Joining transparent ceramics

In the framework of many EL-OP projects there was increasing interest in large optical windows for protecting infrared sensing systems. There are many solutions for dual visible and midwave infrared windows, but for windows larger than 300 mm in diameter only clear Zinc Sulfide is available. When large area windows are required Zinc Sulfide becomes heavy, costly, and with significant optical scattering. Sapphire and ALON TM (Aluminum -oxynitride) were chosen as candidates for the transparent ceramic due to their high strength, availability and low optical scattering. As mentioned above these materials are not available in the form of large windows thus a joining technique was necessitated. Three main joining processes were investigated: Adhesive Bonding, Optical Glass Bonding -OGB and diffusion bonding, which were expected to result in good optical transmittance and moderate to good mechanical performance.