Chapter 50. Transparent MgAl₂O₄ Spinel — Revisited

Summary

Magnesium aluminate spinel (MgAl,₂O₄), aluminum oxynitride (ALON) and sapphire (Al₂O₃) have been well documented in the past for a range of applications (armor, domes and windows) requiring transparency in the 0.3μm to 5.5μm range. Over the past thirty years the need for improved, light-weight transparent armor systems, and IR domes and windows with low erosion rates, has supported the development of these materials to their present capability. Preliminary tests suggest that the ballistic properties of spinel are similar to ALON and sapphire, and that the transmission properties at 4.5μm and beyond are better, particularly as temperature increases. Although qualified for several window and dome applications there is presently no commercial supplier of spinel. A Cooperative Research and Development Agreement between the U.S. Army Research Laboratory (ARL) and the Advanced Ceramic Development Group of Technology Assessment and Transfer, (TA&T) is presently underway to fabricate large transparent spinel armor plates, thus establishing TA&T as a commercial supplier. In the fbture TA&T will also pursue the fabrication of domes up to 8” in diameter. This paper describes the achievements to date which have focused on extending existing process capabilities and establishing optimal processing parameters for powder processing and hot-pressing, followed by HIPing.