Transparent magnesium aluminate ceramics have been in existence for many decades. However, at few times in history has spinel been available as a commercial product and until now, there has not been as large an interest or effort to make transparent polycrystalline spinel a marketable reality. Due to the ever-increasing performance demands of current and next-generation electro-optic platforms, transparent magnesium aluminate spinel is suitable in more applications because of its extended transparency in the mid-wave IR (MWIR). Spinel is also emerging as a transparent armor solution for tactical and combat vehicles against escalating threats. Furthermore, as a simple ceramic oxide, its processability affords economy of scale that makes it attractive for meeting the ever demanding cost targets of advanced weapons systems and commercial products.

Technology Assessment & Transfer Inc. (TA&T), is leading the effort in the United States to develop and commercialize transparent polycrystalline spinel ceramics to meet these future needs. Current development efforts have benefited by on-going and previous support from the Army, Navy, and Air Force as well as the Missile Defense Agency and Department of Energy.

Spinel (MgAl2O4) Optical Ceramic is a transparent polycrystalline ceramic whose combination of high hardness, light weight and broadband optical properties make it a leading candidate for stringent optical applications and transparent armor. Its transmission range spans the range from 0.19 um to 6.0 um and exceeds that of sapphire and ALON™

Spinel Optical Components are fabricated using proprietary processing methods in a wide variety of sizes up to 18” in diameter and 14” x 16” windows. Detailed quotes can be provided on request for specific components by contacting the TA&T Optical Ceramics Division, 215 Najoles Rd., Millersville MD 21108; Attn: Mr. Cliff Parsons, 410-987-1656 phone.

TYPICAL PROPERTIES
Composition	. . . . . . . . . .	MgAl2O4
Grain Size	. . . . . . . . . .	100-200 microns
Structure	. . . . . . . . . .	Cubic, Spinel, Isotropic
Density	. . . . . . . . . .	3.58 g/cc
Form	. . . . . . . . . .	polycrystalline
Melting Point	. . . . . . . . . .	2135 °C
Young's Modulus	. . . . . . . . . .	277 GPa
Shear Modulus	. . . . . . . . . .	192 GPa
Poisson's Ratio	. . . . . . . . . .	0.26
Hardness	. . . . . . . . . .	1645 Kg/mm (Knoop Indentation, 200 g load)
Fracture Toughness	. . . . . . . . . .	1.5-2MPa-m1/2
Flexure Strength	. . . . . . . . . .	185-250 GPa
Specific Heat	. . . . . . . . . .	0.21 cal/g-°C
Thermal Conductivity	. . . . . . . . . .	14.7 W/moK @25 °C
Coeff. Ther.Expansion	. . . . . . . . . .	25-100 °C - 6.09x10-6 25-500 °C - 7.30x10-6 25-1000 °C - 7.90x10-6
Thermal Shock
Parameter R'	. . . . . . . . . .	1.39 vs. ALON™ 1.2* (Higher is Better)
Wavefront Error Potential	. . . . . . . . . .	¼ wave over 11" aperture at 0.5" thickness
* Gentilman , R.L. "Infrared and Optical Transmitting Materials" SPIE Vol. 683, 1986