Papers by Keyword: Nanotube

Abstract: In this paper the self-buckling of nanostructures, such as nanotubes, fullerenes and peapods, is analytically treated; this surprising phenomenon is due to the interaction among the nanostructures caused by the surface energy; it is peculiar of the nanoscale and has not a macroscopic counterpart. The influence of the surrounding nanostructures on one of them in a crystal is nearly identical to that of a liquid having surface tension equal to the surface energy of the solid. For the beneficial implications of the self-buckling on the overall mechanical strength see Pugno (2010; The design of self-collapsed super-strong nanotube bundles, Journal of the Mechanics and Physics of Solids, Available Online).

Abstract: Titania ceramics have many applications due to its surface properties and, recently, its nanostructured compounds, prepared by hydrothermal treatments, have been described to improve these properties. In this work, commercial titanium dioxide was treated with 10% sodium hydroxide solution in a pressurized reactor at 150°C for 24 hours under vigorous stirring and then washed following two different procedures. The first one consisted of washing with water and ethanol and the second with water and hydrochloric acid solution (1%). Resulting powders were characterized by X-ray diffraction, N2 gas adsorption and field emission gun scanning and transmission electronic microscopy. Results showed that from an original starting material with mainly rutile phase, both anatase and H2Ti3O7 phase could be identified after the hydrothermal treatment. Surface area of powders presented a notable increase of one order of magnitude and micrographs showed a rearrangement on the microstructure of powders.

Abstract: Third neighbor analytic tight-binding formulae were obtained for graphene sheets and nanotubes. After fitting the corresponding of-diagonal matrix elements can be used in numerical electronic structure calculations of nanotubes and corrugated graphene.

Abstract: TiO2 derived nanotubes were prepared by hydrothermal treatment of TiO2 (anatase) powder in 10 M NaOH aqueous solution. The crystalline structure, band gap, and morphology of the TiO2 nanotubes were determined by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Transmission Electron microscopy (TEM) and N2 adsorption (BET) at 77 K, respectively. It was observed that the surface area of the nanotubes was increased twelve times compared with TiO2 (anatase) powder. The results demonstrated that the photocatalytic activity of TiO2 nanotubes was higher than that of TiO2 (anatase) powder. The photocatalytic activity of the nanotubes was evaluated in presence of sunlight by degradation of aqueous nitrobenzene. Complete degradation of nitrobenzene was obtained in 4 hours using TiO2 nanotubes whereas 85% degradation was observed in case of TiO2 (anatase).

Abstract: Concentrated sulfuric and concentrated nitric acids treated multi-walled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were fabricated via a conventional wet spinning process. Mechanical properties of the composite fibers were studied by tensile testing and structures of the fibers were investigated via SEM and DMA. The results showed that the strength, storage modulus and glass translation temperature of the composite fiber containing 5% content of MWNTs were improved compared with those of pure PAN. The fiber with 5wt% MWNTs showed its conductivity of an order of 10-3S/cm.

Abstract: Micropore and nanotube formation on the Ti oxide are important to improve the cell adhesion and proliferation in clinical use. In this study, nanotube and micropore of Ti alloy for biocompatibility have been investigated using FE-SEM and XRD. Ternary alloys were prepared by using high purity sponge Ti Ta, Zr and Nb sphere (99.95% wt.%). Two-step anodizing was used for surface modification of the titanium alloys. Micropore formation was first performed using a potentiostat in 1 M H3PO4 electrolyte and nanotube formation was performed in 1M H3PO4 + 0.8wt% NaF solution by using a potentiostat. The two-step anodizing process is an efficient method for forming micropores and nanotubes on the surfaces of ternary titanium alloys, and the morphology of micropore and nanotube is dependent on the alloying element and composition of ternary alloy.

Abstract: BNC nanotubes were prepared by a high-energy ball milling and annealing method. Graphite carbon (C) and hexagonal boron nitride (h-BN) powder was first milled at room temperature to generate highly disordered nanoporous particles with a metastable structure. Upon elevated temperature annealing up to 1300 °C, these nanoporous particles were chemically and thermally activated to grow BNC nanotubes with both cylindrical and bamboo-like morphology. The cylindrical tubes have smaller diameters from 40 to 60 nm and lengths up to 2 μm. The bamboo tubes have larger diameters from 80 to 150 nm and lengths up to 10 μm. The formation mechanisms of different nanostructures are discussed.

Abstract: The optical properties of two kinds of single-wall silicon nanotubes (sw-SiNTs) [(n, 0) and (n, n)] with small diameters are investigated by using the first-principles method. For these two kinds of nanotubes, the absorptive part  of dielectric functions exhibits a broad band from 4 to 8eV in the region of 4-11eV, which is attributed to the transition of the  band to the * and  bands. Particularly, another small peak (inter- band transition) at 1.2-2.3 eV in the low-energy region is also identified. In addition, the loss function of these nanotubes are calculated and discussed.

Abstract: Boron Nitride nanotubes (BNNTs) together with carbon nanotubes (CNTs) have attracted the wide attention of the scientific community and have been considered as promising materials due to their unique structural and physical properties. In this paper, the behavior of BNNTs of different diameters under compressive loading has been studied through molecular dynamic (MD) simulations. We have used a Lennard-Jones pair potential to characterize the interactions between non-bonded atoms and harmonic potentials for bond stretching and bond angle vibrations. Results of the MD simulations determine the critical buckling loads of the BNNTs of various diameters under uniaxial compression, and indicate that for the simulated BNNTs of length L = 6 nm, the critical buckling loads increase by increasing the nanotube diameters.