Sintering behavior of nano yttria powder compacts fabricated by various forming processes

The sintering behavior of 10 nm sized, nano yttria powder was investigated with powder compacts prepared by various forming methods with an aqueous system. A well dispersed nano yttria slurry and gelation conditions were determined by examining rheological behavior according to the pH and the amount of dispersant content. Slip casting was performed on the slurry prepared under optimum dispersion conditions. For comparison, the powder compacts were prepared by uni-axially pressing the nano powder and the gel powder. When a granular-type gel powder was applied, dry pressing was conducted with less agglomeration, and the green density was improved, unlike the case of using the nano-powder. The most homogeneous microstructure was observed for the slip casting sample. As a result of sintering at 1650 degrees C for 2 hours in atmospheric conditions, the green sample prepared by slip casting showed the highest densification of 98% relative density with 41% shrinkage. In particular, fracture behavior and circular pores were present in the intra-granular area, unlike the cases of press formed samples. The powder compact using gel powder showed higher sintered density of 93% compared with the press formed powder compact using nano powder.