Carbon Nanofibers (carbon + nanofiber)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science


Selected Abstracts


Effectual dispersion of carbon nanofibers in polyetherimide composites and their mechanical and tribological properties

POLYMER ENGINEERING & SCIENCE, Issue 10 2010
Bin Li
The use of proliferation of nanotechnology in commercial applications is driving requirements for minimal chemical processing and simple processes in industry. Carbon nanofiber (CNF) products possess very high purity levels without the need of purification processing before use and are in growing demand for this quality. Polyetherimide (PEI) has excellent mechanical and thermal performance, but its high viscosity makes its nanocomposites processing very challenging. In this study, a facile melt-mixing method was used to fabricate PEI nanocomposites with as received and physically treated CNFs. The dispersion of CNFs was characterized by scanning electron microscopy, transmitted optical microscopy, and electrometer with large-area electrodes. The results showed that the facile and powerful melt-mixing method is effective in homogeneously dispersing CNFs in the PEI matrix. The flexural and tribological characteristics were investigated and the formation of spatial networks of CNFs and weak interfacial bonding were considered as competitive factors to enhanced flexural properties. The composites with 1.0 wt% CNFs showed flexural strength and toughness increased by more than 50 and 550%, respectively, but showed very high wear rate comparable with that of pure PEI. The length of the CNFs also exerted great influences on both mechanical and tribological behaviors. POLYM. ENG. SCI., 50:1914,1922, 2010. © 2010 Society of Plastics Engineers [source]


Preparation and properties of nanoparticle and long-fiber-reinforced unsaturated polyester composites

POLYMER COMPOSITES, Issue 7 2009
Gang Zhou
In this study, a new approach was used to prepare polymer composites reinforced by both nanoparticles and continuous fibers. Carbon nanofibers were prebound onto glass fiber mats, and then unsaturated polyester composites were prepared by vacuum-assisted resin transfer molding. Mechanical and thermal properties of these composites were measured and compared with those of the composites synthesized by premixing carbon nanofibers with the polymer resin. Flexural strength and modulus of composites improved with the incorporation of nanoparticles. Specifically, the property improvement was higher in the case of the composites prepared by the new prebound method. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficient of unsaturated polyester composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]


Effect of hydrogen on the synthesis of carbon nanofibers by CO disproportionation on ultrafine Fe3O4

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Wenxin Lu
Abstract Carbon nanofibers (CNFs) are grown by catalytic CO disproportionation over ultrafine Fe3O4 catalyst at a hydrogen concentration of 0,29.17%, and the time-depending rates of CNFs growth are continuously monitored and the morphologies of the as-synthesized CNFs are analyzed. Increasing H2 concentration will lower CO dissociation energy and assist catalyst reconstruction so as to shorten the induction period and increase the growth rate of CNFs, but it will also increase the rate of catalyst deactivation because carbon hydrogasification is not possible and carbon diffusion in the catalyst particle is rate limiting. As a result of H2 -induced catalyst reconstruction and carbon deposition, the morphology of the CNFs changes from twisty to helical and to straight and becomes less entangled when the H2 concentration is increased. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Selective Bifunctional Catalytic Conversion of Cellulose over Reshaped Ni Particles at the Tip of Carbon Nanofibers

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 6 2010
Stijn Van, Vyver
Access to cellulose: Carbon nanofibers grown over Ni supported on ,-Al2O3 act as efficient catalysts for the one-pot conversion of cellulose to sugar alcohols, owing to the enhanced accessibility of the water-insoluble substrate towards the active catalytic sites. The new catalyst design concept yields unprecedented results for selective cellulose conversion using inexpensive Ni catalysts. [source]


Cone calorimeter testing of S2 glass reinforced polymer composites

FIRE AND MATERIALS, Issue 7 2009
Alexander B. Morgan
Abstract With the ever increasing demand for fuel savings on vehicles, there is a strong push to replace metal with polymeric + fiber (carbon/glass) composites. However, the replacement of metal with polymeric composites can lead to additional fire risk. Our study focused on glass fiber reinforced polymer composites meant for vehicular structural applications, and flammability performance of these composites was studied by cone calorimetery. The effects of fiberglass loading, nanocomposite use (clay, carbon nanofiber) and polymer type (epoxy, phenolic) were studied under a heat flux of 50kW/m2 to better understand the potential effects that these variables would have on material flammability. It was found that as fiberglass loading increased, flammability decreased, but at a cost to structural integrity of the residual polymer + fiber char. The use of nanocomposites has little effect on reducing flammability in this set of samples, but the use of phenolic resins in comparison with epoxy resins was found to yield the greatest improvements in flammability performance. Further, the phenolic system yielded a higher level of structural integrity to the final polymer + fiberglass char when compared with the other polymer systems of low heat release. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Temperature and strain rate dependences of yield stress of polypropylene composites reinforced with carbon nanofibers

POLYMER COMPOSITES, Issue 12 2009
S.P. Bao
Polypropylene (PP) nanocomposites filled with 0.1, 0.3, 0.5, and 1.0 wt% carbon nanofiber (CNF) were prepared via melt compounding in a twin-screw extruder followed by injection molding. The effects of CNF additions on the structure, mechanical and tensile yielding behavior of PP were investigated. TEM and SEM observations showed that CNFs were dispersed uniformly within PP matrix. Tensile test showed that the yield strength and Young's modulus of PP were improved considerably by adding very low CNF loadings. The reinforcing effect of CNF was also verified from the dynamic mechanical analysis. Impact measurement revealed that the CNF additions were beneficial to enhance the impact toughness of PP. The yield stress of the PP/CNF nanocomposites was found to be strain rate and temperature dependent. The yielding responses of PP/CNF nanocomposites can be described successfully by the Erying's equation and a reinforcing index n. The structure and mechanical property relationship of the nanocomposites is discussed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]


Temperature dependence of electrical resistivity in carbon nanofiber/unsaturated polyester nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 7 2008
Toshiaki Natsuki
This article described the temperature dependence of electrical resistivity for carbon nanofiber (CNF)/unsaturated polyester resin (UPR) nanocomposites prepared by a solvent evaporation method. It was found that the CNF/UPR nanocomposites had quite low electrical percolation threshold due to CNFs having a large aspect ratio and being well dispersed into the UPR matrix. A sharp decrease in the electrical resistivity was observed at about 1 wt% CNF content. The influence of CNF content on the electrical resistivity was investigated as a function of temperature in detail. The nanocomposites showed a positive temperature coefficient effect for the resistivity, and had a strong temperature dependence near the percolation threshold. When the number of thermal cycles was increased, the electrical resistivity decreased and had a weak temperature dependence, especially in the case of melting temperature. Moreover, the size influences of CNFs on the electrical properties of nanocomposites were analyzed and discussed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]


Pt immobilization on TiO2 -embedded carbon nanofibers using photodeposition

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010
S. Kim
Abstract Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO2 using the electrospinning technology. These TiO2 -embedded carbon nanofiber composites (TiO2/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt-deposited TiO2/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2-5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Voltammetric Antioxidant Analysis in Mineral Oil Samples Immobilized into Boron-Doped Diamond Micropore Array Electrodes

ELECTROANALYSIS, Issue 12 2009
Xiaohang Zhang
Abstract Mineral oil microdroplets containing the model antioxidant N,N -didodecyl- N,,N, -diethyl-phenylene-diamine (DDPD) are immobilized into a 100×100 pore-array (ca. 10,,m individual pore diameter, 100,,m pitch) in a boron-doped diamond electrode surface. The robust diamond surface allows pore filling, cleaning, and reuse without damage to the electrode surface. The electrode is immersed into aqueous electrolyte media, and voltammetric responses for the oxidation of DDPD are obtained. In order to further improve the current responses, 20,wt% of carbon nanofibers are co-deposited with the oil into the pore array. Voltammetric signals are consistent with the oxidation of DDPD and the associated transfer of perchlorate anions (in aqueous 0.1,M NaClO4) or the transfer of protons (in aqueous 0.1,M HClO4). From the magnitude of the current response, the DDPD content in the mineral oil can be determined down to less than 1,wt% levels. Perhaps surprisingly, the reversible (or midpoint) potential for the DDPD oxidation in mineral oil (when immersed in 0.1 NaClO4) is shown to be concentration-dependent and to shift to more positive potential values for more dilute DDPD in mineral oil solutions. An extraction mechanism and the formation of a separate organic product phase are proposed to explain this behavior. [source]


Synthesis of Carbon Nanofibers for Mediatorless Sensitive Detection of NADH

ELECTROANALYSIS, Issue 15 2008
Yang Liu
Abstract Highly sensitive amperometric detection of dihydronicotinamide adenine dinucleotide (NADH) by using novel synthesized carbon nanofibers (CNFs) without addition of any mediator has been proposed. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were applied without any oxidation pretreatment to construct the electrochemical sensor. In amperometric detection of NADH, a linear range up to 11.45,,M with a low detection limit of 20,nM was obtained with the CNF-modified carbon paste electrode (CNF-CPE). Good selectivity was exhibited for the simultaneous detection of NADH and its common interferent of ascorbic acid (AA) by differential pulse voltammogram. The attractive electrochemical performance and the versatile preparation process of the CNF-CPE made it a promising candidate for designing effective NADH sensor. [source]


The NADH Electrochemical Detection Performed at Carbon Nanofibers Modified Glassy Carbon Electrode

ELECTROANALYSIS, Issue 14 2007
Adina Arvinte
Abstract In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300,mV is observed in the case of the assembled carbon nanofiber-glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber-modified electrode exhibited a wide linear response range of 3×10,5 to 2.1×10,3,mol L,1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (,A/M cm2), a low detection of limit (LOD=3,) of 11,,M, and a fast response time (3,s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors. [source]


Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Jorge Barcena
Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [source]


The Selective Heating of Iron Nanoparticles in a Single-Mode Microwave for the Patterned Growths of Carbon Nanofibers and Nanotubes

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
Tamara Druzhinina
Abstract The fast and cheap synthesis of carbon nanotubes is addressed in a large number of recent publications. At the same time, microwave-assisted synthesis has also gained interest. Besides the fact that reaction kinetics can be positively influenced by the use of microwave irradiation and advanced reaction conditions can be applied, absorption of microwave radiation depends on the material properties, thus resulting in a selective heating mechanism. The selective heating process allows for locally created temperatures high enough to promote the growth of carbon nanofibers and nanotubes on patterned iron catalyst layers. The resulting fibers are micrometers long, and can be synthesized in short time scales of a few minutes, yielding dense films of carbon fibers with uniform height. Here, the selective heating of surface bound iron nanoparticles is investigated in more detail, and experimental evidence for this effect is provided by utilizing a self-assembled monolayer of n -octadecyltrichlorosilane, which acts as a sensitive indicator for locally elevated temperatures. Special emphasis is placed on the development of an improved and controllable experimental setup that permits the safe and fast fabrication of the desired carbon objects. [source]


Carbon Nanofibers Uniformly Grown on ,-Alumina Washcoated Cordierite Monoliths,

ADVANCED MATERIALS, Issue 12 2006
E. García-Bordejé
A uniform layer of carbon nanofibers is grown on a cordierite monolith by first coating the monolith with a thin layer of ,-alumina. The nanofibers form a thick, uniform layer on the monolith walls as shown in the figure, leading to the formation of a mesoporous and mechanically robust composite. The absence of microporosity in the composite and the ability to tune the thickness of the nanofiber layer suggests that these nanofibers/monolith composites may be useful as catalyst supports for liquid-phase catalytic reactions. [source]


Mechanical behavior of carbon nanofibre-reinforced epoxy composites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010
Sohel Rana
Abstract Epoxy resins are widely used in a variety of applications because of their high chemical and corrosion resistance and good mechanical properties. But few types of epoxy resins are brittle and possess low toughness which makes them unsuitable for several structural applications. In this work, carbon nanofibres have been dispersed uniformly into the epoxy resin at a very low concentration (0.07 vol. %). Improvement of 98% in Young modulus, 24% in breaking stress and 144% in work of rupture was achieved in the best sample. The emphasis is on achieving uniform dispersion of carbon nanofibers into epoxy resin using a combination of techniques such as ultrasonication, use of solvent and surfactants. The fracture surfaces of the specimens were studied under scanning electron microscope to see the fracture mechanism of nanocomposites under tensile load and correlate it to the enhancement in their properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


Functionalization of carbon nanofibers (CNFs) through atom transfer radical polymerization for the preparation of poly(tert -butyl acrylate)/CNF materials: Spectroscopic, thermal, morphological, and physical characterizations

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2008
Marcos Ghislandi
Abstract Vapor-grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert -butyl acrylate (t -BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert -butyl acrylate) (poly(t -BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t -BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326,3335, 2008 [source]


Raman spectroscopic evaluation of polyacrylonitrile-based carbon nanofibers prepared by electrospinning

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2004
Chan Kim
Abstract Poly(acrylonitrile) (PAN) solutions in N,N -dimethylformamide were electrospun into webs consisting of 350 nm ultra-fine fibers. The webs were oxidatively stabilized and followed by heat treatment in the range of 700,1000°C. Characterization of the microstructure of PAN-based carbon nanofibers was performed by x-ray diffraction, field-emission scanning electron microscopy, electrical conductivity and Raman spectroscopy. The Lc(002) and La(10) values were calculated to be 1.85,2.15 and 2.23,3.36 nm, respectively. The Lc(002) and La(10) values increased by about 86% and 66%, respectively, when the heat treatment temperature (HTT) was increased from 700 to 1000°C. The electrical conductivity of carbonized PAN nanofiber webs increased with increasing carbonization temperature, being 6.8 × 10,3 and 1.96 S cm,1 at 700 and 1000°C, respectively. The D and G bands from Raman scattering were fitted into a Gaussian,Lorentzian hybridized function, and the crystallite sizes in the nanofibers were evaluated from the R -values determined from the ratios of the intensity of the G band to that of the D band. The domain size of the graphitic layers was in the range 1.6,3.2 nm with higher values at higher HTT. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Temperature and strain rate dependences of yield stress of polypropylene composites reinforced with carbon nanofibers

POLYMER COMPOSITES, Issue 12 2009
S.P. Bao
Polypropylene (PP) nanocomposites filled with 0.1, 0.3, 0.5, and 1.0 wt% carbon nanofiber (CNF) were prepared via melt compounding in a twin-screw extruder followed by injection molding. The effects of CNF additions on the structure, mechanical and tensile yielding behavior of PP were investigated. TEM and SEM observations showed that CNFs were dispersed uniformly within PP matrix. Tensile test showed that the yield strength and Young's modulus of PP were improved considerably by adding very low CNF loadings. The reinforcing effect of CNF was also verified from the dynamic mechanical analysis. Impact measurement revealed that the CNF additions were beneficial to enhance the impact toughness of PP. The yield stress of the PP/CNF nanocomposites was found to be strain rate and temperature dependent. The yielding responses of PP/CNF nanocomposites can be described successfully by the Erying's equation and a reinforcing index n. The structure and mechanical property relationship of the nanocomposites is discussed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]


Preparation and properties of nanoparticle and long-fiber-reinforced unsaturated polyester composites

POLYMER COMPOSITES, Issue 7 2009
Gang Zhou
In this study, a new approach was used to prepare polymer composites reinforced by both nanoparticles and continuous fibers. Carbon nanofibers were prebound onto glass fiber mats, and then unsaturated polyester composites were prepared by vacuum-assisted resin transfer molding. Mechanical and thermal properties of these composites were measured and compared with those of the composites synthesized by premixing carbon nanofibers with the polymer resin. Flexural strength and modulus of composites improved with the incorporation of nanoparticles. Specifically, the property improvement was higher in the case of the composites prepared by the new prebound method. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficient of unsaturated polyester composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]


Effectual dispersion of carbon nanofibers in polyetherimide composites and their mechanical and tribological properties

POLYMER ENGINEERING & SCIENCE, Issue 10 2010
Bin Li
The use of proliferation of nanotechnology in commercial applications is driving requirements for minimal chemical processing and simple processes in industry. Carbon nanofiber (CNF) products possess very high purity levels without the need of purification processing before use and are in growing demand for this quality. Polyetherimide (PEI) has excellent mechanical and thermal performance, but its high viscosity makes its nanocomposites processing very challenging. In this study, a facile melt-mixing method was used to fabricate PEI nanocomposites with as received and physically treated CNFs. The dispersion of CNFs was characterized by scanning electron microscopy, transmitted optical microscopy, and electrometer with large-area electrodes. The results showed that the facile and powerful melt-mixing method is effective in homogeneously dispersing CNFs in the PEI matrix. The flexural and tribological characteristics were investigated and the formation of spatial networks of CNFs and weak interfacial bonding were considered as competitive factors to enhanced flexural properties. The composites with 1.0 wt% CNFs showed flexural strength and toughness increased by more than 50 and 550%, respectively, but showed very high wear rate comparable with that of pure PEI. The length of the CNFs also exerted great influences on both mechanical and tribological behaviors. POLYM. ENG. SCI., 50:1914,1922, 2010. © 2010 Society of Plastics Engineers [source]


Composites of carbon nanofibers and thermoplastic polyurethanes with shape-memory properties prepared by chaotic mixing

POLYMER ENGINEERING & SCIENCE, Issue 10 2009
Guillermo A. Jimenez
Composites of carbon nanofibers (CNFs), oxidized carbon nanofibers (ox-CNFs), and shape-memory thermoplastic polyurethane (TPU) were prepared in a chaotic mixer and their shape-memory properties evaluated. The polymer was synthesized from 4,4,-diphenylmethane diisocyanate, 1,4-butanediol chain extender, and semicrystalline poly(,-caprolactone) diol soft segments. The shape-memory action was triggered by both conductive and resistive heating. It was found that soft segment crystallinity and mechanical reinforcement by nanofibers produced competing effects on shape-memory properties. A large reduction in soft segment crystallinity in the presence of CNF and stronger mechanical reinforcement by well-dispersed ox-CNF determined the shape-memory properties of the respective composites. It was found that the maximum shape recovery force, respectively, 3 and 4 MPa, was obtained in the cases of 5 and 1 wt% CNF and ox-CNF, respectively, compared with ,1.8 MPa for unfilled TPU. The degree of soft segment and hard segment phase separation and thermal stability of the composites were analyzed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers. [source]


Orientated crystallization in drawn thermoplastic polyimide modified by carbon nanofibers

POLYMER ENGINEERING & SCIENCE, Issue 2 2009
Valentina E. Smirnova
The solid state crystallization in drawn thermoplastic polyimide films is studied as a function of draw ratio (DR) under the effect of vapor grown carbon fiber nanoinclusions. The nucleating effect of the nanoinclusions coupled with the orientation effect of drawing generates a unique orientated layered lamellar structure, characteristic of smectic-like mesophase. The degree of draw induced orientated crystallization increases with the content of nanoinclusions and with the DR, and is reflected in the mechanical behavior of the film. Generally, the Young's modulus and the yield point of the drawn crystalline films in the drawing direction are significantly higher compared with the noncrystalline counterparts. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source]


Effect of hydrogen on the synthesis of carbon nanofibers by CO disproportionation on ultrafine Fe3O4

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Wenxin Lu
Abstract Carbon nanofibers (CNFs) are grown by catalytic CO disproportionation over ultrafine Fe3O4 catalyst at a hydrogen concentration of 0,29.17%, and the time-depending rates of CNFs growth are continuously monitored and the morphologies of the as-synthesized CNFs are analyzed. Increasing H2 concentration will lower CO dissociation energy and assist catalyst reconstruction so as to shorten the induction period and increase the growth rate of CNFs, but it will also increase the rate of catalyst deactivation because carbon hydrogasification is not possible and carbon diffusion in the catalyst particle is rate limiting. As a result of H2 -induced catalyst reconstruction and carbon deposition, the morphology of the CNFs changes from twisty to helical and to straight and becomes less entangled when the H2 concentration is increased. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Catalytic decomposition of methane over supported Ni catalysts with different particle sizes

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Sun Yunfei
Abstract Methane decomposition on ,-Al2O3 -supported Ni catalysts, as a method for the production of carbon nanofibers (CNFs) and CO-free hydrogen, has been investigated to show the effect of catalyst particle size on the rate and yield of CNFs formation. The catalysts were prepared by deposition,precipitation with different calcination temperature ranging from 725 to 1025 K so as to have different initial particle sizes. The results show that catalysts with smaller initial particle sizes had higher initial growth rate but experienced fast deactivation. The lifetime of the catalyst, ending at the inflection point on the rate curve of CNFs growth, could well represent the yield of CNFs of the catalyst, and the maximal yield of CNFs was achieved on the Ni catalysts calcinated at 823 K and with a particle size of around 56 nm. However, the diameters of the grown CNFs were not directly related to the initial size of the catalysts, because of particle sintering and breaking during catalyst reduction or CNFs formation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Fabrication and Characteristics of Carbon Nanofiber-Reinforced Carbon/Carbon Composites by Fast Catalytic Infiltration Processes,

CHEMICAL VAPOR DEPOSITION, Issue 1-3 2009
Jin-Cao Zhang
Abstract The simultaneous in-situ growth of carbon nanofibers (CNFs) and densification of a CNFs/CF hybrid multiscale felt are accomplished in a single step by thermal gradient chemical vapor infiltration using Fe as the catalyst and vaporized kerosene under atmospheric pressure. A three-dimensional CNF network which could bridge dissimilar components of composites is formed on carbon fibers (CFs). The length of CNFs can reach several micrometers and the diameters are about 80,nm. Smooth and rough surface densified CNFs can be produced after further higher temperature infiltration. CNFs, anchoring to CFs by the adherence of the catalyst nanoparticles, enhance the bonding between CFs and pyrocarbon as well as promoting the formation of a rough laminar pyrocarbon matrix. The deposition mechanisms and physical model are also discussed. This fast catalytic infiltration process can be applied to other ceramic materials and has significant enlargement potential. [source]


In-Situ Encapsulation of Nickel Particles in Electrospun Carbon Nanofibers and the Resultant Electrochemical Performance

CHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009
Liwen Ji
Loaded nanofibers: Ni nanoparticle-loaded carbon nanofibers, which exhibit high reversible lithium-storage capacity, excellent cycling performance, and remarkably enhanced rate capability, are fabricated by using the electrospinning technique and the subsequent stabilization and carbonization processes (see figure). [source]


The Use of Natural Materials in Nanocarbon Synthesis

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 11 2009
Dang Sheng Su Dr.
Abstract Nanomaterials are shifting from laboratory-scale preparation to industrial production. The energy costs and starting materials (feedstock, catalyst, and support) consumed or used in the mass production of nanomaterials are issues that limit their broad application. Natural materials, such as sand, rock, and lava, contain small or trace amounts of metals or metal oxides of nanometer-scale sizes and have been recently used as catalysts for the production of carbon nanotubes (CNTs), providing an interesting way to lower the production cost of CNTs. However, the sustainability of the whole production process still needs to be explored. Layered minerals (e.g., clays) are used to produce CNT,clay hybrids, which can be further used to synthesize polymer,CNT,clay nanocomposites. Natural materials and some byproducts of industrial production processes have been explored as carbon sources for nanocarbon synthesis. This Minireview highlights some recent promising work and prospects for the use of natural materials in the synthesis of CNTs, carbon nanofibers (CNFs), and nanocomposites, and their applications in catalysis and in materials science. [source]


Highly Sensitive Thin Film Sensor Based on Worm-like Carbon Nanofibers for Detection of Ammonia in Workplace

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2008
Jia-Zhi WANG
Abstract A thin film sensor was fabricated using the mixture of worm-like carbon nanofibers (WCNF), which were synthesized using aluminium supported iron catalysts via chemical vapour deposition, and glass dust in proportion of 3:2, combined by drops of terpineol. The morphology of the catalyst, the worm-like carbon nanofibers and the film surface were investigated with the help of TEM and SEM. Low single-potential signal was employed to investigate gas sensitivity of the sensor to the deleterious ammonia, in atmospheric pressure at room temperature. The results suggest that the sensor has high sensitivity at low concentration (0.175,0.35 mg/m3), perfect reproducibility, and a fast response time (0.05 s) and restoration time (1 min). [source]


Single Negative Metamaterials in Unstructured Polymer Nanocomposites Toward Selectable and Controllable Negative Permittivity

ADVANCED MATERIALS, Issue 41 2009
Bin Li
Negative permittivity is realized in unstructured imide polymer/carbon nanofiber (CNF) nanocomposites. The microstructure of CNFs is one of the factors that exert profound effects on the permittivity. Compared with cup-stacked CNFs-filled polyetherimide nanocomposites, the negative permittivity in the herringbone CNFs-filled nanocomposites is inhibited, occurring only at the frequencies near resonance, where the permittivity dips slightly into the negative region. [source]