Sintering of Si 3 N 4 with the Addition of Rare‐Earth Oxides

The effect of rare‐earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N 2 at 1800° to 2000°C was studied. When a single‐component oxide, such as CeO 2 , Nd 2 O 3 , La 2 O 3 , Sm 2 O 3 , or Y 2 O 3 , was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y 2 O 3 –Ln 2 O 3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare‐earth oxides is discussed in relation to the additive compositions.