Polyborosilazanes with Controllable B/N Ratio for Si-B-C-N Ceramics

Polyborosilazanes with controllable B/N ratio were synthesized using high-boron-content m-carborane, dichloromethylsilane, and hexamethydisilazane. After high-temperature pyrolysis, Si-B-C-N quaternary ceramics with SiC and B₄C as the main phases were obtained. The B/N ratio in the precursors corresponded to the change in the feeding ratio of carborane and dichloromethylsilane. The effects of boron content and B/N ratio on the ceramic precursors and microphase structure in Si-B-C-N quaternary ceramics were explored in detail through a series of analytical characterization methods. A high boron content results in a significant increase in the ceramic yield (up to 71 wt%) of polyborosilazanes, and at the same time, the B/N molar ratio was regulated from 28.4:1 to 1.62:1. The appearance of the B₄C structure in the Si-B-C-N quaternary ceramics through the regulation of the B/N ratio, has rarely been reported.