Development of titanium-doped carbon–carbon composites

The development of titanium-doped carbon matrix–carbon fibre reinforced composites (CCCs) via liquid impregnation of carbon fibre preforms using mesophase pitch is studied. Two different approaches for introducing the dopant into the carbon material are investigated. One consists of doping the matrix precursor followed by the densification of the preform with the doped precursor. The second approach consists of doping the porous preform prior to densification with the undoped mesophase pitch. Titanium-doped CCCs with a very fine distribution of dopant (in the nanometric scale) are obtained by adding TiC nanoparticles to the matrix precursor. Thermal decomposition of titanium butoxide on the carbon preform prior to densification yields doped CCCs with higher titanium content, although with larger dopant size. The combination of these two methods shows the best results in terms of dopant content.     

Modelling of carbon–carbon composite manufacturing processes

This paper is devoted to the modelling of technological processes of manufacturing of siliconized carbon–carbon composites. The developed model describes the changes that occur in the properties of the composites (strength, elastic moduli, shrinkage) during the technological cycle of manufacturing and also the residual stresses generated in composite structures. It is shown that the level of the residual stresses and the character of changes in the properties of carbon–carbon composites essentially differ from those of polymer–matrix composites.     

Modelling nanofiber Mach–Zehnder interferometers for refractive index sensors

In a single-mode silica nanofibre a large amount of the energy of the guided light is in the form of evanescent waves, making it possible to develop a novel sensing element with high sensitivity. Based on theoretical modelling, a highly-sensitive sensor employing a nanofibre-assembled Mach–Zehnder structure is suggested and investigated here. The sensor is used to measure the refractive indices of isopropyl alcohol (IPA) solutions of different concentrations. A phase shift of the guided mode, originating from the change of refractive index of the ambient medium, is obtained. In addition, the important parameters, including sensitivity and detection limit, are also estimated. The results show that Mach–Zehnder interferometric sensor based on nanofibres exhibits the capability of measuring an index variation of ～10^?6. Our simulations are helpful for studying and developing new miniaturised high-performance sensors with high sensitivity.     

Advances in carbon nanotubes as efficacious supports for palladium-catalysed carbon–carbon cross-coupling reactions

Since the 1970s, palladium-catalysed carbon–carbon (C–C) bond formation has made a critical impact in organic synthesis. In early studies, homogeneous palladium catalysts were extensively used for this reaction with limitations such as difficulty in separation and recycling ability. Lately, heterogeneous palladium-based catalysts have shown promise as surrogates for conventional homogeneous catalysts in C–C coupling reactions, since the product is easy to isolate, while the catalyst is reusable and hence sustainable. Recently, a better part of these heterogeneous palladium catalysts are supported on carbon nanotubes (Pd/CNTs), that have shown superior catalytic performance and better recyclability since the CNT support imparts stability to the palladium catalyst. This review discusses the wide variety of surface functionalization techniques for CNTs that improve their properties as catalyst supports, as well as the methods available for loading the catalyst nanoparticles onto the CNTs. It will survey the literature where Pd/CNTs catalysts have been utilized for C–C coupling reactions, with particular emphasis on Suzuki–Miyaura and Mizoroki–Heck coupling reactions. It will also highlight some of the important parameters that affect these reactions.     

Modelling of carbon–carbon composite ablation in rocket nozzles

The modelling of ablation of carbon/carbon (C/C) composites utilized as rocket engine hot parts is addressed under the angle of the competition between bulk transport of reactants and heterogeneous mass transfer, associated to reactivity contrasts between constituent phases. A numerical solver based on a simple model and built on a VOF technique allows direct simulation at two scales. Its application to actual complex materials is performed; the results are consistent with experimental data and help understanding the origin of the material behaviour, either in terms of acquired surface morphology or in terms of effective recession rate.     

Influence of carbon-fiber felts on the development of carbon–carbon composites

Oxidized PAN-fiber felt was carbonized to 600, 1000, and 1800 °C, respectively. Different carbon/carbon composites (C/C composites) were prepared from oxidized PAN-fiber felt, the carbonized felts, and resol-type phenol–formaldehyde resin. These composites were then carbonized and graphized at temperatures of between 600 and 2400 °C. The C/C composite made with oxidized PAN-fiber felt showed a strong fiber/matrix bonding, and those developed from the carbonized felt (heat-treatment of 1800 °C) showed a poor fiber/matrix bonding. The graphitized composites reinforced with the oxidized PAN-fiber felt resulted in having a high flexural strength (325 MPa), and the graphitized composites reinforced with the carbonized felt (carbonized at 1800 °C) had a low flexural strength (9 MPa). It was found that the stress-orientation promoted the formation of the anisotropic texture around the fibers as well as between the fibers. This felt may very well be able to provide a low-cost route for producing multidimensional C/C composites.     

Photoluminescence–electricity–magnetism trifunction simultaneously assembled into one flexible nanofiber

In order to develop new-typed multifunctional composite nanofibers, Eu(BA)₃phen/PANI/Fe₃O₄/PVP trifunctional composite nanofibers with photoluminescence, electricity and magnetism have been successfully fabricated via electrospinning technology. Polyvinyl pyrrolidone (PVP) is used as a matrix to construct composite nanofibers containing different amounts of Eu(BA)₃phen, polyaniline (PANI) and magnetite Fe₃O₄ nanoparticles (NPs). X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, fluorescence spectroscopy and Hall effect measurement system are used to characterize the morphology and properties of the obtained composite nanofibers. The results indicate that the trifunctional composite nanofibers possess excellent luminescent, electrical conductivity and magnetic properties. Fluorescence emission peaks of Eu³⁺ are observed in the Eu(BA)₃phen/PANI/Fe₃O₄/PVP photoluminescent-electrical-magnetism trifunctional composite nanofibers and assigned to the of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (593 nm) of Eu³⁺, and the ⁵D₀ → ⁷F₂ hypersensitive transition at 615 nm is the predominant emission peak. The electrical conductivity reaches up to the order of 10^?3 S/cm. The luminescent intensity, electrical conductivity and saturation magnetization of the composite nanofibers can be tunable by adding various amounts of Eu(BA)₃phen, PANI and Fe₃O₄ NPs. The multifunctional composite nanofibers are expected to possess many potential applications in areas such as electromagnetic interference shielding, microwave absorption, molecular electronics and biomedicine.     

Computational analysis of the thermal conductivity of the carbon–carbon composite materials

Experimental data for carbon–carbon constituent materials are combined with a three-dimensional stationary heat-transfer finite element analysis to compute the average transverse and longitudinal thermal conductivities in carbon–carbon composites. Particular attention is given in elucidating the roles of various micro-structural defects such as de-bonded fiber/matrix interfaces, cracks and voids on thermal conductivity in these materials. In addition, the effect of the fiber precursor material is explored by analyzing PAN-based and pitch-based carbon fibers, both in the same type pitch-based carbon matrix. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibers and (b) a macro scale comparable with the thickness of carbon–carbon composite structures used in the thermal protection systems for space vehicles. The results obtain at room temperature are quite consistent with their experimental counterparts. At high temperatures, the model predicts that the contributions of gas-phase conduction and radiation within the micro-structural defects can significantly increase the transverse thermal conductivity of the carbon–carbon composites.     

Microstructure and mechanical properties of carbon–carbon composites with multilayered pyrocarbon matrix

The effect of matrix microstructure on the mechanical properties of carbon fiber felts infiltrated by isothermal chemical vapor infiltration (CVI) has been studied by optical microscopy, scanning electron microscopy and three-point bending tests. The nonbrittle fracture behavior of the investigated composites is related to multiple crack deflections caused by the interfacial sliding between pyrocarbon layers with a varying texture degree and the delamination microcracking within the highly textured pyrocarbon layer. An increase of the flexural strength is observed by the composite having a multilayered pyrocarbon matrix.     

Tensile properties of carbon fibres and carbon fibre–polymer composites in fire

The effect of fire on the tensile properties of carbon fibres is experimentally determined to provide new insights into the tensile performance of carbon fibre–polymer composite materials during fire. Structural tests on carbon–epoxy laminate reveal that thermally-activated weakening of the fibre reinforcement is the dominant softening process which leads to failure in the event of a fire. This process is experimentally investigated by determining the reduction to the tensile properties and identifying the softening mechanism of T700 carbon fibre following exposure to simulated fires of different temperatures (up to 700 °C) and atmospheres (air and inert). The fibre modulus decreases with increasing temperature (above ～500 °C) in air, which is attributed to oxidation of the higher stiffness layer in the near-surface fibre region. The fibre modulus is not affected when heated in an inert (nitrogen) atmosphere due to the absence of surface oxidation, revealing that the stiffness loss of carbon fibre composites in fire is sensitive to the oxygen content. The tensile strength of carbon fibre is reduced by nearly 50% following exposure to temperatures over the range 400–700 °C in an air or inert atmosphere. Unlike the fibre modulus, the reduction in fibre strength is insensitive to the oxygen content of the atmosphere during fire. The reduction in strength is possibly attributable to very small (under ～100 nm) flaws and removal of the sizing caused by high temperature exposure.     

A global carbon market?

This paper explores the prospects for a global carbon market as the centerpiece of any serious attempt to reach the ambitious goal for greenhouse gas (GHG) reductions set by climate scientists. My aim is to clarify the extent to which we know what policy might best support global decarbonisation. We begin by discussing what we might mean by a global carbon market and its theoretical properties. We then go on to discuss the EU Emissions Trading System experience and the recent experience with the Australian carbon tax. Next, we assess recent carbon market initiatives in the US and in China. My argument is that while establishing the amount of emissions required and dividing it up acceptably between countries requires an enormous scientific and international negotiations effort, the economic instruments to deliver the agreed targets are readily at hand.     

CA SELECTS carbon Graphite Fibers

标题复合材料是由60—95％的熔融含氟高聚物及5—40％碳纤维组成。碳纤维表面用氟气改性。此复合材料在负荷及刚性下具有很高的弯曲温度。例如,把500gMLD(PAN基CF)用(1/9)F/N气在450℃处理1小     

A carbon nanotube gated carbon nanotube transistor with 5 ps gate delay

Semiconducting carbon nanotubes (CNTs) are attractive as channel material for field-effect transistors due to their high carrier mobility. In this paper we show that a local CNT gate can provide a significant improvement in the subthreshold slope of a CNT transistor compared to back gate switching and provide gate delays as low as 5?ps. The CNT gated CNT transistor devices are fabricated using a two-step chemical vapour deposition technique. The measured transfer characteristics are in very good agreement with theoretical modelling results that provide confirmation of the operating principle of the transistors. Gate delays below 2?ps should be readily achievable by reducing the thickness of the gate dielectric.     

A new strategy to assemble enhanced magnetic–photoluminescent bifunction into a flexible nanofiber

A new type of magnetic–photoluminescent bifunctional [Fe₃O₄@Y₂O₃:Eu³⁺]/polyvinyl pyrrolidone (PVP) flexible composite nanofibers were successfully prepared via electrospinning through dispersing Fe₃O₄@Y₂O₃:Eu³⁺ core–shell structured nanoparticles (NPs) into the PVP matrix. The structure, morphology, and properties of the flexible composite nanofibers were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and fluorescence spectroscopy. The diameter of [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers is ca. 128.57 ± 36.72 nm. Fluorescence emission peaks of Eu³⁺ in both Fe₃O₄@Y₂O₃:Eu³⁺ NPs and [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers are observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (533, 586, 592, 599 nm), ⁵D₀ → ⁷F₂ (612 nm), and ⁵D₀ → ⁷F₃ (629 nm) of Eu³⁺ ions. Compared with Fe₃O₄/Y₂O₃:Eu³⁺/PVP nanofibers, [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers possess much stronger luminescence. The as-prepared [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers simultaneously exhibit excellent magnetism and photoluminescent performance. The intensities of magnetism and luminescence of the composite nanofibers can be simultaneously tuned by adjusting the amount of Fe₃O₄@Y₂O₃:Eu³⁺ NPs introduced into the nanofibers. The high performance [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers have potential applications in bioimaging, cell separation, and future nanomechanics.     

Synthesis of β-silicon carbide nanofiber from an exfoliated graphite and amorphous silica

Silicon carbide (SiC) nanofibers were synthesized from exfoliated graphite containing silica particles at 1425 °C in a 25% H₂/Ar atmosphere. Two types of SiC nanofibers with different morphologies were formed depending on the silica content. A higher silica content led to straight nanofibers with a regular diameter size. The SiC nanofibers derived from the exfoliated graphite/40 wt% SiO₂ powder mixture contained a large number of stacking faults and grew along the [1 1 1] direction. A gas–gas reaction mechanism was proposed to explain the formation of SiC nanofibers.     

Fabrication and characterization of three-dimensional nanofiber membrance of PCL–MWCNTs by electrospinning

The uniform and highly smooth nanofibers of poly(ε-caprolactone) (PCL) composited with different multi-walled carbon nanotubes (MWCNTs) content (ranging from 0.1 wt.% to 5 wt.%) were successfully prepared by electrospinning method without the occurrence of bead defects in this study. The PCL–0.5 wt.%MWCNTs nanofiber membrane exhibited the maximum tensile strength (about 1.42 MPa), which was increased by 46% compared with that of electrospun pure PCL nanofiber membrane. Moreover, the PCL–MWCNTs nanofiber membrane exhibited three-dimensional porous structure with a high porosity over 90%. The average diameter of PCL–MWCNTs nanofibers decreased with the addition of MWCNTs and there was a narrow diameter distribution in the range of 52–244 nm when the amount of MWCNTs was 0.5 wt.%. Compared with pure PCL nanofibers, PCL–MWCNTs nanofibers showed accelerating degradation behavior. In addition, the cytotoxicity results revealed that the electrospun PCL–MWCNTs nanofiber membranes possessed good in vitro biocompatibility, and hemolysis and kinetic clotting tests indicated that the PCL nanofiber membranes did not enhance blood coagulation after the addition of MWCNTs. It can be concluded that such kind of electrospun PCL–MWCNTs nanofibers may be promising candidate for tissue engineering scaffold application.     

A novel shortened electrospun nanofiber modified with a ‘concentrated’ polymer brush

Abstract

We report the fabrication of shortened electrospun polymer fibers with a well-defined concentrated polymer brush. We first prepared electrospun nanofibers from a random copolymer of styrene and 4-vinylbenzyl 2-bromopropionate, with number-average molecular weight M_n=105 200 and weight-average molecular weight M_w=296 700 (M_w/M_n=2.82). The fibers had a diameter of 593±74 nm and contained initiating sites for surface-initiated atom transfer radical polymerization (SI-ATRP). Then, SI-ATRP of hydrophilic styrene sodium sulfonate (SSNa) was carried out in the presence of a free initiator and the hydrophobic fibers. Gel permeation chromatography confirmed that M_n and M_w/M_n values were almost the same for free polymers and graft polymers. M_n agreed well with the theoretical prediction, and M_w/M_n was relatively low (<1.3) in all the examined cases, indicating that this polymerization proceeded in a living manner. Using the values of the graft amount measured by Fourier transform infrared spectroscopy, the surface area, and M_n, we calculated the graft density σ as 0.22 chains nm^?2. This value was nearly equal to the density obtained on silicon wafers (σ=0.24 chains nm^?2), which is categorized into the concentrated brush regime. Finally, we mechanically cut the fibers with a concentrated poly(SSNa) brush by a homogenizer. With increasing cutting time, the fiber length became shorter and more homogenous (11±17 μm after 3 h). The shortened fibers exhibited excellent water dispersibility owing to the hydrophilic poly(SSNa) brush layer.     

A new carbon structure in annealed film coatings of the carbon–lead system

Carbon–lead solid solutions coexisting with amorphous carbon have been obtained for the first time in a film coating deposited by ion-plasma sputtering. During subsequent vacuum annealing of carbon–lead films containing more than 68.5 at % Pb, this element almost completely evaporates to leave an amorphous carbon coating on a substrate. During annealing at 1100°C, this amorphous carbon crystallizes into a new hexagonal lattice with unit cell parameters a = 0.7603 nm and c = 0.8168 nm. Characteristic X-ray diffraction data for the identification of this phase are determined.

     

Synthesis of carbon and carbon–nitrogen nanotubes using green precursor: jatropha-derived biodiesel

The jatropha-derived biodiesel, a green precursor was found to be a new and promising precursor for the synthesis of carbon nanotubes (CNTs) and carbon–nitrogen (C–N) nanotubes. The CNTs and C–N nanotubes have been synthesised by spray pyrolysis of biodiesel with ferrocene and ferrocene–acetonitrile, respectively, at elevated temperature under an argon atmosphere. The typical length and diameter of as-grown CNTs are 20?µm and 20–50?nm, respectively. The C–N nanotubes are found in bundles with effective length of ～30?µm and diameter ranging between 30 and 60?nm with bamboo-shaped morphology. The as-grown CNTs and C–N nanotubes were characterised through scanning and transmission electron microscopes, X-ray photoelectron, Raman and Fourier transform infrared spectroscopic techniques. These investigations revealed that the nanotubes synthesised by jatropha-derived biodiesel are clean from carbonaceous impurities and the bamboo compartment formations in C–N nanotubes are due to nitrogen incorporation. The nitrogen concentration in C–N nanotubes decreases with the increase in synthesis temperature.     

In vitro bioactivity of sol–gel-derived hydroxyapatite particulate nanofiber modified titanium

A chemically-etched titanium surface was modified by electrospinning a sol–gel-derived hydroxyapatite (HAp) that was subjected to calcination within the temperature range of 200–1400°C in the normative atmospheric condition. After heat treatment, crystal structures of the filmed titanium oxide and HAp on the titanium’s surface were identified using wide-angle X-ray diffraction. A highly porous layer of HAp was found to have formed on the oxidized titanium surfaces. The surfaces of three different samples; (1) electrospun HAp, (2) HAp calcined at 600°C, and (3) HAp calcined at 800°C, were investigated for their ability to foster promotion, proliferation, and differentiation of human osteoblasts (HOB) (in the 9th passage) in vitro up to 6 days. Among the three samples, cells cultured on the HAp calcined at 800°C titanium surfaces displayed the best results with regard to adhesion, growth, and proliferation of HOB. This novel method for fabrication of titanium substrates would provide a promising improvement for titanium-based medical devices over the current standards, which lack such substrates. These titanium substrates explicitly provide enhanced HOB proliferation in terms of both desired surface properties and their produced bulk quantity.