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 without any artificial adjustments. The mole fractions of hydrogen, acetylene, ethylene, and benzene increased with a decreasing growth rate as the residence time and the initial methane pressure increased. Sensitivity analysis and reaction paths were conducted to identify the crucial reaction steps and explain how they impact in this pyrolysis process. Results showed that methane pyrolysis had an incubation stage to form a necessary gas atmosphere for the pyrolysis to move forward and C3 species were the main direct source for benzene formation. These results should be useful to understand methane pyrolysis at a molecular level in CVD, as well as the relationship between the gas species and the pyrocarbon.
Last. Mark H. Rümmeli(PAN: Polish Academy of Sciences)H-Index: 69
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The discovery of graphene and carbon nanotubes (rolled-up graphene) has excited the world because their extraordinary properties promise tremendous developments in many areas. Like any materials with application potential, it needs to be fabricated in an economically viable manner and at the same time provides the necessary quality for relevant applications. Graphene and carbon nanotubes are no exception to this. In both cases, chemical vapor deposition (CVD) has emerged as the dominant synthesi...
It is important to understand the growth of CNT-diamond composite films in order to improve the inter-link between two carbon allotropes, and, in turn, their physical properties for field emission and other applications. Isolated diamond particles, continuous diamond thin films, and thin films of carbon nanotubes (CNTs) having non-uniformly distributed diamond particles (CNT-diamond composite films) were simultaneously grown on unseeded, seeded, and catalyst pre-treated substrates, respectively,...
Last. Xin Wang(Nanjing University of Science and Technology)H-Index: 131
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The reduction of graphene oxide has been widely used to control the properties of graphene-based materials. Traditional methods thoroughly remove oxygenated functional groups in graphene oxides. We show that ethanol, ethylene glycol and glycerol can selectively reduce epoxy groups in graphene oxide while hydroxyl and carboxyl groups remain unchanged. Hydrazine hydrate can reduce oxygen functional groups except carboxyl groups. These selective removals can be used to control the reduction degree ...
#1Liang-Hsun Lai(NCHU: National Chung Hsing University)H-Index: 4
#2Huei-Cheng Li(NCHU: National Chung Hsing University)H-Index: 1
Last. Hung-Yi Lin(ITRI: Industrial Technology Research Institute)H-Index: 7
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When ethylene/ammonia (C2H4/NH3) mixtures are used to deposit carbon films by thermal chemical vapor deposition (CVD), effects of C2H4/(C2H4+NH3) ratios on the deposition rate and microstructures of carbon films are investigated. Experimental results reveal that the deposition rate of carbon films increases with the C2H4/(C2H4+NH3) ratio, and also, raises with the residence time, deposition temperature, and working pressure. The kinetics of this thermal CVD process is discussed. The deposition r...
Abstract Effects of the propane concentration in the preparation of C/C composites by the Chemical Vapor Infiltration (CVI) of propane were studied. The amount of deposited carbon and the compositions of the product gas were measured at 5, 10, 20, and 100% propane. Numerical simulations were also carried out. The rate of deposition increases slightly as time passes. The mathematical modeling of the system estimated well the experimental results with the deposition rate constant from the referenc...
Last. Jinhua Lu(NPU: Northwestern Polytechnical University)H-Index: 22
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Carbon/carbon (C/C) composites with two different matrixes of pitch carbon and pyrolytic carbon were fabricated using 2-dimensional (2D) carbon felts preform. In order to study the effects of matrixes on mechanical properties, C/C composites with single matrix of pitch carbon were prepared. The mechanical properties were tested on CMT5304-30KN universal testing machine. Polarization microscope and scanning electron microscope were used to investigate the microstructures and fracture surface of C...
Abstract Alternative chemical reaction pathways leading to polycyclic aromatic hydrocarbons (PAHs) in the pyrolysis of unsaturated light hydrocarbons were investigated to extend the previously proposed chemical kinetic model [K. Norinaga, O. Deutschmann, Ind. Eng. Chem. Res. 46 (2007) 3547–3557]. Although the previous model provided a reasonably good description of the pyrolysis behaviors observed in flow reactor experiments at 1073–1373 K, the concentration profiles for large PAHs were underest...
#1Aijun Li(KIT: Karlsruhe Institute of Technology)H-Index: 6
#2Koyo Norinaga(KIT: Karlsruhe Institute of Technology)H-Index: 29
Last. Olaf Deutschmann(KIT: Karlsruhe Institute of Technology)H-Index: 58
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Numerical simulation of materials synthesis based on detailed models for the chemical kinetics and transport processes is expected to support development and optimization of production processes. Exemplarily, chemical vapor deposition and infiltration of pyrolytic carbon for the production of carbon fiber reinforced carbon is studied by recently developed modeling approaches and computational tools. First, the development of a gas phase reaction mechanism of chemical vapor deposition (CVD) of ca...
The chemical kinetics of the pyrolysis of the hydrocarbons ethylene, acetylene, and propylene are modeled in detail under conditions relevant to the chemical vapor deposition of pyrolytic carbon. A mechanism that consisted of 227 species and 827 reactions (most of which are reversible) is developed and computed using a software package designed for computing time-dependent homogeneous reaction systems. Experimental results used for model validation are obtained using a vertical flow reactor at 9...
Last. Kezhi Li(NPU: Northwestern Polytechnical University)H-Index: 56
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Abstract A parallel-consecutive reaction model of chemistry and kinetics is proposed to simulate homogeneous gas-phase reactions of propylene pyrolysis in CVI processes. An improved bipore model is also suggested to describe the changes of the pore topology with densification. The competition between the heterogeneous reactions of pyrolytic carbon deposition and the homogeneous reactions is analyzed by a numerical simulation method. Numerical simulation shows that continuous higher density regio...
#2Jincan Zhang(University of Cambridge)H-Index: 15
Last. Zhongfan Liu(PKU: Peking University)H-Index: 126
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Since its first successful isolation over a decade ago, academic and industrial interest has triggered the steady progress of the commercialization of graphene, as evidenced by a wealth of graphene-related patents, products, institutes, and startups. Among currently available graphene materials, graphene films derived from chemical vapor deposition (CVD) techniques, with fine controllability and uniformity, have been proven to be a promising candidate for various applications, with exciting demo...
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...
#1Vijay M. Shinde(IIT: Indian Institute of Technology (BHU) Varanasi)H-Index: 11
#2Prashun Pradeep(IIT: Indian Institute of Technology (BHU) Varanasi)
Abstract A detailed gas-phase kinetic model consisting of 37 species and 318 reactions is developed for methane pyrolysis involved in the CVD/CVI processes. The model was used to perform the simulations of CH4 pyrolysis in a hot-wall CVD reactor over a wide range of operating conditions and validated against the experimental data. The overall trend of the concentration profiles of notable species is in good agreement with experimental results. The sensitivity analysis and reaction path flux diag...
#2He Shen(California State University, Los Angeles)H-Index: 29
Last. Li Hejun(NPU: Northwestern Polytechnical University)H-Index: 25
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Abstract The density functional theory has been successfully applied in analyzing pyrolytic carbon deposition by methane pyrolysis from the view of thermodynamics and kinetics based on a total number of 39 elementary reactions. M06-2X/def2-TZVP level was employed to optimize species structures and locate the transition states. The enthalpy changes and Gibbs free energy changes of all the reactions in the temperature range of 298.15–1800 K were derived with optimized species. Results show that th...
Last. Qiang Song(NPU: Northwestern Polytechnical University)H-Index: 26
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A density functional theory (DFT) study was employed to explore the mechanism of the conversion of methane to benzene in chemical vapor infiltration (CVI) based on the concluded reaction pathways from C1-species to C6-species. The geometry optimization and vibrational frequency analysis of all the chemical species and transition states (TS) were performed with B3LYP along with a basis set of 6–311 +G(d, p), and Gaussian 09 software was used to perform the study. The rate constants were calculate...
Last. Ni Li(California State University, Los Angeles)H-Index: 1
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A complete mechanism of methane pyrolysis is proposed for chemical vapor infiltration of pyrocarbon with different textures, which contains a detailed homogeneous mechanism for gas reactions and a lumped heterogeneous mechanism for pyrocarbon deposition. This model is easily applied to simulate gas compositions and pyrocarbon deposition in a vertical hot-wall flow reactor in the temperature range of 1,323–1,398 K without any adjusting parameters and presents better results than previous mechanis...
#1Fatin Bazilah Fauzi(IIUM: International Islamic University Malaysia)H-Index: 5
#2Edhuan Ismail(IIUM: International Islamic University Malaysia)H-Index: 4
Last. Mohd Hanafi Ani(IIUM: International Islamic University Malaysia)H-Index: 8
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Abstract Chemical vapor deposition (CVD) is a well-known process as the most favourable for high-quality large area graphene production. However, it is a complex method where each parameter will contribute to significant effect on the deposition process. One of them, fluid dynamics, was reported to be one of the major governing factors for better deposition. Heat transfer process at high temperature will influence gas phase dynamics during the deposition process. In this study, the influence of ...
Last. Zhigang Zhao(NPU: Northwestern Polytechnical University)H-Index: 1
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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) ...
Since the first isolation of graphene over a decade ago, research into graphene has exponentially increased due to its excellent electrical, optical, mechanical and chemical properties. Graphene has been shown to enhance the performance of various electronic devices. In addition, graphene can be simply produced through chemical vapor deposition (CVD). Although the synthesis of graphene has been widely researched, especially for CVD growth method, the lack of understanding on various synthetic pa...
