Polyborosilazane with Broadly Tunable Boron Content for SiBCN Ceramics

The high-temperature durability of SiBCN ceramics is significantly influenced by the boron concentration and synthesis methods. Although single-source synthetic routes allow one to obtain homogeneous ceramics at the atomic level, the content of the boron element therein is limited by borane (BH₃). In this study, the synthesis of carborane-substituted polyborosilazanes was performed via a simple one-pot reaction of polysilazanes with alkyne bonds on the main chain and decaborododecahydrodiacetonitrile complexes with different molar ratios. This enabled one to vary the boron content from ∼0 to 40.00 wt %. The ceramic yields were in the range of 50.92-90.81 wt %. Independently of the borane concentration, SiBCN ceramics started to crystallize at 1200 °C, and B₄C appeared as a new crystalline phase with increasing boron content. The introduction of boron inhibited the crystallization of Si₃N₄ and increased the crystallization temperature of SiC. The presence of the B₄C phase improved both thermal stability and functional properties such as neutron-shielding characteristics of the ceramics. Therefore, this research opens up new prospects for the design of novel polyborosilanzes with great application potential.