Papers by Author: Wen Chen

Abstract: Ba0.6Sr0.4TiO3 powder was synthesized by a citrate method. The powder with a pure pervoskite phase and superfine particle morphology was produced at low calcining temperature of 550°C by controlling heating rate during the calcination. Microstructure and nonlinear dielectric properties of the ceramic specimens were investigated with respect to sintering temperature. It was found that the superfine morphology of the powder effectively reduced the sintering temperature of the ceramic specimens. The ceramic specimen sintered at 1260 °C attained about 95% of the theoretical density. At room temperature, the ceramic specimen showed a dielectric constant of 3010 and a dielectric loss of 0.48% at 10 kHz together with a tunability of 32.4% at 10 kHz and 20 kV/cm.

Abstract: Polythiophene (PTP) coated V2O5 nanotubes were prepared by an in-situ polymerization of thiophene monomers in the presence of prepared V2O5 nanotubes. The nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which proved the polymerization of thiophene monomer and the strong interaction between polythiophene and V2O5 nanotubes (VONTs). The gas sensing properties of PTP coated V2O5 nanotubes were studied at room temperature, which was found that PTP coated V2O5 nanotubes could detect ethanol with much higher sensitivity than pure VONTs. The sensing mechanism of PTP coated V2O5 nanotubes to ethanol is presumed to be the synergetic interaction between polythiophene (PTP) and V2O5 nanotubes.

Abstract: Vanadium oxide nanotubes were synthesized via a rheological self-assembling process followed by a hydrothermal reaction. V2O5 gas sensors were fabricated from vanadium oxide nanotubess with an average diameter of around 90 nm and their gas-sensing properties were investigated. It was found that the sensors based on vanadium oxide nanotubes exhibit high responses ethanol gas at 270°C. The results indicate that vanadium oxide nanotube sensors will be promising candidates for practical detectors for ethanol.

Abstract: Effect of stacking layers on the structure and properties of Ca(Mg1/3Nb2/3)O3/CaTiO3 (CMN/CT) microwave dielectric heterogeneous thin films prepared was investigated. Precursor solutions for CMN and CT synthesis were obtained by Pechini method. The arrangement pattern has affected structure and properties of heterogeneous thin film. The CMN-CT arrangement heterostructure thin film has second phase from the CMN films layer. The CT-CMN heterostructure film which has a smooth and dense microstructure was composed of pure perovskite phase without any second phase, this result was attributed to the CT film layer which is a buffer layer between substrate and CMN film layer. At 1MHz frequency, CT-CMN exhibits the dielectric properties of εr=47.5, tanδ=0.020.

Abstract: The relationship between the character of the B-site cation–oxygen bond and the microwave dielectric properties in perovskites dielectric materials was studied in this paper. The atomic net charge of CaTiO3 (CT) and Ca(Zn1/3Nb2/3)O3 (CZN) was calculated respectively. The calculating result implies that the covalency of B-O bonds in CZN is stronger than that in CT. This predicted that the dielectric constant and loss of the ceramics will decrease after CZN incorporated in CT. To confirme the prediction, (1-x)CT-xCZN microwave dielectric ceramics were prepared by solid state reaction method with ZnNb2O6 as precursor. The structure analysis in terms of tolerance factor gives an identical result as calculation. The microwave dielectric properties, such as dielectric constants, Q×f values and τf were studied as a function of composition. With x increasing from 0.2 to 0.8, the dielectric constant linearly decreases from 109 to 49.37, the Q×f value increases from 8,340 to 13,200 GHz, and τf decreases from 321 to -18 ppm/°C. The properties trends are consistent with the previous calculation results, and confirm the relationship between the character of B-O bond and dielectric properties.

Abstract: Vanadium oxide/carbon nanotubes (VOx/CNTs) composites were prepared by sol-gel hydrothermal synthesis. The composites were characterized in terms of surface morphology and structure using SEM, TEM, XRD, FT-IR, respectively. The electrochemical behaviors of the composites were investigated by means of galvanostatic charge-discharge cycling. The result shows that the vanadium oxides nanotubes and carbon nanotubes contacted each other and the composites have great cycleability as well as capacity characteristics which arrived at 303.5 mAh/g in the first discharge process and 200.4 mAh/g after 50th discharge cycles.

Abstract: Large scale BaTiO3 nanorods were successfully synthesized by a template method based on a precipitation process. The templates used in our method are H2Ti8O17 nanorods, which can be synthesized from K2Ti4O9 fibers. The unique process of the synthesis is BaC2O4•0.5H2O shell was coated on the 1-dimensional H2Ti8O17 nanorods (the core). The as-prepared products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the BaTiO3 nanorods are ~100-300 nm in diameter and ~2-10 m in length. The process described provides a general route to fabricate this kind of perovskite 1-dimensional nanostructures, such as SrTiO3 and PbTiO3.

Abstract: In the present work, a novel titanate (H2Ti5O11•3H2O) nanotubes are synthesized by a simple hydrothermal method, and their thermal stability such as the phase transformations and microstructures change are also studied. The as-grown samples are heated in the air at 300-800 °C. The titanate nanotubes will be completely destroyed when the temperatures are above 600 °C, which show that the present titanate nanotubes possess good thermal stabilization. The experiment results reveal that the phase transformations and microstructure changes of present titanate nanotubes follow the process from titanate nanotubes to anatase and rutile TiO2 nanobelts, the Na2Ti6O13 nanwires are formed over 700 °C.

Abstract: Nanostructured flakes α-Ni(OH)2 microspheres were successfully synthesized by a facile solvothermal method using sodium dodecyl sulfate as a soft template and urea as a hydrolysis-controlling agent. The obtained products were characterized by Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Electrochemical properties studies were carried out using cyclic voltammetry, galvanostaitc charge/discharge method, respectively. The results exhibited that the α-Ni(OH)2 single electrode had high specific capacitance in KOH electrolyte. A maximum specific capacitance of the α-Ni(OH)2 single electrode was up to 2398F/g in 6M KOH electrolyte concentration with 0 to 0.4V potential at 4mA/cm2 current density. Furthermore, the effects of the heat treatment temperatures on the electrochemical capacitance of the α-Ni(OH)2 electrodes were investigated.

Abstract: The cross-linked polystyrene prepolymer was synthesized with divinylbenzene (DVB) as crosslinker via free-radical crosslinking copolymerization (FCC) and used as the matrix materials for E-glass fiber reinforced composites. The surface modification was performed by treatment of E-glass fiber with γ-methacryloylpropyl trimethoxysilane (MPS) solution. Fourier transform infrared spectroscopy (FTIR) was used to identify the functional groups on the surface modified glass fibers. Dynamic mechanical thermal analysis (DMTA) of these composites revealed that the dynamic storage modulus (E′) was gradually enhanced with the increasing content of DVB (0~3.0 wt %) whereas the damping parameter (tanδ) peaks are lower and broader, indicating better load bearing capacity. Moreover, the Tg was shifted to higher temperature corresponding to the increasing of crosslinking density. Morphology of fracture surfaces for these composites showed different fiber-matrix interfacial adhesion which was mainly attributed to the variation of crosslinking network structure in the interface.