新型炭材料

Progress in the synthesis of one-dimensional |carbon nanometer heterojunctions

PAN Chun-xu

2009, 23(01): 1-7.

Abstract(1837)

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Abstract:
One-dimensional carbon nanometer heterojunctions (1D-CNHJs) have attracted tremendous interest owing to their distinctive microstructures, properties and potential applications in nanometer devices. The progress for various synthesizing methods for 1D-CNHJs, such as vapor-phase, solution-phase, template-based, electric-field induction, spark plasma sintering, electron beam irradiation, mechanical manipulation, and chemical interconnection, were reviewed. It is considered that future research for 1D-CNHJs should be focused on large-scale production, controllable synthesis, interfacial microstructure control, properties and device building.

Preparation of a polymer-based conductive film filled with single-walled carbon nanotubes

WANG Guo-jian|

2009, 23(01): 8-12.

Abstract(2675)

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Abstract:
A single-walled carbon nanotube (SWCNT) filled styrene-acrylate latex conductive film was prepared using a polymer-latex-based technology. SWCNTs were dispersed in a gum arabic(GA) water solution by means of sonication, and mixed with styrene-acrylate latex to form a conductive composite film after drying at room temperature. The formation of a conductive network of SWCNTs in the polymer matrix was also studied. TEM images showed that SWCNTs were effectively dispersed from bundles to single tubes under the sonication in the GA solution and the surfaces of the SWCNTs were wrapped by GA molecules. The percolation threshold concentration of SWCNTs was as low as 0.03%, when they formed a conductive network.

Structural changes in carbon produced by a sulfur-aided catalytic chemical vapor deposition catalytic chemical vapor deposition

MA Hai-long, WANG Ying-yong

2009, 23(01): 13-17. doi: 10.1016/S1872-5805(08)60031-1

Abstract(2285)

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Abstract:
Branched carbon structures were formed by a chemical vapor deposition of toluene using ferrocene as a catalyst precursor and thiophene as a promoter. The effects of sulfur on the carbon products were investigated by SEM, XRD, and EDX. Results show that the product microstructure changes from tree-like to worm-like when the thiophene volume fraction in the toluene increases from 0.01 to 1%. The carbon trees consist of long, straight, and well-developed branches, while the worm carbons are composed of short and curled fibers. There is no obvious difference in d₀₀₂, La and Lc for the two products.

Synthesis of a metal chloride-graphite intercalation compound by a molten salt method compound by a molten salt method

REN Hui, KANG Fei-yu

2009, 23(01): 18-22. doi: 10.1016/S1872-5805(08)60032-3

Abstract(2776)

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Abstract:
A criterion for the intercalation of a metal chloride in a molten state into graphite was proposed based on the thermodynamics of the intercalation reaction and chemical band theory. The valence electronegativity of element and ionic potential are taken as the chemical band parameters and a band parameter function λ is defined as a criterion to select a guest metal chloride to prepare a graphite intercalation compound (GIC). The ability of a metal chloride to be intercalated into graphite and the stability of the resulting GIC are estimated. The results show that GICs synthesized at a temperature lower than 700 ℃ are more stable when a metal chloride is chosen from the region of λ≤1.2. A metal chloride with λ between 1.2 and 1.8 cannot be easily intercalated into graphite alone. The metal chlorides with λ≥1.8, most of which are alkaline earth chlorides or alkali metal chlorides, are not appropriate as guests to prepare GICs by a molten salt method. The criterion is consistent with the experimental data and some new expected results are also obtained.

Stability of mesopores in organic aerogels produced from melamine, phenolic resole and formaldehyde in pyrolysis

2009, 23(01): 23-27.

Abstract(3147)

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Abstract:
Organic aerogels were synthesized by the solution-sol-gel polymerization of melamine (M), phenolic resole (PR), m-cresol (m-C) and formaldehyde in a basic aqueous solution followed by supercritical petroleum ether drying. The stability of the nanostructure of the organic aerogels in pyrolysis was investigated. It was found that bimodal mesopores are formed in organic aerogels and the sintering of a nanonetwork that forms the mesopores occurs during the pyrolysis of the aerogels, leading to a decrease of mesopore size and volume. The sizes and volumes of the large mesopores (5-50 nm) decrease with pyrolysis temperature and/or time for the same reactant formulation. In all cases the small mesopores (2-5 nm) are more stable during pyrolysis than the large mesopores. The large mesopores prepared at PR concentration of 7.5 g/100 mL are more stable during pyrolysis than those at 10 g/100 mL. The stability of the large mesopores during pyrolysis for organic aerogels increases with M/PR ratio or decreases with m-C/PR ratio, which can be ascribed to an increase of intermolecular interaction in the nanonetwork of the organic aerogels with increasing M/PR ratios or with decreasing m-C/PR ratios.

Microwave assisted chemical vapor infiltration for the rapid fabrication of carbon/carbon composites

2009, 23(01): 28-32. doi: 10.1016/S1872-5805(08)60033-5

Abstract(2196)

PDF(1375)

Abstract:
Microwave assisted chemical vapor infiltration for the rapid fabrication of carbon/carbon (C/C) composites was investigated at 1 000-1 150 °C for different times using carbon felts as substrates and methane as carbon precursor. The temperature and density distribution in the felts were measured and the densification kinetics were investigated. It is found that the highest density of the C/C composite prepared by this method is 1.84 g/cm³ with a densification rate of 0.063 g·cm⁻³·h^-1. The mechanism of the effective and rapid densification is accounted for by a densification from the inside to the outside of the felts under an inverted temperature gradient, an increase of the available active sites for carbon deposition, an increase of collision probability between hydrocarbon species and carbon fibers, and a catalytic effect of microwaves for the pyrolysis of methane.

Large-scale production of multi-walled carbon nanotubes by low-cost spray pyrolysis of hexane

Z.Sadeghian

2009, 23(01): 33-38.

Abstract(3020)

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Abstract:
Multi-walled carbon nanotubes (MWCNTs) were prepared by spray pyrolysis, using hexane as a carbon source and ferrocene as a catalyst precursor, followed by purification with acid leaching and air oxidation. The as-grown and purified MWCNTs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, thermogravimetry, and Raman spectroscopy. The sublimation temperature of ferrocene, the ferrocene concentration in hexane, pyrolysis temperature and time, and the flow rate of hexane and H₂ were optimized to obtain MWCNTs with a high quality and a high yield. The MWCNTs have a typical sausage-like structure and their lengths are more than several tens of micrometers. The inner and outer diameters of the MWCNTs were in the range of 15-45 and 25-70 nm, respectively. The purity and yield of the purified MWCNTs were more than 95% and 70% mass fraction, respectively.

Carbon nanotubes synthesized by mechanothermal method

S. A. Manafi, M. H. Amin, M. R. Rahimipour, E. Salahi| A. Kazemzadeh

2009, 23(01): 39-44. doi: 10.1016/S1872-5805(08)60035-9

Abstract(2154)

PDF(1402)

Abstract:
A mechanothermal method is one of the methods used for the large scale production of carbon nanotubes (CNTs). The flake graphite was milled under argon atmosphere to nanometer sized carbon in amorphous state, and was then annealed at high temperature(1 350-1 380℃) to yield CNTs. The milled graphites and CNTs were characterized by XRD, SEM, FE-TEM, HRTEM, and Raman spectroscopy. It is found that the CNTs have a length of several millimeters and a diameter of 30-70 nm with different morphologies. The spring-like MWCNTs have a high aspect ratio (~1000) and a high crystallinity (I_D/I_G~0.03).

Effect of different oxide additives on the properties of a SiC coating on carbon/carbon composites

SHI Xiao-hong

2009, 23(01): 45-49.

Abstract(2479)

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Abstract:
Double-layer SiC-based coatings on carbon/carbon composites were prepared by a wrapping cementation method with different oxides (MgO, Al₂O₃ or B₂O₃) as additives to the inner layer. The phase morphologies and antioxidation properties of the SiC coated carbon/carbon composites were investigated by SEM, EDS and XRD. Results show that the SiC coating with B₂O₃as an additive to the inner layer is more compact than those with MgO or Al₂O₃ as the additive. Different phases exist in the three different inner layer SiC coatings. The double-layer SiC coating modified by B₂O₃ is dense and uniform with few flaws and holes, and can protect carbon/carbon composites from oxidation at 1 500℃ for 200 h in air.

A eutectic effect in the formation of coal based mesophase pitch

CHENG Xiang-lin

2009, 23(01): 50-54.

Abstract(2295)

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Abstract:
The toluene soluble part of coal tar pitch (TS) was co-carbonized with waste polystyrene (WPS) to produce mesophase pitch. Results showed that the properties of the mesophase were improved greatly due to the eutectic effect. The solubilities of the TS mesophase pitch and TS-WPS mesophase pitch were 10 and 52 wt. % respectively. The anisotropic volume fractions of the TS mesophase pitch and TS-WPS mesophase pitch were 65% (coarse mosaic texture) and 100% (flow domain texture) respectively. Apparent viscosities showed that the mesophase pitch was changed from thixotropic to unthixotropic by adding WPS to TS. FT-IR and ¹H-NMR spectroscopy showed that an alkylation reaction took place accompanied by an increase of methylene groups when WPS was added to TS. The increase of alkyl groups led to an assembly of mesogen molecules, resulting in a eutectic effect.

Preparation of polystyrene-based activated carbon spheres and their adsorption of dibenzothiophene

2009, 23(01): 55-60. doi: 10.1016/S1872-5805(08)60036-0

Abstract(2026)

PDF(1678)

Abstract:
Polystyrene-based activated carbon spheres (PACS) were prepared by steam activation and their adsorption performance to a sulfur-containing dibenzothiophene (DBT) was studied. The textural structure of PACS was characterized by scanning electron microscopy, N₂ adsorption, thermal gravimetric, and aqueous adsorption. Results showed that PACS with BET surface areas up to 979-1672 m²/g were obtained. The BET surface areas and pore volumes increased with activation time and steam flow rate except for the volume of narrow micropores (< 0.7 nm). The maximum adsorption capacity of PACS to DBT was 109.36 mg/g and the adsorption capacity was related to the volume of narrow micropores, independent of surface area and total pore volume. Irreversible adsorption existed between DBT and PACS. The larger the volume of the narrow micropores, the higher the desorption temperature and the larger the amount of sulfur retained after heating.

Bubble growth in the preparation of mesophase-pitch-based carbon foams

WANG Mei-xian

2009, 23(01): 61-66. doi: 10.1016/S1872-5805(08)60037-2

Abstract(2345)

PDF(1305)

Abstract:
A synthetic mesophase pitch from naphthalene was used as a precursor to prepare carbon foams under different temperatures in order to study the bubble growth process and the effect of temperature on the bubble shape during the formation of carbon foams. Scanning electron microscopy and optical microscopy were used to analyze the microstructure of the as-prepared foams. Results show that the bubble size increases from 500µm to 800µm when the temperature increases from 480℃ to 540℃. The initial bubbles are not uniformly dispersed in the molten pitch, but start to grow at the upper section of the pitch. The cross-section bubble shape in the direction of gravitational forcey is elliptical but perpendicular to the direction it is circular. The non-spherical shape of the bubble is closely related to the bulk density of the mesophase-pitch based carbon foams, and there is a bulk density gradient in the Z direction of the as-prepared foam.

The gelation mechanism of carbon aerogel spheres

LIU Ning|

2009, 23(01): 67-72.

Abstract(2480)

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Abstract:
Carbon aerogel (CA) spheres were prepared by an inverse phase suspension polymerization of resorcinol and formaldehyde (RF) monomers with hexadecyltrimethylammonium bromide as catalyst. The gelation mechanism of RF gel was investigated by analyzing the changes of viscosity, pH, temperature and the UV spectra of the as-formed sol. Results indicate that the gelation of resorcinol and formaldehyde is a condensation polymerization, which can be divided into four stages including linear condensation, cross-linking, growth of colloidal particles and macroscopic gelation.

The dispersion of SWCNT bundles on interaction with p-Terphenyl

Theresa G. Hedderman, Anika S. Mostaert, Anne E. Shanahan, Hugh J. Byrne

2009, 23(01): 73-82. doi: 10.1016/S1872-5805(08)60038-4

Abstract(1847)

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Abstract:
The interaction and dispersion of single-walled carbon nanotube (SWCNT) bundles were investigated . SWCNTs were produced by arc discharge and by the high pressure decomposition of carbon monoxide (HiPco method), in the presence of the molecule p-terphenyl. The dispersion of SWCNT bundles and their interaction with p-terphenyl in their as-produced state and after purification were compared. A number of spectroscopic and microscopic techniques were used to probe the SWCNTs and their interaction with p-terphenyl. X-ray energy dispersive analysis was used to give an elemental analysis of the SWCNT samples before and after purification. Fluorescence and atomic force microscopy are used as techniques to assess the degree of interaction and dispersion of the SWCNT bundles. Results show that the extent of bundle dispersion and the degree of interaction with p-terphenyl is related to the purity of the SWCNTs

Preparation and characterization of pitch-based carbon fibers

Arshad Hussain Wazir, Lutfullah Kakakhel

2009, 23(01): 83-88. doi: 10.1016/S1872-5805(08)60039-6

Abstract(2121)

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Abstract:
A petroleum pitch was heated at 420 ^oC for 7 h in nitrogen to prepare a carbon fiber precursor with a softening point of 295^oC. The precursor was successfully melt-spun into fibers through a circular nozzle of a monofilament spinning apparatus, and these were then stabilized at 320^oC in air and finally carbonized at 1 000^oC in nitrogen to produce carbon fibers. SEM, TGA, FT-IR, and XRD were performed to characterize the petroleum pitch, the precursor, the as-spun fibers, the stabilized fibers, and the carbon fibers. It is found that the precursor contains 70.5% mass fraction of mesophase that is aligned upon spinning, and aliphatic side chains that are beneficial to spinning. The carbon fibers have a radial core structure with a linear and bent type anisotropic texture. The maximum tensile strength of the carbon fiber is 650 MPa.

Effect of surface treatments of short carbon fibers on the properties of pitch-based C/C composites

GUO Ling-jun

2009, 23(01): 89-92.

Abstract(3969)

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Abstract:
C/C composites were fabricated in air using mold pressing and semi-carbonization shaping technology. The effects of surface treatment methods for short carbon fibers on the density and mechanical properties of the C/C composites were investigated by an electronic universal testing machine and a scanning electron microscope. Results showed that the compressive strength of the as-fabricated C/C composites increased with an enhancement in intensity of surface treatment for short carbon fibers. The compressive strength of the C/C composites with surface-treated carbon fibers was increased by 138.5％ compared with that of the C/C composites without surface treatment.

The influence of nickel nitrate on the structure of mesoporous carbon prepared by a template method

TANG Zhi-hong, SONG Yan

2009, 23(01): 93-96.

Abstract(2444)

PDF(1221)

Abstract:
Mesoporous carbons (MCs) were synthesized using thermosetting phenol resin as carbon precursor, commercial nanometer sized silica dioxide particles as template and nickel nitrate as additive. The pore structure as well as the crystalline structure of the as-prepared carbons before and after the addition of nickel nitrate was investigated by nitrogen adsorption and X-ray diffraction. Results indicated that the addition of an appropriate amount of nickel nitrate not only increased the BET specific surface area, but also led to the formation of graphite crystallite. At the same time, bimodal pores with the size of about 4nm and 10nm were developed by adjusting the content of nickel nitrate.

2009 Vol. 23, No. 01

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