Aluminum precursor engineering enables high-strength continuous mullite fibers

Continuous mullite fibers are attractive for aerospace and high-temperature applications owing to their low thermal conductivity, excellent thermal and chemical stability. However, the properties of mullite fibers are highly dependent on the chemistry and hydrolysis-polycondensation behavior of aluminum precursors. Herein, an aluminum precursor engineering strategy is proposed to improve the property of continuous mullite fibers. By synergistically regulating the aluminum isopropoxide/aluminum chloride hexahydrate (AIP/AC) ratio and optimizing thermal treatment, high-strength and flexible mullite fibers were successfully prepared via dry spinning. The optimized AIP/AC ratio promotes synchronized hydrolysis-polycondensation of aluminum and silicon precursors, significantly improving the homogeneity, stability and spinnability of the precursor solutions while suppressing structural defects in the fibers. At an AIP content of 80%, the fibers exhibit a tensile strength of 1.3 GPa, elastic modulus of 57 GPa, toughness of 12 MJ m −3 , and elongation at break of 2.2%. These mullite fibers show strong potential for thermal insulation, thermal protection, and heat-resistant textile applications.