Spinel - Domes
Magnesium aluminate Spinel is a durable, broadband, electro-optical material that can be readily manufactured into transparent domes for multimode seeker applications. Spinel offers the high temperature and thermal shock resistance, hardness, scratch and rain erosion resistance that are prerequisites for missile windows, in addition to excellent optical properties. Legacy window materials such as zinc sulfide, magnesium fluoride, and calcium aluminate offer excellent optical properties, but their strength and hardness are deemed inadequate for increasingly severe applications.
Three transparent ceramic materials, polycrystalline Spinel, single crystal sapphire, and polycrystalline aluminum oxynitride (AlON) are capable of meeting severe duty requirements. Of these, Spinel offers both a cost advantage and better optical performance. TA&T has developed a robust manufacturing process for Spinel dome blanks that can be generated and polished into high performance domes. TA&T is ready to meet the challenge of manufacturing thousands of transparent Spinel dome blanks for new and legacy missile programs.
TA&T produced Spinel dome held against the sky
The difficulty of designing windows and other components that operate reliably in harsh aerodynamic heating environments is complicated further because future designs must anticipate transition into the hypersonic flight regime. At room temperature Spinel possesses measurably better transmission than AlON and slightly better than sapphire in the mid IR. The transmission advantage of Spinel in the mid IR increases with flight-imposed aerodynamic heating. The transmission curves for Spinel, sapphire and AlON at room temperature, 250°C and 500°C shown above are shown superimposed over a typical exhaust spectrum with its characteristic emission at 4.8 microns. The cubic crystal lattice and associated optical isotropy of Spinel give it an additional advantage of image quality over sapphire, whose hexagonal crystal structure makes it optically bi-refringent; i.e., light does not travel at the same speed in all directions through sapphire.
