纳米晶掺钇硬质合金粉末的制备

采用高能球磨法制备了纳米晶掺Y硬质合金粉末。用XRD，SEM和DTA等分析检测手段，研究了纳米晶掺Y硬质合金粉末的结构、形貌和相的变化。结果表明：高能球磨45h，可获得晶粒尺寸约为8nm的掺Y硬质合金粉末；微量Y的加入，有利于硬质合金粉末晶粒的细化；在25～45h范围内，随着高能球磨时间的延长，粉末晶粒尺寸减小，且掺Y硬质合金粉末的晶粒尺寸比未掺Y的硬质合金粉末晶粒尺寸要细一倍；高能球磨25h，粉末中Co的X射线衍射峰消失。高能球磨掺Y硬质合金粉末的DTA曲线在626℃出现了1个尖锐的放热峰。高能球磨掺Y硬质合金粉末固结之后，其合金晶粒细小，机械性能较好。     

Small ball probabilities for a Wiener process under weighted sup-norms,with an application to the supremum of bessel local times

LetR be the radial part of ad-dimensional Wiener process, starting from 0. In this paper, small ball probabilities are evaluated for sup_0<11(t ^–p R(t)) and sup _t 0(e ^–1 R(t)), withp[0, 1/2]. Chung's law of the iterated logarithm is established for the supremum of the local times of a two-dimensional Bessel process.     

球磨-溶剂热诱导法合成WS2纳米棒及其摩擦性能

采用行星式高能球磨机，将WS₂与S粉末混合球磨，得到纳米片状结构的前驱体，然后添加分散剂聚乙二醇(PEG)用溶剂热诱导的方法使纳米片状前驱体发生结构转变，制备了棒状结构的WS₂纳米材料。用XRD、SEM、TEM等方法对WS₂纳米棒进行了形貌和结构表征，并对其作为润滑油添加剂的摩擦性能进行了初步的研究。     

Mg／Mgl．8La0．2Ni纳米复合材料的吸放氢性能研究

应用高能球磨法制备Mg-x％Mg1.8La0.2Ni（x=10、20和30）纳米复合储氢材料．X射线衍射（XRD）、透射电镜（TEM）和选区电子衍射（SAED）测试表明，该复合材料具有纳米晶和非晶态混合结构的性质，吸氢温度降低，较好的吸放氢动力学性能，在423K，2．5MPa氢压的条件下，50s内即可达到最大吸氢量．     

锂离子电池高比容量FeSn2-C复合负极材料的合成与性能

Sn基合金负极材料具有高达990 mAh·g^-1的理论比容量,但其也存在因脱嵌锂过程发生巨大的体积变化而导致循环性能较差的问题. 本文以Sn、Fe、石墨为原料利用简易的高能球磨法成功制备了具有核壳结构的FeSn₂-C复合物,系统研究了球磨时间、FeSn₂相含量对材料物相结构及电化学性能的影响,并分析了电极的失效机理. 研究表明,球磨时间的增加有利于FeSn₂金属间化合物相的形成及材料颗粒的细化,进而有利于材料比容量的增加及循环性能的提升;FeSn₂相含量的增加能够提高FeSn₂-C材料的比容量,但会降低FeSn₂-C电极的循环稳定性. 经工艺优化及组分调节,球磨24 h合成的Sn₂₀Fe₁₀C₇₀材料具有最优的电化学性能,材料的比容量在540 mAh·g^-1左右,并能稳定循环100次,是一种非常有发展前途的锂离子电池高比容量负极材料.     

Use of blowing catalysts for integral skin polyurethane applications in a controlled molecular architectural environment: Synthesis and impact on ultimate physical properties

Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (T_g) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher T_g values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002     

On a mechanical lens

In this paper, we consider the dynamics of a heavy homogeneous ball moving under the influence of dry friction on a fixed horizontal plane. We assume the ball to slide without rolling. We demonstrate that the plane may be divided into two regions, each characterized by a distinct coefficient of friction, so that balls with equal initial linear and angular velocity will converge upon the same point from different initial locations along a certain segment. We construct the boundary between the two regions explicitly and discuss possible applications to real physical systems.     

Golf ball-assisted electrospray ionization of mass spectrometry for the determination of trace amino acids in complex samples

During the electrospray ionization (ESI) process, ions move through a heated capillary aperture to be detected on arrival at a mass analyzer. However, the ESI process creates an ion plume, which expands into an ion cloud with an area larger than that of the heated capillary aperture, significantly contributing to an ion loss of 50% due to coulombic repulsion. The use of DC and RF fields to focus ions from the ion source into the vacuum chamber has been proposed in the literature, but the improvement of ion transmission efficiency is limited. To improve ion transmission, in this study we propose a novel method using a home-made golf ball positioned between the ion source and the inlet of the mass analyzer to hydrodynamically focus the ions passing through the golf ball. The ion plume produced by the ESI process passes through the golf ball will reduce the size of the ion cloud then be focused and most of them flowed into the mass analyzer. Therefore, the sensitivity will be improved, the aim of this investigation is to study the enhancing of the signal using golf ball-assisted electrospray ionization liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine 20 trace amino acids in complex samples, including tea, urine and serum. The results showed that the analytical performance of the determination of the 20 amino acids in tea, urine and serum samples using the home-made golf ball-assisted ESI source is better than that of a commercial ESI source. The signal intensities of the 20 amino acids were enhanced by factors of 2–2700, 11–2525, and 31–342680 in oolong tea, urine and serum analyses, respectively. The precision of the proposed method ranged from 1–9%, 0.4–9% and 0.4–8% at low, medium and high concentration levels of amino acids, respectively. The home-made golf ball-assisted ESI source effectively increased the signal intensity and enhanced the ion transmission efficiency and is also an easy, convenient and economical device. This technique can be applied to the analysis of trace compounds in complex matrices.     

Monocyclic rod-type liquid crystals; 2,5-dialkanoyloxytropones and 5-alkanoyloxy-2-alkoxytropones

Two kinds of monocyclic troponoid mesogens, 2,5-dialkanoyloxytropones (4) and 5-alkanoyloxy2-alkoxytropones (5), were prepared. The former showed monotropic smectic A phases and the virtual isotropic liquid-smectic A transitions of the latter were determined by extrapolation of results in a binary phase diagram. Comparing the mesogenic properties between the tropones 4 and the 2-alkanoyloxy-5-alkoxytropones (1), the alkanoyloxy group at C-5 enhances both the melting points and the transition temperatures of the smectic A phases. From the comparison between 5 and 1, the alkanoyloxy group at C-2 lowers the melting points.     

Synergetic catalytic effect of rGO,Pd, Fe3O4 and PPy as a magnetically separable and recyclable nanocomposite for coupling reactions in green media

In this paper, rGO/Pd–Fe₃O₄@PPy as an efficient stable nanocomposite was synthesized. To understand the synergetic effects of rGO, Pd, Fe₃O₄ and PolyPyrrole, the performance of rGO/Pd–Fe₃O₄@PPy as a heterogeneous recyclable nanocatalyst in the green synthesis of C‐C and C‐O coupling products, as well as different conditions are studied. Synthesized rGO/Pd–Fe₃O₄@PPy was characterized by FT‐IR, XRD, FE‐SEM, EDS, TGA and AFM analysis. Best results are obtained under sonication in H₂O for C‐C coupling and by ball‐milling for C‐O coupling. The benefits of this method include: green solvents and conditions, absence of external base, low reaction times with high yield and easy work‐up method.