The effect of carbon nanotubes on the microstructure and morphology of pyrolytic carbon matrices of C-C composites obtained by CVI

Traditional isothermal CVI technology was used to explore the effect of carbon nanotubes (CNTs) on the microstructure of pyrocarbon. Polarized-light optical microscopy, SEM and Raman spectroscopy were used to analyze the textures of pyrocarbons in pure carbon/carbon composites (as contrast), aligned carbon nanotube/carbon (ACNT/C) composites and carbon/carbon composites doped with multi-walled CNTs. Tests show that even though deposition conditions in this study bring about typical smooth laminar typed pyrocarbon in pure C/C composites, pyrocarbons in the other two composites exhibit microstructure of rough laminar type, which indicates that CNTs conduced to formation of high-textured pyrocarbon. Such effects of CNTs might be ascribed to the following two sides: on the one hand, CNTs act as in-situ nuclei for the various sized polyaromatic molecules in gas phase, thus led to growth mechanism in pyrocarbon formation, and on the other hand, their π orbitals would attract those molecules with similar hybridized atomic orbitals by Van Der Waals forces to form orderly stacked layers, which has been proved by HRTEM observations.