新型炭材料

Catalyst-free synthesis of onion-like carbon nanoparticles

M. Bystrzejewski, M.H. Rummeli, T. Gemming| H. Lange, A. Huczko

2010, 25(01): 1-8. doi: 10.1016/S1872-5805(09)60011-1

Abstract(2358)

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Abstract:
A one-step process for the synthesis of onion-like carbon nanoparticles is described. The process is based on a thermolysis of a NaN₃-C₆Cl₆ mixture. The effect of buffer gas (Ar or air) on the yield, morphology, and structure of the carbon products was investigated by electron microscopy, X-ray diffraction, and Raman spectroscopy. The products contained carbon-onions, amorphous carbon nanoparticles, and NaCl. The byproducts were completely removed using a simple purification process. The formation of onion-like nanoparticles is likely caused by a shock wave, a rapid increase of pressure, during thermolysis, which induced the coalescence of phenyl radicals.

Synthesis of carbon foams with a high compressive strength from arylacetylene

ZHANG Shu-ping, LIU Ming-xian, GAN Li-hua, WU Fang-rui, XU Zi-jie

2010, 25(01): 9-14. doi: 10.1016/S1872-5805(09)60012-3

Abstract(2159)

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Abstract:
Carbon foams with high mechanical strength were prepared by polymerization of arylacetylene using sulfuric acid as a catalyst, pentane as a blowing agent and Tween 80 as a bubble stabilizer, followed by carbonization. Through controlling the preparation conditions such as the proportion of blowing agent, the concentration and volume of the catalyst, and the amount of the bubble stabilizer, carbon foams with good porous structure, smooth ligaments, and junctions without microcracks could be fabricated. The representative carbon foam possesses a high compressive strength of 25.8 MPa and a high strength/density ratio of 43.0 MPa/(g · cm^-3), owing to a high char yield of the arylacetylene polymer, which is up to 86% after carbonization, and a good pore structure of the products.

The electromagnetic loss characteristics of SiC/C materials with a three-dimensionally connected porous structure

FANG Zhi-gang, | LI Chu-sen, SUN Jia-yan, ZHANG Hong-tao, Zhang Jin-song

2010, 25(01): 15-21.

Abstract(1887)

PDF(1346)

Abstract:
SiC/C foams and their monoliths of the same compositions, with various electrical conductivities were prepared by polymer sponge replication/carbonization and hot-press solidification/carbonization respectively. Both materials have a threedimensionally connected pore structure with the former on a macroscopic scale and the latter a microscopic scale. The electromagnetic parameters of the SiC/C foams and the monoliths versus their electric conductivities were measured at a frequency of 2 450 MHz by the TE10 resonant cavity perturbation method. Results show that when the electrical conductivities of the SiC/C foams and the monoliths increase gradually, their dielectric constants ε_r′ increase gradually and their dielectric losses tg δe exhibit a maximum. The magnetic loss tg δm of the SiC/C foams increases continually while that of the monoliths first increases quickly then decreases slowly with increasing electric conductivities. When the effective electric conductivities of the SiC/C foams and the monoliths are the same, the ε_r′ values of the SiC/C foams are about a half and the tg δe values are at least 2 times larger than those of the monoliths, while the tg δm values of the monoliths are more than 4 times those of the SiC/C foams. The SiC/C foams and the monoliths are both non-magnetic, and their magnetic losses are found to be caused by their special structures interacting with the incident electromagnetic waves. Thus it is apparent that this kind of magnetic loss is extrinsic.

Preparation of high purity graphite by an alkaline roasting-leaching method

GE Peng, WANG Hua-jun, ZHAO Jing, XIE Lin, ZHANG Qiang

2010, 25(01): 22-28.

Abstract(2075)

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Abstract:
An alkaline roasting-leaching method was used to prepare high purity graphite from flake graphite from Hubei Jinchang instead of the commonly-used alkaline-acid method. The process parameters were optimized. Results showed that the fixed carbon mass fraction achieved by this method could be as high as 99.9% under the optimal conditions while that by the alkaline-acid method was only 85.8%, indicating that the alkaline roasting-leaching method was very effective to improve the fixed carbon content of the graphite.

Pitch spheres stabilized by HNO₃oxidation and their carbonization behavior

LIU Xiao-jun, LIANG Xiao-yi, LIU Chao-jun, ZHANG Rui, ZHAN Liang, QIAO Wen-ming

2010, 25(01): 29-34. doi: 10.1016/S1872-5805(09)60013-5

Abstract(1986)

PDF(1334)

Abstract:
Pitch spheres were stabilized by HNO₃ oxidation at room temperature using HNO₃ solutions of 10, 20, 30, and 40% mass fraction. The chemical structure and morphology changes of the oxidized pitch spheres and their carbonized samples were investigated by FT-IR, XPS, elemental analysis, and SEM. Results showed that the pitch spheres oxidized by 30% HNO₃ for 12 h could be carbonized at 900 ℃ to produce carbonized spheres without any change in shape. The successful carbonization can be ascribed to the contribution of nitrogen functional groups in the form of -NO₂, which were introduced in the HNO₃ oxidation process. In the early stage of the heat treatment around 400 ℃, the transformation of -NO2 groups to amine groups occurred, which promoted the cross-linking of pitch molecules. As the pitch spheres were carbonized at 900 ℃, cyclization and aromatization reactions led to the formation of pyridine and quaternary nitrogen groups.

Gas products and carbon deposition kinetics in chemical vapor deposition from propylene

LU Cui-ying, CHENG Lai-fei, ZHANG Li-tong, ZHAO Chun-nian

2010, 25(01): 35-40. doi: 10.1016/S1872-5805(09)60014-7

Abstract(2629)

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Abstract:
Gas products and chemical vapor deposition kinetics of pyrocarbon (PyC) formed during pyrolysis of a propylene/argon mixture in the range 700-1 200 ℃ were analyzed by out-line gas chromatography coupled with mass spectrometry and by an insitu magnetic suspension balance, respectively. More than 30 components were identified. Benzene was the main product, substituting for naphthalene as the temperature increased. PyC was formed with an apparent activation energy of (137±25) kJ/mol, assumed to be controlled by the acetyleneforming reaction from 800 ℃ to 1 000 ℃. Whereas, above 1 000 ℃, the deposition behavior was representative of a combination between gas phase diffusion from the bulk flow to the solid surface and gas phase nucleation. Reaction models describing homogeneous gas phase PyC deposition reactions were derived. On the basis of these results, a reaction path scheme of PyC formation from propylene was proposed.

Evolution of microvoids in PAN-based carbon fibers

LI Deng-hua, WU Gang-ping, LU Chun-xiang, LI Yong-hong, HE Fu

2010, 25(01): 41-47.

Abstract(1981)

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Abstract:
Microvoids, formed in spinning, oxidation and carbonization during the preparation of PAN-based carbon fibers, were investigated by two-dimensional small angle X-ray scattering. Results indicated that microvoids in PAN fibers had a preferred elongation and orientation along the fiber axis with an average length of 24.3 nm, diameter of 19.2 nm and aspect ratio of around 1.27. The size of the microvoids remained almost unchanged during oxidation, while their aspect ratio increased to 1.85, possibly due to a crystalline transformation from a linear structure in PAN fibers to a heatresistant ladder structure in oxidized fibers. However, the size of the microvoids decreased dramatically to about 3.56 nm in the long axis and 2.85 nm in the short axis during carbonization. The surface fractal dimension (Ds) increased in these processes from 2.42 to 2.88 and the most severe change occurred in low-temperature carbonization, indicating that surface roughness increased during processing, and carbonization was the most important process for such a transformation

Preparation of SiCN crystals using microwave plasma CVD assisted by pulsed nitrogen ion beam sputtering

WAN Jun, MA Zhi-bin, CAO Hong, WU Zhen-hui, WANG Jian-hua

2010, 25(01): 48-52.

Abstract(1614)

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Abstract:
Crystalline silicon carbon nitrides were synthesized on quartz glass substrates by microwave plasma chemical vapor deposition, using precursors produced from a pulsed nitrogen ion beam sputtering dicyandiamide target. The effects of deposition temperature on the morphology, composition and structure of the samples were investigated by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the surface morphologies of the deposits change from well crystallized hexagonal crystals at 800 ℃ to semi-developed multi-sheet crystals at 700 ℃ and to an amorphous solid with small grains at 550 ℃. The intensity of the diffraction peaks decreases and the values of the cell parameters a and c increase with the deposition temperature. The as-prepared crystalline films are silicon carbonitride with the crystalline structure of Si3N4 modified by replacing some of the Si atoms with C atoms. The N atoms are mainly bonded to Si, and C atoms are in the form of sp³C—N, sp²C=N and sp²C=C bonds. Decreasing deposition temperature favors an increase of C atom content and sp³C—N bond fraction.

The effect of particle size on the interaction of Pt catalyst particles with a carbon black support

GAN Lin, DU Hong-da, LI Bao-hua, KANG Fei-yu

2010, 25(01): 53-59. doi: 10.1016/S1872-5805(09)60015-9

Abstract(2354)

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Abstract:
Pt catalysts with different average particle sizes (1.7, 3.0, and 5.0 nm) were supported on Vulcan XC-72 carbon black through ethylene glycol reduction of H₂PtCl₆. Using transmission electron microscopy, we found a geometric interaction between the micropores on the surface of carbon black support and the supported Pt catalysts. Small Pt nanoparticles (with an average particle size of 1.7 nm) were found to be frequently incorporated into the micropores, and thus appeared to be covered by a thin carbon layer and embedded in the carbon matrix. However, such a phenomenon was absent for Pt particles with larger average particle sizes (3.0 and 5.0 nm), which generally showed an exposed clean surface. The different interaction with the micropores therefore induced an abnormal particle size effect of the supported Pt catalysts on their electrochemically active surface area, and had an influence on their mass electrocatalytic activity towards methanol oxidation.

The thermal expansion behavior of 3D C/C composites

LIAO Xiao-ling, LI He-jun, SUN Guo-dong, LI Ke-zhi

2010, 25(01): 60-64.

Abstract(2206)

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Abstract:
Three dimensional braided carbon/carbon composites (3D C/C composites) were fabricated by chemical vapor infiltration. The thermal expansion behavior of these materials with various densities before and after heat treatment was investigated. It is found that PAN-based carbon fibers (CFs) have an obviously negative coefficient of thermal expansion (CTE) after heat treatment at 1 200 ℃. The CTE of the 3D C/C composites is negative from room temperature to 100 ℃ and is proportion to their density. In the temperature range of 100-1 000 ℃, CTE vs. T curves have an almost a constant slope and expansion behavior of the composite is similar to that of pyrocarbon. When the temperature is above 1 000 ℃, a peak is found in the CTE vs. T curves, indicating that expansion of the pyrocarbon is limited by CFs and the thermal expansion behavior of the composites is determined by both CFs and matrix.

Electroless plating of Co-Fe on the surface of MWCNTs

ZHAO Yan| XUE Ya-juan| ZHENG Hao| DUAN Yue-xin

2010, 25(01): 65-70. doi: 10.1016/S1872-5805(09)60016-0

Abstract(2491)

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Abstract:
Multiwalled carbon nanotubes (MWCNTs) were electroless plated with cobalt-iron (Co-Fe) . Palladium-atom centers were formed on the surface of MWCNTs by a pretreatment before the plating. Three main parameters, the molar ratio of C_Co2+∶C_Fe2+, the concentration of complexing agent, and the temperature of plating bath, were changed to investigate their effects, whereas the concentrations of metal salts and reducing agent and pH were kept unchanged. A layer of metal deposited neatly with a Co-Fe content above 90% was obtained when the molar ratio of C_Co2+∶C_Fe2+ was 9∶1, the concentration of complexing agent was 0.32 mol/L, and the temperature of plating bath was 60 ℃. Metal granules were obtained, or the content of Co-Fe was much less in the other conditions investigated.

Preparation and ablation behavior of carbon fiber reinforced nitride composites

LI Bin, ZHANG Chang-rui, CAO Feng, WANG Si-qing, CAO Ying-bin

2010, 25(01): 71-74.

Abstract(1954)

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Abstract:
A hybrid precursor containing borazine and perhydropolysilazane was synthesized and characterized, and used to produce three-dimensional carbon fiber reinforced nitride matrix composites (3D Cf /Nitrides) through vacuum infiltration of the precursor followed by pyrolysis under inert atmosphere. The oxidation resistance and ablation behavior of the Cf/Nitrides were studied. Results showed that there were several bonds such as B-N, B-H, Si-N, Si-H and N-H in the hybrid precursor and the as-formed matrix had a good oxidation resistance. The matrix weight did not change distinctly when the temperature was increased from room temperature to 1 000 ℃. The surface of the ablated composites was flat and the nitride matrix had a much better ablation resistance than did the carbon fibers.

Adsorption thermodynamics of isoliquiritin on multi-walled carbon nanotubes

HAN Bo, CHEN Wen, WANG Xin-chun, LI Le, YAN Huan, LI Wen-xin

2010, 25(01): 75-78.

Abstract(1855)

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Abstract:
Multiwalled carbon nanotubes (MWCNTs) can selectively adsorb structurallysimilar liquiritin and isoliquiritin, both of which are flavonoid compounds. The adsorption thermodynamics of isoliquiritin on MWCNTs was investigated. Results indicate that the quantity of isoliquiritin adsorbed increases with isoliquiritin concentration and decreases with temperature. Adsorption data can be well described by the Freundlich Equation. The values of ΔH₀ and ΔG₀ indicate that the adsorption is a spontaneous exothermic process.

Professor Fu He and his research activities

LU Chun-xiang

2010, 25(01): 79-80.

Abstract(1751)

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Abstract:
Professor Fu He was born in Jiaocheng County, Shanxi Province, China. He has been working in the Institute of Coal Chemistry, Chinese Academy of Sciences since graduation from Shanxi University in 1964. He had undertaken and completed many research projects as a principal or main investigator during R&D and industrialization studies in the field of carbon fibers for over forty years. He has authored four books, held twelve patents, and published 120 research papers. Two of his books, "The preparation, properties and applications of carbon fibers" and "Carbon fibers and the techniques for application" have been recognized as classic textbooks by many researchers in the field of carbon fibers in China. A total of fifteen scientific achievements have been developed by him, five of which have been applied in the industrialization of carbon fibers. He received the State Council Special Allowance in 1992, and was awarded the National Young and Middle-aged Experts with Outstanding Contribution Award in 1988, the Excellent Graduate Supervisor of Chinese Academy of Sciences in 1998, the SecondClass Merit by the Labor Emulation Committee of Shanxi Province in 1999, and the Distinguished Achievement Award on Carbon Materials in 2009.

2010 Vol. 25, No. 01

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