Pressureless sintering of silicon nitride with lithia and yttria

Pressureless sintering of Si3N4 with additives from the Li2O–Y2O3 system was investigated. LiYO2 and equimolar mixtures of Li2O+Y2O3 were added to Si3N4, 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 LiYO2 additive. Hence LiYO2 is a more effective sintering additive than a mixture of the oxides.