摘要
在碳/碳复合材料化学气相致密化(CVI)制备工艺中,影响致密化速率的因素主要有两方面:气体前驱体的传输和化学反应(热解反应和表面沉积反应)动力学。微波热解化学气相致密化(MCVI)将微波引入CVI工艺中,旨在缓解气体前驱体的输运和气相反应之间的矛盾,避免表面结壳现象,实现预制体从内到外逐步沉积致密。本文在工艺实验的基础上,结合微波加热的特点,分析了MCVI工艺制备碳/碳复合材料致密化过程中的气相热解反应特点。研究表明:微波选择性加热的特点,甲烷作为非极性分子,不能吸收微波而加热,可以抑制前驱气体在传输过程中的预热解;同时,碳纤维预制体经微波加热后,自发产生一定的温度梯度(预制体表面温度低于内部),抑制了预制体表面的气相热解反应,从而避免了由于在表面沉积引起的结壳现象,使前驱气体能保持线性小分子的状态向预制体内部输送,为实现预制体从内到外逐步致密提供了条件。
In the CVI for the preparation of carbon/carbon composite, densification rate is influenced mainly by two main factors ： transmission of source gas and chemical reaction kinetics. In order to change the reaction kinetic and transmission path of source gas, microwave is introduced into CVI process to weaken the contradiction between transmission of source gas and chemical reaction kinetics, avoid pore choking at the surface of perform, achieve the densification of preform from center to surface. In this paper, the feather of gasphase reaction of MCVI process for the fabrication of carbon/carbon composites was analyzed with feather of microwave heating on the basis of experiment. Result show that nonpolar methane can not be heated by microwave due to the characterization of microwave selectively heating; and temperature gradient was produced by itself, pyrolyzation reaction of source gas was inhibited in the course of transmission, pore choking on the surface of perform is avoided, carbon source gas is kept linear small molecule diffusing into performs and fed continuously into the center of perform. Thus performs can be densified progressively from center to surface.
出处
《硅酸盐通报》
CAS
CSCD
北大核心
2009年第4期796-799,共4页
Bulletin of the Chinese Ceramic Society
基金
国家自然科学基金项目(50672059
50702034)
广东科技攻关计划项目(2004B10301006)
深圳大学科研启动基金资助项目(200804)资助
关键词
微波
CVI
碳/碳复合材料
热解反应
microwave
CVI
carbon/carbon composites
gasphase reaction
