(Image: Craig Mackie)
Almost as light as air, aerogels are a heavyweight solution for everything from heat-bleeding windows to carbon emissions
In the 1930s, a US chemist called Samuel Kistler made the world’s lightest solid. His trick was to gently remove the liquid from a gel of silica, leaving a fine skeleton riddled with nanoscale holes. Made up of 99 per cent air, it looked like frozen smoke. Kistler named it “aerogel”.
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Aerogel was regarded as a mere curiosity for decades: it was extremely brittle, limiting its potential uses. Over the past decade, though, that has begun to change. Chemists have reinforced aerogel with glass fibres, and impregnated it with thin polymer chains to make it more flexible. An all-polymer aerogel devised by a team at NASA’s Glenn Research Center in Cleveland, Ohio, is claimed to be , while being 500 times stronger than Kistler’s original.
In parallel, there’s been an explosion of applications. On the home front, all that trapped air makes aerogels insulating superstars: a 1-centimetre thickness is enough to replace 5 centimetres of high-performance foam insulation. Translucent eco-windows incorporating aerogels can keep buildings with a fraction of the weight. High-end winter sports clothing increasingly incorporates the stuff, and a version of Google’s Nexus 7 tablet computer features a plastic aerogel casing that is half the weight of a conventional plastic case.
But a new type of aerogel holds perhaps the most revolutionary promise. Metal “nanofoams” have a framework of metal atoms rather than silica or polymers. A team at Los Alamos National Laboratory in New Mexico accidentally discovered a simple way to make them in 2005. Setting alight pellets made from certain transition-metal compounds, they found a curious aerogel-like structure left behind.
Although useless as insulation, metal nanofoams provide an intriguing combination of high surface area – up to 3000 square metres in a single gram – electrical conductivity and chemical activity. Above all, these properties could provide us with radical new ways of cleaning up our energy act. Chemically active iron or nickel skeletons, for example, could help reduce the amount of expensive metals like platinum in the next generation of catalytic converters.
Suck it and see
Meanwhile beryllium nanofoams make for a lightweight structure that could store 10 per cent hydrogen by weight. Other hydrogen storage materials such as metal hydrides do better, but only release their hydrogen when heated to high temperatures, says Fedor Naumkin at the University of Ontario Institute of Technology in Oshawa, Canada, who has worked on the foams. That could give nanofoams an advantage as a fuel store for, say, hydrogen powered vehicles ().
Work this year by a team at Brown University in Providence, Rhode Island, also found indications that catalytic copper nanofoams could help to provide a new, inexpensive way to suck carbon dioxide out of the air to make industrially useful hydrocarbons (). Couple that with research into using more conventional aerogels as highly absorbent chemical mops , and frozen smoke might promise a cleaner world all round.
“Frozen smoke might promise a cleaner world all round, as a highly absorbent chemical mop”
Read more: “Wonder stuff: Seven new materials to change the world“
This article appeared in print under the headline “Future stuff: Aerogels”
