Thermal stability of polymer derived SiBNC ceramics

To study the thermal stability of polymer derived SiBNC ceramics, a polyborosilazane was pyrolyzed in N2 and NH3/N2 atmosphere, respectively. The as-pyrolyzed products were annealed in N2 atmosphere at 1200–1850 °C for 2 h. The chemical composition and phase structure of the as-pyrolyzed and annealed ceramics were investigated by element analysis, XRD and FT-IR. The results show that all the ceramics exhibit excellent high temperature stability. They are fully amorphous to 1700 °C, and only partial crystallization, giving a mixture of Si3N4, BN and SiC phases, is observed upon heating at 1850 °C. The N2 pyrolyzed products show better stability than the NH3/N2 pyrolyzed products and have less tendency to crystalline at higher temperatures. Better retention of nitrogen at high temperatures is also observed for the N2 pyrolyzed products.