Achieving Robust α-Alumina Nanofibers by Ligand Confinement Coupled with Local Disorder Tuning

As high-performance thermal protection and structure enhancement materials, oxide ceramic fibers have become indispensable in numerous areas, ranging from deep-sea exploration to supersonic aircraft. However, under extreme energy input, abnormal grain growth and inevitable vermiculate structure would break the fiber integrity, causing catastrophic structure failure. Nowadays, the design of nanoceramics brings potential answers for strengthening of mechanical properties, but with the diameter downsized to the nanoscale, the increasing structural susceptibility of ceramic fiber to phase transformation and grain growth becomes a huge barrier. Here, we propose a strong carboxylic ligand confinement strategy by the combination of formic and acetic acids to control the inorganic colloid growth for fabricating robust α-alumina nanofibers. The rapid hydrolysis and coordination of the carboxylate groups with aluminum together with subsequent concentration synergistically promote the formation of small and compact precursor colloids, laying a solid foundation for suppressing abnormal grain growth and achieving refined alumina grain structure. The local disorder induced by silica and boron oxide surrounding α-alumina grains imparts excellent mechanical properties and flexibility with no fractures observed even after 500 buckling cycles and a wide range of temperatures from -196 to 1100 °C, providing an enlightening paradigm for ceramic fiber strengthening.