Characterization of porous sintered reaction-bonded silicon nitride containing three different rare-earth oxides

The effect of rare-earth oxides on the characteristics of porous sintered reaction-bonded silicon nitride (SRBSN) was investigated. Three types of raw Si powder mixtures containing different rare-earth oxide (La 2 O 3 , Er 2 O 3 , and Yb 2 O 3 ) were prepared and nitrided in the form of compacts. The nitriding profiles of the respective raw powder mixtures with elevating temperature indicated that Yb 2 O 3 clearly promoted the nitridation of Si compacts at low temperature compared with other rare-earth oxides, and the β-Si 3 N 4 ratio after completion of the nitriding reaction was different at which temperature the major nitridation occurred. Yb 2 O 3 was found to be the most effective additive to achieve a strong porous SRBSN, having the flexural strength of 441 MPa. The reason why Yb 2 O 3 promotes the nitridation reaction and has excellent mechanical properties after post-sintering is that oxygen was removed during the nitriding reaction, which was supported by the analysis of oxygen content via the laser-induced breakdown spectroscopy.