Near Net Shape Forming of Spinel Hemispherical Domes

The current method for producing dome blanks for multimode optics is to spray dry powders, followed by isopressing around metal mandrels. Yield losses during spray drying, and excess material requirements in the pressing step represent a significant portion of the final part cost. Unfortunately, few opportunities are available to minimize these losses. Slurry casting processes represent an alternative to isopressing, and in the case of hemispherical domes, are particularly well suited. Both slip casting and gel casting provide the opportunity to prepare domes at near-net shape with minimal yield loss. To date, spinel has been particularly difficult to cast, however, due to its fine particle size. Identification of a suitable dispersion system for spinel that supports casting, despite the particular issues related to the material, is the key to developing this new, more efficient processing route. We propose herein to develop a casting method suitable for producing hemispherical domes of suitable optical quality from spinel powders. Our efforts build on current capabilities for dispersing spinel in preparation for dry processing of lenses, domes and windows. Both slip and gel casting will be investigated in Phase I, with one process selected for further development in Phase II.