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

Colloidally processed near-monosized, agglomerate-free submicron alumina po wder compacts were sintered under different conditions to study the evoluti on 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 differen t co-ordination numbers. Inter-agglomerate channel-like pores were formed a s a result, which eventually evolved into an isolated pore on further sinte ring. The densification rate was controlled by mass transport via grain bou ndary diffusion before the formation of isolated inter-agglomerate pores, a fter which it was controlled by the sinterability of the pores. From this s tage on, grain growth was required to bring about further sintering. At low sintering temperatures, grain growth was sluggish, probably a result of im purity controlled grain growth. This resulted in an abrupt drop in the dens ification rate and the phenomenon of end density at low sintering temperatu res. The present work shows that an initial agglomerate-free green structur e of fine, monosized particles is essential to resist particle agglomeratio n and grain growth during sintering, so as to achieve a low sintering tempe rature and a fine grain size sintered product. (C) 2000 Acta Metallurgica I nc. Published by Elsevier Science Ltd. All rights reserved.