ALON® Optical Ceramic - An advanced transparent polycrystalline material

I teach, admittedly, a simplified version of material science. That's partially because my students aren't quite ready for more advanced versions but also because I'm not always aware of just how much more there is to material science.

For example, when we study ceramics and glasses, one of the things I explain is that glass is amorphous, and one indicator of that is the fact that it's transparent to visible light. Ceramics, on the other hand, are generally crystalline, and that's why they're opaque.

It turns out things are much more subtle than that. Check out Surmet's ALON (aluminum oxynitride.) From the wikipedia article...

AlON is optically transparent (≥80%) in the near-ultraviolet, visible and midwave-infrared regions of the electromagnetic spectrum. It is 4 times harder than fused silica glass, 85% as hard as sapphire, and nearly 15% harder than magnesium aluminate spinel. Since it has a cubic spinel structure, it can be fabricated to transparent windows, plates, domes, rods, tubes and other forms using conventional ceramic powder processing techniques. AlON is the hardest polycrystalline transparent ceramic available commercially. Combination of optical and mechanical properties makes this material a leading candidate for lightweight high-performance transparent armor applications such as bulletproof and blast-resistant windows and for many military infrared optics. AlON-based armor has been shown to stop multiple armor-piercing projectiles of up to 50 cal. It is commercially available in sizes as big as 18x35-inch monolithic windows.

There is so much to learn...for my students and for me, too.