Crystallization and wetting behavior of bismuth-borate-zinc glass and its application in low temperature joining alumina ceramics

Bismuth glass, 50Bi(2)O(3) -40B(2)O(3) -10ZnO, was designed, prepared and employed to join polycrystalline alumina with 95 wt.% purity (95Al(2)O(3)) in air. Crystallization behavior of the glass was studied. The results showed that Bi4B2O9 and Bi24B2O39 were formed in the glass in the heating process. The glass transition temperature (T-g) and the softening temperature (T-f) were 385 and 419 degrees C, respectively. Prior to the joining process, the wettability of the glass on the ceramic was studied. The wetting angle of the glass/95Al(2)O(3) system at 700 and 750 degrees C was 26.6 degrees and 12.6 degrees, respectively, exhibiting excellent wetting performance. Joining parameters influencing microstructure and mechanical property of the joint was researched, showing the in-situ formation of Bi4B2O9, Bi24B2O39 and ZnAl2O4 crystals in the joints when brazed at 600, 625 and >= 635 degrees C, respectively. The joint microstructure evolved considerably with temperature increasing (T >= 635 degrees C): (i)ZnAl2O4 particles grew steadily (ii) the aggregation of ZnAl2O4 particles was more and more serious, as well as the infiltration of the glass melt into the 95Al(2)O(3). The joint shear strength was proved to be a function of temperature, optimized average value of 58 MPa was acquired when the joints were joined at 625 degrees C.