Abstract To investigate the mechanism of the heterogenous reactions during the Chemical vapor infiltration (CVI) process of carbon/carbon composites, the dissociation of CH4 on graphene was calculated by density functional theory (DFT). Graphene was used as the adsorption surface in the course of the heterogenous reactions. Based on the energy analysis, the preferred adsorption sites of CHx(x = 0–4) and H on graphene were obtained. Then, the stable co-adsorption configurations of CHx/H(x = 0–3) on graphene were located. The calculation results show that CH4, CH3 and H prefer to be adsorbed at the top of a carbon atom of graphene, while CH2, CH and C are favorable on the midpoint of a C C bond of graphene. Transition state (TS) calculation shows that the dissociation of CH4 into CH3 and H is a rate-determining step. Additionally, by comparing the dissociation of CH3 into CH2 and H and the formation of C2H6 during the dissociation of CH4, it is obvious that the CH3 groups are more likely to produce ethane rather than dissociating into CH2 and H.
Last. Guangsheng Song(Anhui University of Technology)H-Index: 2
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Abstract Nanofilamentous carbon (NFC) reinforced carbon/carbon composites were produced by floating catalyst chemical vapor infiltration with ferrocene content ranging 0–2.0 wt%. The NFCs and increased graphitization degree led to an improvement on the mechanical and thermal properties. An excellent combination of high strength and thermal conductivity (TC), and low coefficient of thermal expansion (CTE) was reached by adding 0.5–0.8 wt% catalyst. When the content exceeded 0.8wt%, the strength a...
Last. Qiang Song(NPU: Northwestern Polytechnical University)H-Index: 26
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Abstract Carbon nanotubes have been electrophoretically deposited on carbon fibers to improve the flexural performance of laminated carbon/carbon composites. The synergy effect between carbon nanotubes and different textured pyrocarbon matrix has been investigated. Mechanical testing results showed that after introducing nanotubes into low-texture-matrix and high-texture-matrix composites, their flexural strength increased by 13.9% (up to 197 MPa) and 89.6% (up to 309 MPa), respectively. Excessi...
Last. Ying Wang(CAS: Chinese Academy of Sciences)H-Index: 29
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Abstract The mechanism of CH 4 dissociation and carbon nucleation process on the Fe doped Cu(100) surface were investigated systematically by using the density functional theory (DFT) calculations and microkinetic model. The activity of the Cu(100) surface was improved by the doped Fe atom and the atomic Fe on the Fe-Cu(100) surface was the reaction center due to the synergistic effect. In the dissociation process of CH 4 , CH 3 → CH 2 + H was regarded as the rate-determining step. The results o...
Recently, the domains of low-dimensional (low-D) materials and disordered materials have been brought together by the demonstration of several new low-D, disordered systems. The thermal transport properties of these systems are not well-understood. Using amorphous graphene and glassy diamond nanothreads as prototype systems, we establish how structural disorder affects vibrational energy transport in low-dimensional, but disordered, materials. Modal localization analysis, molecular dynamics simu...
Last. Wei Li(NPU: Northwestern Polytechnical University)H-Index: 99
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This work describes a modeling study of methane pyrolysis in chemical vapor deposition (CVD). The model consists of a detailed chemical kinetic model, which includes 241 species and 909 gas-phase reactions for methane pyrolysis mechanism, and a plug-flow model, which describes the transport conditions in CVD. Reasonably good agreements were obtained between the simulation results and the experimental results of methane pyrolysis in CVD of pyrocarbon in a vertical hot-wall deposition reactor with...
Last. Tao Fang(Xi'an Jiaotong University)H-Index: 20
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Abstract Using density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation mechanisms of methane on clean and oxygen-covered Pd (1 0 0) surfaces have been studied systematically. Different adsorption geometries were investigated for CH 4 and related intermediates (CH 3 , CH 2 , CH, C, H, O and OH). It was found that CH 4 and CH 3 prefer to adsorb on the top site, CH 2 and OH are favorable on the bridge site, while CH, C, O and H species adsorb preferent...
Using nonequilibrium molecular dynamics and lattice dynamics, we investigate phonon conduction on two-dimensional graphene/boron nitride superlattices with varying periods and interface structures. As the period of superlattice increases to a critical value near 5 nm the lattice thermal conductivity drops sharply to a minimum, and beyond that it smoothly increases with the period. We show that the minimum in the thermal conductivity arises from a competition between lattice dispersion and anharm...
Nanocarbons doped with nitrogen (N) and/or metal-N coordination structures hold great promise in replacing Pt for catalyzing the oxygen reduction reaction (ORR) in fuel cells. The lack of clear views on the natures of ORR active sites in these materials has hindered the progress in reducing their activity gap to Pt through a rational desire of doping structures. Using 14 types of N and Fe–N doping structures in graphene as model systems, systematic density-functional-theory (DFT) calculations ar...
Last. Kezhi Li(NPU: Northwestern Polytechnical University)H-Index: 56
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Abstract A Ta x Hf 1− x B 2 –SiC coating was prepared by in-situ reaction method on SiC coated C/C composites. Ta x Hf 1− x B 2 phase is the form of solid solution between TaB 2 and HfB 2 . Isothermal oxidation behavior at 1773 K and ablation behavior of the coated C/C were tested. Ta x Hf 1− x B 2 –SiC/SiC coating could protect the C/C from oxidation at 1773 K for 1480 h and ablation above 2200 K for 40 s. During oxidation, oxides of Ta and Hf atoms exist as “pinning phases” in the compound gla...
Last. Jiaping Zhang(NPU: Northwestern Polytechnical University)H-Index: 15
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Abstract Ablation behavior of C/C–ZrSiO 4 composites prepared by a three-step process was studied using oxyacetylene torch. After ablation for 120 s, the linear and mass ablation rates of the composites were 5.91 μm/s and 1.13 mg/s, respectively, which were lower than those of pure C/C composites. The evolution processes of microstructure and composition of the ablation surface with the extension of ablation time were investigated in detail. The heat from the ablation flame was absorbed by the d...
#1Zeng Liang(USTB: University of Science and Technology Beijing)
#2Kejiang Li(USTB: University of Science and Technology Beijing)H-Index: 14
Last. Jianliang Zhang(USTB: University of Science and Technology Beijing)H-Index: 23
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More attention needs to be drawn to the high application value of the gasification reaction between carbonaceous materials and water in industry. In this study, density functional theory is used to investigate the adsorption and reaction mechanism of water molecules on graphene surfaces with various kinds of defects. The desorption mechanism of the reaction product is also analyzed. The optimal and stable physical adsorption configuration of water molecules on the pristine graphene and various d...
Last. Shouyang Zhang(NPU: Northwestern Polytechnical University)H-Index: 19
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The microstructure of pyrolytic carbon significantly affects the performance of aircraft brake discs. In this study, to explore the effect of precursor on the microstructure of pyrocarbon, two types of pyrocarbon films were grown on the quartz glass substrates by isothermal isobaric chemical vapor infiltration using methane and acetaldehyde as precursors. The microstructures of both the films and their formation mechanisms were investigated and compared. The thicknesses of the pyrocarbon films f...
Last. Guoqing Wang(NPU: Northwestern Polytechnical University)
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To improve the pyrolytic carbon (PyC) deposition rate of Carbon/Carbon (C/C) composites prepared by the traditional chemical vapor infiltration (CVI) method, the 3D Ni/wood-carbon (3D Ni/C) catalyst was introduced into the CVI process. The effects of catalyst on the density of C/C composites were studied, and the deposition rate and morphologies of PyC were investigated after catalytic CVI. The morphologies of catalyst and PyC were characterized by scanning electron microscope and polarized ligh...
Last. Lehua Qi(NPU: Northwestern Polytechnical University)H-Index: 26
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Abstract Methane is used as the carbon precursor for the fabrication of C/C composites by using chemical vapor infiltration. Demystify the heterogeneous reactions on the carbon surface during the pyrolysis of methane is important for us to understand the formation and growth of the pyrocarbon. In this paper, the dissociation mechanisms from CH4 to C2H2 on pristine graphene, N-doped graphene, and vacancy graphene during the chemical vapor infiltration process are systematically studied using the ...
#1Ge Yan(NCEPU: North China Electric Power University)H-Index: 4
#2Zhengyang Gao(NCEPU: North China Electric Power University)H-Index: 16
Last. Xunlei Ding(NCEPU: North China Electric Power University)H-Index: 12
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Abstract Dry (CO2) reforming of methane is an important reaction in environmental catalysis, which can both reduce the greenhouse gas content and utilize syngas production. Density functional theory (DFT) calculations were carried out to investigate the reaction mechanism of CO2 and CH4 on Pt4 cluster doped single-vacancy graphene (Pt4/SV) catalyst. The adsorption configurations are optimized in advance to determine the initial states and final states in reactions. Then, the detailed reaction pa...
Last. Hejun Li(NPU: Northwestern Polytechnical University)H-Index: 68
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Abstract In this paper, the adsorption mechanisms between different species (CH3, CH4, C2H2, C2H4, C2H6, and C6H6) and the carbon-based materials (pristine graphene, N-doped graphene, and vacancy graphene) during the chemical vapor infiltration process were systematically studied using the density functional theory. The optimized adsorption configurations were obtained by using Dmol3 code in Material Studio. The adsorption energies, Mulliken atomic charges, density of states, and charge density ...
The newly developed penta-graphene is a two-dimensional (2D) carbon allotrope with promising mechanical properties. This paper investigates the nonlinear post-buckling and vibration of imperfect three-dimensional penta-graphene composite plates resting on elastic foundations and subjected to uniform external pressure and axial compressive load. The elastic constants of the single-layer penta-graphene are fully determined by the density functional theory by fitting the equation of strain energy t...
#2Ryota Okino(TITech: Tokyo Institute of Technology)H-Index: 1
Last. Katsunori Hanamura(TITech: Tokyo Institute of Technology)H-Index: 13
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Abstract This paper investigated the structural evolution of carbon deposition on a Ni/YSZ cermet of a SOFC. The Ni/YSZ cermet was heated in CH4/Ar environment with a thermobalance. It was observed that carbon deposition preferentially occurred on Ni particles, and the area on which carbon deposited touched the Ni/YSZ interfaces. Meanwhile, carbon deposition was not found on some of the Ni/YSZ interfaces. The Ni/Zr interfaces had various defects, suggesting that the defect pattern may be an impo...