Papers by Keyword: Nanotube

Abstract: The two-step anodization process was adopted for the preparation of Al/Al₂O₃ (AAO) template with about 100 nm porous diameter. Then, the semi-terminated silica nanotubes were synthesized with the AAO template by the sol-gel method. The AAO template and semi-terminated silica nanotubes were observed by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The results showed that the porous diameter was increased with the increasing of the electrolyte concentration, the electrolysis temperature and the anodic oxidation voltage, respectively. The formation of semi-terminated silicon nanotubes might be important relationship with the method of embedding silane sol into the porous, drying temperature and drying time of AAO template with the sol-gel silica precursor.

Abstract: Mesoporous silica nanotube bundles with short channels were synthesized through a surfactant-templated process with the addition of dodecane. Transmission electron microscope (TEM) and high resolution scanning electron microscope (HRSEM) studies show that the channels of the silica nanotubes are parallel gathered in nano-size bundles. Each particle of these nano-size bundles contains less than 10 silica nanotubes. The length of the silica nanotube channel is about 200 nm while the pore size of the channels is about 11 nm. Dodecane solubilized in the hydrophobic cores of P123 micelles leads to large pore size and the unique bundle structure of the silica nanotubes.

Abstract: The formation of self-aligned titania and zirconia nanotubes is achieved by the anodisation of Ti and Zr in a fluorine contained electrochemical bath. The anodic oxidation was performed at 30 V for 60 min in a two-electrode glycerol (15% water) bath containing varying amount of NH4F. Despite the fact that a self-aligned nanotubular structure is formed on both titanium and zirconium, the dimensions of zirconia and titania nanotubes are different under the same anodisation parameters. It appears that by using 30 V as the anodisation voltage, the diameter of zirconia nanotubes (30-60 nm) is much smaller compared to that of titania nanotubes (80-100 nm). The length of zirconia nanotubes in the bath consisting of 0.7 g NH4F is 3 µm whereas titania nanotubes formed in the same bath have a length of ~700 nm. The fundamental difference between the nanotubes formed on titanium and zirconium may be related to the rate of oxidation, initial oxide formation during anodisation, pits formation and rate of pits growth for pores formation and stabilisation. Moreover, investigation on the crystallinity of the nanotubes reveals that titania nanotubes are weakly crystalline with crystallite sizes of <5 nm. Whereas, zirconia nanotubes are much more crystalline in cubic modification. The stabilisation of the high temperature phase is thought to originate from the size of the nanotubes walls and the deficiency in oxygen during the growth of the anodic oxide by anodisation.

Abstract: The behavior of an electrochemical cell for anodic formation of titanium oxide nanotubes is calculated from an electrical model obtained from the DC Current-time plot. The result can predict the behavior beyond the voltage source used in the experiment and in conditions that are impossible to achieve in a real experiment. This clarifies the speculation around the cell voltage versus cell current limited experimental data and its behavior is explained in terms of the source used in the experiment.

Abstract: One-dimensional titanate nanotubes and nanowires were synthesized by hydrothermally treating TiO₂ nanoparticles (P25) with an aqueous NaOH solution in a revolving autoclave. The effect of the reaction temperature and time on the morphology and crystal structure of titanate nanomaterials was systematically studied. When the hydrothermal treatment was carried out in a revolving autoclave, nanotubes with Na_xH_1-xTi_2-x/4Υ_x/4O₄•H₂O crystal structure were obtained and favor to self-assemble in shape of clusters and bundles, and nanotube bundles tended to transform into nanowires with the crystal structure transforming into Na_xH_2-xTi₃O₇ within 48 h at a hydrothermal temperature higher than 130 °C. Based on the experimental results, a possible mechanism for the formation of titanate nanotube by wrapping of nanosheets and nanowires formed via the cooperation of oriented attachment and Ostwald ripening was proposed.

Abstract: In this work magnetic nanorods have been synthesized by electrodeposition inside the nanotubes fixed to anodic alumina oxide (AAO). The used templates have the pore diameter of 120 nm. In the first step different combinations of 3d elements oxide nanotubes such as: CoO, NiO, NiFe2O4, CoFe2O4 and Fe3O4, have been successfully fabricated inside the nanopores by wetting chemical deposition followed by thermal decomposition. Oxide/Fe, wires were obtained in the next step by electrodeposition The morphology of obtained structures were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The magnetic properties of the nanostructures were determined on the base of behavior of the structures in external magnetic field. Local magnetic moment orientation is not strictly determined up to now. The potential biological application as an enzyme carrier was tested.

Abstract: Tribological behavior of ZrO2 and Si3N4 based nanocomposites with addition of carbon nanofibres and nanotubes has been studied by the pin-on-disc technique. Friction coefficients were measured and recorded, wear rates were calculated in terms of material volume loss per load and sliding distance. The wear damage was studied using optical and electron microscopy and its mechanisms were identified. In monolithic materials the dominant wear mechanism was abrasion, in composites with CNF and with higher volume fraction of CNTs (5 and 10%) fiber pull-out and lubricating by the carbon phases occurred.

Abstract: In this paper, the double-wall carbon nanotube oscillator resonant phenomena and energy dissipation are simulated by use of molecular dynamics simulation. The simulation run at different temperatures , and the double-walled carbon nanotube oscillator resonance phenomenon is verified，the vibration displacement curve which carbon tubes versus time and the changes in restoring force of carbon tubes suffered in the process of oscillation process are obtained and the friction is discussed from the point of view of energy dissipation. By statistical calculation, the double-walled carbon nanotube resonant amplitude of the process is found quickly decay with temperature increasing, and the friction per atom will enlarge with temperature increased, but the restoring force of inner tube is almost constant.

Abstract: Among all of the one dimensional nanostructures other than titania (TiO2) and carbon, zirconia (ZrO2) have started to gain interest due to its potential in catalytic and energy applications. ZrO2 nanotubes arrays have been prepared using electrochemical anodizing method of Zr foil in fluorine containing glycerol electrolyte. The morphology and structure of the ZrO2 nanotubes are strongly controlled by the applied electrochemical condition especially voltage. Nanotubes with diameter of 30 to 60 nm has been produced by controlling the anodization voltage from 10 to 40 V. The ZrO2 nanotubes formed in this method is partially crystalline even without the heat treatment. The wall thickness is ~10 nm. The self-aligned nanotubes produced by this method could be used for phocatalytic application. The degradation of methylene orange under UV light was successful when ZrO2 nanotubes made in 30 V is used.

Abstract: Lead strontium titanate (PST) nanotubes were fabricated with sol-gel method on AAO template. Thermal evolution and phase transformation process of PST were characterized by Thermogravimetry and Differential thermal analysis (TG/DTA) and X-ray diffraction (XRD). It was found that PST began to crystallize at 560°C and became perovskite structure without other phases. The morphology and structure of PST nanostructures was characterized by SEM and TEM. The capacitor of AAO and PST-AAO compound aluminum foil annealed at different temperature were tested with precision impedance analyzer. It revealed that the microstructures of PST were polycrystalline nanotube array and the capacitor of compound aluminum foil was increased for PST existing in the AAO, which indicated that this compound method could improve the capacitor of aluminum foil effectively.