The Preparation And Research Of Fiber/Graphene Aerogel Modified ZrC Composites

The development of hypersonic vehicle requires ultra high-temperature resistant materials quite badly. Fiber reinforced ultra high-temperature ceramic matrix composites overcome the defects of the brittleness and poor thermal shock resistance in ceramics, and have advantages such as low density, low rate of expansion and high thermostability. Their performance can be designed as well, thus they are promising in the field of ultrasonic aircraft thermal protection system. In this paper, a new high-temperature resistant composite, was prepared and its properties were studied, Other studies were also carried out on graphene aerogel modified carbon fibers, the selection of ZrC precursor used for PIP process, and then the C_f/ZrC fabricated by PIP process. The effects of pyrolysis temperature and impregnation times on the properties of the composite material had detailed studied.The graphene oxide was prepared through a method of improved Hummers. It was found that during the experiment of sedimentation the thickness of graphene oxide sheet was about 1.24 nm after a process of ultrasound for 2.5h. After analysis, it is found that there were C-O-C,-OH, COOH and other oxygen-containing functional groups in the graphene oxide sheet. Melamine acts as the cross-linker agent which can make graphene oxide gelled, and the change of p H value can make sol-gel transition happen. The reduced graphene aerogel was prepared by two different methods. The results show that aerogel has uniform pore distribution. The pore size of graphene aerogel reduced by hydrazine vapor is relatively larger and a thiner layer of grapheme compared with the graphene aerogel reduced by hydrothermal. The analysis found that the C-O-C of graphene oxide was reduced, the content of-COOH,-OH and other oxygen-containing groups were decreased, and the reduction did not make the defects of graphene decreased, but further undermined the graphene crystal regularity.We had prepared carbon fiber/reduced graphene oxide aerogel composites reduced by hydrazine vapor and hydrothermal, respectively. We has found that, little graphene aerogel uniformly dispersed and coated on the surface of carbon fibers in the carbon fiber/reduced graphene oxide aerogel composites reduced by hydrazine vapor, while the increased content of graphene, and more graphene aerogel with interconnection network structure uniformly dispersed in the pores of the carbon fibers were found by hydrothermal reduction. The analysis found that the C-O-C of graphene oxide was reduced, the content of-COOH,-OH and other oxygen-containing groups were decreased, peak-differentiating and imitating of N1 s peaks has found quaternary N（-NH3+）, which also proves that the-NH₂ of melamine and-COOH of carbon fiber or graphene oxide have react with ionic bonding. The thermal stability of carbon fiber/reduced graphene aerogel composites have been greatly improved under Ar atmosphere.In this paper, we had prepared carbon fiber/graphene aerogel modified ZrC ceramics by different impregnation times using vacuum impregnation method, and pyrolysis at different temperatures to obtain composite materials. Pyrolysis ZrC ceramic precursor at different temperatures, we found only t-Zr O₂ phase was produced under 1000℃, t-Zr O₂ conversion to m-Zr O₂ phase occurs above 1000℃, the system obtained ZrC ceramics by carbothermal reduction reaction when the temperature is higher than 1500℃,and the product of pyrolysis was ZrC ceramics under 1600℃. But the rate of pyrolysis is very low. The effect of different pyrolysis temperatures on material properties has found that the carbon fiber involved carbothermal reduction in system, and as the temperature increased, the carbon fibers were more serious corrosion. The introducement of graphene could decrease carbon fibers participation carbothermal reduction. Studying on material properties by impregnation different times, we found that the density has increased with the introduction of graphene compared with pure carbon fiber, and the porosity is correspondingly low. With increasing impregnation times, the density of composites has increased and the porosity has also reduced.