2012 Vol. 27, No. 1

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A review of methods for the separation of metallic- and semiconducting single-walled carbon nanotubes
QIU Han-xun, ZHENG Yi-xin, YANG Jun-he
2012, 27(1): 1-11.
Abstract(1995) PDF(1604)
Abstract:
Single-walled carbon nanotubes (SWCNTs) continue to fascinate the scientific community. However, any commercially available SWCNTs obtained directly from the viable synthesis procedures are mixtures of semiconducting and metallic species. That shortcoming of present technologies hinders further studies and limits the scalable applications for a series of promising SWCNT-based electronics. Separation of the two species is one way to solve the present dilemma. The methods and techniques used for the enrichment of semiconducting- and metallic-SWCNTs are reviewed. Their advantages and disadvantages are compared and commented on. We believe that the research emphasis on SWCNT separation will continue to pursue a technique with operational simplicity, high efficiency, low-cost that is easily scalable.
Improvement of the oxidation stability and the mechanical properties of flexible graphite foil by
boron oxide impregnation
D.V. Savchenko, A.A.Serdan, V.A.Morozov, G.Van Tendeloo, S.G.Ionov
2012, 27(1): 12-18. doi: 10.1016/S1872-5805(12)60001-8
Abstract(1577) PDF(1170)
Abstract:
Flexible graphite foil produced by rolling expanded graphite impregnated with boron oxide was analyzed by laser mass spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and thermogravimetry. It was shown that the modification of the graphite foil by boron oxide increases the onset temperature of oxidation by ~150℃. Impregnation of less than 2mass% boron oxide also increased the tensile strength of the materials. The observed improvement was attributed to the blocking of active sites by boron oxide, which is probably chemically bonded to the edges of graphene sheets in expanded graphite particles.
Chemical modification of multiwalled carbon nanotubes by polyethylene-grafted maleic anhydride
WANG Guo-jian, |　JIN Ji-qiong
2012, 27(1): 19-26.
Abstract(1874) PDF(1349)
Abstract:
Multiwalled carbon nanotubes (MWCNTs) were oxidized by an acid mixture (concentrated H2SO4∶HNO3 =3∶1v/v) to form carboxyl groups, which were then reacted with anhydride ethylene diamine by an amidation reaction to introduce amine end groups that were subsequently grafted to polyethylene/maleic anhydride copolymer (PE-g-MA) to increase the dispersion of the modified MWCNTs in a polyethylene (PE) matrix. The chemical modification of the MWCNTs was verified by FTIR, XPS and Raman spectroscopy. The modified MWCNT/PE composites exhibited an electrical percolation threshold at 0.67 vol% MWCNTs. The volume resistivities of the modified MWCNT/PE composites decreased from 1016 to 105Ω · m with increasing MWCNT content from 0.1 to 1.2 vol%
Thermophysical properties of high-density graphite foams and their paraffin composites
Jin-liang, GUO Quan-gui, ZHONG Ya-juan, GAO Xiao-qing, FENG Zhi-hai, FAN Z
2012, 27(1): 27-34. doi: DOI: 10.1016/S1872-5805(12)600
Abstract(1667) PDF(1353)
Abstract:
High-density graphite foams (GFs) were prepared from mesophase pitch with or without mesocarbon microbeads at different foaming temperatures and pressures, followed by carbonization and graphitization at 1273 and 2973K, respectively. In one case, pitch was repeatedly infiltrated into the graphitized foam at 573K followed by carbonization to increase its density. Paraffin was infiltrated into the GFs to form GF/paraffin composites. Factors determining the thermophysical properties of the GFs and thermal behavior of the GF/paraffin composites were investigated. The microstructure and thermophysical properties of the foams were found to be greatly influenced by the pitch fraction, foaming temperature and foaming pressure. The thermal conductivity of the foams determines the thermal behavior of the GF/paraffin composites. The thermal diffusivity of the GF/paraffin composites investigated can be increased 768 to 1588-fold compared with that of paraffin. The latent heat of the composites has an almost linear relationship with the mass fraction of paraffin in the composites. The composites are suitable candidates for passive cooling of electronics.
Synthesis of Ni/graphene sheets by an electroless Ni-plating method
HU Qing-hua, WANG Xi-tang, CHEN Hao, WANG Zhou-fu
2012, 27(1): 35-41. doi: 10.1016/S1872-5805(12)60003-1
Abstract(2289) PDF(1575)
Abstract:
Ni/graphene sheets were synthesized from graphene oxide sheets using electroless Ni-plating in a NiSO4 solution, with NaBH4 as a reducing agent. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy. Ni deposited on the surface of the reduced graphene oxide sheets had a high dispersion without aggregation, although the amount of Ni was as high as 32.9% by mass., The stacking of Ni/graphene sheets resulted in the formation of meso- and macropores. Nitrogen adsorption showed that the meso- and macropores had a slit shape and that the Brunauer-Emmett-Teller specific surface area reached 91m2/g. The average pore size calculated by the Barret-Joyner-Halenda method from desorption studies was 3.83nm, with a pore volume of 0.28cm3/g.
Synthesis of Ni/graphene sheets by an electroless Ni-plating method
ZHANG Yun-feng, LUO Rui-ying
2012, 27(1): 42-48. doi: 10.1016/S1872-5805(12)60004-3
Abstract(2122) PDF(1046)
Abstract:
Ni/graphene sheets were synthesized from graphene oxide sheets using electroless Ni-plating in a NiSO4 solution, with NaBH4 as a reducing agent. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy. Ni deposited on the surface of the reduced graphene oxide sheets had a high dispersion without aggregation, although the amount of Ni was as high as 32.9% by mass., The stacking of Ni/graphene sheets resulted in the formation of meso- and macropores. Nitrogen adsorption showed that the meso- and macropores had a slit shape and that the Brunauer-Emmett-Teller specific surface area reached 91m2/g. The average pore size calculated by the Barret-Joyner-Halenda method from desorption studies was 3.83nm, with a pore volume of 0.28cm3/g.
Effect of cycle time of in-situ polymerization of naphthalene |on the densification and performance of C/C composites
SUN Chao, ZHANG Bo, YANG Xiao-guang, XU Zheng-hui, SONG Huai-he, HUA Shuang-
2012, 27(1): 49-54.
Abstract(1768) PDF(1105)
Abstract:
A rapid densification approach for the fabrication of C/C composites was developed by in-situ polymerization of naphthalene with a Lewis acid as catalyst in two preforms of 3D braided carbon fiber/pyrocarbon composites with different densities. The effects of cycle time on the fracture morphology, bulk density, electrical resistivity and flexural strength of the C/C composites were investigated. Results showed that the bulk densities of the C/C preforms increased from 1.05 to 1.52g/cm3and from 1.68 to 1.83g/cm3, their electrical resistivity decreased from 4.44 to 1.09mΩ · cm and 0.84 to 0.28mΩ · cm, and their flexural strength increased from 26 to 95MPa and 86 to 211MPa respectively after five cycles. In-situ polymerization is a simple, effective, competitive and rapid densification approach for the fabrication of C/C composites
Preparation of high surface area, graphitic porous carbon monolith
using magnetite nanoparticles as catalyst and porogens
WANG Guang-hui, LI Wen-cui
2012, 27(1): 55-60.
Abstract(1859) PDF(1193)
Abstract:
A method to prepare monolithic porous graphitic carbon with high surface area was investigated using nanosize monodispersed magnetite particles (~10nm) as graphitization catalysts and a porogen template, and an oligomer derived from the polymerization of 2,4-dihydroxybenzoic acid with formaldehyde catalyzed by sodium carbonate as carbon source. The magnetite/oligomer composites were carbonized at 700-900℃ under a nitrogen atmosphere to generate graphitized carbon composites. Finally, monolithic porous graphitic carbon was obtained after HCl treatment to remove the iron-based particles. Results show that carbonization temperature has a great influence on the graphitization degree and the Brunauer-Emmett-Teller （BET） surface area of the resultant products. The BET surface areas decreased and the graphitization degree of the products increased with carbonization temperature from 700 to 900℃. At a low carbonization temperature of 700℃, the templating effect of the magnetite particles (as porogens) can be clearly observed. Highly graphitic carbon with a high surface area can be obtained at 800℃.
Preparation of carbon molecular sieve membranes by KOH activation for gas separation
ZHANG Xiao-yong, LIU Rui, HU Hao-quan, ZHENG Ming-dong
2012, 27(1): 61-66.
Abstract(2219) PDF(1182)
Abstract:
Carbon molecular sieve membranes were prepared by the pyrolysis of a mixture containing phenolic novolac resin and KOH. The effects of KOH on the properties of the membranes were investigated. Results showed that membranes with homogeneous pore size distributions and high gas permeation rates can be obtained by controlling the amount of KOH . Their H2 gas permeability increased from 23.68×10-10 to 28.6×10-10mol · m-2 · s-1 · Pa-1 and H2/N2 and H2/CH4 selectivity decreased from 471.3 to 147.5 and 540 to 270 respectively, while the CO2/CH4 and O2/N2 selectivity changed little with increasing KOH content in the coating solution from 0 to 4mass%.
Irradiation treatment of multiwalled carbon nanotubes and its effect on the thermal properties of their composites with epoxy resin
CHEN Ya-jun, |　YANG Chun-zhuang|　GUO Zheng-hong|　ZHANG Yan|CHENG Jie, FANG
2012, 27(1): 67-73.
Abstract(1923) PDF(1138)
Abstract:
Multi-walled carbon nanotubes (MWCNTs) were irradiated to different doses by high-energy electron beams. The structure of the irradiated MWCNTs was characterized by Fourier transform infrared spectroscopy, X-ray energy dispersion spectroscopy，Raman spectroscopy and transmission electron microscopy. MWCNT/epoxy composites were prepared by a cast-molding method. The effect of the irradiation on the properties of the composites was studied by scanning electron microscopy, thermogravimetry and dynamic mechanical analysis. Results showed that oxygen-containing groups were covalently bonded on the MWCNTs. The MWCNTs were collapsed and even broken after irradiation. The percentage of the oxygen-containing groups had a maximum of 4% at a radiation dose of 170kGy. It was found that the irradiated MWCNTs could be easily dispersed in epoxy resin. Addition of 0.5mass% MWCNTs irradiated with 170kGy to epoxy resin improved the glass transition temperature and the initial decomposition temperature by 8 and 14℃, respectively.
Performance of unidirectional carbon fibre cloth/carbon composite laminates fabricated by hot-pressing
2012, 27(1): 74-80.
Abstract(1857) PDF(1153)
Abstract:
Unidirectional carbon fibre cloth/carbon composite laminates were fabricated by hot-pressing alternating stacks of unidirectional carbon fibre cloth and uniformly-spread powder mixtures of phenolic-resin coated nature graphite flakes and pitch. The effects of the contents of carbon fibre cloth on the density, porosity, flexural strength, friction and wear properties of the composite laminates were investigated by SEM, a friction-and-wear testing machine and a universal testing machine. Results showed that the sample with the best overall performance had a mass fraction of carbon fibre cloth of 50%. This material had a flexural strength of 112.2 MPa, a density of 1.72g/cm3, a friction coefficient of 0.28, and a wear rate of 3.68×10-13m3 · N-1 · m-1. Failure behavior was pseudoplastic and there were a large number of fibre pullouts on the fracture surface. An increase of graphite content was favorable for the formation of a film during wear, which reduced the wear rate and resulted in a steady value of the coefficient of friction.

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