Influence of rare-earth oxide additives on microstructure and properties of RBSN

The addition of rare-earth oxide can improve the properties of high temperature structural ceramics. For example, Y₂O₃ is somewhat more efficient than Al₂O₃ and MgO in improving the properties of Si₃N₄. To discover new kinds of additives is considered an important area of research. In this paper, the authors study systematically, the influence of rare-earth oxide additives La₂O₃ and CeO₂ on the microstructure and properties of RBSN. Experimental results show that different rare-earth oxides have different effects on RBSN. La₂O₃ is able to promote the process of nitride reaction and sintering. As a result, the sintered body has high density and flexural strength. With the sintering time increased from 5h to 32h, the porosity is decreased and the room temperature strength and high temperature strength are increased by 160% and 80% respectively. Obviously, La₂O₃ is an excellent additive for Si₃N₄. The addition of CeO₂ to Si₃N₄ results in cracks on matrix and the decrease of density and strength. It is unsuitable for RBSN. The above results furnish reliable information for choosing additives. Moreover they add to the accumulation of evidence needed for exploring the mechanism underneath the action of additives.