Novel design of sapphire/spinel transparent ceramic joints with double glass interlayers by coating and bonding

Transparent sapphire and magnesium aluminum spinel (MgAl2O4) ceramic was first brazed using La2O3-SiO2- B2O3-Nb2O5 (LSBN) or La2O3-SiO2-B2O3-Nb2O5-MgO (LSBNM) glass filler. The Al2O3 layer was formed at MgAl2O4/LSBN interface or sapphire/LSBNM interface, which caused the decrease of light transmission of joints. To avoid the formation of this interface layer, sapphire/LSBN/LSBNM/MgAl2O4 joints with double glass in-terlayers were fabricated by using a two-step joining method consisting of high-temperature coating and low-temperature bonding. After the first step of high-temperature coating, no interfacial layer was observed in sapphire/LSBN glass and MgAl2O4/LSBNM glass samples. During the bonding process, low bonding temperature (750 degrees C) resulted in cracks and unbonding, while high bonding temperature (950 degrees C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 degrees C, the in-line transmission and shear strength of the sapphire/MgAl2O4 joints reached 78.3% and 52 MPa, respectively.