Binglin Zou

Strong photoluminescence of nanostructured crystalline tungsten oxide thin films

Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.

Magnetic properties of nanosized MnFe2O4 particles

Nanosized MnFe2O4 particles were prepared by chemical ultrasonic emulsion method. The as-prepared sample was found to be in amorphous state and showed spin-glass behavior at low temperature. The Curie temperature of the annealed sample is 160 K higher than that of the bulk material, which is thought to be due to finite-size scaling and also may be related to a nonequilibrium cation distribution

Formation mechanism of Fe2O3 hollow fibers by direct annealing of the electrospun composite fibers and their magnetic, electrochemical properties

Fe2O3 hollow fibers have been fabricated by direct annealing electrospun polyvinylpyrrolidone (PVP)/Fe(NO3)3 composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/Fe(NO3)3 solution, and then calcined at high temperature with an appropriate heating rate to form hollow Fe2O3 fibers. The solvent composition, the addition amount of Fe(NO3)3·9H2O and PVP, and the heating rate have important influences on the morphologies of Fe2O3 fibers. Morphologies of Fe2O3 could be tuned from solid belt to hollow belts and hollow fibers by controlling appropriate preparation conditions. The crystal structure, morphology, surface composition, magnetic and electrochemical properties of the Fe2O3 hollow fibers were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, SQUID magnetometry and cyclic voltammetry, respectively.

Magnetic properties of nanostructured Mn oxide particles

Nanostructured Mn oxide particles with an average size of about 7 nm have been prepared by a microemulsion method. X-ray diffraction analysis indicates that the particles possess orthorhombic structure of MnO(OH). The particles are ferromagnetic at low temperature. The Curie temperature is about 35 K and each MnO(OH) molecule generates a magnetic moment of about 0.7 μB. The appearance of the ferromagnetism at low temperature may result from size effect.

Fabrication of CoFe2O4 hollow fibers by direct annealing of the electrospun composite fibers and their magnetic properties

CoFe2O4 hollow fibers have been fabricated by direct annealing of electrospun polyvinylpyrrolidone (PVP)/nitrate salts composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/nitrate salts solution, and then calcined at high temperature with appropriate heating rate to form hollow CoFe2O4 fibers. The crystal structure, morphology and magnetic properties of the CoFe2O4 hollow fibers were investigated by using the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and SQUID magnetometry, respectively. The results indicate that the phase structure of hollow fibers belongs to cubic spinel structure, hollow fibers after annealing at high temperature still remain the one-dimensional texture and the wall of hollow fibers consists of many nanoparticles. The magnetic measurement showed that the hollow one dimensional structure has some novel magnetic properties, which may make them useful in electromagnetic and spintronic devices

Doping concentration of Eu3+ as a fluorescence probe for phase transformation of zirconia

Abstract The Eu 3+ –Y 3+ double-doped ZrO 2 (8YSZ:Eu 3+ ) phosphors with different doping concentrations of Eu 3+ were synthesized by hydrothermal method. The dependences of the intensities of visible emission, decay lifetimes and crystal structures on Eu 3+ doping concentration were investigated. The optimal doping concentration of Eu 3+ in 8YSZ:Eu 3+ nanophosphors was determined. The morphology and crystal structure of the resulting phosphors were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectra. The fluorescence properties of the resulting phosphors were investigated by photoluminescence spectra and decay curve. In this paper, 3 mol.% Eu 3+ ions in 8YSZ:Eu 3+ phosphors was the optimal doping concentration. When doping concentration was 3 mol.%, the nanophosphor had a pure tetragonal phase structure, the emission intensity was intense and decay lifetime was long, furthermore this system could be used to indicate the extent of phase transformation of thermal barrier coatings.

Synthesis and luminescence properties of CeF3:Tb3+ nanodisks via ultrasound assisted ionic liquid method

Abstract CeF3 and CeF3:Tb3+ nanocrystals were successfully synthesized by the ultrasound assisted ionic liquid (IL) method at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron micrographs (HRTEM) and photoluminescence (PL) spectra were employed to characterize the nanocrystals. The results of XRD indicated that the obtained samples crystallized well with a hexagonal phase crystal structure. SEM and TEM images demonstrated that the obtained CeF3:Tb3+ nanocrystals had a discoid shape in the presence of ultrasound and IL, whereas only granular nanoparticles were obtained by magnetic stirring. The possible formation mechanisms of the crystal growth were proposed. The PL spectra of the CeF3:Tb3+ nanodisks exhibited a strong green emission when excited at 254 nm. Furthermore, the photoluminescence intensity of CeF3:Tb3+ of the discoid particles was largely improved compared with that of the granular nanoparticles.

Corrosion behavior of coating with plasma sprayed 8YSZ on the surface of carbon steel

Abstract The corrosion behavior of plasma sprayed 8YSZ (ZrO 2 stabilized by 8 wt.% Y 2 O 3 ) coating on the surface of carbon steel in seawater was investigated. The electrochemical impedance spectroscopy was used as a non-destructive evaluation technique to monitor the protection properties of the coating when it was immersed in seawater, and corrosion products were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray photoelectron spectroscopy. The results indicated that three time constants were obtained during the initial immersion period, and then a new time constant appeared due to the formation of rust layer, which was corresponding to the corrosion process. Corrosion products were formed on the coating surface as well as inside the coating, and the crystalline composition of the rust layer mainly consisted of γ-FeOOH.

In situ synthesis and formation mechanism of ZrC and ZrB2 by combustion synthesis from the Co-Zr-B4C system

Abstract ZrC-ZrB2-based composites were prepared by combustion synthesis (CS) reaction from 10 wt.% to 50 wt.% Co-Zr-B4C powder mixtures. With increasing Co contents, the particle sizes of near-spherical ZrC and platelet-like ZrB2 decreased from 1 μm to 0.5 μm and from 5 μm to 2 μm, respectively. In addition, the formation mechanism of ZrC and ZrB2 was explored by the phase transition and microstructure evolution on the combustion wave quenched sample in combination with differential scanning calorimeter analysis. The results showed that the production of ZrC was ascribed to the solid-solid reaction between Zr and C and the precipitation from the Co-Zr-B-C melt, while ZrB2 was prepared from the saturated liquid. The low B concentration in the Co-Zr-B-C liquid and high cooling rate during the CS process led to the presence of Co2B and ZrCo3B2 in the composites. The addition of Co in the Co-Zr-B4C system not only prevented ZrC and ZrB2 particulates from growing, but also promoted the occurrence of ZrC-ZrB2-forming reaction.

Mechanism in reactive plasma spraying synthesis of TiC–TiB2 composite coating

Abstract Self-propagating high-temperature synthesis reaction in the LaMgAl11O19–Ti–B4C system was quenched in the glove box and during plasma spraying, respectively, in order to clarify the formation mechanism of in situ TiC–TiB2 composite coating. Microstructure of the quenched samples was investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometer. The results showed that the formation mechanism of TiC and TiB2 during reactive plasma spraying is same as that in the glove box, namely the Ti–B–C melt is first formed by B4C particles dissolving into the Ti–B eutectic liquid as well as the molten Ti, and then TiC and TiB2 are formed and precipitated from the saturated Ti–B–C melt.