Sintering Curve Inflection in Densification of Fine CeO₂ Powders at High Temperature

Abstract

The sintering behavior of fine cerium dioxide (CeO₂) powders from direct homogeneous precipitation using hexamethylenetetramine was examined by monitoring the continuous shrinkage of powder compacts during heating from 30 to 1700°C. Depending on the pre-heat-treatment condition of powders, the sintering curves of two starting powder compacts showed different shrinkage behavior. A powder heated at 650°C showed a normal sintering curve (S-type) with the highest shrinkage rate at around 1000°C. However, a powder heated at 350°C showed an extremely high shrinkage rate with inflection points in the sintering curve at 1300-1500°C. We analyzed the microstructure, pore structure and the secondary particle size of sintered bodies after sintering curve inflection. Grains 0.08 μm in size were roughly packed one another in the microstructure at 900°C after local sintering in the interior part of aggregated particles. The rapid shrinkage after rearrangement started at higher temperatures of 1300-1500°C, inducing large grain growth. The combination of rapid rearrangement and grain growth, which resulted in a sintering curve inflection, was assumed at temperatures as high as 900-1500°C.