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1

A new method of chaining carbon nanofibers in epoxy  

International Nuclear Information System (INIS)

In this paper, a new and innovative process for assembling chains of carbon nanofibers (CNFs) in epoxy, uniquely different from those generally used for chaining particles in a liquid medium, is presented. Chains of aligned CNFs are assembled in a region rich in CNFs and extended into regions where there are no CNFs. A physical explanation of the process is provided based on the conductive nature of the CNFs. By contacting the chains with the electrodes, the process of chain growth is expedited and well-ordered parallel chains with equal spacing are grown over distances of 2 cm

2008-08-13

2

A new method of chaining carbon nanofibers in epoxy  

Energy Technology Data Exchange (ETDEWEB)

In this paper, a new and innovative process for assembling chains of carbon nanofibers (CNFs) in epoxy, uniquely different from those generally used for chaining particles in a liquid medium, is presented. Chains of aligned CNFs are assembled in a region rich in CNFs and extended into regions where there are no CNFs. A physical explanation of the process is provided based on the conductive nature of the CNFs. By contacting the chains with the electrodes, the process of chain growth is expedited and well-ordered parallel chains with equal spacing are grown over distances of 2 cm.

Sharma, A; Bakis, C E [Department of Engineering Science and Mechanics, Penn State University, University Park, PA 16802 (United States); Wang, K W [Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109 (United States)], E-mail: axs923@psu.edu, E-mail: cbakis@psu.edu, E-mail: kwwang@umich.edu

2008-08-13

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Controllable synthesis of helical, straight, hollow and nitrogen-doped carbon nanofibers and their magnetic properties  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: The helical, straight and hollow carbon nanofibers can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. Display Omitted Highlights: ? CNFs were synthesized via pyrolysis of acetylene on copper NPs. ? The helical, straight, hollow and N-doped CNFs can be selectively synthesized. ? The growth mechanism of different types of CNFs was proposed. -- Abstract: Carbon nanofibers (CNFs) with various morphologies were synthesized by catalytic pyrolysis of acetylene on copper nanoparticles which were generated from the in situ decomposition of copper acetylacetonate. The morphology of the pristine and acid-washed CNFs was investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. Helical, straight and hollow CNFs can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. The growth mechanism for these three types of CNFs was proposed.

Li, Xun [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China); State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China); Xu, Zheng, E-mail: zhengxu@nju.edu.cn [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China)

2012-12-15

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Controllable synthesis of helical, straight, hollow and nitrogen-doped carbon nanofibers and their magnetic properties  

International Nuclear Information System (INIS)

Graphical abstract: The helical, straight and hollow carbon nanofibers can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. Display Omitted Highlights: ? CNFs were synthesized via pyrolysis of acetylene on copper NPs. ? The helical, straight, hollow and N-doped CNFs can be selectively synthesized. ? The growth mechanism of different types of CNFs was proposed. -- Abstract: Carbon nanofibers (CNFs) with various morphologies were synthesized by catalytic pyrolysis of acetylene on copper nanoparticles which were generated from the in situ decomposition of copper acetylacetonate. The morphology of the pristine and acid-washed CNFs was investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. Helical, straight and hollow CNFs can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. The growth mechanism for these three types of CNFs was proposed.

2012-12-01

5

Modification of powdered activated carbon for the production of carbon nano fibers (CNFs)  

International Nuclear Information System (INIS)

Full text: In the present work, powdered activated carbon (PAC) was modified and used for the production of carbon nano fibers (CNFs). The modification of PAC was done by the impregnation of nickel on the surface of the activated carbon using the wet impregnation method. Variable weight percentage ratios of the catalyst (nickel) ratio were used. The nano fibers were synthesized on the surface of modified PAC by using the Chemical Vapor Deposition (CVD) method at a temperature of ?680 degree Celsius for one hour in the presence of acetylene as a carbon source. FESEM, TEM, and TGA were used for the characterization of the product. (author)

2009-11-03

6

Laccase Biosensor Based on Electrospun Copper/Carbon Composite Nanofibers for Catechol Detection  

Directory of Open Access Journals (Sweden)

Full Text Available The study compared the biosensing properties of laccase biosensors based on carbon nanofibers (CNFs and copper/carbon composite nanofibers (Cu/CNFs. The two kinds of nanofibers were prepared by electrospinning and carbonization under the same conditions. Scanning electron microscopy (SEM, X-ray diffraction (XRD and Raman spectroscopy were employed to investigate the morphologies and structures of CNFs and Cu/CNFs. The amperometric results indicated that the Cu/CNFs/laccase(Lac/Nafion/glass carbon electrode (GCE possessed reliable analytical performance for the detection of catechol. The sensitivity of the Cu/CNFs/Lac/Nafion/GCE reached 33.1 ?A/mM, larger than that of CNFs/Lac/Nafion/GCE. Meanwhile, Cu/CNFs/Lac/Nafion/GCE had a wider linear range from 9.95 × 10?6 to 9.76 × 10?3 M and a lower detection limit of 1.18 ?M than CNFs/Lac/Nafion/GCE. Moreover, it exhibited a good repeatability, reproducibility, selectivity and long-term stability, revealing that electrospun Cu/CNFs have great potential in biosensing.

Jiapeng Fu

2014-02-01

7

Carbon nanofibers grown on metallic filters as novel catalytic materials  

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Carbon nanofibers (CNF) were synthesized on sintered metal fibers (SMF) filters of nickel and Ni-containing alloys (Inconel, stainless steel (SS)) by thermal chemical vapor deposition of ethane in the presence of hydrogen at not, vert, similar660 °C. The CNFs were formed directly over the SMF filters without deposition of metal particles. The catalytic active sites leading to the CNF formation were attained by oxidation–reduction of the SMF filter. The CNFs present platelet morphology as d...

Tribolet, Pascal; Kiwi-minsker, Lioubov

2005-01-01

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Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic-CNFs composites  

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Alumina-carbon nanofibres (CNFs) and silicon carbide-CNFs nanocomposites with different volume fraction of CNFs (0-100vol.%) were obtained by spark plasma sintering. The effect of CNFs content on the tribological behaviour in dry sliding conditions on the ceramic-carbon nanocomposites has been investigated using the ball-on-disk technique against alumina balls. The wear rate of ceramic-CNFs nanocomposites decreases with CNFs increasing content. The friction coefficient of the Al 2O 3/CNFs and...

Borrell Toma?s, Mari?a Amparo; Torrecillas San Milla?n, Ramo?n; Rocha, Victoria G.; Ferna?ndez Valde?s, Adolfo; Bonache, V.; Salvador, M. D.

2012-01-01

9

Growth of bridging carbon nanofibers in cracks formed by heat-treating iron oxide thin sheets in acetylene gas  

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Full Text Available We produced novel carbon nanofibers (CNFs by oxidizing high-purity iron foil and then carburizing it in acetylene gas flow. This formed cracks in the heat-treated iron foil with CNFs bridging the two walls of each crack. The CNFs were drawn out from the walls as the crack opened during heat treatment. This will be a new method to grow and arrange carbon nanotubes and nanosheets without using metal nanoparticles or template substrates.

Takeshi Hikata

2013-04-01

10

Effects of Microstructure of Carbon Nanofibers for Amperometric Detection of Hydrogen Peroxide  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) with different microstructures, including platelet-carbon nanofibers (PCNFs), fish-bone-carbon nanofibers (FCNFs), and tube-carbon nanofibers (TCNFs), were synthesized, characterized, and evaluated for electrochemical sensing of hydrogen peroxide. The CNFs studied here can show several microstructures in which various stacked morphologies and their sizes and graphite-layer ordering can be well controlled. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of hydrogen peroxide. Sensors of PCNFs/GC, FCNFs/GC, and TCNFs/GC were used in the amperometric detection of H2O2 in a solution of 0.05 M phosphate buffered saline solution (pH 7.4).

Li, Zhizhou; Cui, Xiaoli; Zheng, Junsheng; Wang, Qingfei; Lin, Yuehe

2007-08-10

11

Pulsed laser dewetting of nickel catalyst for carbon nanofiber growth  

International Nuclear Information System (INIS)

We present a pulsed laser dewetting technique that produces single nickel catalyst particles from lithographically patterned disks for subsequent carbon nanofiber growth through plasma enhanced chemical vapor deposition. Unlike the case for standard heat treated Ni catalyst disks, for which multiple nickel particles and consequently multiple carbon nanofibers (CNFs) are observed, single vertically aligned CNFs could be obtained from the laser dewetted catalyst. Different laser dewetting parameters were tested in this study, such as the laser energy density and the laser processing time measured by the total number of laser pulses. Various nickel disk radii and thicknesses were attempted and the resultant number of carbon nanofibers was found to be a function of the initial disk dimension and the number of laser pulses

2008-06-11

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Preparation and Catalytic Activity of Carbon Nanofibers Anchored Metallophthalocyanine in Decomposing Acid Orange 7  

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Full Text Available Amine-modified CNFs (AN-CNFs were first obtained through the Billups reaction from carbon nanofibers (CNFs, and were used as supports of cobalt tetracarboxylphthalocyanine (CoTCPc for the catalytic oxidation of Acid Orange 7 (AO7 in the CoTCPc-AN-CNFs/H2O2 system. CNFs, AN-CNFs and CoTCPc-AN-CNFs were characterized by X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy and N2 adsorption-desorption. The oxidative decoloration of AO7 in the presence of CoTCPcNa-AN-CNFs and H2O2 was investigated by UV-Vis absorption spectra. The results showed that AO7 was oxidized efficiently in the CoTCPcNa-AN-CNFs /H2O2 system. The benzene ring was first introduced between CNFs and MPcs. However, its catalytic efficiency and electronic properties would not weaken. New catalytic mechanism may display in this CoTCPcNa-AN-CNFs /H2O2 system.

Baocheng Zhou

2014-02-01

13

Boric oxide deposition on carbon nanofibers for oxidation resistance.  

Science.gov (United States)

The boric oxide deposition was performed to improve the oxidation resistivity of carbon nanofiber (CNF) from electrospinning at elevated temperatures. The stabilized electrospun polyacrylonitrile (PAN) nanofibers were coated with boric oxide, followed by heat treatment up to 1000, 1200, and 1400 degrees C in an inert nitrogen atmosphere. The relative oxidation resistance of boric oxide-coated CNFs showed oxidation resistive property, which was determined by weight loss after running a thermogravimetric analyzer (TGA) under air flow. The data were used for the calculations of activation energies through Arrhenius plot. The oxidation resistance of the boric oxide-coated CNFs was depended on the heat treatment temperature, the higher the temperature more resistive to oxidation. The boric oxide-coated CNFs showed extended oxidation resistivity as remaining 40-83% (w) of the original weight at the high temperature 1000 degrees C under air. PMID:23882810

Chae, Hyang Hoon; Kim, Bo-Hye; Yang, Kap Seung; Woo, Hee-Gweon

2013-08-01

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Tuning the Acid/Metal Balance of Carbon Nanofiber-Supported Nickel Catalysts for Hydrolytic Hydrogenation of Cellulose  

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Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/ ...

2012-01-01

15

Growth of carbon nanofibers on metal-catalyzed substrates by pulsed laser ablation of graphite  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) were grown on metal-catalyzed Si substrates by pulsed laser ablation of graphite. Metal catalysts, Ni, NiCo, Pd and PdNi, were respectively deposited on Si substrates with a SiO2 layer of 200-nm thickness by a dip coat method, and the substrates placed in a laser oven apparatus. By pulsed laser ablation of graphite for 2 hours, CNFs were grown at oven temperatures ? 1000deg. C. Diameters of grown CNFs were about 20-30 nm by scanning electron microscopy, and increased with oven temperature. The difference of CNF growth by the catalysts was shown. Pd-contained catalysts grew thicker CNFs than the other catalysts; while PdNi and NiCo yielded a higher number density of CNFs than the other catalysts. CNF diameter and length changed according to the substrate position from the target. We also discussed the growth mechanism of CNFs with this method

2007-04-01

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Surface decoration and dispersibility of carbon nanofibers in aqueous surfactant solution  

Science.gov (United States)

As a novel functional nanomaterial, the dispersion effect of carbon nanofibers (CNFs) has a significant influence on the application of CNFs in the composites. Two effective surfactants, methylcellulose (MC) and polycarboxylate superplasticizer, were used to analyze the dispersion of CNFs in aqueous solution. A method utilizing ultrasonic processing was employed to achieve a homogenous CNF suspension, and the dispersion effect was further characterized by the method of measuring ultraviolet absorbency (UV absorbency), zeta potential, surface tension and transmission electron microscopy (TEM) micrographs. The results show that the zeta potential and surface tension reach the saturation plateau at MC concentration and polycarboxylate superplasticizer concentration of about 0.4 and 0.8 g/L, respectively, which reflects that the optimum concentration ratio of MC to CNFs is 2: 1, and the optimum dispersing polycarboxylate superplasticizer to CNFs ratio of 4: 1 is required to achieve dispersions with maximum achievable dispersion of CNFs.

Wang, B. M.; Zhang, Y.; Liu, S.

2014-03-01

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Catalytic growth of carbon nanofibers on Cr nanoparticles on a carbon substrate: adsorbents for organic dyes in water  

Energy Technology Data Exchange (ETDEWEB)

We have produced carbon nanofibers (CNFs) using leather waste that had been tanned with a chromium bath, and when dried contained Cr{sub 2}O{sub 3}. Suitable reduction processing produced a carbon substrate with supported nanoparticles of chromium metal. Powder X-ray diffraction showed that the Cr{sub 2}O{sub 3} is reduced on the carbon surface to produce CrC and metal Cr, which is the effective catalyst for the CNFs growth. The CNF arrays were confirmed by TEM images. Raman data revealed that the synthesized CNFs have a poor-quality graphite structure which favors their use in adsorption processes. These CNFs presented higher affinity to adsorb anionic dyes, whereas the cationic dyes are better adsorbed on the carbon substrate. The low-cost and availability of the carbon precursor makes their potential use to produce CNFs of interest.

Alves de Oliveira, Luiz Carlos, E-mail: luizoliveira@qui.ufmg.br; Candido da Silva, Adilson; Rodrigues Teixeira Machado, Alan [ICEx, Universidade Federal de Minas Gerais, Departamento de Quimica (Brazil); Diniz, Renata [Universidade Federal de Juiz de Fora, Departamento de Quimica (Brazil); Cesar Pereira, Marcio [Universidade Federal dos Vales do Jequitinhonha e Mucuri, Instituto de Ciencia, Engenharia e Tecnologia (Brazil)

2013-05-15

18

Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials  

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In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as ...

Mudimela, Prasantha R.; Nasibulina, Larisa I.; Nasibulin, Albert G.; Andrzej Cwirzen; Markus Valkeapää; Karin Habermehl-Cwirzen; Malm, Jari E. M.; Karppinen, Maarit J.; Vesa Penttala; Koltsova, Tatiana S.; Tolochko, Oleg V.; Kauppinen, Esko I.

2009-01-01

19

Production of Carbon Nanofibers Using a CVD Method with Lithium Fluoride as a Supported Cobalt Catalyst  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanofibers (CNFs have been synthesized in high yield (>70% by catalytic chemical vapor deposition (CCVD on Co/LiF catalyst using acetylene as carbon source. A novel catalyst support (LiF is reported for the first time as an alternative for large-scale production of carbon nanofibers while purification process of nanofibers is easier. In our experiment, the sealed furnace was heated at 700∘C for 0.5 hour (the heating rate was 10∘C/min and then cooled to room temperature in the furnace naturally. Catalytic chemical vapor deposition is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanofibers (CNFs. The obtained sample was sequentially washed with ethanol, dilutes acid, and distilled water to remove residual impurities, amorphous carbon materials, and remaining of catalyst, and then dried at 110∘C for 24 hours. The combined physical characterization through several techniques, such as high-resolution transmission electron microscope (TEM, scanning electron microscope (SEM, thermogarvimetric analysis (TGA, and zeta-sizer and Raman spectroscopy, allows determining the geometric characteristic and the microstructure of individual carbon nanofibers. Catalytic chemical vapor deposition is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanofibers (CNFs. As a matter of fact, the method of CCVD guarantees the production of CNFs for different applications.

S. A. Manafi

2008-02-01

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Preparation of Size-Controlled Hat-Stacked Carbon Nanofibers  

Science.gov (United States)

Hat-stacked carbon nanofibers (H-CNFs) were size-separated using a multi-step microfiltration process employing polycarbonate membrane filters with respective cylindrical pore diameters of 2.0, 1.2 and 0.4 ?m after being cut and dispersed in distilled water using sonication in a mixture of concentrated H2SO4 and HNO3. The average length of separated H-CNFs was 2.4 ?m, 1.2 ?m and 0.6 ?m, respectively.

Sato, Y.; Yokoyama, A.; Motomiya, K.; Jeyadevan, B.; Tohji, K.

2007-03-01

 
 
 
 
21

A novel catalyst for synthesis of styrene: carbon nanofibers immobilized on activated carbon.  

Science.gov (United States)

Carbon NanoFibers (CNFs) with hierarchically structure have been immobilized onto Activated Carbon (AC) by impregnation with an aqueous solution of Fe(CH3COO)2, reduction and subsequent chemical vapor decomposition of ethylene. The morphology of the CNFs can be modulated by adjusting the pH of the Fe(CH3COO)2 solution used for impregnating the AC. A stable yield of 35% in the oxidative dehydrogenation of ethylbenzene to styrene was obtained at a temperature of 673 K, around 200 K lower than the current industrial process. The immobilized CNFs on AC catalysts combine the catalytic properties of the carbon nanofibers and the suprastructure of the AC host. The final material is an easy to handle active catalyst, with an open structure of immobilized CNFs avoiding the pressure drop problem, which is typically observed for fine powder forms of CNFs. The immobilized CNFs on AC are attractive for gas-phase fixed-bed industrial applications. PMID:18330163

Delgado, J J; Chen, X W; Su, D S; Hamid, Sharifah B A; Schlögl, R

2007-10-01

22

A catechol biosensor based on electrospun carbon nanofibers.  

Science.gov (United States)

Carbon nanofibers (CNFs) were prepared by combining electrospinning with a high-temperature carbonization technique. And a polyphenol biosensor was fabricated by blending the obtained CNFs with laccase and Nafion. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FE-SEM) were, respectively, employed to investigate the structures and morphologies of the CNFs and of the mixtures. Cyclic voltammetry and chronoamperometry were employed to study the electrocatalysis of the catechol biosensor. The results indicated that the sensitivity of the biosensor was 41 µA·mM(-1), the detection limit was 0.63 µM, the linear range was 1-1310 µM and the response time was within 2 seconds, which excelled most other laccase-based biosensor reported. Furthermore, the biosensor showed good repeatability, reproducibility, stability and tolerance to interferences. This novel biosensor also demonstrated its promising application in detecting catechol in real water samples. PMID:24778958

Li, Dawei; Pang, Zengyuan; Chen, Xiaodong; Luo, Lei; Cai, Yibing; Wei, Qufu

2014-01-01

23

A catechol biosensor based on electrospun carbon nanofibers  

Science.gov (United States)

Summary Carbon nanofibers (CNFs) were prepared by combining electrospinning with a high-temperature carbonization technique. And a polyphenol biosensor was fabricated by blending the obtained CNFs with laccase and Nafion. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FE-SEM) were, respectively, employed to investigate the structures and morphologies of the CNFs and of the mixtures. Cyclic voltammetry and chronoamperometry were employed to study the electrocatalysis of the catechol biosensor. The results indicated that the sensitivity of the biosensor was 41 µA·mM?1, the detection limit was 0.63 µM, the linear range was 1–1310 µM and the response time was within 2 seconds, which excelled most other laccase-based biosensor reported. Furthermore, the biosensor showed good repeatability, reproducibility, stability and tolerance to interferences. This novel biosensor also demonstrated its promising application in detecting catechol in real water samples.

Li, Dawei; Pang, Zengyuan; Chen, Xiaodong; Luo, Lei; Cai, Yibing

2014-01-01

24

Acetylene decomposition to helical carbon nanofibers over supported copper catalysts  

International Nuclear Information System (INIS)

The helical carbon nanofibers (CNFs), synthesized at relatively low temperatures (lower than 250 deg. C) by using Cu as a catalyst, SiO2, TiO2, Al2O3, MgO as supports and acetylene as gas source, has been investigated. The products were characterized by field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The morphologies of obtained products influenced by the types of supports and weight ratios (Cu/support = 1:1, 1:5, and 1:10) were discussed. The average diameter of the helical CNFs was about 80 nm, and these CNFs had the same coil pitch, and coil diameter

2007-12-04

25

Electron gun using carbon-nanofiber field emitter  

International Nuclear Information System (INIS)

An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10< E<20 keV were focused by the electrostatic lens and impinged on a W target for x-ray radiography. Analyzing the recorded x-ray radiographs, the focal spot size of the electron beam extracted from the CNFs was estimated to be D<50 ?m in diameter. Superior performance was realized by using CNFs with larger fiber radii (100-500 nm) grown sparsely on the metal tips, which were installed in a holder at the short length L=0.5 mm

2007-01-01

26

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers composite film electrodes  

International Nuclear Information System (INIS)

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The large area CNTs-CNFs film was directly grown on Ni plate by low pressure and low temperature thermal chemical vapor deposition. The CNTs-CNFs electrodes have great advantages such as low cost, easy operation, long-term reproducibility, and integrity of monolithic CNTs-CNFs film and current collector. Batch-mode experiments at low voltage (0.4-2 V) were conducted in a continuously recycling system to investigate the electrosorption process. Purification of water with good reproducibility was achieved because of optimal pore size distribution of CNTs-CNFs composite films

2006-07-31

27

Electrochemical catalytic activity for oxygen reduction reaction of nitrogen-doped carbon nanofibers.  

Science.gov (United States)

The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer. PMID:22121714

Kim, Jiyoung; Lim, Seongyop; Kim, Sang-Kyung; Peck, Dong-Hyun; Lee, Byungrok; Yoon, Seong-Ho; Jung, Doohwan

2011-07-01

28

Carbon nanofibers grown on activated carbon fiber fabrics as electrode of supercapacitors  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) were grown directly on activated carbon fiber fabric (ACFF), which was then used as the electrode of supercapacitors. Cyclic voltammetry and ac impedance were used to characterize the electrochemical properties of ACFF and CNF/ACFF electrodes in both aqueous and organic electrolytes. ACFF electrodes show higher specific capacitance than CNF/ACFF electrodes due to larger specific surface area. However, the spaces formed between the CNFs in the CNF/ACFF electrodes are more easily accessed than the slit-type pores of ACFF, and much higher electrical-double layer capacitance was obtained for CNF/ACFF electrodes

2007-12-01

29

Synthesis of nitrogen-doped porous carbon nanofibers as an efficient electrode material for supercapacitors.  

Science.gov (United States)

Supercapacitors (also known as ultracapacitors) are considered to be the most promising approach to meet the pressing requirements of energy storage. Supercapacitive electrode materials, which are closely related to the high-efficiency storage of energy, have provoked more interest. Herein, we present a high-capacity supercapacitor material based on the nitrogen-doped porous carbon nanofibers synthesized by carbonization of macroscopic-scale carbonaceous nanofibers (CNFs) coated with polypyrrole (CNFs@polypyrrole) at an appropriate temperature. The composite nanofibers exhibit a reversible specific capacitance of 202.0 F g(-1) at the current density of 1.0 A g(-1) in 6.0 mol L(-1) aqueous KOH electrolyte, meanwhile maintaining a high-class capacitance retention capability and a maximum power density of 89.57 kW kg(-1). This kind of nitrogen-doped carbon nanofiber represents an alternative promising candidate for an efficient electrode material for supercapacitors. PMID:22769051

Chen, Li-Feng; Zhang, Xu-Dong; Liang, Hai-Wei; Kong, Mingguang; Guan, Qing-Fang; Chen, Ping; Wu, Zhen-Yu; Yu, Shu-Hong

2012-08-28

30

Fabrication and electron field-emission of carbon nanofibers grown on silicon nanoporous pillar array  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Carbon nanofibers were grown on silicon nanoporous pillar array by a CVD method. Black-Right-Pointing-Pointer Low turn-on field, high density and stable FE current were obtained in CNTs/Si-NPA. Black-Right-Pointing-Pointer Defects in CNTs and Si array substrate contributes the excellent FE property. - Abstract: Random orientation carbon nanofibers (CNFs) were grown on silicon nanoporous pillar array (Si-NPA) by thermal chemical vapor deposition (CVD) method with acetylene (C{sub 2}H{sub 2}) as carbon precursor and Ni as the catalyst. The synthesized CNFs were mainly composed of amorphous carbon and disordered graphite layers with a core-shell like structure. And, the tangled CNFs and the regular silicon-pillar array formed a nanometer-micron hierarchy structure. The electron field-emission (FE) property of CNFs/Si-NPA was measured and low turn-on field, high-density and stable FE current, high enhancement factor were obtained. The outstanding FE performance of the CNFs/Si-NPA emitters was attributed to the random orientation and defects of CNFs, the undulate surface of the Si-NPA substrate.

Wang Haiyan, E-mail: wanghaiyan@zzuli.edu.cn [Department of Technological Physics, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); Wang Yongqiang; Xue Renzhong [Department of Technological Physics, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); Kang Liping [Department of Technological Physics, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); Department of Physics and Laboratory of Materials Physics, Zhengzhou University, Zhengzhou 450052 (China); Li Xinjian [Department of Physics and Laboratory of Materials Physics, Zhengzhou University, Zhengzhou 450052 (China)

2012-11-15

31

Fischer-Tropsch synthesis on hierarchically structured cobalt nanoparticle/carbon nanofiber/carbon felt composites.  

Science.gov (United States)

The hierarchically structured carbon nanofibers (CNFs)/carbon felt composites, in which CNFs were directly grown on the surface of microfibers in carbon felt, forming a CNF layer on a micrometer range that completely covers the microfiber surfaces, were tested as a novel support material for cobalt nanoparticles in the highly exothermic Fischer-Tropsch (F-T) synthesis. A compact, fixed-bed reactor, made of disks of such composite materials, offered the advantages of improved heat and mass transfer, relatively low pressure drop, and safe handling of immobilized CNFs. An efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature profile, whereas the open structure of the CNF layer afforded an almost 100?% effectiveness of Co nanoparticles in the F-T synthesis in the fixed bed. The greatly improved mass and heat transport makes the compact reactor attractive for applications in the conversion of biomass, coal, and natural gas to liquids. PMID:21563315

Zarubova, Sarka; Rane, Shreyas; Yang, Jia; Yu, Yingda; Zhu, Ye; Chen, De; Holmen, Anders

2011-07-18

32

Production of Carbon Nanofibers Using a CVD Method with Lithium Fluoride as a Supported Cobalt Catalyst  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers (CNFs) have been synthesized in high yield (>70%) by catalytic chemical vapor deposition (CCVD) on Co/LiF catalyst using acetylene as carbon source. A novel catalyst support (LiF) is reported for the first time as an alternative for large-scale production of carbon nanofibers while purification process of nanofibers is easier. In our experiment, the sealed furnace was heated at 700∘C for 0.5 hour (the heating rate was 10∘C/min) and then cooled to room t...

2008-01-01

33

Graphene nanoribbons hybridized carbon nanofibers: remarkably enhanced graphitization and conductivity, and excellent performance as support material for fuel cell catalysts.  

Science.gov (United States)

High electronic conductivity of the support material and uniform distribution of the catalyst nanoparticles (NPs) are extremely desirable for electrocatalysts. In this paper, we present our recent progress on electrocatalysts for fuel cells with simultaneously improved conductivity of the supporting carbon nanofibers (CNFs) and distribution of platinum (Pt) NPs through facile incorporation of graphene nanoribbons (GNRs). Briefly, GNRs were obtained by the cutting and unzipping of multiwalled carbon nanotubes (MWCNTs) and subsequent thermal reduction and were first used as novel nanofillers in CNFs towards high performance support material for electrocatalysis. Through electrospinning and carbonization processes, GNR embedded carbon nanofibers (G-CNFs) with greatly enhanced graphitization and electronic conductivity were synthesized. Chemical deposition of Pt NPs onto G-CNFs generated a new Pt-G-CNF hybrid catalyst, with homogeneously distributed Pt NPs of ?3 nm. Compared to Pt-CNF (Pt on pristine CNFs) and Pt-M-CNF (Pt on MWCNT embedded CNFs), Pt-G-CNF hybrids exhibit significantly improved electrochemically active surface area (ECSA), better CO tolerance for electro-oxidation of methanol and higher electrochemical stability, testifying G-CNFs are promising support materials for high performance electrocatalysts for fuel cells. PMID:24305657

Wang, Chaonan; Gao, Hongrong; Li, Hong; Zhang, Yiren; Huang, Bowen; Zhao, Junhong; Zhu, Yan; Yuan, Wang Zhang; Zhang, Yongming

2014-01-16

34

Preparation of a new adsorbent from activated carbon and carbon nanofiber (AC/CNF) for manufacturing organic-vacbpour respirator cartridge  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract In this study a composite of activated carbon and carbon nanofiber (AC/CNF) was prepared to improve the performance of activated carbon (AC) for adsorption of volatile organic compounds (VOCs) and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbon nanofibers (CNF) were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropor...

Jahangiri Mehdi; Adl Javad; Shahtaheri Seyyed Jamaleddin; Rashidi Alimorad; Ghorbanali Amir; Kakooe Hossein; Forushani Abbas Rahimi; Ganjali Mohammad Reza

2013-01-01

35

Carbon nanofiber–sulfur composite cathode materials with different binders for secondary Li/S cells  

International Nuclear Information System (INIS)

A sulfur-coated carbon nanofiber (CNF–S) composite cathode material was prepared by a chemical deposition method in an aqueous solution. This CNF–S material was evaluated as the cathode material in lithium/sulfur cells with three different binders. The results of the SEM and TGA measurements reveal that CNF–S has a typical core–shell structure, containing 75.7 w/o sulfur coated uniformly on the surface of the CNFs. The effects of different binders on the potential profiles, electrode capacity and capacity retention with cycling were investigated. The electrode prepared with CMC + SBR binder has the best performance compared with PVdF and PEO binders, exhibiting a specific capacity of up to 1313 mAh g?1 S at the initial discharge and a specific capacity of 586 mAh g?1 S after 60 cycles.

2012-03-30

36

Carbon Nanofiber Nanoelectrodes for Biosensing Applications  

Science.gov (United States)

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here, we report two studies using vertically aligned CNF nanoelectrodes for biomedical applications. CNF arrays are investigated as neural stimulation and neurotransmitter recording electrodes for application in deep brain stimulation (DBS). Polypyrrole coated CNF nanoelectrodes have shown great promise as stimulating electrodes due to their large surface area, low impedance, biocompatibility and capacity for highly localized stimulation. CNFs embedded in SiO2 have been used as sensing electrodes for neurotransmitter detection. Our approach combines a multiplexed CNF electrode chip, developed at NASA Ames Research Center, with the Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS) system, developed at the Mayo Clinic. Preliminary results indicate that the CNF nanoelectrode arrays are easily integrated with WINCS for neurotransmitter detection in a multiplexed array format. In the future, combining CNF based stimulating and recording electrodes with WINCS may lay the foundation for an implantable smart therapeutic system that utilizes neurochemical feedback control while likely resulting in increased DBS application in various neuropsychiatric disorders. In total, our goal is to take advantage of the nanostructure of CNF arrays for biosensing studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.

Koehne, Jessica Erin

2014-01-01

37

Structure, mechanical properties and friction behavior of UHMWPE/HDPE/carbon nanofibers  

International Nuclear Information System (INIS)

Effects of untreated and pretreated carbon nanofibers (CNFs) on the crystallization behavior, friction behavior, and mechanical properties of ultra high molecular weight polyethylene (UHMWPE)/high density polyethylene (HDPE) nanocomposites prepared by a twin-screw extrusion were studied. The differential scanning calorimetry and wide angle X-ray diffraction measurements indicated that the addition of CNFs impacted the temperature of crystallization, but had no significant effects on the crystalline structure of the UHMWPE/HDPE blend. The degree of crystallinity, and the tensile strength and modulus of the UHMWPE/HDPE systems exhibited an increasing trend initially with addition of CNFs, followed by a decrease at higher contents. With the increase of untreated CNF content, the friction coefficient of UHMWPE/HDPE was decreasing and displayed less change in the process of friction. The microstructure features on the fracture surfaces and friction surfaces of the polymer blend and the nanocomposites were analyzed in detail by scanning electron microscope observations. The degree of crystallinity of the nanocomposites with the pretreated CNFs exhibited a decrease due to the better interface adhesion compared to that in the nanocomposites with the same loading untreated CNFs. The enhancement in tensile strength of nanocomposites containing 0.5 wt% treated CNFs was four times higher (32%) than that of the nanocomposites containing untreated CNFs (8%) over that of the pure polymer

2009-05-15

38

Direct production of carbon nanofibers decorated with Cu2O by thermal chemical vapor deposition on Ni catalyst electroplated on a copper substrate  

Directory of Open Access Journals (Sweden)

Full Text Available  Carbon nanofibers (CNFs decorated with Cu2O particles were grown on a Ni catalyst layer deposited on a Cu substrate by thermal. chemical vapor deposition from liquid petroleum gas. Ni catalyst nanoparticles with different sizes were produced in an electroplating system at 35?C. These nanoparticles provide the nucleation sites for CNF growth, removing the need for a buffer layer. High temperature surface segregation of the Cu substrate into the Ni catalyst layer and its exposition to O2 at atmospheric environment, during the CNFs growth, lead to the production of CNFs decorated with Cu2O particles. The surface morphology of the Ni catalyst films and grown CNFs over it was studied by scanning electron microscopy. Transmission electron microscopy and Raman spectroscopy revealed the formation of CNFs. The selected area electron diffraction pattern and electron diffraction studies show that these CNFs were decorated with Cu2O nanoparticles.

MA Vesaghi

2012-12-01

39

Occupational nanosafety considerations for carbon nanotubes and carbon nanofibers.  

Science.gov (United States)

Carbon nanotubes (CNTs) are carbon atoms arranged in a crystalline graphene lattice with a tubular morphology. CNTs exhibit high tensile strength, possess unique electrical properties, are durable, and can be functionalized. These properties allow applications as structural materials, in electronics, as heating elements, in batteries, in the production of stain-resistant fabric, for bone grafting and dental implants, and for targeted drug delivery. Carbon nanofibers (CNFs) are strong, flexible fibers that are currently used to produce composite materials. Agitation can lead to aerosolized CNTs and CNFs, and peak airborne particulate concentrations are associated with workplace activities such as weighing, transferring, mixing, blending, or sonication. Most airborne CNTs or CNFs found in workplaces are loose agglomerates of micrometer diameter. However, due to their low density, they linger in workplace air for a considerable time, and a large fraction of these structures are respirable. In rat and mouse models, pulmonary exposure to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or CNFs causes the following pulmonary reactions: acute pulmonary inflammation and injury, rapid and persistent formation of granulomatous lesions at deposition sites of large CNT agglomerates, and rapid and progressive alveolar interstitial fibrosis at deposition sites of more dispersed CNT or CNF structures. Pulmonary exposure to SWCNTs can induce oxidant stress in aortic tissue and increases plaque formation in an atherosclerotic mouse model. Pulmonary exposure to MWCNTs depresses the ability of coronary arterioles to respond to dilators. These cardiovascular effects may result from neurogenic signals from sensory irritant receptors in the lung. Pulmonary exposure to MWCNTs also upregulates mRNA for inflammatory mediators in selected brain regions, and pulmonary exposure to SWCNTs upregulates the baroreceptor reflex. In addition, pulmonary exposure to MWCNTs may induce levels of inflammatory mediators in the blood, which may affect the cardiovascular system. Intraperitoneal instillation of MWCNTs in mice has been associated with abdominal mesothelioma. MWCNTs deposited in the distal alveoli can migrate to the intrapleural space, and MWCNTs injected in the intrapleural space can cause lesions at the parietal pleura. However, further studies are required to determine whether pulmonary exposure to MWCNTs can induce pleural lesions or mesothelioma. In light of the anticipated growth in the production and use of CNTs and CNFs, worker exposure is possible. Because pulmonary exposure to CNTs and CNFs causes inflammatory and fibrotic reactions in the rodent lung, adverse health effects in workers represent a concern. NIOSH has conducted a risk assessment using available animal exposure-response data and is developing a recommended exposure limit for CNTs and CNFs. Evidence indicates that engineering controls and personal protective equipment can significantly decrease workplace exposure to CNTs and CNFs. Considering the available data on health risks, it appears prudent to develop prevention strategies to minimize workplace exposure. These strategies would include engineering controls (enclosure, exhaust ventilation), worker training, administrative controls, implementation of good handling practices, and the use of personal protective equipment (such as respirators) when necessary. NIOSH has published a document containing recommendations for the safe handling of nanomaterials. PMID:23210709

Castranova, Vincent; Schulte, Paul A; Zumwalde, Ralph D

2013-03-19

40

Enhancement of electrosorption capacity of activated carbon fibers by grafting with carbon nanofibers  

International Nuclear Information System (INIS)

The composite films of activated carbon fibers (ACFs) and carbon nanofibers (CNFs) are prepared via chemical vapor deposition of CNFs onto ACFs in different times from 0.5 to 2 h and their electrosorption behaviors in NaCl solution are investigated. The morphology, structure, porous and electrochemical properties are characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, N2 adsorption at 77 K, contact angle goniometer and electrochemical workstation, respectively. The results show that CNFs have been hierarchically grown on the surface of ACFs and the as grown ACF/CNF composite films have less defects, higher specific capacitances, more suitable mesoporous structure and more hydrophilic surface than the pristine ACFs, which is beneficial to their electrosorption performance. The ACFs/CNFs with CNFs deposited in 1 h exhibit an optimized NaCl removal ratio of 80%, 55% higher than that of ACFs and the NaCl electrosorption follows a Langmuir isotherm with a maximum electrosorption capacity of 17.19 mg/g.

2011-03-30

 
 
 
 
41

Growth of carbon nanofibers using resol-type phenolic resin and cobalt(II) catalyst.  

Science.gov (United States)

This study investigated carbon nanofibers (CNFs) grown on reticulated vitreous carbon (RVC) foam through catalytic deposition of ethylene. Before growing the CNFs, Co(II) on the RVC foam was expected to act as a catalyst by deposition. The preparation of the CNFs was a two-step process. The first step was preparing the RVC from polyurethane (PU) foam. Changes in weight over time were evaluated using two kinds of resol. The change in the mass and state of the sample with the change in temperature was studied during the carbonization process. The second step was to prepare the CNFs. An OH group was attached by the oxidation of the RVC foam. A change in the shape and mass of the sample was observed due to a change in nitric acid concentration and oxidation time. Then, cobalt was deposited to grow CNFs on the RVC foam. Hydrolysis helped to deposit the Co(ll) on the RVC foam. The appropriate time and temperature were investigated for the reduction process. In the last step, CNFs were prepared by the introducing ethylene gas. The resulting samples were analyzed using scanning electron microscopy, energy dispersive spectroscopy, N2-sorption, and X-ray photoelectron spectroscopy. PMID:24245253

Kim, Taeyun; Mees, Karina; Park, Ho-Seon; Willert-Porada, Monika; Lee, Chang-Seop

2013-11-01

42

Catalytic Growth of Macroscopic Carbon Nanofibers Bodies with Activated Carbon  

International Nuclear Information System (INIS)

Carbon-carbon composite of activated carbon and carbon nanofibers have been synthesized by growing Carbon nanofiber (CNF) on Palm shell-based Activated carbon (AC) with Ni catalyst. The composites are in an agglomerated shape due to the entanglement of the defective CNF between the AC particles forming a macroscopic body. The macroscopic size will allow the composite to be used as a stabile catalyst support and liquid adsorbent. The preparation of CNT/AC nanocarbon was initiated by pre-treating the activated carbon with nitric acid, followed by impregnation of 1 wt% loading of nickel (II) nitrate solutions in acetone. The catalyst precursor was calcined and reduced at 300 deg. C for an hour in each step. The catalytic growth of nanocarbon in C2H4/H2 was carried out at temperature of 550 deg. C for 2 hrs with different rotating angle in the fluidization system. SEM and N2 isotherms show the level of agglomeration which is a function of growth density and fluidization of the system. The effect of fluidization by rotating the reactor during growth with different speed give a significant impact on the agglomeration of the final CNF/AC composite and thus the amount of CNFs produced. The macrostructure body produced in this work of CNF/AC composite will have advantages in the adsorbent and catalyst support application, due to the mechanical and chemical properties of the material.

2009-06-01

43

Deposition of vertically oriented carbon nanofibers in atmospheric pressure radio frequency discharge  

International Nuclear Information System (INIS)

Deposition of vertically oriented carbon nanofibers (CNFs) has been studied in an atmospheric pressure radio frequency discharge without dielectric barrier covering the metallic electrodes. When the frequency is sufficiently high so that ions reside in the gap for more than one rf cycle ('trapped ions'), the operating voltage decreases remarkably and the transition from a uniform glow discharge to an arc discharge is suppressed even without dielectric barriers. More importantly, the trapped ions are able to build up a cathodic ion sheath. A large potential drop is created in the sheath between the bulk plasma and the electrode, which is essential for aligning growing CNFs. At the same time, the damage to CNFs due to ion bombardment can be minimized at atmospheric pressure. The primary interest of the present work is in identifying the cathodic ion sheath and investigating how it influences the alignment of growing CNFs in atmospheric pressure plasma-enhanced chemical-vapor deposition. Spectral emission profiles of He (706 nm), H? (656 nm), and CH (432 nm) clearly showed that a dark space is formed between the cathode layer and the heated bottom electrode. However, increasing the rf power induced the transition to a nonuniform ?-mode discharge which creates intense plasma spots in the dark space. Aligned CNFs can be grown at moderate input power during the initial stage of the deposition process. Catalyst particles were heavily contaminated by precipitated carbon in less than 5 min. Alignment deteriorates as CNFs grow and deposition was virtually terminated by the deactivation of catalyst particles

2006-01-15

44

Effects of the catalyst and substrate thickness on the carbon nanotubes/nanofibers as supercapacitor electrodes  

International Nuclear Information System (INIS)

The different growth conditions of carbon nanotubes (CNTs)/carbon nanofibers (CNFs) which lead to different characteristics when used as supercapacitor electrodes are reported. A layer of SiO2 was coated onto the Si substrate and then a layer of Ti was evaporated as a current collector. CNTs/CNFs were synthesized on the Ti surface via a water-assisted chemical vapor deposition method at 800 °C and at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C2H4) as the precursor gas and argon (Ar) and hydrogen (H2) as the carrier gases. The effects of different thicknesses of the catalyst (5 and 10 nm) and Ti substrate layer (10, 30 and 150 nm) on the specific capacitance of the CNFs were studied and the capacitance of the CNTs/CNFs-based device was dependent on CNT/CNF morphology of the CNFs that varied for different combinations of the catalyst and Ti layer thicknesses. The characterization of CNTs/CNFs was carried out using scanning electron microscopy, electron dispersive spectroscopy, transmission electron microscopy and electron diffraction. The specific capacitance was measured using cyclic voltammetry via a three-electrode system. The highest specific capacitance (60 F g-1) was obtained in the sample grown with 5 nm of Fe catalyst onto 10 nm of Ti substrate.

2012-12-01

45

Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials  

Directory of Open Access Journals (Sweden)

Full Text Available In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs and nanofibers (CNFs in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750?C. 5–10 walled CNTs with diameters of 10–15?nm at 600?C and 12–20?nm at 750?C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30?nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles.

Prasantha R. Mudimela

2009-01-01

46

Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions  

International Nuclear Information System (INIS)

Glassy carbon was Ar+-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ?10 ?m, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs

2004-05-10

47

Multi-scale carbon micro/nanofibers-based adsorbents for protein immobilization.  

Science.gov (United States)

In the present study, different proteins, namely, bovine serum albumin (BSA), glucose oxidase (GOx) and the laboratory purified YqeH were immobilized in the phenolic resin precursor-based multi-scale web of activated carbon microfibers (ACFs) and carbon nanofibers (CNFs). These biomolecules are characteristically different from each other, having different structure, number of parent amino acid molecules and isoelectric point. CNF was grown on ACF substrate by chemical vapor deposition, using Ni nanoparticles (Nps) as the catalyst. The ultra-sonication of the CNFs was carried out in acidic medium to remove Ni Nps from the tip of the CNFs to provide additional active sites for adsorption. The prepared material was directly used as an adsorbent for proteins, without requiring any additional treatment. Several analytical techniques were used to characterize the prepared materials, including scanning electron microscopy, Fourier transform infrared spectroscopy, BET surface area, pore-size distribution, and UV-vis spectroscopy. The adsorption capacities of prepared ACFs/CNFs in this study were determined to be approximately 191, 39 and 70 mg/g for BSA, GOx and YqeH, respectively, revealing that the carbon micro-nanofibers forming synthesized multi-scale web are efficient materials for the immobilization of protein molecules. PMID:24656351

Singh, Shiv; Singh, Abhinav; Bais, Vaibhav Sushil Singh; Prakash, Balaji; Verma, Nishith

2014-05-01

48

Characterization of field emission from carbon nanofibers on a metal tip  

International Nuclear Information System (INIS)

Field electron emission from carbon nanofibers (CNFs) grown on a tungsten tip has been characterized by measuring emission current-voltage (I-V) curves and observing emission patterns on a phosphor screen. CNFs were vertically grown on the tip by plasma-enhanced chemical vapor deposition. Field emission from the CNFs over 100 ?A was strongly dependent on emitter-anode distance, and the dominant field electrons were emitted within an angular spread of ???25 deg., indicating the electron emission took place mainly from the emitter's apex area. By analyzing the I-V curves with the aid of the Fowler-Nordheim theory, the maximum current density was estimated to be about J=2x109 A/m2.

2009-08-17

49

Mechanical and electrical properties of carbon nanofiber–ceramic nanoparticle–polymer composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The present research is focused on the manufacturing and analysis of composites consisting of a thermosetting polymer reinforced with fillers of nanometric dimensions. The materials were chosen to be an epoxy resin matrix and two different kinds of fillers: electrically conductive carbon nanofibers (CNFs) and ceramic titanium dioxide (TiO2) and aluminium dioxide (Al2O3) nanoparticles. In an initial step of the work, in order to understand the effect that each kind of filler had when added sep...

Carballeira, Pablo

2010-01-01

50

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A composite material consisting of carbon nanofibers (CNFs) grown on sintered metal fiber filters was modified by H2O2 or plasma-generated O3. Coupling temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) techniques in the same UHV apparatus allowed the direct correlation of the nature of the created O-functional groups and their evolution as CO and CO2 upon heating. The two oxidative treatments yielded different distributions of O-containing groups. The relative...

2010-01-01

51

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated)-reinforced high-density polyethylene (HDPE) composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure f...

Liu, Tian; Wood, Weston; Zhong, Wei-hong

2010-01-01

52

Processing and properties of carbon nanofibers reinforced epoxy powder composites  

International Nuclear Information System (INIS)

Commercially available CNFs (diameter 30–300 nm) have been used to develop both bulk and coating epoxy nanocomposites by using a solvent-free epoxy matrix powder. Processing of both types of materials has been carried out by a double-step process consisting in an initial physical premix of all components followed by three consecutive extrusions. The extruded pellets were grinded into powder and sieved. Carbon nanofibers powder coatings were obtained by electrostatic painting of the extruded powder followed by a curing process based in a thermal treatment at 200 °C for 25 min. On the other hand, for obtaining bulk carbon nanofibers epoxy composites, a thermal curing process involving several steps was needed. Gloss and mechanical properties of both nanocomposite coatings and bulk nanocomposites were improved as a result of the processing process. FE-SEM fracture surface microphotographs corroborate these results. It has been assessed the key role played by the dispersion of CNFs in the matrix, and the highly important step that is the processing and curing of the nanocomposites. A processing stage consisted in three consecutive extrusions has reached to nanocomposites free of entanglements neither agglomerates. This process leads to nanocomposite coatings of enhanced properties, as it has been evidenced through gloss and mechanical properties. A dispersion limit of 1% has been determined for the studied system in which a given dispersion has been achieved, as the bending mechanical properties have been increased around 25% compared with the pristine epoxy resin. It has been also demonstrated the importance of the thickness in the nanocomposite, as it involves the curing stage. The complex curing treatment carried out in the case of bulk nanocomposites has reached to reagglomeration of CNFs.

2011-11-01

53

Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction.  

Science.gov (United States)

For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors. PMID:23171171

Pan, David; Ombaba, Matthew; Zhou, Zhi-You; Liu, Yang; Chen, Shaowei; Lu, Jennifer

2012-12-21

54

Thermal Expansion of Carbon Nanofiber-Reinforced Multiscale Polymer Composites  

Science.gov (United States)

Improved dimensional stability of composites is desired in applications where they are exposed to varying temperature conditions. The current study aims at analyzing the effect of vapor-grown carbon nanofibers (CNFs) on the thermal expansion behavior of epoxy matrix composites and hollow particle-filled composites (syntactic foams). CNFs have a lower coefficient of thermal expansion (CTE) than epoxy resin, which results in composites with increased dimensional stability as the CNF content is increased. The experimental measurements show that with 10 wt.% CNF, the composite has about 11.6% lower CTE than the matrix resin. In CNF-reinforced syntactic foams, the CTE of the composite decreases with increasing wall thickness and volume fraction of hollow particle inclusions. With respect to neat epoxy resin, a maximum decrease of 38.4% is also observed in the CNF/syntactic foams with microballoon inclusions that range from 15 vol.% to 50 vol.% in all composite mixtures. The experimental results for CNF/syntactic foam are in agreement with a modified version of Kerner's model. A combination of hollow microparticles and nanofibers has resulted in the ability to tailor the thermal expansion of the composite over a wide range.

Poveda, Ronald L.; Achar, Sriniket; Gupta, Nikhil

2012-10-01

55

Nondestructive evaluation of ±45° flat-braided carbon-fiber-reinforced polymers with carbon nanofibers using HTS-SQUID gradiometer  

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Tensile load was applied to braided CFRPs with and without CNFs and cutting edges. ? Visualization method using SQUID gradiometer was also applied to the braided CFRPs. ? Different destructive mechanisms and current distributions were obtained. ? Dispersed CNFs enhanced mechanical and electrical properties of the braided CFRPs. -- Abstract: Step-by-step tensile tests were applied to flat-braided carbon-fiber-reinforced polymers with and without added dispersions of carbon nanofibers (CNFs) and with and without sample sides cut off to study their mechanical properties and destructive mechanisms by means of in situ observation and stress–strain measurements. An ex situ nondestructive evaluation technique, using a high-temperature superconductor superconducting quantum interference device gradiometer, was also applied to the samples to study their electrical properties; the relationships between the mechanical and electrical properties by visualizing current maps in the samples during ac current injection was also studied. Clear differences were observed in the mechanical and electrical properties and the destructive mechanisms between the samples with and without CNFs and with and without cut off sides. These differences were mainly attributed to the addition of CNFs, which enhanced the mechanical and electrical connections between the carbon fiber bundles.

Hatsukade, Y., E-mail: hatukade@ens.tut.ac.jp [Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580 (Japan); Shinyama, Y.; Yoshida, K. [Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580 (Japan); Takai, Y. [Osaka Sangyo University, 3-1-1 Nakagaito, Daito, Osaka 574-8530 (Japan); Aly-Hassan, M.S.; Nakai, A.; Hamada, H. [Advanced Fibro-Science Division, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585 (Japan); Adachi, S.; Tanabe, K. [International Superconductivity Technology Center, Superconductivity Research Laboratory, 10-13, Shinonome 1-chome, Koto-ku, Tokyo 135-0062 (Japan); Tanaka, S. [Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580 (Japan)

2013-01-15

56

Nondestructive evaluation of ±45° flat-braided carbon-fiber-reinforced polymers with carbon nanofibers using HTS-SQUID gradiometer  

International Nuclear Information System (INIS)

Highlights: ? Tensile load was applied to braided CFRPs with and without CNFs and cutting edges. ? Visualization method using SQUID gradiometer was also applied to the braided CFRPs. ? Different destructive mechanisms and current distributions were obtained. ? Dispersed CNFs enhanced mechanical and electrical properties of the braided CFRPs. -- Abstract: Step-by-step tensile tests were applied to flat-braided carbon-fiber-reinforced polymers with and without added dispersions of carbon nanofibers (CNFs) and with and without sample sides cut off to study their mechanical properties and destructive mechanisms by means of in situ observation and stress–strain measurements. An ex situ nondestructive evaluation technique, using a high-temperature superconductor superconducting quantum interference device gradiometer, was also applied to the samples to study their electrical properties; the relationships between the mechanical and electrical properties by visualizing current maps in the samples during ac current injection was also studied. Clear differences were observed in the mechanical and electrical properties and the destructive mechanisms between the samples with and without CNFs and with and without cut off sides. These differences were mainly attributed to the addition of CNFs, which enhanced the mechanical and electrical connections between the carbon fiber bundles

2013-01-15

57

A nonlinear effective thermal conductivity model for carbon nanotube and nanofiber suspensions  

International Nuclear Information System (INIS)

It has been experimentally demonstrated that suspensions of carbon nanotubes (CNTs) and nanofibers (CNFs) significantly increase the thermal conductivity of nanofluids; however, a physically sound theory of the underlying phenomenon is still missing. In this study, the nonlinear nature of the effective thermal conductivity enhancement with the particle concentration of CNT and CNF nanofluids is explained physically using the excluded volume concept. Specifically, the number of contacting CNTs and CNFs could be calculated by using the excluded volume concept, where the distance for heat to travel in a cylinder between the contacting cylinders in the thermal network of percolating CNTs and CNFs increased with the excluded volume. In contrast to the effective thermal conductivity model of Sastry et al (2008 Nanotechnology 19 055704) the present revised model could reproduce the nonlinear increase of the thermal conductivity with particle concentration, as well as the dependence on the diameter and aspect ratio of the CNTs and CNFs. It was found that the alignment of CNTs and CNFs due to the long range repulsion force decreases the excluded volume, leading to both the convex and concave nonlinear as well as linear increase of the thermal conductivity with particle concentration. The difference between various carrier fluids of the suspensions could be explained as the result of the change in the excluded volume in different base fluids

2008-09-17

58

Preparations of carbon nanofiber emitters for diode type field emission display with organic luminescence thin films  

International Nuclear Information System (INIS)

Carbon nanofiber (CNF), which was massively synthesized by thermal vapor deposition, emitters were fabricated by following easy processes: screen printing (SP), spin coating (SC) and spray spreading (SS) methods. Emission current density of 23 ?A/cm2 at 300 V was obtained after treatment by nitric acid to CNF paste in the SP method. Specimen prepared by the SC method with nanofibers of which length is approximately 1.5 ?m showed 85.2 ?A/cm2 at 350 V. The surface was sufficiently smooth and CNFs were dispersive with the density of 1.0 * 107 cm-2. Such the surface structure is suitable for electric field being applied to CNFs uniformly. The result of the SS method insisted that the existence of the nanofibers with the length less than 1 ?m on the substrate was important to obtain a high performance of emitter. In the SS method sparse CNFs were obtained, that is suitable surface structure for emission, with the decanted suspension from tetrahydrofuran (THF) rather than that of dimethylformamide (DMF). The boiling temperature of solution for suspension and substrate temperature during spray were significant parameters in the SS method. The electric field enhancement factor was 2560 in the specimen with DMF

2007-09-01

59

Fabrication of Uniform Au–Carbon Nanofiber by Two-Step Low Temperature Decomposition  

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Full Text Available Abstract This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs. Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 ?m long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces.

Lee Myeongsoon

2009-01-01

60

Efficient synthesis of Pt nanoparticles supported on hydrophobic graphitized carbon nanofibers for electrocatalysts using noncovalent functionalization  

Energy Technology Data Exchange (ETDEWEB)

As an alternative to the oxidative acid treatment, a noncovalent {pi}-{pi} interaction method is employed to deposit Pt electrocatalysts on highly hydrophobic carbon nanofibers (CNFs) for the application of polymer electrolyte membrane (PEM) fuel cells. Three different functionalization agents, namely benzyl mercaptan (BM), 1-aminopyrene (AP), and 1-pyrenecarboxylic acid (PCA), are used to functionalize CNFs and the effect of these groups on the electrochemical properties is examined. While the BM and AP act as a poison to Pt catalyst, the functionalization of CNF with PCA improves the distribution and loading of Pt as well as reducing the sintering of Pt particles. From the carbon corrosion test, unlike the oxidative acid treatment, the PCA treatment sustains the corrosion resistance of CNFs because it preserves the intrinsic properties of CNFs without damaging their surface structure. Therefore, the PCA treatment is a very effective way to prepare catalysts for PEM fuel cells and also extended to the fabrication of graphitized-carbon-supported catalysts of other precious metal for various applications. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Oh, Hyung-Suk; Kim, Hansung [Department of Chemical and Biomolecular Engineering, Yonsei University, 134 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

2011-10-21

 
 
 
 
61

In situ growth cupric oxide nanoparticles on carbon nanofibers for sensitive nonenzymatic sensing of glucose  

International Nuclear Information System (INIS)

Highlights: • CuO nanoparticles were directly and homogeneously grown on carbon nanofibers. • The obtained nanocomposite showed high electrooxidize activity to glucose. • A nonenzymatic glucose sensor was constructed based on the functional nanocomposite. • This sensor showed good performance to glucose. • The proposed sensor was successfully applied in detection of glucose in blood serum. -- Abstract: A novel method was employed to directly and homogeneously attaching cupric oxide nanoparticles (CuONPs) on carbon nanofibers (CNFs) for sensitive amperometric nonenzymatic sensing of glucose. The obtained CuONPs-CNFs nanocomposite was characterized by transmission electron microscopy and X-ray diffraction. The CuONPs-CNFs nanocomposite modified glassy carbon electrode showed high electrocatalytic activity toward the oxidation of glucose in alkaline media and a nonenzymatic glucose sensor was constructed based on the functional nanocomposite modified electrode. Under optimal experimental conditions, the designed sensor exhibited a wide linear response to glucose ranging from 5.0 × 10?7 to 1.1 × 10?2 M with a high sensitivity of 2739 ?A mM?1 cm?2 and a low detection limit down to 0.2 ?M at the signal to noise ratio of 3. This sensor showed good accuracy, acceptable precision and reproducibility. Moreover, the proposed sensor was successfully applied in the detection of glucose in human blood serum indicating its possibility in practical application

2013-08-30

62

Effect of added nickel nitrate on the physical, thermal and morphological characteristics of polyacrylonitrile-based carbon nanofibers  

International Nuclear Information System (INIS)

Porous carbon nanofibers (CNFs) with enhanced physical, thermal and morphological properties are desirable in many areas like catalyst support in fuel cells and supercapacitors as electrode material. This research addresses the effect of added nickel nitrate in 1, 3 and 5 wt% into polyacrylonitrile (PAN) precursor solution to produce CNF webs using electrospinning method. Based on the quantitative data obtained from field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) images, we can notice that CNFs were formed with diameters in the size range of 100-300 nm after carbonization at 1000 deg. C. Fiber diameter of the random CNFs was decreased by increasing the nickel nitrate contents along with dramatic improvements in porosity and specific surface areas. This study indicated that the optimal nickel nitrate concentration of 5 wt% has produced CNFs with enhanced physical and thermo-chemical properties. The high resolution X-ray diffraction (HR-XRD) showed an increase in intensity of 0 0 2 peak of the CNFs due to the catalytic function of nickel oxide in the carbonized web and these observations are in agreement with the thermal gravimetric data.

2009-05-25

63

Free-standing and binder-free sodium-ion electrodes with ultralong cycle life and high rate performance based on porous carbon nanofibers  

Science.gov (United States)

Free-standing and binder-free porous carbon nanofibers (P-CNFs) electrodes were prepared by pyrolysis of PAN-F127/DMF nanofibers via an electrospinning process as potential anodes for Na-ion batteries (NIB). The P-CNFs delivers a reversible capacity of 266 mA h g-1 after 100 cycles at 0.2 C, corresponding to ~80% of the initial charge capacity. When cycled at a current density as high as 500 mA g-1 (2 C), it still delivers a reversible capacity of ~140 mA h g-1 after 1000 cycles. The improvement of electrochemical performance is attributed to the special design and microstructure of P-CNFs, which conferred a variety of advantages: hierarchical porous channels enabling short transport length for ions and electrons, 3D interconnected structure resulting in low contact resistances, good mechanical properties leading to the excellent morphology stability.Free-standing and binder-free porous carbon nanofibers (P-CNFs) electrodes were prepared by pyrolysis of PAN-F127/DMF nanofibers via an electrospinning process as potential anodes for Na-ion batteries (NIB). The P-CNFs delivers a reversible capacity of 266 mA h g-1 after 100 cycles at 0.2 C, corresponding to ~80% of the initial charge capacity. When cycled at a current density as high as 500 mA g-1 (2 C), it still delivers a reversible capacity of ~140 mA h g-1 after 1000 cycles. The improvement of electrochemical performance is attributed to the special design and microstructure of P-CNFs, which conferred a variety of advantages: hierarchical porous channels enabling short transport length for ions and electrons, 3D interconnected structure resulting in low contact resistances, good mechanical properties leading to the excellent morphology stability. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05022j

Li, Weihan; Zeng, Linchao; Yang, Zhenzhong; Gu, Lin; Wang, Jiaqing; Liu, Xiaowu; Cheng, Jianxiu; Yu, Yan

2013-12-01

64

Multi-scale Performance and Durability of Carbon Nanofiber/Cement Composites  

Science.gov (United States)

This paper reports on recent work that is directed at understanding the fundamental controlling mechanisms of multi-scale, environmental weathering of nano-structured cement-based materials through an integrated experimental and computational program. The effect of surface treatment and admixture addition on the incorporation of carbon nanofibers (CNFs) in cement composites was studied. Silica fume and surface treatment with nitric acid facilitated CNF dispersion. The CNFs were found as individual fibers anchored in the hydration products throughout the cement pastes and as entangled networks in cavities. The presence of the CNFs did not modify the compressive or tensile strength of the composite but did provide it with a fair level of mechanical integrity post testing. Preliminary results on durability indicated a residual effect of the CNFs after decalcification of the composites as manifested by a slow load dissipation after peak load under compression. Molecular dynamics modeling of the reinforcing structure-cement phase interface demonstrated that manipulation of the interface characteristics may provide a method to control the composite properties.

Sanchez, F.; Zhang, L.; Ince, C.

65

Optical limiting of high-repetition-rate laser pulses by carbon nanofibers suspended in polydimethylsiloxane  

Science.gov (United States)

The optical limiting (OL) behavior of carbon nanofibers (CNFs) in polydimethylsiloxane (PDMS) was studied and compared with that of CNFs in water, and polyhedral multi-shell fullerene-like nanostructures (PMFNs) also in water. It was shown that when switching from single-shot to pulse-periodic regime of laser pulses (10 Hz), the CNF in PDMS suspension retains its OL characteristics, while in the aqueous suspensions, considerable degradation of OL characteristics is observed. It was also observed that a powerful laser pulse causes the CNF in PDMS suspension to become opaque for at least three seconds, while such a pulse brings out a bleaching effect in aqueous PMFN and CNF suspensions. The processes of OL degradation in aqueous suspensions, bleaching and darkening of the studied materials are discussed herein.

Videnichev, Dmitry A.; Belousova, Inna M.

2014-06-01

66

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

Science.gov (United States)

We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated)-reinforced high-density polyethylene (HDPE) composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure features of the nanocomposites. The results reveal that there exist approximate linear relationships of permittivity with wear coefficient for the nanocomposites. Composites containing silanized CNFs with the sufficiently thick coating exhibited high wear resistance. The change in permittivity was more sensitive to the increased wear coefficient for the nanocomposites with lower wear resistance. This work provides potential for further research on the application of dielectric signals to detect the effects of wear process on lifetime of polymeric materials.

Liu, Tian; Wood, Weston; Zhong, Wei-Hong

2011-12-01

67

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

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Full Text Available Abstract We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated-reinforced high-density polyethylene (HDPE composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure features of the nanocomposites. The results reveal that there exist approximate linear relationships of permittivity with wear coefficient for the nanocomposites. Composites containing silanized CNFs with the sufficiently thick coating exhibited high wear resistance. The change in permittivity was more sensitive to the increased wear coefficient for the nanocomposites with lower wear resistance. This work provides potential for further research on the application of dielectric signals to detect the effects of wear process on lifetime of polymeric materials.

Liu Tian

2011-01-01

68

Carbon nanofiber polymer composites: evaluation of life cycle energy use.  

Science.gov (United States)

Holistic evaluation of emerging nanotechnologies using systems analysis is pivotal for guiding their safe and sustainable development. While toxicity studies of engineered nanomaterials are essential, understanding of the potential large scale impacts of nanotechnology is also critical for developing sustainable nanoproducts. This work evaluates the life cycle energetic impact associated with the production and use of carbon nanofiber (CNF) reinforced polymer nanocomposites (PNC). Specifically, both simple CNF and carbon nanofiber-glass fiber (CNF-GF) hybrid PNCs are evaluated and compared with steel for equal stiffness design. Life cycle inventory is developed based on published literature and best available engineering information. A cradle-to-gate comparison suggests that for equal stiffness design, CNF reinforced PNCs are 1.6-12 times more energy intensive than steel. It is anticipated that the product use phase may strongly influence whether any net savings in life cycle energy consumption can be realized. A case study involving the use of CNF and CNF-GF reinforced PNCs in the body panels of automobiles highlights that the use of PNCs with lower CNF loading ratios has the potential for net life cycle energy savings relative to steel owing to improved fuel economy benefits. Other factors such as cost, toxicity impact of CNF, and end-of-life issues specific to CNFs need to be considered to evaluate the final economic and environmental performance of CNF reinforced PNC materials. PMID:19368217

Khanna, Vikas; Bakshi, Bhavik R

2009-03-15

69

Growth of Y-shaped Carbon Nanofibers from Ethanol Flames  

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Full Text Available Abstract Y-shaped carbon nanofibers as a multi-branched carbon nanostructure have potential applications in electronic devices. In this article, we report that several types of Y-shaped carbon nanofibers are obtained from ethanol flames. These Y-shaped carbon nanofibers have different morphologies. According to our experimental results, the growth mechanism of Y-shaped carbon nanofibers has been discussed and a possible growth model of Y-shaped carbon nanofibers has been proposed.

Cheng Jin

2008-01-01

70

Large-scale and controllable synthesis of metal-free nitrogen-doped carbon nanofibers and nanocoils over water-soluble Na2CO3  

Science.gov (United States)

Using acetylene as carbon source, ammonia as nitrogen source, and Na2CO3 powder as catalyst, we synthesized nitrogen-doped carbon nanofibers (N-CNFs) and carbon nanocoils (N-CNCs) selectively at 450°C and 500°C, respectively. The water-soluble Na2CO3 is removed through simple washing with water and the nitrogen-doped carbon nanomaterials can be collected in high purity. The approach is simple, inexpensive, and environment-benign; it can be used for controlled production of N-CNFs or N-CNCs. We report the role of catalyst, the effect of pyrolysis temperature, and the photoluminescence properties of the as-harvested N-CNFs and N-CNCs.

Ding, Qian; Song, Xueyin; Yao, Xiujuan; Qi, Xiaosi; Au, Chak-Tong; Zhong, Wei; Du, Youwei

2013-12-01

71

In situ transmission electron microscopy study of electrochemical sodiation and potassiation of carbon nanofibers.  

Science.gov (United States)

Carbonaceous materials have great potential for applications as anodes of alkali-metal ion batteries, such as Na-ion batteries and K-ion batteries (NIB and KIBs). We conduct an in situ study of the electrochemically driven sodiation and potassiation of individual carbon nanofibers (CNFs) by transmission electron microscopy (TEM). The CNFs are hollow and consist of a bilayer wall with an outer layer of disordered-carbon (d-C) enclosing an inner layer of crystalline-carbon (c-C). The d-C exhibits about three times volume expansion of the c-C after full sodiation or potassiation, thus suggesting a much higher storage capacity of Na or K ions in d-C than c-C. For the bilayer CNF-based electrode, a steady sodium capacity of 245 mAh/g is measured with a Coulombic efficiency approaching 98% after a few initial cycles. The in situ TEM experiments also reveal the mechanical degradation of CNFs through formation of longitudinal cracks near the c-C/d-C interface during sodiation and potassiation. Geometrical changes of the tube are explained by a chemomechanical model using the anisotropic sodiation/potassiation strains in c-C and d-C. Our results provide mechanistic insights into the electrochemical reaction, microstructure evolution and mechanical degradation of carbon-based anodes during sodiation and potassiation, shedding light onto the development of carbon-based electrodes for NIBs and KIBs. PMID:24823874

Liu, Ying; Fan, Feifei; Wang, Jiangwei; Liu, Yang; Chen, Hailong; Jungjohann, Katherine L; Xu, Yunhua; Zhu, Yujie; Bigio, David; Zhu, Ting; Wang, Chunsheng

2014-06-11

72

Synthesis of carbon nano-fibers on p-Si having improved temperature sensing capability  

International Nuclear Information System (INIS)

Highlights: ? Synthesis of carbon nanofibers on p-Si. ? RBM in Raman spectra. ? Superior temperature sensing capability. - Abstract: Synthesis of an innovative material for temperature sensor based on carbon nano-fibers (CNFs) on p-Si substrates has been demonstrated. The CNF films were characterized by SEM, Raman and FTIR studies. First order Raman spectra indicated a G band at ?1597 cm?1 corresponding to the E2g tangential stretching mode of an ordered graphitic structure with sp2 hybridization and a D band located ?1350 cm?1 originated from disordered carbon. Gold fingers were deposited on the p-Si/CNF surface for resistance measurement. Temperature sensing properties were also investigated critically. Resistance changes with temperature (?R/R) in p-Si/CNF films are found to be significantly large 30–60% Very stable, reproducible and improved temperature sensing properties would make this material superior to commonly available temperature sensors.

2013-01-01

73

In situ characterization of vertically oriented carbon nanofibers for three-dimensional nano-electro-mechanical device applications  

International Nuclear Information System (INIS)

We have performed mechanical and electrical characterization of individual as-grown, vertically oriented carbon nanofibers (CNFs) using in situ techniques, where such high-aspect-ratio, nanoscale structures are of interest for three-dimensional (3D) electronics, in particular 3D nano-electro-mechanical-systems (NEMS). Nanoindentation and uniaxial compression tests conducted in an in situ nanomechanical instrument, SEMentor, suggest that the CNFs undergo severe bending prior to fracture, which always occurs close to the bottom rather than at the substrate-tube interface, suggesting that the CNFs are well adhered to the substrate. This is also consistent with bending tests on individual tubes which indicated that bending angles as large as ? 700 could be accommodated elastically. In situ electrical transport measurements revealed that the CNFs grown on refractory metallic nitride buffer layers were conducting via the sidewalls, whereas those synthesized directly on Si were electrically unsuitable for low-voltage dc NEMS applications. Electrostatic actuation was also demonstrated with a nanoprobe in close proximity to a single CNF and suggests that such structures are attractive for nonvolatile memory applications. Since the magnitude of the actuation voltage is intimately dictated by the physical characteristics of the CNFs, such as diameter and length, we also addressed the ability to tune these parameters, to some extent, by adjusting the plasma-enhanced chemical vapor deposition growth parameters with this bottom-up synthesis approach.

2010-08-06

74

Occupational Exposure to Carbon Nanotubes and Nanofibers  

Science.gov (United States)

... Current Intelligence Bulletin 65: Occupational Exposure to Carbon Nanotubes and Nanofibers The Occupational Safety and Health Act ... composed of engineered nanoparticles, such as metal oxides, nanotubes, nanowires, quantum dots, and carbon fullerenes (buckyballs), among ...

75

Performance of carbon nanofiber-cement composites subjected to accelerated decalcification  

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Full Text Available The effect of decalcification on the chemo-mechanical behavior of carbon nanofiber (CNF-cement composites was studied. Portland cement pastes with and without 0.2% CNFs were subjected to accelerated decalcification by exposure to ammonium nitrate solutions. The influence of microstructural alterations during decalcification on the physical and mechanical properties of the composites was examined. The presence of CNF agglomerates influenced the chemo-mechanical behavior of the composite during decalcification. Precipitation of secondary hydrates within the agglomerates during decalcification resulted in a decrease in local porosity, which strengthened the composite and slowed the loss of flexural strength.

Arnold J.

2013-07-01

76

In situ synthesis of Pt/carbon nanofiber nanocomposites with enhanced electrocatalytic activity toward methanol oxidation.  

Science.gov (United States)

Pt/carbon nanofiber (Pt/CNF) nanocomposites were facilely synthesized by the reduction of hexachloroplatinic acid (H(2)PtCl(6)) using formic acid (HCOOH) in aqueous solution containing electrospun carbon nanofibers at room temperature. The obtained Pt/CNF nanocomposites were characterized by TEM and EDX. The Pt nanoparticles could in situ grow on the surface of CNFs with small particle size, high loading density, and uniform dispersion by adjusting the concentration of H(2)PtCl(6) precursor. The electrocatalytic activities of the Pt/CNF nanocomposites were also studied. These Pt/CNF nanocomposites exhibited higher electrocatalytic activity toward methanol oxidation reaction compared with commercial E-TEK Pt/C catalyst. The results presented may offer a new approach to facilely synthesize direct methanol fuel cells (DMFCs) catalyst with enhanced electrocatalytic activity and low cost. PMID:22082800

Wang, Dawei; Liu, Yang; Huang, Jianshe; You, Tianyan

2012-02-01

77

Carbon nanofiber electrode for neurochemical monitoring.  

Science.gov (United States)

The ability to rapidly detect neurotransmitter release has broad implications in the study of a variety of neurodegenerative diseases. Electrochemical detection methods using carbon nanofiber nanoelectrodes integrated into the Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) offer many important advantages including biocompatibility, selectivity, sensitivity, and rapid adsorption kinetics. Carbon nanofiber nanoelectrodes exhibit greater selectivity and sensitivity in the electrochemical detection of neurotransmitters compared to macroelectrodes and are able to resolve a ternary mixture of dopamine (DA), serotonin (5-HT), and ascorbic acid as well as to detect individual neurotransmitters in concentrations as low as 50 nM for DA and 100 nM for 5-HT using differential pulse voltammetry. Adsorption kinetics studies and isopropyl alcohol treatments modeled on previous studies on carbon fiber microelectrodes were conducted to investigate the analogous properties on carbon nanofiber electrodes using fast-scan cyclic voltammetry with WINCS and showed analogous results in carbon nanofiber electrodes compared with carbon fiber microelectrodes. PMID:23975638

Zhang, David A; Rand, Emily; Marsh, Michael; Andrews, Russell J; Lee, Kendall H; Meyyappan, M; Koehne, Jessica E

2013-10-01

78

Carbon nanofibers: catalytic synthesis and applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers (diameter range, 3-100 nm; length range, 1.1-1000 µm) have been known for a long time as a nuisance that often merges during catalythic conversion of carbon-containing gases. The recent outburst of interest in these graphitic materials originates from their potential for unique applications as well as their chemical similarity to fullerenes and carbon nanotubes. In this review, we focus on the growth of nanofibers using matallic particles as a catalyst to precipitate the gr...

Jong, K. P.; Geus, John W.

2000-01-01

79

How do vapor grown carbon nanofibers nucleate and grow from deoiled asphalt?  

International Nuclear Information System (INIS)

Research highlights: ? A modified growth mechanism of carbon nanofibers was proposed. ? Growth process includes (1) pyrolysis and aggregation, (2) nucleation, coalescence and self-assembly and (3) deveplopment and maturation. ? The nucleation and rearrangement of graphitic layers depend on the crystal orientation of the metal nanoparticles. - Abstract: During the experiments aimed at understanding the evolution mechanism by which vapor grown carbon nanofibers (VGCNFs) nucleate and grow, a series of carbon nanomaterials were synthesized by chemical vapor deposition (CVD) using deoiled asphalt (DOA) as carbon source and ferrocene as catalyst precursor with an experimental strategy developed to quench the CVD at different deposition times (3-30 min). The morphology and microstructure of the products were investigated by field emission scanning electron microscope, high resolution transmission electron microscope and X-ray powder diffractometer. The formation of hollow/metal-encapsulating carbon nanoparticles at short deposition time (3 min) of CVD and the subsequent evolution of these nanoparticles into carbon nanotubes/nanofibers at longer deposition time suggest a multi-step growth model for VGCNFs, which includes the stages of (1) pyrolysis and aggregation, (2) nucleation, coalescence and self-assembly, and (3) development and maturation. At first, C, Fe and Fe/C clusters are produced by decomposition and agglomeration of C and Fe species from the pyrolysis of DOA and ferrocene; second, the carbon nanoparticles are self-assembled into nanowires with dispersive metal nanoparticles, which are further developed into nanotubes for structural stability and minimum surface energy, meanwhile fishbone-like CNFs might be formed by rearranging carbon layers at an angle against the tube axis under the nucleation of small graphitic layers on certain crystal orientation of the metal particles; finally, CNFs are formed by the synergistic action of metal catalysis and continuous rearrangement of graphitic layers.

2011-03-15

80

How do vapor grown carbon nanofibers nucleate and grow from deoiled asphalt?  

Energy Technology Data Exchange (ETDEWEB)

Research highlights: {yields} A modified growth mechanism of carbon nanofibers was proposed. {yields} Growth process includes (1) pyrolysis and aggregation, (2) nucleation, coalescence and self-assembly and (3) deveplopment and maturation. {yields} The nucleation and rearrangement of graphitic layers depend on the crystal orientation of the metal nanoparticles. - Abstract: During the experiments aimed at understanding the evolution mechanism by which vapor grown carbon nanofibers (VGCNFs) nucleate and grow, a series of carbon nanomaterials were synthesized by chemical vapor deposition (CVD) using deoiled asphalt (DOA) as carbon source and ferrocene as catalyst precursor with an experimental strategy developed to quench the CVD at different deposition times (3-30 min). The morphology and microstructure of the products were investigated by field emission scanning electron microscope, high resolution transmission electron microscope and X-ray powder diffractometer. The formation of hollow/metal-encapsulating carbon nanoparticles at short deposition time (3 min) of CVD and the subsequent evolution of these nanoparticles into carbon nanotubes/nanofibers at longer deposition time suggest a multi-step growth model for VGCNFs, which includes the stages of (1) pyrolysis and aggregation, (2) nucleation, coalescence and self-assembly, and (3) development and maturation. At first, C, Fe and Fe/C clusters are produced by decomposition and agglomeration of C and Fe species from the pyrolysis of DOA and ferrocene; second, the carbon nanoparticles are self-assembled into nanowires with dispersive metal nanoparticles, which are further developed into nanotubes for structural stability and minimum surface energy, meanwhile fishbone-like CNFs might be formed by rearranging carbon layers at an angle against the tube axis under the nucleation of small graphitic layers on certain crystal orientation of the metal particles; finally, CNFs are formed by the synergistic action of metal catalysis and continuous rearrangement of graphitic layers.

Yang Yongzhen [Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Liu Xuguang, E-mail: liuxuguang@tyut.edu.cn [Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024 (China); College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Jia Husheng; Xu Bingshe [Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China)

2011-03-15

 
 
 
 
81

Carbon Nanofibers and Their Composites: A Review of Synthesizing, Properties and Applications  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanofiber (CNF, as one of the most important members of carbon fibers, has been investigated in both fundamental scientific research and practical applications. CNF composites are able to be applied as promising materials in many fields, such as electrical devices, electrode materials for batteries and supercapacitors and as sensors. In these applications, the electrical conductivity is always the first priority need to be considered. In fact, the electrical property of CNF composites largely counts on the dispersion and percolation status of CNFs in matrix materials. In this review, the electrical transport phenomenon of CNF composites is systematically summarized based on percolation theory. The effects of the aspect ratio, percolation backbone structure and fractal characteristics of CNFs and the non-universality of the percolation critical exponents on the electrical properties are systematically reviewed. Apart from the electrical property, the thermal conductivity and mechanical properties of CNF composites are briefly reviewed, as well. In addition, the preparation methods of CNFs, including catalytic chemical vapor deposition growth and electrospinning, and the preparation methods of CNF composites, including the melt mixing and solution process, are briefly introduced. Finally, their applications as sensors and electrode materials are described in this review article.

Lichao Feng

2014-05-01

82

Thermal?Electrical Character of in Situ Synthesized Polyimide-Grafted Carbon Nanofiber Composites  

Energy Technology Data Exchange (ETDEWEB)

Notwithstanding the success of polymer-carbon nanotube (CNT) nanocomposites, a solid understanding of the impact of external perturbations, including temperature and stress, on the electrical response, its reproducibility, and the subsequent relationship to the topology of the percolative morphology and molecular details of the CNT-CNT contact junction is not complete. Using an in situ synthesis approach, two series of polymide (CP2)-carbon nanofiber (CNF) composites are prepared with quantitatively (small-angle X-ray scattering) comparable CNF dispersions, but differing in the structure of the CNF-polymer interface. Amino-functionalized CNFs (FCNFs) enable direct formation of CP2 grafts onto the CNFs, whereas pristine CNFs (PCNFs) result in a relatively weak interface between the carbon nanofiber and CP2 matrix. In general, low-frequency ac impedance measurements are well described by the percolation bond model, yielding a percolation threshold below 1 vol % (0.24 and 0.68 vol % for PCNF-CP2 and FCNF-CP2, respectively). However, the design of the interface is determined to be crucial for controlling the electrical behavior in four substantial ways: magnitude of the limiting conductivity, linearity of the I-V response, magnitude and direction of temperature-dependent resistivity, and reproducibility of the absolute value of the resistivity with thermal cycling. These observations are consistent with a direct CNF-CNF contact limiting transport in the PCNF-CP2 system, where the CP2 grafts onto the FCNF from a dielectric layer, limiting transport within the FCNF-CP2 system. Furthermore, the grafted CP2 chains on the FCNF reduce local polymer dewetting at the CNF surfaces when the temperature exceeds the CP2 glass transition. This appears to stabilize the structure of the percolation network and associated conductivity. The general behavior of these interfacial extremes (pristine and fully functionalized CNFs) set important bounds on the design of interface modification for CNFs when the intended use is for electrical performance at elevated temperatures or under extreme current loads.

Arlen, Michael J.; Wang, David; Jacobs, J. David; Justice, Ryan; Trionfi, Aaron; Hsu, Julia W.P.; Schaffer, Dale; Tan, Loon-Seng; Vaia, Richard A. (Sandia); (UCIN); (AFRL)

2008-12-09

83

Lithium aluminosilicate reinforced with carbon nanofiber and alumina for controlled-thermal-expansion materials  

Science.gov (United States)

Materials with a very low or tailored thermal expansion have many applications ranging from cookware to the aerospace industry. Among others, lithium aluminosilicates (LAS) are the most studied family with low and negative thermal expansion coefficients. However, LAS materials are electrical insulators and have poor mechanical properties. Nanocomposites using LAS as a matrix are promising in many applications where special properties are achieved by the addition of one or two more phases. The main scope of this work is to study the sinterability of carbon nanofiber (CNFs)/LAS and CNFs/alumina/LAS nanocomposites, and to adjust the ratio among components for obtaining a near-zero or tailored thermal expansion. Spark plasma sintering of nanocomposites, consisting of commercial CNFs and alumina powders and an ad hoc synthesized ?-eucryptite phase, is proposed as a solution to improving mechanical and electrical properties compared with the LAS ceramics obtained under the same conditions. X-ray diffraction results on phase compositions and microstructure are discussed together with dilatometry data obtained in a wide temperature range (-150 to 450 °C). The use of a ceramic LAS phase makes it possible to design a nanocomposite with a very low or tailored thermal expansion coefficient and exceptional electrical and mechanical properties.

Borrell, Amparo; García-Moreno, Olga; Torrecillas, Ramón; García-Rocha, Victoria; Fernández, Adolfo

2012-02-01

84

Controlled Growth of NiCo2O4 Nanorods and Ultrathin Nanosheets on Carbon Nanofibers for High-performance Supercapacitors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two one-dimensional hierarchical hybrid nanostructures composed of NiCo2O4 nanorods and ultrathin nanosheets on carbon nanofibers (CNFs) are controllably synthesized through facile solution methods combined with a simple thermal treatment. The structure of NiCo2O4 can be easily controlled to be nanorods or nanosheets by using different additives in the synthesis. These two different nanostructures are evaluated as electrodes for high performance supercapacitors, in view of their apparent adva...

Zhang, Genqiang; Lou, Xiong Wen

2013-01-01

85

Immobilization of nanofibrous A- or B-site substituted LaMnO3 perovskite-type oxides on macroscopic fiber with carbon nanofibers templates  

International Nuclear Information System (INIS)

The immobilization of nanofibrous A- or B-site substituted LaMnO3 perovskite-type oxides on macroscopic silica fiber via a unique and facile carbon nanofibers (CNFs) template-based method was reported. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and the existence of nanofibrous materials immobilized on silica fiber.

2010-09-01

86

Study of Pb Adsorption by Carbon Nanofibers Grown on Powdered Activated Carbon  

Directory of Open Access Journals (Sweden)

Full Text Available The sorption of lead (Pb from aqueous solutions by using carbon nanofibers (CNFs grown on nickel impregnated Powdered Activated Carbon (PAC was studied. In this study, we investigated the affection of the lead initial concentration on the sorption of the heavy metal from water. The isotherm of the sorption of the heavy metal onto the nanocomposite was also studied. Firstly, the optimum pH for the sorption of the lead ions was determined. The maximum sorption capacity of the heavy metal onto the adsorbent was achieved at initial pH of 5.5. The effects of initial lead ions concentration were examined and the results showed that the adsorption capacities of the carbon nanofibers to uptake the heavy metal increased from about 16 to 89 mg g-1 with increasing the initial lead concentration from 5 to 70 mg L-1. The process sorption could be best fitted by the Langmuir isotherm. The equilibrium sorption capacities of lead ion were determined and found to be 100 mg g-1.

Ma`an Fahmi R. Al-Khatib

2010-01-01

87

Surface Characterization and Functionalization of Carbon Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers are high-aspect ratio graphitic materials that have been investigated for numerous applications due to their unique physical properties such as high strength, low density, metallic conductivity, tunable morphology, chemical and environmental stability, as well as compatibility with organochemical modification. Surface studies are extremely important for nanomaterials because not only is the surface structurally and chemically quite different from the bulk, but its properties tend to dominate at the nanoscale due to the drastically increased surface-to-volume ratio. This review surveys recent developments in surface analysis techniques used to characterize the surface structure and chemistry of carbon nanofibers and related carbon materials. These techniques include scanning probe microscopy, infrared and electron spectroscopy, electron microscopy, ion spectrometry, temperature programmed desorption and atom probe analysis. In addition, this article evaluates the methods used to modify the surface of carbon nanofibers in order to enhance their functionality to perform across an exceedingly diverse application space.

Klein, Kate L [ORNL; Melechko, Anatoli Vasilievich [ORNL; McKnight, Timothy E [ORNL; Retterer, Scott T [ORNL; Rack, Philip D [ORNL; Fowlkes, Jason Davidson [ORNL; Joy, David Charles [ORNL; Simpson, Michael L [ORNL

2008-01-01

88

Using Converter Dust to Produce Low Cost Cementitious Composites by in situ Carbon Nanotube and Nanofiber Synthesis  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanotubes (CNTs and nanofibers (CNFs were synthesized on clinker and silica fume particles in order to create a low cost cementitious nanostructured material. The synthesis was carried out by an in situ chemical vapor deposition (CVD process using converter dust, an industrial byproduct, as iron precursor. The use of these materials reduces the cost, with the objective of application in large-scale nanostructured cement production. The resulting products were analyzed by scanning electron microscopy (SEM, transmission electron microscopy (TEM and thermogravimetric analysis (TGA and were found to be polydisperse in size and to have defective microstructure. Some enhancement in the mechanical behavior of cement mortars was observed due to the addition of these nano-size materials. The contribution of these CNTs/CNFs to the mechanical strength of mortar specimens is similar to that of high quality CNTs incorporated in mortars by physical mixture.

Péter Ludvig

2011-03-01

89

Stable, self-ballasting field emission from zinc oxide nanowires grown on an array of vertically aligned carbon nanofibers  

Science.gov (United States)

A structure composed of zinc oxide nanowires (ZNWs) grown hydrothermally on an array of vertically aligned carbon nanofibers (CNFs) was fabricated and its field emission properties determined and compared with bare CNF arrays. The combination produced a macroscopic turn-on field of 1.2 V/?m which was found to be the lowest reported from ZNWs deposited on a two-dimensional substrate and much less than the equivalent CNFs array (5.2 V/?m). Crucially, field emission was found to be much more stable at higher pressures of 5×10-6 mbar without exhibiting current degradation for a fixed external field, while emitting with a current density of 1 mA/cm2, the current density typically required for backlighting and field emission displays. We propose a self-ballasting mechanism, in which the low carrier density in the zinc oxide prevents current runaway in the presence of adsorbed species.

Li, C.; Zhang, Y.; Mann, M.; Hiralal, P.; Unalan, H. E.; Lei, W.; Wang, B. P.; Chu, D. P.; Pribat, D.; Amaratunga, G. A. J.; Milne, W. I.

2010-04-01

90

Purification process for vertically aligned carbon nanofibers  

Science.gov (United States)

Individual, free-standing, vertically aligned multiwall carbon nanotubes or nanofibers are ideal for sensor and electrode applications. Our plasma-enhanced chemical vapor deposition techniques for producing free-standing and vertically aligned carbon nanofibers use catalyst particles at the tip of the fiber. Here we present a simple purification process for the removal of iron catalyst particles at the tip of vertically aligned carbon nanofibers derived by plasma-enhanced chemical vapor deposition. The first step involves thermal oxidation in air, at temperatures of 200-400 degrees C, resulting in the physical swelling of the iron particles from the formation of iron oxide. Subsequently, the complete removal of the iron oxide particles is achieved with diluted acid (12% HCl). The purification process appears to be very efficient at removing all of the iron catalyst particles. Electron microscopy images and Raman spectroscopy data indicate that the purification process does not damage the graphitic structure of the nanotubes.

Nguyen, Cattien V.; Delziet, Lance; Matthews, Kristopher; Chen, Bin; Meyyappan, M.

2003-01-01

91

A review of catalytically grown carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (sometimes known as carbon filaments) can be produced in a relative large scale by the catalytic decomposition of certain hydrocarbons on small metal particles. The diameter of the nanofibers is governed by that of the catalyst particles responsible for their growth. By careful manipulation of various parameters it is possible to generate carbon nanofibers in assorted conformations and at the same time also control the degree of their crystalline order. This paper is a review of the recent advances made in the development of these nanostructures, with emphasis both on the fundamental aspects surrounding the growth of the material and a discussion of the key factors which enable one to control their chemical and physical properties. Attention is also given to some of the possible applications of the nanostructures which center around the unique blend of properties exhibited by the material.

Rodriguez, N.M. (Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States))

1993-12-01

92

Electrical resistance of carbon-nanofiber concrete  

International Nuclear Information System (INIS)

Concrete is the most widely used construction material, and carbon nanofibers have many advantages in both mechanical and electrical properties such as high strength, high Young's modulus and high conductivity. In this paper, the mechanical and electrical properties of concrete containing carbon nanofibers (CNF) are experimentally studied. The test results indicate that the compressive strength and per cent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete

2009-09-01

93

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon fiber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/e...

André Navarro de Miranda; Luiz Claudio Pardini; Carlos Alberto Moreira dos Santos; Ricardo Vieira

2011-01-01

94

Interweaved Si@C/CNTs and CNFs composites as anode materials for Li-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: In summary, a serious of high-energy wet ball milling, closed spray drying and subsequent chemical vapor deposition methods were introduced successfully to fabricated novel Si@C/CNTs and CNFs composites with carbon nanotubes and carbon nanofibres interweaved with carbon coated silicon spherical composites as superior anodes in lithium-ion batteries. The core-shell structure of Si@C composites can accommodate the volume change of electrode during charge and discharge. Meanwhile, the citric acid pyrolyzed carbon was coated on the surface of the silicon perfectly and constructs the connection network of nano silicon particles. Moreover, the carbon nanotubes and carbon nanofibres, which is interweaved with nano-silicon, also allows high electrical conductivity, improved solid–electrolyte interface formation and structural integrity. Compared with pure silicon and Si@C composites, the novel Si@C/CNTs and CNFs composites had the best combination of reversible capacity and cycleablity, and this anode materials exhibited excellent electrochemical performance. The Si/C composite had a fairly high initial discharge capacity of 2168.7 mA h g{sup ?1} with an efficiency of 73%, and the discharge capacity of the 50th cycle maintained surprisingly of 1194.9 mA h g{sup ?1}. Meanwhile, spray drying and chemical vapor deposition are environmentally friendly, economical, and relatively high-yield method for the production of the Si@C/CNTs and CNFs composites in large quantities. Consequently, the novel Si@C/CNTs and CNFs composite electrodes may be a potential alternative to graphite for high energy density lithium ion batteries. Highlights: • The core/shell structured silicon/carbon composites were prepared by a facile way. • The as-prepared Si@C/CNTs and CNFs composites shows excellent electrochemical performance. • The preparation method has mild experiment conditions and high production rate. • The structure benefited electronic transfer and accommodated volume expansion. -- Abstract: Novel silicon@ carbon/carbon nanotubes and carbon nanofibres (Si@C/CNTs and CNFs) composites have been successfully synthesized by a serious of high-energy wet ball milling, closed spray drying and subsequently chemical vapor deposition methods, in which carbon nanotubes and carbon nanofibers are interweaved with carbon coated silicon (Si@C) spherical composites. As anode materials for lithium-ion batteries, the Si@C/CNTs and CNFs composites demonstrate a high first discharge capacity and excellent cycle ability. The high initial specific discharge capacity is approximately 2169 mA h g{sup ?1} and a reversible specific capacity approached 1195 mA h g{sup ?1} after 50 cycles at a high current density of 300 mA g{sup ?1}.

Zhang, Miao [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Hou, Xianhua, E-mail: houxh@scnu.edu.cn [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Engineering Research Center of Materials and Technology for Electrochemical Energy Storage Ministry of Education, Guangzhou 510006 (China); Wang, Jie; Li, Min [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Hu, Shejun [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Engineering Research Center of Materials and Technology for Electrochemical Energy Storage Ministry of Education, Guangzhou 510006 (China); Shao, Zongping [Nanjing University of Technology, College of Chemistry and Chemical Engineering, Nanjing 210009 (China); Liu, Xiang [Institute of Advanced Materials, Nanjing University of Technology, Nanjing 210009 (China)

2014-03-05

95

Zinc Sulfide Tubes Reinforced with Carbon Nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Zinc sulfide submicron and nanotubes with outer diameters in the range from 100 to 1000?nm were produced through chemical deposition from vapor under argon pressure. The novel process provides formation of ZnS tubes reinforced with carbon nanofibers. This is the first time that the ZnS tubes are grown with fibers during deposition.

Kolesnikov, N. N.; Borisenko, D. N.; Borisenko, E. B.; Timonina, A. V.; Kveder, V. V.

2009-01-01

96

Zinc Sulfide Tubes Reinforced with Carbon Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Zinc sulfide submicron and nanotubes with outer diameters in the range from 100 to 1000?nm were produced through chemical deposition from vapor under argon pressure. The novel process provides formation of ZnS tubes reinforced with carbon nanofibers. This is the first time that the ZnS tubes are grown with fibers during deposition.

N. N. Kolesnikov

2009-01-01

97

Enhanced electrical capacitance of porous carbon nanofibers derived from polyacrylonitrile and boron trioxide  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) containing boron and nitrogen are prepared from polyacrylonitrile and boron trioxide (B2O3) by using simple electrospinning. The B2O3 introduction into a PAN solution causes a porous structure with stabilized [O]BN functional groups to develop in the processes of stabilization and carbonization. The pore structure and the functional groups such as B atoms and [O]BN introduce synergistic effects by not only increasing the power density but also the energy density, as shown by the results. The energy storage capabilities of the electrode prepared from 20 wt% B2O3 added to the PAN solution are as follows: a capacitance of 184.0 F g?1 and an energy density of 18.7–25.2 Wh kg?1 in the respective power density range of 400–10,000 W kg?1 in 6 M KOH electrolyte. Hence, these CNFs exhibit a very promising potential as electrode materials for electrical double-layer capacitors due to their unique microstructure and proper proportion of heteroatoms

2013-01-15

98

Electrocatalytic properties of Pt/carbon composite nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H{sub 2}SO{sub 4} and 5.0 mM K{sub 4}[Fe(CN){sub 6}] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm{sup -2} has the highest activity.

Lin Zhan; Ji Liwen [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States); Zhang Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States)], E-mail: xiangwu_zhang@ncsu.edu

2009-11-30

99

Carbon nanofibers: a versatile catalytic support  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electr [...] odes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition) employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Nelize Maria de Almeida, Coelho; Jomar Livramento Barros, Furtado; Cuong, Pham-Huu; Ricardo, Vieira.

100

Carbon nanofibers: a versatile catalytic support  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electrodes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Nelize Maria de Almeida Coelho

2008-09-01

 
 
 
 
101

Damping Augmentation of Nanocomposites Using Carbon Nanofiber Paper  

Directory of Open Access Journals (Sweden)

Full Text Available Vacuum-assisted resin transfer molding (VARTM process was used to fabricate the nanocomposites through integrating carbon nanofiber paper into traditional glass fiber reinforced composites. The carbon nanofiber paper had a porous structure with highly entangled carbon nanofibers and short glass fibers. In this study, the carbon nanofiber paper was employed as an interlayer and surface layer of composite laminates to enhance the damping properties. Experiments conducted using the nanocomposite beam indicated up to 200–700% increase of the damping ratios at higher frequencies. The scanning electron microscopy (SEM characterization of the carbon nanofiber paper and the nanocomposites was also conducted to investigate the impregnation of carbon nanofiber paper by the resin during the VARTM process and the mechanics of damping augmentation. The study showed a complete penetration of the resin through the carbon nanofiber paper. The connectivities between carbon nanofibers and short glass fibers within the carbon nanofiber paper were responsible for the significant energy dissipation in the nanocomposites during the damping tests.

Gangbing Song

2006-06-01

102

Synthesis of carbon nano-fibers on p-Si having improved temperature sensing capability  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Synthesis of carbon nanofibers on p-Si. Black-Right-Pointing-Pointer RBM in Raman spectra. Black-Right-Pointing-Pointer Superior temperature sensing capability. - Abstract: Synthesis of an innovative material for temperature sensor based on carbon nano-fibers (CNFs) on p-Si substrates has been demonstrated. The CNF films were characterized by SEM, Raman and FTIR studies. First order Raman spectra indicated a G band at {approx}1597 cm{sup -1} corresponding to the E{sub 2g} tangential stretching mode of an ordered graphitic structure with sp{sup 2} hybridization and a D band located {approx}1350 cm{sup -1} originated from disordered carbon. Gold fingers were deposited on the p-Si/CNF surface for resistance measurement. Temperature sensing properties were also investigated critically. Resistance changes with temperature ({Delta}R/R) in p-Si/CNF films are found to be significantly large 30-60% Very stable, reproducible and improved temperature sensing properties would make this material superior to commonly available temperature sensors.

Hussain, S. [UGC-DAE CSR, Kalpakkam Node, Kokilamedu 603104 (India); Ghosh, D.; Ghosh, B.; Chaudhuri, Subhajyoti; Bhar, R. [Department of Instrumentation Science, USIC Building, Jadavpur University, Calcutta 700032 (India); Pal, A.K., E-mail: msakp2002@yahoo.co.in [Department of Instrumentation Science, USIC Building, Jadavpur University, Calcutta 700032 (India)

2013-01-01

103

Improving the cyclability and rate capability of carbon nanofiber anodes through in-site generation of SiOx-rich overlayers  

International Nuclear Information System (INIS)

SiOx-rich overlayed carbon nanofibers (SiOx-CNFs) are facilely fabricated through the electrospinning of tetraethyl orthosilicate (TEOS) and polyacrylonitrile (PAN) solution and subsequent hydrolyzation and heat treatments. The SiOx-rich overlayer is apparently observed by high-resolution transmission electron microscopy (HR-TEM), which is also identified using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). The SiOx-CNF electrode shows greatly improved cycle stability and rate capability, remaining 84.2% of its initial discharge capacity in contrast to only 61.4% for pure CNFs and exhibiting a reversible capacity of 288 mAh g?1 at 2 A g?1 compared with that (218 mAh g?1) of pure CNFs. This result is ascribed to the formation of a dense and stable SEI film and the highly improved ionic conductivity of SiOx-CNFs during the Li+ insertion/extraction processes. These results suggest that the introduction of SiOx-rich overlayer onto electrodes is an effective strategy to enhance the stability of SEI film and facilitate the surface Li-ion transfer of electrodes, and thus to improve their cycle stability and rate capability

2013-10-01

104

The synthesis of titanium carbide-reinforced carbon nanofibers  

International Nuclear Information System (INIS)

Tailoring hard materials into nanoscale building blocks can greatly extend the applications of hard materials and, at the same time, also represents a significant challenge in the field of nanoscale science. This work reports a novel process for the preparation of carbon-based one-dimensional hard nanomaterials. The titanium carbide-carbon composite nanofibers with an average diameter of 90 nm are prepared by an electrospinning technique and a high temperature pyrolysis process. A composite solution containing polyacrylonitrile and titanium sources is first electrospun into the composite nanofibers, which are subsequently pyrolyzed to produce the desired products. The x-ray diffraction pattern and transmission electron microscopy results show that the main phase of the as-synthesized nanofibers is titanium carbide. The Raman analyses show that the composite nanofibers have low graphite clusters in comparison with the pure carbon nanofibers originating from the electrospun polyacrylonitrile nanofibers. The mechanical property tests demonstrate that the titanium carbide-carbon nanofiber membranes have four times higher tensile strength than the carbon nanofiber membranes, and the Young's modulus of the titanium carbide-carbon nanofiber membranes increases in direct proportion to the titanium quantity.

2009-06-24

105

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Directory of Open Access Journals (Sweden)

Full Text Available Polycaprolacton (PCL and multiwalled carbon nanotubes/PCL (P-MWNT/PCL were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNTs at high concentration. The thermal stability of the P-MWNT/PCL nanofibers was higher than PCL nanofibers. The conductivity of the adsorbed P-MWNT on PCL (

nanofibers was 1.27 x 10-4 S/cm.

KHALID SAEED

2009-12-01

106

Effect of carbon nanofiber surface groups on oxygen reduction reaction of supported Pt electrocatalyst  

International Nuclear Information System (INIS)

Highlights: ? We studied the effect of oxygen-groups on the particle size and deposition of Pt particles. ? Pt/CNF-OH exhibits smaller Pt mean particle size compared with Pt/CNF-OX. ? Pt/CNF-OH/GC electrode exhibits a better ORR activity than Pt/CNF-OX/GC electrode. -- Abstract: Pt nanoparticles supported on the acid-treated carbon nanofiber (CNF-OX) and LiAlH4-treated carbon nanofiber (CNF-OH) are synthesized via ethylene glycol reduction method. The nature of oxygen-containing surface groups on the CNF-OX and CNF-OH is investigated by potentiometric titration and XPS characterization. Titration of the support materials shows that LiAlH4 can effectively convert the carboxylic acid groups (from 0.21 mmol g?1 to 0.06 mmol g?1) to hydroxyl groups (from 0.09 mmol g?1 to 0.17 mmol g?1), which is agreed well with the results of XPS characterization. High resolution transmission electron microscopy (HRTEM) characterization shows that the Pt nanoparticles are highly dispersed on the two modified CNFs, and the Pt nanoparticles supported on the CNF-OH have a smaller particle size and a more uniform particle size distribution. Rotating disk electrode (RDE) analysis reveals that Pt/CNF-OH exhibits a better activity for ORR than Pt/CNF-OX, and this may be associated with the smaller particle size and better dispersion of Pt nanoparticles on the CNF-OH

2013-02-01

107

Controlling dispersion and electric-field-assisted alignment of carbon nanotubes and nanofibers for multi-functional epoxy composites  

Science.gov (United States)

The objective of this investigation is to enhance the elastic modulus and tailor the electrical conductivity of nanoreinforced epoxy composites. The resin employed in this investigation is a bisphenol F epoxide with an aromatic diamine curative, extensively used for high performance composites. The nanofillers are unfunctionalized and functionalized carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWCNTs). The objectives are achieved by controlling the dispersion and alignment of unfunctionalized and functionalized CNFs and CNTs. The process of ultrasonic agitation was used to disperse nanofillers in epoxy resin. The dispersed nanofillers were aligned using alternating current electric field (AC). Continuous use of ultrasonic agitation reduced the lengths, and increased the degree of dispersion of CNFs and CNTs. The parameters of the ultrasonic agitation process were optimized to minimize the reduction in CNF and CNT lengths while achieving good dispersion of CNFs and CNTs in the resin. The composites manufactured with well dispersed CNFs and CNTs increased the elastic modulus as expected based on the theory of short fiber reinforced composites. The alignment and chaining of CNFs and CNTs dispersed in resin were investigated by experiments and modeling. The assembly of chains was found to depend on the frequency of AC electric field used. The mechanism of CNF/CNT chain assembly and growth in a low viscosity epoxy was investigated by developing a finite element model of a chain attached to an electrode. The model includes the combined effects of electrostatic and electro-hydrodynamic forces on chain morphology. The electro-hydrodynamic forces are modeled using the theory of AC electroosmosis. Predictions of the model are compared to experimental results. The experiments were conducted on a CNF/epoxide/curative mixture by applying an AC field at frequencies ranging from 100 -- 100,000 Hz. Predictions of the model qualitatively capture the variations of chain morphology and growth rate as functions of AC frequency. Higher frequencies promote a more uniform and denser network of chains. The rate of growth of chains is highest at an intermediate frequency. A uniform network of chains was observed at frequencies of 1 kHz and greater in the experiments. The rate of growth of chains was maximized at a frequency of 1 kHz for a liquid viscosity of 0.03 Pa?s. Based on the knowledge of chaining mechanisms, networks of aligned CNFs and CNTs were developed over a 25-mm distance in CNF and CNT epoxy composites. This distance is roughly an order of magnitude greater than previously reported distances obtained with AC electric fields and was accomplished without highly sophisticated electrical equipment. A wide range of anisotropy in direct current (DC) resistivity of CNT/epoxy and CNT/glass fiber/epoxy composites was engineered by using electric fields at different frequencies. The use of AC and DC electric fields in manufacturing buckypapers of aligned CNFs and CNTs was explored. The methods developed to use DC and AC electric fields were found unsuitable for making functional buckypapers with aligned CNFs and CNTs.

Sharma, Ambuj

108

IN-SITU SYNCHROTRON SAXS/WAXD STUDIES DURING MELT SPINNING OF MODIFIED CARBON NANOFIBER AND ISOTACTIC POLYPROPYLENE NANOCOMPOSITE  

International Nuclear Information System (INIS)

The structural development of a nanocomposite, containing 95 wt% isotactic polypropylene (iPP) and 5 wt% modified carbon nanofiber (MCNF), during fiber spinning was investigated by in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. The modification of carbon nanofibers (CNFs) was accomplished by a chemical surface treatment using in situ polymerization of olefin segments to enhance its compatibility with iPP, where the iPP/MCNF nanocomposite was prepared by twostep blending to ensure the dispersion of MCNF. X-ray results showed that at low spin-draw ratios, the iPP/MCNF nanocomposite fiber exhibited much higher iPP crystalline orientation than the control iPP fiber. At higher spin-draw ratios, the crystalline orientation of the nanocomposite fiber and that of the pure iPP fiber was about the same. The crystallinity of the composite fiber was higher than that of the control iPP fiber, indicating the nucleating effect of the modified carbon nanofibers. The nanocomposite fiber also showed larger long periods at low spin-draw ratios. Measurements of mechanical properties indicated that the nanocomposite fiber with 5 wt% MCNF had much higher tensile strength, modulus and longer elongation to break. The mechanical enhancement can be attributed to the dispersion of MCNF in the matrix, which was confirmed by SEM results

2004-01-01

109

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Polycaprolacton (PCL) and multiwalled carbon nanotubes/PCL (P-MWNT/PCL) were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNT...

KHALID SAEED; PARK SOO-YOUNG; MOHAMMAD ISHAQ

2009-01-01

110

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english Polycaprolacton (PCL) and multiwalled carbon nanotubes/PCL (P-MWNT/PCL) were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the [...] mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNTs at high concentration. The thermal stability of the P-MWNT/PCL nanofibers was higher than PCL nanofibers. The conductivity of the adsorbed P-MWNT on PCL (

KHALID, SAEED; PARK, SOO-YOUNG; MOHAMMAD, ISHAQ.

111

In-situ synthesis and thermal-electrical properties of CP2- polyimide/pristine and amine-functionalized carbon nanofiber composites  

Science.gov (United States)

Vapor-grown carbon nanofibers (VGCNF) functionalized with amine-containing pendants, viz.H2N-VGCNF, reacted with 2,2-bis(phthalic anhydride)-1,1,1,3,3,3-hexafluoroisopropane, which was the dianhydride monomer used in in-situ polymerization with 1,3-bis(3-aminophenoxy)benzene to afford a series of CP2-polyimide nanocomposite films (FCNFCP2), containing 0.18-9.19 wt % of H2N-VGCNF (corresponding to 0.10-5.0 wt % of pristine VGCNF), via conventional poly(amic acid) precursor method. For comparison, another series of in situ nanocomposites containing pristine VGCNF (0.10-5.0 wt %) was also prepared similarly. While H2N-VGCNFs enabled direct formation of CP2 grafts on the nanofibers, pristine VGCNFs would result in a relatively weak interface between nanofibers and the CP2 matrix. Conducting-tip atomic force microscopy (C-AFM) showed that the electrical transport was solely through the nanofiber networks in the PCNF-CP2. In general, low-frequency ac impedance measurements followed well the percolation bond model with low percolation threshold; 0.24 and 0.68 vol % for PCNF-CP2 and FCNF-CP2, respectively. However, the design of interface is determined to be crucial for controlling the electrical behavior in four substantial ways: (i) magnitude of limiting conductivity, (ii) linearity of I-V response, (iii) magnitude and direction of temperature-dependent resistivity, and (iv) reproducibility of the absolute value of resistivity with thermal cycling. These observations are consistent with a direct CNF-CNF contact limiting transport in the PCNF-CP2 system, where the CP2 grafts on FCNF form a dielectric layer between individual CNFs, limiting transport within the FCNF-CP2 system. Furthermore, the CP2 grafts on the FCNF surface reduce local polymer dewetting at the nanofiber surfaces when the temperatures exceed the CP2 glass transition, and stabilize the structure of the percolation network and associated conductivity. The general behavior of these interfacial extremes (pristine and fully functionalized CNFs) set important bounds on the design of interface modification for CNFs when the intended use is for electrical performance at elevated temperatures or under extreme current loads. The influence of processing conditions resulting in the spread of measured conductivity by several orders of magnitude for films containing the same type and same amount of CNFs is also reported.

Wang, David H.; Jacobs, J. David; Trionfi, Aaron; Arlen, Michael J.; Hsu, Julia W. P.; Vaia, Richard A.; Tan, Loon-Seng

2009-07-01

112

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon fiber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

André Navarro de Miranda

2011-12-01

113

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon f [...] iber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy) composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

André Navarro de, Miranda; Luiz Claudio, Pardini; Carlos Alberto Moreira dos, Santos; Ricardo, Vieira.

114

Preparation and Application of Fiber Composites made of Carbon nanofibers and Carbide Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Fabrication of carbon fiber reinforced composites was carried out by hand lay-up method. Carbon nanofibers and SiC nanofibers were used as filler in the composites fabrication. Carbon nanofibers, one of the new carbon materials, have 5{approx}500 nm in diameter and 5-100 nm in length. SiC nanofibers were modified by silicon monoxide vapor with carbon nanofibers. The composites were carbonized at 1000 deg. C in a nitrogen atmosphere, and then densified by molten pitches impregnated in vacuum. Multiple cycles of liquid pitch impregnation and carbonization were carried out to obtain a desired density. The composites were characterized by density, microstructure. The inter-laminar shear strength (ILSS) test was performed for mechanical properties. For the new application, the microwave reflective property of composites was investigated. Dielectric constant and permeability spectrum were measured in 12{approx}18 GHz frequency ranges. On the basis of the wave propagation theory in a lossy media, the reflection loss from the composite inter-layer was predict as a function of frequency. (author). 14 refs., 2 tabs., 5 figs.

Lim, Y.S.; Kim, G.D.; Lee, J.C.; Kim, M.S. [Myongji University, Yongin (Korea); Kim, S.S. [Chungbuk National University, Chongju (Korea)

2000-06-01

115

Preparation of a new adsorbent from activated carbon and carbon nanofiber (AC/CNF for manufacturing organic-vacbpour respirator cartridge  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract In this study a composite of activated carbon and carbon nanofiber (AC/CNF was prepared to improve the performance of activated carbon (AC for adsorption of volatile organic compounds (VOCs and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbon nanofibers (CNF were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropores, were activated by CO2 to recover the surface area and micropores. Surface and textural characterizations of the prepared composites were investigated using Brunauer, Emmett and Teller’s (BET technique and electron microscopy respectively. Prepared composite adsorbent was tested for benzene, toluene and xylene (BTX adsorption and then employed in an organic respirator cartridge in granular form. Adsorption studies were conducted by passing air samples through the adsorbents in a glass column at an adjustable flow rate. Finally, any adsorbed species not retained by the adsorbents in the column were trapped in a charcoal sorbent tube and analyzed by gas chromatography. CNFs with a very thin diameter of about 10-20 nm were formed uniformly on the AC/CNF. The breakthrough time for cartridges prepared with CO2 activated AC/CNF was 117 minutes which are significantly longer than for those cartridges prepared with walnut shell- based activated carbon with the same weight of adsorbents. This study showed that a granular form CO2 activated AC/CNF composite could be a very effective alternate adsorbent for respirator cartridges due to its larger adsorption capacities and lower weight.

Forushani Abbas Rahimi

2013-01-01

116

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

This paper studies the mechanism of the formation of carbon nanostructures on carbon nanofibers with Pd nanoparticles by using different carbon sources. The carbon nanofibers with Pd nanoparticles were produced by carbonizing electrospun polyacrylonitrile (PAN) nanofibers including Pd(Ac){sub 2}. Such PAN-based carbon nanofibers were then used as substrates to grow hierarchical carbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbon sources for the carbon nanostructures. With the Pd nanoparticles embedded in the carbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine or chlorobenzine were decomposed into carbon species which were dissolved into the Pd nanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbon nanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffraction analysis and transmission electron microscopy (TEM) were utilized to capture the mechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shaped carbon nanotubes and carbon nano-ribbons. It was observed that the Y-shaped carbon nanotubes and carbon nano-ribbons were formed on carbonized PAN nanofibers containing Pd-nanoparticle catalyst, and the carbon sources played a crucial role in the formation of different hierarchical carbon nanostructures.

Lai Chuilin; Guo Qiaohui; Hou Haoqing [Chemistry College of Jiangxi Normal University, Nanchang 330027 (China); Wu Xiangfa [Department of Engineering Mechanics, University of Nebraska-Lincoln, Lincoln, NE 68588-0526 (United States); Reneker, Darrell H [Department of Polymer Science, University of Akron, Akron, OH 44325 (United States)], E-mail: haoqing@jxnu.edu.cn

2008-05-14

117

Interfacial engineering of carbon nanofiber-graphene-carbon nanofiber heterojunctions in flexible lightweight electromagnetic shielding networks.  

Science.gov (United States)

Lightweight carbon materials of effective electromagnetic interference (EMI) shielding have attracted increasing interest because of rapid development of smart communication devices. To meet the requirement in portable electronic devices, flexible shielding materials with ultrathin characteristic have been pursued for this purpose. In this work, we demonstrated a facile strategy for scalable fabrication of flexible all-carbon networks, where the insulting polymeric frames and interfaces have been well eliminated. Microscopically, a novel carbon nanofiber-graphene nanosheet-carbon nanofiber (CNF-GN-CNF) heterojunction, which plays the dominant role as the interfacial modifier, has been observed in the as-fabricated networks. With the presence of CNF-GN-CNF heterojunctions, the all-carbon networks exhibit much increased electrical properties, resulting in the great enhancement of EMI shielding performance. The related mechanism for engineering the CNF interfaces based on the CNF-GN-CNF heterojunctions has been discussed. Implication of the results suggests that the lightweight all-carbon networks, whose thickness and density are much smaller than other graphene/polymer composites, present more promising potential as thin shielding materials in flexible portable electronics. PMID:24914611

Song, Wei-Li; Wang, Jia; Fan, Li-Zhen; Li, Yong; Wang, Chan-Yuan; Cao, Mao-Sheng

2014-07-01

118

Improved fire retardancy of thermoset composites modified with carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Multifunctional thermoset composites were made from polyester resin, glass fiber mats and carbon nanofiber sheets (CNS). Their flaming behavior was investigated with cone calorimeter under well-controlled combustion conditions. The heat release rate was lowered by pre-planting carbon nanofiber sheets on the sample surface with the total fiber content of only 0.38 wt.%. Electron microscopy showed that carbon nanofiber sheet was partly burned and charred materials were formed on the combusting surface. Both the nanofibers and charred materials acted as an excellent insulator and/or mass transport barrier, improving the fire retardancy of the composite. This behavior agrees well with the general mechanism of fire retardancy in various nanoparticle-thermoplastic composites.

Zhao Zhongfu [State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, 158 Zhongshan Road, Dalian 116012 (China); Gou Jan [Department of Mechanical, Materials and Aerospace Engineering University of Central Florida, FL 32816 (United States)], E-mail: zhongfuzhao@gmail.com

2009-01-15

119

Improved fire retardancy of thermoset composites modified with carbon nanofibers  

International Nuclear Information System (INIS)

Multifunctional thermoset composites were made from polyester resin, glass fiber mats and carbon nanofiber sheets (CNS). Their flaming behavior was investigated with cone calorimeter under well-controlled combustion conditions. The heat release rate was lowered by pre-planting carbon nanofiber sheets on the sample surface with the total fiber content of only 0.38 wt.%. Electron microscopy showed that carbon nanofiber sheet was partly burned and charred materials were formed on the combusting surface. Both the nanofibers and charred materials acted as an excellent insulator and/or mass transport barrier, improving the fire retardancy of the composite. This behavior agrees well with the general mechanism of fire retardancy in various nanoparticle-thermoplastic composites.

2009-01-01

120

Structural transformation of vapor grown carbon nanofibers studied by HRTEM  

International Nuclear Information System (INIS)

Vapor grown carbon nanofibers have been extensively manufactured and investigated in recent years. In this study commercially available vapor grown carbon nanofibers subjected to different processing and post processing conditions were studied employing high resolution TEM images. The analysis showed that the fibers consist primarily of conical nanofibers, but can contain a significant amount of bamboo nanofibers. Most conical nanofibers were found to consist of an ordered inner layer and a disordered outer layer, with the cone angle distribution of the inner layers indicating that these cannot have a stacked cone structure but are compatible with a cone-helix structure. Fibers that have been heat treated to temperatures above 1,500 oC undergo a structural transformation with the ordered inner layers changing from a cone-helix structure to a highly ordered multiwall stacked cone structure. The bamboo nanofibers were found to have a tapered multiwall nanotube structure for the wall and a multishell fullerene structure for the cap of each segment, surrounded by a disordered outer layer. When these fibers are heat treated the disordered outer layers transform to an ordered multiwall nanotube structure and merge with the wall of each segment. The end caps of each segment transform from a smooth multiwall fullerene structure to one consisting of disjointed graphene planes. A reaction-diffusion mechanism is proposed to explain the growth and structure of the bamboo nanofibers.

2008-10-01

 
 
 
 
121

Structural transformation of vapor grown carbon nanofibers studied by HRTEM  

Energy Technology Data Exchange (ETDEWEB)

Vapor grown carbon nanofibers have been extensively manufactured and investigated in recent years. In this study commercially available vapor grown carbon nanofibers subjected to different processing and post processing conditions were studied employing high resolution TEM images. The analysis showed that the fibers consist primarily of conical nanofibers, but can contain a significant amount of bamboo nanofibers. Most conical nanofibers were found to consist of an ordered inner layer and a disordered outer layer, with the cone angle distribution of the inner layers indicating that these cannot have a stacked cone structure but are compatible with a cone-helix structure. Fibers that have been heat treated to temperatures above 1,500 {sup o}C undergo a structural transformation with the ordered inner layers changing from a cone-helix structure to a highly ordered multiwall stacked cone structure. The bamboo nanofibers were found to have a tapered multiwall nanotube structure for the wall and a multishell fullerene structure for the cap of each segment, surrounded by a disordered outer layer. When these fibers are heat treated the disordered outer layers transform to an ordered multiwall nanotube structure and merge with the wall of each segment. The end caps of each segment transform from a smooth multiwall fullerene structure to one consisting of disjointed graphene planes. A reaction-diffusion mechanism is proposed to explain the growth and structure of the bamboo nanofibers.

Lawrence, Joseph G. [University of Toledo, Chemical and Environmental Engineering Department (United States); Berhan, Lesley M. [University of Toledo, Mechanical, Industrial and Manufacturing Engineering Department (United States); Nadarajah, Arunan, E-mail: nadarajah@utoledo.ed [University of Toledo, Chemical and Environmental Engineering Department (United States)

2008-10-15

122

On the growth of carbon nanofibers on glass with a Cr layer by inductively coupled plasma chemical vapor deposition: The effect of Ni film thickness  

International Nuclear Information System (INIS)

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrogen, during the ICP-CVD growth. A field emission measurement apparatus based on a metallic probe of spherical anode structure was also constructed in this study. An electrostatic image model was employed to determine the electric field distribution on the cathode surface. Along with the standard F-N field emission model, the dependence of field emission current density on the cathode surface electric field, as well as an effective field enhancement factor, were extracted from the current-voltage measurement results. The threshold electric field (Ethreshold, for a current density of 1 mA/cm2) increases from 9.2 V/?m to 13.1 V/?m, and then drops to 11.5 V/?m for the CNFs with Ni film thicknesses of 20 nm, 30 nm, and 40 nm, respectively. The electrostatic model results also indicate that the 20 nm case has the greatest space-charge effect on the emission current, consistent with the growth results that the 20 nm case has the lowest CNF density. On the other hand, the CNF length of the 40 nm case is longer than that of the 30 nm one, while the densities are nearly the same; as a result, Ethreshold for the 30 nm case is higher

2007-12-01

123

Synthesis of carbon nanofiber films and nanofiber composite coatings by laser-assisted catalytic chemical vapor deposition  

International Nuclear Information System (INIS)

Uniform carbon nanofiber films and nanofiber composite coatings were synthesized from ethylene on nickel coated alumina substrates by laser-assisted catalytic chemical vapor deposition. Laser annealing of a 50 nm thick nickel film produced the catalytic nanoparticles. Thermal decomposition of ethylene over nickel nanoparticles was initiated and maintained by an argon ion laser operated at 488 nm. The films were examined by scanning electron microscopy and by transmission electron microscopy. Overall film uniformity and structure were assessed using micro-Raman spectroscopy. Film quality was related to the experimental parameters such as incident laser power density and irradiation time. For long irradiation times, carbon can be deposited by a thermal process rather than by a catalytic reaction directly over the nanofiber films to form carbon nanocomposite coatings. The process parameters leading to high quality nanofiber films free of amorphous carbon by-products as well as those leading to nanofiber composite coatings are presented

2007-01-22

124

Preparation of Electrically Conductive Polystyrene/Carbon Nanofiber Nanocomposite Films  

Science.gov (United States)

A simple and effective approach to prepare conductive polystyrene/carbon nanofiber (PS/CNF) nanocomposite films via a solution dispersion method is presented. Inexpensive CNF, which has a structure similar to multi-walled carbon nanotubes, is chosen as a nanofiller in this experiment to achieve conductivity in PS films. A good dispersion is…

Sun, Luyi; O'Reilly, Jonathan Y.; Tien, Chi-Wei; Sue, Hung-Jue

2008-01-01

125

Health effects of exposure to carbon nanofibers: Systematic review, critical appraisal, meta analysis and research to practice perspectives  

International Nuclear Information System (INIS)

Background: Literature reviews examining the relationship between exposure to carbon nanofibers (CNFs) and health consequences are qualitative in nature and do not employ an evidence-based assessment. Objective: This research deals with a systematic review, critical appraisal, and meta-analysis designed to examine the potential health effects associated with exposure to CNFs. The utilization of research findings into practice is also explored. Methods: Published articles were obtained from a search of electronic databases and bibliographies of identified articles. A critical appraisal was conducted using an 'Experimental Appraisal Instrument' developed in this study. The meta-analysis was established using statistical techniques with/without the incorporation of overall study quality. The likelihood of utilizing research findings into practice (i.e., from research to practice) was computed using a four-step algorithm based on the criteria of: strength of association, consistency among studies, temporality, biological gradient, type of experimental unit, type of CNF (single- and multi-wall nanotubes), CNF grade (commercial or altered), exposure dose, exposure duration, and support by analogy from the published literature. Results: Twenty-one experimental studies satisfied the inclusion criteria and were performed on human cells, experimental animal models and animal cells as experimental units. The methodological qualities of published studies ranged from 'very poor' to 'excellent', with 'overall study description' scoring 'good' and 'study execution' equal to 'moderate'. The random-effects model was applied in the meta-analysis calculations as heterogeneity was significant at the 10% for all outcomes reported. The mean standardized meta-estimates for the experimental groups were significantly lower than those for the control groups for cell viability and cell death, respectively. Incorporating the effect of overall study quality score widened the gap between the experimental and control groups. Assessment of research findings on the basis of the four-step algorithm revealed that the likelihood of the results to occur in practice is 'somewhat possible' at this time. That is, if exposure conditions to CNF in the reported studies are similar to those in nano-manufacturing plants, it is somewhat possible that CNFs alter the function of human cells resulting in loss of cell viability and cell death. Conclusions: Our findings suggest that it is 'somewhat possible' for the CNF to penetrate the human cells in the targeted organs and to cause cellular damage. Although the weight of evidence is not sufficient, it is advisable that actions be taken to ensure the protection of workers exposed to CNFs, that is, (a) engineering controls should be established to contain exposure to CNF, and (b) simultaneously rigorous personnel protective equipment should be planned to further minimize the risk of CNF exposure.

2009-06-01

126

Preparation of a New Adsorbent from Activated Carbon and Carbon Nanofiber (AC/CNF for Manufacturing Organic-Vacbpour Respirator Cartridge  

Directory of Open Access Journals (Sweden)

Full Text Available In this study a composite of activated carbon and carbon nanofiber (AC/CNF was prepared to improve the performance of activated carbon (AC for adsorption of volatile organic compounds (VOCs and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbonnanofibers (CNF were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropores, were activated by CO2 to recover the surface area and micropores.Surface and textural characterizations of the prepared composites were investigated using Brunauer, Emmett andTeller’s (BET technique and electron microscopy respectively. Prepared composite adsorbent was tested forbenzene, toluene and xylene (BTX adsorption and then employed in an organic respirator cartridge in granularform. Adsorption studies were conducted by passing air samples through the adsorbents in a glass column at an adjustable flow rate. Finally, any adsorbed species not retained by the adsorbents in the column were trapped in a charcoal sorbent tube and analyzed by gas chromatography. CNFs with a very thin diameter of about 10-20 nmwere formed uniformly on the AC/CNF. The breakthrough time for cartridges prepared with CO2 activated AC/CNF was 117 minutes which are significantly longer than for those cartridges prepared with walnut shell- based activated carbon with the same weight of adsorbents. This study showed that a granular form CO2 activated AC/CNF composite could be a very effective alternate adsorbent for respirator cartridges due to its larger adsorption capacities and lower weight.

Mehdi Jahangiri

2013-01-01

127

Surface functionalization of carbon nanofibers by sol-gel coating of zinc oxide  

International Nuclear Information System (INIS)

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers

2008-08-15

128

Surface functionalization of carbon nanofibers by sol gel coating of zinc oxide  

Science.gov (United States)

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers.

Shao, Dongfeng; Wei, Qufu; Zhang, Liwei; Cai, Yibing; Jiang, Shudong

2008-08-01

129

Surface functionalization of carbon nanofibers by sol-gel coating of zinc oxide  

Energy Technology Data Exchange (ETDEWEB)

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers.

Shao Dongfeng [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China); Changzhou Textile Garment Institute, Changzhou 213164 (China); Wei Qufu [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)], E-mail: qfwei@jiangnan.edu.cn; Zhang Liwei; Cai Yibing; Jiang Shudong [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)

2008-08-15

130

Plasma-enhanced chemical vapor deposition of multiwalled carbon nanofibers  

Science.gov (United States)

Plasma-enhanced chemical vapor deposition is used to grow vertically aligned multiwalled carbon nanofibers (MWNFs). The graphite basal planes in these nanofibers are not parallel as in nanotubes; instead they exhibit a small angle resembling a stacked cone arrangement. A parametric study with varying process parameters such as growth temperature, feedstock composition, and substrate power has been conducted, and these parameters are found to influence the growth rate, diameter, and morphology. The well-aligned MWNFs are suitable for fabricating electrode systems in sensor and device development.

Matthews, Kristopher; Cruden, Brett A.; Chen, Bin; Meyyappan, M.; Delzeit, Lance

2002-01-01

131

Differences between carbon nanofibers produced using Fe and Ni catalysts in a floating catalyst reactor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers were produced by the catalytic CVD process by the floating catalyst method, in semi-industrial systems at temperatures above 1350 K. Iron-derived carbon nanofibers were produced from natural gas and xylene, using ferrocene as catalyst source, yielding a thickened submicron vapor grown carbon fibers with a core of multi-wall nanotubes. For the production of Ni derived nanofibers, natural gas was used as the carbon feedstock, and the Ni was added in a nickel compound ...

Marti?n Gullo?n, Ignacio; Vera Agullo?, Jose?; Conesa Ferrer, Juan Antonio; Gonza?lez, Jose? L.; Merino Sa?nchez, Ce?sar

2006-01-01

132

Carbon Nanofibers as Catalyst Support for Noble Metals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the quest for new and well-defined support materials for heterogeneous catalysts we explored the potential of carbon nanofibers (CNF). CNF belongs to the by now extensive family of synthetic graphite-like carbon materials with advantageous and tunable physico-chemical properties. Aim of the work described in this thesis has been the exploration of the potential of CNF as catalyst support material, notably for platinum and ruthenium, and its role in the performance of these catalysts in hyd...

Toebes, M. L.

2004-01-01

133

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection  

Science.gov (United States)

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

Manea, Florica; Motoc, Sorina; Pop, Aniela; Remes, Adriana; Schoonman, Joop

2012-06-01

134

Vertically Aligned Carbon Nanofiber Based Biosensor Platform for Glucose Sensor  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned carbon nanofibers (VACNFs) have recently become an important tool for biosensor design. Carbon nanofibers (CNF) have excellent conductive and structural properties with many irregularities and defect sites in addition to exposed carboxyl groups throughout their surfaces. These properties allow a better immobilization matrix compared to carbon nanotubes and offer better resolution when compared with the FET-based biosensors. VACNFs can be deterministically grown on silicon substrates allowing optimization of the structures for various biosensor applications. Two VACNF electrode architectures have been employed in this study and a comparison of their performances has been made in terms of sensitivity, sensing limitations, dynamic range, and response time. The usage of VACNF platform as a glucose sensor has been verified in this study by selecting an optimum architecture based on the VACNF forest density. Read More: http://www.worldscientific.com/doi/abs/10.1142/S0129156414500062

Mamun, Khandaker Abdullah Al [ORNL; Tulip, Fahmida S [ORNL; Macarthur, Kimberly C [ORNL; McFarlane, Nicole M [ORNL; Islam, Syed K [ORNL

2014-01-01

135

Genotoxicity of carbon nanofibers: Are they potentially more or less dangerous than carbon nanotubes or asbestos?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and gen...

2011-01-01

136

Carbon nanotube/nanofiber embedded nanoporous anodized aluminium oxide surface and its tribological properties.  

Science.gov (United States)

Nanoporous alumina has been prepared by anodization of pure aluminium using phosphoric acid electrolyte. Carbon nanotubes/nanofibres (CNTs/CNFs) are grown within the pores by chemical vapour deposition technique, using acetylene gas as carbon precursor. Such synthesis of nanostructured carbonaceous materials within the nanoporous oxide template has high potential for many applications (e.g., electronics, magnetic, etc.) in nanotechnology. Possibility of using such material combination for engineering systems where abrasion resistance coupled with self-lubrication (at comparatively higher loads) are the key requirements, has been explored through the present work. Pore structure has been characterized by SEM/FE-SEM in this study and CNTs/CNFs have been examined by TEM, FE-SEM and Raman spectroscopy. While the pore diameters are found to lie in the range of 180-220 nm, the CNTs/CNFs diameter are observed to be in the range of 50 to 220 nm. The CNTs/CNFs growing from bottom of the pores are found to replicate the pore diameter, while those grown above the surface are varying significantly in diameter and probably matching the diameter of the catalyst, which remains adsorbed on the top surface and inner walls of the pores. On comparing friction and wear properties of both materials (viz. anodized alumina and CNTs/CNFs embedded anodized alumina) as determined by pin-on-disc machine using hardened steel disc as counterface, it is found that wear rate and coefficient of friction of CNTs embedded composite surface is significantly lower which is attributed to formation of transfer layer of hard wear resistant alumina mechanically mixed with graphitic CNTs/CNFs. PMID:19049193

Kushwaha, M K; Sil, Anjan; Ray, S

2008-08-01

137

Pt/carbon nanofibers electrocatalysts for fuel cells: effect of the support oxidizing treatment  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Different Pt-based electrocatalysts supported on carbon nanofibers and carbon black (Vulcan XC-72R) have been prepared using a polymermediated synthesis. The electrocatalysts have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and cyclic voltammetry. The effect of carbon nanofibers treatment with HNO3 solution on Pt particle size and electroactive area has been analyzed. Highly

Zaragoza Marti?n, Francisco; Sopen?a Escario, Daniel; Morallo?n Nu?n?ez, Emilia; Salinas Marti?nez Lecea, Concepcio?n

2007-01-01

138

Template Synthesis of Carbon Nanofibers Containing Linear Mesocage Arrays  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Carbon nanofibers containing linear mesocage arrays were prepared via evaporation induced self-assembly method within AAO template with an average channel diameter of about 25 nm. The TEM results show that the mesocages have an elongated shape in the transversal direction. The results of N2 adsorption–desorption analysis indicate that the sample possesses a cage-like mesoporous structure and the average mesopore size of the sample is about 18 nm.

Wang Yongwen

2010-01-01

139

Template synthesis of carbon nanofibers containing linear mesocage arrays.  

Science.gov (United States)

Carbon nanofibers containing linear mesocage arrays were prepared via evaporation induced self-assembly method within AAO template with an average channel diameter of about 25 nm. The TEM results show that the mesocages have an elongated shape in the transversal direction. The results of N2 adsorption-desorption analysis indicate that the sample possesses a cage-like mesoporous structure and the average mesopore size of the sample is about 18 nm. PMID:20671793

Wang, Yongwen; Zheng, Mingbo; Lu, Hongling; Feng, Shaoqing; Ji, Guangbin; Cao, Jieming

2010-01-01

140

Direct imaging of copper catalyst migration inside helical carbon nanofibers  

Science.gov (United States)

By using a double-aberration-corrected (scanning) transmission electron microscope (STEM/TEM) at an acceleration voltage of only 80 kV, we demonstrate that, due to the low solubility of copper (Cu) in carbon and its affinity with oxygen (O), single-crystal Cu catalysts dissociate into small cuprous oxide (Cu2O) nanoparticles after the growth of carbon nanofibers, and Cu2O nanoparticles ultimately localize on the fiber surfaces. This new finding is a step toward a better understanding of the interactions between Cu catalysts and carbon nanomaterials and could suggest a simple and effective method for eliminating Cu impurities from the fibers.

Dong, Lifeng; Yu, Liyan; Cui, Zuolin; Dong, Hongzhou; Ercius, Peter; Song, Chengyu; Duden, Thomas

2012-01-01

 
 
 
 
141

Effect of carbon nanofiber dispersion on the properties of PIP-SiC/SiC composites  

Energy Technology Data Exchange (ETDEWEB)

SiC/SiC composites with and without dispersed carbon nanofiber were fabricated by the polymer impregnation and pyrolysis process. The effect of dispersing carbon nanofiber on the mechanical and thermal properties of SiC/SiC composites was investigated. The bending strength and elastic modulus of SiC/SiC composites with carbon nanofiber decreased slightly compared to those of the SiC/SiC composites without the nanofiber. On the other hand, the thermal conductivity of SiC/SiC composites increased with increasing amount of dispersed nanofiber. The dominant reason is considered to be that the pore shape changed from an oblong shape perpendicular to the direction of heat flow to an isotropic. The shape change resulted from the dispersed carbon nanofiber.

Taguchi, T., E-mail: taguchi.tomitsugu@jaea.go.jp [Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195 (Japan); Hasegawa, Y., E-mail: hasegawa@artkagaku.co.jp [Art Kagaku Co., Ltd., 3129-40 Muramatsu, Tokai, Ibaraki 319-1231 (Japan); Shamoto, S., E-mail: shamoto.shinichi@jaea.go.jp [Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195 (Japan)

2011-10-01

142

The use of carbon nanofibers as a novel catalyst support for hydrogenation reactions  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers, grown catalytically by the decomposition of selected hydrocarbons and carbon monoxide, possess unique physical and chemical properties which make them very attractive materials for use as catalyst supports. Three different structures of these carbon nanofibers have been utilised in these hydrogenation studies as a novel catalyst support material. The activity of a metal supported on these different forms of nanofibers were compared against the more traditional catalyst supports, Al{sub 2}O{sub 3}, TiO{sub 2} and active carbon. The different structures and graphitic nature of the carbon nanofibers have been shown to have a profound effect on the activity and selectivity of the hydrogenation reaction. Initial hydrogenation studies have revealed that the catalytic performance of a metal supported on carbon nanofibers was found to be superior when compared to that found fro the same metal supported on traditional catalyst supports or on active carbon.

Park, C.; Rodriguez, N.M.; Baker, R.T.K. [Pennsylvania State Univ., University Park, PA (United States)

1996-10-01

143

Hydrogen storage in CO2-activated amorphous nanofibers and their monoliths  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Amorphous carbon nanofibers (CNFs), produced by the polymer blend technique, are activated by CO2 (ACNFs). Monoliths are synthesized from the precursor and from some ACNFs. Morphology and textural properties of these materials are studied. When compared with other activating agents (steam and alkaline hydroxides), CO2 activation renders suitable yields and, contrarily to most other precursors, turns out to be advantageous for developing and controlling their narrow microporosity (< 0.7 nm), V...

Kunowsky, Mirko; Marco Lozar, Juan Pablo; Oya, Asao; Linares Solano, A?ngel

2011-01-01

144

Relationship between Single Walled Carbon Nanotubes Individual Dispersion Behavior and Properties of Electrospun Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available The dispersion stability behavior of single walled carbon nanotube (SWCNT has important effects on morphological and mechanical properties of SWCNT/polymer composite nanofibers. The relationship of the dispersion conditions with morphological and mechanical characteristics for SWCNT / polyacrylonitrile (PAN / polyvinylpyrrolidone (PVP composite nanofibers have been examined. The SEM and TEM analyses of the nanofibers revealed that the deformation in the nanofiber structures increases with increasing SWCNT concentration. Our data indicate that with increasing the amount of SWCNT (from 0 to 2 wt %, the average nanofiber diameter was increased from 163±19 nm to 307±34 nm. Tensile results showed that only 2 wt % SWCNT loading to the electrospun composite nanofibers gave rise to 10-fold and 3-fold increase in the tensile modulus and tenacity of nanofiber layers, respectively. Essentially, high mechanical properties and uniform morphology of the composite naofibers were found at SWCNT concentration of ~2 wt % due to their stable and individual dispersion.

Haji A.

2013-09-01

145

CoSn/carbon composite nanofibers for applications as anode in lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

CoSn/carbon composite nanofibers were prepared by electrospinning followed by heat treatment. Uniform morphologies and microstructures were observed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The results demonstrated that well-dispersed nanoparticles of CoSn intermetallic compound and Sn with diameter of about 30-50 nm embedded in carbon nanofibers were prepared after carbonization at 850 Degree-Sign C. Compared with pure carbon nanofibers without the nanoparticles, CoSn/carbon composite nanofibers showed a high reversible capacity and excellent cycling performance, resulting from the formation of CoSn intermetallic nanoparticles and buffering by the carbon nanofiber matrix. The nanofiber mats with good flexibility were utilized as anodes in lithium-ion batteries, and the CoSn/carbon composite nanofibers exhibited a good fibrous morphology after the discharge/charge processes. Results indicated that electrospinning could be a feasible method to prepare Co-Sn-C composite nanofibers as anodes in lithium-ion batteries.

Lu, Weili; Luo, Chenghao; Li, Yu; Feng, Yiyu; Feng, Wei, E-mail: weifeng@tju.edu.cn; Zhao, Yunhui; Yuan, Xiaoyan, E-mail: yuanxy@tju.edu.cn [Tianjin University, School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials (China)

2013-09-15

146

Carbon-coated Li3 N nanofibers for advanced hydrogen storage.  

Science.gov (United States)

3D porous carbon-coated Li3 N nanofibers are successfully fabricated via the electrospinning technique. The as-prepared nanofibers exhibit a highly improved hydrogen-sorption performance in terms of both thermodynamics and kinetics. More interestingly, a stable regeneration can be achieved due to the unique structure of the nanofibers, over 10 cycles of H2 sorption at a temperature as low as 250 °C. PMID:23966063

Xia, Guanglin; Li, Dan; Chen, Xiaowei; Tan, Yingbin; Tang, Ziwei; Guo, Zaiping; Liu, Huakun; Liu, Zongwen; Yu, Xuebin

2013-11-20

147

EFFECT OF CELLULOSE NANOFIBERS ISOLATED FROM BAMBOO PULP RESIDUE ON VULCANIZED NATURAL RUBBER  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nanocomposites were prepared using two bioresources, viz., cellulose nanofibers (CNFs) extracted from bamboo paper-pulp waste as the reinforcing phase and natural rubber (NR) as the matrix phase. CNFs with diameters up to 50 nm were isolated from bamboo pulp waste, and nanocomposites with 5 and 10% CNFs were obtained via two-roll mill mixing of solid natural rubber with a master batch containing 20 wt% CNFs. The NR phase was cross-linked using sulphur vulcanization. The morphology studies sho...

2012-01-01

148

Ellipsometric investigations of photonic crystals based on carbon nanofibers  

CERN Multimedia

Carbon nanofibers (CNF) are used as components of planar photonic crystals (PC). Square and rectangular lattices as well as random patterns of vertically aligned CNF were fabricated and their properties studied using ellipsometry. Conventional methods of ellipsometric analysis used in thin film ellipsometry are not applicable to these samples due to their nanostructured nature. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam.

Rehammar, R; Arwin, H; Kinaret, J M; Campbell, E E B

2010-01-01

149

Mechanical properties of carbon nanotubes and nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanotubes (CNTs) have extraordinary electrical and mechanical properties, and many potential applications have been proposed, ranging from nanoscale devices to reinforcement of macroscopic structures. However, due to their small sizes, characterization of their mechanical properties and deformation behaviours are major challenges. Theoretical modelling of deformation behaviours has shown that multi-walled carbon nanotubes (MWCNTs) can develop ripples in the walls on the contracted side...

2012-01-01

150

Electromagnetic Properties of Novel Carbon Nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbonized bacterial cellulose (CBC) with a three dimensional net-linked framework were synthesized from carbonized bacterial cellulose and investigated by X-ray diffraction, Raman spectrum and Transmission electron microscopy. The complex permittivity and permeability of CBC/paraffin wax composite with certain ratio of the composite were measured by vector network analysis in the frequency range of 0.1–18 GHz. It is found that the composite has high permittivity and dielectric loss, es...

Wang Gai-hua, Dai Bo

2013-01-01

151

Soft-templated synthesis of mesoporous carbon nanospheres and hollow carbon nanofibers  

Science.gov (United States)

Using coal tar pitch based amphiphilic carbonaceous materials (ACMs) as the precursor and amphiphilic triblock copolymer Plutonic P123 as the only soft template, carbon nanospheres with partially ordered mesopores and hollow carbon nanofibers were synthesized. The concentration of P123, cp, and the mass ratio of P123 to ACM, r, are the key parameters of controlling the shape of the as-prepared products. Mesoporous carbon nanospheres with diameter of 30-150 nm were prepared under the condition of cp = 13.3 g/L and r = 1.2. When cp = 26.7 g/L and r = 2, hollow carbon nanofibers with diameters of 50-200 nm and mesopores/macropores were obtained. Carbon nanospheres and hollow carbon fibers were amorphous materials. The mesoporous carbon nanospheres show good stability in the cyclic voltammograms and their specific capacitance at 10 mV s-1 is 172.1 F/g.

Cheng, Youliang; Li, Tiehu; Fang, Changqing; Zhang, Maorong; Liu, Xiaolong; Yu, Ruien; Hu, Jingbo

2013-10-01

152

Branched carbon nanofiber network synthesis at room temperature using radio frequency supported microwave plasmas  

Science.gov (United States)

Carbon nanofibers have been grown at room temperature using a combination of radio frequency and microwave assisted plasma-enhanced chemical vapor deposition. The nanofibers were grown, using Ni powder catalyst, onto substrates kept at room temperature by using a purposely designed water-cooled sample holder. Branched carbon nanofiber growth was obtained without using a template resulting in interconnected carbon nanofiber network formation on substrates held at room temperature. This method would allow room-temperature direct synthesized nanofiber networks over relatively large areas, for a range of temperature sensitive substrates, such as organic materials, plastics, and other polymers of interest for nanoelectronic two-dimensional networks, nanoelectromechanical devices, nanoactuators, and composite materials.

Boskovic, Bojan O.; Stolojan, Vlad; Zeze, Dagou A.; Forrest, Roy D.; Silva, S. Ravi P.; Haq, Sajad

2004-09-01

153

Titanium carbide/carbon composite nanofibers prepared by a plasma process  

Energy Technology Data Exchange (ETDEWEB)

The incorporation of metal or metal carbide nanoparticles into carbon nanofibers modifies their properties and enlarges their field of application. The purpose of this work is to report a new non-catalytic and easy method to prepare organized metal carbide-carbon composite nanofibers on nanopatterned silicon substrates prepared by laser interference lithography coupled with deep reactive ion etching. Titanium carbide-carbon composite nanofibers were grown on the top of the silicon lines parallel to the substrate by a hybrid plasma process combining physical vapor deposition and plasma enhanced chemical vapor deposition. The prepared nanofibers were analyzed by scanning electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. We demonstrate that the shape, microstructure and the chemical composition of the as-grown nanofibers can be tuned by changing the plasma conditions.

El Mel, A A; Gautron, E; Angleraud, B; Granier, A; Tessier, P Y [Universite de Nantes, CNRS, Institut des Materiaux Jean Rouxel, UMR 6502, 2 rue de la Houssiniere BP 32229-44322 Nantes cedex 3 (France); Choi, C H [Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)

2010-10-29

154

Characterization of Nanostructure and Electronic Properties of Catalytically Grown Carbon Nanofiber  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers were prepared from the decomposition of various carbon- containing gases over pure Ni, pure Fi and their alloys with Cu. The yields, properties and structure of carbon nanofibers obtained from the various reaction conditions were analyzed. Type of reacting gas, reaction temperature and catalyst composition were changed as the reaction variable. With Ni-Cu catalysts, the maximum yields of carbon nanofibers were obtained at temperatures between 550 and 650 deg. C according to the reacting gas mixtures of C{sub 2}H{sub 2}-H{sub 2}, C{sub 2}H{sub 4}-H{sub 2} and C{sub 3}H{sub 8}-H{sub 2}, and the surface areas of the carbon nanofibers produced were 20{approx}350m{sup 2}/g. In the case of CO-H{sub 2} mixture, the rapid deposition of carbon nanofibers occurred with Fe-Cu catalyst and the maximum yield were obtained around 550 deg. C with the range of surface areas of 140{approx}170m{sup 2}/g. The electrical resistivity of carbon nanofiber regarded as the key property of filler for the application of electromagnetic interference shielding was very sensitive to the type of reactant gas and the catalyst composition ranging 0.07{approx}1.5{omega}cm at a pressure of 10000 psi, and the resistivity of carbon nanofibers produced over pure nickel catalyst were lower than those over allot catalysts. SEM observation showed that the carbon nanofibers produced had the diameters ranging 20{approx}300 nm and the straight structure of carbon nanofibers changed into the twisted or helical conformation by the variation of reacting gas and catalyst composition. (author). 19 refs., 6 tabs., 5 figs.

Kim, M.S.; Woo, W.J.; Song, H.S.; Lee, Y.S.; Lee, J.C. [Myoungji University, Yongin (Korea)

2000-04-01

155

Synthesis and electrocatalysis of 1-aminopyrene-functionalized carbon nanofiber-supported platinum-ruthenium nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Platinum-ruthenium/carbon composite nanofibers were prepared by depositing PtRu nanoparticles directly onto electrospun carbon nanofibers using a polyol processing technique. The morphology and size of PtRu nanoparticles were controlled by 1-aminopyrene functionalization. The noncovalent functionalization of carbon nanofibers by 1-aminopyrene is simple and can be carried out at ambient temperature without damaging the integrity and electronic structure of carbon nanofibers. The resulting PtRu/carbon composite nanofibers were characterized by cyclic voltammogram in 0.5 M H{sub 2}SO{sub 4} and 0.125 M CH{sub 3}OH + 0.2 M H{sub 2}SO{sub 4} solutions, respectively. The PtRu/carbon composite nanofibers with 1-aminopyrene functionalization have smaller nanoparticles and a more uniform distribution, compared with those pretreated with conventional acids. Moreover, PtRu/1-aminopyrene functionalized carbon nanofibers have high active surface area and improved performance towards the electrocatalytic oxidation of methanol. (author)

Lin, Zhan; Ji, Liwen; Krause, Wendy E.; Zhang, Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, NC 27695-8301 (United States)

2010-09-01

156

Carbon Nanofibers Synthesized on Selective Substrates for Nonvolatile Memory and 3D Electronics  

Science.gov (United States)

A plasma-enhanced chemical vapor deposition (PECVD) growth technique has been developed where the choice of starting substrate was found to influence the electrical characteristics of the resulting carbon nanofiber (CNF) tubes. It has been determined that, if the tubes are grown on refractory metallic nitride substrates, then the resulting tubes formed with dc PECVD are also electrically conducting. Individual CNFs were formed by first patterning Ni catalyst islands using ebeam evaporation and liftoff. The CNFs were then synthesized using dc PECVD with C2H2:NH3 = [1:4] at 5 Torr and 700 C, and approximately equal to 200-W plasma power. Tubes were grown directly on degenerately doped silicon substrates with resistivity rho approximately equal to 1-5 meterohm-centimeter, as well as NbTiN. The approximately equal to 200-nanometer thick refractory NbTiN deposited using magnetron sputtering had rho approximately equal to 113 microohm-centimeter and was also chemically compatible with CNF synthesis. The sample was then mounted on a 45 beveled Al holder, and placed inside a SEM (scanning electron microscope). A nanomanipulator probe stage was placed inside the SEM equipped with an electrical feed-through, where tungsten probes were used to make two-terminal electrical measurements with an HP 4156C parameter analyzer. The positive terminal nanoprobe was mechanically manipulated to physically contact an individual CNF grown directly on NbTiN as shown by the SEM image in the inset of figure (a), while the negative terminal was grounded to the substrate. This revealed the tube was electrically conductive, although measureable currents could not be detected until approximately equal to 6 V, after which point current increased sharply until compliance (approximately equal to 50 nA) was reached at approximately equal to 9.5 V. A native oxide on the tungsten probe tips may contribute to a tunnel barrier, which could be the reason for the suppressed transport at low biases. Currents up to approximately 100 nA could be cycled, which are likely to propagate via the tube surface, or sidewalls, rather than the body, which is shown by the I-V in figure (a). Electrical conduction via the sidewalls is a necessity for dc NEMS (nanoelectromechanical system) applications, more so than for the field emission applications of such tubes. During the tests, high conductivity was expected, because both probes were shorted to the substrate, as shown by curve 1 in the I-V characteristic in figure (b). When a tube grown on NbTiN was probed, the response was similar to the approximately equal to 100 nA and is represented by curve 2 in figure (b), which could be cycled and propagated via the tube surface or the sidewalls. However, no measureable currents for the tube grown directly on Si were observed as shown by curve 3 in figure (b), even after testing over a range of samples. This could arise from a dielectric coating on the sidewalls for tubes on Si. As a result of the directional nature of ion bombardment during dc PECVD, Si from the substrate is likely re-sputtered and possibly coats the sidewalls.

Kaul, Anupama B.; Khan, Abdur R.

2011-01-01

157

Activated carbon nanofiber webs made by electrospinning for capacitive deionization  

International Nuclear Information System (INIS)

Activated carbon fiber (ACF) webs with a non-woven multi-scale texture were fabricated from polyacrylonitrile (PAN), and their electrosorption performance in capacitive deionization for desalination was investigated. PAN nanofibers were prepared by electrospinning, followed by oxidative stabilization and activation with carbon dioxide at 750–900 °C, resulting in the ACF webs that were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and nitrogen adsorption. The results show that the as-made ACFs have a specific surface area of 335–712 m2/g and an average nanofiber diameter of 285–800 nm, which can be tuned by varying the activation temperature. With the ACF webs as an electrode, an electrosorption capacity as high as 4.64 mg/g was achieved on a batch-type electrosorptive setup operated at 1.6 V. The ACF webs made by electrospinning are of potential as an excellent electrode material for capacitive deionization for desalination.

2012-05-01

158

A comparative study of EMI shielding properties of carbon nanofiber and multi-walled carbon nanotube filled polymer composites.  

Science.gov (United States)

Electromagnetic interference shielding properties of carbon nanofiber- and multi-walled carbon nanotube-filled polystyrene composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness of composites was frequency independent, and increased with the increase of carbon nanofiber or nanotube loading. At the same filler loading, multi-walled carbon nanotube-filled polystyrene composites exhibited higher shielding effectiveness compared to those filled with carbon nanofibers. In particular, carbon nanotubes were more effective than nanofibers in providing high EMI shielding at low filler loadings. The experimental data showed that the shielding effectiveness of the composite containing 7 wt% carbon nanotubes could reach more than 26 dB, implying that such a composite can be used as a potential electromagnetic interference shielding material. The dominant shielding mechanism of carbon nanotube-filled polystyrene composites was also discussed. PMID:16060155

Yang, Yonglai; Gupta, Mool C; Dudley, Kenneth L; Lawrence, Roland W

2005-06-01

159

Potential and challenges of metal-matrix-composites reinforced with carbon nanofibers and carbon nanotubes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract With a continuous improvement of the production techniques for carbon nanofibers and carbon nanotubes along with an improvement of the available qualities of the materials, these reinforcements have been introduced into polymers, ceramics and metals. While in the field of polymers first success stories have been published on carbon nanofiller reinforcements, up to now metals containing these types of nanofillers are still a topic of intensive research. Basically a similar ...

2010-01-01

160

Binder-free Si nanoparticles@carbon nanofiber fabric as energy storage material  

International Nuclear Information System (INIS)

A nonwoven nanofiber fabric with paper-like qualities composed of Si nanoparticles and carbon as binder-free anode electrode is reported. The nanofiber fabrics are prepared by convenient electrospinning technique, in which, the Si nanoparticles are uniformly confined in the carbon nanofibers. The high strength and flexibility of the nanofiber fabrics are beneficial for alleviating the structural deformation and facilitating ion transports throughout the whole composited electrodes. Due to the absence of binder, the less weight, higher energy density, and excellent electrical conductivity anodes can be attained. These traits make the composited nanofiber fabrics excellent used as a binder-free, mechanically flexible, high energy storage anode material in the next generation of rechargeable lithium ions batteries

2013-07-15

 
 
 
 
161

Electromagnetic Properties of Novel Carbon Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Carbonized bacterial cellulose (CBC with a three dimensional net-linked framework were synthesized from carbonized bacterial cellulose and investigated by X-ray diffraction, Raman spectrum and Transmission electron microscopy. The complex permittivity and permeability of CBC/paraffin wax composite with certain ratio of the composite were measured by vector network analysis in the frequency range of 0.1–18 GHz. It is found that the composite has high permittivity and dielectric loss, especially at the low frequency. The electromagnetic characteristics of the CBC/Fe3O4 complex absorbers synthesized by mixing a small quantity of CBC with Fe3O4 were also studied, aiming at improving the microwave absorbing properties of Fe3O4/Wax composite. When the sample’s thickness was 1.2 mm, the reflection loss reached a minimal value of –21 dB for CBC - Fe3O4/Wax and of –2 dB for Fe3O4/Wax as well.

WANG Gai-Hua, DAI Bo, MA Yong-Jun, REN Yong

2013-04-01

162

Pt/carbon nanofibers electrocatalysts for fuel cells. Effect of the support oxidizing treatment  

Energy Technology Data Exchange (ETDEWEB)

Different Pt-based electrocatalysts supported on carbon nanofibers and carbon black (Vulcan XC-72R) have been prepared using a polymer-mediated synthesis. The electrocatalysts have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and cyclic voltammetry. The effect of carbon nanofibers treatment with HNO{sub 3} solution on Pt particle size and electroactive area has been analyzed. Highly dispersed Pt with homogeneous particle size and an electroactive area around of 100 m{sup 2} g{sup -1} is obtained in raw carbon nanofibers. The oxidizing treatment of the carbon nanofibers produces agglomeration of the platinum nanoparticles and an electroactive area of 53 m{sup 2} g{sup -1}. Durability studies indicate a decrease of 14% in the electroactive area after 90 h at 1.2 V in 0.5 M H{sub 2}SO{sub 4} for platinum supported on raw carbon nanofibers and Vulcan XC-72R. The electrocatalyst supported on oxidized carbon nanofibers are stable under similar conditions. (author)

Zaragoza-Martin, F.; de Lecea, C. Salinas-Martinez [Departamento de Quimica Inorganica, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain); Sopena-Escario, D. [Fundacion CIDAUT, Parque tecnologico de Boecillo, E-47151 Boecillo (Valladolid) (Spain); Morallon, E. [Departamento de Quimica Fisica e Instituto Universitario de Materiales, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)

2007-09-27

163

Nanocomposite hybrid material based on carbon nanofibers and polyoxometalates  

Directory of Open Access Journals (Sweden)

Full Text Available Sintetizamos y caracterizamos materiales h ? ?bridos nanocompositos a base de nanofibras de carb ? on previamente oxidadas (fCNFs y poliox- ometalatos (POM. Las fCNF se analizaron por TEM y XRD donde detectamos la presencia de nanoespirales de carbono y la eliminaci ? on de carbono amorfo y de las fibras mas delgadas. La microestructura del material h ? ?brido nanocomposito (fCNFs-POM se observ ? o por SEM, y los an ? alisis de EDX mostraron la presencia de Cs, P, Mo, y O del POM y C de fCNFs. Adem ? as, los espectros de FTIR confirmaron la presencia de ambos componentes del h ? ?brido, donde su interacci ? on no ha sido clarificada pero intuimos la quimisorci ? on del POM a las fCNFs mediante grupos carbonilos. Finalmente, ensamblamos celdas sim ? etricas supercapacitivas de estado s ? olido, donde la celda con electrodos h ? ?bridos mostr ? o una capacitancia mucho mayor de 120 mF/g, mostrando tanto la contribuci ? on pseudocapacitiva del POM como la doble capa de las nanofibras de carbono. Descriptores:

A.K. Cuentas-Gallegos

2007-01-01

164

Electrospun vanadium pentoxide/carbon nanofiber composites for supercapacitor electrodes  

International Nuclear Information System (INIS)

The vanadium pentoxide (V2O5)/carbon nanofiber composites (CNFCs) were prepared from polyacrylonitrile/V2O5 in N,N-dimethylformamide by a simple electrospinning method, and their electrochemical properties as supercapacitor electrodes were investigated. Different loadings of V2O5, the microstructures of the CNFCs (e.g., nanometer-size diameters, high specific surface areas, narrow pore size distributions, and tunable porosities) were changed, and the textural parameters significantly affected the electrochemical properties of the composites. The CNFC capacitors delivered the high specific capacitances of 150.0 F g?1 for the CNFCs in an aqueous, with promising energy densities of 18.8 Wh kg?1, over a power density range of 400–20,000 W kg?1. The CNFCs simultaneously exhibited excellent capacity retention.

2012-11-30

165

Supercapacitance from Cellulose and Carbon Nanotube Nanocomposite Fibers  

Science.gov (United States)

Multiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from ?230 to ?180 kJ mol–1. They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g–1 at a current density of 10 A g–1, which increases to 145 F g–1 upon the addition of 6% of MWNTs.

2013-01-01

166

Cobalt/copper-decorated carbon nanofibers as novel non-precious electrocatalyst for methanol electrooxidation.  

Science.gov (United States)

In this study, Co/Cu-decorated carbon nanofibers are introduced as novel electrocatalyst for methanol oxidation. The introduced nanofibers have been prepared based on graphitization of poly(vinyl alcohol) which has high carbon content compared to many polymer precursors for carbon nanofiber synthesis. Typically, calcination in argon atmosphere of electrospun nanofibers composed of cobalt acetate tetrahydrate, copper acetate monohydrate, and poly(vinyl alcohol) leads to form carbon nanofibers decorated by CoCu nanoparticles. The graphitization of the poly(vinyl alcohol) has been enhanced due to presence of cobalt which acts as effective catalyst. The physicochemical characterization affirmed that the metallic nanoparticles are sheathed by thin crystalline graphite layer. Investigation of the electrocatalytic activity of the introduced nanofibers toward methanol oxidation indicates good performance, as the corresponding onset potential was small compared to many reported materials; 310 mV (vs. Ag/AgCl electrode) and a current density of 12 mA/cm2 was obtained. Moreover, due to the graphite shield, good stability was observed. Overall, the introduced study opens new avenue for cheap and stable transition metals-based nanostructures as non-precious catalysts for fuel cell applications. PMID:24387682

Barakat, Nasser A M; El-Newehy, Mohamed; Al-Deyab, Salem S; Kim, Hak Yong

2014-01-01

167

Platinum nanocluster growth on vertically aligned carbon nanofiber arrays: Sputtering experiments and molecular dynamics simulations  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Molecular dynamics simulation of platinum cluster growth on model carbon nanofibers. Black-Right-Pointing-Pointer We compare modeled and experimental cluster growth. Black-Right-Pointing-Pointer We determine sticking coefficient evolution among deposition time and type of nanofibers. Black-Right-Pointing-Pointer We determine cluster size distribution on various model nanofibers. - Abstract: Sputtered platinum nanocluster growth on previously plasma enhanced chemical vapor deposition - PECVD - grown vertically aligned carbon nanofiber arrays is presented. Experimental cluster size distribution is shown to decrease from the CNF top to bottom, as observed by transmission electron microscopy. Molecular dynamics simulations are carried out for understanding early stages of Pt growth on model CNF arrays. Especially, sticking coefficients, concentration profiles along CNF wall, cluster size distributions are calculated. Simulated cluster size distribution are consistent with experimental finding. Sticking coefficient decreases against deposition time. The shape of the sticking curve reflects the nanocluster growth process.

Brault, Pascal, E-mail: Pascal.Brault@univ-orleans.fr [GREMI, UMR7344 CNRS-Universite d' Orleans BP 6744, 45067 Orleans Cedex 2 (France); Caillard, Amaeel [GREMI, UMR7344 CNRS-Universite d' Orleans BP 6744, 45067 Orleans Cedex 2 (France); Charles, Christine; Boswell, Rod W. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Graves, David B. [Department of Chemical and Biomolecular Engineering, 201 Gilman Hall 1462, University of California Berkeley, CA 94720-1462 (United States)

2012-12-15

168

Platinum nanocluster growth on vertically aligned carbon nanofiber arrays: Sputtering experiments and molecular dynamics simulations  

International Nuclear Information System (INIS)

Highlights: ? Molecular dynamics simulation of platinum cluster growth on model carbon nanofibers. ? We compare modeled and experimental cluster growth. ? We determine sticking coefficient evolution among deposition time and type of nanofibers. ? We determine cluster size distribution on various model nanofibers. - Abstract: Sputtered platinum nanocluster growth on previously plasma enhanced chemical vapor deposition – PECVD – grown vertically aligned carbon nanofiber arrays is presented. Experimental cluster size distribution is shown to decrease from the CNF top to bottom, as observed by transmission electron microscopy. Molecular dynamics simulations are carried out for understanding early stages of Pt growth on model CNF arrays. Especially, sticking coefficients, concentration profiles along CNF wall, cluster size distributions are calculated. Simulated cluster size distribution are consistent with experimental finding. Sticking coefficient decreases against deposition time. The shape of the sticking curve reflects the nanocluster growth process.

2012-12-15

169

Development of radiation processing to functionalize carbon nanofiber to use in nanocomposite for industrial application  

International Nuclear Information System (INIS)

Radiation can be used to modify and improve the properties of materials. Electron beam and gamma ray irradiation has potential application in modifying the structure of carbon fibers in order to produce useful defects in the graphite structure and create reactive sites. In this study was investigated a methodology for radiation grafting processing to modify carbon nanofiber surfaces by grafting acrylic acid. The samples were submitted to direct radiation process. Several parameters were changed such as acrylic acid concentration, radiation dose and percentage of inhibitor to achieve functionalization with higher percentage of oxygen functional groups on carbon nanofiber surface and better dispersion. The samples were characterized by X-ray Photoelectron Spectroscopy and the dispersion stability upon storage was visually investigated. Carbon nanofiber directed irradiated with electron beam and gamma ray in a solution of acrylic acid with 6% of inhibitor (FeSO4.7H2O) and irradiated at 100 kGy had an increase of 20% of oxygen content onto carbon nanofiber surface. The Auger D-parameter for the samples direct irradiated grafted ranged between 17.0-17.7 compared to 21.1-18.9 of the unirradiated ones. This indicated that these samples had less sp2 and more sp3 bonding characteristics than unirradiated samples. This can be an indication of C=C bond breaking leading to the formation of new sp3 carbon atoms on carbon nanofiber surface with oxygen functional groups grafted. The samples grafted presented a good and stable dispersion. (author)

2013-11-24

170

Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries.  

Science.gov (United States)

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy. PMID:21916442

Zheng, Guangyuan; Yang, Yuan; Cha, Judy J; Hong, Seung Sae; Cui, Yi

2011-10-12

171

Orientation of Carbon Nano-fiber in Carbon/Silica Composite Prepared under High Magnetic Field  

International Nuclear Information System (INIS)

Carbon/silica composite films were prepared from colloidal silica aqueous solution in which vapour grown carbon nano-fibers dispersed. The orientation of nano-fibers was attempted by dip-coating substrates under high magnetic field up to 10 T. The fibers started to align along the direction of magnetic field below 1 T. The degree of orientation was saturated at about 6 T. The anisotropic susceptibility, ?? = ?||-?perpendicular, was estimated to be (3.05±1.10)x10-7 cm3/mol from the fitting of numerical simulation. It was smaller than that reported in previous studies. It was deduced that perturbation of fiber orientation in the sol during drawing and drying, and the existence of coupled fibers in the starting materials suppressed the orientation of fibers.

2011-02-01

172

Orientation of Carbon Nano-fiber in Carbon/Silica Composite Prepared under High Magnetic Field  

Science.gov (United States)

Carbon/silica composite films were prepared from colloidal silica aqueous solution in which vapour grown carbon nano-fibers dispersed. The orientation of nano-fibers was attempted by dip-coating substrates under high magnetic field up to 10 T. The fibers started to align along the direction of magnetic field below 1 T. The degree of orientation was saturated at about 6 T. The anisotropic susceptibility, ?? = ?//-??, was estimated to be (3.05±1.10)×10-7 cm3/mol from the fitting of numerical simulation. It was smaller than that reported in previous studies. It was deduced that perturbation of fiber orientation in the sol during drawing and drying, and the existence of coupled fibers in the starting materials suppressed the orientation of fibers.

Kitamura, N.; Fukumi, K.; Takahashi, K.; Mogi, I.; Awaji, S.; Watanabe, K.

2011-02-01

173

The Optical Excitation of Zigzag Carbon Nanotubes with Photons Guided in Nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider the excitation of electrons in semiconducting carbon nanotubes by photons from the evanescent field created by a subwavelength-diameter optical fiber. The strongly changing evanescent field of such nanofibers requires dropping the dipole approximation. We show that this leads to novel effects, especially a high dependence of the photon absorption on the relative orientation and geometry of the nanotube-nanofiber setup in the optical and near infrared domain. In p...

Broadfoot, S.; Dorner, U.; Jaksch, D.

2011-01-01

174

Electrospun single-walled carbon nanotube/polyvinyl alcohol composite nanofibers: structure-property relationships  

International Nuclear Information System (INIS)

Polyvinyl alcohol (PVA) nanofibers and single-walled carbon nanotube (SWNT)/PVA composite nanofibers have been produced by electrospinning. An apparent increase in the PVA crystallinity with a concomitant change in its main crystalline phase and a reduction in the crystalline domain size were observed in the SWNT/PVA composite nanofibers, indicating the occurrence of a SWNT-induced nucleation crystallization of the PVA phase. Both the pure PVA and SWNT/PVA composite nanofibers were subjected to the following post-electrospinning treatments: (i) soaking in methanol to increase the PVA crystallinity, and (ii) cross-linking with glutaric dialdehyde to control the PVA morphology. Effects of the PVA morphology on the tensile properties of the resultant electrospun nanofibers were examined. Dynamic mechanical thermal analyses of both pure PVA and SWNT/PVA composite electrospun nanofibers indicated that SWNT-polymer interaction facilitated the formation of crystalline domains, which can be further enhanced by soaking the nanofiber in methanol and/or cross-linking the polymer with glutaric dialdehyde

2008-07-30

175

A novel nano-nonwoven fabric with three-dimensionally dispersed nanofibers: entrapment of carbon nanofibers within nonwovens using the wet-lay process  

Science.gov (United States)

This study demonstrates, for the first time, the manufacturing of novel nano-nonwovens that are comprised of three-dimensionally distributed carbon nanofibers within the matrices of traditional wet-laid nonwovens. The preparation of these nano-nonwovens involves dispersing and flocking carbon nanofibers, and optimizing colloidal chemistry during wet-lay formation. The distribution of nanofibers within the nano-nonwoven was verified using polydispersed aerosol filtration testing, air permeability, low surface tension liquid capillary porometry, SEM and cyclic voltammetry. All these characterization techniques indicated that nanofiber flocks did not behave as large solid clumps, but retained the ‘nanoporous’ structure expected from nanofibers. These nano-nonwovens showed significant enhancements in aerosol filtration performance. The reduction-oxidation reactions of the functional groups on nanofibers and the linear variation of electric double-layer capacitance with nanofiber loading were measured using cyclic voltammetry. More than 65 m2 (700 ft2) of the composite were made during the demonstration of process scalability using a Fourdrinier-type continuous pilot papermaking machine. The scalability of the process with the control over pore size distribution makes these composites very promising for filtration and other nonwoven applications.

Karwa, Amogh N.; Barron, Troy J.; Davis, Virginia A.; Tatarchuk, Bruce J.

2012-05-01

176

A novel nano-nonwoven fabric with three-dimensionally dispersed nanofibers: entrapment of carbon nanofibers within nonwovens using the wet-lay process  

International Nuclear Information System (INIS)

This study demonstrates, for the first time, the manufacturing of novel nano-nonwovens that are comprised of three-dimensionally distributed carbon nanofibers within the matrices of traditional wet-laid nonwovens. The preparation of these nano-nonwovens involves dispersing and flocking carbon nanofibers, and optimizing colloidal chemistry during wet-lay formation. The distribution of nanofibers within the nano-nonwoven was verified using polydispersed aerosol filtration testing, air permeability, low surface tension liquid capillary porometry, SEM and cyclic voltammetry. All these characterization techniques indicated that nanofiber flocks did not behave as large solid clumps, but retained the ‘nanoporous’ structure expected from nanofibers. These nano-nonwovens showed significant enhancements in aerosol filtration performance. The reduction–oxidation reactions of the functional groups on nanofibers and the linear variation of electric double-layer capacitance with nanofiber loading were measured using cyclic voltammetry. More than 65 m2 (700 ft2) of the composite were made during the demonstration of process scalability using a Fourdrinier-type continuous pilot papermaking machine. The scalability of the process with the control over pore size distribution makes these composites very promising for filtration and other nonwoven applications. (paper)

2012-05-11

177

Pt supported on carbon nanofibers as electrocatalyst for low temperature polymer electrolyte membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers synthesized via the thermo catalytic decomposition of methane were investigated for the first time as an electrocatalyst support in PEMFC cathodes. Their textural and physical properties make them a highly efficient catalyst support for cathodic oxygen reduction in low temperature PEMFC. Tests performed in MEAs showed that Pt supported on carbon nanofibers exhibited an enhancement of ca. 94% in power density at 0.600 V, in comparison with a commercial catalyst supported on conventional carbon black, Pt/Vulcan XC-72R. (author)

Alcaide, Francisco; Alvarez, Garbine; Miguel, Oscar [Dpto. de Energia, CIDETEC, Paseo Miramon, 196, 20009 Donostia/San Sebastian (Spain); Lazaro, Maria Jesus; Moliner, Rafael [Instituto de Carboquimica, CSIC, Miguel Luesma Castan 4, 50018 Zaragoza (Spain); Lopez-Cudero, Ana; Solla-Gullon, Jose; Herrero, Enrique; Aldaz, Antonio [Instituto de Electroquimica, Universidad de Alicante, Apdo. 99, E-03080 Alicante (Spain)

2009-05-15

178

Effect of twist and porosity on the electrical conductivity of carbon nanofiber yarns.  

Science.gov (United States)

This study focuses on the effect of twist and porosity on the electrical conductivity of carbon nanofiber (CNF) yarns. The process of fabrication of CNF yarns included the synthesis of aligned ribbons of polyacrylonitrile (PAN) nanofibers via electrospinning. The PAN ribbons were twisted into yarns with twist levels ranging from zero twist to high twists of 1300 turn per meter (tpm). The twist imposed on the ribbons substantially improved the interactions between nanofibers and reduced the porosity. The PAN yarns were subsequently stabilized in air, and then carbonized in nitrogen at 1100 °C for 1 h. Compressive stresses developed between the PAN nanofibers as a result of twist promoted interfusion between neighboring nanofibers, which was accelerated by heating the yarns during stabilization to temperatures above the glass transition of PAN. The electrical conductivity of the yarns was measured with a four point probe measurement technique. Although increasing the twist promotes electrical conductivity between nanofibers by forming junctions between them, our results indicate that the electrical conductivity does not continuously increase with increasing twist, but reaches a threshold value after which it starts to decrease. The causes for this behavior were studied through experimental techniques and further explored using a yarn-equivalent electrical circuit model. PMID:23727878

Chawla, S; Naraghi, M; Davoudi, A

2013-06-28

179

Carbonized Micro- and Nanostructures: Can Downsizing Really Help?  

Directory of Open Access Journals (Sweden)

Full Text Available In this manuscript, we discuss relationships between morphology and mechanical strength of carbonized structures, obtained via pyrolysis of polymeric precursors, across multiple length scales, from carbon fibers (CFs with diameters of 5–10 µm to submicron thick carbon nanofibers (CNFs. Our research points to radial inhomogeneity, skin–core structure, as a size-dependent feature of polyacrylonitrile-based CFs. This inhomogeneity is a surface effect, caused by suppressed diffusion of oxygen and stabilization byproducts during stabilization through skin. Hence, reducing the precursor diameters from tens of microns to submicron appears as an effective strategy to develop homogeneous carbonized structures. Our research establishes the significance of this downsizing in developing lightweight structural materials by comparing intrinsic strength of radially inhomogeneous CFs with that of radially homogeneous CNF. While experimental studies on the strength of CNFs have targeted randomly oriented turbostratic domains, via continuum modeling, we have estimated that strength of CNFs can reach 14 GPa, when the basal planes of graphitic domains are parallel to nanofiber axis. The CNFs in our model are treated as composites of amorphous carbon (matrix, reinforced with turbostratic domains, and their strength is predicted using Tsai–Hill criterion. The model was calibrated with existing experimental data.

Mohammad Naraghi

2014-05-01

180

Conductivity of carbon nanofiber/polypyrrole conducting nanocomposites  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofiber (CNF) / Polypyrrole (Ppy) composite materials were fabricated by two newly invented processes - filtering, washing and drying the mixture of CNF dispersion and Ppy-NMP solution (FWP process) and heating an aqueous solution of CNF (SH process). CNF/Ppy composite materials have never been reported before in any other research papers. Conductivities of the composite films were obtained by using a four-probe method. To compare the conductivity of CNF/Ppy with that of a pure single-walled carbon nanotube (SWNT), SWNT films were also fabricated and voltage was measured. SEM images were taken for both a surface and a cross-section of composite samples fabricated by the two processes. The CNF/Ppy by FWP was a little brittle because of the low solubility of Ppy in the NMP, and on the other hand, the same material by SH became flexible enough. The conductivity of the pure SWNT film was as high as double the similar case. The conductivity of the pure SWNT film was 20.11 S/cm and 0.013 cm thick. The CNF/Ppy composite films with the thicknesses of 0.062 cm and 0.085 cm gave a conductivity of 63.32 S/cm and 40.57 S/cm, respectively, which are higher than that of the pure SWNT film or SWNT/Polyaniline (PANi) film. The good conductivity of CNF/Ppy composites shows the improved potential for developing the materials for a small actuator

Kim, Cheol; Zhang, Shuai [Kyungpook National University, Daegu (Korea, Republic of)

2009-01-15

 
 
 
 
181

Genotoxicity of carbon nanofibers: Are they potentially more or less dangerous than carbon nanotubes or asbestos?  

International Nuclear Information System (INIS)

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf (registered) -III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos > CNF > SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominately centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity.

2011-04-01

182

Genotoxicity of carbon nanofibers: are they potentially more or less dangerous than carbon nanotubes or asbestos?  

Science.gov (United States)

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf®-III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos>CNF>SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominantly centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity. PMID:21310169

Kisin, E R; Murray, A R; Sargent, L; Lowry, D; Chirila, M; Siegrist, K J; Schwegler-Berry, D; Leonard, S; Castranova, V; Fadeel, B; Kagan, V E; Shvedova, A A

2011-04-01

183

Synthesis of beaded and entwined carbon nanofibers in Ni:Al alloy catalyst.  

Science.gov (United States)

This paper reports two new types of carbon nanofibers synthesis by thermal decomposition of n-hexane in presence of Ni-Al alloy in hydrogen atmosphere at 1100 degrees C. One type is "beaded fibers" in which spherical carbon beads (approximately 1 microm) are regularly grown from outer surface of fibers (approximately 0.3 microm). The other new microstructure is "entwined fibers" in which multiple nanofibers of diameter approximately 100 nm grow self-entwined like a braid of hair. Both bead-fiber bonding (in beaded fibers) and fiber-fiber interaction (in entwined fibers) are strong to be detached/unfolded by 30-min ultrasonication. PMID:17450871

Pradhan, Debabrata; Sharon, Maheshwar; Kumar, Mukul; Ando, Yoshinori

2007-03-01

184

Self-heating function of carbon nanofiber cement pastes  

Directory of Open Access Journals (Sweden)

Full Text Available The viability of carbon nanofiber (CNF composites incement matrices as a self-heating material is reported in this paper. This functional application would allow the use of CNF cement composites as a heating element in buildings, or for deicing pavements of civil engineering transport infrastructures, such as highways or airport runways. Cement pastes with the addition of different CNF dosages (from 0 to 5% by cement mass have been prepared. Afterwards, tests were run at different fixed voltages (50, 100 and 150V, and the temperature of the specimens was registered. Also the possibility of using a casting method like shotcrete, instead of just pouring the fresh mix into the mild (with no system’s efficiency loss expected was studied. Temperatures up to 138 °C were registered during shotcrete-5% CNF cement paste tests (showing initial 10 °C/min heating rates. However a minimum voltage was required in order to achieve a proper system functioning.En este artículo se estudia la viabilidad del uso de matrices cementicias con adición de nanofibras de carbono (NFC como elementos calefactores. Esto permitiría aumentar la temperatura de estancias en edificación o el deshielo de pavimentos en obras civiles. Se han fabricado pastas de cemento con distintas dosificaciones de NFC (0, 1, 2 y 5% respecto masa del cemento y sometidas al paso de corriente continua a distintos potenciales fijos (50, 100 y 150 V, mientras se controlaba la temperatura en distintos puntos. Se ha estudiado la viabilidad de utilizar la proyección de la pasta fresca como método de puesta en obra, sin perjudicar la eficiencia del sistema. Se consiguieron temperaturas de hasta 138 °C (con velocidades iniciales de 10 °C/min para pasta proyectada con 5% NFC. Además se ha detectado la necesidad de un potencial mínimo para que la densidad de corriente resultante sea suficiente para producir el efecto esperado.

Galao, O.

2014-05-01

185

Electrochemical behavior of TiO2/carbon dual nanofibers  

International Nuclear Information System (INIS)

The charge transfer processes are favored in dual nanofibers composed by TiO2Rutile-Csemigraphitic/Csemigraphitic over other systems such as TiO2Anatase and Rutile-Camorphous/Camorphous and TiO2Rutile-Camorphous, dual and single nanofibers respectively. The study of electrochemical impedance spectroscopy (EIS) shows that the net of nanofibers presented a charge transfer resistance value (Rct) of 3.15 ?. The increased ability of these materials to favor the diffusion of electroactive species in individual nanofibers is that the junction between the n-type semiconductor TiO2 and the semigraphitic material can be of the ohmic kind. Moreover, this observation was supported by cyclic voltammetry (CV) and electrical conductivity studies by two-probe method. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) confirmed the continuity and duality in the morphology of these materials. The effect of heat treatment on crystallinity was evident in the results obtained from the X-Ray Diffraction (XRD) and Selected Area Electron Diffraction (SAED) studies. Due to the electrochemical performance and morphological features of TiO2Rutile-Csemigraphitic/Csemigraphitic dual nanofibers; this novel nanostructured material can be regarded as an excellent candidate for applications such as a base material for electronic devices, photocatalysis, among other similar technologies

2014-01-10

186

High-performance lithium storage in nitrogen-enriched carbon nanofiber webs derived from polypyrrole  

International Nuclear Information System (INIS)

Highlights: • N-enriched carbon nanofiber webs are prepared via direct carbonization route with polyporrole as template. • The pyrolysis time plays an important role in N doping level and existing type. • Effect of N-doping on performance of the carbon anode material is investigated. • High reversible capacity of 238 mAh g?1 at 5 A g?1 is attained. -- Abstract: Nitrogen-doped carbon nanofiber webs (N-CNFWs) are prepared by direct pyrolyzation of polypyrrole (PPy) nanofiber webs at 600 °C. The structure and morphology of N-CNFWs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Raman spectra and elemental analysis. Both the doped N content and the N existing type in carbon, change with the pyrolysis time. As anode material for lithium-ion battery, the N-CNFWs show high capacity and good rate capability. The reversible capacity is up to 668 mAh g?1 at a current density of 0.1 A g?1 and 238 mAh g?1 at 5 A g?1, which can be ascribed to the nanofiber structure and high nitrogen content

2013-09-01

187

Controlling the optimum surfactants concentrations for dispersing carbon nanofibers in aqueous solution  

Science.gov (United States)

As a new nano-scale functional material, it is necessary to achieve a uniform distribution in the composites for gaining the CNFs' excellent reinforcing effect. In this paper, CNFs were purified by the method of high temperature annealing treatment. Six surfactants, methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), sodium dodecyl sulfate (SDS), dodecylamine (DDA), N, N-dimethyl formamide (DMF) and cetyltrimethyl ammonium bromide (CTAB) were used individually and combinatorially in a certain concentration to disperse the CNFs in aqueous solution. To achieve a good dispersion of the CNFs, a method utilizing ultrasonic processing was employed. The CNFs treated by the method of high temperature annealing treatment were characterized by differential thermal analysis (DTA) and thermogravimetry analysis (TGA), and the ultrasonication-driven dispersion of CNFs in aqueous solutions were monitored by UVvis spectroscopy and transmission electron microscopy (TEM). The experiments reveal that the method of high temperature annealing treatment purified the CNFs and the maximum achievable dispersion of CNFs corresponds to the maximum UV absorbance of the solution. All results show that the surfactants mixture of MC and SDS in a certain concentration of 0.4 and 2.0 g/L has the maximum dispersion effect on CNFs in aqueous solution, the optimum concentration ratio of MC, SDS, and CNFs was 2: 10: 1.

Wang, Bao-Min; Yuan, Zhang; Guo, Zhi-Qiang; Ma, Hai-Nan; Lai, Chuan Fook

2013-12-01

188

Tribological and mechanical properties of carbon nanofiber-filled polytetrafluoroethylene/polyimide composites.  

Science.gov (United States)

The tribological and mechanical properties of carbon nanofiber filled polytetrafluoroethylene/ polyimide composites were studied in this paper. The effect of filler contents (0.5, 1, 1.5, 2, 2.5, 3 and 5 wt%) on the tribological and mechanical properties was examined. Also, the influence of various loads (100 N, 150 N and 200 N) and velocities (0.69 m/s and 1.4 m/s) on the tribological performance was investigated. The results show that the best friction and wear performance would obtained under different loads and velocities, which reduced by 56.7% (150 N, 1.4 m/s) and 72.6% (200 N, 0.69 m/s), respectively. And also, optimal mechanical properties were obtained. In comparison with the mechanical properties of polytetrafluoroethylene/polyimide composites, the tensile strength, elongation-to-break and impact strength of 1 wt% carbon nanofiber filled polytetrafluoroethylene/polyimide composites increased by 5%, 50% and 75%, respectively. The transfer films, worn surfaces and impact fracture surfaces were studied by scanning electron microscopy. The micrographs show that a proper content of carbon nanofiber is helpful for forming a smooth and continuous transfer film, which is essential for achieving good anti-wear property. Meanwhile, mechanical properties have been improved due to the interfacial interaction between the matrix and carbon nanofibers. PMID:19908481

Zhu, Jiahua; Feng, Xin; Shi, Yijun; Wang, Huaiyuan; Lu, Xiaohua

2009-10-01

189

Surface modified PLGA/carbon nanofiber composite enhances articular chondrocyte functions  

Science.gov (United States)

Since articular cartilage has a limited self regeneration capability, alternative methods are needed for repairing cartilage defects. The purpose of the present in vitro study was to explore the effects of material surface properties and external stimulation on chondrocyte (cartilage-synthesizing cell) functions. Based on this information, a goal of this research was to propose a scaffold composite material for enhancing articular chondrocyte function. To improve functions of chondrocytes, material (namely, poly(lactic-co-glycolic acid); PLGA) surfaces were modified via chemical (NaOH) etching techniques. Chondrocytes were cultured on surface-modified 2-D PLGA films and 3-D PLGA tissue engineering scaffolds, which were created by a salt-leaching method. Carbon nanofibers were imprinted on PLGA matrices in an aligned pattern for controlled electrically-active surface features. Electrical stimulation was applied to expedite and enhance chondrocyte functions. Results demonstrated that both NaOH-treated 2-D and 3-D substrates enhanced chondrocyte functions (cell numbers as well as extracellular matrix production) compared to non-treated PLGA substrates. Furthermore, chondrocytes preferred to attach along the carbon nanofiber patterns imprinted on PLGA. Electrical stimulation also enhanced chondrocyte functions on carbon nanofiber/PLGA composites. Underlying material properties that may have enhanced chondrocyte functions include a more hydrophilic surface, surface energy differences due to the presence of carbon nanofibers, increased surface area, altered porosity, and a greater degree of nanometer roughness. Moreover, these altered surface properties positively influenced select protein adsorption that controlled subsequent chondrocyte adhesion. Collectively, this study provided a scaffold model for osteochondral defects that can be synthesized using the above techniques and a layer by layer approach to accommodate the property differences in each layer of natural cartilage. Specifically, these results suggest that the superficial zone, middle zone, and deep zone of cartilage should be composed of carbon nanofibers aligned parallel to the surface in PLGA, randomly oriented carbon nanofibers in PLGA, and carbon nanofibers aligned perpendicular to the surface in PLGA, respectively. Clearly, such scaffolds may ultimately enhance the efficacy of scaffolds used for articular cartilage repair.

Park, Grace Eunseung

190

Rheological and electrical analysis in carbon nanofibre reinforced polypropylene composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin-screw extrusion. The electrical characterization of both CNFs / PP composites as a function of volume fraction show different electrical performance: conducting and non-conducting. The objective of this work is to study the rheological behaviour of both composites with the aim of relating it to the electrical behaviour. The results indicate that the rheological behavio...

Lanceros-me?ndez, S.; Paleo, A. J.; Silva, J.; Hattum, F. W. J.; Ares, A. I.

2013-01-01

191

Fabrication of transition metal oxide-carbon nanofibers with novel hierarchical architectures.  

Science.gov (United States)

We report a facile two-step methodology; electrospinning followed by high temperature treatment, to produce manganese oxide-based nanofibers with well-controlled nanoscale architectures. Electrospinning of manganese acetate-based solution (MnOx precursor) has been utilized to fabricate meso-porous manganese oxide nanofibers. These fibers have diameters of about 200-300 nm and fiber mats have been shown to have specific surface area of over 12 m2/g. Scanning and transmission electron microscopy results show that electrospinning has been successfully utilized to create nanofibers with deep inter-connected internal meso-pores for high surface area. In addition, fibers have been spun in a co-axial arrangement to fabricate hollow meso-porous nanofibers, or to develop core-shell nanofibers with nanoparticles of manganese oxides decorated over current conducting carbon core. X-ray diffraction analysis of the oxide fibers confirms the presence of manganese oxides (MnO2, Mn3O4) after calcination at 700 degrees C. These architectures, we believe, are potentially favorable for use in Li-ion batteries, Li-air batteries and supercapacitors. PMID:24758057

Hu, Alice; Curran, Chris; Tran, Chau; Kapllani, Alda; Kalra, Vibha

2014-07-01

192

Decomposition of Fe5C2 catalyst particles in carbon nanofibers during TEM observation  

Directory of Open Access Journals (Sweden)

Full Text Available The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (?-Fe3C. However, for Hägg carbide nanoparticles (?-Fe5C2, explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and ?-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.

Vladimir D Blank, Boris A Kulnitskiy, Igor A Perezhogin, Yuriy L Alshevskiy and Nikita V Kazennov

2009-01-01

193

Hollow carbon-nanotube/carbon-nanofiber hybrid anodes for Li-ion batteries.  

Science.gov (United States)

By a novel in situ chemical vapor deposition, activated N-doped hollow carbon-nanotube/carbon-nanofiber composites are prepared having a superhigh specific Brunauer–Emmett–Teller (BET) surface area of 1840 m(2) g(–1) and a total pore volume of 1.21 m(3) g(–1). As an anode, this material has a reversible capacity of ~1150 mAh g(–1) at 0.1 A g(–1) (0.27 C) after 70 cycles. At 8 A g(–1) (21.5 C), a capacity of ~320 mAh g(–1) fades less than 20% after 3500 cycles, which makes it a superior anode material for a Li-ion battery. PMID:24144455

Chen, Yuming; Li, Xiaoyan; Park, Kyusung; Song, Jie; Hong, Jianhe; Zhou, Limin; Mai, Yiu-Wing; Huang, Haitao; Goodenough, John B

2013-11-01

194

Cobalt on carbon nanofiber catalysts: auspicious system for study of manganese promotion in Fischer-Tropsch catalysis.  

Science.gov (United States)

STEM-EELS and XPS investigation shows manganese oxide to be closely associated with cobalt nanoparticles supported on carbon nanofibers thereby improving selectivity in Fischer-Tropsch catalysis. PMID:15685319

Bezemer, G Leendert; Falke, Uwe; van Dillen, A Jos; de Jong, Krijn P

2005-02-14

195

Simple Forster resonance energy transfer evidence for the ultrahigh quantum dot quenching efficiency by graphene oxide compared to other carbon structures  

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Forster resonance energy transfer (FRET) entails the transfer of energy from a photoexcited energy donor to a close energy acceptor. In this regard, quantum dots (QDs), as donors, are quenched when they are next to an acceptor material. Graphite, carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphene oxide (GO) were explored as energy acceptors of QD FRET donors in the solid phase. In our setup, the higher estimated values of quenching efficiency for each material are as follows: grap...

Morales-narvaez, Eden; Perez-lopez, Briza; Baptista Pires, Luis; Merkoci, Arben

2012-01-01

196

Photocatalytic Oxidation of Volatile Organic Compounds Over Electrospun Activated TIO2/CARBON Nanofiber Composite  

Science.gov (United States)

In this study, TiO2/PAN-based fibers were prepared by electrospinning a composite solution containing both the desirable contents of TiO2 and a 10 wt. % PAN polymer solution dissolved in N, N-dimethylformamide. The TiO2 loaded electrospun PAN nanofibers were then carbonized at 1000 °C in N2 atmosphere furnace after stabilization at 230 °C in air. Then CNF/TiO2 nanofibers were oxidized at 450 °C in air. The morphology and structure of the TiO2-embeded carbon nanofibers were investigated by SEM and Raman spectroscopy. Specific surface area was determined using BET equation from N2 adsorption analysis. Photocatalytic tests were conducted in a UV illuminated set-up specialized for the filters using ethanol vapor. The results have shown that ethanol vapor was efficiently degraded on TiO2/CNF composite nanofiber mat under UV illumination. The aim of this study was to further investigate the feasibility of TiO2/ACF for practical indoor air purification.

Gholamvand, Zahra; Aboutalebi, Seyed Hamed; Keyanpour-Rad, Mansoor

197

Study on glow discharge effects on catalyst films for growing aligned carbon nanofibers in negative bias-enhanced hot filament chemical vapor deposition system  

Energy Technology Data Exchange (ETDEWEB)

Aligned carbon nanofibers (ACNFs) were grown on silicon substrates coated with NiFe catalyst films by negative bias-enhanced hot filament chemical vapor deposition (CVD). The growth and structure of the aligned carbon nanofibers were investigated by scanning electron microscopy (SEM). The results indicate that the aligned carbon nanofibers could be synthesized after the glow discharge appears when the negative bias is higher than a certain value, while they are bent if the glow discharge does not appear. Furthermore, the diameters of the aligned carbon nanofibers are reduced and their lengths are increased with increasing the negative bias. It is shown that the glow discharge resulting from the negative bias plays an important role in the growth of aligned carbon nanofibers. Here, the effects of the glow discharge on the growth and structure of the aligned carbon nanofibers are discussed.

Wang, B.B. [College of Applied Mathematics and Physics, Beijing University of Technology, No. 100, Pingleyuan, Chaoyang District, Beijing 100022 (China) and Key Laboratory of Advanced Functional Materials of China Education Ministry, Beijing University of Technology, No.100, Pingleyuan, Chaoyang District (China)]. E-mail: bibenw@bjut.edu.cn; Lee, Soonil [Department of Molecular Science and Technology, Ajou University, Suwon 442-749 (Korea, Republic of); Yan, H. [Key Laboratory of Advanced Functional Materials of China Education Ministry, Beijing University of Technology, No.100, Pingleyuan, Chaoyang District (China); Hou, B.H. [College of Applied Mathematics and Physics, Beijing University of Technology, No. 100, Pingleyuan, Chaoyang District, Beijing 100022 (China); Choi, Seungho [Department of Molecular Science and Technology, Ajou University, Suwon 442-749 (Korea, Republic of)

2005-03-01

198

Fe3O4/carbon composite nanofiber absorber with enhanced microwave absorption performance  

International Nuclear Information System (INIS)

Highlights: ? PAN/AAI/DMF solutions for electrospinning. ? Fe3O4/carbon composite nanofibers as microwave absorbers. ? Microwave absorption performance has been much enhanced than pure carbon naonfibers. ? Microwave absorption mechanisms have been discussed as a key point. - Abstract: Fe3O4/carbon composite nanofibers were prepared by electrospinning polyacrylonitrile (PAN)/acetyl acetone iron (AAI)/dimethyl formamide (DMF) solution, followed by stabilization and carbonization. SEM and TEM observations reveal that the fibers are lengthy and uniform, and are loaded with well-distributed Fe3O4 nanoparticles, which are evidenced by XRD. Electrical and magnetic properties of the samples were studied to show the effect of enhancement of electrical conductivity and magnetic hysteresis performance. Finally, the permittivity and permeability parameters were measured by a vector network analyzer, and the reflectivity loss was calculated based on Transmission Line Theory. Results show that Fe3O4/C composite nanofibers exhibit enhanced properties of microwave absorption as compared to those of pure carbon nanofibers by: decreasing reflectivity loss values; widening absorption width and improving performance in low frequency (2–5 GHz) absorption. Absorption properties can be tuned by changing AAI content, carbonization temperature, composite fiber/paraffin ratio and coating thickness. It is shown that with coating thickness of 5 mm and fiber/paraffin ratio of 5 wt.%, the bandwidth for reflection loss under ?5 dB can reach a maximum of 12–13 GHz in the range of 2–18 GHz, accompanying with a minimum reflection loss of ?40 to ?45 dB, and preferred low frequency band absorption can also be obtained. The mechanisms for the enhanced absorption performance were briefly discussed. It is supposed that this kind of composite material is promising for resolving the problems of weak absorption in the low frequency range and narrow bandwidth absorption.

2013-01-01

199

LiCoPO4—3D carbon nanofiber composites as possible cathode materials for high voltage applications  

International Nuclear Information System (INIS)

Electrospun and carbonized 3D nanofiber mats coated with olivine structured lithium cobalt phosphate (LiCoPO4) were formed by a Pechini-assisted sol–gel process as cathode material for lithium ion batteries. 3D nonwoven nanofibers were soaked in aqueous solution containing lithium, cobalt salts and phosphates at 80 °C for 2 h. Then, the composites were dried and annealed at 730 °C for 2 to 12 h in nitrogen atmosphere. Crystalline deposits were uniformly distributed on the carbon nanofiber surface. The “loading” of the cathode material on the 3D carbon nanofiber composites reached 300 wt%. The electrochemical measurements revealed the discharge specific capacity (measured at a discharge rate of 0.1 C and room temperature) reaching a maximum value of 46 mAh g?1 after annealing time t = 5 h

2013-04-15

200

Cyclability study of silicon-carbon composite anodes for lithium-ion batteries using electrochemical impedance spectroscopy  

International Nuclear Information System (INIS)

Research highlights: ? Silicon-carbon anode materials for Li-ion batteries were synthesized. ? Carbonization and annealing processes were used in electrode preparation. ? Capacity fading mechanism was investigated by electrochemical impedance spectroscopy. ? Impedance evolution revealed better stability of the carbonized anode material. - Abstract: The effects of carbonization process and carbon nanofiber/nanotube additives on the cycling stability of silicon-carbon composite anodes were investigated by monitoring the impedance evolution during charge/discharge cycles with electrochemical impedance spectroscopy (EIS). Three types of Si-C anodes were investigated: the first type consisted of Si nanoparticles incorporated into a network of carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWNTs), with annealed polymer binder. The second type of Si-C anodes was prepared by further heat treatment of the first Si-C anodes to carbonize the polymer binder. The third Si-C anode was as same as the second one except no CNFs and MWNTs being added. Impedance analysis revealed that the carbonization process stabilized the Si-C anode structure and decreased the charge transfer resistance, thus improving the cycling stability. On the other hand, although the MWNTs/CNFs additives could enhance the electronic conductivity of the Si-C anodes, the induced inhomogeneous structure decreased the integrity of the electrode, resulting in a poor long term cycling stability.

2011-04-15

 
 
 
 
201

Cobalt supported on carbon nanofibers as catalysts for the Fischer-Tropsch synthesis  

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The Fischer-Tropsch (FT) process converts synthesis gas (H2/CO) over a heterogeneous catalyst into hydrocarbons. Generally, cobalt catalysts supported on oxidic carriers are used for the FT process, however it appears to be difficult to obtain and maintain fully reduced cobalt particles. To overcome these problems we started to use carbon nanofibers (CNF), a novel support material on which cobalt-support compounds are not expected to form.

2006-01-01

202

Fracture Toughness of Vapor Grown Carbon Nanofiber-Reinforced Polyethylene Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The impact fracture behavior of a vapor grown carbon nanofiber (VGCNF) reinforced high-density polyethylene (PE) composite was evaluated. The samples consisting of pure PE and composites with 10?wt% and 20?wt% of VGCNFs were prepared by a combination of hot-pressing and extrusion methods. Extrusion was used to produce samples with substantially different shear histories. The fracture behavior of these samples was analyzed using the essential work of fracture (EWF) approa...

Adhikari, A. R.; Partida, E.; Petty, T. W.; Jones, R.; Lozano, K.; Guerrero, C.

2009-01-01

203

Novel catalytic applications of carbon nanofibers on sintered metal fibers filters as structured supports  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Supported metal catalysts are important from both an industrial and a scientific point of view. They are used, amongst others, in large-scale processes such as catalytic reforming, hydrotreating, polymerization reactions and hydrogenations. Often, these catalysts consist of nanosized metal particles deposited on a suitable support, which acts as an anchor for the active phase and, in several cases, contributes to improve the overall catalyst performances. The growth of carbon nanofibers on si...

2008-01-01

204

Novel catalytic applications of carbon nanofibers on sintered metal fibers filters as structured supports  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Supported metal catalysts are important from both an industrial and a scientific point of view. They are used, amongst others, in large-scale processes such as catalytic reforming, hydrotreating, polymerization reactions and hydrogenations. Often, these catalysts consist of nanosized metal particles deposited on a suitable support, which acts as an anchor for the active phase and, in several cases, contributes to improve the overall catalyst performances. The growth of carbon nanofibers on si...

2009-01-01

205

Palladium on carbon nanofibers grown on metallic filters as novel catalytic materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A novel composite material based on carbon nanofibers (CNF) grown on sintered metal fibers (SMFInconel) filter was investigated for its favorable properties as catalytic support. The CNF were formed directly over the SMFInconel by thermal (650 degrees C) chemical vapor deposition of ethane-hydrogen mixture. The CNF/SMFInconel composite consists of metal fibers entangled by CNF network of microns thickness and strongly anchored to the metal surface. The properties of the CNF/SMFInconel were co...

2005-01-01

206

High efficient electrical stimulation of hippocampal slices with vertically aligned carbon nanofiber microbrush array  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Long-term neuroprostheses for functional electrical stimulation must efficiently stimulate tissue without electrolyzing water and raising the extracellular pH to toxic levels. Comparison of the stimulation efficiency of tungsten wire electrodes (W wires), platinum microelectrode arrays (PtMEA), as-grown vertically aligned carbon nanofiber microbrush arrays (VACNF MBAs), and polypyrrole coated (PPy-coated) VACNF MBAs in eliciting field potentials in the hippocampus slice indicates that, at low...

Asis, Edward D.; Nguyen-vu, T. D. Barbara; Arumugam, Prabhu U.; Chen, Hua; Cassell, Alan M.; Andrews, Russell J.; Yang, Cary Y.; Li, Jun

2009-01-01

207

Carbon Nanofibers enhance the Fracture toughness and Fatigue Performance of a Structural Epoxy system  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract This study investigates the monotonic and dynamic fracture characteristics of a discontinuous fiber reinforced polymer matrix. Specifically, small amounts (0-1 wt%) of a helical-ribbon carbon nanofiber (CNF) were added to an amine cured epoxy system. The resulting nanocomposites were tested to failure in two modes of testing; Mode I fracture toughness and constant amplitude of stress tension-tension fatigue. Fracture toughness testing revealed that adding 0.5 and 1.0 wt% C...

2010-01-01

208

Electrical conductivity of polyvinylidene fluoride nanocomposites with carbon nanotubes and nanofibers.  

Science.gov (United States)

Polyvinylidene fluoride nanocomposites with low loading levels of pristine multiwalled carbon nanotubes, carboxyl functionalized multiwalled carbon nanotubes and vapor grown carbon nanofibers were prepared by a versatile coagulation method. The alternating current electrical conductivity of these composites in the frequency range of 40-12 MHz was investigated. The alternating current conductivity of percolating nanocomposites followed a universal dynamic response. Therefore, both the direct current plateau and frequency dependent regime were observed. The percolation threshold of three composite systems was determined to be 1.0, 0.98, and 1.46 vol.%, respectively. Moreover, the percolative nanocomposites exhibited nonlinear current-voltage responses, demonstrating the presence of tunneling conduction. PMID:22408970

He, Linxiang; Tjong, Sie Chin

2011-12-01

209

Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes.  

Science.gov (United States)

Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe(2+/3+), [Fe(CN)6](3-/4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe(2+/3+) was accelerated and that of [Fe(CN)6](3-/4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices. PMID:24817367

Ko, Seongjae; Tatsuma, Tetsu; Sakoda, Akiyoshi; Sakai, Yasuyuki; Komori, Kikuo

2014-05-28

210

Carbon nanotube-incorporated multilayered cellulose acetate nanofibers for tissue engineering applications.  

Science.gov (United States)

We report the fabrication of a novel carbon nanotube-containing nanofibrous polysaccharide scaffolding material via the combination of electrospinning and layer-by-layer (LbL) self-assembly techniques for tissue engineering applications. In this approach, electrospun cellulose acetate (CA) nanofibers were assembled with positively charged chitosan (CS) and negatively charged multiwalled carbon nanotubes (MWCNTs) or sodium alginate (ALG) via a LbL technique. We show that the 3-dimensional fibrous structures of the CA nanofibers do not appreciably change after the multilayered assembly process except that the surface of the fibers became much rougher than that before assembly. The incorporation of MWCNTs in the multilayered CA fibrous scaffolds tends to endow the fibers with improved mechanical property and promote fibroblast attachment, spreading, and proliferation when compared with CS/ALG multilayer-assembled fibrous scaffolds. The approach to engineering the nanofiber surfaces via LbL assembly likely provides many opportunities for new scaffolding materials design in various tissue engineering applications. PMID:23044152

Luo, Yu; Wang, Shige; Shen, Mingwu; Qi, Ruiling; Fang, Yi; Guo, Rui; Cai, Hongdong; Cao, Xueyan; Tomás, Helena; Zhu, Meifang; Shi, Xiangyang

2013-01-01

211

Electrospinning fabrication of high strength and toughness polyimide nanofiber membranes containing multiwalled carbon nanotubes.  

Science.gov (United States)

Polyimide (PI) and PI nanocomposite fibers containing different amounts of multiwalled carbon nanotubes (MWNTs) were produced for the first time by electrospinning. The membranes prepared were composed of highly aligned nanofibers and showed significant enhancement in mechanical properties, compared with the membranes prepared by conventional solution-casting method. Surface-functionalized MWNTs were homogeneously dispersed and highly aligned along the fiber axis, whereas most of the pristine MWNTs formed aggregates or bundles and even protruded out of the electrospun nanofibers. The thermal and mechanical properties of polyimide matrix were significantly improved with the incorporation of MWNTs. And the elongation at break of the nanofiber membranes can reach 100% for the nanotube loading level of 3.5 wt %. It was found that electrospinning the in situ prepared MWNT/poly(amic acid) solution can achieve better polymer chain orientation and thus better mechanical properties of the as-prepared membranes. Our study demonstrates a good example for the preparation of high-performance polymer/carbon nanotube nanocomposites by using electrospinning. PMID:19603838

Chen, Dan; Liu, Tianxi; Zhou, Xiaoping; Tjiu, Wuiwui Chauhari; Hou, Haoqing

2009-07-23

212

Synthesis of palladium nanoparticles decorated helical carbon nanofiber as highly active anodic catalyst for direct formic acid fuel cells  

International Nuclear Information System (INIS)

Highlights: ? We present a single metal synthesis of highly active catalysts based on Pd-helical carbon fibers. ? Our catalyst material show better performance than Pd-decorated multi-walled nanotubes. ? Formic acid fuel cell tests with Pd-helical carbon nanofibers as anode show high power densities. ? Helical carbon nanofibers have several good properties for electrochemical applications. - Abstract: We present a single metal approach to produce highly active catalyst materials based on Pd-decorated helical carbon nanofibers. Helical carbon fibers are synthesized by a chemical vapor deposition process on a C60 supported Pd catalyst and the obtained fibers are functionalized by H2O2 followed by a decoration with Pd nanoparticles. Although transmission electron microscopy images show that the decoration is relatively inhomogeneous the electrocatalytic activity for formic acid oxidation is very high. Cyclic voltammetry measurements (CV) show that the generated current peak value for Pd-decorated helical carbon nanofibers is 300 mA/mgPd for a scan rate of 10 mV/s. This is significantly higher than the corresponding value of a reference sample of multiwalled carbon nanotubes decorated with Pd nanoparticles by the same process. Fuel cell tests for our Pd-decorated helical carbon nanofibers also displayed a high power density, although not as superior to Pd-decorated multiwalled nanotubes as measured by CV. Our results show that helical carbon nanofibers have several good properties, such as a rigid anchoring of catalyst nanoparticles and a suitable structure for creating functionalization defects which make them an interesting candidate for electrochemical applications.

2012-02-29

213

Characterization of poly(methyl methacrylate) and thermoplastic polyurethane-carbon nanofiber composites produced by chaotic mixing  

Science.gov (United States)

Chaotic mixing is a novel mixing technique offering high mixing efficiency even under mild shearing conditions. In this work, chaotic mixing was used to prepare composites of carbon nanofibers and two thermoplastic polymers---poly (methyl methacrylate) (PMMA) and thermoplastic polyurethanes (TPU)---and their electrical, mechanical, and thermal properties were evaluated. The TPU systems were based on the reaction products of 4,4'-diphenylmethane diisocyanate, (MDI), soft segment polyol, and 1,4-butanediol as chain extender. Soft segment polyols in the form of poly(propylene glycol) (PPG), and poly(epsilon-caprolactone)diol (PCL) were used to obtain respectively amorphous and crystalline soft segments. Of these, the TPU system based on crystalline soft segment exhibited shape memory effects. Both, as-received untreated carbon nanofibers (CNF) with a very low amount of atomic oxygen on the surface, and oxidized carbon nanofibers (CNFOX) were used. CNFOX was also modified by esterifying with PPG to produce a third type of carbon nanofiber named CNFOL. These carbon nanofibers were examined by X-ray photoelectron spectroscopy to determine the elemental composition of the surface, and by scanning electron microscopy and transmission electron microscopy to determine the surface morphology.

Jiminez, Guillermo A.

214

Electrospinning of carbon/CdS coaxial nanofibers with photoluminescence and conductive properties  

International Nuclear Information System (INIS)

Carbon/CdS coaxial nanofibers (NFs) have been prepared using polyacrylonitrile (PAN)/CdS composite NFs as precursors. The synthesis strategy involves immersing the as-spun PAN fibers into cadmium acetate aqueous solution, followed by reaction with H2S gas and carbonization. SEM and TEM showed the morphology of the obtained coaxial NFs. The structures were examined by XRD, FT-IR and Raman spectra. The NFs displayed photoluminescence and conductive properties which were characterized by room-temperature photoluminescent spectra and standard four-probe method

2007-05-25

215

Influence of the support on the structural characteristics of carbon nanofibers produced from the metal-catalyzed decomposition of ethylene  

Energy Technology Data Exchange (ETDEWEB)

The notion of using support materials to achieve high dispersions of metal particles has been extended to the synthesis of carbon nanofibers from the catalyzed decomposition of ethylene. By using this approach it has been possible to generate nanofibers whose widths are dictated by the dimensions of the supported metal particles. In addition, the support may alter the state of the bulk and/or the surface of the catalyst particle through metal-support interactions, and the impact of this effect is manifested by modifications in the structural characteristics of the nanofibers deposits. In an attempt to gain a clearer insight into the influence of metal-support interaction on the growth characteristics of GNF, three metals, FE,Ni, and Co that are known to be active catalysts for this process were impregnated onto silica, graphite, and well-characterized graphite nanofiber supports. Characterization of the solid carbon products was performed by a variety of approaches including high-resolution transmission electron microscopy (HRTEM), gas-phase analysis, and thermal-programmed oxidation (TPO). The goal of this study was to correlate each nanofiber product with the behavior of the specific metal/support precursor system. The advantages of using selected support materials to control the morphologies and sizes of nanofibers is present.

Anderson, P.E.; Rodriguez, N.M.

2000-03-01

216

Preparation and electrochemical performance of heteroatom-enriched electrospun carbon nanofibers from melamine formaldehyde resin.  

Science.gov (United States)

Melamine formaldehyde resin was used to prepare heteroatom-enriched carbon nanofibers by electrospinning for the first time. The melamine formaldehyde resin-based carbon fibers without any activation treatment showed a moderate specific surface area ranging from 130 to 479 m2/g and rich surface functionalities (2.56-5.34 wt.% nitrogen and 10.39-11.2 9 wt.% oxygen). Both the specific surface area and surface functionality greatly depended on the carbonization temperature. The capacitive performance was evaluated in 6M KOH aqueous solution. The electrochemically active surface functionalities played an important role in improving the surface capacitance of the electrodes. The sample carbonized at 600°C showed the highest specific surface capacitance of 1.4 F/m2, which was attributed to the most active functionalities (10.69 wt.% of N and O). In addition, the sample carbonized at 750°C exhibited the highest specific capacitance of 206 F/g. PMID:23375805

Ma, Chang; Song, Yan; Shi, Jingli; Zhang, Dongqing; Guo, Quangui; Liu, Lang

2013-04-01

217

Influence of copper on the structural characteristics of carbon nanofibers produced from the cobalt-catalyzed decomposition of ethylene  

Energy Technology Data Exchange (ETDEWEB)

We have used a combination of techniques to examine modifications in the structural characteristics of carbon nanofibers produced from the interaction of cobalt and copper-cobalt powders with ethylene at temperatures over the range 425 to 700{degree}C. The nanofibers generated from the interaction of cobalt with ethylene at 600{degree}C were found to be highly crystalline in nature. Incorporation of as little as 2{percent} copper into the cobalt created a major modification in the conformation of the solid carbon deposit, which was composed of multiple nanofiber limbs emanating from a single catalyst particle, and in this state the carbon structures tended to be disordered. As the composition of the bimetallic was progressively changed to the point where copper became the major component, there was a significant increase in the degree of crystalline perfection of the nanofibers even though they maintained their multidirectional form. The transformation in structural characteristics of the carbon nanofibers is rationalized, according to a concept wherein the crystalline order of the deposit is related to the wetting properties of the bimetallic particles with graphite. {copyright} {ital 1996 Materials Research Society.}

Chambers, A.; Rodriguez, N.M.; Baker, R.T. [Catalytic Materials Center, Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-4800 (United States)

1996-02-01

218

In-situ preparation and characterization of acid functionalized single walled carbon nanotubes with polyimide nanofibers.  

Science.gov (United States)

Nanofiber composites (Polyimide/f-SWCNT) of Pyromellitic dianhydride, 4,4'-Oxydianiline, and 4,4'-(4,4'-isopropylidene diphenyl-1,1'-diyl dioxy) dianiline (PMDA-ODA/IDDA) and surface-functionalized single walled carbon nanotubes (f-SWCNT) were made by electrospinning a solution of poly(amic acid) (PAA) containing 0-2 wt% f-SWCNT followed by thermal imidization. X-ray photoelectron spectroscopy spectra verified the oxidation of SWCNT surface after acid treatment, and indicated possible hydrogen bonding interactions between the f-SWCNTs and polyamic acid. High-resolution scanning electron microscopy images showed the average diameter of nanofibers to be below 150 nm, and transmission electron microscopy images showed that SWCNTs were aligned inside the polymer nanofiber. In thermogravimetric analysis, all composites showed increased thermal stability with increasing f-SWCNT content compared to neat PI. Storage modulus also increased from 124 MPa to 229 MPa from neat PI to 2% f-SWCNT composite. PMID:24757974

Dhakshnamoorthy, M; Ramakrishnan, S; Vikram, S; Kothurkar, Nikhil K; Rangarajan, Murali; Vasanthakumari, R

2014-07-01

219

Hydrazine decomposition over iridium supported on carbon nanofibers composite for space applications: near actual flight conditions tests  

Energy Technology Data Exchange (ETDEWEB)

Hydrazine-type monopropellant propulsion is well suited to attitude and orbit control systems on satellites. These systems are powered by micro thrusters with 30-40wt.% iridium supported on alumina as catalyst for hydrazine decomposition. Carbon nanofibers with macroscopic shaping can be used as an alternative to the traditional support. This new material is prepared by chemical vapor deposition of ethane on nickel particles dispersed upon the surface of the graphite felt. The carbon nanofiber-based composite was impregnated with 30wt.% of iridium. The overall performances of these catalysts have been evaluated for the hydrazine catalytic decomposition reaction in a 2N micro thruster into a vacuum chamber, i.e., under near actual flight conditions. The results obtained were compared with those of a commercial catalyst (Shell 405). The carbon nanofibers-based catalysts showed far better performance than the commercial catalyst from a standpoint of activity due to its texture and its high thermal conductivity.

Vieira, Ricardo; Ledoux, Marc-Jacques; Pham-Huu, Cuong [Laboratoire des Materiaux, Surfaces et Procedes pour la Catalyse LMSPC, UMR 7515 du CNRS, ECPM-ULP, 25 rue Becquerel, F-67087 Cedex 2, Strasbourg (France); Bastos-Netto, Demetrio [Laboratorio de Combustao e Propulsao, Instituto Nacional de Pesquisas Espaciais, rodovia Presidente Dutra Km 40, 12630-000, Cachoeira Paulista, SP (Brazil)

2005-01-28

220

Transport properties of spiral carbon nanofiber mats containing Pd metal clusters using Pd2(dba)3 as catalyst  

CERN Document Server

We have grown spiral carbon nanofibers containing Pd metal clusters using the Pd2(dba)3 catalyzed decomposition of gaseous acetylene on molecular sieves (AlPO4-5) support. The microstructure and composition of the spiral carbon nanofibers were examined by the powder x-ray diffractometer and transmission electron microscope. The conductivity of the mat in the temperature range from 14 to 250 K could be described by the form of exp[-(T-1/4)]. The thermopower shows a remarkably linear behavior down to 40 K, reminiscent of some conducting polymers. The sign change of the thermopower suggests there exists more than one type of charge carrier, which could be ascribed to the different types of nanotube with various sizes of radius. The transport behavior of spiral carbon nanofibers containing Pd metal clusters will be discussed in the framework of the heterogeneous model.

Liu, C J; Hsu, L S; Su, C J; Wang, C C; Shieu, F S

2004-01-01

 
 
 
 
221

Preparation using Pectinase and Characterization of Nanofibers from Orange Peel Waste in Juice Factories.  

Science.gov (United States)

This study reports the preparation and characterization of nanofibers consisting mainly of cellulose microfibrils from orange peel (OP), which is a significant byproduct of orange juice production. Three treatments (boiling, alkaline, and pectinase) were investigated with and without subsequent grinding treatment. It was possible to prepare the cellulose nanofibers (CNFs) using these methods, except for the boiling treatment with grinding. Interestingly, only pectinase and a mild-physical blender treatment without grinding produced nanofibers. The width of the nanofibers from OP was approximately 10 to 50 nm. The microfibril bundles of OP were considered to be thinner than those of commercial CNFs. Our data indicated that the removal of pectic polysaccharides and hemicelluloses covering the cellulose microfibrils was important for the preparation of nanofibers from OP. These nanofibers from OP using pectinase are proposed to be applicable as food materials, pharmaceuticals, and filters for the tractive characteristics of the sheet. PMID:24806523

Hideno, Akihiro; Abe, Kentaro; Yano, Hiroyuki

2014-06-01

222

Preparation of macroporous carbon nanofibers with macroscopic openings in the surfaces and their applications  

Science.gov (United States)

Macroporous carbon nanofibers with mesoscale surface openings were produced by electrospinning. During the electrospinning of polyacrylonitrile (PAN) solution including crosslinked polymer colloids, the polymer colloids were concentrated in the center of PAN fibers. Carbonization left interconnected spherical pores inside the carbon fibers and mesoscale openings in the fiber surfaces. The existence of surface openings facilitated inward diffusion of various solvent molecules, nanoparticles, and large molecules such as proteins. The porous fibers could be dispersed in both hydrophilic and hydrophobic solvents and materials, which enabled production of polymer composites in which the fibers and polymers were interpenetrating through the pores. Silica coating on the macroporous carbon fibers enriched the surface chemistry to effectively immobilize proteins helped by easy diffusion through surface openings.

Lee, Sungwon; Lee, Kipoong; Moon, Geon Dae; Won, Yong Sun; Yoon, Yeo-Joo; Park, Sung Soo; Kim, Young-Rok; Jeong, Unyong

2009-11-01

223

Preparation of macroporous carbon nanofibers with macroscopic openings in the surfaces and their applications  

International Nuclear Information System (INIS)

Macroporous carbon nanofibers with mesoscale surface openings were produced by electrospinning. During the electrospinning of polyacrylonitrile (PAN) solution including crosslinked polymer colloids, the polymer colloids were concentrated in the center of PAN fibers. Carbonization left interconnected spherical pores inside the carbon fibers and mesoscale openings in the fiber surfaces. The existence of surface openings facilitated inward diffusion of various solvent molecules, nanoparticles, and large molecules such as proteins. The porous fibers could be dispersed in both hydrophilic and hydrophobic solvents and materials, which enabled production of polymer composites in which the fibers and polymers were interpenetrating through the pores. Silica coating on the macroporous carbon fibers enriched the surface chemistry to effectively immobilize proteins helped by easy diffusion through surface openings.

2009-11-04

224

Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a superhigh capacity and rate capability  

Energy Technology Data Exchange (ETDEWEB)

Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g{sup -1} at a current density of 2 A g{sup -1} even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Qie, Long; Chen, Wei-Min; Wang, Zhao-Hui; Shao, Qing-Guo; Li, Xiang; Yuan, Li-Xia; Hu, Xian-Luo; Zhang, Wu-Xing; Huang, Yun-Hui [State Key Laboratory of Material Processing and Die and Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei (China)

2012-04-17

225

Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions  

Science.gov (United States)

To address oil spillage and chemical leakage accidents, the development of efficient sorbent materials is of global importance for environment and water source protection. Here we report on a new type of carbon nanofiber (CNF) aerogels as efficient sorbents for oil uptake with high sorption capacity and excellent recyclability. Importantly, the oil uptake ability of the CNF aerogels can be maintained over a wide temperature range, from liquid nitrogen temperature up to ca. 400°C, making them suitable for oil cleanup under harsh conditions. The outstanding sorption performance of CNF aerogels is associated with their unique physical properties, such as low density, high porosity, excellent mechanical stability, high hydrophobicity and superoleophilicity.

Wu, Zhen-Yu; Li, Chao; Liang, Hai-Wei; Zhang, Yu-Ning; Wang, Xin; Chen, Jia-Fu; Yu, Shu-Hong

2014-02-01

226

Platinum nanocluster growth on vertically aligned carbon nanofiber arrays: Sputtering experiments and molecular dynamics simulations  

Science.gov (United States)

Sputtered platinum nanocluster growth on previously plasma enhanced chemical vapor deposition - PECVD - grown vertically aligned carbon nanofiber arrays is presented. Experimental cluster size distribution is shown to decrease from the CNF top to bottom, as observed by transmission electron microscopy. Molecular dynamics simulations are carried out for understanding early stages of Pt growth on model CNF arrays. Especially, sticking coefficients, concentration profiles along CNF wall, cluster size distributions are calculated. Simulated cluster size distribution are consistent with experimental finding. Sticking coefficient decreases against deposition time. The shape of the sticking curve reflects the nanocluster growth process.

Brault, Pascal; Caillard, Amaël; Charles, Christine; Boswell, Rod W.; Graves, David B.

2012-12-01

227

Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions  

Science.gov (United States)

To address oil spillage and chemical leakage accidents, the development of efficient sorbent materials is of global importance for environment and water source protection. Here we report on a new type of carbon nanofiber (CNF) aerogels as efficient sorbents for oil uptake with high sorption capacity and excellent recyclability. Importantly, the oil uptake ability of the CNF aerogels can be maintained over a wide temperature range, from liquid nitrogen temperature up to ca. 400°C, making them suitable for oil cleanup under harsh conditions. The outstanding sorption performance of CNF aerogels is associated with their unique physical properties, such as low density, high porosity, excellent mechanical stability, high hydrophobicity and superoleophilicity.

Wu, Zhen-Yu; Li, Chao; Liang, Hai-Wei; Zhang, Yu-Ning; Wang, Xin; Chen, Jia-Fu; Yu, Shu-Hong

2014-01-01

228

A nanobursa mesh: a graded electrospun nanofiber mesh with metal nanoparticles on carbon nanotubes.  

Science.gov (United States)

A new type of material, a "nanobursa" mesh (from "bursa" meaning "sac or pouch"), is introduced. This material consists of sequential layers of porous polymeric nanofibers encapsulating carbon nanotubes, which are functionalized with different metal nanoparticles in each layer. The nanobursa mesh is fabricated via a novel combination of twin-screw extrusion and electrospinning. Use of this hybrid process at industrially-relevant rates is demonstrated by producing a nanobursa mesh with graded layers of Pd, Co, Ag, and Pt nanoparticles. The potential use of the fabricated nanobursa mesh is illustrated by modeling of catalytic hydrocarbon oxidation. PMID:24958514

Senturk-Ozer, Semra; Chen, Tao; Degirmenbasi, Nebahat; Gevgilili, Halil; Podkolzin, Simon G; Kalyon, Dilhan M

2014-07-10

229

Synthesis of worm-shaped carbon nanofibers over a sodium chloride support  

International Nuclear Information System (INIS)

Worm-shaped carbon nanofibers (WCNFs) were synthesized in bulk by chemical vapour deposition at 680 °C using iron carboxylate as catalyst precursors and sodium chloride as catalyst support. The products were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction method. The purity of the purified products was determined by thermal analysis. The WCNF yield was 6700% relative to catalyst. The simplicity, environmental friendliness and use of easily available low-cost precursors are the advantage of this synthesis technique.

2012-01-01

230

Superhydrophobic and conductive carbon nanofiber/PTFE composite coatings for EMI shielding.  

Science.gov (United States)

This paper presents a solvent-based, mild method to prepare superhydrophobic, carbon nanofiber/PTFE-filled polymer composite coatings with high electrical conductivity and reports the first data on the effectiveness of such coatings as electromagnetic interference (EMI) shielding materials. The coatings are fabricated by spraying dispersions of carbon nanofibers and sub-micron PTFE particles in a polymer blend solution of poly(vinyledene fluoride) and poly(methyl methacrylate) on cellulosic substrates. Upon drying, coatings display static water contact angles as high as 158° (superhydrophobic) and droplet roll-off angles of 10° indicating self-cleaning ability along with high electrical conductivities (up to 309 S/m). 100 ?m-thick coatings are characterized in terms of their EMI shielding effectiveness in the X-band (8.2-12.4 GHz). Results show up to 25 dB of shielding effectiveness, which changed little with frequency at a fixed composition, thus indicating the potential of these coatings for EMI shielding applications and other technologies requiring both extreme liquid repellency and high electrical conductivity. PMID:20889160

Das, Arindam; Hayvaci, Harun T; Tiwari, Manish K; Bayer, Ilker S; Erricolo, Danilo; Megaridis, Constantine M

2011-01-01

231

Label-free detection of C-reactive protein using a carbon nanofiber based biosensor.  

Science.gov (United States)

We report the sensitive detection of C-reactive protein (CRP), a biomarker for cardiac disease, using a carbon nanofiber based biosensor platform. Vertically aligned carbon nanofibers were grown using plasma enhanced chemical vapor deposition to fabricate nanoelectrode arrays in a 3×3 configuration. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the CRP detection. The CV responses show a 25% reduction in redox current upon the immobilization of anti-CRP on the electrode where as a 30% increase in charge transfer resistance is seen from EIS. Further reduction in redox current and increase in charge transfer resistance result from binding of CRP on anti-CRP immobilized surface, proportional to the concentration of the CRP target. The detection limit of the sensor is found to be ~90pM or ~11ng/ml, which is in the clinically relevant range. Control tests using non-specific myoglobin antigen confirmed the specificity of the present approach. PMID:24709327

Gupta, Rakesh K; Periyakaruppan, Adaikkappan; Meyyappan, M; Koehne, Jessica E

2014-09-15

232

Controlling thin film structure for the dewetting of catalyst nanoparticle arrays for subsequent carbon nanofiber growth  

International Nuclear Information System (INIS)

Vertically aligned carbon nanofiber (CNF) growth is a catalytic chemical vapor deposition process in which structure and functionality is controlled by the plasma conditions and the properties of the catalyst nanoparticles that template the fiber growth. We have found that the resultant catalyst nanoparticle network that forms by the dewetting of a continuous catalyst thin film is dependent on the initial properties of the thin film. Here we report the ability to tailor the crystallographic texture and composition of the nickel catalyst film and subsequently the nanoparticle template by varying the rf magnetron sputter deposition conditions. After sputtering the Ni catalyst thin films, the films are heated and exposed to an ammonia dc plasma, to chemically reduce the native oxide on the films and induce dewetting of the film to form nanoparticles. Subsequent nanoparticle treatment in an acetylene plasma at high substrate temperature results in CNF growth. Evidence is presented that the texture and composition of the nickel thin film has a significant impact on the structure and composition of the formed nanoparticle, as well as the resultant CNF morphology. Nickel films with a preferred (111) or (100) texture were produced and conditions favoring interfacial silicidation reactions were identified and investigated. Both compositional and structural analysis of the films and nanoparticles indicate that the properties of the as-deposited Ni catalyst film influences the subsequent nanoparticle formation and ultimately the catalytic growth of the carbon nanofibers

2007-11-21

233

Controlling thin film structure for the dewetting of catalyst nanoparticle arrays for subsequent carbon nanofiber growth  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned carbon nanofiber (CNF) growth is a catalytic chemical vapor deposition process in which structure and functionality is controlled by the plasma conditions and the properties of the catalyst nanoparticles that template the fiber growth. We have found that the resultant catalyst nanoparticle network that forms by the dewetting of a continuous catalyst thin film is dependent on the initial properties of the thin film. Here we report the ability to tailor the crystallographic texture and composition of the nickel catalyst film and subsequently the nanoparticle template by varying the rf magnetron sputter deposition conditions. After sputtering the Ni catalyst thin films, the films are heated and exposed to an ammonia dc plasma, to chemically reduce the native oxide on the films and induce dewetting of the film to form nanoparticles. Subsequent nanoparticle treatment in an acetylene plasma at high substrate temperature results in CNF growth. Evidence is presented that the texture and composition of the nickel thin film has a significant impact on the structure and composition of the formed nanoparticle, as well as the resultant CNF morphology. Nickel films with a preferred (111) or (100) texture were produced and conditions favoring interfacial silicidation reactions were identified and investigated. Both compositional and structural analysis of the films and nanoparticles indicate that the properties of the as-deposited Ni catalyst film influences the subsequent nanoparticle formation and ultimately the catalytic growth of the carbon nanofibers.

Randolph, S J [University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996 (United States); Fowlkes, J D [University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996 (United States); Melechko, A V [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831 (United States); Klein, K L [University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996 (United States); III, H M Meyer [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831 (United States); Simpson, M L [University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996 (United States); Rack, P D [University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996 (United States)

2007-11-21

234

Fabrication of carbon nanofiber-driven electrodes from electrospun polyacrylonitrile/polypyrrole bicomponents for high-performance rechargeable lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers were prepared through electrospinning a blend solution of polyacrylonitrile and polypyrrole, followed by carbonization at 700 C. Structural features of electrospun polyacrylonitrile/polypyrrole bicomponent nanofibers and their corresponding carbon nanofibers were characterized using scanning electron microscopy, differential scanning calorimeter, thermo-gravimetric analysis, wide-angle X-ray diffraction, and Raman spectroscopy. It was found that intermolecular interactions are formed between two different polymers, which influence the thermal properties of electrospun bicomponent nanofibers. In addition, with the increase of polypyrrole concentration, the resultant carbon nanofibers exhibit increasing disordered structure. These carbon nanofibers were used as anodes for rechargeable lithium-ion batteries without adding any polymer binder or conductive material and they display high reversible capacity, improved cycle performance, relatively good rate capability, and clear fibrous morphology even after 50 charge/discharge cycles. The improved electrochemical performance of these carbon nanofibers can be attributed to their unusual surface properties and unique structural features, which amplify both surface area and extensive intermingling between electrode and electrolyte phases over small length scales, thereby leading to fast kinetics and short pathways for both Li ions and electrons. (author)

Ji, Liwen; Yao, Yingfang; Toprakci, Ozan; Lin, Zhan; Liang, Yinzheng; Shi, Quan; Medford, Andrew J.; Millns, Christopher R.; Zhang, Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States)

2010-04-02

235

Investigation of Lithium-Air Battery Discharge Product Formed on Carbon Nanotube and Nanofiber Electrodes  

Science.gov (United States)

Carbon nanotubes have been actively investigated for integration in a wide variety of applications since their discovery over 20 years ago. Their myriad desirable material properties including exceptional mechanical strength, high thermal conductivities, large surface-to-volume ratios, and considerable electrical conductivities, which are attributable to a quantum mechanical ability to conduct electrons ballistically, have continued to motivate interest in this material system. While a variety of synthesis techniques exist, carbon nanotubes and nanofibers are most often conveniently synthesized using chemical vapor deposition (CVD), which involves their catalyzed growth from transition metal nanoparticles. Vertically-aligned nanotube and nanofiber carpets produced using CVD have been utilized in a variety of applications including those related to energy storage. Li-air (Li-O2) batteries have received much interest recently because of their very high theoretical energy densities (3200 Wh/kgLi2O2 ). which make them ideal candidates for energy storage devices for future fully-electric vehicles. During operation of a Li-air battery O2 is reduced on the surface a porous air cathode, reacting with Li-ions to form lithium peroxide (Li-O2). Unlike the intercalation reactions of Li-ion batteries, discharge in a Li-air cell is analogous to an electrodeposition process involving the nucleation and growth of the depositing species on a foreign substrate. Carbon nanofiber electrodes were synthesized on porous substrates using a chemical vapor deposition process and then assembled into Li-O2 cells. The large surface to volume ratio and low density of carbon nanofiber electrodes were found to yield a very high gravimetric energy density in Li-O 2 cells, approaching 75% of the theoretical energy density for Li 2O2. Further, the carbon nanofiber electrodes were found to be excellent platforms for conducting ex situ electron microscopy investigations of the deposition Li2O2 phase, which was found to have unique disc and toroid morphologies. Subsequent studies were conducted using freestanding carpets of multi-walled CNT arrays, which were synthesized using a modified CVD process. The freestanding CNT arrays were used as a platform for studying the morphological evolution of Li2O2 discharge product as a function of rate and electrode capacity. SEM imaging investigations found that the Li2O 2 particles underwent a shape evolution from discs to toroids as their size increased. TEM imaging and diffraction studies showed that the microscale Li2O2 particles are composed of stacks of thin Li 2O2 crystallites and that splaying of the stacked crystallite array drives the observed disc to toroid transition. Modeling was performed to gain insights into the nucleation and growth processes involved during discharge in Li-O2 cells. The modeling study suggests that poor electronic conductivity of the depositing phase limits the rate capability obtainable in Li-O2 cells. Modeling can provide substantial insights into paths toward electrode optimization. Understanding the size and shape evolution of Li2O2 particles and engineering improved electrode architectures is critical to efficiently filling the electrode void volume during discharge thereby improving the volumetric energy density of Li-O2 batteries. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

Mitchell, Robert Revell, III

236

The study of hydrogen electrosorption in layered nickel foam/palladium/carbon nanofibers composite electrodes  

International Nuclear Information System (INIS)

In the present work, the process of hydrogen electrosorption occurring in alkaline KOH solution on the nickel foam/palladium/carbon nanofibers (Ni/Pd/CNF) composite electrodes is examined. The layered Ni/Pd/CNF electrodes were prepared by a two-step method consisting of chemical deposition of a thin layer of palladium on the nickel foam support to form Ni/Pd electrode followed by coating the palladium layer with carbon nanofibers layer by means of the CVD method. The scanning electron microscope was used for studying the morphology of both the palladium and carbon layer. The process of hydrogen sorption/desorption into/from Ni/Pd as well as Ni/Pd/CNF electrode was examined using the cyclic voltammetry method. The amount of hydrogen stored in both types of composite electrodes was shown to increase on lowering the potential of hydrogen sorption. The mechanism of the anodic desorption of hydrogen changes depending on whether or not CNF layer is present on the Pd surface. The anodic peak corresponding to the removal of hydrogen from palladium is lower for Ni/Pd/CNF electrode as compared to that measured for Ni/Pd one due to a partial screening of the Pd surface area by CNF layer. The important feature of Ni/Pd/CNF electrode is anodic peak appearing on voltammetric curves at potential ca. 0.4 V more positive than the peak corresponding to hydrogen desorption from palladium. The obtained results showed that upon storing the hydrogen saturated Ni/Pd/CNF electrode at open circuit potential, diffusion of hydrogen from carbon to palladium phase occurs due to interaction between carbon fibers and Pd sites on the nickel foam support

2007-05-10

237

EFFECT OF CELLULOSE NANOFIBERS ISOLATED FROM BAMBOO PULP RESIDUE ON VULCANIZED NATURAL RUBBER  

Directory of Open Access Journals (Sweden)

Full Text Available Nanocomposites were prepared using two bioresources, viz., cellulose nanofibers (CNFs extracted from bamboo paper-pulp waste as the reinforcing phase and natural rubber (NR as the matrix phase. CNFs with diameters up to 50 nm were isolated from bamboo pulp waste, and nanocomposites with 5 and 10% CNFs were obtained via two-roll mill mixing of solid natural rubber with a master batch containing 20 wt% CNFs. The NR phase was cross-linked using sulphur vulcanization. The morphology studies showed that the dispersion of CNF in NR matrix was not optimal, and some aggregates were visible on the fracture surface. The tensile strength and modulus at 50% elongation increased for the nanocomposites with the addition of CNFs, accompanied by a moderate decrease in elongation at break. The storage modulus of the natural rubber significantly increased above its glass-rubber transition temperature upon nanofiber addition. The addition of CNFs also had a synergistic impact on the thermal stability of natural rubber. The susceptibility to organic solvents decreased significantly for the nanocomposites compared to crosslinked NR, which indicated restriction of polymer chain mobility in the vicinity of the nanosized CNFs in the NR matrix.

P. M. Visakh,

2012-02-01

238

In situ Polymerization of Multi-Walled Carbon Nanotube/Nylon-6 Nanocomposites and Their Electrospun Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Multiwalled carbon nanotube/nylon-6 nanocomposites (MWNT/nylon-6 were prepared by in situ polymerization, whereby functionalized MWNTs (F-MWNTs and pristine MWNTs (P-MWNTs were used as reinforcing materials. The F-MWNTs were functionalized by Friedel-Crafts acylation, which introduced aromatic amine (COC6H4-NH2 groups onto the side wall. Scanning electron microscopy (SEM images obtained from the fractured surfaces of the nanocomposites showed that the F-MWNTs in the nylon-6 matrix were well dispersed as compared to those of the P-MWNTs. Both nanocomposites could be electrospun into nanofibers in which the MWNTs were embedded and oriented along the nanofiber axis, as confirmed by transmission electron microscopy. The specific strength and modulus of the MWNTs-reinforced nanofibers increased as compared to those of the neat nylon-6 nanofibers. The crystal structure of the nylon-6 in the MWNT/nylon-6 nanofibers was mostly ?-phase, although that of the MWNT/nylon-6 films, which were prepared by hot-pressing the pellets between two aluminum plates and then quenching them in icy water, was mostly ?-phase, indicating that the shear force during electrospinning might favor the ?-phase, similarly to the conventional fiber spinning.

Baek Jong-Beom

2008-01-01

239

Effect of the nature the carbon precursor on the physico-chemical characteristics of the resulting activated carbon materials  

International Nuclear Information System (INIS)

Carbon materials, including amorphous carbon, graphite, carbon nanospheres (CNSs) and different types of carbon nanofibers (CNFs) [platelet, herringbone and ribbon], were chemically activated using KOH. The pore structure of carbon materials was analyzed using N2/77 K adsorption isotherms. The presence of oxygen groups was analyzed by temperature programmed desorption in He and acid-base titration. The structural order of the materials was studied by X-ray diffraction and temperature programmed oxidation. The morphology and diameter distribution of CNFs and CNSs were characterized by transmission electron microscopy. The materials were also characterized by temperature-desorption programmed of H2 and elemental composition. The ways in which the different structures were activated are described, showing the type of pores generated. Relationships between carbon yield, removed carbon, activation degree and graphitic character were also examined. The oxygen content in the form of oxygen-containing surface groups increased after the activation giving qualitative information about them. The average diameter of both CNFs and CNSs was decreased after the activation process as consequence of the changes produced on the material surface.

2010-11-01

240

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition  

International Nuclear Information System (INIS)

Vertically aligned carbon nanofibers (VACNFs) with vastly different spacing were grown by catalytically controlled dc glow discharge chemical vapor deposition. Both densely packed VACNFs and essentially isolated VACNFs were studied using scanning electron microscopy and x-ray energy dispersive spectroscopy. The morphology and chemical composition of isolated VACNFs were found to have a strong dependence upon the growth conditions, in particular on the C2H2/NH3 gas mixture used. This is attributed to the sidewalls of isolated VACNFs being exposed to reactive species during growth. In contrast, the sidewalls of densely packed VACNFs were shielded by the neighboring VACNFs, so that their growth occurred mainly in the vertical direction, by diffusion of carbon through the catalyst nanoparticle and subsequent precipitation at the nanofiber/nanoparticle interface. These striking differences in the growth process result in the formation of flattened carbon nanostructures (carbon nanotriangles) and also are quite important for the realization of VACNF-based devices

2002-01-21

 
 
 
 
241

Graphitic carbon nanofiber (GCNF)/polymer materials. I. GCNF/epoxy monoliths using hexanediamine linker molecules.  

Science.gov (United States)

Processing methods have been optimized for the formation of graphitic carbon nanofiber (GCNF)/epoxy nanocomposites containing GCNFs highly dispersed throughout a thermoset epoxy matrix. GCNFs having a herringbone atomic structure are surface-derivatized with bifunctional hexanediamine linker molecules (GCNF-HDA) capable of covalent binding to an epoxy matrix during thermal curing and are cut to smaller dimension using high-power ultrasonication. GCNF-HDA nanofibers are dispersed in epoxy resin at 0.3 wt.% loading using variable levels of ultrasonication processing prior to thermal curing. Effects of sonication power on the quality of the GCNF-HDA/epoxy material obtained after curing have been determined from flexural property measurements, thermomechanical analysis and SEM/TEM imaging. GCNF-HDA/epoxy material of the highest quality is obtained using low-power sonication, although high-power sonication for short periods gives improved flexural properties without lowering the glass transition temperature. Good dispersion and polymer wetting of the GCNF component is evident on the nanoscale. PMID:15570962

Zhong, Wei-Hong; Li, Jiang; Xu, Luoyu R; Michel, Jason A; Sullivan, Lisa M; Lukehart, Charles M

2004-09-01

242

Synthesis and characterization of magnetically active carbon nanofiber/iron oxide composites with hierarchical pore structures  

International Nuclear Information System (INIS)

Polyacrylonitrile (PAN) solution containing the iron oxide precursor iron (III) acetylacetonate (AAI) was electrospun and thermally treated to produce electrically conducting, magnetic carbon nanofiber mats with hierarchical pore structures. The morphology and material properties of the resulting multifunctional nanofiber mats including the surface area and the electric and magnetic properties were examined using various characterization techniques. Scanning electron microscopy images show that uniform fibers were produced with a fiber diameter of ?600 nm, and this uniform fiber morphology is maintained after graphitization with a fiber diameter of ?330 nm. X-ray diffraction (XRD) and Raman studies reveal that both graphite and Fe3O4 crystals are formed after thermal treatment, and graphitization can be enhanced by the presence of iron. A combination of XRD and transmission electron microscopy experiments reveals the formation of pores with graphitic nanoparticles in the walls as well as the formation of magnetite nanoparticles distributed throughout the fibers. Physisorption experiments show that the multifunctional fiber mats exhibit a high surface area (200-400 m2 g-1) and their pore size is dependent on the amount of iron added and graphitization conditions. Finally, we have demonstrated that the fibers are electrically conducting as well as magnetically active.

2008-11-12

243

Morphological characterization of carbon nanofiber aerosol using tandem mobility and aerodynamic size measurements  

Energy Technology Data Exchange (ETDEWEB)

Characterizing microstructural and transport properties of non-spherical particles, such as carbon nanofibers (CNF), is important for understanding their transport and deposition in human respiratory system and engineered devices such as particle filters. We describe an approach to obtain morphological information of non-spherical particles using a tandem system of differential mobility analyzer (DMA) and an electrical low-pressure impactor (ELPI). Effective density, dynamic shape factors (DSF), particle mass, and fractal dimension-like mass-scaling exponent of nanofibers were derived using the measured mobility and aerodynamic diameters, along with the known material density of CNF. Multiple charging of particles during DMA classification, which tends to bias the measured shape factors and particle mass toward higher values, was accounted for using a correction procedure. Particle mass derived from DMA-ELPI measurements agreed well with the direct mass measurements using an aerosol particle mass analyzer. Effective densities, based on mobility diameters, ranged from 0.32 to 0.67 g cm{sup -3}. The DSF of the CNF ranged from 1.8 to 2.3, indicating highly non-spherical particle morphologies.

Deye, Gregory J.; Kulkarni, Pramod, E-mail: pskulkarni@cdc.gov; Ku, Bon Ki [National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention (United States)

2012-09-15

244

Electrochemical behavior of activated carbon nanofiber-vanadium pentoxide composites for double-layer capacitors  

International Nuclear Information System (INIS)

Mesopore-enriched activated carbon nanofiber (ACNF) mats are produced by incorporating vanadium(V) oxide (V2O5) into polyacrylonitrile (PAN) via electrospinning, and their electrochemical properties are investigated as an electrode in supercapacitors. The microstructures of the ACNFs (e.g., nanometer-size diameter, high specific surface area, narrow pore size distribution, and tunable porosity) are changed, and the textural parameters are found to affect the electrochemical properties significantly through the different V2O5 loadings and activation process. The V2O5/PAN-based ACNF electrodes with well-balanced micro/mesoporosity having an optimal pore range for effective double layer formation in an organic medium are expected to be useful electrode materials for supercapacitor applications

2013-10-30

245

Flexible Sensing Arrays Fabricated with Carbon Nanofiber Composite Thin Films for Posture Monitoring  

Science.gov (United States)

Faulty posture increases joint stress and causes postural pain syndrome. In this paper, we present a portable strain sensing system with flexible sensor arrays to warn patients to correct inappropriate posture. A 3× 3 flexible strain sensing array system was fabricated using patterned surface treatment and the tilted-drop process with carbon nanofiber composite solutions on polyimide substrates. Atmospheric plasma was used to enhance or reduce the surface energy in specific areas for patterned surface treatment. A scanning circuit was also developed to capture the signal from the flexible sensing array. The developed system has been used to measure the bent angle of the human neck from 15 to 60°. The results indicate that human posture can be successfully captured by analyzing the measured strains from a flexible strain sensing array.

Chang, Fuh-Yu; Wang, Ruoh-Huey; Lin, Yu-Hsien; Chen, Tse-Min; Lee, Yueh-Feng; Huang, Shu-Jiuan; Liu, Chia-Ming

2011-06-01

246

Direct Measurement of the Percolation Probability in Carbon Nanofiber-Polyimide Nanocomposites  

Science.gov (United States)

We present the first experimental measurement of the geometric critical exponent ? associated with the percolation probability, the probability a metallic filler belongs to the conducting network, of an electrical composite. The technique employs conducting-tip atomic force microscopy to obtain a conducting areal density, and is demonstrated on polyimide nanocomposites containing different concentrations of carbon nanofibers. We find ??1 and t (the exponent for bulk conductivity) ?3. These values are consistent with the predictions for the Bethe lattice and larger than the values predicted in the 3D lattice percolation model. Hence, this electrical composite likely belongs to the same universality class as the Bethe lattice. The ability to measure geometric and transport critical exponents on the same material is critical to drawing this conclusion.

Trionfi, A.; Wang, D. H.; Jacobs, J. D.; Tan, L.-S.; Vaia, R. A.; Hsu, J. W. P.

2009-03-01

247

Fracture Toughness of Vapor Grown Carbon Nanofiber-Reinforced Polyethylene Composites  

Directory of Open Access Journals (Sweden)

Full Text Available The impact fracture behavior of a vapor grown carbon nanofiber (VGCNF reinforced high-density polyethylene (PE composite was evaluated. The samples consisting of pure PE and composites with 10?wt% and 20?wt% of VGCNFs were prepared by a combination of hot-pressing and extrusion methods. Extrusion was used to produce samples with substantially different shear histories. The fracture behavior of these samples was analyzed using the essential work of fracture (EWF approach. The results showed an increase of 292% in the essential work of fracture for the loading of 10?wt%. Further increasing fiber loading to 20?wt% caused the essential work of fracture to increase only 193% with respect to the unmodified material. Evaluation of the fracture surface morphology indicated that the fibril frequency and microvoid size within the various fiber loadings depended strongly on processing conditions.

A. R. Adhikari

2009-01-01

248

Mechanisms for catalytic carbon nanofiber growth studied by ab initio density functional theory calculations  

DEFF Research Database (Denmark)

Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported from the deposition site at the free nickel surface to the perimeter of the growing graphene layer via surface or subsurface diffusion. Three different processes are identified to govern the growth of graphene layers, depending on the termination of the graphene perimeter at the nickel surface, and it is argued how these processes may lead to different nanofiber structures. The proposed growth model is found to be in good agreement with previous findings.

Abild-Pedersen, Frank; Nørskov, Jens Kehlet

2006-01-01

249

Carbon Nanofiber Reinforced and PU-toughened POM Ternary Composites: Friction, Wear and Creep Properties  

Directory of Open Access Journals (Sweden)

Full Text Available Composites composed of polyoxymethylene (POM, polyurethane (PU and carbon nanofiber (CNF were produced by water-mediated melt compounding. PU latex and/or aqueous CNF dispersion were introduced into the molten POM in laboratory kneader to prepare toughened and/or nanoreinforced POM composites. The dispersion of the CNF was inspected using scanning electron microscopy (SEM. The mechanical properties (friction, wear and creep strain of the composites were determined by roller (steel-on-plate (ROP and creep tensile tests. It was found that CNF worked as a reinforcement and improved the coefficient of friction (COF and wear. It was also found that, the creep resistance decreases with increasing time, temperature and addition of CNF.

Suchart Siengchin

2011-12-01

250

Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading  

Science.gov (United States)

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity.

Howser, R. N.; Dhonde, H. B.; Mo, Y. L.

2011-08-01

251

Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading  

International Nuclear Information System (INIS)

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity

2011-08-01

252

Manufacturing of Nanocomposite Carbon Fibers and Composite Cylinders  

Science.gov (United States)

Pitch-based nanocomposite carbon fibers were prepared with various percentages of carbon nanofibers (CNFs), and the fibers were used for manufacturing composite structures. Experimental results show that these nanocomposite carbon fibers exhibit improved structural and electrical conductivity properties as compared to unreinforced carbon fibers. Composite panels fabricated from these nanocomposite carbon fibers and an epoxy system also show the same properties transformed from the fibers. Single-fiber testing per ASTM C1557 standard indicates that the nanocomposite carbon fiber has a tensile modulus of 110% higher, and a tensile strength 17.7% times higher, than the conventional carbon fiber manufactured from pitch. Also, the electrical resistance of the carbon fiber carbonized at 900 C was reduced from 4.8 to 2.2 ohm/cm. The manufacturing of the nanocomposite carbon fiber was based on an extrusion, non-solvent process. The precursor fibers were then carbonized and graphitized. The resultant fibers are continuous.

Tan, Seng; Zhou, Jian-guo

2013-01-01

253

Scanning atom probe study of carbon nanotubes and graphite nanofibers with hydrogen terminated defects  

International Nuclear Information System (INIS)

Graphite nanofibers (GNF) and multi-wall carbon nanotubes (MWCNT) are mass analyzed utilizing the unique capability of the scanning atom probe. Various clusters of carbon and hydrogen are detected from MWCNT. These are mostly H+, H2+, C+, CH3+ and C2H5+. Few cluster ions are detected for the mass rang of 100-300. The largest mass peak is C28H4+ with two satellite mass peaks. The abundance of the satellites well agrees with the expected abundance of 12C2713CH4 and 12C2613C2H4, 28% and 4%, respectively. No H+ mass peak was found for GNF but the significant number of the ions such as C2H5+, C3H7+ and C4H9+ are detected. These ions are detected at the beginning of the mass analysis. After the removal of the surface layer, the detection rate of the largest cluster, C23H2, increases. The proposed structure of the C28H4 cluster is a rectangle formed three rows by three rows of hexagonal cells and that of C23H2 is the triangularly arranged six hexagonal cells. Four carbon atoms of C28H4 and two carbon atoms of C23H2 clusters are terminated by hydrogen

2008-03-01

254

TECHNICAL NOTE: A feasibility study of self-heating concrete utilizing carbon nanofiber heating elements  

Science.gov (United States)

This paper presents the development of an electric, self-heating concrete system that uses embedded carbon nanofiber paper as electric resistance heating elements. The proposed system utilizes the conductive properties of carbon fiber materials to heat a surface overlay of concrete with various admixtures to improve the concrete's thermal conductivity. The development and laboratory scale testing of the system were conducted for the various compositions of concrete containing, separately, carbon fiber, fly ash, and steel shavings as admixtures. The heating performances of these concrete mixtures with the carbon fiber heating element were experimentally obtained in a sub-freezing ambient environment in order to explore the use of such a system for deicing of concrete roadways. Analysis of electric power consumption, heating rate, and obtainable concrete surface temperatures under typical power loads was performed to evaluate the viability of a large scale implementation of the proposed heating system for roadway deicing applications. A cost analysis is presented to provide a comparison with traditional deicing methods, such as salting, and other integrated concrete heating systems.

Chang, Christiana; Ho, Michelle; Song, Gangbing; Mo, Yi-Lung; Li, Hui

2009-12-01

255

A feasibility study of self-heating concrete utilizing carbon nanofiber heating elements  

International Nuclear Information System (INIS)

This paper presents the development of an electric, self-heating concrete system that uses embedded carbon nanofiber paper as electric resistance heating elements. The proposed system utilizes the conductive properties of carbon fiber materials to heat a surface overlay of concrete with various admixtures to improve the concrete's thermal conductivity. The development and laboratory scale testing of the system were conducted for the various compositions of concrete containing, separately, carbon fiber, fly ash, and steel shavings as admixtures. The heating performances of these concrete mixtures with the carbon fiber heating element were experimentally obtained in a sub-freezing ambient environment in order to explore the use of such a system for deicing of concrete roadways. Analysis of electric power consumption, heating rate, and obtainable concrete surface temperatures under typical power loads was performed to evaluate the viability of a large scale implementation of the proposed heating system for roadway deicing applications. A cost analysis is presented to provide a comparison with traditional deicing methods, such as salting, and other integrated concrete heating systems. (technical note)

2009-12-01

256

Durability of Carbon Nanofiber (CNF) & Carbon Nanotube (CNT) as Catalyst Support for Proton Exchange Membrane Fuel Cells  

DEFF Research Database (Denmark)

Durability issues have recently been given much attention in Proton Exchange Membrane Fuel Cell (PEMFC) research. It gives fundamental definition for cell life time, capital cost, system stability and technique reliability. Loss of catalyst surface area due to corrosion of supporting material (normally carbon black) is one of the essential degradation mechanisms during cell operation. In this work, durability of Carbon Nanofibers (CNF) & Carbon Nanotubes (CNT) as alternative platinum catalyst supports for Proton Exchange Membrane Fuel Cells (PEMFCs) was assessed. Platinized CNF and CNT using a standard polyol method were prepared and fabricated as cathodes of Membrane Electrode Assemblies (MEA) for PEMFC. Both the catalysts as such and the MEAs made out of them were evaluated regarding to thermal and electrochemical stability using traditional carbon black (Vulcan XC72) as a reference. Thermal gravimetric analysis (TGA), cyclic voltammetry (CV), polarization curve and impedance spectroscopy were applied on the samples under accelerated stress conditions. The carbon nano-materials demonstrated better stability as support for nano-sized platinum catalyst under PEMFC related operating conditions. Due to different morphology of the nano carbons compared to Vulcan XC 72 the electrode structures may still need optimization to improve overall cell performance.

Andersen, Shuang Ma; Borghei, Maryam

2013-01-01

257

Chamber-confined silicon-carbon nanofiber composites for prolonged cycling life of Li-ion batteries  

Science.gov (United States)

Silicon is a promising high capacity (4200 mA h g-1) anode material for lithium ion batteries but the significant volume change (over 300%) of silicon during lithiation/delithiation remains a challenge in terms of silicon pulverization and solid-electrolyte-interphase (SEI) accumulation in the silicon composite electrode. To alleviate the volumetric change of silicon, we built a flexible and self-supporting carbon-enhanced carbon nanofiber (CNF) structure with vacant chamber to encapsulate Si nanoparticles (vacant Si@CNF@C). This composite was tested directly without any polymer and current collector. The confined vacant chamber allowed the increasing volume of silicon and SEI accumulates to be well retained for a long cycle life. This chamber-confined silicon-carbon nanofiber composite exhibited an improved performance in terms of good cycling performance (620 mA h g-1), high coulombic efficiency (99%), and good capacity retention (80%) after 200 cycles. This self-supported silicon-carbon nanofiber structure showed high flexibility and good electrochemical performance for the potential as flexible electrode for lithium-ion batteries.

Fu, Kun; Lu, Yao; Dirican, Mahmut; Chen, Chen; Yanilmaz, Meltem; Shi, Quan; Bradford, Philip D.; Zhang, Xiangwu

2014-06-01

258

Nitrogen-doped porous carbon nanofiber webs/sulfur composites as cathode materials for lithium-sulfur batteries  

International Nuclear Information System (INIS)

Nitrogen-doped porous carbon nanofiber webs-sulfur composites (N-CNFWs/S) were synthesized for the first time with sulfur (S) encapsulated into nitrogen-doped porous carbon nanofiber webs (N-CNFWs) via a modified oxidative template route, carbonization-activation and thermal treatment. The composites were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), and thermogravimetry (TG) measurements. The results show that sulfur is well dispersed and immobilized homogeneously in the micropores of nitrogen-doped porous carbon nanofiber webs (N-CNFWs) with high electrical conductivity, surface area and large pore volume. The electrochemical tests show that the N-CNFWs/S composites with 60 wt. % of S have a high initial discharge capacity of 1564 mA h g?1, a good cycling stability at the current density of 175 mA g?1, and excellent rate capability (reversible discharging capacity of above 400 mA h g?1 at 1600 mA g?1)

2014-01-10

259

Effects of carbon nanoparticles on properties of thermoset polymer systems  

Science.gov (United States)

Polymer nanocomposites are novel materials in which at least one of the dimensions of the reinforcing material is on the order of 100 nm or less. While thermoplastic nanocomposites have been studied very widely, there are fewer studies concerning the effect of nanoparticles on thermoset systems. Low temperature cure thermoset systems are very important for many important applications. In this study, the processing, mechanical and thermal properties and reaction kinetics of carbon nanofiber (CNF) and/or carbon nanotubes (CNT) reinforced low temperature vinyl ester and epoxy nanocomposites were studied. In the first part, the processing challenge of incorporating CNFs into conventional fiber reinforced composites made by Vacuum infusion resin transfer molding (VARTM) was addressed by a new technique. The CNFs are pre-bound on the long fiber mats, instead of mixing them in the polymer resin, thereby eliminating several processing drawbacks. The resulting hybrid nanocomposites showed significant improvements in tensile, flexural and thermal properties. The effect of CNFs on the mold filling in VARTM was also studied and shown to follow the Darcy's law. In the second part, the effect of CNFs on the low temperature cure kinetics of vinyl ester and epoxy resins is studied using a thermal analysis technique, namely Differential scanning calorimetry (DSC). The effect of CNFs on the free radical polymerization of vinyl esters was found to be very complex as the CNFs interact with the various curing ingredients in the formulation. Specifically, the interaction effects of CNFs and the inhibitor were studied and a reaction mechanism was proposed to explain the observed phenomenon. The effect of surface modification of the carbon nanoparticles on the cure kinetics of wind-blade epoxy was studied. The surface functionalization reduced the activation energy of the epoxy reaction and was found to have an acceleration effect on the cure kinetics of epoxy resin at room temperature. In the final part, the preparation, properties and characterization of a thin film of carbon nanoparticles, also called a "nanopaper" was studied. Specifically, a new layer-by-layer multiparticle nanopaper was prepared and this layer-by-layer approach improved the mechanical properties of the stand alone nanopaper. The cure kinetics of epoxy resin in the presence of unmodified CNF paper and polyethyleneimine modified CNF paper were studied and modeled using an autocatalytic model. The nanopaper was also used as a functional coating in conventional fiber reinforced epoxy composites and improved several properties such as abrasion resistance and electromagnetic shielding effectiveness.

Movva, Siva Subramanyam

260

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels  

Energy Technology Data Exchange (ETDEWEB)

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures. -- Highlights: ? The influence of dispersion of carbon nanofibers on epoxy is investigated. ? A homogeneous dispersion does not imply better electrical properties. ? The conduction mechanism has an ionic nature below the percolation threshold. ? Above the percolation threshold it is dominated by hopping between the fillers. ? The granular system theory allows explaining conduction at low temperatures.

Cardoso, P. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Silva, J. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Agostinho Moreira, J. [IFIMUP and IN—Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Klosterman, D. [Chemical and Materials Engineering, University of Dayton, 300 College Park, Dayton, OH 45469-0246 (United States); Hattum, F.W.J. van [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Simoes, R. [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); School of Technology, Polytechnic Institute of Cávado and Ave, Campus do IPCA, 4750-810 Barcelos (Portugal); Lanceros-Mendez, S., E-mail: lanceros@fisica.uminho.pt [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); INL—International Iberian Nanotechnology Laboratory, 4715-330 Braga (Portugal)

2012-10-01

 
 
 
 
261

Grafting of vapor-grown carbon nanofibers (VGCNF) with a hyperbranched poly(ether-ketone)  

International Nuclear Information System (INIS)

An in-situ polymerization of an A2B monomer, 5-phenoxyisophthalic acid, in the presence of various amounts (5, 10 and 20 wt%) of vapor-grown carbon nanofibers (VGCNF) was carried out in poly(phosphoric acid)/phosphorus pentoxide (PPA/P2O5; 1:4, w/w) medium. 5-Phenoxyisophthalic acid polymerizes via Friedel-Crafts acylation in PPA to form a CO2H-terminated hyperbranched poly(ether-ketone) or HPB-PEK. The resulting (HPB-PEK)-g-VGCNF composites were not soluble in dichlorobenzene or toluene, but also showed significant solubility in polar solvents such as NMP, DMF, DMAC, ethanol, and significantly higher solubility in ethanol/triethylamine mixture or in aqueous ammonia solution, apparently stemming from the ionization of the numerous surface CO2H groups. This is in contrast to the nanocomposites derived from VGCNF grafted with a linear meta-poly(ether-ketone), mPEK, with 1-10 wt% VGCNF content that have much lower solubility in these polar solvents but are more soluble in methanesulfonic acid [J.-B. Baek, C.B. Lyons, L.-S. Tan, Macromolecules 37 (2004) 8278]. The overall evidence based on the data from elemental analysis, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR) as well as scanning electron microscopy of the resulting materials implicates that under our reaction conditions, HPB-PEK was grafted to the surfaces of VGCNF resulting in the formation of highly coated nanofibers. TGA data also support that VGCNF has remained more or less structurally intact under the mildly acidic, relatively high-shearing and hot polymerization conditions

2006-07-25

262

Fabrication of Homogeneous Multi-walled Carbon Nanotube/ Poly (vinyl alcohol) Composite Nanofibers for Microwave Absorption Application  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Poly (vinyl alcohol) (PVA) / sodium dodecyl sulfate (SDS) / multi walled carbon nanotubes (MWCNT) camposite nanofibers with various MWCNT contents (up to 10 wt%) were fabricated by electrospinning process and their microwave absorption properties were evaluated by a vector network analyzer in the frequency range of 8-12 GHz (X-band) at room temperature. The uniform, stable dispersion and well oriented MWCNT within the PVA matrix were achieved through using SDS as dispersing agent. The SEM ana...

Shoushtari A.M.; Salimbeygi G.; Nasouri K.; Haji A.

2013-01-01

263

Mechanical, thermal and morphological characterization of polycarbonate/oxidized carbon nanofiber composites produced with a lean 2-step manufacturing process.  

Science.gov (United States)

In this study we report the advantages of a 2-step method that incorporates an additional process pre-conditioning step for rapid and precise blending of the constituents prior to the commonly used melt compounding method for preparing polycarbonate/oxidized carbon nanofiber composites. This additional step (equivalent to a manufacturing cell) involves the formation of a highly concentrated solid nano-nectar of polycarbonate/carbon nanofiber composite using a solution mixing process followed by melt mixing with pure polycarbonate. This combined method yields excellent dispersion and improved mechanical and thermal properties as compared to the 1-step melt mixing method. The test results indicated that inclusion of carbon nanofibers into composites via the 2-step method resulted in dramatically reduced ( 48% lower) coefficient of thermal expansion compared to that of pure polycarbonate and 30% lower than that from the 1-step processing, at the same loading of 1.0 wt%. Improvements were also found in dynamic mechanical analysis and flexural mechanical properties. The 2-step approach is more precise and leads to better dispersion, higher quality, consistency, and improved performance in critical application areas. It is also consistent with Lean Manufacturing principles in which manufacturing cells are linked together using less of the key resources and creates a smoother production flow. Therefore, this 2-step process can be more attractive for industry. PMID:21780388

Lively, Brooks; Kumar, Sandeep; Tian, Liu; Li, Bin; Zhong, Wei-Hong

2011-05-01

264

The Optimization of Electrical Conductivity Using Central Composite Design for Polyvinyl Alcohol/Multiwalled Carbon Nanotube-Manganese Dioxide Nanofiber Composites Synthesised by Electrospinning  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This research reports the characterization and statistical analysis of electrical conductivity optimization for polyvinyl alcohol (PVA)/multiwalled carbon nanotube (MWCNT)-manganese dioxide (MnO2) nanofiber composite. The Central Composite Design (CCD), the most common design of Response Surface Methodology (RSM) had been used to optimise the synthesis process of PVA/MWCNT-MnO2 nanofiber composite. The process parameters studied were; applied voltage (16 kV - 30 kV), sol...

Mohd Faiz Muaz Ahmad Zamri; Sharif Hussein Sharif Zein; Ahmad Zuhairi Abdullah; Nor Irwin Basir

2012-01-01

265

Leidenfrost temperature increase for impacting droplets on carbon-nanofiber surfaces  

CERN Multimedia

Droplets impacting on a superheated surface can either exhibit a contact boiling regime, in which they make direct contact with the surface and boil violently, or a film boiling regime, in which they remain separated from the surface by their own vapor. The transition from the contact to the film boiling regime depends not only on the temperature of the surface and kinetic energy of the droplet, but also on the size of the structures fabricated on the surface. Here we experimentally show that surfaces covered with carbon-nanofibers delay the transition to film boiling to much higher temperature compared to smooth surfaces. We present physical arguments showing that, because of the small scale of the carbon fibers, they are cooled by the vapor flow just before the liquid impact, thus permitting contact boiling up to much higher temperatures than on smooth surfaces. We also show that, as long as the impact is in the film boiling regime, the spreading factor of impacting droplets follows the same $\\We^{3/10}$ sc...

Nair, Hrudya; Tran, Tuan; van Houselt, Arie; Prosperetti, Andrea; Lohse, Detlef; Sun, Chao

2013-01-01

266

A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers.  

Science.gov (United States)

Polyacrylamide (PAM) was used as a matrix material for fabricating novel nanocomposite hydrogels reinforced with natural chitosan nanofibers (CNFs) via in situ free-radical polymerization. The nanocomposite's structure, strength, morphology and rheological properties were investigated. The results showed that the CNFs had a strong interaction with PAM through hydrogen and covalent bondings. The CNFs acted as a multifunctional cross-linker and a reinforcing agent in the hydrogel system. The compression strength and storage modulus of the nanocomposite hydrogels were significantly higher than those of the pure PAM hydrogels and the corresponding PAM/chitosan semi-interpenetrating polymer network (PAM-SIPN) hydrogels. The swelling ratio (SR) of the nanocomposite hydrogels was lower than that of the PAM hydrogel, but was similar to that of the PAM-SIPN hydrogel. Among the CNF contents used, the 1.5 wt% CNF loading level showed the best combined swelling and mechanical properties for the hydrogels. PMID:21273050

Zhou, Chengjun; Wu, Qinglin

2011-05-01

267

Preparation of carbon nanoparticles and nanofibers by a simple microwave based method and studying the field emission properties  

International Nuclear Information System (INIS)

Research highlights: ? A novel and simple microwave based method for preparation of carbon nanostructures were developed. ? The mw-plasma method can produce catalyst nanoparticles from a solid metallic source. ? The resulting nanostructure exhibit good field emission (FE) properties. ? Deposition of nanoparticles through the mw-plasma method improves field emission properties. - Abstract: A novel, simple and fast method for preparation of graphitic nanostructures such as nanofibers and nanospheres which uses a standard microwave oven is described. In this method polystyrene is used as carbon source and a solid metal such as nickel or iron provides both the trigger to initiate the plasma, as well as a source for sputtering catalyst particles which are required for formation of nanofibers. The mechanism of this process is discussed through analysis of different properties of the resulting products, by examining the effect of changing the microwave processing time and the nature of the metallic trigger/catalyst source. The effect of morphology of nanoparticles (nanofibers vs. nanospheres), as well as the effect of trigger/catalyst material and the deposition method on electron field emission properties of these samples, are also investigated.

2011-05-16

268

Preparation of Surface Adsorbed and Impregnated Multi-walled Carbon Nanotube/Nylon-6 Nanofiber Composites and Investigation of their Gas Sensing Ability  

Directory of Open Access Journals (Sweden)

Full Text Available We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled carbon nanotubes (MWCNTs onto the surface of Nylon-6 fibers using Triton® X-100 to form a MWCNTs/Nylon-6 nanofiber composite. The dispersed MWCNTs have been found to be stable in hexafluoroisopropanol for several months without precipitation. A MWCNTs/Nylon-6 nanofiber composite based chemical sensor has demonstrated its responsiveness towards a wide range of solvent vapours at room temperature and only mg quantities of MWCNTs were expended. The large surface area and porous nature of the electrospun Nylon-6/MWCNT nanofibers facilitates greater analyte permeability. The experimental analysis has indicated that the dipole moment, functional group and vapour pressure of the analytes determine the magnitude of the responsiveness.

Velmurugan Thavasi

2009-01-01

269

Three-Dimensional Force Sensing Device Using Carbon Nanofiber Polymer Composites: Design and Fabrication  

Science.gov (United States)

We propose an innovative three-dimensional force sensing device fabricated with carbon nanofiber (CNF) polymer composites. The device has four piezoresistive strain sensors made onto a polyimide substrate using surface patterning treatment and tilted-drop process with CNF polymer solutions. The proposed design and fabrication process is simpler than that of other three-dimensional force sensors and the device is suitable for mass production. The fabricated strain sensor properties using CNF polymer solutions with different composition ratios were investigated. An equation was derived using simple percolation theory to predict the conductivity of CNF polymer composites. The measured gauge factors were in the 4.84 to 17.68 range for CNF polymer composites with CNF 8.85--45.2 wt %. A programmable system on chip (PSoC) with built-in operational (OP) amplifier, analog-to-digital (AD) converter and multiplexer was used to develop a scanning and analyzing circuit for the three-dimensional force sensing device. The proposed integrated system was successfully applied to control a computer screen cursor.

Chang, Fuh-Yu; Liu, Chia-Ming; Chen, Tse-Min; Chen, Chia-Ming; Lin, Yu-Hsien; Huang, Shu-Jiuan

2012-06-01

270

An amperometric uric acid biosensor based on chitosan-carbon nanotubes electrospun nanofiber on silver nanoparticles.  

Science.gov (United States)

A novel amperometric uric acid biosensor was fabricated by immobilizing uricase on an electrospun nanocomposite of chitosan-carbon nanotubes nanofiber (Chi-CNTsNF) covering an electrodeposited layer of silver nanoparticles (AgNPs) on a gold electrode (uricase/Chi-CNTsNF/AgNPs/Au). The uric acid response was determined at an optimum applied potential of -0.35 V vs Ag/AgCl in a flow-injection system based on the change of the reduction current for dissolved oxygen during oxidation of uric acid by the immobilized uricase. The response was directly proportional to the uric acid concentration. Under the optimum conditions, the fabricated uric acid biosensor had a very wide linear range, 1.0-400 ?mol L(-1), with a very low limit of detection of 1.0 ?mol L(-1) (s/n?=?3). The operational stability of the uricase/Chi-CNTsNF/AgNPs/Au biosensor (up to 205 injections) was excellent and the storage life was more than six weeks. A low Michaelis-Menten constant of 0.21 mmol L(-1) indicated that the immobilized uricase had high affinity for uric acid. The presence of potential common interfering substances, for example ascorbic acid, glucose, and lactic acid, had negligible effects on the performance of the biosensor. When used for analysis of uric acid in serum samples, the results agreed well with those obtained by use of the standard enzymatic colorimetric method (P?>?0.05). PMID:24718436

Numnuam, Apon; Thavarungkul, Panote; Kanatharana, Proespichaya

2014-06-01

271

Bending actuation in a single-layer carbon-nanofiber/polypyrrole composite film and its fabrication  

International Nuclear Information System (INIS)

Thin CNF/PPy composite single-layer films were produced by the electrophoretic deposition and polymerization process which was developed for this study. It was demonstrated that the films could generate a bending motion subjected to an actuating electric voltage even though they consisted of only single-layer. Carbon nanofiber and polypyrrole composite films were obtained from only one side of a working electrode. Several different CNF/PPy films were synthesized, as varying the CNF weight ratios from 3%, 5%, and 7% to 10%. Conductivity of pure PPy and CNF/PPy composite films were measured. Conductivity of the films is improved linearly from 77.9S/cm (pure PPy film) to 124.3 S/cm (10% CNF/PPy) as the CNF weight ratio increases. Adding CNF was effective for improving the conductivity of PPy. As results of electromechanical actuation tests with the films, it was noticed that the strain of the films was reduced a little as the CNF weight ratio increased. Bending motions were observed for both PPy and CNF/PPy films subjected to a voltage. The tip bending deflections was in the range of 0.5 mm to 2 mm. CNF/PPy films showed a great potential to be a good candidate for small light actuators

2011-07-01

272

Dielectric properties and conductivity of carbon nanofiber/semi-crystalline polymer composites  

International Nuclear Information System (INIS)

The properties of semi-crystalline polymer nanocomposites are affected by the nanofillers directly and indirectly, as two phases, i.e., crystalline and amorphous, exist in the polymer. The effects of nanofillers on the two phases could be competitive. The dielectric properties and conductivity of carbon nanofibers (CNF)/semi-crystalline polymer nanocomposites are studied in this paper. CNF/polypropylene (PP) nanocomposites are prepared in experiment by melt blending. The resulting morphology and crystalline structure are characterized by means of differential scanning calorimetry, wide angle X-ray diffraction and scanning electron microscopy. The PP nanocomposite containing 5 wt.% CNF exhibits a surprisingly high dielectric constant under wide sweep frequencies attended by low dielectric loss. Its dielectric constant is >600 under lower frequency, and remains >200 at a frequency of 4000 Hz. The electrical and thermal conductivities of the nanocomposites are studied, and enhancements are seen with increased CNF content. Theoretical analyses on the physical properties are carried out by applying the existing models. Research results indicate that a common commercial plastic with good comprehensive performance, which exhibited the potential for applications in advanced electronics, was obtained by a simple industry benign technique

2008-06-01

273

Platinum/carbon nanofiber nanocomposite synthesized by electrophoretic deposition as electrocatalyst for oxygen reduction  

Energy Technology Data Exchange (ETDEWEB)

A platinum/carbon nanofiber (Pt/CNF) nanocomposite with a platinum loading of 15 wt% is prepared by a modified electrophoretic deposition (EPD) method, and the as-grown nanocomposite is used as the electrocatalyst for oxygen reduction reaction (ORR). For comparison, a Pt/CNF composite with 40 wt% platinum loading is prepared by chemical reduction. High resolution transmission electron microscope (HRTEM) images show that the size of platinum nanoparticles formed by EPD is about 1 nm, much smaller than those by chemical reduction (about 3-5 nm). Cyclic voltammetric analysis in a nitrogen saturated electrolyte shows that the electrochemical surface area of electrocatalyst by EPD is larger than that by chemical reduction. Moreover, although the electrocatalyst prepared by chemical reduction has a higher electrochemical capacity, it is less active than that prepared by EPD. Analysis of the electrode kinetics using Tafel plot suggests that the electrocatalyst prepared by EPD provides a strong ORR activity. Cyclic voltammetric measurements at different scan rates confirm that the ORR on the nanocomposites prepared by EPD is a diffusion-controlled process. This work demonstrates that the Pt/CNF composites synthesized by EPD are effective for ORR. (author)

Zheng, Jun-Sheng; Wang, Ming-Xia; Zhang, Xin-Sheng; Wu, Yun-Xia; Li, Ping; Zhou, Xing-Gui; Yuan, Wei-Kang [UNILAB, State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 (China)

2008-01-03

274

Cellulose nanofiber/single-walled carbon nanotube hybrid non-woven macrofiber mats as novel wearable supercapacitors with excellent stability, tailorability and reliability  

Science.gov (United States)

Non-woven macrofiber mats are prepared by simply controlling the extrusion patterns of cellulose nanofiber/single-walled carbon nanotube suspensions in an ethanol coagulation bath, and drying in air under restricted conditions. These novel wearable supercapacitors based on non-woven macrofiber mats are demonstrated to have excellent tailorability, electrochemical stability, and damage reliability.Non-woven macrofiber mats are prepared by simply controlling the extrusion patterns of cellulose nanofiber/single-walled carbon nanotube suspensions in an ethanol coagulation bath, and drying in air under restricted conditions. These novel wearable supercapacitors based on non-woven macrofiber mats are demonstrated to have excellent tailorability, electrochemical stability, and damage reliability. Electronic supplementary information (ESI) available: Experimental, TEM image, IR spectra, and XRD spectra of cellulose nanofibers, photograph of the cellulose nanofiber/single-walled carbon nanotube suspension, cellulose nanofiber/single-walled carbon nanotube non-woven macrofiber mat and non-woven macrofiber mat wearable supercapacitors. The electrochemical performance of the CNF/SWCNT hybrid fiber wearable supercapacitor. Photograph of the non-woven macrofiber mat wearable supercapacitors integrated within textiles. See DOI: 10.1039/c3nr05929d

Niu, Qingyuan; Gao, Kezheng; Shao, Ziqiang

2014-03-01

275

Monolithically Integrated, Mechanically Resilient Carbon-Based Probes for Scanning Probe Microscopy  

Science.gov (United States)

Scanning probe microscopy (SPM) is an important tool for performing measurements at the nanoscale in imaging bacteria or proteins in biology, as well as in the electronics industry. An essential element of SPM is a sharp, stable tip that possesses a small radius of curvature to enhance spatial resolution. Existing techniques for forming such tips are not ideal. High-aspect-ratio, monolithically integrated, as-grown carbon nanofibers (CNFs) have been formed that show promise for SPM applications by overcoming the limitations present in wet chemical and separate substrate etching processes.

Kaul, Anupama B.; Megerian, Krikor G.; Jennings, Andrew T.; Greer, Julia R.

2010-01-01

276

Li2MnSiO4/Carbon Composite Nanofibers as a High-Capacity Cathode Material for Li-Ion Batteries  

Directory of Open Access Journals (Sweden)

Full Text Available Li2MnSiO4 has an extremely high theoretical capacity of 332 mAh?g?1. However, only around half of this capacity has been realized in practice and the capacity retention during cycling is also low. In this study, Li2MnSiO4/carbon composite nanofibers were prepared by a combination of electrospinning and heat treatment. The one-dimensional continuous carbon nanofiber matrix serves as long-distance conductive pathways for both electrons and ions. The composite nanofiber structure avoids the aggregation of Li2MnSiO4 particles, which in turn enhances the electrode conductivity and promotes the reaction kinetics. The resultant Li2MnSiO4/carbon composite nanofibers were used as the cathode material for Li-ion batteries, and they delivered high charge and discharge capacities of 218 and 185 mAh?g?1, respectively, at the second cycle. In addition, the capacity retention of Li2MnSiO4 at the first 20th cycles increased from 37% to 54% in composite nanofibers.

Xiangwu Zhang

2012-06-01

277

Li2MnSiO4/Carbon Composite Nanofibers as a High-Capacity Cathode Material for Li-Ion Batteries  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Li2MnSiO4 has an extremely high theoretical capacity of 332 mAh?g?1. However, only around half of this capacity has been realized in practice and the capacity retention during cycling is also low. In this study, Li2MnSiO4/carbon composite nanofibers were prepared by a combination of electrospinning and heat treatment. The one-dimensional continuous carbon nanofiber matrix serves ...

Shu Zhang; Ying Li; Guanjie Xu; Shuli Li; Yao Lu; Ozan Topracki; Xiangwu Zhang

2012-01-01

278

Investigation of promoter effects of manganese oxide on carbon nanofibers supported cobalt catalysts for Fischer-Tropsch synthesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effects of the addition of MnO were studied on a carbon nanofiber-supported cobalt catalyst. The starting sample, cobalt loading 9.5 wt% and 8% cobalt dispersion, was promoted by impregnation with small amounts of MnO (0.03, 0.1, 0.3, 0.6, and 1.1 wt%). XPS and STEM-EELS showed MnO to be associated with Co in both dried and reduced catalyst. In the drying step, MnO was deposited on the passivated cobalt particles, because of the tendency of both metals to form stable mixed compou...

Bezemer, G. L.; Radstake, P. B.; Falke, U.; Oosterbeek, H.; Dillen, A. J.; Jong, K. P.

2006-01-01

279

Ecotoxicological effects of carbon nanotubes and cellulose nanofibers in Chlorella vulgaris  

Science.gov (United States)

Background MWCNT and CNF are interesting NPs that possess great potential for applications in various fields such as water treatment, reinforcement materials and medical devices. However, the rapid dissemination of NPs can impact the environment and in the human health. Thus, the aim of this study was to evaluate the MWCNT and cotton CNF toxicological effects on freshwater green microalgae Chlorella vulgaris. Results Exposure to MWCNT and cotton CNF led to reductions on algal growth and cell viability. NP exposure induced reactive oxygen species (ROS) production and a decreased of intracellular ATP levels. Addition of NPs further induced ultrastructural cell damage. MWCNTs penetrate the cell membrane and individual MWCNTs are seen in the cytoplasm while no evidence of cotton CNFs was found inside the cells. Cellular uptake of MWCNT was observed in algae cells cultured in BB medium, but cells cultured in Seine river water did not internalize MWCNTs. Conclusions Under the conditions tested, such results confirmed that exposure to MWCNTs and to cotton CNFs affects cell viability and algal growth.

2014-01-01

280

Cobalt particle size effects in the Fischer-Tropsch reaction studied with carbon nanofiber supported catalysts.  

Science.gov (United States)

The influence of cobalt particle size in the range of 2.6-27 nm on the performance in Fischer-Tropsch synthesis has been investigated for the first time using well-defined catalysts based on an inert carbon nanofibers support material. X-ray absorption spectroscopy revealed that cobalt was metallic, even for small particle sizes, after the in situ reduction treatment, which is a prerequisite for catalytic operation and is difficult to achieve using traditional oxidic supports. The turnover frequency (TOF) for CO hydrogenation was independent of cobalt particle size for catalysts with sizes larger than 6 nm (1 bar) or 8 nm (35 bar), while both the selectivity and the activity changed for catalysts with smaller particles. At 35 bar, the TOF decreased from 23 x 10(-3) to 1.4 x 10(-3) s(-1), while the C5+ selectivity decreased from 85 to 51 wt % when the cobalt particle size was reduced from 16 to 2.6 nm. This demonstrates that the minimal required cobalt particle size for Fischer-Tropsch catalysis is larger (6-8 nm) than can be explained by classical structure sensitivity. Other explanations raised in the literature, such as formation of CoO or Co carbide species on small particles during catalytic testing, were not substantiated by experimental evidence from X-ray absorption spectroscopy. Interestingly, we found with EXAFS a decrease of the cobalt coordination number under reaction conditions, which points to reconstruction of the cobalt particles. It is argued that the cobalt particle size effects can be attributed to nonclassical structure sensitivity in combination with CO-induced surface reconstruction. The profound influences of particle size may be important for the design of new Fischer-Tropsch catalysts. PMID:16551103

Bezemer, G Leendert; Bitter, Johannes H; Kuipers, Herman P C E; Oosterbeek, Heiko; Holewijn, Johannes E; Xu, Xiaoding; Kapteijn, Freek; van Dillen, A Jos; de Jong, Krijn P

2006-03-29

 
 
 
 
281

Dye-sensitized solar cells based on anatase TiO2/multi-walled carbon nanotubes composite nanofibers photoanode  

International Nuclear Information System (INIS)

Highlights: ? TiO2/multi-walled carbon nanotubes (MWCNTs) hybrid nanofibers are prepared via electrospinning. ? Dye-sensitized solar cells (DSSCs) are assembled using TiO2/MWCNTs nanofibers film as photoanode. ? Energy conversion efficiency of DSSCs is greatly dependent on the content of MWCNTs. ? Moderate MWCNTs incorporation can substantially enhance the performance of DSSCs. - Abstract: Anatase TiO2/multi-walled carbon nanotubes (TiO2/MWCNTs) hybrid nanofibers (NFs) film was prepared via a facile electrospinning method. Dye-sensitized solar cells (DSSCs) based on TiO2/MWCNTs composite NFs photoanodes with different contents of MWCNTs (0, 0.1, 0.3, 0.5, 1 wt.%) were assembled using N719 dye as sensitizer. Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), and Raman spectrometer were used to characterize the TiO2/MWCNTs electrode films. The photocurrent–voltage (I–V) characteristic, incident photo-to-current conversion efficiency (IPCE) spectrum, and electrochemical impedance spectroscopy (EIS) measurements were carried out to evaluate the photoelectric properties of the DSSCs. The results reveal that the energy conversion efficiency is greatly dependent on the content of MWCNTs in the composite NFs film, and a moderate incorporation of MWCNTs can substantially enhance the performance of DSSCs. When the electrode contains 0.3 wt.% MWCNTs, the corresponding solar cell yield the highest efficiency of 5.63%. This efficiency value is approximately 26% larger than that of the unmodified counterpart.

2013-01-01

282

In situ synthesis of MnO2 coated cellulose nanofibers hybrid for effective removal of methylene blue.  

Science.gov (United States)

A one-step and energy-efficient synthetic method was developed to fabricate manganese dioxide (MnO2)/cellulose nanofibers (CNFs) hybrid. In this process, bamboo CNFs acted as both a reducing reagent for the Mn (VII) and an ultralight support for the generated MnO2 nanosheets. Neither additional reducing reagents nor heating were adopted during the synthesis process. The phase constitutions, crystal structure and morphology of the hybrid were systematically investigated. Both oxidative and adsorptive decolorization of methylene blue (MB) were investigated to evaluate its efficiency on dye wastewater treatment. The results showed that the few-layer MnO2 nanosheets deposited on CNFs exhibited high decolorization efficiency for the oxidation and adsorption of MB. When slurry containing 25mg MnO2/CNFs hybrid was dispersed in 25mL 80mgL(-1) MB solution, the removal of MB was more than 99.8% within 2min. PMID:24906760

Wang, Yaru; Zhang, Xiaofang; He, Xu; Zhang, Wei; Zhang, Xinxing; Lu, Canhui

2014-09-22

283

Carbon nanotubes and nanofibers synthesized by CVD on nickel coatings deposited with a vacuum arc  

International Nuclear Information System (INIS)

Nanotubes and nanofibers were grown on Ni coatings deposited by plasma generated with a pulsed vacuum arc on silicon wafers using three different bias conditions: at floating potential (approximately +30 V respect to the grounded cathode); at ground potential; and at -60 V. An atomic force microscopy study showed that the Ni film morphology was affected by the bias condition of the substrate. The morphology of carbonaceous species depended on Ni-films characteristics. FE-SEM and TEM analyses have shown that nanofibers growth was favoured on Ni coatings deposited at -60 V whereas nanotubes grew mainly on Ni coatings obtained at floating and ground potentials. Hence, this new method to produce the precursor can be optimized to obtain nanotubes or nanofibers varying the substrate bias for the Ni deposition.

2010-04-16

284

Reversible Hydrogen Storage in Electrospun Composite Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Composite nanofibers containing single-walled carbon nanotubes (SWNT were prepared by using electrospinning technique and hydrogen adsorption/desorption isotherms were carried out by a Sieverts apparatus at room temperature. The SEM analysis of the nanofibers revealed that the deformation of the nanofiber increases with increasing SWNT concentration. The diameter of neat nanofibers was below 200 nm and had smooth surface. The surface of the composite nanofibers was rough even by adding low quantity of SWNT. The hydrogen storage results showed an improvement in the adsorption capacity with increasing the SWNT content in composite nanofibers. These nanofibers were evacuated again to remove the adsorbed hydrogen at room temperature. Moreover, even though specific surface area and total pore volume were important factors for increasing the capacity of hydrogen adsorption. Finally, maximum adsorption capacity was 0.29 wt % in case of nanofibers with 10 wt % SWNT under 30 bar at 298 K.

Haji A.

2013-09-01

285

Risk analysis and protection measures in a carbon nanofiber manufacturing enterprise: an exploratory investigation.  

Science.gov (United States)

The emerging US carbon nano-manufacturing sector accounts for 40% of nanotechnology product marketplace, thus, there is a significant potential for increased risks arising from workers' exposure to carbon nanofibers (CNF). This research aims at developing a low-cost/evidence-based tool, thereby, increasing the sustainability of CNF manufacturing firms. The following specific aims achieve the study objective: Aim 1 - To present a technical discussion of the proposed concept for risk analysis and protection measures; Aim 2 - To describe the manufacturing process utilized for the CNF production; Aim 3 - To describe the hazards typically encountered in a CNF manufacturing facility; and, Aim 4 - To document the application of the proposed tool for risk analysis and intervention strategy development. In this study, a four-step methodology was developed to protect worker health in the nano-manufacturing enterprise through the generation of improvement actions (i.e., suggested changes in the hazard/work environment characteristics and individual capabilities without specifying how changes are made) followed by interventions (i.e., workplace solutions which specify how changes are being implemented). The methodology was implemented in a CNF manufacturing enterprise in the Midwest of the US. The data collected were based on detailed observations and interviews with worker and management personnel. A detailed flow process analysis was conducted for the nano-manufacturing operation. Eleven hazards were identified at the facility. Analysis indicated that the computed risk scores ranged from moderate (i.e., requiring one to start with incremental changes, then, explore substantial changes, if needed) to very high (i.e., substantial changes should be planned in the short term, followed by incremental changes). A detailed intervention plan was presented for the identified hazards on the basis of criteria of applicability, cost, benefit and feasibility. Management personnel were in agreement with the findings of the study. In conclusion, a low-cost/evidence-based tool was developed and implemented to assess and manage the risks associated with exposure to CNF production in a manufacturing enterprise. Preliminary validation of the tool suggests that management personnel were in agreement with the study findings. Further application of the systematic methodology is warranted. PMID:19712959

Genaidy, Ash; Sequeira, Reynold; Rinder, Magda; A-Rehim, Amal

2009-11-01

286

Processing, wear, and mechanical properties of polyethylene composites prepared with pristine and organosilane-treated carbon nanofibers  

Science.gov (United States)

Polymers and nanocomposites have been increasingly used for tribological applications over the last few decades. In particular, ultrahigh molecular weight polyethylene (UHMWPE) is a high performance polymer with excellent strength, toughness, and wear resistance. Because of these properties, UHMWPE is an ideal material for a variety of applications including body armor, components of sporting goods such as skies and snowboards, and liners in total joint replacement. Though the toughness and wear resistance far exceed that of most other polymeric materials, there is a high demand for improving the tribological and mechanical properties of UHMWPE for many applications. The approach used in this work for improving such properties is through nanocomposite technology, specifically via the incorporation of carbon nanofibers. In order to obtain the full potential of nanocomposite technology, two critical issues need to be addressed: appropriate interactions between the filler and matrix and proper dispersion of the nano-reinforcement. These critical issues are particularly important for UHMWPE nanocomposites in that UHMWPE is an extremely viscous polymer and thus cannot be processed conventionally, typically resulting in dispersion issues far worse than that of other composite systems. Furthermore, UHMWPE is non-polar, so interactions between filler and matrix will be limited to Van der Waals forces for untreated nanofillers. Therefore, the research presented aims at solving these issues by using a paraffin-assisted processing method and applying appropriate surface treatment to the carbon nanofibers. Under optimized processing conditions, wear and mechanical properties of UHMWPE composites can be substantially improved.

Wood, Weston

287

Activated nitrogen-doped carbon nanofibers with hierarchical pore as efficient oxygen reduction reaction catalyst for microbial fuel cells  

Science.gov (United States)

Oxygen reduction reaction (ORR) in microbial fuel cell (MFC) was evaluated by using chemical activated nitrogen-doped carbon nanofibers (ANCNFs) as cathode catalyst. ANCNFs are synthesized through modified oxidative template assembly route and then activated by KOH reagent. The as-prepared ANCNFs formed three-dimensional carbonfiber framework with large specific surface area and hierarchical tetramodal pore size distribution spanning the micro-, meso- and macro pore range, centered at 0.48, 4.0, 18 and 70 nm. Compared with unactivated nitrogen-doped carbon nanofibers (NCNFs), ANCNFs exhibited a more positive onset potential, higher current density as well as higher electron transfer number in neutral environment, highlighting the importance of chemical activation process for improving the ORR performance. MFCs equipped with ANCNFs catalyst exhibited a high power output of 1377 ± 46 mW m-2, which is about 1.5 times the output of NCNFs cathode (921 ± 29 mW m-2), and as high as nearly 4 times of plain cathode (341 ± 9 mW m-2).

Yang, Xiaoling; Zou, Wenjian; Su, Yunhe; Zhu, Yihua; Jiang, Hongliang; Shen, Jianhua; Li, Chunzhong

2014-11-01

288

Effect of Annealing on the Photoconductivity of Carbon Nanofiber/TiO2 Core-Shell Nanowires for Use in Dye-Sensitized Solar Cells.  

Science.gov (United States)

Electrical transport properties and photoresponse of individual TiO2- coated carbon nanofibers were studied in an attempt to elucidate the limiting factors of core-shell nanowire-based dye-sensitized solar cells (DSSC). The role of the semiconductor shell...

C. Rochford J. Baca J. Li J. Liu Z. Li

2010-01-01

289

Mechanical and electromagnetic interference shielding Properties of poly(vinyl alcohol)/graphene and poly(vinyl alcohol)/multi-walled carbon nanotube composite nanofiber mats and the effect of Cu top-layer coating.  

Science.gov (United States)

We report the mechanical property and electromagnetic interference shielding effectiveness (EMI SE) of poly(vinyl alcohol) (PVA)/graphene and PVA/multi-walled carbon nanotube (MWCNT) composite nanofibers prepared by electrospinning. The metal (Cu) was deposited on the resultant PVA composite nanofibers using metal deposition technique in order to improve the mechanical properties and EMI shielding properties. The resulting PVA composite nanofibers and Cu-deposited corresponding nanofibers were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Tensile tests were performed on the PVA/graphene and PVA/MWCNT composite nanofibers. The tensile strength of the PVA/graphene and PVA/MWCNT composite nanofibers was found to be 19.2 +/- 0.3 MPa at graphene content - 6.0 wt% and 12.2 +/- 0.2 MPa at MWCNT content - 3.0 wt%, respectively. The EMI SE of the Cu-deposited PVA/graphene composite nanofibers was significantly improved compared to pure PVA/graphene composite nanofibers, and also depended on the thickness of Cu metal layer deposited on the PVA composite nanofibers. PMID:23755586

Fujimori, Kazushige; Gopiraman, Mayakrishnan; Kim, Han-Ki; Kim, Byoung-Suhk; Kim, Ick-Soo

2013-03-01

290

Carbon nanotubes functionalized electrospun nanofibers formed 3D electrode enables highly strong ECL of peroxydisulfate and its application in immunoassay.  

Science.gov (United States)

A new biosensing platform based on electrospun carbon nanotubes nanofibers (CNTs@PNFs) composite, which enabled strong electrochemiluminescent emission of peroxydisulfate, was firstly developed for immunoassay with favorable analytical performances, and then was utilized to evaluate the interaction between antibody and antigen in vitro. Moreover, the obvious ECL image of peroxydisulfate on the prepared sensing platform was firstly recorded in this report. In order to expand the application of peroxydisulfate ECL, the specific recognization biomolecules, ?-fetoprotein (AFP) antibody was bound to the functionalized film via electrostatic interaction for fabricating label-free ECL immunosensor to detect ?-AFP. Based on the ECL change resulting from the specific immunoreaction between antigen and antibody, the quantitative analysis for AFP with wide dynamic response in the range from 0.1pgmL(-1) to 160ngmL(-1) was realized. And the limit of detection was estimated to be 0.09pgmL(-1). Therefore, the flexible sensing platform not only acted as the sensitized sensing element, but also offered a suitable carrier for immobilization of biological recognition elements with low-toxicity and eco-friendliness, which opened a promising approach to developing further electrospun nanofiber based amplified ECL biosensor with favorable analytical performances. PMID:24953845

Dai, Hong; Xu, Guifang; Zhang, Shupei; Gong, Lingshan; Li, Xiuhua; Yang, Caiping; Lin, Yanyu; Chen, Jinghua; Chen, Guonan

2014-11-15

291

Effects of feed gas composition and catalyst thickness on carbon nanotube and nanofiber synthesis by plasma enhanced chemical vapor deposition.  

Science.gov (United States)

Many engineering applications require carbon nanotubes with specific characteristics such as wall structure, chirality and alignment. However, precise control of nanotube properties grown to application specifications remains a significant challenge. Plasma-enhanced chemical vapor deposition (PECVD) offers a variety of advantages in the synthesis of carbon nanotubes in that several important synthesis parameters can be controlled independently. This paper reports an experimental study of the effects of reacting gas composition (percentage methane in hydrogen) and catalyst film thickness on carbon nanotube (CNT) growth and a computational study of gas-phase composition for the inlet conditions of experimentally observed carbon nanotube growth using different chemical reaction mechanisms. The simulations seek to explain the observed effects of reacting gas composition and to identify the precursors for CNT formation. The experimental results indicate that gas-phase composition significantly affects the synthesized material, which is shown to be randomly aligned nanotube and nanofiber mats for relatively methane-rich inlet gas mixtures and non-tubular carbon for methane-lean incoming mixtures. The simulation results suggest that inlet methane-hydrogen mixture coverts to an acetylene-methane-hydrogen mixture with minor amounts of ethylene, hydrogen atom, and methyl radical. Acetylene appears to be the indicator species for solid carbon formation. The simulations also show that inlet methane-hydrogen mixture does not produce enough gas-phase precursors needed to form quality CNTs below 5% CH4 concentrations in the inlet stream. PMID:18681048

Garg, R K; Kim, S S; Hash, D B; Gore, J P; Fisher, T S

2008-06-01

292

Rapid preparation of Pt-Ru/graphitic carbon nanofiber nanocomposites as DMFC anode catalysts using microwave processing.  

Science.gov (United States)

Pt-Ru/graphitic carbon nanofiber (GCNF) nanocomposites have been prepared on two different GCNF supports, with the use of a bimetallic precursor as a source of metal and microwave processing for thermal treatments. Pt-Ru nanoparticles appear as the major metal-containing component of these nanocomposites along with variable trace amounts of Ru metal. Use of microwave heating permits rapid preparation of these nanocomposites and affords metal nanoclusters of nearly uniform size. The performance of these nanocomposites as anode electrocatalysts in direct-methanol fuel cells (DMFCs) is compared with that of unsupported Pt-Ru colloid at identical total metal loading. The Pt-Ru/narrow tubular herringbone GCNF nanocomposite shows DMFC performance comparable to that recorded for an unsupported Pt-Ru colloid. PMID:14503410

Steigerwalt, Eve S; Deluga, Gregg A; Lukehart, C M

2003-06-01

293

The development, fabrication, and material characterization of polypropylene composites reinforced with carbon nanofiber and hydroxyapatite nanorod hybrid fillers  

Science.gov (United States)

This study focuses on the design, fabrication, microstructural and property characterization, and biocompatibility evaluation of polypropylene (PP) reinforced with carbon nanofiber (CNF) and hydroxyapatite nanorod (HANR) fillers. The purpose is to develop advanced PP/CNF–HANR hybrids with good mechanical behavior, thermal stability, and excellent biocompatibility for use as craniofacial implants in orthopedics. Several material-examination techniques, including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, tensile tests, and impact measurement are used to characterize the microstructural, mechanical, and thermal properties of the hybrids. Furthermore, osteoblastic cell cultivation and colorimetric assay are also employed for assessing their viability on the composites. The CNF and HANR filler hybridization yields an improvement in Young’s modulus, impact strength, thermal stability, and biocompatibility of PP. The PP/2% CNF–20% HANR hybrid composite is found to exhibit the highest elastic modulus, tensile strength, thermal stability, and biocompatibility.

Liao, Cheng Zhu; Wong, Hoi Man; Yeung, Kelvin Wai Kwok; Tjong, Sie Chin

2014-01-01

294

Pd-ni alloy nanoparticle/carbon nanofiber composites: preparation, structure, and superior electrocatalytic properties for sugar analysis.  

Science.gov (United States)

Novel Pd-Ni alloy nanoparticle/carbon nanofiber (Pd-Ni/CNF) composites were successfully prepared by a simple method involving electrospinning of precursor polyacrylonitrile/Pd(acac)2/Ni(acac)2 nanofibers, followed by a thermal process to reduce metals and carbonize polyacrylonitrile. The nanostructures of the resulting Pd-Ni/CNF nanocomposites were carefully examined by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM), energy dispersive X-ray (EDX), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). For all the nanocomposites, the Pd-Ni alloy nanoparticles (NPs) were dispersed uniformly and embedded firmly within the framework or on the surface of CNF. The size, composition, and alloy homogeneity of the Pd-Ni alloy NPs could be readily tailored by controlling the feed ratio of metal precursors and the thermal treatment process. Cyclic voltammetric studies showed enhanced redox properties for Pd-Ni/CNF-based electrodes relative to the Ni-metal electrode and significantly improved electrocatalytic activity for sugar (e.g., glucose, fructose, sucrose, and maltose) oxidation. The application potential of Pd-Ni/CNF-based electrodes in flow systems for sugars detection was explored. A very low limit of detection for sugars (e.g., 7-20 nM), high resistance to surface fouling, excellent signal stability and reproducibility, and a very wide detection linear range (e.g., 0.03-800 ?M) were revealed for this new type of Pd-Ni/CNF nanocomposite as the detecting electrode. Such detection performances of Pd-Ni/CNF-based electrodes are superior to those of state-of-the-art nonenzymatic sugar detectors that are commercially available or known in the literature. PMID:24837693

Guo, Qiaohui; Liu, Dong; Zhang, Xueping; Li, Libo; Hou, Haoqing; Niwa, Osamu; You, Tianyan

2014-06-17

295

Growth of La2CuO4 nanofibers under a mild condition by using single walled carbon nanotubes as templates  

International Nuclear Information System (INIS)

La2CuO4 nanofibers (ca. 30 nm in diameter and 3 ?m in length) have been grown in situ by using single walled carbon nanotubes (SWNTs; ca. 2 nm in inner diameter; made via cracking CH4 over the catalyst of Mg0.8Mo0.05Ni0.10Co0.05O x at 800 deg. C) as templates under mild hydrothermal conditions and a temperature around 60 deg. C. During synthesis, the surfactant poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and H2O2 were added to disperse SWNTs and oxidize the reactants, respectively. The structure of La2CuO4 nanofibers was confirmed by powder X-ray diffraction (XRD) and their morphologies were observed with field emission scanning electron microscope (FESEM) at the hydrothermal synthesis lasting for 5, 20 and 40 h, respectively. The La2CuO4 crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. Twenty hours is an optimum reaction time to obtain regular crystal fibers. The La2CuO4 nanofibers are probably cubic rather than round and may capsulate SWNTs. - Graphical abstract: La2CuO4 nanofibers have been grown in situ by using single walled carbon nanotubes as templates under mild hydrothermal conditions and a temperature around 60 deg. C. The La2CuO4 crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. The La2CuO4 nanofibers are probably cubic rather than round and may capsulate SWNTs

2006-07-01

296

Towards the control of the diameter of individualized single walled carbon nanotubes in CVD process at low temperature  

Energy Technology Data Exchange (ETDEWEB)

In the current work, we show that it is possible to favor the selective growth of single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution on supported catalyst particles with a broad size distribution. Carbon nanotubes were grown at 600 C on silicon substrates. The structure of carbon deposits was controlled by managing the carbon feedstock for adjusting the rate of carbon nanostructures formation on the surface of catalyst particles. Either carbon nanofibers (CNFs) carpets or isolated SWCNTs were obtained. With the fine tune of carbon feedstock, small isolated SWCNTs with a narrow diameter distribution were obtained by limiting the catalytic activity of the largest catalyst particles. HRTEM observations of nanotube embryos have suggested a possible mechanism of multi-walled carbon nanotubes (MWCNTs) formation that can explain why the growth of MWCNTs with parallel walls seems to be more difficult than SWCNTs or CNFs at low temperature. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Tsareva, Svetlana [Institut Jean Lamour UMR 7819, CNRS - Universite de Lorraine, Parc de Saurupt, 54011 Nancy (France); Structure et Reactivite des Systemes Moleculaires Complexes UMR 7565, CNRS - Universite de Lorraine, Vandoeuvre les Nancy (France); Devaux, Xavier [Institut Jean Lamour UMR 7819, CNRS - Universite de Lorraine, Parc de Saurupt, 54011 Nancy (France); Dossot, Manuel [Laboratoire de Chimie Physique et Microbiologie pour l' Environnement UMR 7564, CNRS - Universite de Lorraine, 54602 Villers les Nancy (France)

2012-12-15

297

Towards the control of the diameter of individualized single walled carbon nanotubes in CVD process at low temperature  

International Nuclear Information System (INIS)

In the current work, we show that it is possible to favor the selective growth of single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution on supported catalyst particles with a broad size distribution. Carbon nanotubes were grown at 600 C on silicon substrates. The structure of carbon deposits was controlled by managing the carbon feedstock for adjusting the rate of carbon nanostructures formation on the surface of catalyst particles. Either carbon nanofibers (CNFs) carpets or isolated SWCNTs were obtained. With the fine tune of carbon feedstock, small isolated SWCNTs with a narrow diameter distribution were obtained by limiting the catalytic activity of the largest catalyst particles. HRTEM observations of nanotube embryos have suggested a possible mechanism of multi-walled carbon nanotubes (MWCNTs) formation that can explain why the growth of MWCNTs with parallel walls seems to be more difficult than SWCNTs or CNFs at low temperature. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

2012-12-01

298

Mesoporous Li4Ti5O12/carbon nanofibers for high-rate lithium-ion batteries  

International Nuclear Information System (INIS)

Highlights: • Facile electrospinning method combined with soft-template self-assembly. • Abundant mesopores and large specific surface area. • Superior rate capability and excellent cycling stability. -- Abstract: Mesoporous Li4Ti5O12/carbon nanofibers (LTO/C NFs) are prepared by a facile electrospinning method combined with soft-template self-assembly. The morphology and structure are characterized by field-emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The diameter of as-prepared LTO/C NFs is approximately 400 nm with highly crystallinity LTO nanoparticle completely embedded in carbon framework. Nitrogen adsorption–desorption isotherms and corresponding pore size distribution reveal that the mesoporous LTO/C NFs exhibite high specific surface area (212.1 m2/g?1) and large pore volume. Compared with the regular LTO/C NFs, the mesoporous LTO/C NFs show much higher rate capability and better capacity retention. At a current rate of 5 C, the reversible capacity of the mesoporous LTO/C NFs electrode is up to 127.4 mA h g?1 and still remains at 122.7 mA h g?1 after 100 cycles. The excellent electrochemical performances are closedly related to well-defined one-dimensional (1D) mesoporous nanostructure with LTO nanoparticles embedded in the carbon framework, which efficiently shortened the path length of Li+ diffusion, enhanced electrolyte-active material contact area and facilitated rapid electron transfer

2014-02-25

299

Preparation and electrochemical performance of hyper-networked Li4Ti5O12/carbon hybrid nanofiber sheets for a battery-supercapacitor hybrid system  

International Nuclear Information System (INIS)

Hyper-networked Li4Ti5O12/carbon hybrid nanofiber sheets that contain both a faradaically rechargeable battery-type component, namely Li4Ti5O12, and a non-faradaically rechargeable supercapacitor-type component, namely N-enriched carbon, are prepared by electrospinning and their dual function as a negative electrode of lithium-ion batteries (LIBs) and a capacitor is tested for a new class of hybrid energy storage (denoted BatCap). An aqueous solution composed of polyvinylpyrrolidone, lithium hydroxide, titanium(IV) bis(ammonium-lactato)dihydroxide and ammonium persulfate is electrospun to obtain hyper-networked nanofiber sheets. Next, the sheets are exposed to pyrrole monomer vapor to prepare the polypyrrole-coated nanofiber sheets (PPy-HNS). The hyper-networked Li4Ti5O12/N-enriched carbon hybrid nanofiber sheets (LTO/C-HNS) are then obtained by a stepwise heat treatment of the PPy-HNS. The LTO/C-HNS deliver a specific capacity of 135 mAh g-1 at 4000 mA g-1 as a negative electrode for LIBs. In addition, potentiodynamic experiments are performed using a full cell with activated carbon (AC) as the positive electrode and LTO/C-HNS as the negative electrode to estimate the capacitance properties. This new asymmetric electrode system exhibits a high energy density of 91 W kg-1 and 22 W kg-1 at power densities of 50 W kg-1 and 4000 W kg-1, respectively, which are superior to the values observed for the AC||AC symmetric electrode system.

2011-10-07

300

Controllable growth of Prussian blue nanostructures on carboxylic group-functionalized carbon nanofibers and its application for glucose biosensing  

International Nuclear Information System (INIS)

Glucose detection is very important in biological analysis, clinical diagnosis and the food industry, and especially for the routine monitoring of diabetes. This work presents an electrochemical approach to the detection of glucose based on Prussian blue (PB) nanostructures/carboxylic group-functionalized carbon nanofiber (FCNF) nanocomposites. The hybrid nanocomposites were constructed by growing PB onto the FCNFs. The obtained PB–FCNF nanocomposites were characterized by scanning electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The mechanism of formation of PB–FCNF nanocomposites was investigated and is discussed in detail. The PB–FCNF modified glassy carbon electrode (PB–FCNF/GCE) shows good electrocatalysis toward the reduction of H2O2, a product from the reduction of O2 followed by glucose oxidase (GOD) catalysis of the oxidation of glucose to gluconic acid. Further immobilizing GOD on the PB–FCNF/GCE, an amperometric glucose biosensor was achieved by monitoring the generated H2O2 under a relatively negative potential. The resulting glucose biosensor exhibited a rapid response of 5 s, a low detection limit of 0.5 ?M, a wide linear range of 0.02–12 mM, a high sensitivity of 35.94 ?A cm?2 mM?1, as well as good stability, repeatability and selectivity. The sensor might be promising for practical application. (paper)

2012-11-16

 
 
 
 
301

Controllable growth of Prussian blue nanostructures on carboxylic group-functionalized carbon nanofibers and its application for glucose biosensing.  

Science.gov (United States)

Glucose detection is very important in biological analysis, clinical diagnosis and the food industry, and especially for the routine monitoring of diabetes. This work presents an electrochemical approach to the detection of glucose based on Prussian blue (PB) nanostructures/carboxylic group-functionalized carbon nanofiber (FCNF) nanocomposites. The hybrid nanocomposites were constructed by growing PB onto the FCNFs. The obtained PB-FCNF nanocomposites were characterized by scanning electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The mechanism of formation of PB-FCNF nanocomposites was investigated and is discussed in detail. The PB-FCNF modified glassy carbon electrode (PB-FCNF/GCE) shows good electrocatalysis toward the reduction of H(2)O(2), a product from the reduction of O(2) followed by glucose oxidase (GOD) catalysis of the oxidation of glucose to gluconic acid. Further immobilizing GOD on the PB-FCNF/GCE, an amperometric glucose biosensor was achieved by monitoring the generated H(2)O(2) under a relatively negative potential. The resulting glucose biosensor exhibited a rapid response of 5 s, a low detection limit of 0.5 ?M, a wide linear range of 0.02-12 mM, a high sensitivity of 35.94 ?A cm(-2) mM(-1), as well as good stability, repeatability and selectivity. The sensor might be promising for practical application. PMID:23090569

Wang, Li; Ye, Yinjian; Zhu, Haozhi; Song, Yonghai; He, Shuijian; Xu, Fugang; Hou, Haoqing

2012-11-16

302

Factoring-in agglomeration of carbon nanotubes and nanofibers for better prediction of their toxicity versus asbestos  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Carbon nanotubes (CNT and carbon nanofibers (CNF are allotropes of carbon featuring fibrous morphology. The dimensions and high aspect ratio of CNT and CNF have prompted the comparison with naturally occurring asbestos fibers which are known to be extremely pathogenic. While the toxicity and hazardous outcomes elicited by airborne exposure to single-walled CNT or asbestos have been widely reported, very limited data are currently available describing adverse effects of respirable CNF. Results Here, we assessed pulmonary inflammation, fibrosis, oxidative stress markers and systemic immune responses to respirable CNF in comparison to single-walled CNT (SWCNT and asbestos. Pulmonary inflammatory and fibrogenic responses to CNF, SWCNT and asbestos varied depending upon the agglomeration state of the particles/fibers. Foci of granulomatous lesions and collagen deposition were associated with dense particle-like SWCNT agglomerates, while no granuloma formation was found following exposure to fiber-like CNF or asbestos. The average thickness of the alveolar connective tissue - a marker of interstitial fibrosis - was increased 28 days post SWCNT, CNF or asbestos exposure. Exposure to SWCNT, CNF or asbestos resulted in oxidative stress evidenced by accumulations of 4-HNE and carbonylated proteins in the lung tissues. Additionally, local inflammatory and fibrogenic responses were accompanied by modified systemic immunity, as documented by decreased proliferation of splenic T cells ex vivo on day 28 post exposure. The accuracies of assessments of effective surface area for asbestos, SWCNT and CNF (based on geometrical analysis of their agglomeration versus estimates of mass dose and number of particles were compared as predictors of toxicological outcomes. Conclusions We provide evidence that effective surface area along with mass dose rather than specific surface area or particle number are significantly correlated with toxicological responses to carbonaceous fibrous nanoparticles. Therefore, they could be useful dose metrics for risk assessment and management.

Murray Ashley R

2012-04-01

303

Synthesis of palladium/helical carbon nanofiber hybrid nanostructures and their application for hydrogen peroxide and glucose detection.  

Science.gov (United States)

We report on a novel sensing platform for H2O2 and glucose based on immobilization of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostructures and glucose oxidase (GOx) with Nafion on a glassy carbon electrode (GCE). HCNFs were synthesized by a chemical vapor deposition process on a C60-supported Pd catalyst. Pd-HCNF nanocomposites were prepared by a one-step reduction free method in dimethylformamide (DMF). The prepared materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits excellent electrocatalytic sensitivity toward H2O2 (315 mA M(-1) cm(-2)) as probed by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified electrodes significantly reduce the overpotential and enhance the electron transfer rate. A linear range from 5.0 ?M to 2.1 mM with a detection limit of 3.0 ?M (based on the S/N = 3) and good reproducibility were obtained. Furthermore, a sensing platform for glucose was prepared by immobilizing the Pd-HCNFs and glucose oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting biosensor exhibits a good response to glucose with a wide linear range (0.06-6.0 mM) with a detection limit of 0.03 mM and a sensitivity of 13 mA M(-1) cm(-2). We show that small size and homogeneous distribution of the Pd nanoparticles in combination with good conductivity and large surface area of the HCNFs lead to a H2O2 and glucose sensing platform that performs in the top range of the herein reported sensor platforms. PMID:24180258

Jia, Xueen; Hu, Guangzhi; Nitze, Florian; Barzegar, Hamid Reza; Sharifi, Tiva; Tai, Cheuk-Wai; Wågberg, Thomas

2013-11-27

304

A hierarchical nanostructured carbon nanofiber-In2S3 photocatalyst with high photodegradation and disinfection abilities under visible light.  

Science.gov (United States)

Photocatalytic degradation of pollutants under visible light provides a new door to solve the water contamination problem by utilizing free and renewable sunlight. The search for highly efficient photocatalysts with hierarchical nanostructures remains crucial for accessing this new door. In this work, a new hierarchical nanostructured photocatalyst is designed and synthesized, for the first time, by anchoring In2S3 flower-like nanostructures on non-woven carbon nanofiber (CNF). The nanostructures of these CNF-In2S3 composites were fine-tuned, with the aim of achieving the highest photocatalytic activity under visible light. The formation mechanism of the hierarchical nanostructure is also investigated. The results indicate that the optimized hierarchical CNF-In2S3 photocatalyst is superior in photodegradation and disinfection efficiency to that of pure In2S3 under visible-light irradiation. The prominent photocatalytic activities of these hierarchical CNF-In2S3 photocatalysts can be attributed to the excellent properties of enhanced light absorption, large surface area, and efficient charge separation, which are all derived from the special three-dimensional hierarchical nanostructures. Therefore, this work presents the great potential of this hierarchical nanostructured CNF-In2S3 photocatalyst in practical environmental remediation fields. PMID:24771718

Gao, Peng; Li, An Ran; Tai, Ming Hang; Liu, Zhao Yang; Sun, Darren Delai

2014-06-01

305

Wafer-scale fabrication of patterned carbon nanofiber nanoelectrode arrays: a route for development of multiplexed, ultrasensitive disposable biosensors.  

Science.gov (United States)

One of the major limitations in the development of ultrasensitive electrochemical biosensors based on one-dimensional nanostructures is the difficulty involved with reliably fabricating nanoelectrode arrays (NEAs). In this work, we describe a simple, robust and scalable wafer-scale fabrication method to produce multiplexed biosensors. Each sensor chip consists of nine individually addressable arrays that uses electron beam patterned vertically aligned carbon nanofibers (VACNFs) as the sensing element. To ensure nanoelectrode behavior with higher sensitivity, VACNFs were precisely grown on 100 nm Ni dots with 1 microm spacing on each micro pad. Pretreatments by the combination of soaking in 1.0 M HNO(3) and electrochemical etching in 1.0M NaOH dramatically improved the electrode performance, indicated by the decrease of redox peak separation in cyclic voltammogram (DeltaE(p)) to approximately 100 mV and an approximately 200% increase in steady-state currents. The electrochemical detection of the hybridization of DNA targets from E. coli O157:H7 onto oligonucleotide probes were successfully demonstrated. The 9 arrays within the chip were divided into three groups with triplicate sensors for positive control, negative control and specific hybridization. The proposed method has the potential to be scaled up to NxN arrays with N up to 10, which is ideal for detecting a myriad of organisms. In addition, such sensors can be used as a generic platform for many electroanalysis applications. PMID:19303281

Arumugam, Prabhu U; Chen, Hua; Siddiqui, Shabnam; Weinrich, Jarret A P; Jejelowo, Ayodeji; Li, Jun; Meyyappan, M

2009-05-15

306

A novel and simple route to prepare a Pt nanoparticle-loaded carbon nanofiber electrode for hydrogen peroxide sensing.  

Science.gov (United States)

A facile wet-chemical method was developed to prepare a novel Pt nanoparticle-loaded carbon nanofiber (Pt/CNF) electrode. Without using any stabilizer or pretreatment procedure, large amounts of Pt nanoparticles could be well deposited on the surface of the electrospun CNF electrode at room temperature, as revealed by scanning electron microscopy (SEM). The effect of the precursor concentration on the formation of Pt catalysts was investigated to optimize the performance of the proposed hybrid electrode. When applied to the electrochemical detection of hydrogen peroxide (H?O?), the Pt/CNF electrode exhibited low overpotential, fast response and high sensitivity. A low detection limit of 0.6 ?M with wide linear range of 1-800 ?M (R=0.9991) was achieved at the Pt/CNF electrode, which was superior to that obtained with other H?O? electrochemical sensors reported previously. In addition, the Pt/CNF electrode showed good selectivity for H?O? detection in the presence of ascorbic acid (AA), acetaminophenol (AP) and uric acid (UA) under physiological pH condition. The attractive analytical performances and facile preparation method made this novel hybrid electrode promising for the development of effective H?O? sensors. PMID:21665458

Liu, Yang; Wang, Dawei; Xu, Lei; Hou, Haoqing; You, Tianyan

2011-07-15

307

Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix: effect on water-oil interfaces  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Novos compósitos magnéticos anfifílicos foram preparados pelo crescimento de nanotubos e nanofibras de carbono contendo partículas magnéticas através de deposição química de vapor (CVD), utilizando etanol como fonte de carbono e lama vermelha (RM, subproduto do processo Bayer de produção de alumina) [...] como suporte e catalisador. Monitoramento da reação CVD à temperatura programada (TPCVD), difração de raios X (XRD), espectroscopia Mössbauer, espectroscopia de energia dispersiva (EDS), espectroscopia Raman, termogravimetria (TG/DTA), análise elementar (CHN), determinação de área superficial (BET), microscopia eletrônica de varredura (SEM) e de transmissão (TEM) e medidas magnéticas mostraram que etanol reduz íons de ferro na RM para formar fases magnéticas, por exemplo Fe3O4 e Fe0, e depósitos de carbono (5-42 wt.%) na forma de nanotubos e nanofibras. A combinação de nanoestruturas hidrofóbicas de carbono com óxidos hidrofílicos de Al, Si e Ti presentes na lama vermelha produziu materiais anfifílicos com excelente interação com a interface água-óleo. Misturas de óleo de soja ou de decalina com água (completamente imiscíveis) foram emulsificadas facilmente na presença dos compósitos anfifílicos. Quando os compósitos foram adicionados a uma emulsão água-biodiesel estável, as partículas anfifílicas difundiram-se para a interface água- óleo. As partículas do compósito foram atraídas por ímãs e carregaram com elas as gotas de óleo, levando à completa desemulsificação e separação entre biodiesel e água. Abstract in english New magnetic amphiphilic composites were prepared by the catalytic carbon vapor deposition (CVD) growth of carbon nanotubes and nanofibers using ethanol as carbon source and red mud waste (RM, a by-product of the Bayer process of alumina production) as catalyst and support. Temperature-programmed CV [...] D (TPCVD), analyses by X-ray diffractometry (XRD), Mössbauer spectroscopy, energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, thermogravimetry (TG/DTA), elemental analysis (CHN), superficial area determination (BET), scanning (SEM) and transmission (TEM) electron microscopies and magnetic measurements showed that ethanol reduces the iron ions in the red mud to form magnetic phases, e.g., Fe3O4 and Fe0, and carbon deposits (5-42 wt.%), particularly nanotubes and nanofibers. The combination of the hydrophobic carbon nanostructures with the hydrophilic Al, Si and Ti oxides present in the RM produced amphiphilic materials with excellent interaction with the water-oil interface. Soybean oil or decalin mixtures with water (completely immiscible) were easily emulsified in the presence of the amphiphilic composites. When the composites were added to stable biodiesel-water emulsions, the amphiphilic particles diffused to the interface oil-water. These composite particles were attracted by a magnet, carrying the oil droplets with them and leading to the complete demulsification and separation of the biodiesel from the water.

Aline A. S., Oliveira; Ivo F., Teixeira; Leandro P., Ribeiro; Juliana C., Tristão; Anderson, Dias; Rochel M., Lago.

308

Hollow nitrogen-containing core/shell fibrous carbon nanomaterials as support to platinum nanocatalysts and their TEM tomography study  

Science.gov (United States)

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic acid with catalyst supports. Compared to the untreated CNF/PANI composites, the carbonized composites were proven to be better supporting materials for the Pt nanocatalysts and showed superior performance as catalyst supports for methanol electrochemical oxidation. The current density of methanol oxidation on the catalyst with the core/shell nanostructured carbon materials is approximately seven times of that on the catalyst with CNF/PANI support. TEM tomography revealed that some Pt nanoparticles were embedded in the PANI shells of the CNF/PANI composites, which might decrease the electrocatalyst activity. TEM-energy dispersive spectroscopy mapping confirmed that the Pt nanoparticles in the inner tube of N-doped hollow CNFs could be accessed by the Nafion ionomer electrolyte, contributing to the catalytic oxidation of methanol.

Zhou, Cuifeng; Liu, Zongwen; Du, Xusheng; Mitchell, David Richard Graham; Mai, Yiu-Wing; Yan, Yushan; Ringer, Simon

2012-03-01

309

Hollow nitrogen-containing core/shell fibrous carbon nanomaterials as support to platinum nanocatalysts and their TEM tomography study  

Science.gov (United States)

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic acid with catalyst supports. Compared to the untreated CNF/PANI composites, the carbonized composites were proven to be better supporting materials for the Pt nanocatalysts and showed superior performance as catalyst supports for methanol electrochemical oxidation. The current density of methanol oxidation on the catalyst with the core/shell nanostructured carbon materials is approximately seven times of that on the catalyst with CNF/PANI support. TEM tomography revealed that some Pt nanoparticles were embedded in the PANI shells of the CNF/PANI composites, which might decrease the electrocatalyst activity. TEM-energy dispersive spectroscopy mapping confirmed that the Pt nanoparticles in the inner tube of N-doped hollow CNFs could be accessed by the Nafion ionomer electrolyte, contributing to the catalytic oxidation of methanol.

2012-01-01

310

Micro porosity Development of Herringbone Carbon Nano fibers by RbOH Chemical Activation  

International Nuclear Information System (INIS)

The influence of different activation conditions, including activating agent/CNFs ratio, activation temperature, and He flow rate, on the pore structure development of herringbone carbon nano fibers (CNFs) was studied. The best results of activated CNFs with larger specific surface area can be achieved using the following optimized factors: RbOH/CNFs ratio = 4/1, activation temperature = 900 degree C ,and a He flow rate = 850 ml/min. The optimization of these three factors leads to high CNFs micropore volume, being the surface area increased by a factor of 3 compared to the raw CNFs. It is important to note that only the creation of micropores (ultra micropores principally) took place, and meso pores were not generated if compared with raw CNFs

2009-01-01

311

Thermal Conductivity of Ethylene Vinyl Acetate Copolymer/Carbon Nanofiller Blends  

Science.gov (United States)

To reduce weight and increase the mobility, comfort, and performance of future spacesuits, flexible, thermally conductive fabrics and plastic tubes are needed for the Liquid Cooling and Ventilation Garment. Such improvements would allow astronauts to operate more efficiently and safely for extended extravehicular activities. As an approach to raise the thermal conductivity (TC) of an ethylene vinyl acetate copolymer (Elvax 260), it was compounded with three types of carbon based nanofillers: multi-walled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNFs), and expanded graphite (EG). In addition, other nanofillers including metallized CNFs, nickel nanostrands, boron nitride, and powdered aluminum were also compounded with Elvax 260 in the melt at various loading levels. In an attempt to improve compatibility between Elvax 260 and the nanofillers, MWCNTs and EG were modified by surface coating and through noncovalent and covalent attachment of organic molecules containing alkyl groups. Ribbons of the nanocomposites were extruded to form samples in which the nanofillers were aligned in the direction of flow. Samples were also fabricated by compression molding to yield nanocomposites in which the nanofillers were randomly oriented. Mechanical properties of the aligned samples were determined by tensile testing while the degree of dispersion and alignment of nanoparticles were investigated using high-resolution scanning electron microscopy. TC measurements were performed using a laser flash (Nanoflash ) technique. TC of the samples was measured in the direction of, and perpendicular to, the alignment direction. Additionally, tubing was also extruded from select nanocomposite compositions and the TC and mechanical flexibility measured.

Ghose, S.; Watson, K. A.; Working, D. C.; Connell, J. W.; Smith, J. G., Jr.; Lin, Y.; Sun, Y. P.

2007-01-01

312

Multiscale Analysis and Nutrient Transport in Carbon Nanotube Reinforced Nanofiber Bioreactor  

Science.gov (United States)

Bioreactors play important role in tissue engineering, as they simulate physiological environment required for the development of tissue substitutes. The significant parameters involved in the efficient working of a bioreactor are the transfer of nutrients and removal of wastes. Use of carbon nanotube polymeric scaffolds for tissue engineering applications has gained recent attention, primarily due to the enhanced mechanical properties of carbon nanotubes. In this study, a hierarchical approach to determine the atomistic properties of carbon nanotube based polymers using molecular dynamics and coupling between the scales through complex multi-scale mathematical homogenization models is discussed. A new computational methodology for the analysis of tissue-fluid interaction problem based on a biphasic representation of fluid and tissue domain is also presented. The significance of this work lies in the use of a multi-physical modelling of complex material geometry as well as physical processes that represent different physiological systems, leading to an efficient multiscale-multi-physical computational algorithm.

Reddy, J. N.; Unnikrishnan, V. U.; Unnikrishnan, G. U.

2010-05-01

313

The production of carbon nanofibers and thin films on palladium catalysts from ethylene oxygen mixtures  

Energy Technology Data Exchange (ETDEWEB)

The characteristics of carbonaceous materials deposited in fuel rich ethylene-oxygen mixtures on three types of palladium: foil, sputtered film, and nanopowder, are reported. It was found that the form of palladium has a dramatic influence on the morphology of the deposited carbon. In particular, on sputtered film and powder, tight 'weaves' of sub-micron filaments formed quickly. In contrast, on foils under identical conditions, the dominant morphology is carbon thin films with basal planes oriented parallel to the substrate surface. Temperature, gas flow rate, reactant flow ratio (C2H4:02), and residence time (position) were found to influence both growth rate and type for all three forms of Pd. X-ray diffraction, high-resolution transmission electron microscopy, temperature-programmed oxidation, and Raman spectroscopy were used to assess the crystallinity of the as-deposited carbon, and it was determined that transmission electron microscopy and x-ray diffraction were the most reliable methods for determining crystallinity. The dependence of growth on reactor position, and the fact that no growth was observed in the absence of oxygen support the postulate that the carbon deposition proceeds by combustion generated radical species.

Phillips, Jonathan [Los Alamos National Laboratory; Doorn, Stephen [Los Alamos National Laboratory; Atwater, Mark [UNM MECH.ENG.; Leseman, Zayd [UNM MECH.ENG.; Luhrs, Claudia C [UNM ENG.MECH; Diez, Yolanda F [SPAIN; Diaz, Angel M [SPAIN

2009-01-01

314

The electronic transport properties and microstructure of carbon nanofiber/epoxy composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibres (CNF) were dispersed into an epoxy resin using a combination of ultrasonication and mechanical mixing. The electronic transport properties of the resulting composites were investigated by means of impedance spectroscopy. It was found that a very low critical weight fraction (pc = 0.064 wt %) which may be taken to correspond to the formation of a tunneling conductive network inside the matrix. The insulator-to-conductor transition region spanned about one order of magnitude f...

Allaoui, Ai?ssa; V Hoa, Suong; D Pugh, Martin

2007-01-01

315

The Optimization of Electrical Conductivity Using Central Composite Design for Polyvinyl Alcohol/Multiwalled Carbon Nanotube-Manganese Dioxide Nanofiber Composites Synthesised by Electrospinning  

Directory of Open Access Journals (Sweden)

Full Text Available This research reports the characterization and statistical analysis of electrical conductivity optimization for polyvinyl alcohol (PVA/multiwalled carbon nanotube (MWCNT-manganese dioxide (MnO2 nanofiber composite. The Central Composite Design (CCD, the most common design of Response Surface Methodology (RSM had been used to optimise the synthesis process of PVA/MWCNT-MnO2 nanofiber composite. The process parameters studied were; applied voltage (16 kV - 30 kV, solution flow rate (3- 5 mL h-1 and surrounding temperature (17-30°C. Analysis of variance (ANOVA was used to analyse the experimental results. The prediction of optimum value and the clarification of the interactions between the specified range factors were done by using the quadratic model. The results revealed that at the parameter condition of 23 kV for applied voltage, 4 mL h-1 solution flow rate and 18°C of surrounding temperature, the highest electrical conductivity of 2.66x10-5 S cm-1 was obtained. The predicted (2.81 x10-5 S cm-1 value after optimization process was in good agreement with the experimental data (3.06 x10-5 S cm-1. The model was able to accurately predict the response of electrical conductivity with less than 10% error. Referring to ANOVA results, it was statistically found that the surrounding temperature parameter given significant effect to electrical conductivity of PVA/MWCNT-MnO2 nanofiber composite in both single parameter and interaction between parameter.

Ahmad Zuhairi Abdullah

2012-01-01

316

Tiny Li4Ti5O12 nanoparticles embedded in carbon nanofibers as high-capacity and long-life anode materials for both Li-ion and Na-ion batteries.  

Science.gov (United States)

Tiny Li4Ti5O12 nanoparticles embedded in carbon nanofibers (Li4Ti5O12@C hierarchical nanofibers) were synthesized using a scalable synthesis technique involving electrospinning and annealing in an Ar atmosphere for the purpose of using them as anode materials for high-capacity and high-rate-capability Li-ion and Na-ion batteries. The Li4Ti5O12@C hierarchical nanofibers exhibited high stable discharge capacities of about 145.5 mA h g(-1) after 1000 cycles at 10C for the Li-ion battery anode. For Na-ion storage performance, a reversible capacity of approximately 162.5 mA h g(-1) is stably maintained at 0.2C during the first 100 cycles. PMID:24202186

Liu, Jun; Tang, Kun; Song, Kepeng; van Aken, Peter A; Yu, Yan; Maier, Joachim

2013-12-28

317

Synthesis of carbon nanotubes and nanofibers by thermal CVD on SiO2 and Al2O3 support layers.  

Science.gov (United States)

In this work, catalytic thermal chemical vapor deposition method, using a mixture of methane and hydrogen at atmospheric pressure in a horizontal tubular quartz furnace, was used to grow carbon nanostructured materials. Silicon wafers with SiO2 or Al2O3 layers were used as support for thin nickel film deposition used as catalyst. It has been shown that the interaction between catalysts and substrates is of critical importance for carbon nanotube growth. However, this mechanism is not completely understood. Here, the interaction between catalyst nickel film and two different oxide layers supported on silicon wafers was studied as well as the influence of both support systems (SiO2/Si and Al2O3/Si) on the carbon nanostructures growth at different temperatures and process running times. The substrates were characterized by atomic force microscopy and the carbon nanostructured materials were studied by Raman spectroscopy, high resolution scanning and transmission electron microscopy. At higher temperatures it was observed a high density of carbon nanotubes grown over Al2O3 support layer when compared to SiO2 support layer showing a different behavior for Ni catalyst on each of the substrates. A quite different Ni catalyst behavior was observed at lower temperatures due to the formation of carbon nanofibers instead of carbon nanotubes on both substrates. PMID:19916421

Aguiar, Marina R; Verissimo, Carla; Ramos, Antonio C S; Moshkalev, Stanislav A; Swart, Jacobus W

2009-07-01

318

Polymethylsilsesquioxane-cellulose nanofiber biocomposite aerogels with high thermal insulation, bendability, and superhydrophobicity.  

Science.gov (United States)

Polymethylsilsesquioxane-cellulose nanofiber (PMSQ-CNF) composite aerogels have been prepared through sol-gel in a solvent containing a small amount of CNFs as suspension. Since these composite aerogels do not show excessive aggregation of PMSQ and CNF, the original PMSQ networks are not disturbed. Composite aerogels with low density (0.020 g cm(-3) at lowest), low thermal conductivity (15 mW m(-1) K(-1)), visible light translucency, bending flexibility, and superhydrophobicity thus have been successfully obtained. In particular, the lowest density and bending flexibility have been achieved with the aid of the physical supporting effect of CNFs, and the lowest thermal conductivity is comparable with the original PMSQ aerogels and standard silica aerogels. The PMSQ-CNF composite aerogels would be a candidate to practical high-performance thermal insulating materials. PMID:24865571

Hayase, Gen; Kanamori, Kazuyoshi; Abe, Kentaro; Yano, Hiroyuki; Maeno, Ayaka; Kaji, Hironori; Nakanishi, Kazuki

2014-06-25

319

Myotube formation on gelatin nanofibers - multi-walled carbon nanotubes hybrid scaffolds.  

Science.gov (United States)

Engineering functional muscle tissue requires the formation of densely packed, aligned, and mature myotubes. To enhance the formation of aligned myotubes with improved contractibility, we fabricated aligned electrospun gelatin multi-walled carbon nanotubes (MWNTs) hybrid fibers that were used as scaffolds for the growth of myoblasts (C2C12). The MWNTs significantly enhanced myotube formation by improving the mechanical properties of the resulting fibers and upregulated the activation of mechanotransduction related genes. In addition, the fibers enhanced the maturation of the myotubes and the amplitude of the myotube contractions under electrical stimulation (ES). Such hybrid material scaffolds may be useful to direct skeletal muscle cellular organization, improve cellular functionality and tissue formation. PMID:24831971

Ostrovidov, Serge; Shi, Xuetao; Zhang, Ling; Liang, Xiaobin; Kim, Sang Bok; Fujie, Toshinori; Ramalingam, Murugan; Chen, Mingwei; Nakajima, Ken; Al-Hazmi, Faten; Bae, Hojae; Memic, Adnan; Khademhosseini, Ali

2014-08-01

320

Carbon Nanofiber-Based, High-Frequency, High-Q, Miniaturized Mechanical Resonators  

Science.gov (United States)

High Q resonators are a critical component of stable, low-noise communication systems, radar, and precise timing applications such as atomic clocks. In electronic resonators based on Si integrated circuits, resistive losses increase as a result of the continued reduction in device dimensions, which decreases their Q values. On the other hand, due to the mechanical construct of bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators, such loss mechanisms are absent, enabling higher Q-values for both BAW and SAW resonators compared to their electronic counterparts. The other advantages of mechanical resonators are their inherently higher radiation tolerance, a factor that makes them attractive for NASA s extreme environment planetary missions, for example to the Jovian environments where the radiation doses are at hostile levels. Despite these advantages, both BAW and SAW resonators suffer from low resonant frequencies and they are also physically large, which precludes their integration into miniaturized electronic systems. Because there is a need to move the resonant frequency of oscillators to the order of gigahertz, new technologies and materials are being investigated that will make performance at those frequencies attainable. By moving to nanoscale structures, in this case vertically oriented, cantilevered carbon nanotubes (CNTs), that have larger aspect ratios (length/thickness) and extremely high elastic moduli, it is possible to overcome the two disadvantages of both bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators. Nano-electro-mechanical systems (NEMS) that utilize high aspect ratio nanomaterials exhibiting high elastic moduli (e.g., carbon-based nanomaterials) benefit from high Qs, operate at high frequency, and have small force constants that translate to high responsivity that results in improved sensitivity, lower power consumption, and im - proved tunablity. NEMS resonators have recently been demonstrated using topdown, lithographically fabricated ap - proaches to form cantilever or bridgetype structures. Top-down approaches, however, rely on complicated and expensive e-beam lithography, and often require a release mechanism. Reso - nance effects in structures synthesized using bottom-up approaches have also recently been reported based on carbon nanotubes, but such approaches have relied on a planar two-dimensional (2D) geometry. In this innovation, vertically aligned tubes synthesized using a bottom- up approach have been considered, where the vertical orientation of the tubes has the potential to increase integration density even further. The simulation of a vertically oriented, cantilevered carbon nanotube was performed using COMSOL Multi - physics, a finite element simulation package. All simulations were performed in a 2D geometry that provided consistent results and minimized computational complexity. The simulations assumed a vertically oriented, cantilevered nanotube of uniform density (1.5 g/cu cm). An elastic modulus was assumed to be 600 GPa, relative permittivity of the nanotube was assumed to be 5.0, and Poisson s ratio was assumed to be 0.2. It should be noted that the relative permittivity and Poisson s ratio for the nanotubes of interest are not known accurately. However, as in previous simulations, the relative permittivity and Poisson s ratios were treated as weak variables in the simulation, and no significant changes were recognized when these variables were varied.

Kaul, Anupama B.; Epp, Larry W.; Bagge, Leif

2011-01-01

 
 
 
 
321

Conductive architecture of Fe2O3 microspheres/self-doped polyaniline nanofibers on carbon ionic liquid electrode for impedance sensing of DNA hybridization.  

Science.gov (United States)

A novel architecture was designed by combining the strong adsorption ability of Fe(2)O(3) microspheres to the DNA probes and excellent conductivity of self-doped polyaniline (SPAN) nanofibers (copolymer of aniline and m-aminobenzenesulfonic acid) on carbon ionic liquid electrode (CILE) for electrochemical impedance sensing of the immobilization and hybridization of DNA. The formed conductive Fe(2)O(3)/SPAN membrane on the CILE was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)(6)](3-/4-) as the indicator. The immobilization of the probe DNA on the surface of electrode and the sensitivity of DNA hybridization recognition were dramatically enhanced due to the unique synergistic effect of Fe(2)O(3) microspheres, SPAN nanofibers and ionic liquid. The DNA hybridization events were monitored with a label-free EIS strategy. Under optimal conditions, the dynamic range of this DNA biosensor for detecting the sequence-specific DNA of phosphoenolpyruvate carboxylase (PEPCase) gene from transgenically modified rape was from 1.0 x 10(-13) to 1.0 x 10(-7)mol/L, and the detection limit was 2.1 x 10(-14)mol/L. This work suggested a simple strategy to prepare a conductive interface for electrochemical detection of DNA hybridization and opened a way for the application of Fe(2)O(3) in DNA electrochemical biosensing. PMID:19713094

Zhang, Wei; Yang, Tao; Li, Xiao; Wang, Debao; Jiao, Kui

2009-10-15

322

Effects of pore structure on the high-performance capacitive deionization using chemically activated carbon nanofibers.  

Science.gov (United States)

Capacitive deionization (CDI) electrodes were constructed from activated carbon fibers prepared using electrospinning and chemical activation. The CDI efficiencies of these electrodes were studied as a function of their specific surface areas, pore volumes and pore sizes via salt ion adsorption. The specific surface areas increased approximately 90 fold and the pore volume also increased approximately 26 fold with the use of greater amounts of the chemical activation agent. There was a relative increase in the mesopore fraction with higher porosity. A NaCI solution was passed through a prepared CDI system, and the salt removal efficiency of the CDI system was determined by the separation of the Na+ and Cl- ions toward the anode and cathode. The CDI efficiency increased with greater specific surface areas and pore volumes. In addition, the efficiency per unit pore volume increased with a reduction in the micropore fraction, resulting in the suppressed overlapping effect. In conclusion, the obtained improvements in CDI efficiency were mainly attributed to mesopores, but the micropores also played an important role in the high-performance CDI under conditions of high applied potential and high ion concentrations. PMID:24745222

Im, Ji Sun; Kim, Jong Gu; Lee, Young-Seak

2014-03-01

323

Hydrogen storage in carbon nanofibers as being studied by Northeastern University. Technical evaluation report  

Energy Technology Data Exchange (ETDEWEB)

As part of the current technical evaluation effort, the author was tasked with going to Northeastern, interviewing Dr. Baker and his team, seeing a demonstration of the storage process, and making an assessment of the validity of the claim and the soundness of the research. Dr. Baker and his group have a process that, if proven to work, could be the breakthrough that is needed in the area of on-board hydrogen storage. One of the biggest problems may be the fact that the results look so good, that even if they are real, they will be viewed with skepticism by many. The chemisorption value of 5.8 liters of hydrogen per gram of carbon that Dr. Baker claimed at the time of his proposal has now been surpassed many times. Dr. Baker has reported reproducible hydrogen take-up levels as high as 30 liters per gram, depending on fiber structure. The fibers are loaded with hydrogen at ambient temperature using a pressurized feed at levels of about 600--900 psi. The hydrogen will be retained at pressure, but can apparently be essentially totally recovered upon pressure release. This paper reports the findings from the trip to Northeastern.

Skolnik, E.G. [Energetics, Inc., Columbia, MD (United States)

1997-06-01

324

Decomposição catalítica da hidrazina sobre irídio suportado em compósitos à base de nanofibras de carbono para propulsão espacial: testes em condições reais Catalytic decomposition of hydrazine over iridium supported on carbon nanofiber composites for propulsion in space: tests under real-life conditions  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this work is to present the catalytic performance of iridium supported on carbon nanofibers with macroscopic shaping in a 2 N hydrazine microthruster placed inside a vacuum chamber in order to reproduce real-life conditions. The performances obtained are compared to those of the commercial catalyst Shell 405. The carbon-nanofiber based catalyst showed better performance than the commercial catalyst from the standpoint of activity due to its texture and its thermal conductivity.

Ricardo Vieira

2005-02-01

325

Direct evidence of water-assisted sintering of cobalt on carbon nanofiber catalysts during simulated Fischer-Tropsch conditions revealed with in situ mossbauer spectroscopy.  

Science.gov (United States)

Cobalt on carbon nanofiber model catalysts with very small dispersed cobalt particles of 5 nm were subjected to H(2)O/H(2) treatments at 20 bar and 220 degrees C. Using in situ Mossbauer spectroscopy we could unambiguously prove that oxidation of the nanoparticles by water will not occur when hydrogen is present. Only in a water/argon atmosphere did oxidation take place. This rules out oxidation as the deactivation mechanism in Fischer-Tropsch synthesis. Even more important, we define the relative humidity (RH) as a key parameter to understanding deactivation by water. At a RH below 25% sintering was absent even when measuring for 4 weeks, whereas at a high RH of 62% as much as half of the small super paramagnetic cobalt particles (Fischer-Tropsch conditions amounted to 73%, which could be directly related to the metal dispersion loss 77% due to sintering as evidenced by detailed TEM analysis of the spent sample. PMID:20524607

Bezemer, G Leendert; Remans, Tom J; van Bavel, Alexander P; Dugulan, A Iulian

2010-06-30

326

Microfiber Supported Nanofiber Membrane.  

Science.gov (United States)

A nanofiber membrane is formed on a microfiber membrane. The nanofiber membrane may be electro sprayed directly onto the microfiber membrane and becomes integrated with the microfiber membrane to form a filter. The microfiber membrane provides structural ...

J. Kameoka K. Nakano

2005-01-01

327

Low-temperature self-assembled vertically aligned carbon nanofibers as counter-electrode material for dye-sensitized solar cells  

International Nuclear Information System (INIS)

Low-temperature AC–DC PECVD is employed for direct growth of vertically aligned carbon nanofibers (VACNFs) on ordinary transparent conductive glass as counter-electrode material for dye-sensitized solar cells (DSSCs). To the best of our knowledge, this is the first report on utilization of VACNFs grown directly on ordinary FTO-coated glass as a cost-effective catalyst material in DSSCs. According to the FESEM images, the as-grown arrays are well aligned and dense, and offer uniform coverage on the surface of the substrate. In-plane and out-of-plane conductivity measurements reveal their good electrical conductivity, and Raman spectroscopy suggests a high number of electrocatalytic active sites, favoring charge transport at the electrolyte/electrode interface. Hybrid VACNF/Pt electrodes are also fabricated for performance comparison with Pt and VACNF electrodes. X-ray diffraction results verify the crystallization of Pt in hybrid electrodes and further confirm the vertical alignment of carbon nanofibers. Electrochemical characterization indicates that VACNFs provide both high catalytic and good charge transfer capability, which can be attributed to their high surface area, defect-rich and one-dimensional structure, vertical alignment and low contact resistance. As a result, VACNF cells can achieve a comparable performance (?5.6%) to that of the reference Pt cells (?6.5%). Moreover, by combination of the excellent charge transport and catalytic ability of VACNFs and the high conductivity of Pt nanoparticles, hybrid VACNF/Pt cells can deliver a performance superior to that of the Pt cells (?7.2%), despite having a much smaller amount of Pt loading, which raises hopes for low-cost large-scale production of DSSCs in the future. (paper)

2013-11-01

328

Low-temperature self-assembled vertically aligned carbon nanofibers as counter-electrode material for dye-sensitized solar cells.  

Science.gov (United States)

Low-temperature AC-DC PECVD is employed for direct growth of vertically aligned carbon nanofibers (VACNFs) on ordinary transparent conductive glass as counter-electrode material for dye-sensitized solar cells (DSSCs). To the best of our knowledge, this is the first report on utilization of VACNFs grown directly on ordinary FTO-coated glass as a cost-effective catalyst material in DSSCs. According to the FESEM images, the as-grown arrays are well aligned and dense, and offer uniform coverage on the surface of the substrate. In-plane and out-of-plane conductivity measurements reveal their good electrical conductivity, and Raman spectroscopy suggests a high number of electrocatalytic active sites, favoring charge transport at the electrolyte/electrode interface. Hybrid VACNF/Pt electrodes are also fabricated for performance comparison with Pt and VACNF electrodes. X-ray diffraction results verify the crystallization of Pt in hybrid electrodes and further confirm the vertical alignment of carbon nanofibers. Electrochemical characterization indicates that VACNFs provide both high catalytic and good charge transfer capability, which can be attributed to their high surface area, defect-rich and one-dimensional structure, vertical alignment and low contact resistance. As a result, VACNF cells can achieve a comparable performance (~5.6%) to that of the reference Pt cells (~6.5%). Moreover, by combination of the excellent charge transport and catalytic ability of VACNFs and the high conductivity of Pt nanoparticles, hybrid VACNF/Pt cells can deliver a performance superior to that of the Pt cells (~7.2%), despite having a much smaller amount of Pt loading, which raises hopes for low-cost large-scale production of DSSCs in the future. PMID:24107390

Mahpeykar, S M; Tabatabaei, M K; Ghafoori-fard, H; Habibiyan, H; Koohsorkhi, J

2013-11-01

329

Novos materiais à base de nanofibras de carbono como suporte de catalisador na decomposição da hidrazina Carbon nanofibers a new catalyst support for hydrazine decomposition  

Directory of Open Access Journals (Sweden)

Full Text Available Today satellites propulsion is based on the use of monopropellant and/or bipropellant chemical systems. The maneuvering of satellite is based on the hydrazine decomposition micropropulsors catalyzed by metallic iridium supported on g-alumina. This reaction is a surface reaction and is strongly exothermic and implies that the operation of the micropropulsor is controlled by the mass and heat diffusions. For this reason and for the fact that the propulsor operation is frequently in pulsed regime, the catalyst should support high pressure and temperature variations within a short time period. The performance and the durability of the commercial catalyst are jeopardized by the low thermal conductivity of the alumina. The low thermal conductivity of the alumina support restricts the heat diffusion and leads to the formation of hot spots on the catalyst surface causing the metal sintering and/or fractures of the support, resulting in loss of the activity and catalyst destruction. This work presents the synthesis and characterization of new carbon composite support for the active element iridium, in substitution of the commercial catalysts alumina based support. These supports are constituted of carbon nanofibers (30 to 40 nm diameter supported on a macroscopic carbon felt. These materials present high thermal conductivity and mechanical resistance, as well as the easiness to be shaped with different macroscopic shapes. The mechanical stability and the performance of the iridium supported on the carbon composite support, evaluated in a laboratory scale test in hydrazine decomposition reaction, are superior compared to the commercial catalyst.

Ricardo Vieira

2003-10-01

330

Graphite-nanoplatelet-decorated polymer nanofiber with improved thermal, electrical, and mechanical properties.  

Science.gov (United States)

Graphite-nanoplatelet (GNP)-decorated polymer nanofiber composites with hierarchical structures were fabricated by the combination of electrospinning and ultrasonication. It was found that GNPs could be well attached or embedded onto the nanofibers when their size was comparable to the nanofiber diameter. X-ray diffraction results indicated that ultrasonic treatment exerted no influence on the carbon crystal layer spacing. Fourier transform infrared spectra and Raman spectroscopy revealed the existence of interfacial interaction between GNPs and polyurethane nanofibers. The prepared nanofiber composite showed enhanced thermal stability and hardness, which originated from uniform dispersion of GNPs as well as strong interaction between GNPs and the nanofibers. The electrical conductivity was significantly improved, derived from the formation of a conductive percolation network in the nanofiber composite. During ultrasonication, cavitation bubbles may be formed in liquid, and microjets and shock waves were created near the GNP surface after collapse of the bubbles. These jets, causing sintering of GNPs, pushed GNPs toward the nanofiber surface at very high speeds. When the fast-moving GNPs hit the nanofiber surface, interfacial collision between GNPs and the nanofibers occurs, the nanofiber may experience partial softening or even melting at the impact sites, and then GNPs could be uniformly anchored onto the nanofibers. This method opens a new door for harvesting GNP-based nanofiber composites with improved material properties. PMID:23910565

Gao, Jiefeng; Hu, Mingjun; Dong, Yucheng; Li, Robert K Y

2013-08-28

331

Electrospun nanofiber membranes for electrically activated shape memory nanocomposites  

Science.gov (United States)

A novel shape memory nanocomposite system, consisting of a thermoplastic Nafion polymer and ultrathin electrospun polyacrylonitrile (PAN)-based carbonization nanofiber membranes, is successfully synthesized. PAN-based carbonization nanofiber networks that offer responses to deformations are considered to be an excellent actuation source. Significant improvement in the electrical conductivity of carbon nanofiber membranes is found by adjusting the applied voltage power in the electrospinning PAN process varying from 7.85 to 12.30 S cm?1. The porous structure of the carbon nanofiber membranes provides a large specific surface area and interfacial contact area when combined with the polymer matrix. Shape memory Nafion nanocomposites filled with interpenetrating non-woven electrospun PAN carbonization membranes can be actuated by applying 14 V electrical voltage within 5 s. The results, as demonstrated through morphology, electrical and thermal measurements and a shape recovery test, suggest a valuable route to producing soft nanocomposites.

Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Leng, Jinsong

2014-06-01

332

High-rate nano-crystalline Li{sub 4}Ti{sub 5}O{sub 12} attached on carbon nano-fibers for hybrid supercapacitors  

Energy Technology Data Exchange (ETDEWEB)

A lithium titanate (Li{sub 4}Ti{sub 5}O{sub 12})-based electrode which can operate at unusually high current density (300 C) was developed as negative electrode for hybrid capacitors. The high-rate Li{sub 4}Ti{sub 5}O{sub 12} electrode has a unique nano-structure consisting of unusually small nano-crystalline Li{sub 4}Ti{sub 5}O{sub 12} (ca. 5-20 nm) grafted onto carbon nano-fiber anchors (nc-Li{sub 4}Ti{sub 5}O{sub 12}/CNF). This nano-structured nc-Li{sub 4}Ti{sub 5}O{sub 12}/CNF composite are prepared by simple sol-gel method under ultra-centrifugal force (65,000 N) followed by instantaneous annealing at 900 C for 3 min. A model hybrid capacitor cell consisting of a negative nc-Li{sub 4}Ti{sub 5}O{sub 12}/CNF composite electrode and a positive activated carbon electrode showed high energy density of 40 Wh L{sup -1} and high power density of 7.5 kW L{sup -1} comparable to conventional EDLCs. (author)

Naoi, Katsuhiko; Isobe, Yusaku; Aoyagi, Shintaro [Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8558 (Japan); Ishimoto, Shuichi [Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8558 (Japan); Nippon Chemi-Con Corporation, 363 Arakawa, Takahagi-shi, Ibaraki 318-8505 (Japan)

2010-09-15

333

Manufacturing and shear response characterization of carbon nanofiber modified CFRP using the out-of-autoclave-vacuum-bag-only cure process.  

Science.gov (United States)

The interlaminar shear response is studied for carbon nanofiber (CNF) modified out-of-autoclave-vacuum-bag-only (OOA-VBO) carbon fiber reinforced plastic (CFRP). Commercial OOA-VBO prepregs were coated with a CNF modified epoxy solution and a control epoxy solution without CNF to make CNF modified samples and control samples, respectively. Tensile testing was used to study the in-plane shear performance of [± 45°]4s composite laminates. Significant difference in failure modes between the control and CNF modified CFRPs was identified. The control samples experienced half-plane interlaminar delamination, whereas the CNF modified samples experienced a localized failure in the intralaminar region. Digital image correlation (DIC) surface strain results of the control sample showed no further surface strain increase along the delaminated section when the sample was further elongated prior to sample failure. On the other hand, the DIC results of the CNF modified sample showed that the surface strain increased relatively and uniformly across the CFRP as the sample was further elongated until sample failure. The failure mode evidence along with microscope pictures indicated that the CNF modification acted as a beneficial reinforcement inhibiting interlaminar delamination. PMID:24688435

McDonald, Erin E; Wallace, Landon F; Hickman, Gregory J S; Hsiao, Kuang-Ting

2014-01-01

334

Novos materiais à base de nanofibras de carbono como suporte de catalisador na decomposição da hidrazina / Carbon nanofibers a new catalyst support for hydrazine decomposition  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese [...] Abstract in english Today satellites propulsion is based on the use of monopropellant and/or bipropellant chemical systems. The maneuvering of satellite is based on the hydrazine decomposition micropropulsors catalyzed by metallic iridium supported on g-alumina. This reaction is a surface reaction and is strongly exoth [...] ermic and implies that the operation of the micropropulsor is controlled by the mass and heat diffusions. For this reason and for the fact that the propulsor operation is frequently in pulsed regime, the catalyst should support high pressure and temperature variations within a short time period. The performance and the durability of the commercial catalyst are jeopardized by the low thermal conductivity of the alumina. The low thermal conductivity of the alumina support restricts the heat diffusion and leads to the formation of hot spots on the catalyst surface causing the metal sintering and/or fractures of the support, resulting in loss of the activity and catalyst destruction. This work presents the synthesis and characterization of new carbon composite support for the active element iridium, in substitution of the commercial catalysts alumina based support. These supports are constituted of carbon nanofibers (30 to 40 nm diameter) supported on a macroscopic carbon felt. These materials present high thermal conductivity and mechanical resistance, as well as the easiness to be shaped with different macroscopic shapes. The mechanical stability and the performance of the iridium supported on the carbon composite support, evaluated in a laboratory scale test in hydrazine decomposition reaction, are superior compared to the commercial catalyst.

Ricardo, Vieira; Cuong, Pham-Huu; Nicolas, Keller; Marc J., Ledoux.

335

Free-standing and mechanically flexible mats consisting of electrospun carbon nanofibers made from a natural product of alkali lignin as binder-free electrodes for high-performance supercapacitors  

Science.gov (United States)

Mechanically flexible mats consisting of electrospun carbon nanofibers (ECNFs) were prepared by first electrospinning aqueous mixtures containing a natural product of alkali lignin together with polyvinyl alcohol (PVA) into composite nanofiber mats followed by stabilization in air and carbonization in an inert environment. Morphological and structural properties, as well as specific surface area, total pore volume, average pore size, and pore size distribution, of the lignin-based ECNF mats were characterized; and their electrochemical performances (i.e., capacitive behaviors) were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The lignin-based ECNF mats exhibited outstanding performance as free-standing and/or binder-free electrodes of supercapacitors. For example, the ECNFs made from the composite nanofibers with mass ratio of lignin/PVA being 70/30 (i.e., ECNFs (70/30)) had the average diameter of ˜100 nm and the Brunauer-Emmett-Teller (BET) specific surface area of ˜583 m2 g-1. The gravimetric capacitance of ECNFs (70/30) electrode in 6 M KOH aqueous electrolyte exhibited 64 F g-1 at current density of 400 mA g-1 and 50 F g-1 at 2000 mA g-1. The ECNFs (70/30) electrode also exhibited excellent cycling durability/stability, and the gravimetric capacitance merely reduced by ˜10% after 6000 cycles of charge/discharge.

Lai, Chuilin; Zhou, Zhengping; Zhang, Lifeng; Wang, Xiaoxu; Zhou, Qixin; Zhao, Yong; Wang, Yechun; Wu, Xiang-Fa; Zhu, Zhengtao; Fong, Hao

336

Mesoporous Li{sub 4}Ti{sub 5}O{sub 12}/carbon nanofibers for high-rate lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Facile electrospinning method combined with soft-template self-assembly. • Abundant mesopores and large specific surface area. • Superior rate capability and excellent cycling stability. -- Abstract: Mesoporous Li{sub 4}Ti{sub 5}O{sub 12}/carbon nanofibers (LTO/C NFs) are prepared by a facile electrospinning method combined with soft-template self-assembly. The morphology and structure are characterized by field-emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The diameter of as-prepared LTO/C NFs is approximately 400 nm with highly crystallinity LTO nanoparticle completely embedded in carbon framework. Nitrogen adsorption–desorption isotherms and corresponding pore size distribution reveal that the mesoporous LTO/C NFs exhibite high specific surface area (212.1 m{sup 2}/g{sup ?1}) and large pore volume. Compared with the regular LTO/C NFs, the mesoporous LTO/C NFs show much higher rate capability and better capacity retention. At a current rate of 5 C, the reversible capacity of the mesoporous LTO/C NFs electrode is up to 127.4 mA h g{sup ?1} and still remains at 122.7 mA h g{sup ?1} after 100 cycles. The excellent electrochemical performances are closedly related to well-defined one-dimensional (1D) mesoporous nanostructure with LTO nanoparticles embedded in the carbon framework, which efficiently shortened the path length of Li{sup +} diffusion, enhanced electrolyte-active material contact area and facilitated rapid electron transfer.

Wang, Jie; Shen, Laifa; Li, Hongsen; Ding, Bing; Nie, Ping; Dou, Hui; Zhang, Xiaogang, E-mail: azhangxg@nuaa.edu.cn

2014-02-25

337

Asymmetric supercapacitors based on graphene/MnO{sub 2} and activated carbon nanofiber electrodes with high power and energy density  

Energy Technology Data Exchange (ETDEWEB)

Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO{sub 2} composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na{sub 2}SO{sub 4} electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO{sub 2} and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0-1.8 V, and exhibits maximum energy density of 51.1 Wh kg{sup -1}, which is much higher than that of MnO{sub 2}//DWNT cell (29.1 Wh kg{sup -1}). Additionally, graphene/MnO{sub 2}//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Fan, Zhuangjun; Yan, Jun; Wei, Tong; Li, Tianyou [Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Material Science and Chemical Engineering, Harbin Engineering University, Harbin 150001 (China); Zhi, Linjie [National Center for Nanoscience and Technology of China, Zhongguancun, Beiyitiao 11, Beijing 100190 (China); Ning, Guoqing [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249 (China); Wei, Fei [Beijing Key Laboratory of Green Chemical Reaction, Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084 (China)

2011-06-21

338

Kinetics of methane decomposition to CO{sub x}-free hydrogen and carbon nanofiber over Ni-Cu/MgO catalyst  

Energy Technology Data Exchange (ETDEWEB)

Kinetic modeling of methane decomposition to CO{sub x}-free hydrogen and carbon nanofiber has been carried out in the temperature range 550-650 C over Ni-Cu/MgO catalyst from CH{sub 4}-H{sub 2} mixtures at atmospheric pressure. Assuming the different mechanisms of the reaction, several kinetic models were derived based on Langmuir-Hinshelwood type. The optimum value of kinetic parameters has been obtained by Genetic Algorithm and statistical analysis has been used for the model discrimination. The suggested kinetic model relates to the mechanism when the dissociative adsorption of methane molecule is the rate-determining stage and the estimated activation energy is 50.4 kJ/mol in agreement with the literature. The catalyst deactivation was found to be dependent on the time, reaction temperature, and partial pressures of methane and hydrogen. Inspection of the behavior of the catalyst activity in relation to time, led to a model of second order for catalyst deactivation. (author)

Borghei, Maryam; Karimzadeh, Ramin [Chemical Engineering Department, Tarbiat Modares University, Tehran (Iran); Rashidi, Alimorad; Izadi, Nosrat [Research Center of Nanotechnology, Research Institute of Petroleum Industry, Tehran (Iran)

2010-09-15

339

Effect of sulfonated carbon nanofiber-supported Pt on performance of Nafion {sup registered} -based self-humidifying composite membrane for proton exchange membrane fuel cell  

Energy Technology Data Exchange (ETDEWEB)

In the present study, the Nafion {sup registered} -based self-humidifying composite membrane (N-SHCM) with sulfonated carbon nanofiber-supported Pt (s-Pt/CNF) catalyst, N-s-Pt/CNF, is successfully prepared using the solution-casting method. The scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) images of N-s-Pt/CNF indicate that s-Pt/CNF is well dispersed in the Nafion {sup registered} matrix due to the good compatibility between Nafion {sup registered} and s-Pt/CNF. Compared with those of the non-sulfonated Pt/CNF-containing N-SHCM, N-Pt/CNF, the properties of N-s-Pt/CNF, including electronic resistivity, ion-exchange capacity (IEC), water uptake, dimensional stability, and catalytic activity, significantly increase. The maximum power density of the proton exchange membrane fuel cell (PEMFC) fabricated with N-s-Pt/CNF operated at 50 C under dry H{sub 2}/O{sub 2} condition is about 921 mW cm{sup -2}, which is approximately 34% higher than that with N-Pt/CNF. (author)

Hung, T.F. [Department of Chemistry and Center for Nanotechnology, Chung Yuan Christian University, 200 Chung Pei Rd., Chung-Li, 32023 (China); Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 (China); Liao, S.H.; Li, C.Y.; Chen-Yang, Y.W. [Department of Chemistry and Center for Nanotechnology, Chung Yuan Christian University, 200 Chung Pei Rd., Chung-Li, 32023 (China)

2011-01-01

340

Achieving highly dispersed nanofibres at high loading in carbon nanofibre-metal composites  

Science.gov (United States)

In order to tap into the advantages of the properties of carbon nanotubes (CNTs) or carbon nanofibres (CNFs) in composites, the high dispersion of CNTs (or CNFs) and strong interfacial bonding are the key issues which are still challenging. In the current work, a novel approach, consisting of in situ synthesis of CNFs within the Cu powders and mixing Cu ions with the in situ CNF(Ni/Y)-Cu composite powders in a solvent, was developed to highly disperse CNFs in a Cu matrix. The composite, produced by vacuum hot pressing, shows extremely high strength, 3.6 times more than that of the matrix material alone. It is worth mentioning that this method can disperse CNFs at high loading in a metal matrix, inferring good potential for applications, such as electronic packaging materials.

Kang, Jianli; Nash, Philip; Li, Jiajun; Shi, Chunsheng; Zhao, Naiqin

2009-06-01

 
 
 
 
341

Optimizing strength and toughness of nanofiber-reinforced CMCs  

Science.gov (United States)

Nanofibers used in current ceramic matrix composites (CMCs) are usually wavy and of finite length. Here, a shear-lag model for predicting the tensile strength and work of fracture of a composite containing a "single matrix crack", as a function of all the material parameters including constant plus Coulomb interfacial friction, is presented for a CMC containing wavy, finite-length nanofibers having a statistical distribution of strengths. Literature results are recovered for straight infinite fibers, with strength and toughness depending on a characteristic strength ?c and a characteristic length ?c. For nanofibers of finite length L, radius of curvature R, and with Coulomb friction coefficient ?, the strength and toughness are found to depend only on ?c, ?c, and two new dimensionless parameters ??c/R and L/?c. Parametric results for a typical carbon nanotube CMC show an optimal region of morphology (L and R) that maximizes composite strength and toughness, exceeding the properties of composites with straight (R=?) and/or long (L=?) reinforcements. Therefore, while factors such as the nanofiber strength distribution and the nanofiber-matrix interface sliding resistance may not be easily controlled, the tuning, via processing, of purely geometrical properties of the nanofibers (L and R) alone can aid in maximizing composite properties. These results have important application in hybrid CMCs such as "fuzzy fiber" CMCs, where micron-scale fibers are covered with a forest of nanofibers such that the nanofiber array can bridge longitudinal cracks and thus improve delamination resistance.

Pavia, F.; Curtin, W. A.

2012-09-01

342

Atomic layer deposition of Al-doped ZnO/Al2O3 double layers on vertically aligned carbon nanofiber arrays.  

Science.gov (United States)

High-aspect-ratio, vertically aligned carbon nanofibers (VACNFs) were conformally coated with aluminum oxide (Al2O3) and aluminum-doped zinc oxide (AZO) using atomic layer deposition (ALD) in order to produce a three-dimensional array of metal-insulator-metal core-shell nanostructures. Prefunctionalization before ALD, as required for initiating covalent bonding on a carbon nanotube surface, was eliminated on VACNFs due to the graphitic edges along the surface of each CNF. The graphitic edges provided ideal nucleation sites under sequential exposures of H2O and trimethylaluminum to form an Al2O3 coating up to 20 nm in thickness. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirmed the conformal core-shell AZO/Al2O3/CNF structures while energy-dispersive X-ray spectroscopy verified the elemental composition of the different layers. HRTEM selected area electron diffraction revealed that the as-made Al2O3 by ALD at 200 °C was amorphous, and then, after annealing in air at 450 °C for 30 min, was converted to polycrystalline form. Nevertheless, comparable dielectric constants of 9.3 were obtained in both cases by cyclic voltammetry at a scan rate of 1000 V/s. The conformal core-shell AZO/Al2O3/VACNF array structure demonstrated in this work provides a promising three-dimensional architecture toward applications of solid-state capacitors with large surface area having a thin, leak-free dielectric. PMID:24689702

Malek, Gary A; Brown, Emery; Klankowski, Steven A; Liu, Jianwei; Elliot, Alan J; Lu, Rongtao; Li, Jun; Wu, Judy

2014-05-14

343

Hydrogen storage in different carbon materials: Influence of the porosity development by chemical activation  

Science.gov (United States)

The hydrogen adsorption capacity of different types of carbon nanofibers (platelet, fishbone and ribbon) and amorphous carbon have been measured as a function of pressure and temperature. The results showed that the more graphitic carbon materials adsorbed less hydrogen than more amorphous materials. After a chemical activation process, the hydrogen storage capacities of the carbon materials increased markedly in comparison with the non-activated ones. BET surface area of amorphous carbon increased by a factor of 3.5 and the ultramicropore volume doubled, thus increasing the hydrogen adsorption by a factor of 2. However, BET surface area in platelet CNFs increased by a factor of 3 and the ultramicropore volume by a factor of 6, thus increasing the hydrogen storage by a factor of 4.5. The dependency of hydrogen storage capacity of carbon materials on the BET surface area was evaluated using both a condensation model and experimental results. Comparison of data suggests that the hydrogen adsorption capacity clearly depends on the pore structure and so, on the accessibility to the internal surface.

Jiménez, Vicente; Ramírez-Lucas, Ana; Sánchez, Paula; Valverde, José Luís; Romero, Amaya

2012-01-01

344

Decomposição catalítica da hidrazina sobre irídio suportado em compósitos à base de nanofibras de carbono para propulsão espacial: testes em condições reais / Catalytic decomposition of hydrazine over iridium supported on carbon nanofiber composites for propulsion in space: tests under real-life conditions  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese [...] Abstract in english The aim of this work is to present the catalytic performance of iridium supported on carbon nanofibers with macroscopic shaping in a 2 N hydrazine microthruster placed inside a vacuum chamber in order to reproduce real-life conditions. The performances obtained are compared to those of the commercia [...] l catalyst Shell 405. The carbon-nanofiber based catalyst showed better performance than the commercial catalyst from the standpoint of activity due to its texture and its thermal conductivity.

Ricardo, Vieira; Demétrio Bastos, Netto; Pierre, Bernhardt; Marc-Jacques, Ledoux; Cuong, Pham-Huu.

345

Synthesis of silicon monoxide-pyrolytic carbon-carbon nanofiber composites and their hybridization with natural graphite as a means of improving the anodic performance of lithium-ion batteries  

Science.gov (United States)

Novel composites of silicon monoxide, pyrolytic carbon and carbon nanofiber (SiO/PyC/CNF) were hybridized with natural graphite (NG) as a means of improving the anodic performance of Li-ion batteries. Samples were made with hybridization levels of 10-30 wt% of NG exhibited excellent cyclability with a discharge capacity of 389-522 mAh g-1 in a Li-ion battery system. SiO/PyC/CNF composite hybrids showed better cyclability than other carbon composites containing SiO/PyC and SiO/CNF. These hybridization effects were attributed to the lower contact resistance of SiO/PyC/CNF in the electrode. The internal spaces created throughout the SiO/PyC/CNF composite and their effect on material dispersion in the hybridized electrodes may have prevented electrode damage by relieving tensions induced by the expansion of SiO particles in the electrode over the course of repeated charge and discharge processes.

Park, Tae-Hwan; Yeo, Jae-Seong; Jang, Sang-Min; Miyawaki, Jin; Mochida, Isao; Yoon, Seong-Ho

2012-09-01

346

Synthesis of silicon monoxide–pyrolytic carbon–carbon nanofiber composites and their hybridization with natural graphite as a means of improving the anodic performance of lithium-ion batteries  

International Nuclear Information System (INIS)

Novel composites of silicon monoxide, pyrolytic carbon and carbon nanofiber (SiO/PyC/CNF) were hybridized with natural graphite (NG) as a means of improving the anodic performance of Li-ion batteries. Samples were made with hybridization levels of 10–30 wt% of NG exhibited excellent cyclability with a discharge capacity of 389–522 mAh g?1 in a Li-ion battery system. SiO/PyC/CNF composite hybrids showed better cyclability than other carbon composites containing SiO/PyC and SiO/CNF. These hybridization effects were attributed to the lower contact resistance of SiO/PyC/CNF in the electrode. The internal spaces created throughout the SiO/PyC/CNF composite and their effect on material dispersion in the hybridized electrodes may have prevented electrode damage by relieving tensions induced by the expansion of SiO particles in the electrode over the course of repeated charge and discharge processes. (paper)

2012-09-07

347

Electrostatic deposition of nanofibers for sensor application  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work addresses the formation of nanofibers (with hundred of nanometers) by using electrospinning (electrostatic deposition) aiming at applications as sensors. Different quantities of a colloidal dispersion of graphite particles were blended with polyacrylonitrile (PAN) and N,N dimethylformamide (DMF), resulting in a series of solutions with carbon concentrations ranging from 0 to 25%. Precipitation was observed depending on the concentration of carbon added to the precursor blend. As a c...

Ana Neilde Rodrigues da Silva; Rogerio Furlan; Idalia Ramos; Jorge Juan Santiago-Avilés

2005-01-01

348

Rhodium complexes and particles on carbon nanofibres : surface chemistry of carbon nanofibres and catalytic properties of supported rhodium species  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The work described in this thesis has provided valuable information about the modification and use of carbon nanofibre supports in catalysis. The potential of CNFs as a catalyst support material is high. The properties of CNFs, such as their mechanical strength and mesoporous structure, make them especially suitable as a catalyst support for liquid-phase applications. A strong incentive for their use is the replacement of activated carbon, whose properties are often difficult to control. The...

Ros, T. G.

2002-01-01

349

Electrospun Gallium Nitride Nanofibers  

International Nuclear Information System (INIS)

The high thermal conductivity and wide bandgap of gallium nitride (GaN) are desirable characteristics in optoelectronics and sensing applications. In comparison to thin films and powders, in the nanofiber morphology the sensitivity of GaN is expected to increase as the exposed area (proportional to the length) increases. In this work we present electrospinning as a novel technique in the fabrication of GaN nanofibers. Electrospinning, invented in the 1930s, is a simple, inexpensive, and rapid technique to produce microscopically long ultrafine fibers. GaN nanofibers are produced using gallium nitrate and dimethyl-acetamide as precursors. After electrospinning, thermal decomposition under an inert atmosphere is used to pyrolyze the polymer. To complete the preparation, the nanofibers are sintered in a tube furnace under a NH3 flow. Both scanning electron microscopy and profilometry show that the process produces continuous and uniform fibers with diameters ranging from 20 to a few hundred nanometers, and lengths of up to a few centimeters. X-ray diffraction (XRD) analysis shows the development of GaN nanofibers with hexagonal wurtzite structure. Future work includes additional characterization using transmission electron microscopy and XRD to understand the role of precursors and nitridation in nanofiber synthesis, and the use of single nanofibers for the construction of optical and gas sensing devices.

2009-04-19

350

Rippling of polymer nanofibers.  

Science.gov (United States)

This paper studies the evolution mechanism of surface rippling in polymer nanofibers under axial stretching. This rippling phenomenon has been detected in as-electrospun polyacrylonitrile in recent single-fiber tension tests, and in electrospun polyimide nanofibers after imidization. We herein propose a one-dimensional nonlinear elastic model that takes into account the combined effect of surface tension and nonlinear elasticity during the rippling initiation and its evolution in compliant polymer nanofibers. The polymer nanofiber is modeled as an incompressible, isotropically hyperelastic Mooney-Rivlin solid. The fiber geometry prior to rippling is considered as a long circular cylinder. The governing equation of surface rippling is established through linear perturbation of the static equilibrium state of the nanofiber subjected to finite axial prestretching. The critical stretch and ripple wavelength are determined in terms of surface tension, elastic property, and fiber radius. Numerical examples are demonstrated to examine these dependencies. In addition, a critical fiber radius is determined, below which the polymer nanofibers are intrinsically unstable. The present model, therefore, is capable of predicting the rippling condition in compliant nanofibers, and can be further used as a continuum mechanics approach for the study of surface instability and nonlinear wave propagation in compliant fibers and wires at the nanoscale. PMID:19256861

Wu, Xiang-Fa; Kostogorova-Beller, Yulia Y; Goponenko, Alexander V; Hou, Haoqing; Dzenis, Yuris A

2008-12-01

351

Study of the fire resistant behavior of unfilled and carbon nanofibers reinforced polybenzimidazole coating for structural applications:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

With increasing interest in epoxy-based carbon fiber composites for structural applications, it is important to improve the fire resistant properties of these materials. The fire resistant performance of these materials can be improved either by using high performance epoxy resin for manufacturing carbon fiber composite or by protecting the previously used epoxy-based composite with some fire resistant coating. In this context, work is carried out to evaluate the fire resistance performance o...

Iqbal, H. M. S.; Stec, A. A.; Patel, P.; Bhowmik, S.; Benedictus, R.

2013-01-01

352

Direct synthesis of suspended single-walled carbon nanotubes crossing plasma sharpened carbon nanofibre tips  

Science.gov (United States)

Herein we report a method for the direct synthesis of suspended single-walled carbon nanotubes (su-SWNTs) using carbon nanofibres (CNFs) as templates via a three-step fabrication process. Plasma-enhanced chemical vapour deposition was first employed to grow vertically aligned CNFs, which were then post-treated with an energetic argon plasma in the same reactor to yield structural transformation by sharpening tips and reducing embedded catalytic nanoparticles to favourable sizes, presumably below 10 nm. A thermal chemical vapour deposition process subsequently followed, for directly synthesizing SWNTs suspended across the tips or sidewalls of post-treated CNFs (PT-CNFs) with a span up to 10 µm. We also demonstrated that one can maximize the yield of su-SWNTs on the tips of PT-CNFs by optimizing the post-treatment conditions to provide a protective coating which suppresses the growth of SWNTs from sidewalls. In this approach, no further catalyst deposition is needed after the nanostructured PT-CNF template is formed. Thus, su-SWNTs can be selectively positioned on the tips of PT-CNFs with a clean substrate surface free from unwanted CNTs and with a suspension span not limited by the flow conditions of the carbon source gas. This method of fabricating su-SWNTs can be extended to position a single isolated SWNT for the purpose of either minimizing the environmental perturbation during SWNT characterization or enhancing the performance in nanodevice applications.

Weng, Cheng-Hui; Lee, Wei-Yang; Juang, Zhang-Yu; Leou, Keh-Chyang; Tsai, Chuen-Horng

2006-01-01

353

Superhydrophobic terpolymer nanofibers containing perfluoroethyl alkyl methacrylate by electrospinning  

International Nuclear Information System (INIS)

A new statistical terpolymer containing perfluoroethyl alkyl methacrylate (Zonyl-TM), methyl methacrylate and butyl acrylate, poly(Zonyl-TM-ran-MMA-ran-BA) was synthesized in supercritical carbon dioxide at 200 bar and 80 °C using AIBN as an initiator by heterogeneous free radical copolymerization. Nanofibers of this terpolymer were produced by electrospinning from its DMF solution. The structural and thermal properties of terpolymers and electrospun poly(Zonyl-TM-MMA-BA) nanofibers were analyzed using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and differential scanning calorimetry. Nanofiber morphology was investigated by scanning electron microscopy. Electrospun nanofiber layer was found to be superhydrophobic with a water contact angle of 172 ± 1° and highly oleophobic with hexadecane, glycerol and ethylene glycol contact angles of 70 ± 1°, 167 ± 1° and 163 ± 1° respectively. The change of the contact angle results on the electrospun fiber layer and flat terpolymer surfaces by varying feed monomer composition were compared and discussed in the text.

2012-05-15

354

Experimental and Theoretical Studies of Carbon Nanotube Hierarchical Structures in Multifunctional Hybrid Composites.  

Science.gov (United States)

Nanoscale reinforcement is locally segregated at the microscopic scale with controlled orientation. During this study, uniform growth of CNFs and CNTs was achieved on large carbon fabric. Catalyst loading, reaction time, catalyst deposition, and hydrogen ...

B. P. Grady D. Papavassiliou D. Resasco M. C. Altan M. C. Saha

2012-01-01

355

Capillography of Mats of Nanofibers  

Science.gov (United States)

Capillography (from the Latin capillus, 'hair', and the Greek graphein, to write ) is a recently conceived technique for forming mats of nanofibers into useful patterns. The concept was inspired by experiments on carpetlike mats of multiwalled carbon nanotubes. Capillography may have the potential to be a less-expensive, less-time-consuming alternative to electron-beam lithography as a means of nanoscale patterning for the fabrication of small devices and instruments. In capillography, one exploits the lateral capillary forces exerted on small objects that pierce the surface of a liquid. If the small objects are identical, then the forces are always attractive. Two examples of the effects of such forces are the agglomeration of small particles floating on the surface of a pond and the drawing together of hairs of a wet paintbrush upon removal of the brush from water. Because nanoscale objects brought into contact remain stuck together indefinitely due to Van der Waals forces, patterns formed by capillography remain even upon removal of the liquid. For the experiments on the mats of carbon nanotubes, a surfactant solution capable of wetting carbon nanotubes (which are ultra-hydrophobic) was prepared. The mats were wetted with the solution, then dried. Once the mats were dry, it was found that the nanotubes had become ordered into various patterns, including nestlike indentations, trenches, and various combinations thereof. It may be possible to exploit such ordering effects through controlled wetting and drying of designated portions of mats of carbon nanotubes (and, perhaps, mats of nanofibers of other materials) to obtain patterns similar to those heretofore formed by use of electron-beam lithography. For making patterns that include nestlike indentations, it has been conjectured that it could be possible to control the nesting processes by use of electrostatic fields. Further research is needed to understand the physics of the patterning processes in order to develop capabilities to control patterns formed in capillography.

Noca, Flavio; Sansom, Elijah; Zhou, Jijie; Gharib, Mory

2008-01-01

356

The preparation of mesoporous SnO2 nanotubes by carbon nanofibers template and their lithium storage properties  

International Nuclear Information System (INIS)

Mesoporous SnO2 nanotubes are prepared by templating against carbon fibers through a facile solution approach followed by calcination at 800 °C for 2 h. The nanotubes are characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and nitrogen adsorption. The electrochemical performances as the anodes of lithium-ions batteries are studied by the cyclic voltammogram (CV) and galvanostatic discharge–charge voltage tests. Because of its unique structure (the mesoporous wall, internal void and open ends), the as-obtained mesoporous SnO2 nanotubes demonstrate a reversible capacity of 585 mA h g?1 up to 50 cycles at a high current density of 400 mA g?1

2013-05-30

357

Electrochemical determination of dopamine based on electrospun CeO2/Au composite nanofibers  

International Nuclear Information System (INIS)

An electrochemical method for the detection of dopamine based on a glass carbon electrode modified with electrospun CeO2/Au composite nanofibers was investigated in this article. The CeO2/Au composite nanofibers were prepared by the electrospinning technique and then annealed in air. The CeO2/Au composite nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. Cyclic voltammetry (CV) showed that the electrospun CeO2/Au composite nanofibers modified carbon glass electrode exhibited an excellent electrocatalytic response to the dopamine (DA). The detection limit (S/N = 3) was as low as 0.056 ?M and the sensitivity could reach 127 ?A mM?1 cm?2. All these demonstrated that the electrospun CeO2/Au composite nanofibers were good electrocatalyst for the oxidation of dopamine

2013-04-15

358

Free-Standing LiNi0.5Mn1.5O4/Carbon Nanofiber Network Film as Lightweight and High-Power Cathode for Lithium Ion Batteries.  

Science.gov (United States)

Lightweight and high-power LiNi0.5Mn1.5O4/carbon nanofiber (CNF) network electrodes are developed as a high-voltage cathode for lithium ion batteries. The LiNi0.5Mn1.5O4/CNF network electrodes are free-standing and can be used as a cathode without using any binder, carbon black, or metal current collector, and hence the total weight of the electrode is highly reduced while keeping the same areal loading of active materials. Compared with conventional electrodes, the LiNi0.5Mn1.5O4/CNF network electrodes can yield up to 55% reduction in total weight and 2.2 times enhancement in the weight percentage of active material in the whole electrode. Moreover, the LiNi0.5Mn1.5O4/carbon nanofiber (CNF) network electrodes showed excellent current rate capability in the large-current test up to 20C (1C = 140 mAh/g), when the conventional electrodes showed almost no capacity at the same condition. Further analysis of polarization resistance confirmed the favorable conductivity from the CNF network compared with the conventional electrode structure. By reducing the weight, increasing the working voltage, and improving the large-current rate capability simultaneously, the LiNi0.5Mn1.5O4/CNF electrode structure can highly enhance the energy/power density of lithium ion batteries and thus holds great potential to be used with ultrathin, ultralight electronic devices as well as electric vehicles and hybrid electric vehicles. PMID:24773079

Fang, Xin; Ge, Mingyuan; Rong, Jiepeng; Zhou, Chongwu

2014-05-27

359

Characterization of nanocarbons (nanotubes and nanofibers) by Inverse Gas Chromatography  

International Nuclear Information System (INIS)

The adsorption of different alkanes (linear and cyclic), aromatics and chlorohydrocarbons on non-microporous carbons-carbon nanotubes (CNTs) and carbon nanofibres (CNFs)- was studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. CNTs present the highest adsorption capacity. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene and chloroform) with the surfaces are mainly dispersive over all the carbons tested, being CNTs the material with the highest dispersive contribution. Adsorption parameters were correlated with morphological and chemical properties of the materials

2007-04-01

360

Characterization of nanocarbons (nanotubes and nanofibers) by Inverse Gas Chromatography  

Science.gov (United States)

The adsorption of different alkanes (linear and cyclic), aromatics and chlorohydrocarbons on non-microporous carbons-carbon nanotubes (CNTs) and carbon nanofibres (CNFs)- was studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. CNTs present the highest adsorption capacity. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene and chloroform) with the surfaces are mainly dispersive over all the carbons tested, being CNTs the material with the highest dispersive contribution. Adsorption parameters were correlated with morphological and chemical properties of the materials.

Díaz, E.; Ordóñez, S.; Vega, A.

2007-04-01

 
 
 
 
361

Uniform and Conformal Carbon Nanofilms Produced Based on Molecular Layer Deposition  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Continuous and uniform carbon nanofilms (CNFs) are prepared by pyrolysis of polyimide films which are produced by molecular layer deposition (MLD). The film thickness can be easily controlled at nanometer scale by altering the cycle numbers. During the annealing process at 600 °C, the polyimide film is subject to shrinkage of 70% in thickness. The obtained CNFs do not exhibit a well-graphitized structure due to the low calcination temperature. No clear pore structures are observed in the pro...

Peng Yang; Guizhen Wang; Zhe Gao; He Chen; Yong Wang; Yong Qin

2013-01-01

362

Electrostatic deposition of nanofibers for sensor application  

Directory of Open Access Journals (Sweden)

Full Text Available This work addresses the formation of nanofibers (with hundred of nanometers by using electrospinning (electrostatic deposition aiming at applications as sensors. Different quantities of a colloidal dispersion of graphite particles were blended with polyacrylonitrile (PAN and N,N dimethylformamide (DMF, resulting in a series of solutions with carbon concentrations ranging from 0 to 25%. Precipitation was observed depending on the concentration of carbon added to the precursor blend. As a consequence, the relative viscosity decreases, due to PAN molecules removal from the solution by carbon particles adsorption, forming precipitates. The resulting fibers show an irregular shape, as observed by SEM and the diameters decrease with the increase of the carbon concentration in the precursor blend. The incorporation of carbon particles in the fibers was confirmed by FTIRS and Raman spectroscopy.

Ana Neilde Rodrigues da Silva

2005-03-01

363

Tailored Surface Structure of LiFePO4/C Nanofibers by Phosphidation and Their Electrochemical Superiority for Lithium Rechargeable Batteries.  

Science.gov (United States)

We offer a brand new strategy for enhancing Li ion transport at the surface of LiFePO4/C nanofibers through noble Li ion conducting pathways built along reduced carbon webs by phosphorus. Pristine LiFePO4/C nanofibers composed of 1-dimensional (1D) LiFePO4 nanofibers with thick carbon coating layers on the surfaces of the nanofibers were prepared by the electrospinning technique. These dense and thick carbon layers prevented not only electrolyte penetration into the inner LiFePO4 nanofibers but also facile Li ion transport at the electrode/electrolyte interface. In contrast, the existing strong interactions between the carbon and oxygen atoms on the surface of the pristine LiFePO4/C nanofibers were weakened or partly broken by the adhesion of phosphorus, thereby improving Li ion migration through the thick carbon layers on the surfaces of the LiFePO4 nanofibers. As a result, the phosphidated LiFePO4/C nanofibers have a higher initial discharge capacity and a greatly improved rate capability when compared with pristine LiFePO4/C nanofibers. Our findings of high Li ion transport induced by phosphidation can be widely applied to other carbon-coated electrode materials. PMID:24786736

Lee, Yoon Cheol; Han, Dong-Wook; Park, Mihui; Jo, Mi Ru; Kang, Seung Ho; Lee, Ju Kyung; Kang, Yong-Mook

2014-06-25

364

Electrorheology of nanofiber suspensions  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Electrorheological (ER fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

Yin Jianbo

2011-01-01

365

Electrorheology of nanofiber suspensions  

Science.gov (United States)

Electrorheological (ER) fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

Yin, Jianbo; Zhao, Xiaopeng

2011-12-01

366

Engineered Polymer Composites Through Electrospun Nanofiber Coating of Fiber Tows  

Science.gov (United States)

Composite materials offer significant weight savings in many aerospace applications. The toughness of the interface of fibers crossing at different angles often determines failure of composite components. A method for toughening the interface in fabric and filament wound components using directly electrospun thermoplastic nanofiber on carbon fiber tow is presented. The method was first demonstrated with limited trials, and then was scaled up to a continuous lab scale process. Filament wound tubes were fabricated and tested using unmodified baseline towpreg material and nanofiber coated towpreg.

Kohlman, Lee W.; Bakis, Charles; Williams, Tiffany S.; Johnston, James C.; Kuczmarski, Maria A.; Roberts, Gary D.

2014-01-01

367

Fabrication of a selective mercury sensor based on the adsorption of cold vapor of mercury on carbon nanotubes: determination of mercury in industrial wastewater.  

Science.gov (United States)

A new sensor for the determination of mercury at microg ml(-1) levels is proposed based on the adsorption of mercury vapor on single-walled carbon nanotubes (SWCNTs). The changes in the impedance of SWCNTs were monitored upon adsorption of mercury vapor. The adsorption behaviour of mercury on SWCNTs was compared with that on multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs). Cold vapor of mercury was generated at 65 degrees C using Sn(II) solution as a reducing agent. The limit of detection was 0.64 microg ml(-1) for Hg(II) species. The calibration curve for Hg(II) was linear from 1.0 to 30.0 microg ml(-1). The relative standard deviation (RSD) of eight replicate analyses of 15 microg ml(-1) of Hg(II) was 2.7%. The results showed no interfering effects from many foreign species and hydride forming elements. The system was successfully applied to the determination of the mercury content of different types of wastewater samples. PMID:19782468

Safavi, Afsaneh; Maleki, Norouz; Doroodmand, Mohammad Mahdi

2010-01-15

368

Application of Nanofiber Technology to Nonwoven Thermal Insulation  

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Full Text Available Nanofiber technology (fiber diameter less than 1 micrometer is under development for future Army lightweight protective clothing systems. Nanofiber applications for ballistic and chemical/biological protection are being actively investigated, but the thermal properties of nanofibers and their potential protection against cold environments are relatively unknown. Previous studies have shown that radiative heat transfer in fibrous battings is minimized at fiber diameters between 5 and 10 micrometers. However, the radiative heat transfer mechanism of extremely small diameter fibers of less than 1 micrometer diameter is not well known. Previous studies were limited to glass fibers, which have a unique set of thermal radiation properties governed by the thermal emissivity properties of glass. We are investigating the thermal transfer properties of high loft nanofiber battings composed of carbon fiber and various polymeric fibers such as polyacrylonitrile, nylon, and polyurethane. Thermal insulation battings incorporating nanofibers could decrease the weight and bulk of current thermal protective clothing, and increase mobility for soldiers in the battlefield.

Phillip W. Gibson, Ph.D

2007-07-01

369

Synthesis of Vertically-Aligned Single-Walled Carbon Nanotubes in Micro Structure of Atmospheric Pressure Non-Equilibrium Plasma  

Science.gov (United States)

Plasma enhanced chemical vapor deposition (PECVD) is recognized as one of the viable fabrication techniques of carbon nanotubes. The outstanding advantage of PECVD is that free-standing, vertically-aligned carbon nanotubes (VA-CNTs) are synthesized due to the electric field normal to the substrate. This feature draws intense attention for the fabrication of nanoelectronic devices such as high-resolution scanning nanoprobes, interconnects, and field emission devices. However, carbon nanotubes synthesized in PECVD are overwhelmingly carbon nanofibers (CNFs) or multi-walled carbon nanotubes (MWNTs) with measurable structural defects. Tremendous interest in the preparation and characterization of vertically-aligned single-walled carbon nanotubes (VA-SWNTs) and related applications had not been realized in the scope of PECVD until recently. Here we present a fabrication technique of high-purity vertically-aligned single-walled carbon nanotubes using atmospheric pressure plasma enhanced chemical vapor deposition. By now, we have developed the atmospheric pressure radio-frequency discharge (APRFD) for this purpose. Although densely mono-dispersed Fe-Co catalysts of a few nanometers is primarily responsible for VA-SWNT growth, carbon precipitation was virtually absent in the thermal CVD regime at 700°C. On the other hand, high-yield VA-SWNTs were grown at 4 ?m min-1 by applying the atmospheric pressure radio-frequency discharge. The results proved that cathodic ion sheath adjacent to the substrates, where a large potential drop exists, also plays an essential role for the controlled growth of SWNTs, while ion damage to the VA-SWNTs is inherently avoided due to high collision frequency among molecules in atmospheric pressure. In this paper, operation regime of APRFD and tentative reaction mechanisms for VA-SWNT growth are discussed along with optical imaging of near substrate region of APRFD.

Ohnishi, Kuma; Nozaki, Tomohiro; Okazaki, Ken; Heberlein, Joachim; Kortshagen, Uwe

370

Nanotubes, nanofibers, and nanohelixes prepared in CVD process  

Science.gov (United States)

Synthesis of carbon nanostructures at low temperature range of 600°C by a filament assisted chemical vapor deposition method was investigated. This system could be used to synthesis carbon nano-tubes, nano-fibers, and nano-helixes by changing the catalyst materials. The results indicated that the synthesis of these carbon structures with diameter from 20- 500 nm range is possible with the current method. It has been reported that random deposition of carbon helix structured in CVD of carbon nanotubes. This paper presents details of these experimental procedures.

Guo, Kun; Jayatissa, Ahalapitiya H.

2010-04-01

371

Electrospun Gallium Nitride Nanofibers (abstract)  

Science.gov (United States)

The high thermal conductivity and wide bandgap of gallium nitride (GaN) are desirable characteristics in optoelectronics and sensing applications. In comparison to thin films and powders, in the nanofiber morphology the sensitivity of GaN is expected to increase as the exposed area (proportional to the length) increases. In this work we present electrospinning as a novel technique in the fabrication of GaN nanofibers. Electrospinning, invented in the 1930s, is a simple, inexpensive, and rapid technique to produce microscopically long ultrafine fibers. GaN nanofibers are produced using gallium nitrate and dimethyl-acetamide as precursors. After electrospinning, thermal decomposition under an inert atmosphere is used to pyrolyze the polymer. To complete the preparation, the nanofibers are sintered in a tube furnace under a NH3 flow. Both scanning electron microscopy and profilometry show that the process produces continuous and uniform fibers with diameters ranging from 20 to a few hundred nanometers, and lengths of up to a few centimeters. X-ray diffraction (XRD) analysis shows the development of GaN nanofibers with hexagonal wurtzite structure. Future work includes additional characterization using transmission electron microscopy and XRD to understand the role of precursors and nitridation in nanofiber synthesis, and the use of single nanofibers for the construction of optical and gas sensing devices.

Meléndez, Anamaris; Morales, Kristle; Ramos, Idalia; Campo, Eva; Santiago, Jorge J.

2009-04-01

372

New High-Energy Nanofiber Anode Materials  

Energy Technology Data Exchange (ETDEWEB)

The overall goal of the proposed work was to use electrospinning technology to integrate dissimilar materials (lithium alloy and carbon) into novel composite nanofiber anodes, which simultaneously had high energy density, reduced cost, and improved abuse tolerance. The nanofiber structure allowed the anodes to withstand repeated cycles of expansion and contraction. These composite nanofibers were electrospun into nonwoven fabrics with thickness of 50 ?m or more, and then directly used as anodes in a lithium-ion battery. This eliminated the presence of non-active materials (e.g., conducting carbon black and polymer binder) and resulted in high energy and power densities. The nonwoven anode structure also provided a large electrode-electrolyte interface and, hence, high rate capacity and good lowtemperature performance capability. Following are detailed objectives for three proposed project periods. • During the first six months: Obtain anodes capable of initial specific capacities of 650 mAh/g and achieve ~50 full charge/discharge cycles in small laboratory scale cells (50 to 100 mAh) at the 1C rate with less than 20 percent capacity fade; • In the middle of project period: Assemble, cycle, and evaluate 18650 cells using proposed anode materials, and demonstrate practical and useful cycle life (750 cycles of ~70% state of charge swing with less than 20% capacity fade) in 18650 cells with at least twice improvement in the specific capacity than that of conventional graphite electrodes; • At the end of project period: Deliver 18650 cells containing proposed anode materials, and achieve specific capacities greater than 1200 mAh/g and cycle life longer than 5000 cycles of ~70% state of charge swing with less than 20% capacity fade.

Zhang, Xiangwu; Fedkiw, Peter; Khan, Saad; Huang, Alex; Fan, Jiang

2013-11-15

373

Mechanism of nanofiber crimp  

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Full Text Available Fabrication of crimped fibers has been caught much attention recently due to remarkable improvement surf