Advanced Materials Research Vols. 55-57

Abstract: The purpose of this study is to assess the effect of van der Waals interactions within multi-walled carbon nanotubes with the three dimensional finite element models. The elastic buckling behaviors of nanotubes are treated under axial compressive force acting on open both ends of nanotubes and considered with various boundary conditions. The analysis is based on the assumptions that the covalent bond of each wall is represented by an elastic beam element while the van der Waals force of adjacent walls are represented by a nonlinear truss element following the Lennard-Jones “6-12” theory. The models of double-walled carbon nanotubes are used to explain the characteristic of multi-walled carbon nanotubes and then results compared with the column theory. The results show that the critical load of nanotubes depends on atomic arrangement, tube length, and number of walls, while the van der Waals force has a small effect on the buckling load for multi-walled carbon nanotubes.

Abstract: Resorcinol and formaldehyde (RF) carbon cryogels are prepared by sol-gel polycondensation by using sodium carbonate (C) as a catalyst with water (W) as solvent, immersed in acid solution, hydrochloric acid (HCl), dried by freeze-drying technique and then carbonized under inert atmosphere, respectively. Compared with their carbon precursors, both Vmes and mesopore size distributions of all carbon cryogels can be developed since the pore shrinkage is the crucial role in the change of pore structure of carbon gels. HCl may promote the strength of small pore structure and increase the pore shrinkage of large pore structure. Consequently, the treatment of HCl does not only enhance the partial collapse of large pore structure, the treatment also increases the strength of small pore structure to inhibit the shrinkage of this structure during carbonization as well.

Abstract: The optimization of chemical vapor deposition synthesis conditions for multiwall carbon nanotubes (MWCNTs) was experimentally investigated. Carbon nanotubes were grown on cobalt substrate thicknesses of 20, 100 and 1000 nm at 700 and 900 0C with 2 replications. The configuration and morphology of the carbon nanotubes were investigated by scanning electron microscope and Fourier transform raman spectrometer, respectively. The tendency of the parameters was evaluated by statistical design of experiment. Observations on samples produced under our optimised production process, showed that a large number of MWCNTs bundles were produced. Diameter of MWCNTs bundles ranges between 30 and 100 nm throughout the samples. From the variance analysis of the Raman spectra we observe that the thickness of cobalt and temperature of synthesis are highly significant in which the coherence length and innermost diameter increase for either the thickness increases or the temperature decreases.

Abstract: Ni catalyst was removed from as received multi-walled Carbon Nanotubes (MWNTs) by acid treatment. Then, the nanotubes were treated with 4M HCl during a ball milling processing yielding mechanochemical treated MWNTs (mech-MWNTs). TEM micrographs indicate that the mech-MWNTs were still of a tubular form but with much shorter length. The equilibrium adsorption of metal ions, e.g Cu2+ and Ni2+, on the mech-MWNTs was investigated at room temperature. The adsorption isotherms gave excellent consistence with the Langmuir theory and the best fit values of K-1 and Κmax can be evaluated using non-linear least-squares. As results, the maximum of Cu2+ and Ni2+ ions uptake on to the mech-MWNTs are 0.93 ± 0.004 mg/g and 2.11 ± 0.01 mg/g respectively. There is no evidence indicating that the pore structure and layer surfaces at both ends of the mech-MWNTs are appropriate sites for metal ions adsorption.

Abstract: The coil-like shape carbon nanotubes (CNTs) were synthesized on stainless steel substrates using acetylene gas (C2H2) at 750oC under pressure of 4110−× bar by thermal chemical vapor deposition (CVD) method. The formation of catalytic nanoparticles used hydrogen (H2) as the environment gas. The scanning electron microscope (SEM) image shown the average coil diameter of CNTs is 0.8µm and 0.1 nm for the average coil pitch of CNTs. The Raman spectrum shown the defect of CNTs and indicate that the carbon samples were tubes.

Abstract: An efficient surface modification technique for fabricating tin dioxide/carbon composite nanotubes has been developed. This technique combines with implantation of acidic groups, interaction between surface oxides and metal ions or hydration molecules, and thermal. To functionalize multi-layered carbon nanotubes (CNTs), gaseous oxidation at 300°C was used to build functional oxygen groups including carboxyl, carbonyl and hydroxyl group, on ends or sidewalls of CNTs. X-ray photoelectron spectroscopy clearly indicated that the atomic ratio of attached tin-oxide on the oxidized CNTs gradually increases with the oxidation level, i.e., surface O/C atomic ratio. This evidence reflected that the surface oxides act as an adsorption center that strongly interacts with metal ions or hydration molecules in aqueous phase.

Abstract: This research studied microstructure and characterizations of Portland cement with carbon nanotubes (CNTs) which were used as an additive material at 0 %, 0.5 % and 1 % by weight of cement. The compressive and flexural strength tests of mixes were conducted using water/cement ratios (w/c) of 0.5. Samples of mixes were selected for SEM analysis and then ground for TGA analysis. The results show that the compressive strength and flexural strength at all aging time of Portland-CNTs cement composites was higher than that of control mix. Microstructure results show that CNTs was filled in pores between matrix phases to show denser phase and TGA graphs show similar phases to PC mix.

Abstract: An experimental was investigated the condition of reinforcement of hemp fiber and hemp fiber/epoxy resin composites with carbon nanotubes (CNTs).The CNTs were mixed with several liquid such as ethanol, latex, water glue and epoxy resin. These mixtures were added to hemp fiber and prepared the hemp fiber/epoxy resin composites. The mechanical properties of both fiber and composite samples were measured. It was found that the mixture of epoxy resin and CNTs with CNTs ratio of 20 vol% in hemp fiber showed the highest tensile strength of 25.43 N. and the same mixture in hemp fiber/epoxy resin composites showed the highest tensile strength of 31.82 MPa and elongation of 7.40 %.

Abstract: This paper presents the diamond nucleation using combustion activation chemical vapor deposition (CACVD) by 0.95 volumetric ratio of O2 /C2H2 under atmospheric pressure. The main point of our work is to develop the CACVD technique for synthesize the semiconductor materials, which is developed for electronic devices application. The surface nucleation of substrate was studied by using surface pretreatment. The results of surface nucleation on mirror-silicon, polished silicon by diamond powder, silicon-dioxide (SiO2), and polished SiO2 by diamond powder, are significantly different. It can be concluded that the silicon-dioxide mask technique is useful for nucleated diamond protection whereas the polished silicon by diamond powder is suitable for nucleated diamond generation. These techniques are applied for the pattern fabrication.

Abstract: Carbon nanotubes (CNTs) and helical nanofibers (HNFs) were selectively grown on copper substrates by chemical vapor deposition using acetylene as a carbon source. The experiments were carried out by using Ni, Fe and Co as single and co-catalysts which were deposited onto the substrates by a sparking method. The catalyst-coated copper substrates were heated at 750°C in a mixed-gas-flowing tube furnace, at an argon flow rate of 100 ml/min and various acetylene flow rates of 3, 5 and 10 ml/min. The larger diameter of HNFs was grown only on Ni and Ni-Fe catalysts at the acetylene flow rates of 5 and 10 ml/min whereas the uniform smaller diameter of CNTs was preferentially grown on Fe-Co and Ni-Fe catalysts at the flow rate of 3 ml/min. We suggest that Co likely prevents the formation of HNFs whereas Ni promotes.