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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]

The La 2 O 3 -SiO 2 -B 2 O 3 (LSB) glass filler with high softening temperature was first used to join MgAl 2 O 4 ceramic. An interfacial layer composed of Al 2 O 3 was formed due to the solubility difference of MgO and Al 2 O 3 in the LSB glass filler. As a result, the addition of Al 2 O 3 into the LSB glass filler caused the increase of interfacial layer thickness. On the contrary, the addition of MgO into the LSB glass filler led to the decrease of interfacial layer thickness. When the adding content of MgO was 6 wt%, the interfacial layer disappeared and completely amorphous brazing seam was obtained. The in-line transmittance of joints decreased with the increase of the thickness of interfacial layer. The optimal in-line transmittance of joint bonded with La 2 O 3 -SiO 2 -B 2 O 3 -MgO (LSB6M) glass filler reached 82.9% at 1000 nm. Meanwhile, the average flexural strength of joints was about 196.2 MPa, which was equal to the strength of MgAl 2 O 4 substrate. [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]

Effects of ZrO 2 content on the crystallization kinetics, formation mechanism of voids and mechanical property of Dy 2 O 3 –Al 2 O 3 –SiO 2 glass were studied. The crystallization method of DAS glasses transforms from surface crystallization into bulk crystallization with an increase in ZrO 2 content from 0-3% to 6–9%. When ZrO 2 content is 0–3%, the crystalline phases of DAS glass ceramics are Dy 2 Si 2 O 7 and Al 2 O 3 , accompanied by formation of voids. When ZrO 2 content is 6–9%, the DAS glass ceramics consist of Dy 2 Si 2 O 7 , Al 2 O 3 and ZrO 2. At the same time, no voids are found in the glass ceramics. Therefore, formation of voids during crystallization can be attributed to combined effect of the crystallization method and the density difference before and after crystallization. In addition, for glassy samples, the flexural strength increases from 80.4 MPa to 219.3 MPa with an increase in ZrO 2 content from 0% to 9%. Moreover, crystallization further improves the mechanical properties of the DAS glass ceramics with bulk crystallization method. [ABSTRACT FROM AUTHOR]

CaO–Al 2 O 3 –SiO 2 –TiO 2 glass ceramic filler with high crystallinity was used for joining alumina ceramic. The influence of joining temperature and crystallization treatment on the microstructure and flexural strength of joints was studied. The results demonstrated that a joining temperature higher than the melting temperature of crystals was essential to obtain dense joints. Furthermore, the formation of CaAl 2 Si 2 O 8 at the alumina/glass filler interface decreased the flexural strength of joints due to the mismatch of coefficient of thermal expansion (CTE) between CaAl 2 Si 2 O 8 and substrate. The maximum flexural strength of 256 MPa at room temperature was achieved when the joining temperature was 1260 °C. After crystallization treatment, a large number of fine CaTiSiO 5 was precipitated in the brazing seam. The flexural strength of joints after crystallization at room temperature was 221 MPa, and increased to 242 MPa at 800 °C. These results can be attributed to the change of CTE value of the brazing seam. [ABSTRACT FROM AUTHOR]