[en] Highlights: • 95 wt.% purity alumina ceramics are successfully joined to themselves using a bismuth borate zinc glass braze. • ZnAl₂O₄ is the main product in the joint domain due to the reaction between the Al₂O₃ substrate and ZnO from the glass. • The size of ZnAl₂O₄ increase with the brazing temperature increasing. • ZnAl₂O₄ forms in the joint and greatly enhances the joining quality. • The maximum lap shear strength of 95 MPa is obtained for the samples brazed at 675 °C for 30 min. Amorphous bismuth borate zinc glass with a composition of 40Bi₂O₃–40B₂O₃–20ZnO (in mol.%) was used as a braze to join 95 wt.% purity alumina ceramics (95Al₂O₃) in air. The interfacial phases in the brazed joints were characterized using scanning electron microscopy, transmission electron microscopy. Zinc aluminate (ZnAl₂O₄) was identified as the main reaction product in the joints due to the chemical reaction between the Al₂O₃ substrate and ZnO from the glass. Typical microstructure of the Al₂O₃/Al₂O₃ brazed joints was Al₂O₃ substrate/glassy matrix phase + ZnAl₂O₄ particles/Al₂O₃ substrate. The dependence of the microstructure and mechanical properties on brazing temperature was investigated. The size of ZnAl₂O₄ increased with an increase in brazing temperature. It was found the room lap shear strength of Al₂O₃/Al₂O₃ joints firstly increased and then declined with increasing brazing temperature. The maximum lap shear strength of 95 MPa was obtained for the samples brazed at 675 °C for 30 min, which was mainly attributed to the formation of ZnAl₂O₄.