Performance of Bi₂O₃-B₂O₃ glass and wetting characteristics on SiO_2f/SiO₂ composites: An experimental and DFT study

SiO_2f/SiO₂ composites offer excellent dielectric and thermal stability, but reliable integration remains difficult due to the limitations of conventional metal brazes, including CTE mismatch and electrical conductivity. This study developed a novel all-dielectric brazing material, Bi₂O₃-B₂O₃ (BB) glass, for joining SiO_2f/SiO₂ composite materials. The BB glass synthesized via melt-quenching exhibits an amorphous structure, a low glass transition temperature (T_g=403 °C), and an adjustable CTE (7–9 × 10^–6/ °C). Wetting experiments demonstrate excellent spreading on the SiO_2f/SiO₂ surface, with a contact angle as low as 16° Density functional theory (DFT) analysis reveals that the formation of Bi-O-Si bonds and B-O-Si networks at the interface enhances the bonding strength. Differential charge density and density of states (DOS) results indicate that the electronic structure of BB glass improves dielectric response and reduces insertion loss in the GHz frequency band. BB glass overcomes the shortcomings of traditional brazing materials, providing a theoretical and technical foundation for reliable joining of SiO_2f/SiO₂ composite materials in extreme environments.