SiO2 migration mechanism at the joints of SiO2f/SiO2 composite brazed by bismuth glass

Joining is an indispensable process for expanding the application of ceramics and composites. Recently, glasses have been extensively explored for ceramic/composite joining owing to their unique functional needs. However, the difficulty in detecting amorphous materials and lack of enthalpy data make the interfacial reaction mechanism challenging to investigate. In this study, the interfacial reaction mechanism of joints of SiO_2f/SiO₂ composite-brazed bismuth glass was thoroughly explored. SiO₂ was dissolved from the matrix and used throughout the brazing process. In the initial stage, silica reacts with the brazing glass to form Bi₄(SiO₄)₃. Then, owing to the decomposition of Bi₄(SiO₄)₃, the silicate glass replaced the bismuth glass. Finally, some precipitation of SiO₂ occurred at the brazing seam owing to an entropy–enthalpy dominating mode. This study may instigate the design of brazing glasses for joining SiO_2f/SiO₂ composites.