新型炭材料

Self-sustaining high-temperature synthesis of carbon-encapsulated magnetic nanoparticles from organic and inorganic metal precursors

M. Bystrzejewski, M. Szala, W. Kiciński, W. Kaszuwara, M.H. Rummeli

2010, 25(2): 81-88. doi: 10.1016/S1872-5805(09)60017-2

Abstract(2531)

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Abstract:
A systematic study on the synthesis of carbon-encapsulated magnetic nanoparticles by self-sustaining hightemperature synthesis (SHS) is presented. The SHS was carried out using NaN₃ as a reducer; and poly(tetrafluoroethene) (C₂F₄)n, hexachloroethane (C₂Cl₆) and hexachlorobenzene (C₆Cl₆) as three various oxidizers. The effect of metal precursor, (Fe(CO)₅ or K₃[Fe(CN)₆]) on the yield, reaction heat, morphology, structure and magnetic properties of the products was investigated. The highest product yield with best magnetic characteristics was obtained from the organometallic iron precursor and C₂Cl₆ oxidizer.

Preparation of a carbon nanofiber/natural graphite composite and an evaluation of its electrochemical properties as an anode material for a Li-ion battery

Sang-Min Jang, Jin Miyawaki, Masaharu Tsuji, Isao Mochida, Seong-Ho Yoon

2010, 25(2): 89-96. doi: 10.1016/S1872-5805(09)60018-4

Abstract(2310)

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Abstract:
A carbon nanofiber (CNF)/natural graphite (NG) composite was prepared to improve the rate capability of asreceived NG to be used as the anode material in a Li-ion battery. Optimum control over both the amount and shape of the CNFs to enable their growth on NG remarkably improved the cycle performance and rate capability of the as-received NG. The first-cycle discharge capacity of the CNF/NG composite was 95% of that of the asreceived NG. The amount of grown CNFs was controlled to be less than 15% of the as-received NG. CNF growth on the surface edges of NG in an ivy leaf shape proved to be most effective in improving the rate capability by controlling the extent of volumetric expansion and shrinkage occurring in the charge and discharge processes. Schematic structural models of the as-received NG and CNF/NG composite were proposed to account for the volumetric stability of the electrode in repeated charge-discharge processes. The improved rate capability is ascribed to the thin solid electrolyte interphase and reduced volumetric change of the anode in the charge/discharge processes, both of which are achieved by growing ivy-like CNFs over the graphite surface

Fabrication of carbon nanowires by detonation-assisted chemical vapor deposition

FENG Shou-ai|, SONG Chang, DU Gui-xiang, ZHAO jiang-hong, ZHU Zhen-ping

2010, 25(2): 97-102.

Abstract(1926)

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Abstract:
High yield carbon nanowires were fabricated by a detonation-assisted chemical vapor deposition approach, using low activity iron-nickel as catalyst or a cobalt catalyst to freeze the growth process of carbon nanotubes. TEM observations indicated that the two kinds of carbon nanowires had rough surfaces. Compared with the nanowires obtained from the iron-nickel catalyst, the products obtained from the cobalt catalyst had uniform diameter and were less coalesced. The difference should be associated with the activity of the metal catalysts. Methylene blue degradation experiments showed that the latter carbon nanowires can enhance the photocatalysis activity of ZnS nanocrystals.

Surface modification of carbon microspheres by KMnO₄

LIU Xu-guang, | GUO Ming-cong, | YANG Yong-zhen, | LIU Hong-yan

2010, 25(2): 103-108.

Abstract(2165)

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Abstract:
Carbon microspheres (CMSs) were synthesized by chemical vapor deposition in an Ar atmosphere using deoiled asphalt as carbon source. KMnO^₄aqueous solutions with different concentrations were used to oxidize the CMSs to form MnO₂-coated CMSs (MnO₂/CMS composites) and H₂C₂O₄ solution was used to wash the MnO₂/CMS composites to remove MnO₂ to obtain oxidized CMSs. The morphology and structure of the CMSs before and after MnO₂ deposition, as well as the oxidized CMSs, were characterized by field-emission scanning electron microscopy and X-ray diffraction. The dispersion of the oxidized CMSs in water and ethanol was also investigated. A uniform MnO₂ nano-coating was formed on surface of the CMSs when a 0.1mol/L KMnO₄ aqueous solution was used. When an excess amount of H₂C₂O₄solution was used to wash away the MnO₂nanocoating, the resulting CMSs have oxygen-containing groups, such as hydroxyl, carbonyl and carboxylic, and can be well dispersed in water and partly dispersed in ethanol.

Preparation of activated carbon microspheres from phenolic resin with metal compounds by sub- and supercritical water activation

LI Ying, HUANG Zheng-hong, KANG Fei-yu| LI Bao-hua

2010, 25(2): 109-113. doi: 10.1016/S1872-5805(09)60019-6

Abstract(2115)

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Abstract:
Activated carbon spheres with well-developed mesopores and high mechanical strength were prepared from phenolic resin with a metal catalyst using sub- and supercritical water (SCW) as an activating agent. A rare earth metal chloride (cerous chloride) was used as catalyst. The effects of different activation methods on the porosity and adsorption characteristics of carbon spheres were investigated. All samples were characterized by nitrogen adsorption at 77K. Results showed that the catalyst could promote the development of pores in SCW. The cerium compound facilitated the development of mesopores with preponderant pore sizes at 4nm and 7nm. The catalyst affected the porosity of the porous carbon the most, whereas the effect of the activation methods was secondary. The activation pressure had the least effect.

Compressive mechanical behavior of carbon/carbon composites under dynamic loading

YUAN Qin-lu, LI Yu-long, LI He-jun, GUO Ling-jun, LI Shu-ping

2010, 25(2): 114-118.

Abstract(4737)

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Abstract:
Both quasistatic and dynamic compressive properties of 2-D carbon/carbon (C/C) composites in their thickness direction were determined using a universal test machine and Split Hopkinson Pressure Bar with pulse shapers. The compressive failure of the composite was photographed to demonstrate the failure mode at different strain rates, and the effects of strain rate on fracture mode are discussed. Results show that the compressive stiffness and strength of the C/C composites increase with strain rate. The compressive stiffness and strength of the C/C composites under dynamic loading with a strain rate of 5×10²/s are increased by about 66% and 55% respectively compared with quasistatic results with a strain rate of 10^-4/s. Under quasistatic conditions, the samples failed by shear with a shear fracture angle of approximately 40^o, and carbon fiber bundles were sheared and crushed. Under dynamic conditions, the samples were broken into many fragments with different sizes, and carbon fiber bundles were fractured by splitting. The different failure modes may be related to the strain rate sensitivity of the carbon matrix and the interface strength.

Real carbon source of diamond single crystals grown in the Fe-Ni-C system under high temperature and high pressure

LI He-sheng, | LI Mu-sen, CUI Jian-jun

2010, 25(2): 119-123.

Abstract(2255)

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Abstract:
Diamond synthesis experiments were carried out in the Fe-Ni-C system under high temperature and high pressure (HTHP). The real carbon source forming diamond was investigated by characterizing the structure and phase of the catalyst and the metal surrounding the carbon films, by analyzing the phase diagram and by thermodynamic calculations. These show that the catalyst and metal are composed mainly of cementite and the catalysts rapidly become supersaturated by absorbing carbon from the graphite and separate out as cementite (Fe₃C or Fe₂C∶Fe) when diamond begins to form a nucleus. According to the phase diagram, the diamond nucleation and growth are accompanied by the decomposition of the cementite. Thermodynamic calculations indicate that the phase transformation free energy of Fe₃C to diamond and γ -Fe is more negative than that of graphite to diamond in the stable diamond growth region. All of these results indicate that the real carbon source for diamond growth in the Fe-Ni-C system under HTHP is cementite, and not graphite.

Oxidation behavior of C/SiC composites with a SiC/Mo-Si multilayer coating

YAN Zhi-qiao, XIONG Xiang, XIAO Peng, CHEN Feng, LIU Gen-shan

2010, 25(2): 124-128.

Abstract(2264)

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Abstract:
A SiC/Mo-Si multilayer coating was prepared on the surface of C/SiC composites by chemical vapor deposition (CVD) combined with slurry painting. The coating was composed of a dense CVD SiC coating alternating with a porous MoSi layer. From inside to outside the coating consisted of CVD SiC, Mo-Si, CVD SiC, Mo-Si and CVD SiC . The coating remained intact and no obvious failure such as destruction or spalling was found during oxidation at 1400℃ and thermal shock between 1400℃ and room temperature. The mass loss and mass loss rate of the coated sample were only 0.25% and 6.61×10^-6g · cm^-2 · h^-1, respectively after oxidation at 1400℃ for 150h. The flexural strength retention was 95.73％ and 81.61％ after 25 and 50 thermal cycles respectively and mass of the coating generally increased after oxidation. The SiC/Mo-Si multilayer coating showed excellent antioxidation ability and a thermal shock resistance and could effectively protect the C/SiC composites at 1400℃ for a long time.

Effect of pore structure on the electrochemical performance of coal-based activated carbons in non-aqueous electrolyte

ZHANG Chuan-xiang, ZHANG Rui, XING Bao-lin, CHENG Guo, Xie Ying-bo

2010, 25(2): 129-133. doi: 10.1016/S1872-5805(09)60020-2

Abstract(2584)

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Abstract:
Anthracite was activated by NaOH to prepare high-performance activated carbons as electrodes for electric double-layer capacitors. The porous structure and electrochemical characteristics of the carbons were investigated by nitrogen sorption and electrochemical methods. The effect of pore structure on the electrochemical performance of the carbons in a 1mol/L (C₂H₅)₄NBF₄/propylene carbonate (PC) electrolyte was investigated. The as-prepared activated carbons exhibit large surface areas (943-2479m²/g) and high-specific capacitances (57-167F/g). The specific capacitance depends not only on the surface area, but also on the pore size distribution (PSD) of the carbon. Pores with a size of 2-3nm are crucial for the ions to penetrate inside them for the (C₂H₅)₄NBF₄/PC electrolyte. Specific capacitance is higher and impedance is lower for the sample with a wider PSD due to the fact that electrolyte ions could easily enter the pores.

Surface functionalization of single-walled carbon nanotubes using photolysis for enhanced dispersion in an organic solvent

Mirza Nadeem Ahmad, XIE Jing-yi, MA Yu-hong, YANG Wan-tai

2010, 25(2): 134-140. doi: 10.1016/S1872-5805(09)60021-4

Abstract(2425)

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Abstract:
Single-walled carbon nanotubes (SWCNTs) were functionalized by the covalent attachment of 2-propanol-2-yl radicals to their surface. These radicals were generated by photolysis of 2-hydroxy-2-methyl-1-phenyl-1-propanone under ultraviolet (UV) light. Pristine SWCNTs were dispersed in a tetrahydrofuran solution, and then free radicals were attached to their surface when the solution was subjected to UV irradiation. The functionalization of SWCNTs was evidenced by UV/visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis-mass spectrometry (TGA-MS) and high resolution transmission electron microscopy (HRTEM). UV/visible results indicated a loss of Van Hove singularities because of the covalent functionalization. The modification was further proved by FTIR. Raman spectra showed that the intensity ratio of the G band and D band (IG/ID) decreased for the functionalized SWCNTs. TGA-MS also showed a signal corresponding to m/z 59 at 400℃, indicating the presence of 2-propanol-2-yl groups. HRTEM and solubility data proved that the sidewall functionalization dissociated the bundle structure, improved the solubility in common organic solvents and retained the original electronic structure of the SWCNTs without severe modification that damages the nanotubes.

Preparation of C/C composites by thermal gradient chemical vapor infiltration with vaporized kerosene as a precursor

ZHANG Yong-hui| WANG Ji-ping| JIN Zhi-hao

2010, 25(2): 141-145.

Abstract(2628)

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Abstract:
A thermal gradient chemical vapor infiltration method with vaporized kerosene as a precursor for the fabrication of C/C composites was studied, in which a disc-shaped carbon felt preform was sandwiched within two flat heating sources, forming a temperature gradient, and the precursor was supplied with a third heating source. The density and open porosity of the composites were investigated by the Archimedes method (in water) and microstructures were studied by SEM. Results shows that the densities of the composites increase linearly with temperature and the C/C composite has a density up to 1.72g/cm³ when a carbon felt with a bulk density of 0.2g/cm³ was infiltrated at 1100℃for 3h.. The interlayer spacing (d₀₀₂) decreases and the composite can be easily graphitized at 2200℃. The carbon fibers in the composites are surrounded by a ring of pyrocarbon. The deposition process is analyzed by dividing the reactor into four regions associated with different functions. The rapid densification can be accounted for by the short convection and diffusion paths for the precursor and the thermal gradients across the preform.

Effects of the amount of ferrocene and ammonium chloride on the diameter distribution of hollow carbon spheres synthesized in high-pressure argon

LIU Bo-yang, JIA De-chang, SHAO Ying-feng

2010, 25(2): 146-150. doi: 0.1016/S1872-5805(09)60022-6

Abstract(2171)

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Abstract:
The effects of the amount of the ferrocene and ammonium chloride on the diameter distribution of hollow carbon spheres (HCSs) prepared in high-pressure argon were investigated. The morphology and diameter distribution of the HCSs were characterized by field-emission scanning electron microscopy which showed that the diameter of most HCSs ranges from 1 to 10 μm. The median diameter increases with the total amount of the reactants with the same weight ratio of ferrocene to ammonium chloride. When excess ammonium chloride is used, HCSs with a bimodal diameter distribution are prepared; however, the median diameter is almost the same. It is proposed that the aggregation of iron particles and liquid Fe(NH₃)₂Cl₂ templates, and the transformation of the iron amine complexes, in the process mainly influence the diameter distribution of the HCSs.

Preparation of high-surface-area activated carbon from coconut shell fibers

CHEN Yong, ZHOU Liu-jiang, HONG Yu-zhen, CAO Feng, LI Ling| LI Jian-bao

2010, 25(2): 151-155.

Abstract(2122)

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Abstract:
Activated carbons (ACs) with high specific surface area and abundant mesopores were prepared from coconut shell fibers through carbonization and NaOH/KOH activation. The influence of NaOH/KOH ratio, carbonization temperature, activation temperature, activation time and heating rate on the adsorption behavior of the ACs were investigated. The specific surface area of the obtained ACs under optimum conditions was 2032m²/g with 28% （volume fraction） of mesopores between 2 to 4nm. The iodine adsorption value and methylene blue adsorption value of the AC were 1435 and 495mg/g, respectively.

Performance of oxidation resistant coatings for C/C composites as aircraft brakes

XIAO Zhi-chao, XUE Ning-juan, SU Jun-min, PENG Zhi-gang, JIN Zhi-hao

2010, 25(2): 156-160.

Abstract(2156)

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Abstract:
A modified phosphate coating on C/C composites used for aircraft brakes was made from zinc chloride, phosphoric acid, zinc phosphate and aluminum phosphate. In order to study the properties of the modified coating, an unmodified phosphate coating and a ceramic coating, which principally consists of silicon and boron, were also investigated. Results showed that all three coatings had excellent oxidation resistance at 500℃ for 100h and the maximum mass loss is 1.25%. The mass loss of the C/C composite with a modified phosphate coating was 1.76% when the composite was subjected to oxidation at 700℃ for 30h in air, and the value was 1.98% when the composite was subjected to thermal shock in air for 30 cycles (from 900℃ for 3min to at room temperature for 2min) followed by shock in air for 10 cycles (from 1100℃ for 3min to room temperature for 2min). The performance of the modified phosphate coating is the best among the three coatings. It has excellent oxidation resistance and thermal shock resistance.

2010 Vol. 25, No. 2

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