Transparent Aluminum

Transparent aluminum starts out as a pile of white aluminum oxynitride powder. That powder gets packed into a rubber mold in the rough shape of the desired part, and subjected to a procedure called isostatic pressing, in which the mold is compressed in a tank of hydraulic fluid to 15,000 psi, which mashes the AlON into a grainy “green body.” The grainy structure is then fused together by heating at 2000 °C for several days. The surface of the resulting part is cloudy, and has to be mechanically polished to make it optically clear.

All that work pays off. AlON can do amazing things. Here, for instance, a 1.6″ thick AlON plate successfully resists a huge, powerful .50 AP bullet that smashes easily through more than twice that thickness of conventional laminated glass armor, with plenty of energy left over to extremely kill a plastic mannequin head.

It’s expensive, of course, and so generally reserved for high-performance applications, especially in military fields. AlON is manufactured by Massachusetts-based Surmet Corporation for use in armored windows, lenses for battlefield optics, and “seeker domes,” which are the clear round windows covering the sensor heads on the business ends of many missiles. If you want to read further, Tom Scheve has prepared a good bibliography over at HowStuffWorks.

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