Bitumen is a carbonaceous material obtained by subjecting organic matter to low temperature distillation (<400 ° C). There are two main types of asphalt used as precursors for C/C composite matrix. One is coal tar pitch, which is a product after coal distillation. The internal components are mainly aromatic structural molecules and contain few aliphatic components. . Petroleum asphalt is a heavy component of petroleum cracking treatment, mainly composed of alicyclic components, and also contains some aromatic components and alkyl groups.
Solvent analysis is a common method for studying the structural composition and properties of asphalt. For example, the petroleum pitch and the benzene solvent are used to dissolve the pitch successively, and the coal pitch can be divided into three components of petroleum ether soluble (component C), benzene soluble (component B), and benzene insoluble (component A). The A component has the largest molecular weight, the B component is the second, and the C component is the smallest. The larger the molecular weight of these substances, the higher their C/H ratio, the higher the carbonization yield, and the higher the softening point.
The results of studying the asphalt and its components by X-ray diffraction and infrared spectroscopy indicate that the component A is a polycondensation product of an aromatic compound during heat treatment, and is a raw material for forming graphite crystals. The component B also contains a polycondensation product, but the condensed aromatic ring has a poor regularity in spatial arrangement and a high content of side chain groups. The C component is a mixture of monomeric compounds in the form of dispersed particles which exhibit a crystal structure. When this asphalt is selected as the matrix precursor, the microstructure and properties of the obtained C/C composite have a close relationship with the content of each component of the asphalt.
The conversion of bitumen to matrix carbon is essentially accomplished by the pyrolysis process of bitumen. This process is very complex, consisting of volatilization of low molecular compounds, polymerization, cleavage and rearrangement of molecular structures (<400 ° C), nucleation. A series of complex chemical processes, such as growth and growth (>400 ° C), followed by carbonization, complete the formation of matrix carbon. The pyrolysis process of asphalt. It can be seen from the figure that a small molecule of an aromatized structure can finally obtain a three-dimensional ordered graphitized structure through polymerization.
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