Yangjia Liu

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.

Preparation of TiO2 hollow nanofibers by electrospining combined with sol–gel process

TiO2 hollow nanofibers have been fabricated by directly annealing electrospun polyvinylpyrrolidone (PVP)/Tetra-butyl titanate (TBT) composite nanofibers. In this approach, PVP/TBT composite fibers were first synthesized by electrospinning PVP/TBT solution, and then calcined at high temperature with an appropriate heating rate to form hollow TiO2 nanofibers. During the heat treatment, the solvent composition, the amount of TBT and the heating rate have important influences on the morphologies of the TiO2 nanofibers. Morphologies of TiO2 could be tuned from solid nanofibers to belts, hollow nanofibers and rods by controlling the appropriate preparation conditions. The crystal structure, morphology, surface composition and specific surface area of the TiO2 hollow nanofibers were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analysis, respectively.

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

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.

Thermal Shock Resistance of APS 8YSZ Thermal Barrier Coatings on Titanium Alloy

Thermal barrier coatings (TBCs) with a typical 8YSZ ceramic top coat and CoNiCrAlY bond coat were deposited on titanium alloy substrate (Ti-6Al-4V in wt.%) by air plasma spraying. Thermal insulation and thermal shock resistance of the TBCs at different temperatures as well as their failure behavior were investigated. The results showed that the test temperature had a significant effect on thermal shock life of the TBCs. Failure of the TBCs systems was caused by the formation of crack, bond coat oxidation and elemental diffusion. The vertical cracks induced by thermal shock cycles were probably responsible for the enhancement in thermal shock resistance of the TBCs. Furthermore, elemental diffusion had a great effect on the acceleration of the TBCs failure. The TBCs could provide a good thermal protection for the titanium alloy substrate.