Preparation of low-cost silica aerogels by high-pressure carbon dioxide methods

Abstract

In this paper, for the first time, hydrophobic silica aerogels were successfully prepared under atmospheric pressure drying using a novel technique of high-pressure carbon dioxide (HPCD). Based on the mechanism of modifying the gels with CO₂ instead of an acid catalyst under the high-pressure environment of 0.3 MPa in the autoclave, the CO₂ enters the gel. It reacts with the water in the gel to form carbonic acid, which makes the hexamethyldisilazane (HMDZ) play a role of hydrophobic modification to the alcohol gels under the acidic environment. The results showed that the SiO₂ aerogels prepared by the high-pressure carbon dioxide method had excellent properties with a low thermal conductivity of 0.020 w/(m·k). Compared with the conventional modification method for preparing SiO₂ aerogels, the HPCD method reduces the HMDZ content by 75 %. The low cost and high preparation performance provide the possibility of industrialized production.