Search

Ca 3− x La x Co 4 O 9+ δ ( x =0, 0.05, 0.10, 0.15 and 0.25) ceramic samples were prepared under two-step external magnetic field during both processes of sol–gel and pre-press, and the influence of La doping and external magnetic field on their microstructure and electrical transport properties has been investigated systematically. Due to La-doping, both the Seebeck coefficient ( S ) and resistivity ( ρ ) were increased simultaneously, which resulted in a slight improvement of the power factor ( PF ). After using external magnetic field, the textured structures of all the samples were enhanced dramatically, as a result, the electrical resistivity were substantially decreased. For example, the ρ value for the sample with x =0.15 subjected to the magnetic field was about 25.46% smaller than for the corresponding sample without magnetic field at room temperature. Moreover, the Seebeck coefficient can be improved by increasing spin-orbital degeneracy of Co 4+ ions under external magnetic field. These combined effects resulted in observable enhancement of PF over the entire temperature range. Thus, the application of magnetic field can effectively improve electrical transport properties of Ca 3 Co 4 O 9+ δ based materials. [ABSTRACT FROM AUTHOR]

A series of Ca 3 Co 4− x Mn x O 9+ δ ( x =0, 0.25 and 0.5) samples were prepared under two-step external magnetic field during both processes of sol–gel and pre-pressing. The effects of Mn doping and external magnetic field on the microstructure and electrical transport properties of the samples have been studied systematically. The investigated results show that Mn-doping can improve the electrical transport properties slightly. After using external magnetic field, the textured structures of all the samples are enhanced dramatically, which results in the obvious decrease of the electrical resistivity and increase of Seebeck coefficient. The difference of ρ between the x =0.5 samples without and with external magnetic field is about 24.73 mΩ cm at room temperature. All the samples with magnetic field show higher power factors ( PF ), for example, the PF at x =0.5 with magnetic field can reach the maximum value of 0.29 mW/m K 2 at 1073 K. [ABSTRACT FROM AUTHOR]

Different surface morphologies of TiO 2 thin films were prepared by hydrothermal synthesis method on Ti substrates through changing reaction time. The microstructure, composition, optical properties and photocatalytic properties of TiO 2 thin films were systematically investigated by x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectrometer and ultraviolet-visible spectroscopy. As the reaction time increases, anatase structure and brookite structure of TiO 2 films respectively increases and decreases, corresponding to surface morphology changes from irregular structure to regular geometrical shape structure. These structural changes are accompanied by significant variations of optical properties and photocatalytic properties including a widening of the band gap from 2.86 to 3.19 eV, photocatalytic degradation efficiency from 92.5 to 98.1% and photocatalytic degradation rate from 0.032 to 0.048 min −1 . Among all samples, TiO 2 -1 shows the best photocatalytic properties. Compositional analysis indicates that TiO 2 surface layer contains Ti and O elements, the ratio of Ti:O is 1:2.28 which is close to the atom ratio of TiO 2 . [ABSTRACT FROM AUTHOR]

Abstract: Uniform copper hydroxyphosphate quadrangle star-like microcrystals with tunable size and microprism bundles have been achieved through a simple hydrothermal method. Reactions are conducted in a water system using CuSO4, NH4H2PO4 and NaOH as reactants without adding any surfactants. Structures and morphologies of the products were characterized by powder X-ray diffraction, scanning electron microscopy, fourier transform infrared spectrometry, and UV–vis spectrometry. It was found that the size and morphology of the products depended strongly on the concentration and the molar ratio of the starting reagents. The possible mechanism of the products was discussed and the size dependent photocatalytic property of the products was investigated. [Copyright &y& Elsevier]

Abstract: Uniform hematite nanoparticles have been successfully synthesized through a surfactant mediated hydrothermal method. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscope, scanning electron microscope, and Fourier transform infrared spectrometer. The results showed that the products were α-Fe2O3 nanoellipsoids of 115–140nm in long axis and 60–80nm in short axis. The growth mechanism of the products was proposed based on the experiments. Uniform nanospindles, nanoellipsoids, nanospheres, and nanopolyhedra with different sizes can be obtained by adjusting the reaction temperature, the amount of additive, and concentration of the reactants. The result may facilitate the exploration of controlled synthesis of α-Fe2O3 nanoparticles. [Copyright &y& Elsevier]

Silver polymer electrolyte membranes containing inorganic nanoparticles have showed excellent facilitated olefin transport properties. However, the application of facilitated transport membranes has been significantly hampered because of the poor stability of silver ions carrier. The structural changes of the facilitated transport membranes corresponding to the reduced separation performance with an extended time have rarely been studied. In this study, titanium dioxide (TiO 2 ) nanoparticles were introduced into poly(ethylene oxide) (PEO)/silver tetrafluoroborate polymer electrolyte membranes for propylene/propane separation. X-ray diffraction (XRD) analysis indicated that the addition of TiO 2 and silver salt reduced the crystallinity of PEO. The selectivity of propylene/propane of the polymer electrolyte membrane increased with increasing concentration of silver salt and TiO 2 in the polymer matrix. However, the propylene/propane selectivity decreased from 19.04 to 5.40 as the silver carrier ions became deactivated over the course of 196 h experiment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the satellite TiO 2 nanoparticles were formed around the silver salt after the composite membrane was placed in the air for 10 d. The findings in this work highlight the understanding of the carrier stability in polymer electrolyte membranes, and provide a potential opportunity to develop more stable polymer/carrier systems for the application of facilitated olefin transport membranes. [ABSTRACT FROM AUTHOR]

Abstract: Various ZnO architectures like novel flowerlike structures radially assembled by rods, nails or towers and novel radialized bundled tubular structures with diverse diameter in entire length were controllably synthesized with different amine precursors by a simple surfactant-free hydrothermal process. It suggests that diverse amine sources, which possibly have different hydroxyl ion releasing rate contributing to different reaction rates, probably play an importance role in controlling the assembly of different ZnO architectures, besides temperature and time. X-ray powder diffraction (XRD) results prove the ZnO belonging to wurtzite structure and room temperature photoluminescence (PL) demonstrates a high quality of the products. [Copyright &y& Elsevier]