Refined continuum model on the behavior of intergranular films in silicon nitride ceramics

A refined continuum model has been proposed, based on the bond-strength consideration between cations and anions in the film, to address the effect of sintering additives on the behavior of intergranular glassy films (IGFs) in silicon nitride ceramics. The refined model indicates that the incorporation of additive ions in the film will modify the attractive van der Waals and repulsive steric forces. The model also implies that the charge and size of the ions, which determine the bond strength between cations and anions, and the amount of ions are important parameters to the force balance and behavior of the IGFs. Experimental evidence for (i) the effect of sintering additives on the thickness of IGFs in Si₃N₄ ceramics and (ii) the occurrences of the `squeezing out' of IGFs in hot-pressed Si₃N₄ under a moderate external pressure (e.g., 25 MPa) are discussed, to confirm the validity of the present model.