The role of dilatancy on expansion during early stage liquid phase sintering of lead magnesium niobate

During an attempt to sinter (900°C/30 min) lead magnesium niobate [Pb(Mg1/3Nb2/3)O3] of average particle (aggregate) size 5.8 μm at by adding 3 wt.% excess PbO as a sintering aid, it has been observed that around 3% volume shrinkage takes place. However, an addition of excess Nb2O5 (6 wt.%) along with the same excess PbO gives rise to an appreciable volume expansion (upto 14%) instead of shrinkage under identical firing conditions. We have concluded after systematic studies that such expansion can be understood primarily by considering the generation of insufficient (for consolidation of powders) capillary pressure owing to the formation of a liquid phase (PbO melt with some dissolved Nb2O5) at 900°C and the subsequent role of dilatancy which considers the expansion of well-packed powders during shear.