Sandwich-structured Si 3 N 4 @SiO 2 nanofiber aerogel: exceptional thermal insulation and mechanical performances for advanced applications

The rapid development of hypersonic vehicles has attracted great attention for scientists to design advanced materials with prominent mechanical and thermal insulation performance in the thermal protection system. In this study, we develop and synthesize Si3N4@SiO2 nanofiber (Si3N4@SiO2nf) aerogel featuring sandwich structure based on the assemble of the laminated Si3N4 nanofiber (Si3N4nf) membrane, self-supporting Si3N4nf and the laminated Si3N4nf membrane. This design imparts Si3N4@SiO2nf aerogel with exceptional characteristics, including ultra-low density, high mechanical performance and low thermal conductivity. The mechanical and thermal insulation performances for Si3N4@SiO2nf aerogel are optimized by adjusting the content of the laminated Si3N4nf membrane. The mechanical performance of Si3N4@SiO2nf aerogel improves when the content of the laminated Si3N4nf membrane increases. Typically, Si3N4@SiO2nf aerogel can maintain mechanical stability across a broad temperature range from -196 to 1300 °C. The excellent mechanical performance of Si3N4@SiO2nf aerogel with sandwich structure can be attributed to the fact that the laminated Si3N4nf membrane in the aerogel provides planar constraints for the deformation of the nanofibers, leading to an increase in the deformation resistance. Additionally, the thermal conductivity at room temperature of Si3N4@SiO2nf aerogel can be as low as 0.0269 W⋅m-1⋅K-1. The high-performance structure establishes fundamental considerations in structural design of inorganic aerogels with great potential for widespread applications.