Advanced Materials Research Vols. 602-604

Abstract: In this paper, we report the synthesis of cubic silicon carbide (3C-SiC) nanoparticles by direction reaction of silicon powders and carbon nanotubes. The as-prepared SiC nanoparticles were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and Raman scattering at room temperature. The possible growth mechanism is proposed.

Abstract: Silver nanoparticles were prepared by sodium borohydride reduction method for analyzing metal-enhanced fluorescence property. Some variables including the dosage of reagent, reacting temperature and pH value had been investigated. Subsequently, a comparison of metal-enhanced fluorescence efficiency was made between two kinds of fluorescent dyes, namely fluorescein and 6-carboxyfluorescein at different silver concentrations. The experimental results show that the fluorescence of both dyes are remarkably enhanced. It is interesting to note that the increase of emission intensity is stronger than that of their corresponding excitation ones. Furthermore, a 5.038-fold increase in fluorescence for 6-carboxyfluorescein while a 2.506-fold increase for fluorescein are observed. This may attribute to the interaction between dyes and silver nanoparticels.

Abstract: Barium titanate (BaTiO3) ceramics with grain size varied from 1000 to 8 nm were prepared by two step sintering method (TSS) and spark plasma sintering (SPS), respectively. Mixture structures of BaTiO3 ceramics were proved by in-situ temperature high resolution x-ray diffraction. Multiple ferroelectric domains present in nano-crystalline BaTiO3 ceramics were observed by transmission electron microscope. The evolution of phase transitions supported the existence of intrinsic mechanism. Dielectric loss of fine grain size BaTiO3 was higher than coarse grain size during Curie phase transition due to diffuse phase transition and grain boundary effects.

Abstract: The synthesis of nano-Ni/B composite particles was studied by diamine hydrate reducing nikel chloride in the water bath at 50 °C, in which nano-Ni was made to cover the surface of micron boron powder. The particle size, the structure and properities of the nano-Ni/B composite particles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). And the thermal stability of nano-Ni/B composite particles was studied by employing thermogravimetry (TG), differential thermal analysis (DTA). The results showed that this method could prepare the compact coating for Ni/B particles. The nano-Ni particles coated on boron particle were uniform and continuous. The average diameter of Ni crystallites was about 21.7 nm. Compared with boron powders, the high temperature of exothermic peak of nano-Ni/B composite particles was decreased about 36 °C. The thermal chemistry behavior of the as-prepared nano-Ni/B composite particles was better than superfine boron powders.

Abstract: Under the model of two-phase multiaxial nanoparticles the dependence of magnetic states and critical elds of the phases magnetic reversal on mechanical stresses has been de ned. By means of phase diagram the e ect of stresses on the basic and metastable magnetic states of heterophase particles has been studied.

Abstract: Nanocrystalline N-doped and Ti-containing MCM-22 catalyst was synthesized by the static hydrothermal method, using sodium azide as nitrogen source for doping, and tetra-n-butyl titanate [Ti(OC4H9)4] as precursors of TiO2. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy.During liquid phase photocatalytic degradation of methylene blue (MB) under high-pressure Hg arc lamp irradiation, the asprepared N-doped Ti-MCM-22 exhibited much higher activity than the undoped Ti-MCM-22, attributed to the effect of nitrogen dopant.

Abstract: ZnO hierarchical microstructures with uniform sea urchin-like morphology have been successfully synthesized through a facile and reliable ultrasound irradiation route by using Zn(CH3COO)2•2H2O and KOH as raw materials. The ZnO sample is investigated with XRD, SEM, TEM and HRTEM. Results indicate that the as-prepared sea urchin-like ZnO microstructures are assembled by numerous needle-like nanocrystals with the size about 2µm in length and about 100nm in diameter. The preferred growth orientation of these ZnO nanoneedles are along [101] direction. A blue shift in UV-vis absorption spectrum of the as-prepared ZnO sample is observed.

Abstract: With an extended service life expectancy of space crafts, fluid lubricants attracted intense interests of the fields of tribology, due to their long life under EDH conditions, higher thermal conductance, lower frictional and torque noise, and rapid processing compared to the solid lubricants. However, there are still some disadvantages of fluid lubricants, such as finite vapor pressure, narrow range of operating temperature, degradation of some oils, viscosity temperature-dependence and so on. So far, there have existed some space fluid lubricants, such as PFPE, MAC, PAO and mineral oil based lubricants. It seems that there will be a challenge for a new type of fluid lubricants to come out without any limits above. Recent arisen nanostructured materials assisted in improvement of the research of space fluid lubricants, and the results indicated that some nanostructured materials exactly promoted the tribological properties of fluid lubricants. This paper reviewed recent development of nanostructured materials as additives in space fluid lubricants.

Abstract: In order to obtain the numerical solution of the heat conduction equation in one dimensional nanometer materials, we discrete the demand equation by Galerkin-Legendre spectral method and obtain a system of order ordinary differential equations, then we solve this system by using a fifth order five stage A-stable new diagonally implicit Runge-Kutta method. Numerical results are presented to demonstrate the accuracy and efficiency of this method.

Abstract: Spheroid hydroxyapatite nanoparticles were successfully prepared by titrating Ca(NO3)2•4H2O and (NH4)2HPO4 aqueous solution in the reverse microemulsion, which consists of mixed OP-10(surfactant), cyclohexane(oil phase), and isobutanol (cosurfactant).The structure and morphology of the prepared powders were characterized by means of X-ray diffraction (XRD) and transmission electron microscope (TEM). The optimum composition was investigated via the analysis of the aqueous solution conductivity, and the mechanism of aqueous reaction. The effect of the pH value and the amount of surfactant on the particle size were studied. The results indicate that the best conditions are which the concentration of OP-10 and isobutanol both are 0.2 M, when the water content is between 130 ml-250 ml，it results in pure nano-hydroxyapatite spheroid-like powders, and the water content is about 200 ml, whose diameters are 50 nm-80 nm, and good particle diameter distribution, the particle microstructure is homogeneous, good crystal structure and higher crystallinity.