The radial stability and the irreversible transformation of triple-wall carbon nanotubes (TWCNTs) bundles are investigated at high pressure conditions both experimentally and theoretically (exp. up ...72 GPa). The tubes having a mean internal diameter of 0.83nm and graphite-like intertube distance, show an onset of the radial collapse evidenced by the evolution of optical phonons. The nanotube collapse onset is observed at ∼22 GPa completes for the two external tubes at ∼29 GPa, however the innermost tube remains stable up to ∼37 GPa. Molecular dynamic calculations performed on smaller diameter TWCNTs bundles, as a model system, confirmed the multiple-stage pressure-induced collapse process. An analytical expression for the collapse pressure of carbon nanotubes having an arbitrary number of walls is proposed. Our experiments and modelling show that for pressures beyond ∼ 60 GPa an irreversible structural transformation of TWCNTs takes place. Ex situ transmission electron microscopy characterization on the recovered sample from 72 GPa revealed the mechanical failure of carbon nanotubes which evolve towards ribbon-like structures as corroborated by Raman spectroscopy. Modelling the tubes evolution at high pressure and high temperature showed the formation of new structures ranging from ribbon-like to graphite-like with either different degrees of amorphization or sp3 interlinking.
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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 388
MPa).
High-pressure resonance Raman experiments were performed on linear carbon chains Cn confined in double-wall carbon nanotubes (Cn@DWCNT). Our results indicate that the frequency of the chain mode ...undergoes a non-linear decreasing as pressure increases, in agreement with previous studies of the behavior of carbon chains into multi-wall carbon nanotubes. After the pressure cycle, the Cn modes present an irreversible frequency downshift together with an irreversible upshift (downshift) of the RBM modes (G+ band) of the inner tube. These spectral changes are interpreted as evidence of cross-linking between the carbon chain and the wall of the inner tube. Density functional theory (DFT) calculations were performed in order to shed light on the interpretation of the experimental data. The theoretical calculations show a pressure-induced charge transfer from the nanotube to the carbon chain, thus resulting in an increasing of the C≡C bond length, and consequently, a softening frequency of the Cn Raman mode. Furthermore, an irreversible cross-linking between the tube and Cn is observed when the maximum applied pressure is higher than the pressure of radial tube collapse is predicted by modelling, thus supporting the experimental results.
A carbon nanofiber‐based electrode, exhibiting a large accessible surface area (derived from the nanometer‐sized fiber diameter), high carbon purity (without binder), relatively high electrical ...conductivity, structural integrity, thin web macromorphology, a large reversible capacity (ca. 450 mA h g–1), and a relatively linearly inclined voltage profile, is fabricated by nanofiber formation via electrospinning of a polymer solution and its subsequent thermal treatment. It is envisaged that these characteristics of this novel carbon material will make it an ideal candidate for the anode material of high‐power lithium‐ion batteries (where a high current is critically needed), owing to the highly reduced lithium‐ion diffusion path within the active material.
High‐purity carbon nanofiber webs are fabricated using an electrospinning technique and thermal treatment (see figure). This fibrous carbon possesses properties (e.g., large accessible surface area, good electrical conductivity, high reversible capacity ca. 450 mA h g–1) that make it a potentially excellent candidate for use as the anode material in high‐power lithium‐ion batteries, owing to the highly reduced lithium‐ion diffusion path within the active material.
In the present paper, we will introduce the synthesis and application of carbon nanotubes as filler for nanocomposite materials. Physical and chemical properties such as mechanical strength, thermal ...and electrical conductivity, chemical stability, density and affinity with the matrix vary a lot among different types of carbon nanotubes. We first will overview the main component of nanocomposite, carbon nanotube and its synthesis and purification, and introduce some of the nanocomposites and its applications that we have taken part in the development.
•Ag@TiO2-active decomposition of methanol, acetic acid, 2-propanol and Escherichia coli.•Possible electron storage in Ag nanoparticles hinders charge recombination.•Plasmon resonance is responsible ...for photocatalytic activity under visible light.•Mineralization of bacteria cells was achieved under UV and visible light.•Mechanism study by action spectra and time-resolved microwave conductivity methods.
Commercial titania photocatalysts were modified with 2wt% of silver by photodeposition. The properties of the samples were characterized by DRS, XPS, XRD, FE-SEM and STEM. The modified samples exhibited activity under visible light and enhanced activity under UV irradiation for 2-propanol and acetic acid oxidation, respectively. The time-resolved microwave conductivity (TRMC) analysis indicated that enhanced activity (2.5–8-fold enhancement depending on titania) under UV irradiation was caused by an electron storage in metallic nanoparticles (NPs), and therefore decreasing the recombination between charge carriers. The action spectrum (AS) analysis proved that localized surface plasmon resonance (LSPR) of silver NPs induced the photocatalytic activity under visible light irradiation. The increase of antimicrobial properties under visible light irradiation indicated that not only intrinsic properties of silver in the dark, but also plasmonic properties of Ag@TiO2 were responsible for overall bacteria killing. The evolution of carbon dioxide under both irradiation ranges indicated mineralization of bacteria cells, and therefore possible application of silver-modified titania for decomposition of chemical and biological pollutants.
Adverse reaction to wear and corrosion debris is a cause for concern in total hip arthroplasty (THA). Modular junctions are a potential source of such wear products and are associated with secondary ...pseudotumour formation. We present a consecutive series of 17 patients treated at our unit for this complication following metal-on-highly cross-linked polyethylene (MoP) THA. We emphasise the risk of misdiagnosis as infection, and present the aggregate laboratory results and pathological findings in this series. The clinical presentation was pain, swelling or instability. Solid, cystic and mixed soft-tissue lesions were noted on imaging and confirmed intra-operatively. Corrosion at the head-neck junction was noted in all cases. No bacteria were isolated on multiple pre- and intra-operative samples yet the mean erythrocyte sedimentation rate was 49 (9 to 100) and C-reactive protein 32 (0.6 to 106) and stromal polymorphonuclear cell counts were noted in nine cases. Adverse soft-tissue reactions can occur in MoP THA owing to corrosion products released from the head-neck junction. The diagnosis should be carefully considered when investigating pain after THA. This may avoid the misdiagnosis of periprosthetic infection with an unidentified organism and mitigate the unnecessary management of these cases with complete single- or two-stage exchange.
A high-pressure resonance Raman spectroscopy study of linear carbon chains encapsulated inside multiwalled carbon nanotubes (MWCNTs) is reported. While the frequencies of the tangential modes of ...carbon nanotubes (G band) harden as the pressure increases, the vibrational frequencies of the chain modes (around 1850 cm–1) decrease, thus indicating a softening of the carbon–carbon bonds in this 1D solid. Pressure-induced irreversible structural changes in the linear carbon chains are unveiled by the red shift in the vibrational modes when pressure is released. These results have been interpreted as being due to a coalescence of carbon chains, and this hypothesis is supported by state-of-the-art atomistic reactive molecular dynamics simulations.
We study a heuristic, core-scale model for the transport of polymer particles in a two-phase (oil and water) porous medium. We are motivated by recent experimental observations which report increased ...oil recovery when polymers are injected after the initial waterflood. We propose the recovery mechanism to be microscopic diversion of the flow, where injected particles can accumulate in narrow pore throats and clog it, in a process known as a log-jamming effect. The blockage of the narrow pore channels leads to a microscopic diversion of the water flow, causing a redistribution of the local pressure, which again can lead to the mobilization of trapped oil, enhancing its recovery. Our objective herein is to develop a core-scale model that is consistent with the observed production profiles. We show that previously obtained experimental results can be qualitatively explained by a simple two-phase flow model with an additional transport equation for the polymer particles. A key aspect of the formulation is that the microscopic heterogeneity of the rock and a dynamic altering of the permeability must be taken into account in the rate equations.
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