Adhesive properties of B₄C-modified phenol-formaldehyde(PF)resin adhesive for the high-temperature bonding of Si₃N₄

High-temperature adhesive was prepared using phenol-formaldehyde resin (PF) as matrix and boron carbide (B₄C) as modifier, silicon nitride (Si₃N₄) ceramics were bonded by the adhesive, and the bonded specimens were heat-treated within 300-800℃ subsequently. The adhesive properties of the high-temperature adhesive were tested. The results indicate that the adhesive has outstanding high-temperature bonding properties for Si₃N₄ at high temperature. The failure of bonded joints treated at 700 and 800℃ were due to the broken of Si₃N₄ matrix. The micro-morphologies at bonding interfaces were also investigated by SEM. It is shown that complex physical and chemical changes occurred during the heat-treatment process. By means of the modification reaction between B₄C and the volatiles of PF resin, the value of carbon residue was prompted effectively; and the formation of fibers and the nanocrystallization of B₂O₃ benefit the achievement of satisfactory high-temperature bonding properties.