Advanced Materials Research Vols. 79-82

Abstract: When high current pulsed electron beam (HCPEB) transferring its energy into a very thin surface layer within a short pulse time, super fast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress induced may impart the surface layer with improved properties. In this paper, HCPEB modification of 45# carbon steel with working parameters of electron energy 25 kV, pulse duration 3.5µs, and energy density 4 J/cm2 was investigated. The microstructures of modified surface were analyzed by scanning electron microscope (SEM) of type JSM 5310 and transmission electron microscope (TEM) of type H-800. It is found that the modified surface layer can be divided into three zones: the white layer or melted layer of depth 3 to10µm, the heat and stress effecting zone 10 µm below and about 250 µm, then matrix, where a nanostructure and/or amorphous layer formed in the near-surface region. It is proved that the whole treatment process is not complex and cost-effective, and has a substantial potential to be applied in industries.

Abstract: Methyl tert-butyl ether (MTBE) is the most prevalent contaminant found in soil and groundwater and classified as a suspect carcinogen by Environmental Protection Agency (USEPA). Due to high water solubility, MTBE is not easy to be removed from contaminated groundwater. This study aimed to develop a novel and simple method to coat TiO2 photocatalyst on magnetic particles, evaluate its photocatalytic degradation effect on MTBE irradiated under visible (λ= 419 nm), and recollect easily from hydroponic systems with magnet. Iron nanoparticles are synthesized and added to TiO2 sol-gel followed by 500 oC calcinations. The results showed that the novel magnetic composite TiO2/Fe3O4 had significantly efficiency of photocatalytic degradation (91.6 %) for 10 ppm of MTBE under visible light irradiation and the recovery rate was relatively high as we recollected easily from recycled water using magnet.

Abstract: Nanopowder CuO was prepared by a new method which involves homogeneous precipitation in high intensity field, and powder so obtained was examined by XRD and TEM. The mechanism and effects of conditions of treatment on process and final products are also discussed. These results indicate that not only the reaction velocity was speed up dramatically under ultrasound field but also the particle size of production was greatly affected by the intensity of ultrasound field, the greater the ultrasound field, the smaller the partical size.

Abstract: Nano-F/Zn/TiO2 particles were prepared by sol-gel method using NH4F and Zn(NO3)2 as dopants. The photocatalytic degradation of methylene blue in aqueous solution as simulated wastewater was used to evaluate their photocatalytic activities. The powders were characterized by energy dispersion X-ray spectrum (EDS), X-ray diffraction (XRD) transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) surface area analysis. The results showed that F and Zn elements were doped into TiO2. The appropriate codoping amount for F and Zn were n(F)/n(TiO2)=2% and n(Zn)/n(TiO2)=3% respectively. The degradation rate of methylene blue at 1 h was improved from 73.2% to 86.2% by using F/Zn/TiO2 as photocatalyst.

Abstract: The hybrid Kevlar/PTFE(polytetrafluroethylene) fabric composites filled with different nano-Tio2 content of matrix resin were fabricated. To determine the tribological properties, the filled and unfilled composites sliding against 45 steel were performed on MM-200 friction and wear tester. Scanning electron microscopy(SEM) was utilized to examine the morphology of worn surface. Differential scanning calorimetry (DSC) analysis was also performed to study the thermal properties of the composites. The results show that the addition of nano-Tio2 improve the wear resistance and decrease the friction coefficient. The friction coefficient become unconstant during test with the increase of nano-Tio2 in the resin matrix, and the optimum fraction of nano-Tio2 in the resin is 1wt%. The SEM observations indicat that microcutting and plastic deformation are the main wear mechanisms. DSC analysis that there is no significant change in the melting points, and that there has been minimum chemical interaction between the resin matrix and nano-Tio2.

Abstract: La2Ce2O7 nano-powders with cubic fluorite structure have been firstly prepared by Molten Salts method. These nano-powders were prepared at relatively low temperatures(800°C and 900 °C) at different time, using La(NO3)3•6H2O and La(NO3)3•6H2O as raw materials, as well as K2SO4 (anhydrous) and Na2SO4 (anhydrous) as molten salts and dispersant. XRD, SEM were used to characterize the composition, morphology and size of prepared products. The procedure is facile and suitable for the synthesis of the La2Ce2O7 nano-particles and it will be an excellent method for preparation of other pyrochlore type of rare earth zirconate (Re2Zr2O7, Re=rare earth).

Abstract: phthalocyanine, porphyrin, sandwich rare earth complex, nanostructure, self-assembly. Abstract. Three novel sandwich-type mixed (phthalocyaninato)(porphyrinato) rear earth complexes, namely Ce(DPP)(Pc)(1), Sm2(DPP)(Pc)2(2) and Sm2(DPP)2(Pc)(3) [Pc = dianion of phthalocyanine, DPP= dianion of 5,15-di(phenyl)porphyrin], have been fabricated into nano-assemblies onto the SiO2 surface by a surface assisted solvent-vapor annealing method. The effect of the number of porphyrin and phthalocyanine ligands on the morphology of self-assembled nanostructures of these double- and triple-decker complexes has been systematically studied. Competition and cooperation between the inter-molecular - interaction, van der Waals, and metal-ligand coordination for different compounds results in nanostructures with different morphology from approximately spherical shape with average size of ~300 nm and ~400 nm for 1 and 2, respectively, nano-rods with aspect ratio (length over width) around 5 for 3, which were characterized by electronic absorption, X-ray diffraction (XRD), and atomic force microscopy (AFM). Electronic absorption spectroscopic results reveal the formation of J-aggregates in the nano-structures and suggest the increasing - interaction in the order of 3, 1, to 2. Examination by XRD reveal that in the nanostructures of compounds 1-3, a dimeric supramolecular structure was formed through an intermolecular - interaction and/or van der Waals between two sandwich-type molecules, which as the building block self-assembles into the target nanostructures.

Abstract: The objective of this study was to incorporate POSS-MA into the polymeric matrix to develop a new kind of nanocomposite. The effect of different weight percentage of POSS incorporated into the matrix on the mechanical properties was also evaluated. Infrared spectroscopic technique and X-ray diffraction were used to characterize their microstructures and double bond conversion. With only 2wt% POSS added, the nanocomposite’s flexural strength increased 15%, compressive strength increased 12%, hardness increased 15% and uncommonly, even the toughness of resins obviously increased. With 5wt% POSS polymerized, compressive strength increased from 192MPa to 251MPa and compressive modulus increased from 3.93GPa to 6.62GPa, but flexure strength began to decline from 87MPa to 75MPa. The nanocomposites incorporated with POSS showed greatly improved mechanical properties, and increased wear resistance and service life. The mechanism of reinforcement was also discussed.

Abstract: Both the complex permittivity and permeability of nanometer SiC and nanometer SiC/CNTs composite were investigated by Hewlett-Packard 8510B Network Analyzer. The results show that the complex permittivity of nanometer SiC/CNTs composite is much higher than that of nanometer SiC. Reflection curves of nanometer SiC and nanometer SiC/CNTs composite calculated with electromagnetic wave transmission-line theory show that the addition of CNTs at 6 wt%, 12 wt% and 18 wt% in nanometer SiC absorber can improve its microwave absorption properties strongly. There is a relationship between the mass fraction of CNTs and microwave absorption ability. With increase of the mass fraction of CNTs, its microwave absorption ability firstly increased then decreased. From the simulation, it was found that nanometer SiC with 12 wt% CNTs gave the optimum microwave absorption. The corresponding frequency of maximum reflection loss value of nanometer SiC/CNTs composite gradually moves to the low frequency range with increase of thickness. The maximum reflection loss value of nanometer SiC/CNTs composite (CNTs content is 12 wt%) was -25.74dB at the corresponding frequency of 11.60 GHz with a bandwidth under -5 dB (68% absorption) is 7.16 GHz when the thickness is 2.0 mm.

Abstract: The polyacrylonitrile(PAN)/poly (methyl methacrylate)(PMMA) blend fibers were prepared by wet-spinning technique and carbonized over the temperature range of 400-1000°C in nitrogen atmosphere. After carbonization of the blend fibers, the PMMA component removed and the PAN component left in the form of carbon nanofibers. Morphology of the carbon nanofibers were investigated via scanning electron microscopy (SEM), and the carbonization behavior of the fibers were examined via x-ray diffraction (XRD), Raman microspectrometry. The optimal condition made carbon fibers with great L/D ratio and diameter less than 200 nm. XRD and Raman spectra shows that the PAN/PMMA blend fibers treated at 600°C produced some graphite crystallite.