Preparation and Pyrolytic Transformation of Borazine Modified Polysilazoxane to Low-Carbon Si–B–N–O Ceramics

Si–B–N–O ceramics are promising materials for wave-transparent windows of hypersonic vehicles due to the excellent thermal stability and low dielectric constant. The polymer-derived ceramics (PDC) route is widely adopted for flexible compositional control of the Si–B–N–O covalent ceramics. In this study, a novel borazine-modified polysilazoxane (RBOSZ) was synthesized using trichlorosilane, tert -butanol, trichloroborazine, and ammonia as starting materials. RBOSZ features a Si–N–Si backbone and borazine rings. The Si–B–N–O ceramic was derived from RBOSZ with a ceramic yield of 61 wt% after pyrolysis under nitrogen atmosphere. Boron facilitates the formation of Si 2 N 2 O nanograins at elevated temperatures and enhances the ceramic’s high-temperature stability. By switching nitrogen to ammonia during organic-inorganic transformation, a low-carbon Si–B–N–O ceramic was obtained and retained its amorphous structure up to 1400 °C. After annealing at 1600 °C, Si 2 N 2 O/β-Si 3 N 4 nanocrystals participated in the Si–B–N–O matrix. This work establishes a facile precursor for high-performance Si–B–N–O ceramics to meet the application demands of heat-resistant wave-transparent windows.