Pyrolysis synthesis of Si-B-C-N ceramics and their thermal stability

Si-B-C-N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane (PCS) and polyborazine (PBN). The pyrolysis behavior and structural evolution of the hybrid precursor, the microstructure and composition of the prepared Si-B-C-N ceramics were fully investigated. It was found that the copyrolysis of hybrid polymeric precursors in Ar led to the release of CH4, CH3NH2 and CH3CN gases at temperatures ranging from 200 to 1100 °C, and finally resulted in the formation of amorphous Si-B-C-N ceramics. In particular, the Si-B-C-N ceramics formed from the hybrid precursor with PBN/PCS mass ratio of 1 could keep amorphous state up to the annealing temperature of 1800 °C with weight change of only 2.08%. But this amorphous ceramics would decompose to form crystalline SiC, BN and Si3N4 at 2000 °C. Additionally, compared with PCS-derived SiC ceramics, the Si-B-C-N ceramics showed improved anti-oxidation performance up to 1300 °C due to the formation of borosilicate layers covering the ceramics.