Preparation Of Carbon Nanofiber/Carbon Fiber Hybrid Reinforced Carbon/Carbon Composites

Two kinds of CNF/CF hybrids (CNF/carbon fiber felt hybrid, CNF/chopped CF hybrid) were synthesized through the chemical vapor deposition (CVD) using carbon felt and chopped CF as the support for metal Ni catalysts. The as-synthesized CNF/CF hybrids were used to reinforce carbon/carbon (C/C) composites using phenolic resin as carbon precursors. The effects of synthesis conditions including growth time, temperature, and C2H4content on the yield, morphology, structure, thermostability and surface area of the hybrids were studied. The density and the friction property of the resulting C/C composites were inverstigated. The main conclusions are as follows.1. The CVD process conditions such as growth time, temperature, and C2H4content played a significant role in the yield, morphology, structure, thermostability and surface area of the CNF/CF hybrids. Consequently, the properties of CNF/CF hybrid can be regulated by changing the above CVD conditions.2. The CNF/CF hybrids were firstly prepared by using carbon felts as the support. There was no obvious change on the CNF diameter while the growth time prolonged. However, the CNF yield showed rapid increased at the first growth duration, and then gradually stable due to the active, loss of the catalysts and the inner diffusion limitation. The growth temperature had great impact on the activity of catalysts, leading to the formation of the smooth, uniform CNF at the relatively high temperature. The carbon source content in the gas steam also affected the morphology and diameter of CNF, and sastifity cotent was around80%.3. The C/C composites were synthesized by a hot-press method using the as-synthesized CNF/CF hybrids as the reinforcements and phenolic resin as the matrix, respectively. The density of C/C composites showed a trend of increasing first and then becoming stable with the increasing impregnation times. In addition, the density increased with the CNF content increasing. The addition of CNF into the C/C composites could greatly improve the friction properties. At a low content of CNF, the resulting composites had a friction coefficient lower with the lubricating film it formed. However, excessive CNF content would soften the friction surface, thus increasing the friction coefficient significantly.4. CNF/CF hybird can also be synthesized using the chopped carbon fibers as the support with the similar processing conditions. The as-obtained hybrids were then used to reinforce the C/C composites. The density of the C/C composites increased gradually with the CNF/CF hybrid content, while the friction coefficient decreased until the hybrid content up to28%.