Achieving Robust\nα‑Alumina Nanofibers\nby Ligand Confinement Coupled with Local Disorder Tuning

As high-performance thermal protection\nand structure\nenhancement\nmaterials, oxide ceramic fibers have become indispensable in numerous\nareas, ranging from deep-sea exploration to supersonic aircraft. However,\nunder extreme energy input, abnormal grain growth and inevitable vermiculate\nstructure would break the fiber integrity, causing catastrophic structure\nfailure. Nowadays, the design of nanoceramics brings potential answers\nfor strengthening of mechanical properties, but with the diameter\ndownsized to the nanoscale, the increasing structural susceptibility\nof ceramic fiber to phase transformation and grain growth becomes\na huge barrier. Here, we propose a strong carboxylic ligand confinement\nstrategy by the combination of formic and acetic acids to control\nthe inorganic colloid growth for fabricating robust α-alumina\nnanofibers. The rapid hydrolysis and coordination of the carboxylate\ngroups with aluminum together with subsequent concentration synergistically\npromote the formation of small and compact precursor colloids, laying\na solid foundation for suppressing abnormal grain growth and achieving\nrefined alumina grain structure. The local disorder induced by silica\nand boron oxide surrounding α-alumina grains imparts excellent\nmechanical properties and flexibility with no fractures observed even\nafter 500 buckling cycles and a wide range of temperatures from −196\nto 1100 °C, providing an enlightening paradigm for ceramic fiber\nstrengthening.