Advanced Materials Research Vols. 712-715

Abstract: Ramie fibres were surface treated in order to enhance the interfacial interaction between ramie natural fibres and vinyl resin matrix. The fibres are exposed to three different treatment ways in this paper. The surface topography and binding force influenced by the treatments were characterized by contact angle and mechanical property. Single fibre pull-out tests combined with SEM characterization of the fracture surfaces were used to identify the interfacial strengths and to reveal the mechanisms of failure.

Abstract: In modern electronic devices overheating has become a critical issue due to high power density and improved performance. In order to overcome this critical issue, the demands for materials having high thermal conductivity with low and tailorable coefficient of thermal expansions are required. This demand can be fulfilled by synthesizing copper/diamond composites, which show excellent thermo-physical properties, compatible with semiconductors and can be used in heat sink and thermal management applications. Copper/Diamond composites were fabricated by Spark Plasma Sintering Method (SPS) by electrolessly copper coated diamond particles pre coated with 1wt% Chromium. The prepared composites were investigated for various properties like thermal conductivity, thermal expansion and characterized by Scanning Electron Microscopy (S.E.M) and X-ray diffraction (X.R.D) analyses. The effect of process parameters were also taken into account. Thermal conductivity of copper/diamond composites fabricated by SPS at 1100°C under pressure of 40MPa, obtained in this case was 400 W/m•K , which is quite higher than those heat sink materials being already in use.

Abstract: In order to study the infrared interference characteristics of nanocarbon materials smoke, a large smoke chamber and laser test device were used to measure the attenuation characteristic of carbon nanofibers and nanographites smoke for laser. The mass concentrations were measured to obtain the rate of forming smokescreen for nanocarbon materials, and the smoke transmittance to infrared laser were measured to get attenuation characteristic of nanocarbon materials with different sizes. The test results provide the application basis of nanocarbon materials in passive interference fields.

Abstract: Carbon nanofibers is a new kind of electromagnetic wave absorbing materials and it is expected as a new kind of smoke interference agent. To study the scattering and extinction characteristics of carbon nanofibers, the electromagnetic scattering calculating model was established, and the induced current equation was solved by moment method, as well as the relationship between the infrared extinction cross section and the length of carbon nanofibers was analyzed and calculated based on MATLAB. The results show that when the conductivity of carbon nanofibers is large, the extinction cross section appears a series of resonant peaks along with the length change, and when the length of carbon nanofibers is equal to the first resonant length, the extinction cross section of unit volume will reach the maximum value, and a good extinction effect can be achieved at the same time. The contribution of scattering to extinction is enhanced with the increase of electrical conductivity.

Abstract: Under the conditions of the presence of surfactants and ultrasonication, the use of different cerium salt, respectively, with 8-quinolinolate under solid state chemical reactions, the synthesis of nanorare earth metal complexes of cerium 8-quinolinolate crystals was formed. The solid phase was characterized by powder X-ray diffraction (XRD) and electron diffraction (ED). The particle size, its distribution, and morphology of the prepared nanocrystallite were observed by transmission electron microscopy (TEM). The results show that particle sizes are relatively uniform, the morphology of the crystal is spherical, the average particle diameter is about 30 nm, and the yield rate is approximately 89.9%. Furthermore, during the synthesis, the solid-state reaction conditions including raw materials, matching proportion of reactants, additions of inert substance, addition of trace solvents, surfactants and porphyrization time, etc, all have some influence on the morphology, particle size and size distribution of the final products. During the synthesis of the cerium 8-quinolinolate nanocrystallites, the solid state reaction conditions such as changing reactant, matching proportion of reactant, adding inert substance, joining a little solvent or surface active solvent and grinding at different times may influence morphology, particle size and the size distribution of final products.

Abstract: BiFeO₃ coated ferromagnetic Fe nanocapsules is synthesized by arc-discharging method. Typical HRTEM images show that the nanocapsules form in a core-shell structure. X-ray photoelectron spectrum (XPS) and X-ray diffraction (XRD) reveal that the core is ferromagnetic Fe, while the shell is BiFeO₃/Bi₂Fe₄O₉.The reflection loss R of less than -10 dB was obtained for the whole frequency within the 2-18GHz range by choosing an appropriate layer thickness between 1.0mm and 7.0mm. An optimal reflection loss of -21.5 dB was reached at 10.6 GHz with an absorber thickness of 2.0mm. It is worth noticing that the BiFeO₃ coated Fe nanocapsules have two absorption peaks below -10 dB at each thickness layer ranging from 4.0nm to 7.0nm, which means the composites nanocapsules absorber simultaneously are able to absorb microwaves in different band of several GHz.

Abstract: CoPt nanoparticles with an average size of 2.8 – 4.7 nm were synthesized by reduction of non-toxic precursors Co(CH₃COO)₂ and Pt(acac)₂ using trioctylamine as a solvent at reaction temperature of 260 – 280 °C. The X-ray diffraction pattern showed that as-prepared particles have a disordered face-centered cubic structure while annealing at 700 °C caused them to be an ordered face-centered tetragonal structure. The annealing increased magnetic coercivity of the particles from zero to 772.4 Oe and their saturated magnetization from 15.04 to 27.95 emu/g.

Abstract: Monodisperse iron nanoparticles were prepared by thermal decomposition of iron carbonyl at low temperature of 160 oC - 180 oC in kerosene. The synthesized iron nanoparticles were spherical and their average size was decreased from 11.2nm to 8.6 nm as increasing the reaction temperature from 160 oC to 180 oC, respectively. The synthesized iron nanoparticles are amorphous, but the surface of the particles is easily oxidized and to be spinel structured iron oxide by HRTEM.

Abstract: Zn-doped CdS dendritic nanostructures were prepared by a simple hydrothermal method. The product displays single-crystalline characteristic. The dendritic crystal is formed by growing along several equivalent directions ([2-1-10],[-1-120]and[-12-10]). Due to doping Zn, the CdS dendritic nanostructures present some beneficial properties and are promising candidates for future applications in optoelectronic nanodevices.

Abstract: Poly (9-vinylcarbazole) (PVK) is a typical hole-transporting polymer and is often used as a host in electroluminescence devices. In this paper, Forster energy transfer from organic molecules (PVK) to inorganic nanoparticles (SiO₂) was discussed. SiO₂ nanoparticles, which are confirmed to be 60nm using transmission electron microscope (TEM), have been synthesized through the sol-gel method. The structure scheme of poly (9-vinylcarbazole) (PVK) molecule is shown firstly. The emission of luminescence is the result from π*-π transition of π electrons. Photoluminescence (PL) spectra of the PVK/ SiO₂ composite film on Si substrates were employed to study the interface effect. In the PL spectra of PVK molecules, three obvious peaks (417, 458, 495nm) can be seen. The emission of 417nm comes from free exciton. The emission of 458nm comes from bound exciton. And the emission around 495nm is correlated to surface defect states. The intensity of short-wavelength emission (about 400nm) is higher than that of visible luminescence (about 495nm). Two luminescence peaks can be observed in the PL spectra of 60nm SiO₂ nanoparticles. In contrast to the PL spectra of PVK molecules, the luminescence intensity about 495nm is higher than that about 400nm in SiO₂ nanoparticles PL spectra. Furthermore, UV-Vis absorption spectroscopy of 60nm SiO₂ nanoparticles was measured. The spectrum indicates that the scale of absorption is wide enough from 200nm to 500nm. The ratio of PVK to SiO₂ in the composite was increased orderly in weight. In the PL spectra of different concentration composite films, we found that Forster energy transfer occurred between PVK and SiO₂ nanoparticles. Overlap is observed between the UV-Vis absorption spectrum of the SiO₂ nanoparticles and the emission spectrum of PVK molecules. This overlap is the necessary condition of Forster energy transfer. Further investigation indicates that 40 % ( the content of PVK in composite films) is regarded as an optimized content for Forster energy transfer from PVK molecules to SiO₂ nanoparticles. The reason maybe is the surfaces of SiO₂ nanoparticles are modified successfully and the disperse of SiO₂ nanoparticles is unified in this concent ration.