Nanocomposite Infrared transparent windows and domes: a low cost and superior replacement for sapphire

Sapphire has been the dominant infrared transparent material for quite some time, and polycrystalline materials such as, magnesium fluoride, aluminum oxynitride and yttrium oxide, have been used to a limited extent when the performance criteria have beenless stringent. Polycrystalline and transparent oxide ceramics that have a cubic crystal structure offer an opportunity as a superior replacement for sapphire, provided a nanocrystalline grain size is maintained in the fully sintered state. However, it hasremained a challenge to produce fully dense and transparent nanocrystalline ceramics, using nanoparticles as starting material and consolidating by established sintering techniques. We propose a radically different approach wherein ultrafine `highlysinterable' nanocomposite particles will be produced using our newly developed chemical synthesis process, and consolidated using a rapid sintering process with exceptionally short soak times. Accordingly, in Phase I of the program, the feasibility ofproducing nanocrystalline and fully dense transparent ceramics will be demonstrated, along with characterization of the mechanical and optical properties. Working with our collaborators in the industry and a federal laboratory, we anticipate transitioningthe technology into military and commercial applications by the end of Phase II. Transparent ceramics offer a number of different opportunities in both military and civilian applications, including infrared windows in heat seeking missiles and opticalsystems. A powder consolidation approach, which is the subject of this proposal, is an attractive low cost alternative to melt processing and vapor deposition processes that are used to produce single crystals.