Microstructural evolution during sintering of near-monosized agglomerate-free submicron alumina powder compacts Original Research Article

Colloidally processed near-monosized, agglomerate-free submicron alumina powder compacts were sintered under different conditions to study the evolution of pore structures during sintering. The results showed that even though the compacts were agglomerate-free to start with, agglomeration took place during sintering due to local densification of the particles with different co-ordination numbers. Inter-agglomerate channel-like pores were formed as a result, which eventually evolved into an isolated pore on further sintering. The densification rate was controlled by mass transport via grain boundary diffusion before the formation of isolated inter-agglomerate pores, after which it was controlled by the sinterability of the pores. From this stage on, grain growth was required to bring about further sintering. At low sintering temperatures, grain growth was sluggish, probably a result of impurity controlled grain growth. This resulted in an abrupt drop in the densification rate and the phenomenon of end density at low sintering temperatures. The present work shows that an initial agglomerate-free green structure of fine, monosized particles is essential to resist particle agglomeration and grain growth during sintering, so as to achieve a low sintering temperature and a fine grain size sintered product.