Space Materials 101: Ceramics

Ceramics in Space

Because we value our people and shuttles, we have some rather unique designs to permit reentry into our atmosphere, and I want to take a moment to mention some of the cool chemistry/particle physics behind a component of the Space Shuttles Thermal Protection system: Ceramics.

Specifically the LI-900 Ceramics.  It is mostly composed of air (94% by volume) and the rest is Silica glass, and can take the extreme temperatures of reentry, and still be reusable.  But even more amazing is just how after being heated to extreme temperatures, they can still be ‘Safe’ to handle.

The main reason for why this can happen is most easily understood if we stop thinking about that glowing block of ceramic as a Solid, and think about it as a gas, after all, that is 94% of its volume!

It’s a matter of density; primarily an issue of particle density.  When you have a larger distance (molecularly speaking) between particles its more difficult for that heat to be transferred within the group of particles itself.  For a transfer to occur, one particle with high amounts of energy (heat) must impact another particle and share or transfer that energy.  Much like a game of pool, but more random; with fewer other pool balls (particles) to impact, the likelihood of transferring energy drops.   This leads to lowered heat Transmission and therefore Retention within the ceramic.  And it is precisely this quality that makes ceramics like the LI-900 very good at protecting Astronauts as they return to earth.

Written by Andrew McAffee

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