SCATTERING-LOSS MECHANISM IN CAF2-FILM-ASSISTED DIFFUSION BONDING OF MGF2 CERAMICS

The present study examined the bonding of MgF2 ceramics by hot-pressin g. A layer of CaF2 2 to approximately 3 mum thick was used as an agent to decrease the bonding temperature and to avoid breaching. The princ ipal factors influencing transmission loss were the cellular growth in the MgF2 layer, which caused about a 5% loss in transmittance, and gr ain growth in the films, as well as voids caused by the lattice mismat ch, which, together with the formation of a recrystallization zone, ca used about a 20% loss in transmittance. Grain growth in the CaF2 film was not the main cause of the scattering loss. The effect of the grain growth in the MgF2 matrix on transmittance was calculated as about 5% . Compositional fluctuations along the interfaces also had an importan t influence on scattering loss. For the sample that bonded at 650-degr ees-C after 5 h, under a pressure of 430 kg/cm2 (42 MPa), the crystall ine solubility limit of CaF2 in MgF2 was measured at approximately 17 at. %.