Dynamic Self-Healing Composite Oxide Layer for Synergistically Enhanced Oxidation Resistance and Thermal Insulation of Si3N4 Nanofiber

Silicon nitride (Si 3 N 4 ) ceramic nanofibers are promising candidates for high-temperature thermal insulation due to their high fracture toughness, excellent thermal stability, and superior creep resistance. However, their vulnerability to oxidative corrosion in oxygen-rich environments at elevated temperatures can severely degrade mechanical integrity and thermal stability, thereby limiting practical deployment. To address this, this study proposes a core-shell architectural design strategy. Composite precursor fibers were produced by coaxial electrospinning using a polysilazane (PSZ)-based core solution and a shell dispersion containing yttrium oxide (Y 2 O 3 ) particles, followed by pyrolysis at 1400 °C to yield Si 3 N 4 /Y 2 O 3 core-shell ceramic nanofibers. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirm the formation of a well-defined core-shell structure featuring a dense surface composite layer composed of Y 2 Si 2 O 7 /Si 2 N 2 O/Y 2 O 3 , which substantially enhances high-temperature oxidation resistance. Mechanistic insights derived from combined XRD, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and post-oxidation characterization indicate that oxidation proceeds via limited initial reactions, followed by partial oxidation of Si 2 N 2 O to generate molten SiO 2 at high temperatures. This highly fluid SiO 2 phase can migrate and spread over the fiber surface, dynamically sealing pores and microcracks, thereby establishing an effective oxygen-diffusion barrier with an intrinsic self-healing function. As a result, the materials exhibit exceptional integrated properties: high-temperature thermal conductivity remains stable at 0.385-0.404 W·m -1 ·K -1 at 1300 °C; oxidation resistance is remarkable, with only 2.91 % mass loss after 2 h at 1400 °C in air; and the fibrous mats retain excellent mechanical flexibility. Overall, the Si 3 N 4 /Y 2 O 3 core-shell structural design enables a synergistic enhancement of oxidation resistance while preserving thermal insulation and flexibility, offering a viable strategy for next-generation ultrahigh-temperature insulation materials.