AEROGEL SOLID SMOKE

A new version of aerogel, the particle-collecting substance on NASA's Stardust spacecraft, has been recognized by Guinness World Records as the solid with the lowest density.

Aerogel is pure silicon dioxide and sand, just as is glass, but aerogel is a thousand times less dense than glass because it is 99.8 percent air. It is prepared like gelatin by mixing a liquid silicon compound and a fast-evaporating liquid solvent, forming a gel that is then dried in an instrument similar to a pressure cooker. The mixture thickens, and then careful heating and depressurizing produce a glassy sponge of silicon.

What remains is sometimes called "solid smoke," for its cloudy translucent color and super-light weight. Surprisingly, this seemingly brittle substance is durable and easily survives launch and space environments.

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via inhabitat