Low-dielectric continuous ceramic fibers with thermal and load-bearing functions serve as critical raw materials for accident-tolerant ceramic composites in aerospace shuttles. Silicon oxynitride ceramics exhibit a temperature resistance exceeding 1700 °C, which holds potential applications in extreme thermal protection materials. According to the attractive potential properties of silicon oxynitride ceramics, this study develops continuous silicon oxynitride (sinoite) fibers with a near-stoichiometric Si₂N₂O ratio and a tensile strength of 1.53 GPa via the precursor conversion method. The research investigates the relationships between composition and microstructure, demonstrating mechanical properties and high-temperature evolution. Sinoite fibers retain 65% of their strength at 1600 °C in a nitrogen atmosphere. After 1700 °C treatment, Si₂N₂O crystallization formed on the surface layer, elucidating the mosaic-shell formation mechanism in high-temperature evolution. Despite extremely low porosity, the strength retention rate remained up to 51%. To the best of our knowledge, this study provides a novel sinoite fiber with outstanding heat resistance up to 1700 °C for the first time. The sinoite fibers exhibit excellent properties compared with alumina, silicon nitride, and mullite fibers, offering promising reinforcement for thermal protection systems and electromagnetic components served in extreme environments.

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 ℃ in air. SiBN fibers started to be oxidized at 1100 ℃, with Si₃N₄ and BN phase oxidized to SiO₂ and B₂O₃, respectively. Due to the gasification and the escape of molten B₂O₃ at high temperatures, amorphous SiO₂ could be remained at the fiber surface. As the fiber further oxidized, the molten B₂O₃ at the inside may infiltrate into the fiber interior to react with Si₃N₄, causing the precipitation of hexagonal boron nitride (h-BN) nanoparticles and the formation of SiO₂/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.