Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003 · 23 citations · 0 references
Natural SciencesMaterials EngineeringMaterials ScienceCeramic MaterialsCeramicsOptical MaterialsCeramic CompositesCeramic ProcessingInfrared Optical MaterialsOptical CeramicsOptical Properties Of SolidsSinteringCeramic Shielding MaterialsInfrared Dome MaterialsInfrared Transparent MaterialsOxide CeramicsPorosityTransmissivityTransparent Ceramic CompositesTransparent Ceramics
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 Al<sub>2</sub>O<sub>3</sub> ceramics 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 transmissivity equals that of sapphire approaching the upper theoretical limit for wavelengths of 2.5-4.5 μm. This opens the way to new possible 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.