Transparent Spinel Ceramic
NAVAL RESEARCH LAB WASHINGTON DC OPTICAL SCIENCES DIV
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Spinel MgAl2O4 is a cubic crystalline material with a unique combination of ruggedness and excellent transmission from the ultraviolet 0.2 micron to the mid-infrared 5 micron region. This positions spinel as the de facto material of choice for numerous Department of Defense and commercial infrared window applications. However, single crystal spinel is difficult to make in dimensions greater than a few millimeters using traditional high temperature 2000 deg C melt growth techniques. On the other hand, attempts to make polycrystalline spinel by traditional hot pressing of powder has led to inhomogeneous material, typified by opaque nontransmitting regions, thereby making it unsuitable for practical applications. However, NRL has solved this problem.