Jili Yang

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

Manufacture, microstructure and mechanical properties of Mo-W-N nanostructured hard films

Mo1−xWxNy (x = 0–0.67) hard films were fabricated on wafers of silicon and high speed steel by dc magnetron sputtering technique. The effect of tungsten concentration on the phase composition, microstructure, surface morphology, hardness, adhesion, and corrosion resistance of the films was studied by X-ray diffraction, scanning electron microscopy, nano-indentation, and scratch test. It was found that if the W concentration (x) in the film is in the range of 0–0.52, the films exhibit fcc (Mo,W)Ny single phase where larger W atoms substituted Mo atoms in fcc MoNy. At higher x values (x > 0.52) the films exhibit a two-phase structure consisting of fcc (Mo,W)Ny and pure bcc tungsten phase. The hardness of the Mo1−xWxNy films increases at first with increasing x, and then decreases after passing a maximum. The maximum hardness of 47 GPa is obtained at x = 0.37 corresponding to an adhesion strength of 60 N. The Mo–W–N coated high speed steel has a lower corrosion current density and higher corrosion potential than the bare high speed steel substrates.

Morphology-controlled synthesis of gadolinium fluoride nanocrystalsvia ultrasonic and salt assisted method

Gadolinium fluoride NaxGdyFx+3y crystals with different morphologies and compositions have been successfully synthesized via a facile ultrasonic and salt assisted method at room temperature without any template or organic additive. Crystal structure and morphology of the fluorides were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reaction conditions, such as ultrasonic irradiation, F/Gd molar ratio (R(F/Gd)), concentration of sodium nitrate and ultrasonic time have a close relationship with the morphology and phase composition of the final products. The growth mechanism of the uniform and monodisperse GdF3 nanospindles was proposed based on the time-dependent experiments. The photoluminescent (PL) properties of the as-obtained products revealed that Eu3+ doped NaGdF4 nanocrystals with different morphologies present characteristic luminescence of Eu3+, and their emission intensities strongly depend on morphology.