Thermal-Shock-Resistant Sensor Windows and Domes for High-Speed Flight Made of Low-Expansion Ceramics

This Small Business Technology Transfer Research (STTR) Phase II proposal from Materials and Systems Research, Inc. (MSRI) and University of Utah (research institution) seeks to fabricate single-phase, polycrystalline tungstate ceramics with densities greater than 99.95% and a mean grain size of less than 1 um. These ceramics have been chosen because of their low thermal expansion and low elastic modulus that render them highly thermal-shock resistant and, therefore, suitable for IR windows and domes in high-speed flight. The optical transmittance of these polycrystalline ceramics is expected to be comparable to that of sapphire in the midwave (3-5 um) and long wave (8-14 um) infrared ranges. The high density and small grain size will be achieved by a fabrication route that will combine the following steps: preparation of a stable suspension of submicron powders, forming a green compact by pressure filtration, and a two-stage densification by pressureless sintering followed by hot-isostatic pressing. The proposed fabrication route has two distinct advantages over conventional powder processing methods: (a) it eliminates microstructural inhomogenities that limit strength, durability and optical transmittance in conventional powder processing, (b) it eliminates a number of steps involved in conventional processing and leads to a lower cost. Research in Phase II will fabricate disks 50 mm in diameter and 2-3 mm in thickness. Material characterization will be done by University of Utah under a subcontract.