新型炭材料

Pores in carbon materials——Importance of their control

Michio Inagaki

2009, 24(3): 193-222. doi: 10.1016/S1872-5805(08)60048-7

Abstract(2402)

PDF(2644)

Abstract:
Techniques for controlling the pore structure and its importance in carbon materials are reviewed after a brief explanation on classification and characterization of pores. Recent understanding of conventional activation processes are reviewed and then pore structure control techniques without activation are shown, including the template method, defluorination of PTFE, carbon aerogels, polymer blend method, selection of specific precursors, and selection of preparation conditions. Five examples are presented to show the importance of pore structure control in carbon materials, which included CO₂ capture, water vapor adsorption/desorption, gasoline vapor adsorption, carbon electrodes for electric double layer capacitors, and heavy oil sorption and recovery.

Improved quality of polycrystalline diamond grown by two-stage growth in microwave plasma chemical vapor deposition

Lee Shih-Fong, Yeh Chun-Shin, Chang Yung-Ping, Wang Dau-Chung, Huang Bohr

2009, 24(3): 223-229. doi: 10.1016/S1872-5805(08)60049-9

Abstract(2664)

PDF(1228)

Abstract:
The quality of polycrystalline diamond films grown by chemical vapor deposition is dependent on the growth time, pressure, carbon-to-hydrogen ratio, bias, and nucleation mechanism involved. In this study, reaction gases, methane (CH₄) and hydrogen (H₂), were used to grow polycrystalline diamond on a p-type (111) silicon substrate with a microwave plasma-enhanced chemical vapor deposition system. In addition to the conventional etching, bias-enhanced nucleation, and growth steps, the growth step was further divided into two stages. The first stage (growth I) was carried out at low pressure and the second (growth II) was carried out at high pressure. Results clearly indicate that the use of the growth I stage can considerably improve the quality of the diamond film. In the growth I stage, well-faceted grains with lower contents of graphite and carbide, and fewer defects are obtained. Therefore, the conductivity is drastically decreased by nearly two orders of magnitude and the diamond film exhibits the semi-insulating characteristics of intrinsic diamond. The improvement is caused solely by the addition of the low-pressure growth I stage. Application of bias in the growth I and/or growth II stages can only degrade the synthesized polycrystalline diamond film.

Characterization and properties of PAN-based high modulus carbon fibers

HUA Zhong, YANG Yu-rong, ZHONG Ya-juan, LI Dong-feng| LIU Xin

2009, 24(3): 230-236.

Abstract(1847)

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Abstract:
The surface character, microstructure, and surface chemical composition of PAN-based carbon fibers were investigated by SEM , WAXRD，SAXS, XPS and Raman spectroscopy. The relation between microstructure and mechanical properties was analyzed. Results show that with increase of heat treatment temperature from 2400 to 3000℃, tensile strength decreases, Young’ s modulus increases and the surface activity decreases. It is found that the interlayer spacing d002 decreases, both La and Lc increase，the crystallinity increases, the size of the pores and the volume percentage of large pores all increase, and the surface O/C atom ratio decreases after the heat treatment.

Effect of hydrophilic groups in the polymer matrix on the porosity of organic and carbon aerogels produced from melamine, phenolic resole and formaldehyde

ZHANG Rui, LI Wen, HU Zi-jun, ZHANG Zuo, CHEN Kun, XU Chun-hua

2009, 24(3): 237-242.

Abstract(2639)

PDF(1261)

Abstract:
Organic and carbon aerogels were synthesized by the solution-sol-gel polymerization of melamine (M), phenolic resole (PR), m-cresol and formaldehyde in a basic aqueous solution followed by supercritical petroleum drying and pyrolysis. The effect of hydrophilic groups in the polymer matrix on the porosity of organic and carbon aerogels was investigated by varying the M/PR ratio under otherwise identical conditions. It was found that increasing hydrophilic melamine content increases intermolecular interactions of polymers that form gels, which favors an improvement in the stability of gels in supercritical drying and pyrolysis. The increase of melamine content also increases the mass loss of organic aerogels during pyrolysis, which is unfavorable for their stability. The pore size distributions, surface areas, meso-porosity and macroporosity of carbon aerogels were a compromise between the two opposing factors.

Fabrication of hierarchical porous carbide-derived carbons by chlorination of mesoporous titanium carbides

CHENG Guo, LONG Dong-hui, LIU Xiao-jun, LING Li-cheng

2009, 24(3): 243-250. doi: 10.1016/S1872-5805(08)60050-5

Abstract(2076)

PDF(1319)

Abstract:
Mesoporous titanium carbides were prepared via carbothermal reduction of organicinorganic gels using titanium n-butoxide as a Ti source and sucrose as a carbon precursor. The asmade titanium carbides were used as starting materials for producing carbide-derived carbons (CDCs) through thermochemical treatment in a chlorine environment. The influence of the ratio of titanium n-butoxide to sucrose (R) on the porous structure and physical properties of the mesoporous titanium carbide and the resulting CDCs were investigated using X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and N₂ adsorption. It was found that mesoporosity and macroporosity developed in the course of the formation of the titanium carbides can be preserved and transmitted to the carbon material after chlorine treatment, while microporosity was formed by extraction titanium atoms from the carbide. The obtained CDCs have a hierarchical structure of multiscaled pores, including uniform micropores produced from carbides, mesopores with diameter of 3-4nm original from the residual free carbon and macropores formed by interconnection and overlapping of the carbon particles. By changing the R, the BrunauerEmmettTeller specific surface areas and total pore volumes of the CDCs could be adjusted in the range of 1479-1640m²/g and 1.06-2.03cm³/g, respectively. These hierarchical porous carbons would have potential applications for use in catalysis, adsorption, gas separation, and electrochemical energy storage.

Catalytic carbon deposition on three-dimensional carbon fiber preforms using alkane gas feedstocks

Matthew J Thornton, Gavin S Walker

2009, 24(3): 251-259. doi: 10.1016/S1872-5805(08)60051-7

Abstract(2097)

PDF(1503)

Abstract:
The rate of carbon deposition and the carbon nanostructures formed during the chemical vapor deposition of ethane and synthetic natural gas, with and without added hydrogen, over a nickel catalyst, supported on threedimensional (3D) carbon fiber preforms, was investigated. Graphitic nanofibers, carbon nanotubes, and graphitic carbon shells were observed following carbon deposition; the nanostructured carbon deposited was dependant on deposition temperature and gas feedstock composition. Gas feedstocks ranging from volume fraction 100 to 20% hydrocarbon with a balance of hydrogen were investigated at temperatures ranging from 650 to 800℃, up to 12h total deposition time. The 3D carbon fiber supports were impregnated with a methanolic solution of nickel nitrate hexahydrate that was decomposed and reduced to nickel before carbon deposition. The samples were characterized using weight change measurements, thermogravimetric analysis coupled to a mass spectrometer, scanning and transmission electron microscopy, and X-ray diffraction. Analysis of the samples revealed an increase in the ratio of filamentous to encapsulation with increasing hydrogen content with the reverse being observed with increasing temperature. Unexpectedly, it was found that hydrogen addition did not extend the lifetime of the catalyst. This process shows good potential for the manufacture of carbon-carbon composites.

The adsorption of carbon disulfide on activated carbon fibers

XIE Zun-yuan, LI Jun-ping, ZHAO Ning, WANG Feng, PENG Wei-cai|Mao Bo-yan

2009, 24(3): 260-264.

Abstract(2114)

PDF(1404)

Abstract:
The adsorptive performance of commercial activated carbon fiber (ACF) for CS₂ was investigated and a comparison of the adsorptive performance of ACF with activated carbon (AC) and zeolites was made. The effects of the operating parameters such as CS₂concentration, flux, humidity and water content in ACF on the adsorptive performance were investigated. Results indicated that the ACF had a higher adsorption capacity of 46.5% than AC and zeolites did toward CS₂. The breakthrough time decreased greatly with flow rate and CS₂ concentration. The adsorptive performance deteriorated with increasing humidity and water content in the ACF. The adsorption time was shortened by 28.6% when humidity was increased to 65%. The breakthrough time was decreased by 42.9% when water content in the ACF was increased to 45%. The adsorptive capacity was negligible when water content in the ACF was increased to over 60%.

Effect of alkali metal salt on the macropore structure of rayon-based activated carbon fibers

ZHANG Zhi-hai, WU Qi-lin, CAI Ze-tian, YAN Cheng, SONG Hua-yi, PAN Ding

2009, 24(3): 265-269.

Abstract(1938)

PDF(1287)

Abstract:
Macroporous Rayon-based activated carbon fibers (ACFs) were produced from Rayon precursors impregnated with alkali metal salt and Lewis acid followed by chemical activation or water vapor activation. The effect of pretreatment conditions such as the concentration of alkali metal salt and impregnation time on the properties of the resultant ACFs were investigated by scanning electron microscopy and physical adsorption. Results showed that the pore sizes and their distribution could be controlled by the concentration and impregnation time of the alkali metal salt. A novel ACF with abundant macropores and micropores and with high specific surface area was obtained by an optimum pretreatment with alkali metal salt.

Investigation of PAN-based carbon fiber microstructure by 2D-SAXS

SHENG Yi, ZHANG Cai-hong, XU Yao, LU Chun-xiang, WU Gang-ping

2009, 24(3): 270-276.

Abstract(2156)

PDF(2103)

Abstract:
Two dimensional small angle X-ray scattering (2D-SAXS) was used to characterize the detailed pore structure inside carbon fibers from different azimuth angles. Chinese PAN carbon fibers (MHS) and Japanese carbon fibers (T300 and T800) were investigated and compared by assuming ellipsoidal pores. The pore size of MHS was found to be between those of T300 and T800. Meanwhile, the length/diameter ratio (t) of pores of MHS was the smallest among the three kinds of fibers. Compared to MHS, T300 had a large amount of pores with sizes less than 9.1nm and larger than 15.4nm. T800 mainly contained small pores with size less than 2nm along the short axis. The surface fractal dimension indicated that the interface between pore and solid carbon in MHS was rougher than for T300 and smoother than for T800. The large deviation from the Porod law indicated that there was an electron density fluctuation within the solid matrix of the carbon fibers. This electron density fluctuation was possibly due to the cavities between microcrystallines in the carbon matrix. Among the three kinds of fibers the weakest density fluctuation occurred in T800 and the density fluctuation amplitude F and dimension n decreased from MHS to T300 to T800. Therefore, T800 had the most favorable pore arrangement to improve mechanical strength.

Preparation of coreshell silicon/porous carbon powders

SHI Li-min, ZHAO Hong-sheng, YAN Ying-hui, TANG Chun-he

2009, 24(3): 277-281.

Abstract(1965)

PDF(1473)

Abstract:
Core-shell silicon/porous carbon powders were fabricated by coating silicon powders with phenolic resin, followed by carbonization at 800℃ for 2h. The influence of phenolic resin volume percent, silicon mass percent and aging temperature on the formation of silicon/phenolic resin precursor powders was investigated. The resulting powders were characterized by X-Ray diffraction and scanning electron microscopy The optimum conditions for the formation of silicon/phenolic resin precursor powders are found to be: volume ratio of phenolic resin to alcohol, ＜1; mass ratio of Si to alcohol, ＜2; and aging temperature, at 30-60℃. The resin carbon shell of the resulting powders is formed by the pyrolysis of phenolic resin during carbonization treatment and the carbon content in the core-shell silicon/porous carbon increases with the content of phenolic resin in precursor powders. The large amount of gas produced in the pyrolysis process creates pores in the carbon shell.

The development and prospects of carbon science——A report on the annual world conference on carbon, Carbon’09

LIU Xu-guang

2009, 24(3): 282-288.

Abstract(1872)

PDF(1969)

Abstract:
The annual world carbon conference, Carbon’09, was held in Biarritz, France on 1419, June, 2009, which gathered 602 attendants from 46 countries contributing 4 plenary lectures, 36 keynote lecturess, 208 oral presentations, 2 award lectures and 624 posters under 11 topics including natural carbons, carbons grown or deposited from gas phase and plasmas, carbons from soft precursors, energy storage and conversion, carbonbased composites and their mechanical properties, chemical and physical modifications, liquid and gas storage, adsorption, electronic/optical/optoelectronic properties and applications, nuclear and solar applications, thermal management, biocarbons related to biology/toxicity/health, and advances in processing/characterization/modeling. Carbon in the universe, the carbon cycle, carbon and health, and the direction observation of carbon at the atomic level were the subjects of the plenary lectures. Current active research on carbons can be summarized in the following five aspects: (1) significant efforts have been made on experimental research combined with simulation/modeling on the structure, formation mechanism, properties and applications of porous carbon, carbon nanotubes (CNTs), graphene, composites, aerogels and intercalation compounds. The synthesis of biocarbon or carbon nanomaterials in a green, economic, and effective manner to alleviate the greenhouse gas effect is drawing more and more attention; (2) research on porous carbons in environmental protection and energy storage has been on the top of the agenda of carbon scientists; (3) the electromagnetic, optoelectronic and field emission application of CNTs and graphenes, and the nuclear, solar energy and thermal application of graphite and carbon constitute a main research field of carbon science; (4) research of medical applications, biomaterials and biocompatability of carbon materials is receiving more and more attention; (5) the measurement and observation of carbon materials by means of high resolution transmission electron microscopy, Raman spectrometry and electron energy loss spectrometry have been strengthened by other characterization means and simulations to assure more accurate structural information on carbon materials.

2009 Vol. 24, No. 3

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