Joining of silicon nitride using coating technology

Reaction bonded silicon nitride (RBSN) was joined to itself with MgO formed surface layer using alkoxide. Surface-coated silicon nitride pieces were joined with a single oxide additive (MgO). The mechanism of the joining involves the formation of Mg-Si-O-N liquid to give a dense interface followed by some dissolution of Si3N4 grains. A simple processing technique has been developed for joining Si3N4-based ceramics. Thin MgO-based surface layers were formed, via hydrolysis of magnesium methoxide. RBSN were joined by hot pressing at 1600 °C. Only enough pressure was used to maintain alignment of the parts in the fixture. To compare pieces joined with the thin layer of MgO powder both samples were tested in four point bending test. Silicon nitride samples joined by using MgO powder as the interlayer failed close to the joining point. The bend strengths of samples prepared by coating broke far away from the joint, showing that the strength of the joint is greater than that of the RBSN itself.