Multifunctional mullite fiber reinforced SiBCN ceramic aerogel with excellent microwave absorption and thermal insulation performance

Mullite fibers have been widely used in thermal protection materials, but they still face challenges related to inefficient wave absorption performance. SiBCN aerogel has the advantage of tunable dielectric properties, outstanding microwave absorption performance, low density and low thermal conductivity, making it an ideal candidate for enhancing mullite fibers. Herein, a novel SiBCN aerogel/mullite fiber composite (SiBCN/MF composite) was prepared by sol-gel, freeze-drying and high temperature thermal treatment for the first time. By tuning the concentration of polyborosilazane (PBSZ), the density, microwave absorption performance, and thermal insulation properties were regulated. The obtained composites displayed low density (0.151–0.190 g/cm³), excellent microwave absorption performance (the minimum reflection loss as low as −67.83 dB and effective absorption bandwidth of 5.40 GHz) and low thermal conductivity (0.056–0.081 W/(m·K)). The outstanding comprehensive performance of the fabricated composites makes them promising candidates for use in the thermal protection system of aerospace vehicles.