Sintering of Fine Oxide Powders: II, Sintering Mechanisms

Conventional and new sintering mechanisms have been investigated using fine powders of CeO₂ and Y₂O₃ of excellent sinterability. We have verified the validity of Herrings scaling law for 60%–84% relative density and found that it is consistent with grain-boundary-diffusion control. At lower densities, we have found that pores larger than the critical size, in the sense of Kingery and Francois, can still be sintered readily. This is rationalized by a new sintering mechanism based on particle repacking concurrent with particle coarsening, resulting in a higher packing factor. Very fine, surface-active powders that coarsen rapidly are uniquely capable of taking advantage of this new sintering mechanism, which along with their propensity to homogenization, accounts for their remarkable sinterability even at very low green densities.