Pressureless sintering of silicon nitride with lithia and yttria

Pressureless sintering of Si 3N 4 with additives from the Li 2O–Y 2O 3 system was investigated. LiYO 2 and equimolar mixtures of Li 2O+Y 2O 3 were added to Si 3N 4, respectively. The degree of densification, phase transformation, sample shrinkage and weight loss were measured as a function of the type of additives and the sintering temperature. The results revealed that heterogeneity of the liquid phase formed in the case of the separate oxide additions leads to nonuniform densification and lower of α→ β transformation rates in comparison to the LiYO 2 additive. Hence LiYO 2 is a more effective sintering additive than a mixture of the oxides.