Aerogel -Miracle Material for the 21st Century

Like a substance out of Star Trek, aerogel, one of the world’s lightest solids, is a miracle material for the 21st century that could protect your home against bomb blasts, mop up oil spills and even help man fly to Mars.

Called frozen smoke, aerogel is made by extracting water from a silica gel, then replacing it with gas such as carbon dioxide. The amazing material can withstand a direct blast of 1 kilogram of dynamite and protect against heat from a blowtorch at more than 1,300 degrees C. Scientists are working to discover new applications for the substance, ranging from the next generation of tennis rackets to super-insulated spacesuits for a manned mission to Mars.

Although aerogel is classed as a solid, 99 percent of the substance is made up of gas, which gives it a cloudy appearance. Scientists say that because it has so many millions of pores and ridges, if one cubic centimeter of aerogel were unraveled, it would fill an area the size of a football field.

Mercouri Kanatzidis, chemistry professor at Northwestern University, said: “It is an amazing material. It has the lowest density of any product known to man, yet at the same time it can do so much. I can see aerogel being used for everything from filtering polluted water to insulating against extreme temperatures and even for jewelery.”

The first aerogel was invented by an American chemist on a bet in 1931, but early versions were so brittle and costly that it was largely consigned to laboratories. It was not until a decade ago that NASA started taking an interest in the substance and putting it to a more practical use.

In 1999 the space agency fitted its Stardust space probe with a mitt packed full of aerogel to catch the dust from a comet's tail. It returned with a rich collection of samples last year.

The primary objective of the Stardust mission is to capture both cometary samples and interstellar dust. Main challenges to accomplishing this successfully involve slowing down the particles from their high velocity with minimal heating or other effects that would cause their physical alteration. When the Stardust Spacecraft encountered the Comet Wild 2, the impact velocity of the particles was up to 6 times the speed of a rifle bullet. Although the captured particles will each be smaller than a grain of sand, high-speed capture could alter their shape and chemical composition - or even vaporize them entirely.

To collect particles without damaging them, Stardust used aerogel. When a particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the sample to a relatively gradual stop. Since aerogel is mostly transparent - with a distinctive smoky blue cast - NASA scientists used these tracks to find the tiny particles.

This exotic substance has many unusual properties, such as low thermal conductivity, refractive index and sound speed - in addition to its exceptional ability to capture fast moving dust.

Aerogel was prepared and flight qualified at the Jet Propulsion Laboratory (JPL). JPL also produced aerogel for the Pathfinder missions. This particular JPL-made silica aerogel approaches the density of air. It is strong and easily survives launch and space environments. JPL aerogel capture experiments have flown previously and been recovered on Shuttle flights, Spacelab II and Eureca.

In 2002 Aspen Aerogel, a company created by NASA, produced a stronger and more flexible version of the gel. It is now being used to develop an insulated lining in space suits for the first manned mission to Mars, scheduled for 2018.

Mark Krajewski, a senior scientist at the company, believes that an 18 mm (three-quarters of an inch) layer of aerogel would be sufficient to protect astronauts from temperatures as low as minus 200 degrees Fahrenheit. "It is the greatest insulator we've ever seen," he said.

Aerogel is also being tested for future bombproof housing and armor for military vehicles. In the laboratory, a metal plate coated in 6 mm (a quarter of an inch) of aerogel was left almost unscathed by a direct dynamite blast.

It also has environmental credentials. Aerogel's millions of nano-sized pores can collect pollutants like a sponge making it ideal for absorbing pollutants in water. Northwestern's Kanatzidis has created a new version of aerogel designed to mop up lead and mercury from water. Other versions are designed to absorb oil spills. He is optimistic that it could be used to deal with environmental catastrophes such as the Sea Empress spillage in 1996, when 72,000 tons of crude oil were released into the Irish Sea just off the coast of south Wales.

Posted by Casey Kazan.

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