Weixue Li

Anisotropic properties of aligned SWNT modified poly (methyl methacrylate) nanocomposites

The poly (methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites with good uniformity, dispersion and alignment of SWNT were fabricated in an improved figuration process. The semidried mixture was stretched along one direction at a drawing ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The transmission electron microscopic (TEM) observation demonstrated that SWNT in the PMMA/SWNT composite tends to align in the stretching direction owing to a torque exerting on it in the stretching process. The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of composite rise with the increase of SWNT concentration, and that composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The thermogravimetric analysis (TGA) revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.

Preparation and particle size characterization of Cu nanoparticles prepared by anodic arc plasma

Copper nanoparticles were successfully prepared in large scale by means of anodic arc discharging plasma method in inert atmosphere. The particle size, specific surface area, crystal structure, and morphology of the samples were characterized by X-ray diffraction (XRD), BET equation, transmission electron microscopy (TEM), and the corresponding selected area electron diffraction (SAED). The experimental results indicate that the crystal structure of the samples is fcc structure the same as that of the bulk materials. The specific surface area is 11m^2/g, the particle size distribution is 30 to 90nm, and the average particle size is about 67nm obtained from TEM and confirmed from XRD and BET results. The nanoparticles with uniform size, high purity, narrow size distribution and spherical shape can be prepared by this convenient and effective method.

The microstructure of Ni layer on single-walled carbon nanotubes prepared by an electroless coating process

The single-walled carbon nanotubes (SWNTs, diameter: 2∼3 nm), which were obtained in the suspension of purification solution, with Ni-P coating layers were obtained by an electroless deposition process. The SWNTs before and after coating were characterized by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). An Ni-P layer on individual nanotube with thickness of 20 nmcan be obtained after the deposition process. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis of Ni-P SWNTs before and after heat treatment show that the heat treatment caused the transformation of the amorphous Ni-P layer to the nanocrystalline Ni-P (crystalline Ni and Ni3P intermetallic compound) layer. The XRD pattern of SWNTs with Ni-P layers after heat treatment revealed that the crystal structures of Ni in plating layer contained: hexagonal closepacked (hcp) structure and face-centered cubic (fcc) structure. The lattice parameters of Ni (fcc) and Ni3P are larger than the bulks, indicting that the lattice expansion has taken place. However, the lattice parameter of Ni (hcp) has no difference from the bulks.

Ferromagnetic property of Co and Ni doped TiO 2 nanoparticles

The Co and Ni doped diluted magnetic semiconductor nanoparticle TiO2 is prepared by sol-gel method. Ti0.97Co0.03O2, Ti0.97Ni0.03O2, Ti0.97Co0.06O2, and Ti0.97Ni0.06O2 samples were characterized by X-ray scattering techniques and high resolution transmission electron microscope. The results show that there are no other phases existing in TiO2. As to the sample of high-concentration dopant, the X-ray scattering techniques have explored the existing of CoTiO3 and NiTiO3. The ferromagnetic measurement shows that the magnetization of the sample of high-concentration dopant increases in the same external magnetic field. However, the relatively higher dopant Co and Ni may form more interstitial ions and paramagnet matters, reducing the oxygen vacancy concentration and finally leading to the decrease of remanent magnetization and coercivity of the materials.

Mechanical Behavior of CNTs/SiCp/AZ91D Magnesium Matrix Composites

AZ91D alloy composites reinforced by CNTs/SiCp were fabricated using stir casting process. The mechanical properties of the composites were tested, observed and analyzed the microstructure, the fractographs were observed and analyzed via scanning electron microscope. The results showed that CNTs/SiCp could not only refine the grains of the composites, but also bear the load of resistance to deformation. Compared with the matrix alloy, the tensile strength, the elastic modulus, the micro-hardness and the elongation rate of the composites had been enhanced significantly. But the mechanical properties would be fell down with the more addition of CNTs/SiCp.

HYDROGEN STORAGE PROPERTY OF Mg-Ni-TiO2-CNTs COMPOSITES

In this paper, the nanocrystalling composite Mg-Ni-TiO2-CNTs was made by mechanical ball milling under hydrogen pressure of 5.0×10-5Pa, The hydrogen storage properties and operation temperatures were investigated. It was found that the composite can absorb 7.5wt.% hydrogen in 60s under 5.0×10-5Pa hydrogen pressure and desorb 6.5wt% hydrogen in 600s at 260°C under 5.0×10-5Pa hydrogen pressure. The composite has very high absorption, hydrogen capacity and remarkable kinetic properties in hydriding /dehydeiding process. TiO2, Ni and CNTs were used as additive to improve the hydrogen storage performance. They can be utilized as an effective catalyst to improve hydriding/dehydriding performance of hydrogen storage material and lead to pronounced enhancement on the hydrogen storage property of Mg. The results showed that the composite has potential application in the future.

The transition point of the Chinese multilayer air transportation networks

The air transportation network across a certain area, a typical multilayer complex system, is composed of a number of individual airlines, each of which forms a single layer. A central problem in airline merging is the minimal number of layers, denoted by nml, that is needed for the merged network to function nearly as well as the fully aggregated network. For this purpose, we monitor several structural measures during the network aggregation process in which nml is gradually increased. For China Air Transportation Network (CATN), we identify a common, sharp transition point yielding nml = 9. Whereas, for European Air Transportation Networks (EATN) there is no clear signal of such a transition point. The transition point of CATN is confirmed by means of the Wasserstein distance and the relative entropy. Our results indicate that there is still room in the optimization of CATN while for EATN, it seems better to keep the present structure.

The Lattice Change of Ni-P Layer Coated on Single-Walled Carbon Nanotubes

The electroless deposition is an excellent method for the preparation of the CNTs with Ni-P layers. Pristine CNTs were first oxygen-functionalized by treating them with a mixture of concentrated (HNO3 :H2SO4=1:3) acids. The SWNTs were obtained in the suspension of purification solution, In this work, the heat-treatment at 400°С transformed the amorphous Ni-P layer into the nanocrystalline Ni-P (crystalline Ni and Ni3P intermetallic compound) layer. The Ni-P-SWNTs before and after heat-treatment were studied using XRD and SAED. It is observed that the lattice parameters of Ni-P layers has difference from the bulk’s, indicting that the lattice change has taken place.

Finite Element Analysis of Interfacial Stress of Mg-Baced Composites Reinforced with Short Fiber

In elastic deformation range, this paper reports a finite element study of effect of length and diameter of the fiber on intrfacial stress of AZ91D metal matrix composites reinorced by short fiber. The nuit cell model is developde in ansys. It was found no infuence the fiber length has on the interfacial regions. There is considerable increase in intefacial von-Mises stress near the fiber end with increase in fiber diameter, and the region of stress transfer become wider. So, the risk of crack and debonding increase.

The High Thickness Ni Layer on Single-Walled Carbon Nanotubes Prepared by an Electroless Coating Process

The Single-walled carbon nanotubes were coated with Ni-P layers by an electroless plating technique. A Ni-P layers are thick and smooth and on individual nanotube with thickness of 20 nm can be obtained after the deposition process. The Single-walled carbon nanotubes were obtained in the suspension of purification solution. The samples have been characterized by X-ray diffraction, selected area electron diffraction, transmission electron microscopy and energy dispersive spectrometry.The coating layers after heat-treatment convert the amorphous Ni-P coated layers into the nanocrystalline Ni-P layers.