To obtain new high-temperature resistant composites that can meet the requirements of aircraft development for thermal insulation and mechanical properties, SiBCO aerogel composites were prepared by sol-gel, supercritical drying and high-temperature pyrolysis with trimethyl borate (TMB) or phenylboronic acid (PBA) as the boron source and mullite fiber as reinforcement. The structure and composition of the SiBCO aerogel and its composites were characterized with SEM, FT-IR, ICP and nitrogen adsorption tests. The specific surface area of the SiBCO aerogel is 293.22 m2/g, and the pore size is concentrated in the range of 10–150 nm. The mechanical properties, the thermal insulation properties and the temperature resistance were also studied. Due to the introduction of boron, the temperature resistance of SiBCO aerogel composites is improved greatly, and the service temperature of composites reached 1773 K. When n (TMB)/n (TEOS) = 1/1, the temperature resistance of the composites is the best. After heating in air at 1773 K for 30 min, the shrinkage of SiBCO aerogel composites is only 2.45%, and the thermal conductivity of the composites is 0.138 W/(m·K) at 1773 K. In addition, the type and amount of catalyst also have certain effects on the mechanical properties and temperature resistance of the composites
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