2012 Vol. 27, No. 2

Deposition model and microstructure of low temperature pyrocarbon produced by chemical vapor deposition
LI Ke-zhi, HE Yong-gang, LI He-jun, WEI Jian-feng| ZHANG Lei-lei, LI Shu-ping
2012, 27(2): 81-86.
Abstract(1514) PDF(1422)
Abstract:
Low temperature pyrocarbon (PyC) was prepared by chemical vapor deposition. The microstructure of the deposited PyC was investigated by scanning and transmission electron microscopy with selected area electron diffraction. Results show that the PyC is composed of spherical carbon particles less than 2 μm in diameter. The center of the particles is carbon black, whereas the outer layer is medium-textured PyC. The deposition of the PyC includes four steps: formation of carbon black, growth of the outer layer on the carbon black, deposition of PyC on the surface of carbon particles and aggregation of carbon particles.
Synthesis of 3D hierarchical porous carbon as an electrode material for electric double layer capacitors
JIN Shuang-ling, DENG Hong-gui, ZHAN Liang, QIAO Wen-ming, LING Li-cheng
2012, 27(2): 87-92. doi: 10.1016/S1872-5805(12)60005-5
Abstract(1823) PDF(1423)
Abstract:
A green and efficient method is presented to synthesize 3D hierarchical porous carbon from a metal organic framework (MOF) formed by 1,4-benzenedicarboxylic acid and zinc nitrate hexahydrate using glucose as the carbon precursor. Glucose was infiltrated into the external surface and/or voids of the cubic MOF, then polymerized and carbonized to form porous carbon. In the meantime, MOF was decomposed into ZnO, which was further reduced by carbon (or CO) into Zn that evaporated during carbonization. The morphology and pore characteristics of the products can be adjusted by changing the reaction time. When the synthesized porous carbon was used as the electrode material for electric double layer capacitors, it exhibited a high initial specific capacitance of 175 F · g-1 at 0.6 A · g-1 and a high capacitance retention of 94.2% at 12 A · g-1 in 1 mol/L NEt4BF4/propylene carbonate electrolyte.
Preparation and magnetic properties of Fe/C composite powders
WANG Tong-hua, WANG Feng-xia, QU Xin-chun
2012, 27(2): 93-99.
Abstract(1704) PDF(1345)
Abstract:
Fe/C composite magnetic powders were prepared by a sol-gel method from aqueous-mesophase pitch (AMP) and ferric chloride. The AMP was prepared by the oxidation of coal tar pitch with a mixture of concentrated sulfuric acid and nitric acid (7:3v/v), to which ferric chloride and ammonia were added to form aqueous Fe/C based gels. The gels were displaced by ethanol, dried at ambient temperature and pressure, and carbonized at 900℃ to obtain the Fe/C magnetic powders. The powders were characterized by FT-IR, XRD, TG and TEM. Results show that primary particles in the powders have an ellipsoidal shape with a uniform particle size about 5nm, which are aggregated into secondary particles with a size about 20-30nm. The carbon has a turbostratic structure and the Fe exists in the form of α-Fe、Fe2O3 and Fe3C. The powders are soft magnetic materials with a saturation magnetization increasing with Fe content.
Electromagnetic interference shielding of single-wall carbon nanotube buckypaper/epoxy composites
LIU Gang, MA Wen-jun, AN Xue-feng, XIE Si-shen, YI Xiao-su
2012, 27(2): 100-104.
Abstract(1683) PDF(1183)
Abstract:
Single-wall carbon nanotube (SWCNT) buckypaper/epoxy composites were prepared and their electromagnetic interference (EMI) shielding was investigated. The EMI shielding increased with the thickness of the SWCNT buckypaper. The buckypaper is a large-area freestanding preform that can be easily infiltrated by epoxy, without the dispersion problem associated with a powder conductive filler. At a low content of SWCNTs, the composite exhibited relatively high EMI shielding in the low frequency region.
C/SiC/Si-Mo-Cr multilayer coating for carbon/carbon composites for oxidation protection
ZHANG Yu-lei, LI He-jun, LI Ke-zhi, FEI Jie, ZENG Xie-rong
2012, 27(2): 105-110. doi: 10.1016/S1872-5805(12)60006-7
Abstract(2013) PDF(1344)
Abstract:
To improve the oxidation resistance of carbon/carbon (C/C) composites at high temperature, the C/C composites were first slurry-coated by carbon, then pack cemented by mixtures of Si and graphite powder (60-80∶10-25 wt/wt), followed by heat treatment to form C/C composites coated with a C/SiC layer, and finally a Si-Mo-Cr oxidation protective coating was prepared on the surface of the these composites by pack cementation. Scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy were used to characterize the compositions and microstructure of the coating. The oxidation behavior of the coated C/C composites at 1 873 and 1 973 K in air was investigated. The coating showed excellent oxidation resistance at 1 873 K due to the formation of a glassy layer of SiO2 and Cr2O3 during the oxidation test, which could effectively protect C/C composites from oxidation for 135 h. The coating failed after oxidation for 30 h at 1973 K because the protective glass layer was disrupted.
Preparation and magnetic properties of multiwalled carbon nanotubes decorated by Fe3 O4 nanoparticles
FAN Xiu-juan, LI Xin
2012, 27(2): 111-116. doi: 10.1016/S1872-5805(12)60007-9
Abstract(1635) PDF(1434)
Abstract:
Iron oxide (Fe3 O4) nanoparticles with average sizes of 6 and 10nm were synthesized by a chemical co-precipitation method from mixtures of FeCl2 · 4H2O and FeCl3 · 6H2O. They were ultrasonicated with HNO3-oxidized MWCNTs in a solution (water/ethanol=1∶1v/v) to carry out the decoration. The structure and properties of as-obtained Fe3 O4/MWCNT composites were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometry, X-ray diffraction and thermal gravimetry. Results showed that the Fe3 O4 mass fraction in the composites were 26.6 and 29.3% for particle sizes of 6 and 10nm, and their saturation magnetizations were 16.5 and 7.5emu · g-1 respectively.
The tunable electrical conductivity of a MWCNT-reduced graphene oxide hybrid film
LI Yong-feng, | LIU Yan-zhen, YANG Yong-gang, WANG Mao-zhang, WEN Yue-fang
2012, 27(2): 117-122.
Abstract(1950) PDF(1177)
Abstract:
Graphene oxide (GO) aqueous colloids mixed with different amounts of multi-walled carbon nanotubes (MWCNTs) were dispersed by ultrasonication to form a stable and homogeneous MWCNT-GO suspension. MWCNT-reduced graphene oxide (MWCNT-RGO) hybrid films were obtained by microfiltration, followed by heat treatment at 200℃ for 1h in a vacuum oven to remove most of oxygen-containing functional groups. Results show that the MWCNT-GO hybrid films exhibit a uniformly-layered "sandwich" structure, forming a 3D conductive network. The electrical conductivity of the MWCNT-RGO hybrid films can be tuned by the amount of MWCNTs present and heat treatment conditions. The electrical conductivities of the hybrid films before and after the heat treatment all increase with the MWCNT content. The heat treatment increases the electrical conductivity of the hybrid film with 50% MWCNTs from 1120 to 5380S/m.
Synthesis and characterization of graphitic carbon with hollow structuresJIN
JIN Quan, XIE Chun-lin, WU Yong-jian, LIU Ying-liang
2012, 27(2): 123-128. doi: 10.1016/S1872-5805(12)60008-0
Abstract(1560) PDF(1165)
Abstract:
Graphitic carbon with a hollow structure (GHS) was hydrothermally prepared at 600℃ by a one-pot method by the pyrolysis of ethanol, with cobalt acetate as catalyst. The characteristics of the samples were investigated by X-ray diffraction, scanning and transmission electron microscropy and Raman spectroscopy. Results show that as-synthesized samples had hollow structures with high graphitization degree. A possible mechanism for GHS formation by the method is proposed.

The electrochemical performance of porous carbon nanofibers produced by electrospinning
LIU Shuang, SONG Yan, MA Chang, | SHI Jing-li| GUO Quan-gui| LIU Lang
2012, 27(2): 129-134.
Abstract(1740) PDF(1576)
Abstract:
Porous carbon nanofibers were prepared by electrospinning of mixed solutions of polyvinylalcohol/phenol formaldehyde and polyvinylalcohol/phenol formaldehyde/potassium carbonate, followed by stabilization and carbonization. The microstructure of the samples was studied by SEM and N2 adsorption/desorption. The electrochemical performance of these porous carbon nanofibers as electrodes of electrical double layer capacitors was investigated by cyclic voltammetry and constant current charge/discharge cycling. Results showed that the BET surface areas of as-prepared porous carbon nanofibers with and without potassium carbonate were 668 and 564 m2 · g-1, and their specific capacitances were 178 and 165 F · g-1 at a current density of 0.2 A · g-1 , respectively.
Effects of the hot shearing of mesophase pitch on the thermal conductivity of the resulting carbon
WANG Lian-xing, JIN Ming-lin, ZHOU Xiao-long
2012, 27(2): 135-140.
Abstract(1704) PDF(1010)
Abstract:
Monolithic carbons were prepared by hot extrusion shearing of mesophase pitch under high pressure in a mould with decreasing diameter, followed by carbonization and graphitization. The influence of the shrinkage ratio(1∶1, 2∶1, 2.5∶1 and 3∶1) of the mould on the microstructure and thermal conductivity of the carbon monoliths was investigated by X-ray diffraction, scanning electron microscopy and polarized light microscopy. Results showed that mesophase carbon microspheres melted and re-combined to form fibrous and orientated domains along the axial direction under the hot extrusion shearing. A favorable microstructure for improving thermal conductivity of the carbon monoliths was obtained by the increase of the shrinkage ratios. With the increase of the ratio from 1∶1 to 3∶1, the thermal conductivity of the monoliths increased from 96.88 to 131.02W/(m · K) and 140.85 to 160.46W/(m · K) in the axial and radial directions, respectively.
Use of amorphous carbon-encapsulated copper nanoparticles in thermal conducting fluids
PANG Jin-shan, ZHANG Hai-ye, LI Li-ping, WU Qi-guang, LIN Jin
2012, 27(2): 141-145.
Abstract(1695) PDF(1027)
Abstract:
Carbon-encapsulated copper nanoparticles (CCNPs) were synthesized by a carbon arc discharge of a copper and carbon mixture and their oxidation resistance in oxygen, dispersion in water and thermal conductivity as fluids were investigated. Results indicated that amorphous carbon made the nanocopper particles more resistive to oxidation. The carboxyl and hydroxyl groups in the outer sphere of the carbon-encapsulated copper improve the dispersion of CCNPs in water after a chemical treatment with H2O2. The smaller the CCNP particle size, the better the thermal conductivity of the fluid.
Reconfigured structure of an expanded graphite worm
ZHAO Jin-ping, CHEN Jian, ZHANG Jing-yu, LIU Qun-qing, ZHANG Sheng-li
2012, 27(2): 146-152.
Abstract(1615) PDF(1085)
Abstract:
The surface structure of an individually-compressed expanded graphite worm was obtained by reconfiguration of a series of analysis results from SEM, AFM, XRD and metallography using a granular analyzing software. The mean grain size was 30-45μm, independent of the granularity of the starting material and the process of expansion. The particles had a perfect crystallinity with La of 3-8μm and Lc of 30-80nm, and were oriented along the plane perpendicular to the pressing direction. The larger the pressure, the better the orientation.
A high strength carbon nanofiber/honeycomb cordierite composite produced by chemical vapor deposition
WANG Yan-li, WANG Xu-jian, ZHAN Liang, QIAO Wen-ming, LIANG Xiao-yi, LING Li-che
2012, 27(2): 153-156. doi:  DOI: 10.1016/S1872-5805(12)60
Abstract(1700) PDF(1099)
Abstract:
A carbon nanofiber (CNF)/honeycomb cordierite composite with a compressive strength of 50MPa was prepared by chemical vapor deposition, using C2H4 as the carbon source and Ni-Cu alloy as the catalyst. The CNFs with a diameter of 20-30nm in the cells of the honeycomb interweave with each other to form a 5μm- thick layer. The CNF content is 25.3wt%. The Cu has remarkable effects on the particle size of the Ni-Cu alloy, which further affects the growth rate, loading level and nanostructures of the CNFs. The CNFs are not well graphitized and the insertion of the CNFs into the honeycomb can increase its compressive strength from 10 to 50MPa.
Zn microcrystal-mediated fabrication of carbon nanotube patterns
QU Jiang-ying, ZHAO Zong-bin, WANG Xu-zhen, QIU Jie-shan
2012, 27(2): 157-160.
Abstract(1406) PDF(1245)
Abstract:
Carbon nanotube (CNT) patterns have been fabricated with the assistance of Zn that possesses a low boiling point and different morphologies. Pre-patterning and post-synthesis patterning by Zn microcrystals were used to prepare the CNT patterns. The pre-patterning approach uses Zn microcrystals deposited on a SiO2 substrate as sacrificial templates for the growth of CNTs by chemical vapor deposition under a floating catalyst. The post-synthesis patterning was carried out by Zn microcrystal deposition onto pre-formed CNT films. The CNT patterns were obtained by both methods after Zn was evaporated despite their differences in process conditions. These novel approaches may become alternative routes for the assembly of CNT-based structures in a simple and controllable way.