Microphase evolution of Si–B–C–N ceramics: A deep insight into the effect of boron on pyrolysis and crystallization

Silicon boron carbonitride (SiBCN) ceramics have garnered significant attention due to their exceptional high-temperature stability, resistance to creep, and favorable electrical properties. However, the ceramicization mechanism of covalently bonded boron atoms in polyborosilazane (PBSN), which is crucial in determining the structural and crystalline phase evolution of silicon boron carbonitride (SiBCN) ceramics through the polymer-to-ceramic process, still needs further clarification for the design of advanced ceramics. Therefore, PBSN precursors constructed with B–C bonds were systematically investigated in the polymer-to-ceramic conversion process. B–C bonds were transformed into B-N bonds between 300°C and 600°C, ultimately resulting in the formation of h-BN at high temperatures. Meanwhile, higher levels (8.11–14.12%) of B facilitated the formation of SiC at equivalent temperatures but hindered the formation of Si 3 N 4 crystal nuclei. That is due to the formation of B–N and NB 3 units, which inhibited the formation of Si–N bonds and SiN 4 units, thereby interfering with the nucleation process of Si 3 N 4 and facilitating the crystallization of SiC. This study offers valuable insights for regulating the microphase evolution and properties of PDC nanocomposites.