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 beta-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 m(2)/kg in the wavelength range of 2.5-7.5 mu m. The thermal conductivity of Al2O3-SiO2 aerogel composites reinforced by SiC-coated fibers at 1000 degrees C was 0.049 W/m K, which was lower than that of composites reinforced by blank mullite fibers (0.062 W/m K). (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.