Fabrication of SiCN(O) Aerogel Composites with Low Thermal Conductivity by Wrapping Mesoporous Aerogel Structures over Mullite Fibers

Silicon-based ceramic aerogels obtained by the polymer pyrolysis route possess excellent thermophysical properties, but their poor mechanical properties limit their broader applicability in thermal insulation materials. Herein, SiCN(O) ceramic aerogels were prepared under the toughening effect of a crosslinker (hexamethylene diisocyanate, HDI), which maintains the structural integrity of the aerogel during the wet gel-to-aerogel conversion. The aerogel maintained a high surface area (88.6 m² g^-1) and large pore volume (0.21 cm³ g^-1) after pyrolysis. Based on this, mullite-fiber-reinforced SiCN(O) aerogels composites with outstanding thermal insulation properties and better mechanical performance were synthesized via ambient pressure impregnation. Furthermore, the effect of the impregnation concentration on the mechanical and insulation properties of the composites was investigated. The results revealed that the composite prepared with a solution ratio of 95 wt.% exhibited a low density (0.11 g cm^-3) and a low thermal conductivity (0.035 W m^-1 K^-1), indicating an ~30% enhancement in its thermal insulation performance compared to the mullite fiber; the mesoporous aerogel structures wrapped on the mullite fibers inhibited the gas thermal conduction inside the composites.