Fabrication of Polycrystalline IR-Transparent Ceramics: A Potential Substitute for Sapphire

Sapphire (single crystal aluminum oxide) is the most commonly used material in infrared transparent windows and domes in `heat seeking' missiles. A replacement for sapphire is sought for improved performance in high speed missile applications, and at thesame time, reduce the cost of the windows and domes by a factor of two. High purity fine grained (< 1-5 microns) polycrystalline ceramics with a cubic crystal structure have the potential to perform better than sapphire, while simultaneously being muchless expensive. Starting from nanopowders, and sintering to a fine-grained dense material offers a possibility of tuning the final grain size in order to simultaneously optimize optical and mechanical properties. This had not been possible until now dueto the lack of high purity sinterable nanopowders, and a rapid consolidation technique that minimizes grain growth. Overcoming both of these roadblocks, we demonstrated in Phase I for the first time that high purity nanopowders of oxide ceramics,synthesized in house by a scalable process can be sintered at relatively low temperatures to full density and a high degree of transparency. Fully dense MgO was synthesized with a final grain size in the 1 - 3 microns range. The peak value of transmissionwas 80% in the midwave infrared region, compared to a theoretical value of 88%. Building upon the Phase I results, we propose to develop the powder synthesis process as well as the consolidation technology to a state of commercial readiness. Working incollaboration with (a) one of the leading corporations that supplies components and systems to the military, (b) a company that specializes in consolidation of transparent ceramics, (c) a unit of the Navy dedicated to developing infrared window and domematerials for heat seeking missiles, and (d) two university groups, we propose to further develop and optimize synthesis of oxide ceramic nanopowders and sintering of 2 - 6