Ultrahard spinel glazing material
Spinel, or magnesium aluminate, is a durable ceramic material found in some of the world’s most renowned gemstones—such as rubies in the British and French Crown Jewels. Spinel occurs naturally in both colored and colorless states, and it can be synthesized in the laboratory as a high-performing replacement for glass, given its significantly higher strength and hardness (its Mohs’ scale is 7.5–8.0, compared with 5.5 for glass).
The U.S. Naval Research Laboratory developed a method of manufacturing a polycrystalline version of spinel for transparent armor and bulletproof windows. Unlike glass, wherein a surface crack quickly spreads throughout the material, spinel armor is composed of multiple compressed crystal particles that thwart crack propagation. The NRL fabricates sheets and lens-shaped components via sintering, which involves a low-temperature hot press. The resulting material transmits both visible and infrared light, suggesting suitable uses for imaging systems and windows in cold climates.
Contact: U.S. Naval Research Laboratory, Washington, DC, USA.
For more information, see Transmaterial Next: A Catalog of Materials that Redefine Our Future