SiBCN陶瓷前驱体热解机理研究

Study of Pyrolysis Mechanism of SiBCN Polymer Precursor

采用固体NMR和FTIR为主要测试手段对聚硼硅氮烷(PSNB)热解过程中形成的无定型中间体结构进行表征。结合不同温度处理后产物结构的变化将SiBCN前驱体的热解过程分为如下几个阶段:在400℃以下前驱体主要发生转氨基化反应以及Si—H键和N—H键的脱氢耦合反应释放出NH_3和H_2;在400~800℃时,体系中的S—CH_3及其他烃类基团开始发生分子重排并释放出甲烷气体;800~1 000℃,产物进一步发生结构重排形成无定形网络结构。在温度达到1 000℃时体系基本完成陶瓷化转变,此时无定型陶瓷主要由三种成分组成:(1)无定形碳(石墨状);(2)平面BN相;(3)Si—C—N基体(SiC_xN_(4-x)单元,x=0,1,2,3)。

The pyrolysis mechanisms occurring during the conversion of polyborosilazane（ PBSZ） into amorphous SiBCN ceramics have been investigated. TGA has been applied to investigate the mass loss behaviour during ceramization. Solid-state ^（11）B,^（13）C and ^（29）Si NMR spectroscopy has been applied to probe the local environment of all NMR active nuclei in the precursor,the thermolysis intermediates and the ceramic residue. IR spectroscopy has been performed to receive valuable information on the chemical bonding in all materials. At temperature below 400 ℃,NH_3 and H_2 are released via transamination and dehydrocoupling reaction involving N—H and Si—H units. It is followed by evolution of hydrocarbons due to the cleavage of bonds and formation of methane and hydrogen. Ceramization continues at temperature above 800 ℃. After heating to 1 000 ℃,ceramization complete and free carbon,BN_3 domains as well as Si—C—N units coexist（ SiC_xN_（4-x）,x = 0,1,2,3）.