Floating catalyst chemical vapor infiltration of nanofilamentous carbon reinforced carbon/carbon composites – Densification behavior and matrix microstructure

Nanofilamentous carbon (NFC) reinforced carbon/carbon composites were prepared by floating catalyst film boiling chemical vapor infiltration from xylene pyrolysis at 1000–1100 °C using ferrocene as a catalyst. The influence of the catalyst content on the densification behavior and matrix microstructure of the composites was studied. Results showed that the deposition rate of pyrocarbon (PyC) was enhanced remarkably by the catalyst. The density of the composites deposited at a catalyst content of 0–2.0 wt% decreased along both the axial and the negative radial directions. Rough laminar (RL) PyC matrix was formed at 0–0.8 wt% catalyst content by heterogeneous nucleation and growth. A hybrid matrix consisting of RL and isotropic (ISO) PyCs appeared at a catalyst content of 1.2–2.0 wt%. The reasons for this ISO PyC formation were attributed to the deposition of carbon encapsulated iron particles and homogeneous nucleation. A reinforcing network composed of NFCs and vapor grown carbon fibers was formed on the fiber/matrix interface and within the matrix in this floating catalyst process. The structure of NFC transformed from nanotube to nanofiber when the catalyst content was over 0.5 wt%, around which composites of a high density of 1.75 g/cm3 and uniform RL PyC matrix were produced rapidly.