Abstract
Owing to their ultra-low thermal conductivity, silica aerogels are promising thermal insulators; however, their extensive application is limited by their high production cost. Thus, scientists have started to explore low-cost and easy preparation processes of silica aerogels. In this work, a low-cost method was proposed to prepare silica aerogels with industrial silica hydrosol and a subsequent ambient pressure drying (APD) process. Various surfactants (cationic, amphoteric, or anionic) were added to avoid solvent exchange and surface modification during the APD process. The effects of various surfactants on the microstructure, thermal conductivity, and thermal stability of the silica aerogels were studied. The results showed that the silica aerogels prepared with a cationic or anionic surfactant have better thermal stability than that prepared with an amphoteric surfactant. After being heated at 600 °C, the silica aerogel prepared with a cationic surfactant showed the highest specific surface area of 131 m2∙g−1 and the lowest thermal conductivity of 0.038 W∙m−1∙K−1. The obtained low-cost silica aerogel with low thermal conductivity could be widely applied as a thermal insulator for building and industrial energy-saving applications.
Highlights
Silica aerogels [1,2,3,4,5,6], as a kind of highly porous material, have shown great potential application in energy-saving windows and doors [7], solar energy integration, and building energy efficiency [8,9]due to their unique structure and properties such as low density (3–500 mg·cm−3 ), high porosity (80–99.8%), low dielectric constant, and low thermal conductivity [2,10,11]
We report a one-pot ambient pressure drying (APD) synthesis method to fabricate silica aerogel monoliths from industrial silica hydrosol in an aqueous system
The silica wet gels were prepared from silica hydrosol by adding the surfactant under an acid–base two-step catalytic condition, and the mixture was subsequently dried through the APD process
Summary
Silica aerogels [1,2,3,4,5,6], as a kind of highly porous material, have shown great potential application in energy-saving windows and doors [7], solar energy integration, and building energy efficiency [8,9]. The surfactants could form a saturated adsorption layer on the surface of solvent which would reduce the surface tension of the liquid and the pore structure of the silica aerogel would be well preserved after APD. Amphiphilic surfactant molecules could form micelles in solution with a hydrophobic core stabilized by a hydrophilic shell [19,20] Those hydrophilic micelles would attach to the surface of silica particles and become embedded in the silica network through hydroxyl groups, which would influence the structure of the silica aerogel. Using a low-cost industrial silica hydrosol as the raw material and water as the solvent, along with the convenient APD process, this method greatly simplifies the preparation process and reduces the cost
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