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Based on a molecular mechanics coupled with atomistic-based continuum theory, a closed-form formula is presented to examine the elastic properties of single- and double-walled carbon nanotubes subjected to hydrostatic pressure. Following the present model, the effects of the armchair and zigzag CNT structures on the pressure behavior are theoretically investigated. The computational result indicates that the bulk modulus is less sensitive to the chiral structures except for very small tube diameters. Moreover, closed-end nanotubes under hydrostatic pressure exhibit a larger bulking modulus than open ended nanotubes. The cap of the zigzag tubes has a larger effect on the bulk modulus when compared to the armchair tubes, especially in small diameter nanotubes. The predicted strain and the bulk modulus are in good agreement with existing theoretical results. [ABSTRACT FROM AUTHOR]

Abstract: Thin, flexible and tough bucky paper fabricated by filtering a stable suspension of double-walled carbon nanotubes (DWNTs) was characterized from the viewpoint of its pore structure and oxidation stability as compared with that derived from single-walled carbon nanotubes (SWNTs). The N2 adsorption isotherms of DWNTs and SWNTs at 77K were of type II and type IV, respectively, and also the micropore volume in DWNTs was three times greater than that in SWNTs. The onset temperature of oxidation in DWNTs was enhanced by ca. 200°C due to their coaxial structure. The expected high mechanical and electrical properties when combined with their high surface area and high structural integrity make the DWNTs bucky paper promising materials for numerous applications. [Copyright &y& Elsevier]

Abstract: Here we describe synthesis of very unusual multi-walled carbon nanotubes through a catalytic chemical vapor deposition method using a floating reactant method and subsequent thermal treatment up to 2600°C in a large quantity. Main characteristics of these nanotubes are (1) relatively wide distribution of diameters ranging from 20 to 70nm and linear, long macro-morphology (aspect ratio >100), (2) highly straight and crystalline layers, (3) high purity through removal of metallic impurity, (4) very low interlayer spacing (0.3385nm) and low R value (I D/I G =0.0717), (5) high G′ intensity over intensity of G band (G′/G=0.85) and strongly negative magnetoresistance value of −1.08% at 77K and 1T. The unusual microstructure of thin multi-walled carbon nanotubes with a partially facetted cross-sectional shape caused by thermal treatment is mainly ascribed to abrupt density changes (from 1.89 to 2.1g/cm3) within a confined nanosized space, accompanying with the phase separation. [Copyright &y& Elsevier]

Highly disordered carbon nanotube is obtained through a catalytic thermal chemical vapor deposition method, especially, using the floating reactant method. The results of annealing highly disordered carbon nanotube are (1) removal of metallic compounds, (2) structural conversion into multi-wall carbon nanotube with a little faceted cross-section, and (3) development of a tug morphology in carbon nanotubes. The characteristic observed in annealed multi-wall carbon nanotubes make them useful as a filler in advanced composite. [Copyright &y& Elsevier]

Cone-stacked nanotubes with thick layers of deposited carbon obtained by a catalytic chemical vapor deposition method are annealed at high temperature. Phase separation between cone-stacked nanotubes and amorphous carbon layers occurs during annealing due to different structural transformation behaviors, resulting in the formation of multi-wall carbon nanotubes containing a cone-type multi-shell arrangement. The apex angles of the nanocones are about 40°. This type of carbon nanotube shows different physical and electrical properties. [Copyright &y& Elsevier]

The effect of grinding on cup-stacked carbon nanotubes is studied. The application of a bending force on the sidewall of such carbon nanotubes, that is higher than the Van der Waals force acting between the cups, results in the shortening of carbon nanotubes and the formation of nano-barrels exhibiting an increased number of accessible active sites (represented by the ends of graphitic planes) and anisotropic properties at both ends. [Copyright &y& Elsevier]

Carbon nanotubes have a whisker-like structure so an extremely high strength and lack of plasticity are generally predicted. In-situ observations made by transmission electron microscopy, however, prove that carbon nanotubes bend plastically at room temperature. The bending process at the atomic level is suggested by a molecular mechanics calculation: a nanotube deforms elastically until certain critical curvature is attained; then the atomic bonding in the stressed side changes from a graphite-like bonding state to a diamond-like state. [ABSTRACT FROM AUTHOR]

Here, we report a drastically improved anticorrosive characteristic of magnesium alloy composites with the introduction of multiwalled carbon nanotubes. Highly depressed corrosion of nanotube-filled magnesium composite in salt water is due to the formation of stable oxide films along the grain boundaries of magnesium. Our results indicate that carbon nanotube acted as effective multifunctional filler to improve both mechanical and anticorrosive performances of magnesium alloy. [ABSTRACT FROM AUTHOR]

We describe, for the first time, the sequential structural changes of bundles of double-walled carbon nanotubes (DWNTs) as a function of heat treatment temperature. DWNTs (inner diameters >0.9 nm) are structurally stable up to 2000 °C. Above 2100 °C, the outer walls of adjacent DWNTs start coalescing into large diameter tubes. At temperatures higher than 2100 °C, three different types of structures were observed: (a) large-diameter DWNTs; (b) multi-walled carbon nanotubes (MWNTs), and (c) flaky carbons. The results demonstrate that DWNTs are much more stable than SWNTs, and their stability is comparable to that of MWNTs. [Copyright &y& Elsevier]

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives. [ABSTRACT FROM AUTHOR]

This study demonstrates the ability to fabricate lightweight, ductile but mechanically strong magnesium alloy (AZ91D) composites by introducing a small number of high crystalline multi-walled carbon nanotubes. It is demonstrated that 1% of relatively short and straight carbon nanotubes distributed homogeneously on the outer surface of magnesium powders act as an effective reinforcing filler to prevent deformation, thereby contributing to the enhanced tensile strength of magnesium alloy composites (e.g., from 315 to 388MPa). [Copyright &y& Elsevier]

Abstract: Systematic isothermal annealing has been carried out on catalytic chemical vapor deposition-derived highly disordered multi-walled carbon nanotubes in order to understand the structural evolution of carbon nanotubes kinetically. After specified isothermal time the crystallographic parameters strongly depend on annealing temperature, and can be divided into three stages. Rapid structural enhancement in the range from 1800 to 2200°C originates from the abrupt evolution of the residual catalytic compounds and is seen as partially aligned small fringes along the tube length. The lack of further structural ordering at temperatures above 2400°C and the low activation energy (ca. 90kJ/mol) are thought to be the result of the limited space available for further structural development considering the nano-sized multi-walled carbon nanotubes. [Copyright &y& Elsevier]

Abstract: We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. The amount of benzylamine in the solution was varied from 0% to 26% by weight. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes that are related to chemical reactions on N sites. [Copyright &y& Elsevier]

Abstract: We describe the synthesis of cm-long strands consisting of single-walled carbon nanotube ropes. The method involves the thermolysis of ferrocene (FeCp2)–alcohol solutions under an Ar atmosphere at 800–950 °C. The tubes within strands could exhibit large diameters (2–3.5nm OD) in high yields by either increasing the ferrocene concentration in the alcohol solution or by increasing the pyrolysis temperature. We noted that the nanotube material with the highest degree of crystallinity was produced at 950°C, and as the ferrocene concentration in the alcohol solution increases (e.g., 1.2 wt%), the tubes tend to be metallic. This method appears to be simple, safer and more efficient than others reported in the literature because it does not require vacuum, sulphur agents, relatively high temperatures or large amounts of H2. [Copyright &y& Elsevier]

We review the latest advances in the production and state-of-the art characterization of B- and N-doped carbon nanotubes (CNTs) and nanofibers. We briefly discuss different approaches to producing these novel doped nano-systems. The use of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), scanning tunneling spectroscopy (STS), Raman spectroscopy, and allied techniques to characterize these doped systems is reviewed. The field emission properties as well as some applications to the fabrication of novel polymer composites, Li+ batteries, and gas sensors are also discussed. It is clear that these materials possess outstanding properties when compared with pure CNTs, and it is foreseen that these systems will revolutionize some aspects of nanotube science and technology, thus opening a vast field of experimental and theoretical research. [Copyright &y& Elsevier]

We review the latest advances in the production and state-of-the art characterization of B- and N-doped carbon nanotubes (CNTs) and nanofibers. We briefly discuss different approaches to producing these novel doped nano-systems. The use of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), scanning tunneling spectroscopy (STS), Raman spectroscopy, and allied techniques to characterize these doped systems is reviewed. The field emission properties as well as some applications to the fabrication of novel polymer composites, Li+ batteries, and gas sensors are also discussed. It is clear that these materials possess outstanding properties when compared with pure CNTs, and it is foreseen that these systems will revolutionize some aspects of nanotube science and technology, thus opening a vast field of experimental and theoretical research. [Copyright &y& Elsevier]

High yields of graphitic conical nanofibres (5-70 nm OD; <5 µm in length) are produced by pyrolysing various palladium precursors under an Ar atmosphere at 850-1000°C. The fibres exhibit diamond-shaped Pd particles at their tips, which are responsible for the carbon aggregation and its subsequent diffusion. This carbon replication phenomenon on the Pd particles results in the formation of stacked graphene cones, which grow aligned along a common axis, thus creating graphitic nanofibres. The cones within the fibres can be either open (lamp-shade type) or closed. The material has been analysed using sophisticated electron microscopy (HRTEM, SEM, ED) and spectroscopic techniques (Raman, EELS, EDX). Due to the large number of open edges, we envisage that these novel nanofibres may find important applications in the fabrication of field emitters, gas storage devices and composites. [ABSTRACT FROM AUTHOR]

Emission spectroscopy is performed to study the optical transitions between electronic bands of SWCNs formed in AlPO4−5 (AFI) crystal. Strong visible emission is observed under laser light illumination at room temperature. The emission is excited by the light polarized along the c-axis and its polarization is also along this direction. On the other hand, non-linear emission is observed under the resonant excitation of the lowest absorption band of SWCNs. The emission is excited by the light polarized along the c-axis, but it shows the polarization perpendicular to the c-axis. The polarization character is discussed on the basis of the selection rules of the optical transitions predicted by the full line-group symmetry of SWCNs. [Copyright &y& Elsevier]

Abstract: In situ Raman scattering measurements of pristine and fluorinated double-walled carbon nanotube samples under high pressure have been performed. Due to the mechanical shielding effect of the outer tubes of the double-walls to the applied pressure, the Raman scattering lines from the inner tubes of both samples remained to be observed even at high pressure. [Copyright &y& Elsevier]

The authors report a significant enhancement in the thermal conductivity of a conventional carbon fiber/phenolic resin composite system when adding highly crystalline multiwalled carbon nanotubes. They demonstrate that 7 wt % of carbon nanotubes dispersed homogeneously in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and resulted in an enhancement of the thermal conductivity (e.g., from 250 to 393 W/m K). These results indicate that highly crystalline carbon nanotubes can be used as a multifunctional filler to enhance simultaneously the mechanical and thermal properties of the carbon fiber/phenolic resin composites. [ABSTRACT FROM AUTHOR]