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Transparent sapphire and magnesium aluminum spinel (MgAl 2 O 4) ceramic was first brazed using La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 (LSBN) or La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 -MgO (LSBNM) glass filler. The Al 2 O 3 layer was formed at MgAl 2 O 4 /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/MgAl 2 O 4 joints with double glass interlayers 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 MgAl 2 O 4 /LSBNM glass samples. During the bonding process, low bonding temperature (750 °C) resulted in cracks and unbonding, while high bonding temperature (950 °C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 °C, the in-line transmission and shear strength of the sapphire/MgAl 2 O 4 joints reached 78.3% and 52 MPa, respectively. [ABSTRACT FROM AUTHOR]

Transparent sapphire and magnesium aluminum spinel (MgAl 2 O 4) ceramic was first brazed using La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 (LSBN) or La 2 O 3 -SiO 2 -B 2 O 3 -Nb 2 O 5 -MgO (LSBNM) glass filler. The Al 2 O 3 layer was formed at MgAl 2 O 4 /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/MgAl 2 O 4 joints with double glass interlayers 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 MgAl 2 O 4 /LSBNM glass samples. During the bonding process, low bonding temperature (750 °C) resulted in cracks and unbonding, while high bonding temperature (950 °C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 °C, the in-line transmission and shear strength of the sapphire/MgAl 2 O 4 joints reached 78.3% and 52 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this work, crystallization, thermal expansion and wetting behavior of ZnO–Al 2 O 3 –SiO 2 (ZAS) glass were first investigated. The results showed that ZnAl 2 O 4 was precipitated from ZAS glass after crystallization treatment. Crystallization increased the coefficient of thermal expansion (CTE) of ZAS glass ceramic due to the high CTE of ZnAl 2 O 4. In addition, ZAS glass exhibited good wettability on the surface of MgAl 2 O 4 substrate. On this basis, ZAS glass was used to join MgAl 2 O 4 ceramic, and the microstructure and mechanical properties of joints obtained with different cooling methods were investigated. The flexural strength of joints was related to the content of ZnAl 2 O 4 crystals in the brazing seams. Additional nucleation and crystallization treatment during cooling process improved the crystallinity of brazing seam, resulting in better matching of the CTE of brazing seam with that of MgAl 2 O 4 ceramic. The maximum flexural strength of joints reached 201 MPa, which was equivalent to the strength of MgAl 2 O 4 ceramic. [ABSTRACT FROM AUTHOR]

In this study, dysprosium-aluminosilicate (DAS) and neodymium-aluminosilicate (NAS) glasses with high softening temperature were used as fillers to join alumina ceramics. The similarities and differences in the interfacial microstructure and flexural strength of the joints were investigated. Results showed that the glass fillers both could infiltrate into alumina ceramics during the joining process. However, excessive infiltration at high joining temperatures led to the formation of pore defects in the brazing seam. An interfacial reaction layer composed of Dy 3 Al 5 O 12 was formed at the DAS glass/alumina interface. In contrast, no interfacial reaction was observed between the NAS glass and alumina ceramic. Slower cooling rate promoted the crystallization of Dy 2 Si 2 O 7 and Al 2 O 3 in the Al 2 O 3 /DAS/Al 2 O 3 joints, and only Nd 2 Si 2 O 7 in the Al 2 O 3 /NAS/Al 2 O 3 joints. The flexural strength at room temperature of both joints first increased and then decreased with the increased of joining temperature, and showed a declined tendency with the decrease in cooling rate. The flexural strength at 900 °C of Al 2 O 3 /DAS/Al 2 O 3 joints reached 245 MPa, which is higher than that of Al 2 O 3 /NAS/Al 2 O 3 joints. [ABSTRACT FROM AUTHOR]