碳纤维预制体的初始A／V值对化学气相渗透动力学和热解碳结构的影响

采用体积含量分别为7．1％和14．2％的两种碳纤维符向州性针刺毡为预制体，研究厂预圳体内部训始碳纤维表面积与自由体积比值（A／V值）对热解碳的等温等压化学气相渗透动力学以及热解碳纵念结构变化的影响史验研究以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20h到120h不等热解碳沉积后测量了C／C复合材料的表观密度、开气孔率、热解碳的真密度及其内部分布。利用正交偏光显微镜测试了热解碳的织态结构，研究结果表明，热解碳的初始沉积过稃主要受气相-表面形核机制控制，随着致密化的进行，逐渐转变为表面生长机制，这种从彤核到表面生长机制的转化，导致了热解碳的织态结构相应地从低织构向中织构、最后钊高织卡勾的转化。上述沉积机制和结构的变化，都是由于碳纤维编制体初始A／V值的不同以及由于热解碳不断沉秘导致的A／V值的不断增大引起的。增大碳纤维编制体的初始A／V值，可以导致这此转化存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。

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

Abstract： Isothermal, isobaric chemical vapor infiltration of carbon filter telts with fiber volume fl＇actions of 7. 1% and 14.2% were investigated to analyze the influence of initial surface area/ volume ratio, A/V ] , of the fiber pretbrm on infihration kinetics and texture of infiltrated carbon. Experiments were perfbrmed at a temperature of 1 095 ℃ , a methane pressure of 22.5 kPa, a residence time of 0. 1 s and infiltration times being stepwise increased fl＇om 20 to 120 h. Global tmlk density and bulk density, porosity as well as density of matrix carbon as a function of infihration depth were deter- mined. Carbon texture was analyzed with polarized-light microscopy. The results show that infiltration kinetics in the initial stage of infiltration are dominated by the nucleation meehanism and afterwards by the growth mechanism of earbon forma- tion. 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 II ratio. They occur in a significantly earlier stage in the case of the feh with the higher initial A/V I] ratio, as to be expected. These results are a perfect confirmation of eonelusions from ear- lier studies.