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

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 center dot 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.