The critical grain size for liquid flow into pores during liquid phase sintering

A model of grain-liquid mixture containing a spherical pore is analyzed to describe the pore filling during liquid phase sintering. Since the radius of liquid menisci around a pore increases linearly with the grain size, the menisci form a spherical bubble at a critical grain size and the pore is rapidly filled with liquid flowing from numerous menisci at the specimen surface. The values of the critical grain size for pore filling are calculated for various dihedral angles, wetting angles, and liquid contents. Although the predicted critical grain size is subject to errors because of assumptions in the models, the values agree in an order of magnitude with some experimental results. The effect of entrapped gas on pore filling and the expected behavior of irregular pores are also briefly discussed.