Materials Science Forum Vols. 675-677

Abstract: The GaOOH Nanocrystal rods were successfully synthesized by microwavehydrothermal method using Ga2O3 ,HNO3 and NH3·H2O as raw materials. Simple heat treatment of GaOOH in the flow of NH3 gas leads to the formation of submicron GaN rods even at 800°C through GaOOH. The resultant GaOOH and GaN nanomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism of GaOOH and GaN was proposed. The results indicate that the as synthesized GaN were hexagonal nanorods with average aspects ratio of 5:1(diameter 800 nm and length about 4μm). Photoluminescence spectrum shows that a blue emission peak originates at 473.5 nm, indicating that the GaN nanorods displayed luminescence emission in the blue-violet region, which was related to crystal defects, and may be helpful for electro-optical applications of GaN material.

Abstract: Cellulose micro/nano fibrils generated from biomass are relative new reinforcing materials for polymer composites, which have potential lightweight and high strength and are renewable. In the present study, the preparation method of extracting cellulose micro/nano fibrils from wood was introduced. After successful disintegration, the morphological characteristics of the wood fibers, purified cellulose fibers, cellulose fibers activated by ultrasonic-wave and cellulose micro/nano fibrils after homogenization treatment, were compared by visual examination and scanning electron microscopy. The results showed that cellulose micro/nano fibrils have been efficiently extracted from wood, which have great potential in the application areas of papermaking, bio-nanocomposites, food, cosmetics/skin cream, medical/pharmaceutical, and so on.

Abstract: Scanning confocal electron microscopy (SCEM) is a novel technique for threedimensional observation with a nanometer-scale resolution. Annular dark field (ADF) SCEM imaging has been demonstrated to have better depth resolution than bright field (BF) SCEM imaging. However, the depth resolution of ADF-SCEM images is limited by the vertical probe size determined by spherical aberration and convergence angle. Therefore, we attempted to employ a deconvolution image processing method to improve the depth resolution of SCEM images. The result of the deconvolution process for vertically sliced SCEM images showed the improvement in the depth resolution by 35-40%.

Abstract: A 3D model of molecular dynamics for nanoceramic SiC is adopted to simulate the hot pressing sintering and preparation process of SiC, and mechanical properties such as density, hardness and elastic modulus are calculated. Finite element model of indentation is established based on the mechanical performance parameters from MD simulation. Conical indenter is adopted in indentation simulation. The FEM simulation results show that: Maximum equivalent stress appears at the place of indenter tip, and equivalent stress curves are appeared hemispherical. As indentation depth increases, the stress increased. As the distance of away from the indenter increases, the displacement in equivalent displacement nephogram gradually decreased until zero. During unloading process, elastic restitution is occurred. The elastic restitution in the area of below the indenter is obviously. Residual stress in the center of indentation is maximal after unloading.

Abstract: Nanocrystalline SnO2 powder has been synthesized via direct precipitation method starting from Sn, HNO3, HCl, and NH4OH. Thermal properties, crystal structural and morphological properties of the precursor and SnO2 powder were investigated using simultaneous thermogravimetry-differential thermal analysis, X-ray diffraction and transmission electron microscopy. The results indicated that the precursor was SnO2 rather than Sn(OH)2 or Sn(OH)4. On the basis of the precursor, well crystallized SnO2 powder with 4-5 nm in diameter was obtained, after calcined at 350 °C for 2 h.

Abstract: Chitosan (CS) / poly(vinyl alcohol) (PVA) blend nanofibers containing Ag-SiO2 nanoparticles (CS/PVA/Ag-SiO2 nanofibers) were successfully prepared by electrospinning using formic acid (HCOOH) as solvent in this paper. The morphology, diameter and structure of the electrospun nanofibers were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). And the diameter distribution of the nanofibers was measured by Image-Pro Plus. The results showed that the ideal nanofibers with the diameter in 85-165 nm can be obtained with the proper technical parameters as follows: the spinning voltage at 40 kV, the extruding speed at 0.5 mL/h and the collecting distance at 200 mm. The CS/PVA/Ag-SiO2 nanofibers will present potential applications in wound dressing and bandage etc.

Abstract: In this paper, electrospinning method was adopted to prepare tin oxide nanofibers membrane with three kinds of novel precursor solution PVP/C12H24O4Sn, PVP/ C4H10OSn and PVP/SnCl4. The morphology, surface element, thermal analysis and crystal structure of the fibers membrane were investigated by SEM, EDS, TG-DTA and XRD. The results showed that the organic/inorganic hybrid nanofibers with an average diameter of 300～700 nm can be obtained by electrospinning. But after calcined at 600°C, the loose and porous tin oxide nanofibers membrane with an average diameter of 100～250 nm can be obtained only by using PVP/SnCl4 as preceusor solution, moreover, it showed good fiber forming property. From XRD spectra, it was found that the rutile structure tin oxide finally obtained without other crystalline forms.

Abstract: Nanoparticles of sulfur with an average diameter of 5-35 nm were successfully prepared using eggshell membrane (ESM) as template in the the presence of surfactant Tween-80. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). The sizes of the nanoparticles sulfur were estimated by Debye-Scherrer formula according to XRD spectrum. Based on the detailed investigation, a possible synthesis mechanism is discussed here.

Abstract: Some dry and wet grinding experiments have been respectively conducted on titanium dioxide which is a noble photocatalyst material in a mortar, a tumbling mill and a planetary mill. Anatase is apt to transform to rutile via a metastable phase brookite in every kind of mills in the case of dry grinding. And it hardly takes place for phase transformation from rutile to other forms. It is shown that the kind of mill has not decisive effect on the mechanochemical polymorphic transformation of titanium dioxide, which merely influences the rate of phase transformation. On the other hand, the addition of other liquid media, such as water and acetone, is helpless for phase transformation of anatase. Only anatase can transform to metastable phase brookite by wet grinding. When ground titanium dioxide is heated, the amorphous phase is easier to transform to rutile than metastable phase brookite at lower temperature.

Abstract: Reflective liquid-like films of silver nanoparticles simultaneously have metallic luster and the macroscopic properties of a fluid. Owing to their special properties, the films can be potential materials for the component of a new kind of liquid mirrors. The influence of different sizes of nanoparticles on the films reflectivity has been considered in this study. A great improvement on the reflectivity of the films has been found with the increase in the silver nanoparticles’ size. Additionally, the volume of the liquid substrate also has an effect on the reflectivity of the films. Characterization of the films by X-ray diffraction indicates that the liquid-like films are mainly composed of fcc silver nanoparticles rather than silver compounds.