Fumed Silica-Derived, Ambient Dried, and Low-Cost Nanoporous Aerogel-like Monoliths for Thermal Insulation

Abstract

Nanoporous silica aerogels have great potential in the application of thermal insulation. However, the commonly used supercritical drying technology of nanoporous silica aerogels has disadvantages such as high cost, high complexity, and harsh drying conditions. Herein, a template orientation strategy has been proposed for fabricating nanoporous aerogel-like silica monoliths (ASMs) based on the low-cost, rapid ambient drying technology without additional treatments of surface modification and solvent exchanging. The successful implementation of the template orientation strategy depends on the silica slurry, which is composed of commercial fumed silica, hydrolyzed methyltrimethoxysilane (MTMS), and sole water solvent. The solidification of silica slurry has been achieved by a controlled polycondensation reaction catalyzed by ammonia originating from the thermolysis of urea. Owing to the skeleton enhancement of fumed silica powders and the hydrophobic effect of methyl groups, ASMs maintain well monolithic formability during ambient drying. Meanwhile, low-cost fumed silica powders have been seen as template orientation agents for inducing MTMS molecules to generate nanoparticle-based network skeletons, endowing ASMs with typical nanopore features (specific surface area as high as 113 m2/g and pore diameter distribution concentrated at ∼40 nm). The resulting ASMs exhibit low density (0.36 g/cm3), high compressive strength (0.92 MPa), and low thermal conductivity [0.056 W/(m·K)]. This work would provide significant guidelines for the fabrication and thermal insulation applications of nanoporous ASMs derived from ceramic powders. This simple and low-cost preparation strategy would promote the large-scale applications and industrial production of nanoporous silica for thermal insulation materials.