碳源对CVI炭/炭复合材料致密和结构的影响

The influence of hydrocarbon gas on the density and microstructure of C/C composites formed by chemical vapor infiltration

采用自行设计的化学气相渗(CVI)炉以炭毡作为纤维增强体,在坯体内部设计特殊的导电发热层,使坯体内部的温度场、气体反应的中间产物浓度场、电磁场等多元物理场实现耦合,进而达到坯体的快速增密。研究了沉积温度为800℃～1000℃,系统压力0.1kPa～15.0kPa条件下,分别使用石油液化气和丙烯作碳源时对增密速度和沉积热解炭结构的影响;借助偏光显微镜考察了沉积炭的组织结构;用X射线衍射表征了C/C复合材料的石墨化度和微晶尺寸。研究表明:初始密度为0.2g/cm3,尺寸为260mm×60mm×20mm的炭毡坯体沉积20h,经过工艺优化,石油液化气可使坯体增密到1.7g/cm3以上,丙烯可使坯体增密到1.6g/cm3以上;两种碳源沉积所获材料的晶体有序度均随沉积温度的升高和系统压力的降低而升高,其中石油液化气在较高温度(990℃)、较低压力(0.1kPa)下能沉积出织构更高的结构一致的粗糙层结构热解炭;说明不同活化能的复合碳源气体可以发挥与其他物理场梯度的协同耦合作用,有利于提高沉积速度和热解炭的织构。

Chemical vapor infiltration (CVI) of carbon felts to fabricate C/C composites was carried out by implanting a special electrically conductive layer in the carbon felts, which resulted in rapid densification by a coupling effect of temperature gradient, reaction intermediate gradient, and magnetic field. Liquefied petroleum gas (LPG) and C3H6 were employed as carbon sources. The deposition temperatures were in the range of 800 1000 degrees C, and the deposition pressure was in the range of 0.1-15.0 kPa. The textures of the pyrolytic carbons were observed by polarized light microscopy, and the crystallite size of these C/C composites was analyzed by XRD. Results show that infiltration of the porous C/C performs, 260 mm x 60 mm x 20 mm, for 20 h leads to C/C composites with density of more than 1.7 g/cm(3) from LPG, and of more than 1.6 g/cm(3) from C3H6. The deposition rate for LPG under optimized conditions was more rapid than for C3H6. It is shown that LPG mixed with hydrocarbon gas, whose activation energy is different, can cooperate with other physical fields to improve the deposition rate and texture of the pyrolytic carbons.