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Transparent sintered sub-mum Al2O3 with IR transmissivity equal to sapphire

: Krell, A.; Baur, G.M.; Dähne, C.


Tustison, R.W. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Window and dome technologies VIII : 22 - 23 April 2003, Orlando, Florida, USA ; proceedings of the Eighth Annual International Conference and Electro-Optic Windows, Domes, and Materials held in conjunction with the 2003 Aerosense Symposium
Bellingham/Wash.: SPIE, 2003 (SPIE Proceedings Series 5078)
ISBN: 0-8194-4937-7
International Conference and Electro Optic Windows, Domes, and Materials <8, 2003, Orlando/Fla.>
Aerosense Symposium <2003, Orlando/Fla.>
Conference Paper
Fraunhofer IKTS ()
transparente Keramik; Al2O3; Infrarot-Fenster; transparent ceramic; alumina; infrared window; infrared transmissivity; sapphire; ballistic shielding; grain size; residual porosity; IR dome; wet casting approach; sintering; Al2O3

New grades of sintered (polycrystalline) corundum ceramics have been shown to exhibit a ballistic shielding power close to SiC/B4C composites when manufactured with a grain size of about 500 nm. It is demonstrated here that these Al2O3 cera mics become transparent when their residual porosity is decreased to less than 0 .05 %. Specifically, in the IR range between about 2 and 6 µm their transmissivi ty equals that of sapphire approaching the upper theoretical limit at wavelength s of 2.5-4.5 µm. This opens the way to new applications such as IR domes. These optically and mechanically homogeneous ceramics can be manufactured with a wall thickness up to 15 mm by a wet casting approach. The technology enables the manufacture of complex hollow spheres which after sintering are transparent in visible light without polishing.