载气对C/C复合材料CVI热解炭显微结构的影响

在1000℃,0.5 kPa丙烯分压条件下,以N₂、H₂为载气和无载气情况下于热梯度CVI炉中制备了C/C复合材料,研究了载气特别是氢气对材料基体热解炭显微结构的影响。通过偏光显微镜测定材料不同区域CVI热解炭的消光角,分析热解炭显微结构在试样中的分布规律。结果表明: N₂在CVI过程中充当惰性角色,不影响热解炭的显微结构; H₂可以调节热解炭沉积时的微环境气氛,更有利于得到粗糙层结构热解炭。试样增密延长炭源气滞留时间,引起带状结构热解炭中显微结构的突变。借助氢气作为载气,可以实现对C/C复合材料中热解炭显微结构的更优控制。 

EFFECT OF CARRIER GAS ON THE MICROSTRUCTURE OF CVI PYROCARBON IN C/C COMPOSITE

Using nitrogen, hydrogen respectively as the carrier gas, the C/C composite was fabricated by the thermal gradient CVI process under the condition of 1000℃,0.5 kPa propylene partial pressure. The influence of the carrier gas especially hydrogen on the structure of pyrocarbon was researched. Extinction angles of CVI pyrocarbon at different areas of the samples were tested by polarized light microscopy, which were used to analyze the alteration of the microstructure of pyrocarbon. The results show that the addition of nitrogen can not change the microstructure of pyrocarbon which plays an inert role. And the addition of hydrogen has more advantage to obtain rough laminar microstructure pyrocarbon by changing components of the micro-environment during CVI process. The influence of density addition on residence time of the reactants leads to an abrupt change of pyrocarbon microstructure. The better control of the structure of the pyrocarbon in the C/C composite can be achieved by adding hydrogen.