Lamellar matrix enhanced continuous mullite fiber reinforced Al2O3-SiO2 porous composites with improved thermal insulation and mechanical performance

Mullite fiber felt with outstanding thermal stability and excellent thermal insulation performance was widely used as a thermal protection material in the aerospace field. However, the poor mechanical property severely restricted the application of mullite fiber felt. Herein, the mullite fiber felt reinforced Al 2 O 3 -SiO 2 (MF/Al 2 O 3 -SiO 2 ) porous composites with lamellar matrix were fabricated by the sol impregnation combined with the freeze-drying method. Compared to the ambient-dried MF/Al 2 O 3 -SiO 2 composites, freeze-dried MF/Al 2 O 3 -SiO 2 composites with lamellar matrix possessed a lower density (0.32–0.86 g/cm 3 ), higher porosity (73.30–90.03 %) and lower thermal conductivity (0.12–0.22 W m −1  K −1 ). What’s more, due to the dense lamellar Al 2 O 3 -SiO 2 ceramic matrix, the compressive strength of freeze-dried MF/Al 2 O 3 -SiO 2 composites was nearly 4 times higher than that of ambient-dried MF/Al 2 O 3 -SiO 2 composites and up to 4.25 MPa. In addition, the thermal and mechanical properties of MF/Al 2 O 3 -SiO 2 composites were maintained well at 1400 °C. The improved thermal insulation and mechanical properties of MF/Al 2 O 3 -SiO 2 porous composites with lamellar matrix indicated that MF/Al 2 O 3 -SiO 2 porous composites could be a promising candidate as the high-temperature thermal protection material in the aerospace field.