In-Situ Polymerization Rapid Densification Process For Fabrication Of C/C Composites

Carbon/carbon composites exhibit a unique set of properties that make them desirable materials for high-temperature structural uses such as in rocket propulsion components, hypersonic vehicles, and aircraft brakes. In this paper, C/C composites have been densified by a novel in-situ polymerization process, which makes small aromatic hydrocarbon molecules infilter into the holes of the preform and in-situ polymerize and finally turn into matrix carbon after carbonization.In this paper, our research includes the following two parts. Firstly, preparation of matrix mesophase pitch precursor, in which the effects of different polymerization conditions were investigated. The morphologies and structures of products were characterized by TG-DSC and FI-IR. Secondly, the densification of the C/C performs, in which the morphologies and structures of the densified samples were investigated by SEM> XRD and a series of mechanical techniques. The main results are as follows.In the First part, it was found that using naphthalene as the carbon precursor and Lewis acid as catalyst to condense into mesophase pitch is more convenient and easier to control the reaction degree than heavy oil does. The more important is that it can get pitches with higher carbon yield and better microstructures. The optimized condensation condition is:340℃as the reaction temperature and15%as the concentration of the catalyst.Second, The results show that after the fifth cycle, the bulk density of the C/C composite increased to1.52g/cm3and1.83g/cm3from1.05g/cm3and1.68g/cm3of the original samples, and electrical resistivity reduced to1.09mOcm and0.28mOcm from4.44mOcm and0.84mOcm, and flexural strength enhanced to95MPa and211MPa from26MPa and86MPa, respectively. It is indicated that the in-situ polymerization rapid densification process is a simple, effective and competitive approach for the fabrication of C/C composites. The fracture surfaces show the pullout of fibers, which make the C/C composites exhibit a obvious pseudo-plastic failure behavior.Thirdly, compared with the disadvantages of CVD and CVI process such as long preparation cycle, hardness of operation and difficult densification with a higher density, in-situ polymerization process succeeded in densifying the preform with a density of1.67g/cm3. However, for the preform with a lower density, the integration between in-situ process and traditional dipping-carbonization process is supposed to use to densify and low down cost.