As-received Carbon Nanotubes Research Articles

Tension–tension fatigue behavior of carbon nanotube wires

The tension–tension fatigue behavior of three types of as-received carbon nanotube (CNT) wires, comprising of 30-, 60-, and 100-yarn, was investigated. Fatigue tests were conducted at 35%, 50%, 60%, 75% and 80% of their ultimate tensile strengths which provided the fatigue life data (S–N curves). Their electrical conductivities were measured as a function of the number of cycles. Fatigue strength of the CNT wires at a given number of cycles decreased with an increase in the number of yarns. Their electrical conductivity increased with increase of applied fatigue load and number of fatigue cycles. Damage and failure mechanisms involved relative sliding of yarns in CNT wires leading to the formation of kink bands, followed by plastic deformation and then breakage of yarns. Microtomography density measurements provided the evidence that the increase in conductivity was due to the reduction of micro/nano voids between and inside the yarns, which decreased with increasing fatigue load and number of fatigue cycles.

Fatigue characterization of acid-treated carbon nanotube/epoxy composites

This study investigates how the acid treatment of multi-walled carbon nanotubes affects the fatigue behavior of carbon nanotube/epoxy composites. Nanocomposites with 0.5 and 1.0 wt% acid-treated carbon nanotubes display slightly and significantly stronger fatigue strength than those with equal-content as-received carbon nanotubes, respectively. However, excessive addition of carbon nanotubes fails to increase the fatigue resistance of epoxy resins, owing to carbon nanotube agglomeration. Furthermore, the fatigue strength of nanocomposites depend on the ultimate strength rather than the carbon nanotube contents or treatments. Furthermore, how carbon nanotube contents and related treatments influence the fatigue strength of the nanocomposites is elucidated by examining the fractographs of the specimens.

Effect of purification of carbon nanotubes on their electrocatalytic properties for oxygen reduction in acid solution

The oxygen reduction reaction has been investigated on acid-treated single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT) modified glassy carbon (GC) electrodes in acid media using the rotating disk electrode (RDE) method. Different acids were used for the carbon nanotube (CNT) purification. A systematic study was carried out to elucidate whether the metal catalyst impurities of CNTs play a role in the electroreduction of oxygen on the CNT modified GC electrodes. The surface morphology of the carbon nanotube samples was examined by transmission electron microscopy and the concentration of metal catalysts in the CNT materials was determined by energy dispersive X-ray spectroscopy. The acid-treated MWCNTs were also characterised by Raman and X-ray photoelectron spectroscopies. Aqueous suspensions of SWCNTs and MWCNTs used for GC surface modification were prepared in the presence of Nafion. The RDE results indicated that the acid-treated CNT modified GC electrodes are less active catalysts for oxygen reduction than as-received CNTs which could be explained by the absence of metal catalysts on the surface of purified CNTs.

Molten salt synthesis of silicon carbide nanorods using carbon nanotubes as templates

Silicon carbide (SiC) nanorods were synthesised by reacting multi-walled carbon nanotubes (CNTs) with Si particles in a NaCl–NaF binary salt for 4 h at 1100–1200 °C in Ar. Reaction products were analysed by a combination of X-ray diffraction (XRD) and transmission electron microscopy (TEM), including aberration corrected lattice imaging and electron energy loss spectroscopy (EELS). At 1100 °C, 3C–SiC became detectable by XRD but unreacted Si and CNTs were still dominant, while, at 1150 °C, SiC increased at the expense of Si and CNTs. Finally, at 1200 °C, only SiC peaks were seen, indicating the complete conversion from CNTs to SiC nanorods. This synthesis temperature is 200–250 °C lower than that required by the conventional vapour–solid reaction process. The resultant SiC nanorods mostly followed the morphologies of the as-received CNTs, indicating that CNTs had not only served as carbon source but also acted as the templates for the nanorod growth. Most of the resultant SiC nanorods had complex stacking sequences containing various forms of stacking faults, and only some exhibited regular fault-free stacking sequences.

Fabrication of an aluminum–carbon nanotube metal matrix composite by accumulative roll-bonding

Accumulative roll-bonding was adapted to fabricate a carbon nanotube (CNT)-reinforced aluminum matrix composite. Its microstructure was investigated by transmission electron microscopy, and it was confirmed that the nanotubes were embedded into the metal matrix while maintaining their multiwalled structure. Measurements revealed that the as-received CNTs had a bimodal diameter size distribution, while only nanotubes with diameters >30 nm and >30 walls were retained during four consecutive rolling operations at 50% reduction.

Surfactant-modified multiscale composites for improved tensile fatigue and impact damage sensing

This paper documents the mechanical and electrical performance of self-sensing conductive polymer composites prepared with a low-cost technique and small hardware, able to considerably improve the dispersion and the surface adhesion of multi-walled carbon nanotubes (CNTs) in epoxy resin with respect to amine-modified CNTs and as-received CNTs. Surface treatment of the CNTs is performed using hexamethylene diamine, or a mix of sulfuric and nitric acid, and one of two surfactants (for the diamine treatment only): Triton X-100 (non-ionic) and cetyl pyridinium chloride, CPC (cationic). The effects of the treatments are shown in terms of the changes in mechanical properties and interpreted with the use of SEM, FTIR and XRD analyses. Moreover, a key and novel aspect of this work is that the improvements in dispersion and surface adhesion cause improvements of damage sensing capability under fatigue and impact. This was demonstrated on fiberglass-reinforced panels prepared with treated CNT/epoxy through hand lay-up. This study reveals that the diamine/CPC- based configuration is superior, due to improved mechanical performance, higher resistance to fatigue and impact damage (over 30 J) and increased damage sensitivity.

Effect of Ni nanoparticle distribution on hydrogen uptake in carbon nanotubes

Ni decoration on carbon nanotubes (CNTs) performed by electroless nickel (EN) deposition is investigated. The effect of Ni particle distribution on hydrogen uptake of CNTs is also studied. The chemical composition, crystal structure and microstructure of the CNTs with or without Ni loading are characterized using an inductively coupled plasma spectrometer (ICP), X-ray diffraction meter (XRD) and transmission electron microscope (TEM) coupled with an energy dispersive spectroscope (EDS). The hydrogen uptake in CNTs with or without Ni loading is measured using a high-pressure microbalance at room temperature under a hydrogen pressure of 6.89 MPa. The experimental results show that fine and well-dispersed metallic Ni nanoparticles can be obtained by EN. The density and particle distribution depend on deposition temperature and time. An enhanced hydrogen storage capacity of CNTs can be obtained by Ni decoration, which provided a spillover reaction. The hydrogen storage capacity of the as-received CNTs was 0.39 wt.%. As much as 1.27 wt.% of hydrogen can be stored when uniformly distributed nano-sized Ni particles are formed on the surface of the CNTs. However, the beneficial effect is lost when the active sites for either physical or chemical adsorption are blocked by excessive Ni loading.

Inverse Gas Chromatography of As-Received and Modified Carbon Nanotubes

The surface properties of chemical vapor deposition (CVD)-grown, multiwalled carbon nanotubes (CNTs) have been studied using inverse gas chromatography (IGC). By adapting known IGC methodologies to these challenging materials, the surface character of a broad range of CNT materials can be reliably compared and quantified in terms of dispersive and specific surface energies, electron acceptor and donor numbers, and adsorption capacities. The effect of CNT surface modification by high temperature annealing, thermal oxidation, and grafting of methyl methacrylate was explored. The IGC surface characterization of these materials was consistent with results from other surface-sensitive analytical techniques, including X-ray photoelectron spectroscopy (XPS), titration, and electron microscopy, confirming the validity and sensitivity of our approaches. The same IGC methodologies were successfully applied to characterize three as-received CNT materials which differed significantly in their specific surface areas and functional surface group concentrations.

Effects of heat treatment on materials characteristics and hydrogen storage capability of multi-wall carbon nanotubes

Heat treatment on multi-wall carbon nanotubes (CNTs) in ammonia gas was performed in this study. Effects of heating temperature (up to 1000 °C) on material characteristics of the CNTs were systematically investigated. Microstructure of the CNTs was examined using a transmission electron microscope. In addition, their crystallinity and specific surface area were evaluated with a Raman spectrometer and a nitrogen gas sorption analyzer, respectively. It was found that hydrogen storage performance of the CNTs clearly depended on their microstructure and crystallinity, which can be modified by the heat treatment. The hydrogen storage capacity of the as-received CNTs, measured with a high-pressure microbalance under 6.89 MPa, was only 0.39 wt.%. However, this value can be significantly improved to be 2.9 wt.% when the CNTs underwent a heat treatment conducted in the ammonia atmosphere at 1000 °C.

Carbon Nanotubes Contain Residual Metal Catalyst Nanoparticles even after Washing with Nitric Acid at Elevated Temperature Because These Metal Nanoparticles Are Sheathed by Several Graphene Sheets

It is demonstrated that multiwalled (MWCNT) and single-walled (SWCNT) carbon nanotube materials contain residual metal impurities (Fe, Ni, Co, Mo) even after prolonged periods of "washing" with concentrated nitric acid at temperature of 80 degrees C. Transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) reveals that this is because such metal impurities are intercalated in the nanotube channel (in the case of MWCNT) or in the "bamboo" segment of the nanotube (in the case of "bamboo"-like MWCNT), or they create graphene sheet protected metal core/shell nanoparticles (in the case of SWCNT). TEM/energy-dispersive X-ray spectroscopy (TEM/EDS) elucidate that residual metal impurities presented in "washed" carbon nanotube materials are in some cases in the form of metal alloys or that there can be several different pure metal nanoparticles presented in one CNT material. It is shown by thermogravimetric analysis that "washing" with concentrated nitric acid removes up to 88% (w/w) of metal catalyst nanoparticles from as-received carbon nanotubes and that such removal has in some cases a significant effect on the electrochemical reduction of hydrogen peroxide.

Alternative supports for the preparation of catalysts for low-temperature fuel cells: the use of carbon nanotubes

Noble metal catalysts in the form of nanoparticles supported on high surface area carbon exhibit characteristics which depend strongly on the nature of the support. This work presents results with noble metal catalysts supported on carbon nanotubes (MWNT and SWNT) and also on a high surface area carbon powder Vulcan XC-72, for proton exchange membrane fuel cells (PEMFC) fed with hydrogen contaminated with CO and also for the direct methanol fuel cell (DMFC). A high performance was achieved with PtRu supported on nanotubes for H 2 + 100 ppm CO, although it was similar to that presented by PtRu on Vulcan XC-72 with an overpotential of 100 mV at 1 A cm −2. Results for the DMFC showed power densities exceeding 100 mW cm −2 at 90 °C and 0.3 MPa and the activity of the anodes followed the sequence: PtRu/MWNT > PtRu/Vulcan XC-72 > PtRu/SWNT. The electrocatalysts were all prepared with the same method, namely impregnation of the carbons with the precursors in ethanol and reduction under a hydrogen atmosphere. The role of Ni, Fe and other contaminants contained in the as-received carbon nanotubes is discussed.