The effect of carbon nanotubes on the microstructure and morphology of pyrolytic carbon matrices of C–C composites obtained by CVI

Gong, Qianming; Zhi, Li; Bai, Xiaodong; Li, Dan; Ji, Liang

doi:10.1016/j.compscitech.2004.11.005

Cited by 53 publications

(21 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the increased energies are still smaller than those in the rate control elementary steps. It is interesting that the energies for the first [reaction (6)] and the second [reaction (7)] rate control steps remains almost unchanged (from 203.9 to 203.4 and from 206.7 to 193.7 kJ/mol). However, most importantly, that for the third (reaction (10) and also the most energy demanding) step decreased more than 100 kJ/mol (i.e., from 276.0 kJ/mol at 298.15 K to 173.5 kJ/mol at 1200 K).…”

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 95%

“…However, most importantly, that for the third (reaction (10) and also the most energy demanding) step decreased more than 100 kJ/mol (i.e., from 276.0 kJ/mol at 298.15 K to 173.5 kJ/mol at 1200 K). Therefore, the rate control elementary reactions for the C 3 -bearing reactions should be (10) at lower temperatures and be (6) and (7) at higher temperatures. The rate branching ratios, 4.1 3 10 25 in step (4) and 1.2 3 10 28 in step (6), are also large enough to illustrate the most favorable pathways.…”

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 99%

“…Therefore, the rate control elementary reactions for the C 3 -bearing reactions should be (10) at lower temperatures and be (6) and (7) at higher temperatures. The rate branching ratios, 4.1 3 10 25 in step (4) and 1.2 3 10 28 in step (6), are also large enough to illustrate the most favorable pathways. However, the C 3 production channel should be less favored compare with the production of smaller species because Figure 15 shows that the reaction branching to produce ethane and methane at the first step of propene pyrolysis by H attacking has an energy (106.8 kJ/mol at 298.15 K or 18.9 kJ/mol at 1200 K lower) much lower than that (86.5 kJ/mol at 298.15 K or 168.1 kJ/mol at 1200 K higher) going into the C 3 -bearing path.…”

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 99%

“…[1][2][3][4][5] Such PyC layer has generally been prepared with chemical vapor deposition (CVD) or chemical vapor infiltration (CVI) technique by decomposing hydrocarbons. [6][7][8] In fact, PyC is deposited on the carbon fibers before densification with silicon carbide matrix in the CVD/CVI process. 2,9 The layer is important because it provides great thermal expansion mismatch between carbon fibers and SiC matrix because of loose bonding to both of them.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Reaction pathways of propene pyrolysis

Wang

et al. 2010

J Comput Chem

View full text Add to dashboard Cite

The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH(3) radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C(3) to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C(2) and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 +/- 0.6 or 137 +/- 25 kJ/mol.

show abstract

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 95%

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 99%

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reaction pathways of propene pyrolysis

Wang

et al. 2010

J Comput Chem

View full text Add to dashboard Cite

show abstract

“…CNFs act as in-situ nuclei for the various sized polyaromatic molecules in the gas phase and increase A/V, thus leading to chemisorption or growth mechanism. [6] This growth would cease when the densified CNF ''forest'' is fully coated by nascent pyrocarbon which contributes to the decrease of active sites and A/V. Finally, both the decrease of active sites and the high concentration of PAHs in the gas phase would change the former mechanism into physisorption or nucleation mechanism.…”

Section: Deposition Mechanism Of Vapor Infiltrating Cnfs/cfs Hybrid Mmentioning

confidence: 98%

Fabrication and Characteristics of Carbon Nanofiber‐Reinforced Carbon/Carbon Composites by Fast Catalytic Infiltration Processes

Zhang

Luo

et al. 2009

Chemical Vapor Deposition

View full text Add to dashboard Cite

The simultaneous in-situ growth of carbon nanofibers (CNFs) and densification of a CNFs/CF hybrid multiscale felt are accomplished in a single step by thermal gradient chemical vapor infiltration using Fe as the catalyst and vaporized kerosene under atmospheric pressure. A three-dimensional CNF network which could bridge dissimilar components of composites is formed on carbon fibers (CFs). The length of CNFs can reach several micrometers and the diameters are about 80 nm. Smooth and rough surface densified CNFs can be produced after further higher temperature infiltration. CNFs, anchoring to CFs by the adherence of the catalyst nanoparticles, enhance the bonding between CFs and pyrocarbon as well as promoting the formation of a rough laminar pyrocarbon matrix. The deposition mechanisms and physical model are also discussed. This fast catalytic infiltration process can be applied to other ceramic materials and has significant enlargement potential.

show abstract

Carbon/Carbon Composites

Luo

Zhang

et al. 2011

Wiley Encyclopedia of Composites

View full text Add to dashboard Cite

Carbon/carbon (C/C) composites as high temperature structural materials have been widely used in aeronautics and astronautics because of their remarkable mechanical, thermophysical, and tribological properties. For the deep investigation of carbon deposition mechanism, newly developed approaches of fast densification of C/C composites have been indicated, such as thermal gradient chemical vapor infiltration (TCVI), pressure gradient chemical vapor infiltration (PCVI), electrified CVI (ECVI), and chemical liquid‐vaporized infiltration (CLVI). Multilayer coating system provides a new way for the long‐term antioxidation of C/C composites. Carbon nanotubes and nanofibers, forming the bridge between carbon fibers of micrometer size, could also further enhance the mechanical properties of composite materials. Bonded repair of C/C composite structure is used to extend the life of wear or underdesigned components and joins different components at a reasonable cost. All these studies promote the research and development of advanced C/C composites.

show abstract

The effect of carbon nanotubes on the microstructure and morphology of pyrolytic carbon matrices of C–C composites obtained by CVI

Cited by 53 publications

References 28 publications

Reaction pathways of propene pyrolysis

Reaction pathways of propene pyrolysis

Fabrication and Characteristics of Carbon Nanofiber‐Reinforced Carbon/Carbon Composites by Fast Catalytic Infiltration Processes

Carbon/Carbon Composites

Contact Info

Product

Resources

About