Here’s another look at NASA’s fascinating aerogel, which is currently the world’s lightest solid (graphene version that is) with a composition of 99.8% air and 0.2% silica gel – it feels like fragile expanded polystyrene to the touch. Also known as “Blue Smoke”, this material can withstand a 1-kilogram dynamite explosion and shield precious objects, such as the space shuttle, from a flame that exceeds 1400° C. Despite its weight, it can support over 1,000 times its own weight. Production of aerogels is done by the sol-gel process. First a gel is created in solution and then the liquid is carefully removed to leave the aerogel intact. Continue reading for three more videos and information.
In 1931, to develop the first aerogels, Kistler used a process known as supercritical drying. By increasing the temperature and pressure he forced the liquid into a supercritical fluid state where by dropping the pressure he could instantly gasify and remove the liquid inside the aerogel, avoiding damage to the delicate three-dimensional network. While this can be done with ethanol, the high temperatures and pressures lead to dangerous processing conditions. A safer, lower temperature and pressure method involves a solvent exchange. This is typically done by exchanging the initial aqueous pore liquid for a CO2 miscible liquid such as ethanol or acetone, then onto liquid carbon dioxide and then bringing the carbon dioxide above its critical point. A variant on this process involves the direct injection of supercritical carbon dioxide into the pressure vessel containing the aerogel. The end result of either process exchanges the initial liquid from the gel with carbon dioxide, without allowing the gel structure to collapse or lose volume.