Tuning phase transformation and microstructure in alumina-mullite nanofibers by concentration-dependent Sc2O3 doping

Electrospun alumina-mullite ceramic nanofibrous membranes show great potential for high-temperature thermal insulation applications. However, the influence of scandium oxide (Sc 2 O 3 ) addition on their phase evolution and high-temperature stability has rarely been investigated. Herein, the concentration-dependent effect of Sc 2 O 3 (0–5 wt.%) on these membranes was systematically studied. Microstructural and crystallization kinetics analyses reveal a non-monotonic doping behavior. A Sc 2 O 3 content of 1 wt.% delays mullitization and retains a fine-grained, flexible nanofiber architecture after calcination at 1400 °C. In contrast, Sc 2 O 3 additions of 3 wt.% and 5 wt.% induce excessive lattice distortion, accelerate mullite crystallization, and promote abnormal grain growth. These findings demonstrate that the Sc 2 O 3 doping concentration determines the transition from grain refinement to coarsening, providing a basis for designing durable ultra-high-temperature ceramic nanofibrous membranes.