达到199 k J/m³的高性能磁体。本研究将从磁体的制备方法出发,总结当前块状钐铁氮磁体的研究现状及面临的问题,尤其针对不同成型方法出现矫顽力下降的现象提出分析,并对其今后的发展做出展望。     

Polyethylene glycol functionalized gold nanoparticles: the influence of capping density on stability in various media

Thiol-terminated polyethylene glycol (PEG) is commonly used to functionalize the surface of gold nanoparticles (AuNPs) in order to improve their in vivo stability and to avoid uptake by the reticular endothelial system. Although it has been reported that AuNPs functionalized with tethered PEG are stable in biological media, the influence of chain density remains unclear. This study investigates the influence of PEG capping density on the stability of washed and dried AuNPs in: water, phosphate-buffered saline solution (PBS), phosphate-buffered saline solution containing bovine serum albumin (PBS/BSA), and dichloromethane (DCM). PEG coating had a dramatic effect on stability enabling stable suspensions to be produced in all the media studied. A linear relationship was observed between capping density and stability in water and DCM with a somewhat lower stability observed in PBS and PBS/BSA. A maximum PEG loading level of ∼14 wt.% was achieved, equivalent to a PEG surface density of ∼1.13 chains/nm².     

Pulse electrodeposition of catalyst nanoparticles for application in PEM fuel cells

A simple method for the preparation of nanostructured low loading Pt, PtNi and PtCo electrodes for application in PEM fuel cells is proposed. For high utilisation, the catalyst nanoparticles are directly deposited on the microporous layer (MPL) of a commercially available gas diffusion layer by pulse electrodeposition. A special challenge for electrodeposition, in this study, was the hydrophobic character of the MPL. For a homogenous fine-grained electrodeposition, an activation treatment of the substrate surface was advantageous. Plasma etching of the surface, before electrodeposition, significantly improved fuel cell performance. Furthermore, the effects of electrolyte and electrodeposition parameters have been investigated in detail. For use as catalyst, nucleation should be predominant to enable a large surface area. Several electrochemical and optical techniques, including cyclic voltammetry, SEM, XRD, X-ray fluorescence analysis and IR spectroscopy, were used to investigate the catalytically relevant parameters of the deposited nanoparticles.     

Solid-state welding of metals with application of high density current pulses

The results of solid-state welding of homogeneous and heterogeneous metals with application of high density current pulses are presented. A chart of the current treatment allowing obtaining of the welded joint at its heating in an air atmosphere is proposed. The influence of alternating and unipolar current on the deformation of contact surface microroughnesses in the welding zone is considered. The basic parameters of the pulse current and the specific energy of the treatment of steel and copper samples that ensure obtaining of the welded joint are determined.     

Gas sensing properties of SnO2 nanoparticles mixed with gold nanoparticles

SnO₂ nanoparticles mixed with different amounts of gold nanoparticles (GNPs) were synthesized and their CO sensing properties were investigated. The sol–gel method was employed to prepare the initial solution. SEM, TEM, XRD, DLS and spectrophotometry were used to characterize the nanoparticles. The pure sensors showed a response of about 4 to 12.8 for (20–80)×10^?6 CO at operating temperature of 340 °C. The response and recovery time at 50×10^?6 Co is about 10 and 14 s, respectively. The amount of GNPs optimized was used to create high performance GNP-SnO₂ sensors (m(Au)/m(Sn)=3.7663×10^?4) and optimal operating temperature was about 260 °C and the response at concentrations of (20–80)×10^?6 was 8.3 to 29.5, respectively.     

Facile green synthesis of gold nanoparticles with gum arabic as a stabilizing agent and reducing agent

A facile, completely green, and cheap route for the synthesis of Au nanoparticles at 25–75° has been developed by using only hydrogen tetrachloroaurate as the precursor and gum arabic (GA) simultaneously as a reducing agent and a stabilizing agent. No extra reagents are needed. From the analyses of UV/VIS absorption spectra, TEM, HRTEM, SAED, and XRD patterns, the formation of Au nanoparticles with a fcc structure was recognized. The synthesis reaction was usually finished in 2–4 h. Increasing the reaction temperature increased the formation rate but had no significant effect on the optical property and size of Au nanoparticles. With increasing Au(III) ion concentration or GA concentration, the mean diameter of Au nanoparticles slightly increased. Also, the particle size distribution became broader at higher Au(III) ion concentration or lower GA concentration due to the insufficient protection. Although raising the GA concentration was helpful to reduce Au(III) ions completely and stabilize the Au nanoparticles, too high GA concentration was not suitable for the stabilization of Au nanoparticles because the increased intermolecular force of GA might hinder the dispersion of Au nanoparticles. Furthermore, the resultant Au nanoparticles were found to remain highly stable in the NaCl solution.     

One-step synthesis of carbon nanotubes with Ni nanoparticles as a catalyst by the microwave-assisted polyol method

Carbon nanotubes (CNTs) were firstly synthesized by the microwave-assisted polyol method and magnetic Ni nanoparticles were employed as a catalyst in the process. The structures, morphologies and magnetic properties of the as-synthesized samples were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. Our results indicated that CNTs can be synthesized after the observation of a small electric spark with Ni particles used as a catalyst. TEM showed that the length of the hollow carbon nanotubes was of the order of micron. VSM demonstrated that Ni/CNTs composite was ferromagnetic characteristic with hysteretic behavior at room temperature.     

AutoCAD和CAXA在高强度高密度齿轮模具设计中的应用

采用AutoCAD和CAXA绘图软件,进行粉末冶金高密度高强度齿轮模具的设计,研究了获得大于7.3 g/cm3的高密度粉末冶金齿轮的工艺特点,通过对复压装模间隙以及复杂型腔形状的精确控制,得到了精密模具的设计和加工的有效工艺途径,使得设计和加工复杂型腔的模具如齿轮模具等变得简单易行,并且对同类模具的设计加工起到较好的指导作用。     

半导体用高纯金制备技术及应用研究进展

综述了目前制备高纯金的各种方法的原理及工艺,并对其优缺点进行了分析。化学还原分离法效率高、周期短,但酸耗大、污染严重;熔融氯化法对原料适应范围广,但存在氯化过程复杂、工艺难于精准控制和产品质量不稳定等不足;溶剂萃取法效率高、产品质量稳定,但试剂消耗大、有机污染严重和易燃易爆;电解法具有成本低、除杂效果好、产品纯度稳定性强及环境污染小的优点,但原料适应性相对较差、生产周期相对较长且会积压金。高纯金具体应用形式为键合用金丝、溅射靶材及高纯度金基合金,涉及电子、半导体及航空航天等领域。     

Fabrication of gold nanoparticles with different morphologies in HEPES buffer

Gold nanoparticles with different morphologies, such as spindle, octahedron, and decahedron were obtained by using different molar ratios of HAuCl4/HEPES in the presence and absence of surfactants at room temperature.These nanoparticles were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), high-resolution transmission electron microscopy(HRTEM), scanning electron microcopy(SEM), energy-dispersive X-rays analysis(EDX), and selected area electron diffraction(SAED).The kinetics o...     

Ultra-sensitive detection of individual gold nanoparticles: spectroscopy and applications to biology

Gold nanoparticles are now widely used in different fields of chemistry, physics and biology. For many applications, it became crucial to use the smallest ones and at the same time to be able to detect them at the single particle level with versatile optical methods. Such methods should also allow the study of their intimate optical properties. Here we review the ultra-sensitive optical methods based on the photothermal effect which permit the detection of individual gold nanoparticles down to 1.4 nm through their absorption. The absorption spectroscopy of the Surface Plasmon Resonance of individual gold nanoparticles down to 5nm is further presented and revealed intrinsic size effects in the optical response of the smallest nanoparticles. Different applications to biology are also presented such as for new types of gold nanoparticles based DNA microarrays and for live cell molecular imaging owing to the insensitivity of the photothermal methods to scattering environments.     

Intrinsic reactivity of gold nanoparticles: Classical, semi-empirical and DFT studies

Gold nanoparticles used in most experiments (1–10 nm) in gold catalysis show varying degrees of reactivity, with particles below 5 nm generally being more reactive. The origin of this activity is a subject of a number of model experiments and theoretical studies on either clusters of a few atoms in size or extended surfaces (smooth or stepped). In the work described here, a classical theory for the variation of the metal workfunction with cluster size, Extended Hückel Theory (EHT) calculations combined with DFT calculations, as well as a carbon monoxide (CO) chemisorption model are combined to develop a relationship between metal particle size and the particle's reactivity towards CO. For gold, it is shown that while the contribution of the d-band hybridization energy to the total CO chemisorption energy is unfavourable for bulk gold, this is not true for gold particles below 5–6 nm. That is, the d-band hybridization energy is negative for small gold particles. This is believed to be explanation of the onset of high reactivity for small gold particles.     

Tensile behavior of hybrid tungsten composites with zirconium carbide nanoparticles and tungsten fibers

Hybrid tungsten composites reinforced with zirconium carbide (ZrC) nanoparticles and tungsten fibers were developed by the conventional powder metallurgy process (ball-mill mixing of powders and fibers followed by spark plasma sintering). The synergistic and mutual influences of the fibers and nanoparticles on tungsten were investigated in tensile behavior and fracture-energy tests. Aided by the ZrC nanoparticles, up to 30% of the fibers could be embedded in the tungsten matrix. The fracture energy was maximized by co-introducing 0.2 wt% ZrC particles with 20 wt% short tungsten fibers. The fracture-energy enhancement of the short fibers is contributed by pseudo-toughness from the fiber–matrix interface, inherent toughness from the fibers themselves, and grain refinement (by 50%) of the tungsten matrix. The fracture energy of the composite is very sensitive to the ZrC content, because the two-way action of ZrC weakens the pseudo-toughness of the interface energy.     

The combination effects of trivalent gold ions and gold nanoparticles with different antibiotics against resistant Pseudomonas aeruginosa

Despite much success in drug design and development, Pseudomonas aeruginosa is still considered as one of the most problematic bacteria due to its ability to develop mutational resistance against a variety of antibiotics. In search for new strategies to enhance antibacterial activity of antibiotics, in this work, the combination effect of gold materials including trivalent gold ions (Au³⁺) and gold nanoparticles (Au NPs) with 14 different antibiotics was investigated against the clinical isolates of P. aeruginosa, Staphylococcus aureus and Escherichia coli. Disk diffusion assay was carried out, and test strains were treated with the sub-inhibitory contents of gold nanomaterial. Results showed that Au NPs did not increase the antibacterial effect of antibiotics at tested concentration (40 μg/disc). However, the susceptibility of resistant P. aeruginosa increased in the presence of Au³⁺ and methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid, up to 147 %. As an individual experiment, the same group of antibiotics was tested for their activity against clinical isolates of S. aureus, E. coli and a different resistant strain of P. aeruginosa in the presence of sub-inhibitory contents of Au³⁺, where Au³⁺ increased the susceptibility of test strains to methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid. Our finding suggested that using the combination of sub-inhibitory concentrations of Au³⁺ and methicillin, erythromycin, nalidixic acid or vancomycin may be a promising new strategy for the treatment of highly resistant P. aeruginosa infections.     

Schiff-base-rich g-C_xN_4 supported PdAg nanowires as an efficient Mott-Schottky catalyst boosting photocatalytic dehydrogenation of formic acid

Developing an efficient photocatalyst,catalyzing formic acid(FA) dehydrogenation,can satisfy the demand of the H_2 energy.Herein,a graphitic carbon nitride(gC_xN_4)-based nanosheet(x=3.2,3.6 or 3.8) with melem rings conjugated by Schiff-base bond(N=C-C=N) was synthesized,tuning the bandgaps(Eg) of graphitic carbon nitride(g-C_3 N_4) in the range of 1.8 E_g 2.7 eV,and grown PdAg nano wires(NWs) on its surface forming an efficient PdAg NWs/g-C_xN_4 Mott-Schottky heterojunction for enhancing dehydrogenation photocatalysis of FA.The boosting photocatalysis benefits from the Schiff-base bond tuning the Eg of g-C_3 N_4 and strongly coupling from the heterojunction.Among the heterojunction,the Pd_5Ag_5 NWs/g-C_(3.6)N_4 exhibits the best dehydrogenation photocatalysis of FA [turnover frequency(TOF)=1230 h~(-1)]under visible light {λ 400 nm) without any additive at 25℃,which is the best value among ever-reported ones.This work provides a new strategy to boost dehydrogenation photocatalysis of FA,which will be promising for practical application of H_2 in future energy field.     

激光软钎焊技术在高密度封装器件无铅连接中的应用

介绍了激光软钎焊技术的原理及特点，分析了激光软钎焊技术在高密度封装器件无铅连接中的应用优势。由于激光软钎焊技术具有局部加热、快速加热、快速冷却的特点，在高密度封装器件的无铅钎焊时，能够显著改善无铅钎料的润湿性能，细化无铅焊点的微观组织，提高无铅焊点的力学性能，因此激光软钎焊技术在高密度封装器件（如四边扁平封装器件以及球栅阵列封装器件）的无铅连接中有着广阔的应用前景。     

Efficient fabrication of semisolid nondendritic Al alloy slurry with high quality

Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as model material,the temperature field and distribution field of solid or liquid phase during SCS were simulated using COMSOL Multiphysics software to primarily choose the optimal processing parameters.Subsequently,the slurries were prepared with the parameters selected according to the simulation results and the microstructures of the slurries were experimentally investigated.Results indicate that the simulation results could provide a basis for roughly choosing the processing parameters,although the calculated solid fractions are always higher than the experimental ones.The processing parameters affect the primary grain size,shape factor and solid fraction mainly through altering the contact duration of melt on the plate,and thus affecting the cooling effect on the melt,nucleation rate,and grain dissociation and proliferation.Experiments with optimized processing parameters show that the primary grains in the slurry have an average size of about 32μm and shape factor of 1.38,and are quite uniform,even at the highest pouring rate of 2.81 kg·s^-1,the size and shape factor are about 46μm and 1.7,respectively,which implies that the proposed SCS is a promising technology for efficient fabrication of high-quality Al slurry available for engineering applications.     

Development of high density and high efficiency machines

This research on development of high density and high efficiency machines is executed as the project on the Ministry of Economy, Trade and Industry in Japan. The realization of the electrical machines for the high efficiency and high energy density is aimed, by using the high quality magnetic material made in Japan such as the high grade electrical steel sheet and high performance permanent magnet.