In Situ Generated Mullite Reinforced Flexible Zirconia Nanofibers With Exceptional Thermostability up to 1400°C

ABSTRACT Zirconia (ZrO 2 ) nanofibers have emerged as ideal flexible materials for thermal‐field applications in semiconductor crystal growth furnaces, thermal protection of new energy batteries, and flexible thermal insulation layers of aerospace vehicles, attributed to their unique combination of low saturated vapor pressure, ultralow thermal conductivity, and ultrahigh melting point. However, rapid grain coarsening at elevated temperatures restricts their long‐term service temperature, severely hindering their practical deployment in these critical fields. To address this bottleneck, we proposed a novel strategy: sacrificing the theoretical ultrahigh‐temperature stability (> 1600°C) of ZrO 2 nanofibers by in situ generating mullite phases—characterized by relatively low melting points, complex crystal structures, and slow grain growth rates—thereby achieving mullite‐reinforced ZrO 2 nanofibers with exceptional comprehensive high‐temperature performance. Systematic characterizations demonstrated that the introduction of mullite enhanced the flexible service temperature of ZrO 2 nanofibers from 1200°C to 1300°C, while extending the high‐temperature thermal stability to 1400°C, alongside sustained low room‐temperature thermal conductivity and reliable performance under extreme environments. Mechanistic investigations revealed that the in situ formed mullite inhibited particle growth in ZrO 2 nanofibers, thus improving the high‐temperature flexibility and stability. Notably, our findings indicate that the particle size on the fiber surface—rather than the grain size—serves as the key determinant of high‐temperature stability and flexibility, providing a new microstructure‐oriented approach for the optimization and development of advanced oxide fibers. This work not only enhances the comprehensive high‐temperature performance of ZrO 2 nanofibers and expands their ultrahigh‐temperature application scenarios but also offers a novel strategy for the optimization and development of other inorganic fibers.