Deng H.,Xian Aerospace Composite Research Institute |
Zhang X.,Xian Aerospace Composite Research Institute |
Li K.,Northwestern Polytechnical University |
Zheng J.,Xian Aerospace Composite Research Institute |
Yin Z.,Xian Aerospace Composite Research Institute
Proceedings of the International Astronautical Congress, IAC | Year: 2013
Carbon nanofilament (CFC) network reinforced carbon/carbon composites with the average density 1.72-1.75 g/cm3 were successfully produced by floating-catalytic film boiling chemical vapor infiltration from xylene pyrolysis at 1000 to 1100 °C. The catalytic effects of ferrocene content on the densification behavior were investigated such as the relative mass gain, the deposition rate, and the profiles of density and pyrocarbon (PyC) layer thickness. The microstructure of PyC matrix and CFC was observed using polarized light microscopy, scanning electron microscopy, and transmission electron microscopy. Results showed that, under the special floating catalyst method, the initial deposition rate of PyC firstly increased to a higher value at 0.8 wt% catalyst and then decreased as the catalyst content further increased to 2.0 wt%. The final density of the composites tended to decrease along both the axial and negatively radial directions resulted from the enhanced difficulty of mass transfer at the latter densification. A single layer of rough laminar (RL) PyC matrix was formed through heterogeneous nucleation and growth for the deposition at 0-0.8 wt% catalysts. But a hybrid matrix composed of isotropic (ISO) and RL PyCs was produced at 1.2 wt% catalyst, and the thickness of ISO layer increased at the higher catalyst content of 2.0 wt%. The reason for ISO PyC formation was mainly attributed to the deposition of iron encapsulated carbons and the possible homogeneous nucleation. A reinforced network consisted of numerous CFCs and vapor growth carbon fiber (VGCF) was formed probably through tip-growth mechanism. The direct deposition of PyC on CFC was the formation reason of VGCF. A transition of the CFC was generated from nanotube to nanofiber when the catalyst content increased to 0.5 wt% because of the enhanced diffusion rate of carbon atoms through and over the iron particles. The composites with a high density of 1.75 g/cm3 and uniform RL PyC matrix are rapidly produced at the catalyst content about 0.5 wt% resulting from the modified deposition front exhibiting a small thickness and large concave radius. Copyright © 2013 by the International Astronautical Federation.
Xiao C.,Xian Aerospace Composite Research Institute |
Cao M.,Xian Aerospace Composite Research Institute |
Zhou S.-J.,Xian Aerospace Composite Research Institute |
Zhang Z.,Xian Aerospace Composite Research Institute |
Zheng R.,Xian Aerospace Composite Research Institute
Guti Huojian Jishu/Journal of Solid Rocket Technology | Year: 2012
The thermal expansion coefficient is the key parameter related to the thermal stability of C/C composite. The thermal expansion performance characteristics of radial rod preform composite were analyzed in order to understand the linear expansion behavior of C/C composite. Results show that the thermal expansion properties of the radial rod preform composite present significant anisotropic character, and the radial expansion coefficient is the highest. The thermal expansion coefficient increases with the increase of temperature, and it is stable between 800°C and 1000°C. The thermal expansion coefficient of this material increases when the density increases from 1.89 g/cm3 to 1.96 g/cm3. The radial expansion coefficient of this material at 1000°C decreases from 8.486×10-6°C-1 to 3.488×10-6°C-1 after the heat treatment at 900°C.