Mechanism Of Liquid Phase Deposition Of Carbon / Carbon Composite Material Pyrolysis Of Carbon Source Compounds

As far as the practical need of Rapid Densification Process of preparing Carbon/Carbon composites was concerned, a theoretical research of the pyrolysis mechanism for three sorts of carbon matrix compounds, including ethylbenzene, p-xylene and cyclohexane, was carried out. By this way, we hoped to obtain the pyrolysis mechanism of more carbon matrix precursors.1. Standard enthalpy changes of the initial pyrolysis process of ethylbenzene were computed by five methods (UAM1, UHF/3-21G*, UB3LYP/3-21G* and UB3LYP/6-31G*). UB3LYP/6-31G* due to its accuracy compared to the experimental values was chosen to calculate the thermodynamic and kinetic parameters of the process at different temperature ranges (298 1573 K). The computation results showed that ethylbenzene began to pyrolyze at 973 K and the main product was styrene. The activation energy of the major reaction path was 305.04 kJ/mol.2. By UB3LYP/6-31G* method, thermodynamic and kinetic researches on the pyrolysis process of p-xylene at different temperature ranges (298 1473 K) were carried out. The computation results indicated that the thermodynamic results supported the path producing free radical CH₃-C₆H₄-CH₂. as the initially major reaction path and successive reaction that the free radical CH₃-C₆H₄-CH₂. formed CH₃-C₆H₄-CH₂-CH₂-C₆H₄-CH₃ in room temperature. Above 873 K, the calculation results revealed that the path of generating CH₃-C₆H₄. was the originally major reaction path and following reaction formed CH₃-C₆H₄-CH₂-C₆H₄-CH₃ by combining free radicals CH₃-C₆H₄-CH₂. with CH₃-C₆H₄. At every temperature range, the kinetic results displayed that the path of creating CH₃-C₆H₄-CH₂. was the major reaction path. The activation energy of the path was 396.70 kJ/mol.3. By UB3LYP/6-31G* method, thermodynamic and kinetic researches on the pyrolysis process of cyclohexane at different temperature ranges (298 1373 K) were carried out. The results manifested that starting temperature of cyclohexane pyrolyzed was 873 K. The thermodynamic results advocated the path producing methylcyclopentane as the major reaction path at 298 K, the path formation 2-butene and ethane as the major reaction path above 873 K, and the pathproducing butadiene and ethane as the major reaction path above 1173 K. The kinetic results stated that the main products were 2-butene and ethane. The activation energy of the rate-determining step of the major reaction path was 365.75 kJ/mol.Above research results not only coincide with the experimental results but also provide more detailed description to each specific reaction path from theoretical point of view. Moreover, calculated results for the explanation of the experimental results are also reasonable. In general speaking, we could obtain essential reference parameters for the RD process of C/C composites from what the present paper studied and discussed.