High-temperature oxidation behavior of SiBN fibers in air

SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers has not been studied yet. In this work, we studied the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000–1400 °C in air. SiBN fibers started to be oxidized at 1100 °C, with Si 3 N 4 and BN phase oxidized to SiO 2 and B 2 O 3 , respectively. Due to the gasification and the escape of molten B 2 O 3 at high temperatures, amorphous SiO 2 could be remained at the fiber surface. As the fiber further oxidized, the molten B 2 O 3 at the inside may infiltrate into the fiber interior to react with Si 3 N 4 , causing the precipitation of hexagonal boron nitride (h-BN) nanoparticles and the formation of SiO 2 /BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.