Materials Science Forum Vol. 814

Abstract: The perovskite-type oxides have a newly application for alkaline batteries due to the excellent cyclic performance. In this work, La_1-xBa_xCoO₃ (x = 0.2, 0.4, 0.6) powders were prepared by a sol-gel method as negative electrode materials for Ni/MH batteries, and their phase structure and electrochemical properties were investigated in details. The effect of Ba substitution on electrochemical kinetic properties, including the exchange current density I₀ and the hydrogen diffusion coefficient D, of La_1-xBa_xCoO₃ electrodes were also evaluated. X-ray diffraction analysis shows that La_1-xBa_xCoO₃ (x = 0.2, 0.4, 0.6) perovskite-type oxides consist of two phases, La_0.5Ba_0.5CoO₃ and BaCoO_2.70. The discharge capacities of La_1-xBa_xCoO₃ negative electrodes tested at 40 mAg^-1 are 65.6, 76.6 and 88.3 mAhg^-1 when x = 0.2, 0.4 and 0.6, respectively. Among the electrodes, La_0.8Ba_0.2CoO₃ electrode has the highest discharge capacity retention ratio of about 87% after 50 cycles at room temperature.

Abstract: Cerium oxide powder and aluminum foam loaded cerium oxide were prepared by hydrothermal method using cerium nitrate hexahydrate and dimethyl oxalate (DMO) as raw material. Cerium oxide precursors and cerium oxide particles were characterized by field emission scanning electron microscopy (FESEM). Aluminum foam loaded cerium oxide was characterized by environment scanning electron microscopy (ESEM). On the basis of calculation and fitting of the experimental data, effect of the particle size on the adsorption rate, desorption rate and concentration of surface active sites of the powder and composite absorbents were studied. Results show that the removal of fluoride ions can be realized by exchange adsorption of oxhydryl on the cerium oxide particles surface and the fluoride ions in the solution.

Abstract: Bead-on-string nanofibers were prepared by electrospinning, in this work, . The effect of processing parameters and property of solutions on the morphology of bead-on-string nanofibers were systematically investigated. The results revealed that the morphology of beads on nanofibers transformed from spherical into spindle-like with increased concentration of solution, applied voltage and needle-collector distance. Average width of beads became smaller as increasing all the values of processing parameters. Meanwhile, the application for the removal of bisphenol A (BPA) from aqueous solution was investigated, and results showed that the bead-on-string nanofibers could effectively remove BPA from aqueous solution. The kinetic data were analyzed by the pseudo-first-order, pseudo-second-order kinetic models. The reusability of the composite nanofiber was also determined after five adsorption–desorption cycles.

Abstract: Magnesium is one of the elements necessary for the body, is the man behind the body’s content of potassium ions within the cell are involved in a series of metabolic processes in vivo, including the formation of bone cells , acceleration of bone healing ability. Resulting from the good mechanical properties and biocompatibility, magnesium alloy is used in medical intervention material, but the high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide simultaneously corrosion resistance and enhanced biocompatibility. In this work the medical magnesium alloy surface are dipped and coated with polylactic acid, so that obtain a dense uniform polylactic acid coating. And the corrosion resistance of the coating is studied in order to obtain controlled degradable and corrosion resisted magnesium alloy biological material. This paper mainly studies the influence of different concentrations of polylactic acid coating on AZ91D magnesium alloy corrosion resistance. The coated samples were immersed in Hank’s solution and the coating performance was studied by electrochemical impedance spectroscopy and scanning electron microscopy. This research is about the influence of the coating on the corrosion resistance of magnesium alloy through the open circuit potential, polarization curves, electrochemical impedance spectroscopy and Mott-Schottky. The results confirmed that the polylactic acid slow down the corrosion rate of AZ91D magnesium alloys in Hank’s solution. And along with the increase of poly lactic acid concentration, the corrosion resistance of magnesium alloys is improved. There is a wide variation of the corrosion morphology magnesium alloy AZ91D specimens after the surface modification using polylactic acid coating, compared with the unmodified.

Abstract: The composites have a great use in practical application. In common, the phases in composite have different relative dielectric constant and in order to reveal how the phases with different permittivity affect the composite’s dielectric properties, the experiments were carried out using inorganic and organic composite with different dielectric constant phases to make that clear. The barium niobate-based SiO₂ system glass–ceramic and fillers-epoxy resin composites were chosen, and the dielectric properties were tested to compare the difference of those composites. The results show that the existence of high dielectric constant phases in composites can improve the permittivity of composites and make the composites present ferroelectric properties, while the dielectric loss can also increased, and the difference in dielectric constant of the phases can decrease the dielectric breakdown strength.

Abstract: Thermodynamics effects generated by femtosecond laser ablation are very important. In this work, the numerical simulation of high-energy femtosecond laser ablation especially the electro-phonon coupling coefficient influence of high-energy femtosecond laser ablation on metal target was studied. A new two-temperature model (TTM) which considered the effects of electron density of states (DOS) on electron-phonon coupling coefficient was first established, then the temperature evolvement for electron and lattice in different electro-phonon coupling coefficient G, and the effect of G on electron temperature and lattice temperature and electron-phonon coupling time were emphatically analyzed. The results showed that the electron-phonon coupling coefficient strongly affected the surface electron temperature and coupling time in the femtosecond laser ablation. The smaller the electron-phonon coupling coefficient was, the more the energy transmission from electronic to ion subsystem. As a result, the smaller the value of electron-phonon coupling coefficient, a more rapid decline for the temperature of electronic sub-system achieved. This work will offer help for the future investigation of material fabrication by femtosecond laser ablation.

Abstract: Nano/Micro-structured CeO₂ and their nanocomposites have been received considerable attention in basic research and commercial applications, such as, new energy fields, photocatalysts, environmental fields, et al. To extend its visible light response and pave the effective conductive channels for charge transfer and separation in nanoscale is still facing great challenges. To explore these key issues of materials chemistry and physics, CeO₂ nanorods were prepared with aid of soft templates by wet chemical approach. Graphene nanoribbons were obtained with unzipping method of carbon nanotube (CNTs). Entanglement of CeO₂ nanorods and graphene nanoribbons oxides was realized based on the supermolecular interactions between surface active groups of CeO₂ nanorods and graphene nanoribbons oxides and excellent flexibility of graphene nanoribbons. A series of characterizations were examined by SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (X-ray diffraction), the Fourier-Transform Infrared (FTIR) spectra, ultraviolet-visible spectroscopy (UV-Vis) and so on. Photocatalytic efficiency was examined by selecting typical organic pollutants. The results indicated that the entanglement of a small amount of graphene nanoribbons on the surface of CeO₂ nanorods not only expanded the light response of nanocomposite to visible light, but also enhanced the adsorption properties to organic pollutants. Because of excellent charge transfer properties and high mobility of graphene nanoribbons, the nanocomposites of CeO₂/graphene nanoribbons are favor for electron-holes pairs generated by visible light, separation, and transfer, which would be important potential applications in photocatalysts, artificial photosynthesis system, nano/micro-devices, et al.

Abstract: Heterojunction semiconductor composites could enhance the photoelectric conversion efficiency of photocatalysts. We successfully in-situ synthesized the hybrids of Mg-doped ZnO and reduced graphene oxide (MZO/RGO) by one-pot wet chemical method. Ag nanocrystals are loaded onto the MZO/RGO composites by photochemical reduction method. Crystallization of MZO/RGO-Ag upon thermal decomposition of the stearate precursors was investigated by X-ray diffraction technique. XRD studies point toward the particles size with 15-20 nm, which was confirmed by scanning electron microscope and energy dispersive X-ray spectroscopy, and also indicates that Ag nanoparticles were deposited on the surface of nanocomposites. The photocatalytic performance of ZnO nanomaterial was significantly improved by Mg-doping, RGO sheets corporation and Ag hybridization. It was found that the RGO sheets take the role of improving the charge separation during the photocatalytic activity, and the presence of Ag nanocrystals enhances the quick discharge of photoinduced electrons under the UV light. Therefore, the MZO/RGO-Ag nanohybrids are excellent candidates for the applications of environmental issues.

Abstract: TiO₂/VO_x nanofibers were synthesized via electrospinning and dipping technologies. They increased the photocatalytic property by reducing the recombination rate of electrons and holes at the surface of TiO₂. The composition, structure and morphology were characterized. The effect of annealing temperature to the dendritic structure and their photocatalytic property were demonstrated. The results showed dendritic TiO₂/VO_x nanofiers were obtained via dipping in vanadium sol, which was annealed at 550°C in 90% Ar/10% H₂ atmosphere. The average diameter of the samples was 354±42nm. Both the size and the number of dendritic structure were increased as the annealing temperature was rising. The degradation rate of methyl orange (5mg/L) by as-prepared TiO₂/VO_x nanofibers was 76.4% after exposure under UV light for 120min, which was 25.7% higher than which annealed in air atmosphere.

Abstract: TiO₂ thin films with outstanding photocatalysis can potentially be used for photocatalysis device in the field of environmental protection. TiO₂ thin film (99.99%) was fabricated successfully by power metallurgy. The effect of sputtering power on TiO₂ thin films by radio frequency magnetron sputtering was investigated. The results show that the higher sputtering power is beneficial for the growth of Rutile structure with superior photocatalysis. With the increasing of sputtering power, the rate of methyl orange degradation increases under UV light irradiation. The degradation rate of TiO₂ thin film under sputtering power 75W and 165W is 40% and 80% respectively. This is attributed to the increase of the rutile phase with many defects and dislocation network under higher sputtering power.