What Is Aerogel?

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Strong as Steel, Light as Air

It sounds like something from Marvel Comics, but this amazing material is no fiction. So what is aerogel? How is it made and what can it be used for?

The technical definition of aerogel is: An open-celled, mesoporous, solid foam that is composed of a network of interconnected nanostructures that exhibits a porosity (non-solid volume) of no less than 50%. Phew! I suppose that makes sense if you’re a college professor, but what is aerogel in simple terms?

Despite the name, aerogel is actually a rigid, dry material derived from a gel, but in which the liquid part of the gel has been replaced by a gas. The actual process of removing the liquid from the gel is complicated and involves heating the gel in a pressurised container until the liquid portion becomes super-critical.

At the super-critical point the liquid has the same properties as both a liquid and a gas. When this combination of pressure and temperature has been reached, the liquid-gas can be removed by slightly reducing the pressure. The process may have to be repeated several times. Eventually, there is insufficient liquid remaining in the gel for it to re-condense.

Just as the term plastic is used to cover a range of substances, aerogel refers to the form of the material, rather than a specific substance. Aerogels can be formed from a range of materials, such as silica and carbon, as well as organic polymers such as polystyrene.

So what are the properties of aerogel that make it so attractive? Because the heavy liquid component has been removed from the gel, aerogel is incredibly light. A silica aerogel has been produced that was only three times heavier than air. The lowest density aerogel ever produced was 99.98% air in volume.

But despite this incredibly low density, aerogel is one of the strongest materials known. It is able to support thousands of times its own weight. In tests, a single one pound block of aerogel was able to support a weight of half a ton.

Depending on the base material used, aerogel can have widely differing properties. Silica based aerogels can be enormously effective as thermal and electrical insulators, while carbon aerogels have great electrical conductivity.

So diverse and extreme are the properties of aerogel that NASA has used the material in a number of space missions. Both the Mars rover vehicle and astronaut space suits use aerogel for thermal insulation, while the Stardust spacecraft uses aerogel to trap cosmic dust particles which would otherwise vaporize on impact with metals.

Aerogels are still too expensive for widespread use, but keep your eyes open. This wonderful substance could transform your life!

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