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This paper describes MER's recent advances on the development of high strength, transparent magnesium aluminum
spinel technology for large IR windows and domes. The novel spinel material exhibits high optical and IR transparency
in the 0.2 - 5.5 μm wavelength, is very resistant to abrasion, with density higher than 99.9% of theoretical, with very
fine and uniform grain size, and flexural strength of 300 MPa. Spinel domes technology has been scaled up to produce
hemispherical 180° aperture domes in sizes up to 7" in diameter using freeze casting technology to produce the green
dome preforms. MER is also pursuing the production of large size spinel windows by either producing monolithic large
single windows or by edge bonding several smaller size windows. Both approaches present challenges. Production of
monolithic large size windows is limited by equipment size, availability, and investment capital while the edge bonding
approach requires perfect transparency and strength at the bonded edge. MER together with Precision Photonics Corp.
are developing high strength, edge bonded, transparent magnesium aluminum spinel windows for next generation
aircraft and other defense armor applications which require windows as large as 30"x30"x0.5" at an affordable cost.
MER has further improved strength of the spinel by accurate control of the average grain size and grain size scatter
while remarkable transmission is obtained by elimination of the intergrain/intragrain porosity, and by eliminating all
possible contamination. The spinel bonding technology under development consists of chemically activated direct
bonding (CADB®), an epoxy-free solution-assisted optical-contacting process developed by Precision Photonics
Corporation (PPC).
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