From earth to space: Utilizing agrowaste and sand as earthen materials to develop sustainable silica aerogels for aerospace applications

Abstract

Silica aerogel is widely recognized for its extremely low density, high porosity, remarkable optical transparency, and outstanding thermal and acoustic insulation properties—qualities that make it highly suitable for aerospace applications. Despite these advantages, traditional synthesis techniques often depend on costly and hazardous precursors. In this study, we investigate rice husk, an abundant agricultural waste, and beach sand, a naturally occurring geological material in Nigeria, as alternative silica sources. Using sol–gel processing combined with supercritical CO₂ drying, we successfully synthesized and characterized nanostructured silica aerogels. The findings reveal that these aerogels (rice husk and beach sand based, respectively) exhibit a  low density (0.53 and 0.68 g/cm³), large surface area (1214 and 635 m²/g), reduced speed of sound (~ 50 m/s in both aerogels), low thermal conductivity (0.16 and 0.17 W/mk), high transmittance (90 % in both aerogels within the visible range of the electromagnetic spectrum) as their physical properties comparable to those produced from conventional precursors, presenting a more sustainable and cost-effective route for the development of advanced materials in aerospace engineering.