Yichao Gong

A facile approach to synthesize rose-like ZnO/reduced graphene oxide composite: fluorescence and photocatalytic properties

Rose-like ZnO/reduced graphene oxide composites are synthesized by a simple, scalable, and facile route without using any surfactants. The well-defined ZnO microstructure has a hexagonal hierarchical rose-like architecture, which is composed of densely packed uniform thin flakes. The N,N-dimethylformamide/water system employed here acts as an organic solvent as well as a reagent, and two competing reactions give rise to the formation of the hexagonal hierarchical rose-like ZnO architecture. Compared with bare ZnO, the rose-like ZnO/reduced graphene oxide composite displays the fluorescence quenching property. Finally, the as-prepared products possess considerable photocatalytic property under visible light for the degradation of methylene blue.

Fast crystallization of amorphous Gd2Zr2O7 induced by thermally activated electron-beam irradiation

We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd2Zr2O7 synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd2Zr2O7 and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase. Fast crystallization could be induced by 120 keV e-beam irradiation (beam current = 0.47 mA/cm2). The crystallization occurred on the nanoscale upon ionization irradiation at 400 °C after a dose of less than 1017 electrons/cm2. Under e-beam irradiation, the activation energy for the grain growth process was approximately 10 kJ/mol, but the activation energy was 135 kJ/mol by calcination in a furnace. The thermally activated ionization process was considered the fast crystallization mechanism.

Density functional theory calculations of point defects and hydrogen isotopes in Li4SiO4

The Li4SiO4 is a promising breeder material for future fusion reactors. Radiation induced vacancies and hydrogen isotope related impurities are the major types of point defects in this breeder material. In present study, various kinds of vacancies and hydrogen isotopes related point defects in Li4SiO4 are investigated through density functional theory (DFT) calculations. The band gap of Li4SiO4 is determined by UV-Vis diffuse reflectance spectroscopy experiments. Formation energies of all possible charge states of Li, Si and O vacancies are calculated using DFT methods. Formation energies of possible charge states of hydrogen isotopes substitution for Li and O are also calculated. We found that Li-vacancies will dominate among all vacancies in neutral charge state under radiation conditions and the O, Li, and Si vacancies (VO,VLi,VSi) are stable in charge states +2, -1, -4 for most of the range of Fermi level, respectively. The interstitial hydrogen isotopes (Hi) and substitutional HLi are stable in the c...

Low-temperature synthesis of Li4SiO4 pebbles as tritium breeding material by SiO2 coating approach

ABSTRACT Li4SiO4 pebbles are widely selected as attractive ceramic tritium breeding materials for the test blanket modules (TBM) of international thermonuclear experimental reactor (ITER). In this work, SiO2 coating approach was first employed to synthesize precursor powders for fabricating the Li4SiO4 pebbles. Lithium source and silicon source were mixed by hydrolyzing tetraethyl orthosilicate (TEOS) in the Li2CO3 solution. Compared with the traditional solid state method, the precursor powders synthesized by SiO2 coating approach displayed distinct coating structure, which was able to effectively lower the phase formation temperature and the sintering temperature of Li4SiO4 pebbles, and then decrease the grain size of Li4SiO4 pebbles. Thermogravimetry and different scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) analyses indicate that the phase formation temperature of Li4SiO4 synthesized by SiO2 coating approach is far below that of the conventional solid state reaction. Then, wet method was employed to prepare green spheres with the as-prepared precursor powders. Finally, Li4SiO4 pebbles with small grain size (average value 1.12 µm), high phase purity, good sphericity, and uniform microstructure could be obtained by sintering the green spheres at a low temperature of 625°C, which are expected to show favorable tritium release behavior and be used as tritium breeding materials for blankets.