2010 Vol. 25, No. 04

  Previous Issue | Next Issue 
Dissolution of poly( vinyl alcohol)-modified carbon nanotubes in a buffer solution
ZHANG Fa-ming, CHANG Jiang, BURKEL Eberhard
2010, 25(04): 241-243. doi: 10.1016/S1872-5805(09)60030-5
Abstract(3239) PDF(1605)
Abstract:
Multiwalled carbon nanotubes (MWCNTs) were modified with a water-soluble poly( vinyl alcohol) (PVA) polymer (MWCNTs-PVA). The dissolution of the MWCNTs-PVA in Tris-HCl buffer solution was carried out in a shaking water bath by a soaking method. The microstructural changes of the MWCNTs-PVA during soaking was investigated using Fourier transform-infrared spectroscopy, differential scanning calorimetry, transmission electron microscopy, and X-ray diffraction. It is found that part of the MWCNTs-PVA was dissociated into amorphous carbonaceous debris, but most of tubular structures were retained after 21d of soaking. The dissolution process revealed that the C—C bonds of the MWCNTsPVA were broken-down with the generation of carbonaceous debris and residual carbon nanotube layers, and the latter can be further dissociated into amorphous carbonaceous debris. A possible dissolution mechanism of the MWCNTs-PVA in the buffer solution was proposed and discussed. The surface modified MWCNTs have many defects and open C—C bonds on the surfaces of the CNTs. The dissolution of the PVA in the buffer solution leads to a release of carbon atoms on the outer surface of the MWCNTs. It results in a further rupture of the C—C bonds and destroys the tubular structure .
Effect of the surface chemistry of activated carbon on its electrochemical properties in electric double layer capacitors
XIE Ying-bo, QIAO Wen-ming, ZHANG Wei-yan, SUN Gang-wei, LING Li-cheng
2010, 25(04): 248-254. doi: 10.1016/S1872-5805(09)60031-7
Abstract(1964) PDF(2024)
Abstract:
Petroleum coke-based activated carbons (ACs) were modified through H2 reduction and HNO3 oxidation. Pore structures and surface chemistry of the ACs were characterized by N2 adsorption and X-ray photoelectron spectroscopy. The Brunauer-Emmett-Teller surface areas of ACs were slightly decreased after such treatment. Although surface oxygen groups (especially carbonyl groups) were generated when ACs were treated by HNO3, electric double layer capacitance, internal resistance (IR), equivalent series resistance (ESR), and selfdischarge of an AC electrode exhibited a remarkable increase. At the same time, the number of surface oxygen groups of ACs modified by H2 remarkably decreased and the capacitance was markedly increased , while IR, ESR, and self-discharge decreased. This reduction modification of ACs is beneficial in improving electrochemical properties and probably provides suitable pores for electrolyte to penetrate electrochemically.
Production and structure of exfoliated graphite/coke composites modified by ZrO2 nanoparticles
Ivan M. Afanasov, Gustaaf Van Tendeloo, Andrei T. Matveev
2010, 25(04): 255-260. doi: 10.1016/S1872-5805(09)60032-9
Abstract(2243) PDF(1467)
Abstract:
Exfoliated graphite/coke composites modified by ZrO2 nanoparticles were produced using two different techniques and characterized by means of X-ray diffraction, scanning and transmission electron microscopy. In the first, low-density exfoliated graphite/coke blocks were dipped repeatedly and alternately in ZrO(NO3)2 and NH4OH solutions and subsequently heat treated at 1200℃ in nitrogen to deposit thin layers of ZrO2 nanoparticles on the free surfaces of the carbon matrix. In the second, a mixture of expandable graphite, phenol-formaldehyde resin powder, and ZrOC2O4-modified fibrous cellulose in a sealed container was submitted to thermal shock at 900℃ followed by heat treatment at 1200℃ in nitrogen to obtain the modified composites. The ZrO2 nanoparticles formed in the second technique were incorporated into the composites in three length scales: 6-30nm-isolated nanoparticles and small blobs, 200-1000nm-lengthy dendrite-like structures, and thin layer adhering to the surface of the 1-40μm long cellulose carbon fibers.
Molecular dynamics simulation of a single graphene sheet under tension
HAN Tong-wei | HE Peng-fei| WANG Jian|WU Ai-hui
2010, 25(04): 261-266.
Abstract(2541) PDF(1839)
Abstract:
The tensile mechanical properties of zigzag and armchair single graphene sheets were investigated by molecular dynamics simulation using the Tersoff bond-order interatomic potential. The tensile stressstrain curves of the sheets were obtained and analyzed. The deformation mechanism of the sheets under tension was also studied. Results show that the sheets are not perfectly flat after relaxation, but exhibit microscopic corrugations such as waves and ripples. The Young’ s modulus of the zigzag and armchair sheets are 1031.36GPa and 1058.42GPa, respectively, which are in very good agreement with results reported in the literature. It is also found that the defects are formed at the edges of graphene sheets under tension. These are induced by the transformation of the hexagonal carbon rings into pentagons. With a further increase in strain and number of defects, the graphene sheets finally fail through bond breaking.
Synthesis of single-wall and cup-stacked carbon nanotubes by methane decomposition using constrained thermal plasma jet
WANG Jian-cheng, ZHU Zi-ping, CHANG Li-ping, BAO Wei-ren
2010, 25(04): 267-272.
Abstract(2583) PDF(1270)
Abstract:
Single-wall and cup-stacked carbon nanotubes (CS-CNTs) were synthesized by a constrained thermal plasma jet at atmospheric pressure using methane as carbon source and Fe2O3 as catalyst. The plasma jet flowed through a graphite cylinder directly into a graphite bowl where its flow was interrupted and carbon was deposited. Carbon was also deposited on a ceramic filter tube behind the bowl. Deposits at the two locations were characterized by scanning and transmission electron microscopy and differential thermal analysis. The carbon on the filter tube consisted of defect-free single-walled CNTs (SWCNTs), while that in the graphite bowl consisted of high-purity CS-CNTs. Gas flow has a significant influence in the structure of the products. Highly crystalline SWCNTs were formed under laminar gas flow and the CS-CNTs were produced under turbulent gas flow. Diameter and purity of the CS-CNTs increases gradually toward the inner cavity of the graphite bowl due to a temperature increase.
Preparation and performance of carbon composite membranes with ordered mesopores
JIANG Hua-wei, WANG Tong-hua, LI Lin, LIU Ying, SONG Xue-kai
2010, 25(04): 273-278.
Abstract(2179) PDF(1464)
Abstract:
An ordered mesoporous carbon (OMC) was synthesized by the soft templating method using resorcinolformaldehyde as carbon source, and Pluronic F127 and F123 as templates. The carbon composite membrane was prepared by coating the precursors under optimum conditions on the outer surface of a tubular carbon membrane produced from blended coals, followed by carbonization to remove the template and convert the precursors to carbon. The influence of synthesis conditions such as kinds and quantities of the templates and catalysts on the structure and performance of the OMC were investigated by TEM, SEM and XRD. Results indicated that an optimized OMC with a well-ordered pore structure and high permeation flux was synthesized under catalysis of HCl, F127/resorcinol molar ratio of 0.0081 and reaction temperature at 30℃. The largest pore size of carbon membranes decreased from 0.530μm for the tubular carbon membrane to 0.299μm for the composite membrane. The N2 permeability of the composite membrane reached 1.18 · 10-8m3 · m-2 · s-1 · Pa-1, which was four times that of the conventional soft coal-based carbon membrane.
Anti-oxidation property of a multi-layer coating for carbon/carbon composites in a wind tunnel at 1500℃
FU Qian-gang, XUE Hui, LI He-jun, LI Ke-zhi, SHI Xiao-hong, ZHAO Hua
2010, 25(04): 285-290. doi: 10.1016/S1872-5805(09)60033-0
Abstract(2323) PDF(1488)
Abstract:
To protect carbon/carbon (C/C) composites against oxidation at 1500℃ in a wind tunnel, a multi-layer coating was prepared on them by a combination of pack cementation, chemical vapor deposition and slurry coating. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to analyze the phase, microstructure and elemental distribution of the coating. Results show that a three-layer structure is formed including a multi-phase MoSi2-SiC-Si inner layer, a SiC middle layer and a borosilicate glass outer layer with thicknesses of about 80, 20 and 80μm, respectively. The three-layer coating can protect the C/C composites from failure at 1500℃ for 53 h in a wind tunnel. The cracking of the coating by thermal shock and gas-fired impact is the main cause for the failure of the coating.
Preparation of high-performance activated carbons for electric double layer capacitors by KOH activation of mesophase pitches
WANG Mei-xian, WANG Cheng-yang, CHEN Ming-ming, WANG Yan-su, SHI Zhi-qiang
2010, 25(04): 285-290. doi: 10.1016/S1872-5805(09)60034-2
Abstract(1912) PDF(1728)
Abstract:
Two kinds of mesophase pitches with different softening points were prepared at different soaking times and directly activated with KOH to study the effects of the softening point on the textural characteristics of the resulting activated carbons and their behavior as electrodes in capacitors. Results show that the softening points of the two mesophase pitches are 280 and 330°C, and the specific surface areas of the activated carbons are 1337 and 1300m2 · g-1, respectively. The specific capacitance of the higher softening point mesophase pitch-derived carbon is higher (255.6F · g-1) than that of the lower softening point mesophase pitch-derived carbon (190.8F · g-1) at the same current density. Cyclic voltammograms show that the lower softening point mesophase pitchderived carbon exhibits better rectangular-shaped I-V curves. The softening points of the mesophase pitches prepared from even the same precursor can significantly affect the electrochemical performance of the resulting activated carbons.
Functionization of carbon nanotubes by plasma and their compositing with polyaniline
ZHANG Jie, YANG Jun-he| JIA Run-ping, WANG Xia, HUANG Jie
2010, 25(04): 291-296.
Abstract(2316) PDF(1425)
Abstract:
Carbon nanotubes (CNTs) were modified by Ar plasma followed by O2 etching in a plasma assisted chemical vapor deposition apparatus. The modified CNTs were polymerized with aniline in a HCl aqueous solution to produce CNT/polyaniline composites. The CNTs modified by the plasma have a higher conductivity (2.86S/cm) than those modified by acid oxidation (0.936S/cm). The optimum plasma parameters were power (50W), system pressure (0.08torr), treatment time (5min), temperature (110℃), distance between two electrodes (5cm) and current of magnetic loop (0.8A). SEM results revealed that the smooth surface of the CNTs became rough after the plasma modification and the diameters increased by about 80 nm. FTIR, Raman and XRD all revealed the presence of polyaniline on CNT surfaces.
Pyrocarbon transition layer and microstructure of mesophase pitch based carbon/carbon fiber composites
LIU Hao, LI Ke-zhi, LI He-jun, LU Jin-hua, ZHAI Yan-qiang
2010, 25(04): 297-302.
Abstract(2298) PDF(1566)
Abstract:
The microstructure of 2D PAN carbon fiber-reinforced mesophase pitchbased matrix carbon/carbon(C/C) composites having a pyrocarbon transition layer was studied by polarized light microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PLM results indicate that the matrix consisted of pyrocarbon and mesophase pitch carbon, whose structure is anisotropic. TEM and SEM results show that multilayer interfaces are formed inside the composite. The carbon fiber-pyrocarbon interface is generally continuous, with a high degree of perfection and graphitic crystallites oriented parallel to the interface. The interface between the mesophase pitch carbon and the pyrocarbon is amorphous and is micro-fissured. The size and the degree of orientation of the graphitic crystallites gradually increase and the alignment of lattice fringes is gradually ordered from carbon fibers, to pyrocarbon to mesophase pitch carbon. The mesophase pitch matrix is lamellar carbon oriented parallel to the fiber axis. Numerous micro-cracks parallel to the carbon fiber axis are formed within the partially bonded interface and the matrix.
Effect of pre-oxidation on microcracks in graphite foams
LI Juan, WANG Can, ZHANG Cui-cui, ZHAN Liang, QIAO Wen-ming, LIANG Xiao-yi
2010, 25(04): 303-307.
Abstract(2049) PDF(1306)
Abstract:
The formation mechanisms of microcracks in graphite foams were investigated by varying the pre-oxidation temperature of the precursor mesophase pitch. Results indicated that after the mesophase pitch was preoxidized, its quinoline-insoluble component became the dominant fraction, which leads to a decrease in heat stress gradient and as a result, a decrease in the amount, length and width of microcracks.
Stability of multi-wall carbon nanotubes in air
ZHU Shuang-mei| LI Jun-qing| PANG Jin-hui, ZHANG Hua-shun, LIANG Er-jun
2010, 25(04): 308-312.
Abstract(2434) PDF(1310)
Abstract:
Multi-walled carbon nanotubes (MWCNTs) have been synthesized by chemical vapor deposition using xylenes as carbon precursors and ferrocene as a catalyst. The stability of the purified MWCNTs was investigated, their properties were characterized by SEM and volume electric resistivity. Results showed that MWCNTs exposed to air under ambient temperature will be slowly oxidized and shortened. The extent of oxidation increases with time, and MWCNTs were almost completely transformed into amorphous carbon after 15 d. The volume electric resistivity also varied as a result of oxidation. These results indicate that as-prepared MWCNTs should be kept in a well-closed container to prevent them from oxidization.
Influence of filler type on the performance and microstructure of a carbon/graphite material
LIU Zhan-jun, GUO Quan-gui, LIU Lang, SHI Jing-li, ZHAI Geng-tai
2010, 25(04): 313-316. doi: 10.1016/S1872-5805(09)60035-4
Abstract(2014) PDF(1517)
Abstract:
Carbon/graphite material was prepared by subjecting a mixture of coal-tar pitch binder and a relevant filler to uniaxial compression at 150MPa for 10min, followed by calcination at 1300℃ for 1 h, and graphitization at 2300℃ in an induction furnace. Four fillers, carbon black (CB), petroleum-coke powder, needlecoke powder, and natural graphite powder (NG), were used. The effect of filler type on the performance and microstructure of the material was investigated. Results reveal that the CB-based material has excellent flexural and compressive strength, with the highest values of 88.0 and 173.2MPa, respectively, but poor thermal and electrical conductivity. The thermal conductivity of the NGbased material has the highest value of 278W/m · K, but the flexural and compressive strength are limited to 51.1 and 90.2MPa, respectively. Microstructural analysis showed that the NG-based material has the largest crystallite size, as well as the most perfect orientation of graphite layers.
Effect of hydrogen plasma treatment on the field emission of diamond-like films deposited by high power excimer laser ablation
ZHAO Li-xin, PENG Hong-yan, CHEN Yu-qiang, LUO Yu-jie, CHEN Bao-ling
2010, 25(04): 317-320.
Abstract(2152) PDF(1246)
Abstract:
The effect of hydrogen plasma treatment on the electron field emission of diamond-like carbon films (DLCs) deposited by high frequency and high power pulsed XeCl excimer laser ablation of pyrolytic graphite targets at room temperature was studied. Results indicated that the films exhibited improved electron emission, with the threshold field of the films decreased from 26 to 19 V/μm. Meanwhile, the current density increased considerably after the treatment. Two factors were responsible for the results. One was that the graphite-rich DLC film surface formed with low energy carbon atoms or clusters during growth process was removed by the hydrogen plasma with the formation of a new surface comprised of high density sp3 bonded carbons, which exhibited a low electron affinity and good field emission . The other was that the dangling bonds of the carbon atoms on the film surface were saturated with H-atoms after the treatment, which further decreased the electron affinity.

Address： 27 Taoyuan South Road, Yingze District, Taiyuan City, Shanxi Province, ChinaPostCode：030001

Phone/Fax：0351-2025254

Email： tcl@sxicc.ac.cn

Copyright © 2021 Editorial Office of New Carbon Materials. All Rights Reserved This system consists of Beijing Renhe Information Technology Co. Ltd   百度统计