• Interaction and multiscale mechanics
• /
• v.4 no.4
• /
• pp.247-255
• /
• 2011

Understanding the structural stability of carbon nanostructure under heat treatment is critical for tailoring the thermal properties of carbon-based material at small length scales. We investigate the heat resistance of the single carbon nanoball ($C_{60}$) and carbon nanoonions ($C_{20}@C_{80}$, $C_{20}@C_{80}@C_{180}$, $C_{20}@C_{80}@C_{180}C_{320}$) by performing molecular dynamics simulations. An empirical many-body potential function, Tersoff potential, for carbon is employed to calculate the interaction force among carbon atoms. Simulation results shows that carbon nanoonions are less resistive against heat treatment than single carbon nanoballs. Single carbon nanoballs such $C_{60}$ can resist heat treatment up to 5600 K, however, carbon nanoonions break down after 5100 K. This intriguing result offers insights into understanding the thermal-mechanical coupling phenomena of nanodevices and the complex process of fullerenes' formation.

• Carbon letters
• /
• v.4 no.1
• /
• pp.24-30
• /
• 2003

In this study, densified 4D carbon/carbon composites were made from carbon fiber and coal tar pitch through the process of pressure impregnation and carbonization and then followed by carbonization and graphitization. To improve the oxidative resistance of the prepared carbon/carbon composites, the surface of carbon/carbon composites was coated on SiC by the pack cementation method. The SiC coated layer was created by depending on the constitution of pack powder, and reaction time of pack-cementation. The morpology of crystalline and texture of these SiC coated carbon/carbon composites were investigated by XRD, SEM/EDS observation. So the coating mechanism of pack-cementation process was proposed. The oxidative res istance were observed through the air oxidation test, and then the optimal condition of pack cementation was found by them. Besides, the oxidative mechanism of SiC formed was proposed through the observation of SiC coated surface, which was undergone by oxidation test.

• Carbon letters
• /
• v.2 no.3_4
• /
• pp.165-169
• /
• 2001

Modification of C/C composite bipolar plate for improving electrical conductivity was carried out by addition of electroconductive carbon black (EC-CB). Carbon black was carefully mixed to methanol-containing phenolic resin, impregnated into 2D-carbon fabrics, hot pressed and then carbonized to obtain composite plate. Inclusion of electro-conductive carbon black enhanced the electrical conductivity of the C/C composites by increasing the conduction path. Addition of 10 vol% carbon black increased the electrical conductivity from 5.5/${\Omega}cm$ to 32/${\Omega}cm$ and reduced the crack formation by filling effect, resulting in the increase of flexural properties of composite plate. However, at carbon black content over 10 vol%, flexural properties decreased by delaminating role of excess carbon black at the interface in C/C composites.

• Carbon letters
• /
• v.5 no.4
• /
• pp.164-169
• /
• 2004

Carbon-ceramic composites refer to a special class of carbon based materials which cover the main drawbacks of carbon, particularly its proneness to air oxidation, while essentially retaining its outstanding properties. In the present paper, the authors report the results of a systematic study made towards the development of C-SiC-$B_4C$ composites, which involves the effects of compositional parameters, namely, carbon-to-ceramic and ceramic-to-ceramic ratios, on the oxidation behaviour as well as other characteristics of these composites. The C-SiC-$B_4C$ composites, heat-treated to $1400^{\circ}C$, have shown that their oxidation behaviour at temperatures of 800~$1200^{\circ}C$ depends jointly on the total ceramic content and the SiC : $B_4C$ ratio. Good compositions of C-SiC-$B_4C$ composites exhibiting zero weight loss in air at temperatures of 800~$1200^{\circ}C$ for periods of 4~9 h, have been identified. Composites with these compositions undergo a weight gain or a maximum weight loss of less than 3% during the establishment of a protective layer at the surface of carbon in a period of 1~6 h. Significant improvement in the strength of C-SiC-$B_4C$ composites has been observed which increases with an increase in the total ceramic content and also with an increase in the SiC : $B_4C$ ratio.

• Carbon letters
• /
• v.11 no.1
• /
• pp.9-12
• /
• 2010

The synthesis of $C_{60}$@MWCNT was carried out at room temperature (${\sim}25^{\circ}C$) from arc-discharge prepared Multi-wall carbon nanotubes (MWCNTs). They were oxidized and acid treated for tube opening. Then $C_{60}$ molecules were encapsulated into MWCNTs by wetting them with $C_{60}$-toluene solution for several minutes followed by ultrasonification. $C_{60}$@MWCNT was cleaned by pure toluene to remove any excess $C_{60}$. $C_{60}$@MWCNT was characterized by electron microscopy, which showed large scale filling of $C_{60}$ into MWCNTs. It was observed that the mechanism of insertion of $C_{60}$ into MWCNTs may be due to the capillary suction at the opening ends of MWCNTs.

• Journal of Environmental Science International
• /
• v.5 no.4
• /
• pp.429-440
• /
• 1996

A global carbon cycle model (GCCM), that incorporates interaction among the terrestrial biosphere, ocean, and atmosphere, was developed to study the carbon cycling aid global carbon budget, especially due to anthropogenic $CO_2$ emission. The model that is based on C, 13C and 14C mass balance, was calibrated with the observed $CO_2$ concentration, $\delta$13C and $\Delta$14C in the atmosphere, Δ14C in the soil, and $\Delta$14C in the ocean. Also, GCCM was constrained by the literature values of oceanic carbon uptake and CO, emissions from deforestation. Inputs (forcing functions in the model) were the C, 13C and 14C as $CO_2$ emissions from fossil fuel use, and 14C injection into the stratosphere by bomb-tests. The simulated annual carbon budget of 1980s due to anthropoRenic $CO_2$ shows that the global sources were 5.43 Gt-C/yr from fossil fuel use and 0.91 Gt-C/yr from deforestation, and the sinks were 3.29 Gt-C/yr in the atmosphere, 0.90 Gt-C/yr in the terrestrial biosphere and 2.15 Gt-C/yr in the ocean. The terrestrial biosphere is currently at zero net exchange with the atmosphere, but carbon is lost cia organic carbon runoff to the ocean. The model could be utilized for a variety of studies in $CO_2$ policy and management, climate modeling, $CO_2$ impacts, and crop models.

• Carbon letters
• /
• v.6 no.2
• /
• pp.71-78
• /
• 2005

Anti-oxidation coatings are the key technique for carbon/carbon (C/C) composites used as the thermal structural materials. The microstructure and oxidation behavior of several kinds of high-performance ceramic coatings for C/C composites prepared in Northwestern Polytechnical University were introduced in this paper. It showed that the ceramic coatings such as SiC, Si-$MoSi_2$, SiC-$MoSi_2$, $Al_2O_3$-mullite-SiC and SiC/yttrium silicate/glass coatings possessed excellent oxidation resistance at high temperatures, and some of these coatings were characterized with excellent thermal shock resistance. The SiC-$MoSi_2$ coating system has the best oxidation protective property, which can effectively protect C/C composites from oxidation up to 1973 K. In addition, the protection and failure reasons of some coatings at high temperature were also provided.

• Journal of the Korean Ceramic Society
• /
• v.34 no.11
• /
• pp.1151-1158
• /
• 1997

Fracture of uni-directional carbon fiber reinforced carbon matrix composite is strongly dependent on the orientation of basal plane in graphite matrix when it is limited within matrix. The orientation of basal planes are vertically stacked to carbon fiber which results in the weakness for applied tensile or shear force in thermosetting resin derived-carbon matrix composite. Microtextural control of the matrix was tried through chemical interaction between metal carbides and furan resin derived-carbon matrix. SiC and TiO2 addition made the orientation disordered. However, porosity increased due to decomposition of SiC. Interfacial bonding could be controlled by TiO2 addition, but carbon fiber was considerably reacted with TiC during thermal treatment higher than 2$600^{\circ}C$. Therefore, it is desirable to control the thermal treatment temperature at which decomposition of SiC was not serious and TiC/C was not formed eutectoid.

• Carbon letters
• /
• v.5 no.2
• /
• pp.62-67
• /
• 2004

Performance of carbon-carbon composites is known to be influenced by the fibre matrix interactions. The present investigation was undertaken to ascertain the development of microstructure in such composites when carbon fibres possessing different surface energies (T-300, HM-35, P120 and Dialed 1370) and pitch matrices with different characteristics (Coal tar pitch $SP110^{\circ}C$ and mesophase pitch $SP285^{\circ}C$) are used as precursor materials. These composites were subjected to two different heat treatment temperatures of $1000^{\circ}C$ and $2600^{\circ}C$. Quite interesting changes in the crystalline parameters as well as the matrix microstructure are observed and attempt has been made to correlate these observations with the fibre matrix interactions.

• Carbon letters
• /
• v.5 no.3
• /
• pp.127-132
• /
• 2004

Chop molding composites and 2D carbon/carbon composites were manufactured by hot press molding method. Phenol resin of novolac type was used for matrix precursor and PAN-based carbon, PAN-based graphite and pitch-based carbon fiber were used for reinforcement and boron oxide was used for oxidation retardant. All of the composites were treated by $2000^{\circ}C$ and $2400^{\circ}C$ graphitization process, respectively. After graphitization process, amount of a boron residue in carbon/carbon composites is much according to irregularity of used raw materials. Under the presence of boron in carbon/carbon composites, catalytic effect of boron was a little at $2000^{\circ}C$ graphitization temperature. However, it was quite at $2400^{\circ}C$ graphitization.