Low Cost Production of Domes Using Freeze Casting

Multimode seekers for missiles require protective domes that are transparent over a range of wavelengths, including MWIR. Technology Assessment and Transfer, Inc. (TA&T) has successfully manufactured such protective domes from its transparent spinel ceramic material. The most common method of fabricating spinel dome green bodies consists of preparing the ceramic powder using conventional powder preparation techniques, filling a mold with powder, and using cold isostatic pressing (CIP) to form the green body at high pressure. This method is time consuming due to the handling of the powder and mold filling, and expensive due to the cost of CIP equipment, touch labor, and total cycle time. Casting or molding the domes has the potential to reduce the labor and equipment costs. TA&T proposes to develop a freeze casting process for manufacturing transparent spinel domes by first developing two high-solids casting slips – one based on water and the other using a non-aqueous vehicle. The second step will be to design and build a mold suitable for use over a wide range of temperatures. The third step will be to cast test specimens from both slips, sinter/HIP them and characterize the resulting spinel ceramic materials.