Robust and thermally insulating SiBCN/SiOC ceramic aerogel with superior electromagnetic wave absorption performance and high-temperature stability up to 1600℃OA

SiBCN ceramic aerogels have emerged as a new generation of integrated thermal insulation and microwave absorption materials but face great challenges in terms of mechanical properties,high-temperature stability,and absorption bandwidth in practical applications.Herein,SiBCN/SiOC composite ceramic aerogels were prepared by solvent thermal crosslinking,freeze-drying,and pyrolysis of precursors.Polyhydromethylsiloxane(PHMS)was introduced in situ by the hydrosilane addition reaction during the solvothermal process,which endowed the precursor aerogel with a complex and robust three-dimensional network structure and further resulted in a 260%improvement in the compressive strength of the SiBCN/SiOC composite aerogel compared with that of the pure SiBCN aerogel.Additional investigations revealed that the SiBCN/SiOC composite aerogel enjoyed a low thermal conductivity(0.044-0.051 W·m^(-1)·K^(-1))and a light weight(0.13-0.16 g·cm^(-3)),which was favorable for thermal barrier material.Notably,the SiBCN/SiOC composite aerogel exhibited excellent microwave absorption performance with an effective absorption bandwidth of 6.7 GHz and a reflection loss of−43.89 dB at a thickness of 2.5 mm due to improved impedance matching,multiple reflections,and enhanced interfacial polarization.Furthermore,the introduction of SiOC significantly inhibited the crystallization of SiBCN at high temperatures.After heat treatment at 1600℃,the composite aerogel retained its amorphous nanoparticle pearl-chain-like structure,with thermal conductivity remaining as low as 0.052 W·m^(-1)·K^(-1).The in situ introduction of PHMS provided novel insight and a promising strategy for enhancing the overall performance of SiBCN ceramic aerogels,expanding their application in hightemperature environments.