From: Ann M. Anderson, Mary K. Carroll. 2025. Rapid Aerogel Fabrication Facilitates a Range of Applications, Journal of Sol-Gel Science and Technology, pp 1-16, https://doi.org/10.1007/s10971-024-06660-x
A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press.
There are four steps in the Union RSCE process: seal, heat, release and cool. In the first step, the hot press (Figure 1a) applies a force to seal the mold. The second step heats the mold at a specified rate during which the precursor chemicals gel and the wet gel strengthens and ages. During the heating step, the precursor chemicals initially follow the phase line until they expand to fill the mold volume (the take-off point, see Figure 1b). After take-off the pressure follows a constant volume heating process and increases more rapidly with heat addition. While heating, the pressure increases and exerts an increasing force on the hot press platens. When this force reaches the level of the hot press restraining force, the leak point (see Figure 1b) is reached and the fluid in the mold will push against the press releasing a small volume of material in order to maintain a desired pressure in the mold, essentially providing the same function as a safety relief valve. The wet gel continues to heat up until both the temperature and the pressure exceed the critical point conditions. In the third step, release, the hydraulic hot press force is reduced to allow the supercritical fluid to escape the mold and flow into an exhaust hood placed over the hot press, leaving in place a monolithic aerogel. In the final step, cool, the hydraulic press cools the mold at a specified rate to room temperature with a water-cooling system.
We have utilized this method to make monolithic aerogel with a maximum size of 14 x 14 x 1.3 cm [27]. The maximum size achievable is set by the hot press force limit (in our case this is 267 kN). We can also make aerogel granules via the Union RSCE method by placing pieces of wet gel into a mold for processing.
Access entire process here:
Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method
Or watch the Youtube video with Dr Stephen Steiner: Making Aerogels With a Hot Press: Tour of the Union College Aerogel Laboratory