Influence of Initial Surface Area / Volume Ratio of the Fiber Preform on Kinetics of Chemical Vapor Infiltration and Texture of Infiltrated Carbon-中国材料进展

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Title:: Influence of Initial Surface Area / Volume Ratio of the Fiber Preform on Kinetics of Chemical Vapor Infiltration and Texture of Infiltrated Carbon

作者:: 张伟刚1; 2; Hüttinger K.J. 1; (1.卡尔斯鲁厄理工学院化学技术与高分子化学研究所，德国卡尔斯鲁厄 76131)(2.中国科学院过程工程研究所多相复杂系统国家重点实验室，北京100190)

Author(s):: ZHANG Weigang1; 2; Hüttinger K.J. 1; (1. Institute of Chemical Technology and Polymer ChemistryKarlsruhe Institute of Technology, Karlsruhe 76131, Germany)
(2.State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, CAS, Beijing 100190, China)

摘要:: 采用体积含量分别为7.1%和14.2%的两种炭纤维各向同性针刺毡为预制体，研究了预制体内部初始炭纤维表面积与自由体积比值（A/V值）对热解炭的等温等压化学气相渗透动力学以及热解炭织态结构变化的影响。实验研究以22.5kPa纯甲烷为碳源气体，沉积温度为1095℃，气体平均停留时间0.1s，沉积时间从20小时到120小时不等。热解炭沉积后测量了C/C复合材料的表观密度、开气孔率、热解炭的真密度及其内部分布。利用正交偏光显微镜测试了热解炭的织态结构。研究结果表明，热解炭的初始沉积过程主要受气相-表面形核机制控制，随着致密化的进行，逐渐转变为表明生长机制。这种从形核到表面生长机制的转化，导致了热解炭的织态结构相应地从低织构向中织构、最后到高织构的转化。上述沉积机制和结构的变化，都是由于炭纤维编制体初始A/V值的不同以及由于热解炭不断沉积导致的A/V值的不断增大引起的。增大炭纤维编制体的初始A/V值，可以导致这些转化在致密化过程中提前发生。上述结果能够很好地证明以前相关研究的结论。

Abstract:: Isothermal, isobaric chemical vapor infiltration of carbon fiber felts with fiber volume fractions of 7.1% and 14.2% were investigated to analyze the influence of initial surface area / volume ratio, [A/V], of the fiber preform on infiltration kinetics and texture of infiltrated carbon. Experiments were performed at a temperature of 1095oC, a methane pressure of 22.5kPa, a residence time of 0.1s and infiltration times being stepwise increased from 20 to 120h. Global bulk density and bulk density, porosity as well as density of matrix carbon as a function of infiltration depth were determined. Carbon texture was analyzed with polarized杔ight microscopy. The results show that infiltration kinetics in the initial stage of infiltration are dominated by the nucleation mechanism and afterwards by the growth mechanism of carbon formation. These changes of deposition chemistry and kinetics lead to changes of carbon texture from low / medium to medium / high. All changes are caused by an increase of [A/V] ratio. They occur in a significantly earlier stage in the case of the felt with the higher initial [A/V] ratio, as to be expected. These results are a perfect confirmation of conclusions from earlier studies.