液相法快速制备炭/炭复合材料的动力学及微观结构研究

KINETICS AND MICROSTRUCTURE OF CARBON/CARBON COMPOSITES PREPARED BY LIQUIDPHASE DENSIFICATION PROCESS

以航空煤油为前驱体,普通炭毡为预制体,采用液相法快速制备出了炭/炭(C/C)复合材料(150mm×80mm×15mm),系统压力:0.1MPa,沉积温度:980～1180℃。对制备过程的动力学及微观组织结构进行了研究,并初步提出了以航空煤油为前驱体的液相法的沉积模式。研究结果表明:其表观活化能为30.31kJ/mol,沉积速率最快可达0.222g·cm-3·h-1,比传统等温CVI工艺快了近2个数量级;致密化初期,沉积过程受控于化学反应动力学,沉积速率很快,而在致密化中、后期,由于反应气体的传输受到限制,且预制体的表面活性位增加,沉积速率下降,试样的沉积主要包括其内部孔隙的致密和外表面的沉积两部分;沉积温度对致密化过程起着很重要的作用,在1080℃,样品的沉积过程受传输限制的影响最小,孔隙沉积速率最大,可以在10h内将样品的密度从0.167g/cm3提升到1.7g/cm3,致密化结构最均匀,且以RL组织为主,沉积温度偏低或偏高都会降低其沉积速率,且有SL及ISO组织生成。

A new process for the liquid- phase densification of C/C composites which reduces the preparation time greatly has been described. Several sets of samples （150 mm ×80 mm× 15 mm） were prepared at atmospheric pressure in the temperature range 980- 1 180℃for studying the kinetics and the influence of processing temperature. The carbon fiber felt was used as the reinforcement, and the kerosene was as the precursor. A densification rate up to 0. 222 g/cm^3 per hour, which is two or more orders of magnitude larger than that of traditional ICVI process, and the much lower activation energy of 30. 31 kJ/mol determined from the initial stage was obtained. The potential kinetics of reaction have been discussed. At initial stage, the course is controlled by kinetics of the chemical reaction, and the densification rate is accelerated in remarkable extent; at the following stage, the diffusion of the reactive species plays a side role, and the mass increase is mainly caused by the infiltration of the pores and the pyrocarbon deposited at the outer surface. At 1 080 ℃, the sample density can be increased from 0. 167 g/cm3 to 1.7 g/cm3 in 10 hours. Textural characteristics of the pyrocarbon were analyzed by the polarized light microscope （PLM）. It can be demonstrated that the high textured carbon constitutes the majority of the pyrocarbon at 1 080 22, medium- or low- textured pyrocarbon would exist at lower as well as higher processing temperatures.