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.