| Since mesocarbon microbeads (MCMB) was discovered in 1961, numerousresearch and exploitation have been carried out owing to its unique morphology andstructure, which greatly enriched the theory of liquid-phase carbonization and directedthe further development of MCMB. MCMB is endowed with the self-sinterability bythe presence of β resin (Benzene Insoluble-Pyridine Soluble fraction called self-binder),which possesses a great molecular weight and a plastic flow property when it is pressedor heat-treated. If MCMB containing certain β resin component was mixed with carbonfibers (CF), CF reinforced MCMB C/C composite was prepared directly via one-stepself-sintering. The method not only will greatly simplify the manufacture process ofC/C composite, but also makes its performance higher than the carbon block withoutcarbon fiber addition. In this paper, MCMB was prepared from a medium coal tar pitch through heatcondensation and solvent extraction processes. The sinterabilty of MCMB wascontrolled by the oxidation treatment in the air. Then MCMB oxidized for differenttime was mixed mechanically with carbon fiber surface treated by HNO3. Theinfluences of oxidation treatment parameters of MCMB and carbon fiber on theproperties of C/C composites in terms of bulk density,volume shrinkage and bendingstrength were investigated in detail. It was found that the bulk density and volumeshrinkage of C/C composites declined after adding CF, while the bending strengthincreased when CF was oxidized at appropriate conditions. High strength C/C IIIcomposite with a density of 1.64 g/cm3 and a bending strength of 72.0MPa wasobtained by hot press molding and carbonization at 1000℃ for 1h from MCMBoxidized at 250℃ in air for 60min and CF treated in nitric acid for 10h. Using oxidized MCMB as matrix, and liquid-phase oxidized PAN-based carbonfiber as reinforcing agent, C/C composites were obtained by hot pressing andcarbonizing at 1000℃. The influences of oxidation time and fiber content on thedensity,volume contraction,bending strength of composites were studied in detail. Itwas found that with the increase of fiber content, the weight loss,density and volumeshrinkage of C/C composites decreased obviously. In the experiment, when theoxidation time of carbon fiber was 2 hour, and the fiber content was 8wt%, the materialexhibited best performance with a density of 1.54g/cm3 and a bending strength of46.0MPa. According to the above results, we can draw the following conclusions:Comparing the C/C composite material reinforced by pitch-based carbon fiber with thecarbon block without carbon fiber, the physical properties curve of the both materialsalmost keep the same changing trend. It indicates that during the heat treatment, fiberholds the accordant contraction with MCMB. While the composites reinforced byPAN-based carbon fiber has poorer mechanical properties than carbon block withoutfiber. Moreover, from the surface analysis of carbon fiber, it was found that the surfacefunctional group of the 2-hour-oxidized fiber was developed, and can fulfill therequirement of forming a kind of firm interface combination with the matrix. Theappearance of crack or other deficiencies and the reduction of mechanical propertiesshould mainly be caused by the great difference between the fiber and the matrix in thevolume contraction and other physical properties. IV...
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