TECHNOLOGY AREAS: Air Platform, Materials/Processes, Weapons

ACQUISITION PROGRAM: PMA-201

OBJECTIVE: Develop low-thermal-expansion (<0.5 ppm/K), thermal-shock-resistant infrared-transparent sensor windows and domes for high speed flight.

DESCRIPTION: Sapphire is the most thermal-shock-resistant material currently available for high speed sensor domes and windows, but its thermal shock resistance is insufficient for some applications. When subjected to rapid heating, the difference in thermal expansion between hotter and cooler parts of the window shatters the material. Expensive, impractical active cooling systems can protect the window. The purpose of this STTR topic is to identify and develop new infrared-transparent materials with very low thermal expansion (<0.5 ppm/K) and low emissivity at elevated temperature. These materials will survive rapid heating without active cooling and will be able to operate at high temperature.

The selected material must provide good transmission, low optical scatter (<1%), and low emittance (<1%) in the 3-5 micron wavelength range. For infrared transmission and operation at temperatures up to 600ºC or higher, metal oxides are likely candidates. Heavy metallic elements increase the range of infrared transmission wavelengths. Silicates are not likely candidates because they generally do not transmit well at 3-5 ?m. If a composite composition is made, both phases would have to be nanoparticles—much smaller than the wavelength of infrared radiation—so that the 2-phase material does not have significant optical scatter.

The goal by the end of this project is to produce optical quality disks and domes with a diameter of 75 mm and a thickness of 2 mm.

PHASE I: Identify a material or composite system with near zero thermal expansion over a wide range of temperature (0-600ºC) and good infrared transmittance in the 3-5 micron wavelength range. Prepare the material and measure its thermal expansion and infrared transmission. Single crystals, pressed powders or powders could be used for these measurements.

PHASE II: Fabricate optical quality specimens and measure infrared transmission and scatter, thermal expansion, thermal conductivity, Young’s modulus, and mechanical strength. Fabricate optical quality disks and domes.

PHASE III: Develop a commercial process to provide sensor windows and domes.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: In addition to its military market, there is a small commercial market for thermal-shock-resistant windows for industrial process monitoring and spacecraft applications.

REFERENCES:
1. T. Suzuki and A. Omote, "Zero Thermal Expansion in (Al2x(HfMg)1-x)(WO4)3," J. Am. Ceram. Soc. 2006, 89, 691.

2. J. Catafesta, J. E. Zorzi, C. A. Perottoni, M. R. Gallas, and J. A. H. da Jornada, "Tunable Linear Thermal Expansion Coefficient of Amorphous Zirconium Tungstate," J. Am. Ceram. Soc. 2006, 89, 234 and references cited therein.

3. D. C. Harris, "Materials for Infrared Windows and Domes," SPIE Press, 1999.

KEYWORDS: Infrared Window; Infrared Dome; Sensor Window; Thermal Shock; Ceramics; Low Thermal Expansion; High Speed Missiles

TPOC: (760)939-1649
2nd TPOC: (703)636-6681