Wet-milling effect on the properties of ultrafine yttria-stabilized zirconia powders

Chemical coprecipitation was used to produce ultrafine yttria-stabilized zirconia powders. The effect of wet-milling on the properties of the powders derived from different processing conditions was investigated. It was shown that the agglomerates in the as-calcined powders were mainly crushed into smaller agglomerates during wet-milling while the aggregate and primary particle sizes were less affected. Wet-milling might be an efficient way to increase the specific surface area of hard agglomerated powders but had little influence on that of soft agglomerated powders. The as-calcined powders were composed of about 95% tetragonal phase, the balance being monoclinic phase. After wet-milling in alcohol for 4 h, some 50% of the tetragonal phase was transformed into monoclinic phase, which resulted in a decrease of the crystal size from 22 nm in as-calcined powders to 17 nm in wet-milled powders. It was also shown that wet-milling might be useful for the improvement of the compactability of as-calcined powders and the sinterability of hard agglomerated powders. For those soft agglomerated powders, it was proved to be unnecessary for wet-milling to be used to improve the powder sinterability.