N132-125 TITLE: Spinel Reconnaissance Window

TECHNOLOGY AREAS: Air Platform, Materials/Processes, Sensors

ACQUISITION PROGRAM: Unmanned Carrier-Launched Surveillance and Strike Aircraft (UCLASS)

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Scale up the ceramic densification process to make monolithic, strong, optical quality spinel windows with finished dimensions of 28 x 30 x 0.6 inches. Measure mechanical strength, optical transmittance, refractive index homogeneity, and birefringence of the window.

DESCRIPTION: Spinel is a prime candidate for airborne and shipboard electro-optic sensor windows that will operate at midwave infrared (3-5 microns) and shorter wavelengths. Spinel has higher transmission than the competing materials, sapphire and aluminum oxynitride. All three materials are highly resistant to erosion by rain and sand. Spinel and ALON can be made in larger sizes than sapphire. Large windows are required to maximize the area that can be viewed. The goal of this topic is to increase the size of monolithic, optical quality spinel for sensor windows. Optical quality includes low absorption by impurities, low optical scatter, homogeneous refractive index, and low birefringence. A disadvantage of spinel is that it is not as strong as sapphire and aluminum oxynitride. It is critical in scaling up the size of spinel to maintain the highest possible mechanical strength. One potential development challenge in this project is to maintain the optical and mechanical quality of spinel when the pressure available to hot press a large window might not be as great as the pressure available to make a smaller window. Another challenge is to obtain uniform material that maximizes the, high quality area of a blank. Consolidation methods based on sintering, rather than hot pressing, would be considered because sintering obviates the need for a large hot press.

PHASE I: Demonstrate on a less-than-full scale that the conditions that will be used to consolidate and hot isostatically press a full size window will produce strong material of high optical quality. For example, if hot pressing pressure for a full size window is limited, do not exceed that limited pressure when making smaller windows in Phase I. If powder preparation for a large plate will be different from that for a small plate, use the method that applies to the large plate. If sintering will be used instead of hot pressing, demonstrate the sintering process. Fabricate and polish spinel window(s) of at least 8 x 8 x 0.6 inches by the same methods that will be used for a full size window in Phase II. Measure the refractive index homogeneity and birefringence of one or more plates. Measure the transmittance (from ultraviolet through infrared wavelengths) of the plates or of representative samples taken from the plates. Measure the flexure strength of well-polished disks (approximately 5 inch diameter x 0.25 inch thick) taken from the plate(s).

PHASE II: Optimize the fabrication of fully dense spinel blanks capable of producing windows with finished dimensions of 28 x 30 x 0.6 inches. If there is a practical reason (such as the size of available dies) to make different sizes, the proposal should state what size will be made. Produce two inspection polished windows and measure the refractive index homogeneity and birefringence of each window. Extract at least 12 disks representing different regions of one window to make well-polished mechanical test specimens (approximately 5 inch diameter x 0.25 inch thick) and measure the flexure strength. Measure the transmittance (from ultraviolet through infrared wavelengths) of the plate or of representative samples taken from the plate. Provide representative polished coupons to the Government for measurement of transmission and optical scatter.

PHASE III: Demonstrate commercial production capability for large spinel windows.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Large spinel windows will be used for transparent armor (bulletproof windows) for commercial customers, as well as for the military. The transparent armor market dwarfs the demand for high quality sensor windows.

REFERENCES:
1. A. Krell, K. Waetzig, and J. Klimke, "Effects and Elimination of Nanoporosity in Transparent Sintered Spinel (MgAl2O4)," Proc. SPIE 2011, Volume 8016, p 801602.

2. J. L. Sepulveda, R. O. Loutfy, S. Chang, and S. Ibrahim, "High Performance Spinel Ceramics for IR Windows and Domes," Proc. SPIE 2011, Volume 8016, p 801604.

3. J. L. Kutch, E. A. LaRoche, L. Renomeron, L. Fehrenbacher, L. Shaffer, and J. A. Randi, "Large Area Electro-Optic Spinel Windows � Advances in Manufacturing," Proc. SPIE 2011, Volume 8016, p 801606.

KEYWORDS: spinel; sensor window; electro-optical window; reconnaissance window; infrared window

** TOPIC AUTHOR (TPOC) **

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