Infrared-opacified Al2O3–SiO2 aerogel composites reinforced by SiC-coated mullite fibers for thermal insulations

To opacify infrared radiation of mullite fiber-reinforced aerogel composites, SiC coatings were prepared on surfaces of mullite fibers by soaking with polycarbosilane (PCS) solution and then pyrolysis. By impregnating SiC-coated mullite fibers with Al2O3–SiO2 sol, then aging and supercritical drying, opacified Al2O3–SiO2 aerogel thermal insulation composites were prepared. The influences of the pyrolysis process on effective specific extinction coefficient and phase composition of the SiC-coated mullite fibers were investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analyses, and their relationship was discussed. The results indicate that the outer-layer coating is composed of β-SiC. When the concentration of the PCS solution was 10 wt%, the effective specific extinction coefficient increased from less than 30.4 to about 56.3 m2/kg in the wavelength range of 2.5–7.5 μm. The thermal conductivity of Al2O3–SiO2 aerogel composites reinforced by SiC-coated fibers at 1000 °C was 0.049 W/m K, which was lower than that of composites reinforced by blank mullite fibers (0.062 W/m K).