化学气相渗积压力对渗积速率和热解炭组织结构的影响

摘要

Carbon/carbon composites were fabricated by chemical vapor infiltration of needled carbon fiber felts (70％porosity) with natural gas as precursor at different infiltration pressures.The thermodynamics of methane pyrolysis and the densification kinetics were used to investigate the influence of infiltration pressure on the infiltration rate and the microstructure of pyrocarbon.The microstructure of pyrocarbon was examined by polarized light microscopy.Results showed that the initial infiltration rate increased with pressure,whereas it decreased with pressure during the later stages of infiltration,which led to a decrease in the final density of the samples.The pyrocarbon microstructure depended markedly on the infiltration pressure at the given deposition temperature.Rough laminar (RL) carbon is formed as the matrix at the lowest pressure (approximately 1kPa).At medium pressures (3,5,and 10kPa),isotropic (ISO) carbon is formed,followed by RL carbon,in the radial direction of the carbon fiber,with RL being the major matrix.Smooth laminar and ISO structures are the major phases at high pressures ( 15 kPa).%采用天然气为前躯体在不同压力下使用化学气相渗积法制备炭/炭复合材料.利用甲烷分解热力学与沉积动力学研究了渗积压力对渗积速率和热解炭组织结构的影响.采用偏光显微镜观察热解炭的组织结构.结果表明:随着渗积压力的增加,初始渗积速率增大；但在渗积后期,渗积速率随着渗积压力的增大而降低,导致在高渗积压力下相同时间制备样品的最终密度降低.热解炭组织结构对渗积压力具有很强的依赖性.在低压(1 kPa)下渗积得到的热解炭基体全部为粗糙层结构.在适中的压力(3kPa,5 kPa,10 kPa)下,以炭纤维为圆心由内到外依次得到各向同性和粗糙层热解炭,整个基体以粗糙层为主.在15kPa下,得到的热解炭组织结构为各向同性和光滑层组织.