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

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.