2010 Vol. 25, No. 03

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Effect of density and fibre orientation on the ablation behaviour of carbon-carbon composites
Shameel Farhan, LI Ke-zhi, GUO Ling-jun, GAO Quan-ming, LAN Feng-tao
2010, 25(03): 161-240. doi: 10.1016/S1872-5805(09)60023-8
Abstract(2060) PDF(1492)
Abstract:
Five carbon-carbon composites were prepared with different fibre orientations in the preform and were densified by different methods. Their ablation behaviour was examined by an oxy-acetylene test and scanning electron microscopy. The densities of the composites were in the range of 1.77 to 1.85g/cm3. Fibres having an angle of 30° with the oxy-acetylene flame turned into a sharp wedge shape, whereas fibres parallel to the flame had a needlelike shape with diameter up to 3.5-4.5μm after ablation. The needled fibres were easily attacked and ultimately became blunt. Partially filled macropores with sizes of 1.0-1.26mm, needle pores, interfacial cracks and gaps in nonwoven cloth were easily attacked by the flame, resulting in macroscopic ablation pits that decreased with increasing density of the composites. The needled fibres around pitch carbon layers were severely denuded due to their discontinuity with the pyrolytic carbon matrix. A high density (1.85g/cm3) composite had an excellent ablation resistance.
Growth of super long vertically aligned carbon nanotube arrays from cyclohexane via floating catalyst method
2010, 25(03): 168-174.
Abstract(1988) PDF(1433)
Abstract:
Vertically aligned carbon nanotube (VACNT) arrays were obtained using the floating catalyst method with cyclohexane as a carbon source. Results indicated that various factors, such as growth temperature, ferrocene feed rate, feed rate of the solution (ferrocene dissolved in cyclohexane), and composition of carrier gases, had a great effect on the VACNT array growth. A maximum growth rate of the VACNT array was obtained in a quartz tubular reactor with a diameter of 25mm when the growth temperature was 820℃, ferrocene feed rate 0.24mg/min, feed rate of the solution 0.12mL/min, and the flow rate of the H2/Ar (1∶15) carrier gas 640mL/min. A VACNT array with a height of 5.0mm was obtained with a large aspect ratio (>105) and a high purity (96.7%).
Helical multiwalled carbon nanotubes (h-MWCNTs) synthesized by catalytic chemical vapor deposition
T. Somanathan, A. Pandurangan
2010, 25(03): 175-180. doi: 10.1016/S1872-5805(09)60024-X
Abstract(2096) PDF(1500)
Abstract:
Helical multiwalled carbon nanotubes (h-MWCNTs) were synthesized by a catalytic chemical vapor deposition method using acetylene as a carbon source and FeMo/MgO catalyst as a template, which was prepared by a combustion method using citric acid as a foaming and combustion additive. The XRD pattern revealed that the catalyst was crystalline. Furthermore, the synthesized carbon materials were characterized by SEM, TEM, and Raman spectroscopy, where SEM and TEM images showed the formation of thin h-MWCNTs and the Raman spectrum confirmed the crystalline characteristics of the CNTs. This is an easy and simple method to synthesize h-MWCNTs with diameter of 20-30nm.
Synthesis of mesoporous carbon by catalytic activation using rare earth elements
LI Yan-qiu, LI Kai-xi
2010, 25(03): 181-186.
Abstract(2028) PDF(1223)
Abstract:
Y(NO3)3 or Ce(NO3)3 was doped into novolac-type phenolic resin with a solution mixing method, and phenolic resinbased activated carbons rich in mesopores were obtained by steam activation. The as-prepared samples were characterized by infrared spectroscopy, thermogravimetry, nitrogen adsorption and scanning electron microscopy. Results indicate that the doping of Y(NO3)3 or Ce(NO3)3 into phenolic resin is favorable for the activation of phenolic resin-based carbon in steam, improving the activation rate and promoting the formation of pores. The efficiency for carbon gasification increases with increasing catalyst content and reaches a maximum at 4% by weight for both catalysts. The maximum is thought to be due to the agglomeration of metal particles and a decreasing of contact surface area between carbon and metal particles at the high metal content. Y(NO3)3 can accelerate the formation of micropores and mesopores simultaneously with the former more developed. However, Ce(NO3)3 shows an obvious effect on the development of mesopores.
Yttrium silicate coatings for SiC coated C/C composites prepared by atmospheric plasma spraying
HUANG Min, LI Ke-zhi, LI He-jun, HUANG Jian-feng, FU Qian-gang
2010, 25(03): 187-191.
Abstract(2090) PDF(1227)
Abstract:
Different yttrium silicate coatings for SiC-coated C/C composites were designed and prepared by an atmospheric plasma spray method to prevent the C/C composites from oxidation. XRD profiles showed that the coating was composed of Y2SiO5, Y2Si2O7, and Y4Si3O12. SEM showed that the gradient SiC/Y4Si3O12/Y2Si2O7/Y2SiO5 coating had a more compact surface than the other coatings did. Isothermal oxidation tests at 1500℃ in air showed that the weight loss curves of the as-prepared C/C composites showed a linear tendency with time and the weight loss rate of all coated samples increased significantly after 73h. The coating could protect the C/C composites from oxidation at 1500℃ for 73h in air with a weight loss rate of 1.01×10-4g · cm-2 · h-1. The SiC/Y4Si3O12/Y2Si2O7/Y2SiO5 was the better coating at high temperature than other coatings.
An easy approach to encapsulating Fe3O4 nanoparticles in multiwalled carbon nanotubes
LI Jian-hua, HONG Ruo-yu, LUO Guo-hua, ZHENG Ying, LI Hong-zhong
2010, 25(03): 192-198. doi: 10.1016/S1872-5805(09)60026-3
Abstract(2841) PDF(2015)
Abstract:
Carbon nanotubes filled with magnetic materials are very interesting as new materials for applications in biomedicine. A simple and efficient method was developed to encapsulate Fe3O4 nanoparticles in multiwalled carbon nanotubes (MWCNTs). Transmission and scanning electron microscopy, energy dispersive X-ray analysis, and X-ray powder diffraction measurements confirmed that the Fe3O4 nanoparticles are encapsulated in the MWCNTs. The magnetic properties of the MWCNTs and the Fe3O4-filled MWCNTs were measured using a vibrating sample magnetometer. Results showed that the Fe3O4-filled MWCNTs exhibited superparamagnetism at room temperature and possessed a higher saturation magnetization (Ms) (around 13.15emu/g) than that of the unfilled ones (around 0.35emu/g). The MWCNTs encapsulating Fe3O4 nanoparticles have potential applications in engineering and medicine.
Preparation of carbon-encapsulated metal magnetic nanoparticles by an instant pyrolysis method
MA Chen, LUO Bin, SONG Huai-he, ZHI Lin-jie
2010, 25(03): 199-204. doi: 10.1016/S1872-5805(09)60028-7
Abstract(2063) PDF(1646)
Abstract:
Carbon-encapsulated iron and nickel magnetic nanoparticles (CEMNPs) were synthesized from their salt precursors using an instant pyrolysis method. The morphologies, structural features and magnetic properties of the particles were investigated by transmission electron microscopy, X-ray diffraction, simultaneous thermogravimetry-differential scanning calorimetry and vibrating sample magnetometry. It was found that almost all of the CEMNPs were spherical, and their size changed from 10 to 30nm, whereas the size of the carbonencapsulated iron nanoparticles changed from 50 to 60nm. The magnetic properties of the products indicated that the carbon-encapsulated iron nanoparticles were paramagnetic and their properties were tunable with the iron content. The present approach is promising for large-scale production of CEMNPs.
Correlation between properties and microstructure of pitch fluorides
ZHANG Jin-cai, SHI Jin-li, GUO Xue-min, LIU Lang, GUO Quan-gui
2010, 25(03): 205-210.
Abstract(1732) PDF(1192)
Abstract:
Three different pitch fluorides were prepared by the reaction of pitch grains with a gas mixture containing fluorine and nitrogen in a rotating nickel reactor. The raw pitches are mesophase microbeads, mesophase pitch and isotropic pitch. The surface energy, contact angle with water, the stability in acid or alkali media and weight loss upon heating were investigated. Results showed that the fluorinated reaction rate of the raw pitches and the weight loss rate of the pitch fluorides were quite different, which may be caused by the difference in the molecular weight distributions and the compositions of the raw pitches. However, the surface energies of the pitch fluorides were all low and the resistance of the pitch fluorides to acid or alkali was similar.
Surface chemical deposition coating of graphite particles
ZHANG Yong-gang, WANG Cheng-yang, YAN Pei
2010, 25(03): 211-217.
Abstract(1986) PDF(1604)
Abstract:
Surface chemical deposition coating was used to form single "core-shell" graphite grains with medium coal tar pitch as raw material. Scanning electron microscopy and particle size measurement showed that the surface of the graphite grains was obviously changed and the coating layers were formed first on the edges and corners of a graphite sheet and then extended to the whole sheet surface. X-ray diffraction, infrared spectroscopy and differential scanning calorimetry showed that the coating layers were mesophase pitch.
Room-temperature hydrogen sensing properties of SnO2-coated multi-walled carbon nanotubes
SUN Xue, FANG Hai-tao, YU Hui-long, CHU Yi, ZHANG Bao-you, DU Jin-hong
2010, 25(03): 218-224.
Abstract(1947) PDF(1137)
Abstract:
A SnCl2 solution was used to prepare SnO2-coated multi-walled carbon nanotubes (SnO2/MWCNTs), and their hydrogen sensing properties at room temperature was studied. SEM and TEM observations indicate that SnO2 nanoparticles with a size of 5 nm are uniformly coated on the MWCNTs, forming a continuous SnO2 coating. The SnO2/MWCNTs are sensitive to 10-4 hydrogen at room temperature. During the sensing measurement at room temperature for 10-3 hydrogen mixed with argon gas, the current change with gas concentration is reversed after the mixed gas is switched to air. This can be ascribed to the reaction between O2 in air and residual H2 around the SnO2/MWCNTs to form adsorbed H2O and the subsequent desorption of H2O by substitution adsorption of O2 in air. The H2O adsorption may lead to a decrease of the electric resistance of SnO2/MWCNTs and thus an increase of current measured. The reversal of current implies that the SnO2/MWCNTs may possess a good sensitivity to humidity at room temperature.
Manufacture and properties of carbon fibre-reinforced C/SiC dual matrix composites
LI Zhuan, XIAO Peng, XIONG Xiang, HUANG BO-yun
2010, 25(03): 225-231. doi: 10.1016/S1872-5805(09)60029-9
Abstract(2116) PDF(2394)
Abstract:
Carbon fibrereinforced carbon and silicon carbide dual matrix composites (C/C-SiC) were fabricated by a combination of chemical vapor infiltration with liquid silicon infiltration. The structural characteristics, mechanical performance and tribological properties of the C/C-SiC composites and their wear mechanism at different braking speeds were investigated using a QDM150 friction testing machine, SEM and X-ray energy dispersive analysis. Results indicate that the C/C-SiC composites show an increased bonding strength at the fibre/matrix interface, and the value of flexural strength and compressive strength of the C/CSiC composites can reach 240 and 210MPa, respectively. The friction coefficients are between 0.41 and 0.54. Wear rates are not sensitive to the brake speed and remain constant at about 0.02cm3/MJ, and the friction coefficient is stable. Frictional films with a thickness of 1-3μm are formed on the worn surface of the composites upon braking. The wear mechanism changes with increased braking speed, from abrasion at 8m/s, adhesion at 12m/s and 16m/s to fatigue and oxidation at 20m/s and 24m/s, respectively.
Characterization and biological behavior of a carbon fiber/carbon composite scaffold with a porous surface for bone tissue reconstruction
CAO Ning, WANG Qiang-xiu, DONG Jian-wen, HAO Guang-zheng, LI Mu-sen
2010, 25(03): 232-236. doi: 10.1016/S1872-5805(09)60027-5
Abstract(1885) PDF(1449)
Abstract:
A carbon/carbon composite scaffold for bone tissue reconstruction was prepared. The surface morphology and trace elements of the scaffold were analyzed and its biological behavior was studied both in vitro and in vitro. It was found that the scaffold had a good biocompatibility, not only resulting from its high purity and mild cell toxicity, but also from the excellent integration of the bone tissue with the composite scaffold during the reconstruction.
Electrostatic layer-by-layer assembled multilayer films of chitosan and carbon nanotubes
LI Xiao-bo, JIANG Xiao-ying
2010, 25(03): 237-240. doi: 10.1016/S1872-5805(09)60025-1
Abstract(1992) PDF(1489)
Abstract:
Multiwalled carbon nanotubes (MWCNTs) were treated in 1∶3 concentrated nitric-sulfuric acid to cut them into short tubes and to create carboxyl groups at their ends. Homogeneous multilayer films of the shortened MWCNTs were assembled on a silica glass substrate by a layer-by-layer method, based on electrostatic interaction of positively charged cationic polyelectrolyte chitosan (CS) and the negatively charged and shortened MWCNTs. The film assembly and characteristics of the CS/MWCNT multilayer films were investigated. The process of assembly was monitored through ultraviolet-visible spectroscopy, which indicated homogeneous and consecutive growth. Atomic force microscopy and scanning electron microscopy were used to characterize the surface of the films. The films showed stable optical properties and were promising as biosensors.

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