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.