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分别采用H2和CO2作为载气,CH4为前躯体,通过等温化学气相渗积制备炭/炭复合材料,通过偏光显微镜、拉曼光谱、X射线衍射和透射电镜对材料微观结构表征以及渗积过程密度变化,研究载气对沉积速率、体密度和微观结构的影响规律。结果表明:在渗积前50 h,CH4-H2体系的沉积速率明显大于CH4-CO2体系,但在其余渗积时间里,CH4-H2体系的沉积速率小于CH4-CO2体系。当载气从H2变成CO2时,复合材料的体密度从1.626 g/cm3增加到1.723 g/cm3,最大径向密度梯度从0.074 g/cm3减小到0.056 g/cm3。同时,基体炭从纯的粗糙体炭转变为杂化粗糙体炭含有过度生长锥,且平均石墨化度从62.7%下降到50.8%。这些显著的变化是由于CO2的氧化作用降低了表面沉积速率,却没有降低孔内沉积速率,同时大量的缺陷形成于层状石墨烯结构中导致形成过度生长锥,降低了热解炭织构。
Carbon and carbon composites were prepared by isothermal chemical vapor deposition using H2 and CO2 as carrier gases and CH4 as precursors respectively. The microstructure and microstructure of the composites were characterized by polarization microscopy, Raman spectroscopy, X-ray diffraction and transmission electron microscopy. Density changes, carrier gas research on the deposition rate, bulk density and microstructure. The results show that the sedimentation rate of CH4-H2 system is obviously higher than that of CH4-CO2 system 50 h before infiltration, but the deposition rate of CH4-H2 system is smaller than that of CH4-CO2 system during the other infiltration time. When the carrier gas changes from H2 to CO2, the bulk density of the composites increases from 1.626 g / cm3 to 1.723 g / cm3, and the maximum radial density gradient decreases from 0.074 g / cm3 to 0.056 g / cm3. At the same time, the transformation of base char from pure asperitic char to hybrid char increased overgrowth and the average degree of graphitization decreased from 62.7% to 50.8%. These significant changes are due to the reduction of surface deposition rate due to the oxidation of CO2, without decreasing the deposition rate in the pores. Meanwhile, a large number of defects are formed in the layered graphene structure, leading to the formation of overgrowth and reducing the pyrocarbon texture.