WET-MILLING EFFECT ON THE PROPERTIES OF ULTRAFINE YTTRIA-STABILIZED ZIRCONIA POWDERS

Chemical coprecipitation was used to produce ultrafine yttria-stabiliz ed zirconia powders. The effect of wet-milling on the properties of th e powders derived from different processing conditions was investigate d. 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 m ight be an efficient way to increase the specific surface area of hard agglomerated powders but had little influence on that of soft agglome rated powders. The as-calcined powders were composed of about 95% tetr agonal phase, the balance being monoclinic phase. After wet-milling in alcohol for 4 h, some 50% of the tetragonal phase was transformed int o monoclinic phase, which resulted in a decrease of the crystal size f rom 22 nm in as-calcined powders to 17 nm in wet-milled powders. It wa s also shown that wet-milling might be useful for the improvement of t he compactability of as-calcined powders and the sinterability of hard agglomerated powders. For those soft agglomerated powders, it was pro ved to be unnecessary for wet-milling to be used to improve the powder sinterability.