不同分子量聚碳硅烷的性能及对C/C-SiC复合材料增密的影响

Performance of Polycarbosilane With Different Molecular Weigh and Its Effect on Densification of C/C-SiC Composites

以四种分子量级别聚碳硅烷(PCS)为浸渍剂,采用CVD和浸渍-裂解工艺制备了C/C-Si C复合材料,分析了四种分子量级别PCS的分子量、软化点,分子结构和热失重性能,采用压汞法测试试件的孔隙分布特性。分析表明,PCS的软化点和800℃转化率都随着分子量的提高而提高;四种分子量级别的PCS热分解过程基本相同,分子的支化程度差异不大。数均分子量为1 178、1 333的PCS的整体致密化效率要高于数均分子量为1 550的PCS,经过7个周期致密后,分子量为1 178的PCS所致密试样的累积孔隙容积最高,分子量为1 550的PCS所致密的试样最低。前5个浸渍裂解致密周期采用分子量为1 550的PCS,以后周期采用分子量为1 178或1 333的PCS,可以达到较高的致密效率。

C/C-SiC composites were prepared by CVD,impregnation and pyrolysis method using polycarbosilane（PCS） with four number average molecular weight as impregnant. The molecular weight,softening point,molecular structure and thermogravimetic performance of PCS were determined,and the distribution of pores were analyzed by means of mercury intrusion method. The results showed that the softening point and rate of conversion at 800℃ of PCS increased with increasing molecular weight of PCS. The pyrolysis process of PCS with four molecular weight grade were identical,and branch degree did not have significant difference. The integral densification efficiency of PCS with molecular weight 1 178 and 1 333 was higher than that of PCS with molecular weight 1 550. The cumulative pore content of sample densified by PCS with molecular weight 1 178 was maximum after seven densification cycles,and that of sample densified by PCS with molecular weight 1 550 was minimum. When PCS with molecular weight 1 178 and 1 333 was used in previous five-cycles and molecular weight 1 550 was used in other cycles,the material could be densified more efficiently.