Effects of the Sulfate Ion Exerted on Densification of Yttria on Precursor Synthetic

Ammonium hydroxide was used at 10°C as the precipitant to synthesize thin flakes of yttrium hydroxide, agglomerating in a manner resembling houses of card. Onemol% to 50mol% of ammonium sulfate was added to the yttrium hydroxide. Doping of sulfate ion resulted in yttria particles with round edges, in contrast to undoped yttria particles with sharp edges. The amount of doped sulfer was reduced to S/Y=10-3 by calcinations at 1100°C, and to trace by sintering at 1700°C. Doping of 10mol% of ammonium sulfate resulted in the maximum transparency in those of the yttria ceramics. Transparency of the yttria ceramics related to brittleness of agglomerate of the calcined powder which was evaluated by collapsing tendency of the agglomerates by ultrasonic dispersion.