High performance spinel ceramic is required for near-term future applications based on the excellent spinel transmission
properties in the UV-VIS-Mid IR wavelength range. Windows as large as 30"x60" and hemispherical domes 4"-7" in
diameter have been distinguished as applications where the novel spinel technology could be successfully applied. Future
applications involve the use of even more complex 3-D shapes like spinel superdomes and tubes. The thickness of some
of these components has reached 1" and above. MER has been actively pursuing these design objectives and has shown
the feasibility of producing some of these complex shaped parts. Optimization of transmittance and strength are always
the main objective. MER has also been pursuing edge bonding technology, where large thick panes will be edge bonded
into a final large window. The production of monolithic windows as large as 18"x22", which can be used as individual
windows or as panes prior to edge bonding, has also been demonstrated. Using the complex 3-D spinel process, MER
has also demonstrated the feasibility of producing 4"-7" diameter hemispherical domes blanks of very high quality.
After rendering and polishing, defect free domes have been produced. The process has been characterized and qualified
using an optical grade spinel specification. Details of MER's technology to produce low cost, high strength, transparent
magnesium aluminum spinel windows and domes are described. High optical and IR transparency in the 0.3 - 5.5 μm
wavelength range is obtained. Equibiaxial strength averages 180-200 MPa, with individual readings reaching 300-320
MPa maximum. Spinel optical and mechanical properties are provided.
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