Papers by Author: Xiang Gao

Abstract: A possible new phase of carbon nitride was synthesized by shock wave using a precursor of mixture of graphitic carbon nitride (g-C3N4) with iron powder in a weight ratio of 10:90 at the flyer velocity of about 3.0 km/s driven by explosive detonation. The results of XRD and TEM indicate that the new phase possesses four weak diffraction peaks at 2=36.06 (d=2.489Å), 41.90(d=2.154Å), 60.88(d=1.520Å) and 72.98(d=1.295Å) besides a strong diffraction peak of graphitic carbon nitride at 2=27.70 (3.218 Å) and shows a few tube-like structures in a diameter of about 200300nm and in a length of about 10003000nm with the exclusive element composition of carbon and nitrogen identified by EDX characterization.

Abstract: Different TiO2 precursors were impacted by detonation-driven high velocity flyers to obtain high-pressure phases of titania under instantaneous high temperature and pressure. The factors affecting high-pressure phase synthesis such as loading conditions and titanium dioxide precursors were also studied. The structure and phase composition of the shocked samples are determined by X-ray diffraction (XRD). The microstructure of TiO2 after shock treatment was observed by transmission electron microscopy (TEM).

Abstract: In this paper, nitrogen-doped titania was achieved by detonation-driven flyer impacting on the mixtures of TiO2 and different nitrogen precursors. XRD、UV-Vis and XPS spectra were employed to characterize the phase composition, N doping concentration and energy gap of recovered samples. N doping concentration can be effectively regulated by choosing different doping nitrogen resources, changing initial content of doping nitrogen resources and flyer velocity in order to regulate the energy gap of TiO2. The maximum concentration of nitrogen of doped TiO2 by shock loading at 3.37 km/s is 13.45 at%. The results show that anatase transforms to rutile and srilankite appears at a higher flyer velocity (1.9-2.52km/s), the concentration of doped nitrogen in the recovered samples increases with increasing flyer velocity, the maximum concentration of nitrogen is 13.45 at%. The edge adsorption wavelength of nitrogen-doped titania induced by shock wave is shifted from 435nm to 730 nm and the corresponding energy gap is reduced from 2.85 eV to 1.73 eV.

Abstract: Experiments have been conducted to consolidate tungsten powder using hot-shock consolidation technique combining with underwater shock wave. An exothermic mixture (TiO2-C-Al-Fe2O3) was ignited by an electric wire coil to release a large mount of heat via a self-propagating high-temperature synthesis reaction which was used to pre-heat the sample powder. As getting the needed isothermal temperature, the powder was subsequently consolidated by shock wave generated by explosion of nitro methane, with a detonation velocity of 6.3 km/s and a detonation pressure of 11.9 GPa. The density and Vickers micro-hardness of the consolidated sample were determined and its microstructure was analyzed by scanning electron microscope (SEM). High-density tungsten samples were obtained by optimizing the experimental conditions. In this paper, the relative density and hardness of the recovered sample are 96.5% and 670 HV, respectively.