Strength Improvements in Spinel Ceramics

Magnesium aluminate (MgAl2O4) spinel is a material of interest for visible to mid-wavelength infrared (MWIR) windows and domes that operate in demanding environments. However, spinel is not as strong as other materials, such as sapphire or ALON Optical Ceramic, which are currently used for such applications. In order to be acceptable for the most demanding of these applications, the strength of Spinel must be increased. Surmet recently demonstrated a substantial increase in the strength of spinel through modification of its microstructure. Typically, spinel exhibits a bimodal microstructure (i.e., large and small grains), where the large grains act as stress concentrators. By limiting the growth of these grains, and achieving a uniform, fine grain microstructure, the stress is more uniformly distributed, resulting in higher strength. Furthermore, these improvements are expected to be cost neutral and fully scaleable. We propose to further investigate process improvements to yield microstructures for high strength spinel in Phase I. Process refinement should further improve strength from our initial observations. Phase II will then scale the process to large plates. It will also investigate utilizing refined finishing methods to further capitalize on the fine microstructure and further increase the strength– which Surmet has previously demonstrated on ALON.