Microstructure,mechanical And Thermal Properties Of Carbon Nanofiber Reinforced Carbon-graphite Materials

Carbon-graphite material has the characteristics of light weight,high strength,high modulus,high wear resistance,self-lubrication,good electrical and thermal conductivity,high temperature resistance,corrosion resistance and thermal shock resistance,and is widely used in aerospace,transportation,energy,chemistry and other fields.However,due to the pyrolytic polycondensation of the binder in the preparation process,it is difficult to synchronize the contraction between the binder and the aggregate due to the mismatch of the expansion coefficient,so it is easy to cause the initiation of cracks and pore defects in the material,which seriously affects the microstructure and macroscopic properties of the carbon-graphite material.At present,how to control the microstructure of carbon-graphite materials,restrain the initiation and expansion of structural defects,and realize the integration of structure and function of carbon-graphite materials is one of the research hotspots and difficulties in this field.In view of the structural and functional integration problems of carbon-graphite materials due to congenital defects,this paper takes carbon nanofibers as reinforcement phase,pitch based carbon-graphite materials as the research object,and takes "liquid phase mixing process to improve the dispersion of carbon nanofibers--functional surface modification to improve phase interface bonding" as the main line of research.By amination of grafted carbon nanofibers as carbon-graphite material micro area of the bracket of "bridging",using its own carrying reactive as coking basal micro area,in clearance of the aggregate of the micro area construction zone "bridging" strengthen the structure,and to clarify the structure of micro zone microstructure of carbon-graphite material,the effects of thermal properties and the mechanism of action.The main conclusions are as follows:(1)The liquid phase mixing process was used to prepare carbon nanofiber-reinforced carbon-graphite material,which was different from the traditional solid-phase mixing and kneading process.The influence of the preparation process on the structure and properties of carbon-graphite material and the influence of the existence form and dispersion of carbon nanofibers in the matrix was investigated.It is found that the solvent of tetrahydrofuran used in liquid phase mixing process can increase the oxygen content of pitch,enrich its alkyl chain structure and improve the fluidity of pitch.Compared with the traditional solid phase mixing and kneeling process,the carbon nanofibers can be uniformly dispersed in the matrix,and the mechanical properties of the carbon nanofibers reinforced carbon-graphite materials are improved.The flexural strength and compressive strength of the carbon nanofibers are 22.32 MPa and 37.64 MPa,respectively.(2)Using surface modification method,acidification and aminosylation graft surface treatment of carbon nanofibers were carried out to explore the effect of surface treatment on the microstructure and dispersion properties of carbon nanofibers in solvents,and the effect of aminosylation graft carbon nanofibers on the microstructure and mechanical and thermal properties of carbon-graphite materials.The study found that the surface modification of carbon nanofibers surface introduced a large number of functional groups(carboxyl,amino,alkyl chain,etc.).The existence of surface functional groups can improve the carbon nanofibers and interaction between solvent and between each other,hinder the carbon nanofibers reunion caused by intermolecular action,amination grafted carbon nanofibers also has the good interface bonding fiber and matrix.The introduction of amine-grafted carbon nanofibers can effectively improve the structure densification degree and microstructural integrity of carbon-graphite materials.The flexural strength,compressive strength and thermal conductivity of the carbon-graphite material are1.67,1.47 and 1.16 times higher than those of the raw material when the amount of amino grafted carbon nanofibers is 0.7 wt.%,respectively.(3)Based on the experimental data and analysis results obtained by different methods,the mechanism of action of aminoated carbon nanofibers on the micro zone strengthening structure of carbon-graphite materials was explored.The results show that the amine-grafted carbon nanofibers can construct a "micro-area bridge" reinforced structure in the aggregate gap by virtue of the active groups carried on the surface and their excellent mechanical and thermal properties.Micro area of reinforced structure constructing effectively improve the quality of micro area sintering coking and improve the micro area reduces the densification degree caused by inconsistent shrinkage porosity and crack initiation,and rely on amination grafted carbon nanofibers its excellent mechanical and thermal properties of graphite and carbon matrix formation of good interface bonding,effectively restrain the expansion of the micro cracks,The microstructure and macroscopic mechanical properties and thermal properties of carbon-graphite materials were improved.