Polycrystalline MgA12O4 Spinel for High Performance Windows,
COORS PORCELAIN CO GOLDEN CO
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There is a need for optical materials which are highly transparent at wavelengths from the ultraviolet to the infrared, hard enough to resist high speed rain erosion, strong enough to resist mechanically or thermally induced fracturing and are inexpensive to fabricate. Magnesium aluminate spinel possesses an unusual combination of optical, dielectric, physical and mechanical properties that make it an attractive candidate for windows on EP systems that are moving at very high speeds, and is cost effective when compared with sapphire. Spinel is cubic and optically isotropic thus polycrystalline shapes may be fabricated without the severe scattering problems inherent in noncubic materials. In the microwave region the isotropy of spinel prevents localized absorption and heating that occurs in noncubic materials because of differing grain boundary orientation and anisotropic dielectric loss index. Spinel undergoes no polymorphic transformations and is thus free of problems due to thermally induced phase changes.