The Preparation Of CNTs/C/C Composites By MCVI And Its Bending Performance Study

Carbon/Carbon(C/C) composites based on carbon matrix and reinforced by carbon fibers(CF) are advanced materials with many excellent properties, such as low density, high strength, high temperature resistance, stand wear and tear and good biocompatibility. They can be widely applied as both structural and functional materials. As conventional preparation methods, the liquid phase impregnation carbonization and chemical vapor infiltration are not only costly and time consumed but also hard to control the structures of materials. Recently, microwave assist chemical vapor infiltration(MCVI) has been developed to be a promising method to rapidly fabricate C/C composites and can be used to exactly control the structures of materials. In this study, the grafting process of CNTs on CF, the relationship between parameters of MCVI preparation and the effects on bending properties by adding CNTs were investigated, as well as the laws between structures and mechanical properties.Decorating CNTs with carboxylation could bring defects onto the surface, bring in floating charges, lead to the formation of sp3 hybridization within CNTs which are merely consist of sp2 hybridization, which in turn uniformly disperse the CNTs into solvent to overcome the poor dispersibility. Studying the parameters of electrophoretic deposition(EPD) to deposit CNTs on CF surface. The experiment showed that it could deposit well-distributed and the appropriate thickness of CNTs onto CF on the condition that the electric field intensity was 10V/cm and deposition time was about 3 minutes.The relationship between MCVI technological parameters and the materials structures were systematic researched. It was found that the textures of pyrocarbon(Py C) undergo the change rule of LTâ†'MTâ†'L/HTâ†'HT with the decreasing of the concentration of CH4 when the temperature and pressure were fixed. The pressure have tiny effects on texture at the low gas flow. While they became significant when the gas flow turned to larger. Increasing temperature will result in the change of Py C textures which were suitable for the rule of MTâ†'HTâ†'MTâ†'H/MT when the pressure were about 20 k Pa or 30 k Pa. Also, the influence of temperature was great than pressure to Py C textures.The three point bending test on C/C composites were conducted, it could be learned that C/C composites with high texture Py C(HT-C/C) have the largest bending strength, and the elastic stage are the longest. While C/C composites with middle texture(MT-C/C) have the least bending strength, yet have the good plastic properties. The C/C composites with both high texture and middle texture have medium properties. All of three textures have the pseudo-plastic fracture behavior. The Py C combined with CNTs acted as bridge tend to be a kinds of low textures or isotropic under the action of CNTs in microwave electromagnetic field, which make the interfacial adhesion between CF and Py C stronger, forming strong interface bonding. And the bending strength were improved by 71.38% in C/C composites with CNTs than none, but too strong interface bonding caused to brittle fracture. Meanwhile, the bending strength exert firstly increased and then decreased with the increasing of the content of CNTs, and the materials have the largest bending strength when the content were about 2.3%.