Imagine a substance that is nearly as light as air, structurally solid despite its wispy appearance, with amazing properties — like being able to insulate objects encased within it from heat, or having just the right index of refraction to detect Cerenkov radiation in particle accelerators.
That substance is called an aerogel, a.k.a. “frozen smoke,” and now researchers at Lawrence Livermore and Lawrence Berkeley National Laboratories have figured out how to make a new type of diamond aerogel by mimicking the process by which diamond forms in nature. Their paper appeared recently in the Proceedings of the National Academy of Sciences.
Aerogels were first created in 1931, thanks to a bet between two scientists, Samuel Stephens Kistler and Charles Learned, over whether one could replace the liquid in “jellies” with gas and not have the resulting substance shrink — as substances want to do when they dry out.
Kistler won via a process now known as “supercritical drying”: aerogel particles are suspended in a liquid until they form a matrix, then the liquid is slowly drained away, leaving just the gel matrix behind.
NASA loves aerogels. They’ve used aerogels as thermal insulators aboard the Mars rovers, and in designing space suits for their astronauts. Just how good are they at blocking heat? You could hold a blowtorch underneath an aerogel, and a chocolate truffle sitting on top would stay cool and un-melted.
Aerogels played a much bigger role in the Stardust mission to collect particles of space dust from the trails of comets. For Stardust, which has just completed the extended phase of its mission, NASA couldn’t use conventional foams or trapping materials because the particles of dust were traveling too fast. Even though they were smaller than a speck of dust, at those speeds the particles would vaporize instantly if they collided with a solid filter, and would pass right through a gas trap.
Ah, but aerogels have a porous, sponge-like structure and over 99 percent of their volume is empty space. So when a space dust particle hits an aerogel, it burrows through the material and leaves a telltale track in its wake, gradually slowing down and remaining trapped in the aerogel. The stuff fitted quite nicely into a tennis racket shaped “net” (see photo) that could be unfolded when a cometary dust stream was passing by.
Most aerogels are made from silica or carbon, and while they normally soak up moisture — which can ruin their structure over time — they can be treated to repel water so they won’t collapse. And now it’s possible to make diamond aerogels, giving this substance even more interesting properties.
The Livermore and Berkeley scientists simply built a carbon aerogel using the standard process, pumping any spaces in the gel with neon gas. Then they encased the aerogel in a diamond shell, pressurized it, and blasted it with high-intensity lasers to add heat — the same means by which diamonds form in the Earth (extreme heat and pressure). The trick was to keep the original carbon aerogel from collapsing, and the neon gas did just that, since it becomes a solid at high pressures.
Even better, the scientists were able to mold the resulting diamond aerogel like plastic. It’s completely transparent, and 100% biocompatible, since diamond doesn’t react with many elements. So you could use diamond aerogels to coat implants (pacemakers, brain-computer interfaces, etc.), with minimal health risks. You could also coat window glass and instruments in spacecraft, taking advantage of those awesome thermal insulation properties. Oh, and diamonds emit electrons, so there’s a possibility diamond aerogels could one day be used in super-light-but-strong quantum computers.
The catch? Of course there’s a catch. Right now the diamond aerogels are too tiny — roughly 200 microns wide, or twice the width of a human hair — to be of much use to practical applications. But give those scientists time, folks. Figuring out how to make them is just the first step.