Materials Science Forum Vols. 675-677

Abstract: SiO₂ aerogels, the lightest solid material have attracted much attention recently. However, it is difficult to be used in practical applications due to its fragility. A facile one step polymerincorporation sol-gel process, together with a surface modification and a normal temperature drying process, was developed to prepare silica-fiber composite aerogels. Four fibers (polyester fiber, polypropylene fiber, lignin fiber, polycrylonitrile fiber) were selected to enhance the intensity of silica aerogels, respectively. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) specific surface area. Results showed that samples have a plenty of hydrophobic methyl group attached to their surface. The continuous network structure composed of silica aerogels of high purity are non-crystallized, porous, surface areas from 800 to 980 m²/g and light weight nano-materials. Adsorption experiment of the above samples over organic solution (benzene, toluene) was tested. The composite aerogels absorbed the organic liquids by nearly 6-8 times its own mass, showing potential application in organic absorption.

Abstract: Using starch as the stabilizing agent, glucose as reducing agent, nano-size silver particles colloidal sols have been synthesized via ultrasonic irritation in aqueous solution. The synthesis process is completely green and the colloidal sols are safe to environment and human, and can be used as antibacterial agent in biology, medicine, food packaging and hauseware fields. The synthesis technology parameters for the silver particles with diameter of 15 to 45 nm, such as the ultrasonic power, reaction time, reaction temperature, concentrations of silver nitrate and capping agent were determined and discussed. The typical colloidal was characterized by ultraviolet-visible spectroscopy (UV-Vis), transmission electron microscope (TEM), X-ray powder diffractometer (XRD) and Zeta Sizer Nano Series.

Abstract: Recent experiments have indicated that TiO2 co-doped with cerium (Ce) and nitrogen (N) may show enhanced photocatalytic activity in the visible region with respect to TiO2 doped only with Ce. Prompted by these findings, we have investigated Ce-N co-doped TiO2 through a theoretical study. Density functional theory (DFT) calculations have been carried out with the generalized gradient approximation (GGA) to describe the electronic structure and photocatalytic activity of Ce-, N- and N/Ce-doped anatase TiO2; substitutional locations of Ce and N in the TiO2 lattice were considered: an O (Ti) atom is replaced by an N (Ce) atom. It was found that the Ce-N co-doped case narrows the band gap more significantly than the corresponding mono-doped anatase TiO2. These findings give the theoretical understanding for recent experimental results.

Abstract: The aspiration pressure variation at the tip of metal delivery tube in the supersonic atomization nozzle during gas-only atomization performance had been investigated in this work. The results reveal that the aspiration pressure is subambient at all operating pressures. A general trend is that with increasing atomization gas pressure, the value of aspiration pressure decreases at P0 between 0.5 and 1.5MPa, then increases as P0 ranges from 1.5~3.5MPa, finally decreases again at higher gas pressure (P0>~3.5MPa). When P0>2.0MPa, as the included angle α augments, the aspiration pressure ΔP increases. Meanwhile, the change range of aspiration pressure ΔP significantly enlarges when the jet included angle α raises from16 to 28º. The lager is the apex angle β of metal delivery tube, the greater is the aspiration pressure ΔP. And as the protrusion length of melt delivery tube h increases, the aspiration pressure ΔP decreases gradually.

Abstract: Photocatalytic activity of BiVO4 for the water oxidation was found extensively improved by Mo doping. The highest activity of Mo doped BiVO4 for O2 evolution appeared when the photocatalysts was doped by 0.2 at % Mo. The XRD patterens showed that the crystal structure of the photocatalyst was changed by Mo doping. The color and UV-Vis absorption spectra of the photocatalysts were also changed before and after the catalysts were doped by Mo.

Abstract: The reflection and refraction of harmonic SH waves at the interface between a homogeneous solid and a one-dimensional phononic crystal is studied. The effects of wave frequencies on the refraction coefficients are investigated. The results show that for lower frequencies, most part of the energy is reflected into the homogeneous solid and that the frequency has little effects on the energy distribution at the interface. While for higher frequencies, SH waves cannot propagate in some directions because of the existence of the directional band gaps, which results in the discontinuity in the refraction coefficient curve. For waves passing through the interface, the higher the frequency is, the smaller the refraction coefficient is.

Abstract: The enhancement effect of using PAN-based carbon fibers surface modified by ammonium nitrate for removing SO2 and H2S in moist air at room temperature was characterized and investigated. The pore structure of the samples so prepared was examined by adsorption measurement. Surface groups introduced by treatment with ammonium nitrate was assessed by xray photoelectron spectroscopy. The results show that the amount of sulfur dioxide and hydrogen sulfide adsorbed with the treated carbon fibers are increased by 112% and 93% and ammonium nitrate treatment improved original carbon fibers adsorption performance, not only by introducing nitrogen surface groups, but also by extending the surface area.

Abstract: A well known method was used to convert the solid silica spheres to porous silicon spheres with high surface area, with the starting shape retained. The presented work demonstrated that the porous silicon spheres are composed of polycrystal morphology. Due to the quantum confinement effect, the photoluminescence emission centered at 621 nm. The results of N2 adsorption and desorption analysis indicates the mesoporous silicon spheres possess a surface area around 88 m2 g-1 and single point micro-pore volume 0.173 cm3 g-1.

Abstract: In this paper, preparation, property study of ultra-strength mortars with mineral admixture and clear river sand was carried out. The mineral admixture include fly ash, ultra-fine GGBS and silica fume. The experimental results show that the compressive strength of mortar improves with increasing amount of silica fume or ultra-fine GGBS. When the content of silica fume or ultra-fine GGBS is 30~35%, the compressive strength and flexural strength of mortar in curing age of 7 days are 100 MPa and 20MPa, respectively. But strength of mortar decreases with the increase replacement rate of fly ash. When the mortar mixes with combined of silica fume and ultra-fine GGBS, the optimum proportion of siliaca fume to ultra-fine GGBS is 2:3. And the compressive strength of mortar in curing age of 7 days is 75~100MPa when the mixed mineral admixture is 40~60%. The compressive strength of mortar is about 90MPa as it mix 60% of cement, 15% of silica fume, 15% of GGBS and 10% of fly ash. Moreover, the ultra strength mortar refines its pore structure and its capiliary pore (≥100nm) amount reduces by 78% compared to ordinary mortar.

Abstract: The band structure and photonic spectrum of one dimensional Thue-Morse quasicrystal composed by negative-index materials and positive-index materials are studied. We show that a new type of the omnidirectional reflection band (ORB) exists in Thue-Morse photonic heterostructures. Compared to a single Thue-Morse quasicrystal, the frequency range of the ORB in a Thue-Morse photonic heterostructure can be notably enlarged, and the width and location of the ORB do not change with Thue-Morse order. The lower edge of the ORB depends only on transverse electric (TE) polarization, while the higher edge of the ORB depends only on transversemagnetic (TM) polarization. These results imply potential applications in improving planar microcavities, optical fibers, and Fabry–Perot resonators, etc.