Polyborosilazane‐Derived High Temperature Resistant SiBCNO

One of the main features of SiBCN‐based ceramics is their high temperature stability with respect to crystallization and decomposition in protective atmospheres. High temperature studies of a polyborosilazane in air up to 1500 °C show that the formation of coexisting nano‐quartz and amorphous B₂O₃ is suitable for the application as adhesive for bonding advanced ceramics. Spectroscopic and X‐ray studies combined with thermal analysis clearly demonstrate the strong influence of the presence of air on the cross‐linking and pyrolysis behavior and, thus, finally on the ceramization process of the applied SiBCN preceramic polymer. Accordingly, cross‐linking and subsequent pyrolysis of the SiBCN‐precursor up to 1600 °C in air result in the formation of a network structure comprised of SiO₂ and B₂O₃ with minor amounts of residual amorphous SiBCN. In contrast to the polymer‐to‐ceramic transformation of the used polyborosilazane in protective atmospheres like Ar or N₂, the ceramic yield at 1400 °C is high and amounts 85.6 wt%. Furthermore, the elemental composition of the resulting SiBCNO does not change significantly at T > 1200 °C even after heat‐treatment at 1600 °C indicating the high temperature stability of the resulting SiBCNO material.